Title of Invention

2-PYRIDYLCARBOXALDEHYDE ISOMCOTINOYL HYDRAZONE AS IRON CHELATORS.

Abstract There is disclosed a 2-pyridylcarboxaldehyde isonicotinoyl hydrazone (PCIH) analogue suitable for use as an in vivo iron chelator, the PCIH analogue having Formula 1: Formula 1 wherein R2 is either OH or H, such that when R2 is OH, R1 is phenyl, pyridine, furan or thiophene ring optionally with alkyl, halo, nitro, amine or hydroxyl attached to any of the vacant positions on the ring; isomers thereof or salts thereof; or when R2 is H, R1 is thiophene, phenol or 2-, 3- or 4- bromophenyl optionally substituted with alkyl, halo, nitro, or amine attached to any of the vacant positions on the ring; or salts thereof. A pharmaceutical composition containing a 2-pyridylcarboxaldehyde isonicotinoyl hydrazone (PCIH) analogue is also disclosed.
Full Text IRON CHELATORS AND USES THEREOF
Technical Field
The present invention relates to compounds which are capable of
chelating iron and having use in addressing or treating iron-overload
situations.
Background Art
Iron (Fe) is the most abundant metal ion found in cells, reflecting its
crucial roles in the oxidation-reduction reactions upon which life depends.
The rich and unique chemistry of Fe has endowed it with properties
absolutely essential for oxygen transport. ATP production and DNA
synthesis. These characteristics which make Fe an obligate requirement for
life also make it a potential target for preventing the growth of neoplastic
cells.
In order to understand the role of Fe in cellular proliferation and the
possible use of Fe chelators as effective anti-tumour agents, it is important to
describe how this metal ion is transported and metabolised in normal and
neoplastic cells. This is described at length in a review article entitled
"Potential of Iron Chelators as Effective Anti-proliferative Agents" by D.R.
Richardson which is published 1997 in Can J. Physiol. Pharmacol. 75 1164-80
and which is incorporated herein by reference.
Reference is also made to 'Analogues of Piridoxal Isonicotinoyl
Hydrazone (PIH) as Potential Iron Chelators lor the Treatment of Neoplasia"
by D.R. Richardson reported at Leukaemia and Lymphoma. 1998, 31 47-60
which is also incorporated herein by reference and from which most of the
following discussion has been taken.
Transportation of Fe in the serum is performed by the glycoprotein
transferrin (Tf). which binds two atoms of Fe(III). Transferrin donates its Fe
to cells by binding to specific Tf receptors (TfR) on the cell membrane. Upon
binding to the TfR. the Tf-TfR complex is internalized within endocytotic
vesicles and the Fe released from the protein by a decrease in the
intravascular pH to 5.5. Apart from the specific receptor-mediated process of
Fe uptake from Tf. another process consistent with non-specific adsorptive
pinocytosis has also been reported in rat hepatocytes. human hepatoma cells
and human melanoma cells. Once the Fe is released from Tf. it is then
bound by a specific membrane transporter that remains uncharacterized.
Recently, a possible candidate for this latter protein has been identified,
namely the product of the gene Nramp2. This molecule has been called the
divalent cation transporter 1 (DCT1). and may be involved in both Fe
absorption from the gut and also Fe transport across the endosomal
membrane. Once Fe is transported across the membrane, it then enters a
poorly characterized compartment known as the intracellular Fe pool. The
identity of the pool is highly controversial and may be composed of low Mr
Fe complexes of citrate, amino acids and nucleotides or alternatively, the Fe
may be bound to high Mr macromolecules. Experiments have shown that the
pool is composed of molecules containing Fe in the Fe(II) and Fe(III)
oxidation states. In some cells, such as developing erythroid precursors, the
low \L weight Fe pool represents only a very small fraction of the total
amount of Fe in the cell, whereas in other cell types, such as Chang cells, it
may represent a considerable proportion of the total Fe present. Iron in the
pool can be used for incorporation into Fe-containing proteins, such as the
cytochromes and Fe-S proteins, and when in excess. Fe can be incorporated
into the Fe storage protein ferritin.
The role played by Fe in cellular proliferation has been well
demonstrated in numerous studies. For example, in the absence of Fe,
ribonucleotide reductase cannot produce deoxyribonucleotides and this has a
profound effect on the ceil cycle resulting in a GvS block which can lead to
apoptosis. Cancer cells express very high levels of the transferrin receptor
(TfR). suggesting that they have a high Fe requirement. In fact, in vivo, some
neoplastic cell types take up Fe from Tf at a rate that is comparable to
hemoglobin producing cells such as reticulocytes. It is of interest that the
host may withhold Fe during neoplastic cell proliferation, and this is found
in Hodgkins and non-Hodgkins lymphoma where there is a pronounced
decrease in the saturation of Tf with Fe. This latter phenomenon is known as
the hypoferremic shift, which has been suggested to be a physiological
response to hinder tumor cell growth. The importance of the TfR in Fe
uptake and cell proliferation is demonstrated by the fact that the monoclonal
antibody 42/6 which blocks the binding of Tf to the TfR. also inhibits tumor
growth.
Evidence that neoplastic cells are sensitive to Fe chelation comes from
work in vitro in cell culture experiments and in vivo in clinical trials where
the chelator used to treat Fe overload, desferoxamine (DFODFO) and other
Fe chelators effectively inhibit proliferation. One of the most significant
reports demonstrating a pronounced therapeutic effect of DFO comes from a
study done in patients with neuroblastoma (NB). In this latter trial. DFO
given as an 8 hr intravenous infusion resulted in 7 of 9 patients having more
than a 50% decrease in bone infiltration of tumor cells. Moreover, in 1
patient, a 48% decrease in tumor size was reported. In more recent
investigations. DFO was combined with cytotoxic agents (cyclophosphamide,
etoposide. thio-TEPA and carboplatin) in patients with stage III and IV NB.
From 57 patients studied, there were 24 complete responses. 5 very good
partial responses. 21 partial responses. 3 minor responses and 4 with
progressive disease.
It has now been ascertained that DFO, which is now the drug in
current clinical use. is very expensive, orally ineffective and requires long
subcutaneous infusion (12:24 hr/day. 5-7 days/week) to effect significant Fe
mobilization fOlivieri et al. 1997. Blood 89 739-61: Richardson et al.. 1998.
Am. J. Hematol. 58 299-305). The need for an orally effective and economical
Fe chelator has recently been emphasized by the failure of deferiprone (also
known as L1 or 1.2-dimethyl-3-hydroxypyrid-4-one) to successfully chelate
Fe from Fe-overloaded patients (Olivieri et al.. 1998. New Eng. J. Med. 337
417-23). In fact, treatment of patients with this later drug resulted in hepatic
fibrosis and an increase in liver Fe levels.
One important group of chelators that have shown high Fe chelation
efficacy both in vitro and in vivo are those ligands of the pyridoxal
isonicotinoyl hydrazone (PIH) class referred to in Richardson et al., 1998.
supra. These chelators have a very high affinity and specificity for Fe(III)
that is similar to that found for DFO and much greater than that of
ethylenediaminetetracetic acid (EDTA) as reported in Richardson et al.,
1989. supra and Vitolo et al., 1990, Inorg. Chim. Acta 733 39-50. In addition,
these ligands are synthesized by a simple one-step Schiff base condensation,
are economical and orally effective as discussed in Richardson et al.. 1989. J.
Lab Clin. Med. 131 306-15. Interestingly. PIH can chelate Fe from the
mitochondrion, a site that may become loaded with Fe in the
neurodegenerative disease Friedreich's ataxia (Babcock et al.. 1997. Science
276 1709-12: Foury et al.. 1997. FEES Lett. 411 373-7: Rotig et al.. 1997.
Nature Genetics 12 215-71.
Previous studies have characterized the biological and chemical
properties of analogues of PIH. some of which show higher activity on a
molar basis than the parent compound itself. These compounds were
derived from three groups of aromatic aldehydes, namely, pyridoxal.
salicylaldehyde and 2-hydroxyl-1-naphthylaldehyde. Generally, chelators
derived from pyridoxal were shown to possess high chelation efficacy but
low antiproliferative activity, while ligands derived from 2-hydroxy-1-
naphthylaldehyde had high Fe chelation efficacy and potent antiproliferative
activity. Hence, aroylhydrazones derived from pyridoxal were considered to
be possibly useful as agents to treat Fe overload disease while chelators
derived from 2-hydroxyl-1-naphthylaldehyde were considered to have better
potential for the treatment of cancer. It should be noted that many other Fe
chelators have also demonstrated antiproliferative activity, including DFO.
In fact, some of the most potent effects of DFO have been reported when this
drug was used against the pediatric tumor neuroblastoma. In Cory et al.,
1995. Adv. Enzyme Regul. 35 55-63 and Liu e tal., 1995. Prog. Med. Chem. 32
1-35. there are disclosed a closely related group of chelators derived from 2-
pyridylcarboxaldehyde and thiosemicarbazide (e.g. 3-amincpyridine-2-
carboxaldehyde thiosemicarbazone) which were found to be among the most
effective inhibitors of ribonucleotide reductase yet identified. However,
these chelators, while having high antiproliferative properties, were found to
have only moderate chelation efficacy and moderate lipophilicity which
made such chelators less efficient in regard to treatment of Fe overload
diseases.
Friedreich's ataxia (FA) is a severe neurodegenerative condition. In
97% of patients the disease is due to a GAA triplet repeat expansion in intron
1 of the FRDA gene resulting in a marked decrease in its expression. The
protein encoded by this gene is known as frataxin and is found within the
mitochondrion. Over the last few years evidence has accumulated to suggest
that frataxin plays a role in mitochondrial Fe metabolism. Studies using the
yeast cell showed that deletion of the homologous gene (YTH1). resulted in
an accumulation of mitochondrial Fe resulting in the loss of mitochondrial
DN'A. [Fe-S] cluster-containing enzymes, and respiration. Like the human
FRDA gene. YFHl encodes a mitochondrial protein (Yfh1p). When YFHl was
reintroduced back into the yeast, mitochondrial Fe was exported back out
into the cytosol. suggesting a "mitochondrial Fe cycle".
Consistent with the knockout yeast model, it was noted that reductions
in mitochondrial DNA. complex I. complex II/III. and aconitase occurred in
the heart of FA patients, observations consistent with mitochondrial damage.
In addition, it was reported increased Fe deposition in the heart, liver, and
spleen was reported in FA patients in a pattern consistent with a
mitochondrial location. This work suggesting the pathology of FA in humans
is caused by mitochondrial Fe overload was strongly supported by work
showing Fe deposits within the heart myofibrils, defective myocardial and
skeletal muscle mitochondrial respiration, and perturbations in the heme
biosynthesis pathway.
Since the pathology of FA is linked to mitochondrial Fe overload, new
therapies based on these results could provide hope for FA patients. One
strategy is the use of specific Fe chelators that can permeate the
mitochondrion. Already a trial supported by the National Institute of Health
is investigating the use of the clinically used Fe chelator desferoxamine
(DFO) to treat FA patients. Hou-ever. DFO cannot efficiently mobilize Fe
from cells, and previous studies have demonstrated that it is not effective at
mobilizing Fe from Fe-loaded mitochondria in reticulocytes.
In contrast to DFO. another chelator known as pyridoxal isonicotinoyl
hydrazone (PIH) shows high activity at mobilising Fe from an experimental
model of mitochondrial Fe overload in reticulocytes. A variety of studies, in
vitro, in vivo, and a clinical trial, have demonstrated that PIH and its
analogues show potential for the treatment of Fe-overload disease.
Although a lot of work has been done to develop Fe chelators for use in
medical applications, there is still a need for new chelators which have safe
and efficacious characteristics. The present inventors have now developed
new Fe chelators that have been found as suitable candidates for use in
treating Fe overload disease. The present inventors have synthesized a new
group of ligands known as 2-pyridylcarboxaldehyde isonicotinoyl hydrazone
(PCIH) analogues. Several PCIH analogues are more active than DFO or PIH
at mobilizing Fe from a neuroepithelioma cell line (SK-N-MC). and showed
low antiproliferative activity.
Disclosure of Invention
In a first aspect, the present invention provides 2-
pyridylcarboxaldehyde isonicotinoyl hydrazone (PCIH) analogues suitable for
use as in vivo iron chelators, the PCIH analogue having Formula I:
Formula 1
wherein R1 is an aromatic or heterocyclic group except unsubstitued
pyridine and R2 is either H or OH: isomers thereof or salts thereof.
Preferably. R1 is a hydrophobic aromatic or heterocyclic group. More
preferably. Rl is a phenyl, pyridine, furan or thiophene ring optionally with
alkyl. halo, nitro. amine and hydroxyl attached to any of the vacant positions
on the ring. More preferably. Rl is benzoyl, halogenated benzoyl, m-bromo
benzoyl, isonicotinoyl. or thiophene group.
The present inventors have found that when R1 is hydrophilic in
nature, the analogue is more water soluble, but the chelator exhibits poor
efficacy at mobilizing Fe. As a variety of analogues with different Rl groups
have been produced, the invention includes a range of analogues with
different R1 groups.
More preferably, the analogue is selected from 2-
pyridylcarboxaldehyde m-bromobenzoyl hydrazone (PCBBH). 2-
pyridylcarboxaldehyde 2-thiophenecarboxyl hydrazone (PCTH]
The B? substituent of the 2-pyridylcarboxaldehyde m-bromobenzoyl
hydrazone (PCBBH) may be substituted with any other halide group.
In a second aspect, the present invention provides a pharmaceutical
composition suitable for use as an in vivo iron chelator, the composition
comprising a therapeutically effective amount of an 2-pyridylcarboxaldehyde
isonicotinoyl hydrazone (PCIH) analogue having Formula 1 together with a
pharmaceutically suitable carrier or diluent wherein
Formula 1
wherein R1 is an aromatic or heterocyclic and R2 is either H or OH; isomers
thereof or salts thereof.
Preferably. R1 is a hydrophobic aromatic or heterocyclic group. More
preferably. R1 is a phenyl, pyridine, furan or thiophene ring optionally with
alkyl. halo, nitro. amine and hydroxyl attached to any of the vacant positions
on the ring. In one preferred form. Rl is benzoyl, halogenated benzoyl, m-
bromo benzoyl, isonicotinoyl. or thiophene group.
Preferably the analogue is selected from the compounds 2-
pyridylcarboxaldehyde isonicotinoyl hydrazone (PCIH). 2-
pyridylcarboxaldehyde 2-thiophenecarboxyl hydrazone (PCTH). -
pyridylcarboxaldehyde benzoyl hydrazone (PCBH). 2-pyridylcarboxaldehyde
m-bromobenzoyl hydrazone (PCBBH).
The Br substituent of the 2-pyridylcarboxaldehyde m-bromobenzoyl
hydrazone (PCBBH) may be substituted with any other halide group.
In one embodiment, the carrier is an orally administrable carrier.
Preferably, the pharmaceutical composition is in a dosage form formulated as
enterically coated, granules or capsules.
Preferably, the pharmaceutical composition further includes a suitable
buffer to adjust the pH of the stomach of the patient or subject to a level that
will minimize acid hydrolysis. Such a pH should be about 6-3 (more
preferably about 7) for the active compounds per se inclusive of free bases
and hydrochloride salts. More preferably the buffer is a phosphate-citrate
buffer.
The language "administering a therapeutically effective amount" is
intended to include methods of giving or applying an analogue to an
organism which allow the analogue to perform its intended therapeutic
function. The therapeutically effective amounts of the analogue will vary
according to factors such as the type of disease of the individual, the age, sex,
and weight of. and the ability of the analogue to chelate iron in cells of the
individual. Dosage regima can be adjusted to provide the optimum
therapeutic response. For example, several divided doses can be
administered daily or the dose can be proportionally reduced as indicated by
the exigencies of the therapeutic situation.
The analogue can be administered in a convenient manner such as by
injection (subcutaneous, intravenous, etc.). oral administration, inhalation,
transdermal application, or rectal administration. Depending on the route of
administration, the analogue can be coated with a material to protect the
analogue from the action of enzymes, acids and other natural conditions
which may inactivate the analogue chelator.
The analogue can also be administered parenterally or
intraperitoneally. Dispersions can also be prepared in glycerol, liquid
polyethylene glycols, and mixtures thereof and in oils. Under ordinary
conditions of storage and use. these preparations may contain a preservative
to prevent the growth of microorganisms.
Pharmaceutical compositions suitable for injectable use include sterile
aqueous solutions (where water soluble) or dispersions and sterile powders
for the extemporaneous preparation of sterile injectable solutions or
dispersions. In these cases, the composition must be sterile and must be
fluid to the extent that easy syringability exists. It must be stable under the
conditions of manufacture and storage and must be preserved against the
contaminating action of microorganisms such as bacteria and fungi. The
carrier can be a solvent or dispersion medium containing, for example, water,
ethanol. polyol (for example, glycerol, propylene glycol, and liquid
polyetheyleue glycol, and the like), suitable mixtures thereof, and vegetable
oils. The proper fluidity can be maintained, for example, by the use of a
coating such as lecithin, by the maintenance of the required particle size in
the case of dispersion and by the use of surfactants. Prevention of the action
of microorganisms can be achieved by various antibacterial and antifungal
agents, for example, parabens. chlorobutanol. phenol, ascorbic acid.
thimerosal. and the like. In many cases, it will be preferable to include
isotonic agents, for example, sugars, polyalcohols such as mannitol. sorbitol,
sodium chloride in the composition. Prolonged absorption of the injectable
compositions can be brought about by including in the composition an agent
which delays absorption, for example, aluminum monostearate and gelatin.
Sterile injectable solutions can be prepared by incorporating the
analogue in the required amount in an appropriate solvent with one or a
combination of ingredients enumerated above, as required, followed by
filtered sterilization. Generally, dispersions are prepared by incorporating
the analogue into a sterile vehicle which contains a basic dispersion medium
and the required other ingredients from those enumerated above.
The analogue can be orally administered, for example, with an inert
diluent or an assimilable edible carrier. The analogue and other ingredients
can also be enclosed in a hard or soft shell gelatin capsule, compressed into
tablets, or incorporated directly into the individual's diet. For oral
therapeutic administration, the analogue can be incorporated with excipients
and used in the form of ingestible tablets, buccal tablets, troches, capsules,
elixirs, suspensions, syrups, wafers, and the like. Such compositions and
preparations should contain at least l% by weight of active compound. The
percentage of the compositions and preparations can. of course, be varied
and can conveniently be between about 5 to about 80% of the weight of the
unit. The amount of analogue in such therapeutically useful compositions is
such that a suitable dosage will be obtained.
The tablets, troches, pills, capsules and the like can also contain the
following: a binder such as gum gragacanth. acacia.corn starch or gelatin:
excipients such as dicalcium phosphate: a disintegrating agent such as corn
starch, potato starch, alginic acid and the like; a lubricant such as
magnesium stearate: and a sweetening agent such as sucrose, lactose or
saccharin or a flavoring agent such as peppermint, oil of wintergreen. or
cherry flavoring. When the dosage unit form is a capsule, it can contain, in
addition to materials of the above type, a liquid carrier. Various other
materials can be present as coatings or to otherwise modify the physical form
of the dosage unit. For instance, tablets, pills, or capsules can be coated with
shellac, sugar or both. A syrup or elixir can contain the analogue, sucrose as
a sweetening agent, methyl and propylparabens as preservatives, a dye and
flavoring such as cherrv or orange flavor. Of course, anv material used in
preparing any dosage unit form should be pharmaceutically pure and
substantially non-toxic in the amounts employed. In addition, the analogue
can be incorporated into sustained-release preparations and formulations.
The language "pharmaceutically acceptable carrier" is intended to
include solvents, dispersion media, coatings, antibacterial and antifungal
agents, isotonic and absorption delaying agents, and the like. The use of
such media and agents for pharmaceutically active substances is well known
in the art. Except insofar as any conventional media or agent is incompatible
with the analogue, use thereof in the therapeutic compositions and methods
of treatment is contemplated. Supplementary active compounds can also be
incorporated into the compositions according to the present invention. It is
especially advantageous to formulate parenteral compositions in dosage unit
form for ease of administration and uniformity of dosage. Dosage unit form
as used herein refers to physically discrete units suited as unitary dosages for
the individual to be treated: each unit containing a predetermined quantity of
analogue is calculated to produce the desired therapeutic effect in
association with the required pharmaceutical carrier. The specification for
the novel dosage unit forms of the invention are dictated by and directly
dependent on (a) the unique characteristics of the analogue and the
particular therapeutic effect to be achieve, and (b) the limitations inherent in
the art of compounding such an analogue for the treatment of iron-related or
iron overload diseases in individuals. The principal analogue is compounded
for convenient and effective administration in effective amounts with a
suitable pharmaceutically acceptable carrier in an acceptable dosage unit. In
the case of compositions containing supplementary active ingredients, the
dosages are determined by reference to the usual dose and manner of
administration of the said ingredients.
Preferably the pharmaceutical composition is administered in a dosage
regimen of 30 - 500 mg per kg of body weight of a patient. More preferably,
the dosage regimen is 50 - 100 mg per kg of body weight.
In a third aspect the present invention provides a method of iron
chelation therapy comprising administering to a patient a pharmaceutical
composition according to the second aspect of the present invention.
In a fourth aspect, the present invention provides a method of treating
an iron-overload disease in a subject, the method comprising administering
to a subject a pharmaceutical composition according to the second aspect of
the present invention.
In one embodiment, the iron-overload disease is ß-thalassemia.
In an alternate embodiment, the disease is Friedreich's ataxia.
In a fifth aspect, the present invention provide use of a 2-
pyridylcarboxaldehyde isonicotinoyl hydrazone (PCIH) analogue according to
the first or second aspects of the present invention in the manufacture of a
medicament for the treatment of an iron-overload disease.
Considering the high potential of the PIH class of ligands which have
high Fe chelation efficiency both in vivo and in vitro, the present inventors
have synthesized a number of aroylhydrazones so as to identify Fe chelators
more efficient than desferoxamine (DFO) and more soluble than those of
the PIH class. These compounds belong to a new series of tridentate
chelators known as the 2-pyridylcarboxyaldehyde isonicotinoyl hydrazone
(PCIH) analogues. The Fe chelation efficacy and antiproliferative activity of
these chelators have been studied including their effects on the expression of
genes (WAF1 and GADD45) known to be important in mediating cell cycle
arrest at GvS. From chelators synthesized, three analogues, namely 2-
pyridylcarboxaldehyde benzoyl hydrazone (PCBH). 2-pyridylcarboxaldehyde
in-bromobenzoyl hydrazone (PCBBH). and 2-pyridylcarboxaldehyde 2-
thiophenecarboxyl hydrazone (PCTH). showed greater Fe chelation activity
than PIH. These ligands were highly effective at both mobilizing 39Fe from
cells and preventing 39Fe uptake from 39Fe-transferrin and caused a marked
increase in the RNA-binding activity of the iron-regulatory proteins (IRPs).
In comparison to the cytotoxic Fe chelator. 2-hydroxy-1-naphthylaldehyde
isonicotinoyl hydrazone (311). these ligands have far less effect on cellular
growth and 3H-thymidine. 3H-leucine or 3H-uridine incorporation. In
addition, in contrast to 311 that markedly increased WAF1 and GADD45
mRNA expression. PCBH and PCTH did not have any effect, while PCBBH
increased the expression of GADD45 mRNA. Collectively, the present results
demonstrate the potential of several of these ligands as agents for the
treatment of Fe overload disease.
Of these particular compounds, it has now been found that PCTH.
PCBH and PCBBH have the potential tor use as agents for treatment of Fe
overload.
The compositions should also, if desired, contain a suitable buffer to
adjust the pH of the stomach of the patient or subject to a level that will
minimize acid hydrolysis. Such a pH should be about 6-8 (more preferably
about 7) for the active compounds per se inclusive of the free bases and
hydrochloride salts discussed hereinafter.
Such buffers are well known to include single or multiple components
such as those listed in the UA Pharmacopoeia XXII. specifically for example,
ammonium, potassium and/or sodium salts of phosphoric acid, in
conjunction with citric acid. Use of a pharmaceutically acceptable antacid,
such as aluminum and/or magnesium hydroxide or calcium carbonate or
glycine USPNF sufficient to neutralize the normally present 0.1 M HCl in the
200-600 ml of stomach fluids (20 to 60 meq of base). A specific example of
phosphate-citrate buffer. pH 6.8. would result from 9.1 ml of 0.1 M citric acid
combined with 40.9ml 0.2M dibasic sodium phosphate solutions.
Measurement of the bioefficiency of chelators of the invention can be
carried out in accordance with the methods described in Brittenham. 2 April
1990. Seminar in Haematolosy 27 112-116 or as described in US 5334492
which is incorporated herein by reference.
The active compounds of the invention may be made into an enteric
coated granule formulation using the formulations described in US 5834492.
For Example, the drug is combined with sufficient ethanol to make it into a
slightly damp thick paste which is further mixed with providone and
mechanically applied as a layered coating over a spherical support of defined
mesh size. The supports themselves, if desired, are usually
pharmacologically inactive, but an active support may also be utilized. The
spherical matrix could be an acid resistant, biocompatible polymer.
Examples are polycarbonate, polyethylene, teflon, microcrystalline cellulose,
or other plastics. Other biocompatible polymers can also be used.
Enteric polymers and plasticizers are combined in ethanol to form a
solution which is carefully sprayed over the support as a film which covers
the active drug and protects it from premature dissolution in an
environmental pH which is unfavourable for best absorption. The ensuing
product is mechanically dried while preserving the uniformity of the enteric
coating.
Throughout this specification, unless the context requires otherwise,
the word "comprise", or variations such as "comprises" or "comprising", will
be understood to imply the inclusion of a stated element, integer or step, or
group of elements, integers or steps, but not the exclusion of any other
element, integer or step, or group of elements, integers or steps.
Any description of prior art documents herein is not an admission that
the documents form part of the common general knowledge of the relevant
art in Australia.
In order that the present invention may be more clearly understood
preferred forms will be described with reference to the following examples
and drawings.
Brief Description of Drawings
Figure 1. The structures of the iron chelators assessed in this study:
desferoxamine (DFO). pyridoxal isonicotinoyl hydrazone (PIH). 2-hydroxy-
1-naphthylaldehyde isonicotinoyl hydazone [311). 2-pyridylcarboxaldehyde
isonicotinoyl hydrazone (PCIH). 2-pyridylcarboxaldehyde benzoyl hydrazone
[PCBH], 2-pyridylcarboxaldehyde m-bromobenzoyl hydrazone (PCBBH), 2-
pyridylcarboxaldehyde thiophenecarboxyl hydrazone (PCTH). 2-
pyridylcarboxaldehyde p-hydroxybenzoyl hydrazone (PCHH). 2-
pyridylcarboxaldehyde p-aminobenzoyl hydrazone (PCAH). 2-
furoylcarboxaldehyde isonicotinoyl hydrazone (FIH).
Figure 2. The effect of DFO. 311. PIH. or the PCIH analogues on (A)
39Fe release from prelabelled SK-N-MC cells, and (B) 39Fe uptake from 39Fe-
transferrin (39Fe -Tf) by SK-N-MC cells. (A) SK-N-MC neuroepithelioma cells
were labeled with 39Fe -Tf (0.75 mM) for 3 h at 37°C. washed, and then
reincubated for 3 h at 37°C in the presence of medium alone (control) or
medium containing DFO (100 mM) or the other chelators (50 uM). (B) SK-N-
MC cells were incubated for 3 h in media containing 39Fe -Tf (0.75 mM) and
either DFO (100 mM) or the other chelators (50 mM). washed, and then
incubated with pronase (1 mg/ml) for 30 min at 4°C. Results are expressed as
the mean ± SD of 3 replicates in a typical experiment of two experiments
performed.
Figure 3. The effect of chelator concentration on (A) iron release from
prelabelled SK-N-MC cells and (B) 39Fe uptake from 39Fe -transferrin (39Fe-Tf)
by SK-N-MC cells. (A) SK-N-MC neuroepithelioma cells were labeled with
39Fe -Tf [0.75 mM) for 3 h at 37°C. washed, and then reincubated for 3 h at
37ºC in the presence of the chelators (0.5-50 mM). (B) SK-N-MC cells were
incubated for 3 h in media containing 39Fe -Tf (0.75 mM) and the chelators
(0.5-50 µM). washed, and then incubated with pronase (1 mg/ml) for 30 min
at 4°C. Results are expressed as the mean of three replicates in a typical
experiment of two experiments performed.
Figure 4. The effect of chelator concentration on the proliferation of
SK-N-MC neuroepithelioma cells. Cells were incubated in the presence and
absence of the chelators (0-50 mM) for 90 h at 37°C. After this incubation
period, cellular density was measured via the MTT assay. Each data point
represents the mean of four replicates in a typical experiment of two
experiments performed.
Figure 5. The effect of the chelators on the RNA-binding activity of the
iron-regulatory proteins (IRPs) in SK-N'-MC neuroepithelioma cells. Cells
were incubated for 20 h with either medium alone (control), ferric
ammonium citrate (FAC: 100 mg/ml). DFO (100 mM). or the other chelators (25
mM). The result illustrated is a typical experiment from two experiments
performed.
Figure 6. The effect of the chelators on mRNA levels of GADD45,
VYAF1 and ß-actin in SK-N'-MC neuroepithelioma cells. Total RNA was
extracted from cells after a 20 h incubation with medium alone (control) or
medium containing ferric ammonium citrate (100 µg/mL). DFO (100 µM) or
the other chelators (25 µM). The isolated RNA was then electrophoresed on a
1.2 % agarose-formaldehyde gel. transferred to a hybridisation membrane,
and probed under high stringency conditions. The result illustrated is a
typical experiment from three experiments performed.
Figure 7. The effect of reincubation time with the Fe chelators on 39Fe
mobilization from 39Fe-loaded reticulocytes. The cells were labelled with
39Fe-transferrin (3.75 µM) in the presence of the heme synthesis inhibitor,
succinylacetone (1 mM). and incubated with the cells for 1 h at 37°C. The
39Fe-labelled reticulocytes were then incubated with the chelators (200 µM)
for 15-240 min at 37°C. The results are Mean ± SD (3 determinations) in a
typical experiment of three performed.
Figure 3. The effect of reincubation time with the Fe chelators on the
percentage of ethanol-soluble 39Fe in reticulocytes. The cells were treated as
in Figure 7 and the percentage of ethanol-soluble 39Fe determined by lysing
39Fe-labelled reticulocytes with ice-cold water. The proteins precipitated ice-
cold 95% ethanol and soluble and insoluble fractions separated by
centrifugation (see Methods for details). The results are Mean ± SD (3
determinations] in a typical experiment of three performed.
Figure 9. The effect of chelator concentration on 39Fe mobilization
from 39Fe-loaded reticulocytes. The cells were labelled with 39Fe-transferrin
(3.75 µM) in the presence of the heme synthesis inhibitor, succinylacetone (1
mM). and incubated with the cells for 1 h at 37°C. The 39Fe-labelled
reticulocytes were then incubated with the chelators (10-200 µM) for 15-240
min at 37ºC. The results are Mean ± SD (3 determinations] in a typical
experiment of three performed.
Modes for Carrying Out the Invention
EXPERIMENTAL
Synthesis of iron chelators and their preparation for screening in culture
PCIH analogues according to the present invention were synthesized
by Schiff base condensation between 2-pyridinecarboxaldehyde and the
respective acid hydrazides. The chelators were characterized by a
combination of elemental analysis, infrared spectroscopy. 1H-NMR
spectroscopy and X-ray crystallography. Both PIH and the PIH analogue 2-
hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone (311) were synthesized
and characterized as described previously in Richardson et al.. 1995.
Desferoxamine (desferoxamine mesylate: DFO) was purchased from Ciba-
Geigy Pharmaceutical Co.. Summit. NJ. All of the aroylhydrazone chelators
were dissolved in dimethyl sulphoxide (DMSO) as 10 mM stock solutions
immediately prior to an experiment and then diluted in 10% fetal calf serum
(FCS: Commonwealth Serum Laboratories. Melbourne. Australia) so that the
final concentration of DMSO was equal to or less than 0.5% (v/v). After
dilution, the solutions were mixed vigorously to ensure total solubilization.
Previous studies by the inventors have demonstrated that DMSO at this
concentration has no effect on either cellular proliferation. 39Fe release from
prelabelled cells, or the ability of the cells to remove 39Fe from Tf
(Richardson et al.. 1995).
Synthesis of free bases
All chelators were prepared by re fluxing 10 mmol of the acid
hydrazide with 2-pyridine carboxaldehyde (or 2-furfural with isonicotinic
acid hydrazide for FIH) m 50% aqueous ethanol (40 mL) for 30 min. After
cooling, the product was collected by filtration, washed with diethyl ether
and dried in a vacuum desiccator. Yields were typically 70-80%.
Syntheses of the hydrochloride salts
A sample (0.25 g) of each free base was dissolved in ethanol (15 mL).
Concentrated hydrochloric acid (1 mL) was added with stirring followed by
diethyl ether (40 mL) to afford precipitation of the hydrochloride salt. The
compound was filtered off and dried in a vacuum desiccator."
Cell Culture
The human SK-N'-MC neuroepithelioma and SK-Mel-28 melanoma cell
lines were from the American Type Culture Collection (ATCC). Rockville.
MD. USA. The SK-N'-MC cell line was originally classified as a
neuroblastoma, but has been recently reclassified as a neuroepithelioma, a
closely related neuroectodermal malignancy. The BE-2 neuroblastoma cell
line was a kind gift from Dr Greg Anderson. Queensland Institute of Medical
Research. Queensland. The SK-N-MC and SK-Mel-28 cell lines were grown
in Eagle's modified minimum essential medium (MEM: Gibco BRL. Sydney.
Australia) containing 10% FCS. 1% (vv) non-essential amino acids (Gibco).
2 mM L-glutamine (Sigma Chemical Co.. St. Louis. MO. USA) 10 µg/ml of
streptomycin (Gibco). 100 U. ml penicillin (Gibco) and 0.28 µg/ml of
fungizone (Squibb Pharmaceuticals. Montreal. Canada). This growth
medium will be subsequently referred to as a complete medium. The BE-2
cell line was grown in Rosewall Park Memorial Institute (RPMI) medium with
all of the supplements described above for MEM. Cells were grown in an
incubator (Forma Scientific. OH. USA) at 37°C in a humidified atmosphere of
5% CO/95% air and subcultured as described previously (Richardson et al.,
1990. Biochim. Biophys. Acta 1053 1-12). Cellular growth and viability were
monitored using phase-constant microscopy and trypan blue staining.
Effect of Chelators on Cellular Proliferation
The effects of the chelators on the proliferation of SK-N'-MC
neuroepithelioma cells were examined using the MTT (3-(4.5-
dimethylthiazol-2-yl)-2.5-diphenyltetrazolium) assay by essentially the same
method as described previously (Richardson er al.. 1995). Cellular
proliferation was examined by seeding cells in 96-well microtitre plates at
15.000 cells/well in 0.1 mL of complete medium containing human diferric
Tf (1.25 µM). This seeding density resulted in exponential growth of the
cells throughout of the assay. The cells were allowed to grow overnight and
the chelators were then added in 0.1 mL of complete medium containing
diferric transferrin (1.25 uM). The final concentrations of the chelators were
0.39-50 uM. Control samples contained complete medium and diferric Tf
(1.25 µM). Cells were incubated with the chelators for 90 hrs at 37°C in a
humidified atmosphere containing 95% air and 5% CO,. After this
incubation. 0.01 mL of MTT was added to each well and the plates incubated
for 2 hrs at 37°C. The cells were solubilized by adding 0.1 mL of 10% SDS-
50% isobutanol in 0.01 M HCl and the plates then read at 570 nm on a
scanning multiwell spectrophotometer (Titertek Multiscan: Beckman
Instruments Inc.. California). As shown previously for the SK-N-MC cell
line. MTT colour formation was directly proportional to the number of viable
cells (Richardson et al.. 1995): The results of the MTT assays are expressed
as a percentage of the control value.
Preparation of 39Fe-Transferrin
Apotransferrin (Sigma Chemical CO.. St. Louis. U.S.A.) was prepared
and labelled with 39Fe (as ferric chloride in 0.1 M HCl. Dupont NEN. MA.
U.S.A.) to produce 39Fe:-transferrin (39Fe-Tf) using standard procedures
described previously (Richardson et al.. 1990). The saturation of Tf with Fe
was monitored by uv-vis spectrophotometry using the absorbance at 280 nm
(protein) compared with that at 456 nm (Fe-binding site). In all experiments,
fully saturated diferric Tf was used.
Effect of the Chelators on 3H-Thymidine. 3H-Leucine and 3H-Uridine
Incorporation
Labelling of cells with 3H-thymidine (20 Ci/mmol: Dupont NEN. MA,
U.S.A.). 3H-uridine (42.7 Ci/mmol/Dupont NEN. MA. U.S.A.) and 3H-leucine
(52 Ci/mmol: Dupont NEN) was estimated after precipitation with
trichloroacetic acid (TCA). After a 20 hr incubation with the chelators. 3H-
leucine. 3H-uridine or 3H-thymidine (1 mCi/ml) were then added for 2 hrs at
37ºC. Subsequently, petri dishes containing cell cultures were placed on ice
and washed four times with ice-cold Hanks balanced salt solution (BSS) and
the cells detached from the plate using 1 MM EDTA in Ca/Mg-free saline.
The cells were then pelleted by centrifugation, the supernatant removed and
the pellet frozen at -70°C. After thawing the cells on ice. 1 ml of ice-cold
20% TCA was added and the solution then vortexed and kept on ice for 1 hr
with periodic mixing. This solution was then centrifuged at 15.000 rpm for
15 mins at 4ºC and the supernatant removed. The pellet was then washed
twice with 1 ml of ice-cold 10% TCA. The pellet was dissolved in 0.5 ml of 1
M NaOH and transferred to scintillation tubes with 3 ml of scintillant.
Radioactivity was measured on a ß-scintillation counter (LKB Wallace,
Finland).
Iron Uptake and Iron Efflux Experiments
The effect of chelators on 39Fe uptake from39Fe-Tf and 39Fe release from
prelabelled cells was studied using standard procedures reported previously
(Richardson et al.. 1994. J. Lab Clin. Med. 124 660-71). The amount of 39Fe
internalized by the cells was measured by incubation with the general
protease pronase (1 mg, ml) for 30 min at 4ºC to remove membrane-bound
39Fe and Tf (Richardson et al.. 1990: Baker et al., 1998. Biochim. Biophys.
Acta 1380 21-30). Control experiments reported in previous studies have
found that this technique is valid for estimation of 39Fe internalization of
cells (Richardson et al.. 1990: Baker et al.. 1998).
Iron Regulatory Protein Gel-Retardation Assay
A gel-retardation assay was used to measure the interaction between
the IRPs and IRE using established techniques (Leibold et al., 1988. Proc.
Natl. Acad. Sci. USA 85 2171-5: Milliner et al.. 1989 Cell 58 373-82). Briefly,
after incubation with medium alone (control) or medium containing ferric
ammonium citrate (100 mg/ml: Aldrich Ltd.. Sydney. Australia) or the
chelator. 2- 5 x 10° cells were washed with ice-cold phosphate-buffered saline
(PBS) and lysed at 4°C in 40 µl of ice-cold Munro extraction buffer (10 mM
HEPES. pH 7.6. 3 mM MgCl2. 40 mM KCl. 5% glycerol. 1 MM dithiothreitol
and 0.5% Nonidet P-40). After lysis, the samples were then centrifuged at
10.000 rpm for 3 mins at 4°C to remove nuclei and the supernatant stored at
-70ºC. Frozen cytoplasmic extracts were thawed on ice and then centrifuged
at 15.000 rpm for 10 min at 4ºC. The protein concentration of the soluble
supernatant was determined using the BioRad protein assay (BioRad Ltd..
USA). Samples of cytoplasmic extracts were diluted to a protein
concentration of 100 µg/ml in Munro buffer without Nonidet P-40 and 1 µg
aliquots were analyzed for IEP by incubation with 0.1 ng (approximately 1 x
103 cpm) of 32P-labelled pGL66 RNA transcript (Leibold et al., 1988). The
riboprobe was transcribed in vitro from linearized plasmid templates using
SP6 RNA polymerase in the presence of a-32P LTP (Dupont. NEN). This
latter reaction was performed using the Promega Riboprobe In Vitro
Transcription Kit (Promega. Madison, WL USA). The probe was
subsequently purified on a 6% urea/PAGE gel. To form RNA-protein
complexes, cytoplasmic extracts containing 1µg of protein were incubated for
10 mins at room temperature with the "P-labelled riboprobe. Unprotected
probe was degraded by incubation with 1 U of RNAse T1 for 10 mins at room
temperature. Heparin (Sigma) at a final concentration of 5 mg/ml was then
added and incubated with the extract for another 10 mm at room temperature
to exclude non-specific binding. RNA-protein complexes were analyzed in
6% non-denaturing polyacrylamide gels at 4°C as described by Konarska et
al., 1986. Cell 46 845-55. Gels were dried, covered in plastic film and
exposed to Kodak XAR films at -70ºC with an intensifying screen.
Northern Blot Analysis
Northern blot analysis was performed by isolating total RNA using the
Total RNA isolation Reagent from Advanced Biotechnologies Ltd (Surrey.
United Kingdom). The RNA (15 µg) was heat denatured at 90ºC for 2 mins in
RNA-loading buffer and then loaded onto a 1.2% agarose-formaldehyde gel.
After electrophoresis. RNA was transferred to a nylon membrane
(GeneScreen. New England Nuclear. Boston. USA) in 10 x SSC using the
capillary blotting method. The RNA was then cross-linked to the membrane
using a UV-crosslinker (UV Stratalinker 1800. Stragene Ltd.. USA).
The membranes were hybridized with probes specific for human
WAF1. GADD-45 and ß-actin. The VVAF1 probe consisted of a 1 kb fragment
from pSXV(ATTC: Cat. No. 79928). The GADD45 probe consisted of a 760 bp
fragment from human GADD45 cDNA cloned into pHul45B2 (kindly
supplied by Dr. Albert Fornace. National Cancer Institute. NTH. Maryland).
The ß-actin probe consisted of a 1.4 kb fragment from human ß-actin cDNA
cloned into pBluescript SK-(ATCC: at. No 37997).
Hybridization of probes to the membranes and their subsequent
washing were performed as described by Mahmoudi and Lin. 1989.
Biotschniques 7. 331-2 using a Hybaid Shake and Stack Hybridization oven
(Hybaid Ltd.. Middlesex. UK). The membranes were then exposed to Kodak
XAR Films at -70°C with an intensifying screen. The probes were stripped
from the nylon membrane by boiling in a solution containing 10 mM Tris-
HCl (pH 7.0). 1 mM EDTA (pH 8.0) and 1% SDS for 15-30 mins as described
by the membrane manufacturer. Densitometric data were collected with a
Laser Densitometer and analyzed by Kodak Biomax Software (Kodak Ltd,
USA).
Reticulocytes
Reticulocytosis was induced by standard procedures (Richardson, DR.,
Ponka. P and Vyoral. D (1996) Blood 87, 3477-3488) in New Zealand white
rabbits by repeated phlebotomy by cardiac puncture using a protocol
approved by the McGill University Animal Care Committee. Reticulocytes
were identified based on staining with new methylene blue, and cell counts
were determined using an improved Neubauer counting chamber.
Labelling of Transferrin
Apotransferrin (Sigma Chemical Co) was prepared and labelled with
39Fe (as ferric chloride in 0.1 M HCl. Dupont NEN. MA. USA) to produce
39Fe2-transferrin (39Fe-Tf) using established methods (Richardson. D R. and
Baker. E (1992) J Biol Chem 267. 13972-13979).
Mobilisation of 39Fe from 3eFe-Loaded Reticulocytes
The 39Fe-labelled rabbit reticulocyte has been shown to be a useful
model to investigate the ability of an Fe chelator to permeate the cell
membrane and chelate intracellular Fe pools. Reticulocytes were obtained
from chronically bled rabbits as described above and were incubated with 1
mM succinylacetone (SA: Sigma) to inhibit heme synthesis. After a 15 min
preincubation in the presence of SA. 39Fe-Tf (3.75 µM) was added and
incubated with the cells for 1 h at 37ºC with shaking. After this incubation
the reticulocytes were washed three times with ice-cold PBS to remove non-
specifically bound 39Fe-Tf. The washed 39Fe-labelled reticulocytes (30-35 µL)
were incubated in buffered salt solution (250 µL final volume) with the
apochelators. The SA was present in all incubations with the chelators to
prevent the utilization of non-heme 39Fe for heme synthesis. After the
incubation. 39Fe was measured both in washed reticulocytes and in the
medium, and the percentage of 39Fe mobilized from the reticulocytes was
then calculated.
In some experiments, washed 39Fe-labelled reticulocytes were lysed
with 200 uL of ice-cold distilled water and the proteins precipitated with 1
ml ice-cold 95% ethanol. The mixture was then centrifuged (13,000 rpm/30
min/4°C) on a IEC Micromax microcentrifuge (IEC Canada) to result in an
ethanol-soluble fraction containing 39Fe-bound to low Mr chelators, and an
ethanol-precipitated fraction containing protein-bound 39Fe. Previous studies
have demonstrated that this method results in the precipitation of 39Fe in
ferritin and transferrin while 39Fe bound to chelators remains in a soluble
form. An increase of 39Fe in the alcohol-soluble fraction shows that the
chelator can cross the cell membrane and form intracellular Fe complexes
which are released with limited efficiency.
RESULTS
Production of 2-pyridylcarboxaldehyde isonicotinoyl hydrazone (PCIH)
analogues
PCIH-H2O: Anal. Calcd for C12H12N4O2: C. 59.0: H. 5.0: N: 22.9. Found:
C. 59.2: H. 4.9: N. 22.9 %. 1H NMR (MeOH-d4) 5 (ppm vs TMS) 7.44 (m. 1H);
7.90 (m. 3H): 3.26 (d. 1H): 8.41 (s. 1H): 8.57 (d. 1H): 8.74 (dd. 2H).
PCBH-H2O: Anal. Calcd for C13H12N7O2: C. 64.2: H. 5.4; .V. 17.3. Found:
C. 64.1; H. 5.4: N 17.3 %. 1H NMR (MeOH-d4) d (ppm vs TMS) 7.41 (m. IH);
7.51 (m. 3H): 7.92 (d. IH): 7.95 (m. 2H): 8.28 (d. IH): 8.39 (s. IH): 8.55 (d. lH).
PCBBH-H2O: Anal. Calcd for C13H12BrN3O2: C. 48.5; H. 3.8: N, 13.0.
Found: C. 47.8: H. 3.6: N. 12.7 %. 1H NMR (MeOH-d4) d (ppm vs TMS) 7.44
(m. 2H): 7.76 (d. 1H): 7.91 (m. 2H): 8.12 (s. IH): 8.27 (d. IH): 8.39 (s. IH): 8.55
(d. IH).
PCTH: Anal. Calcd for C12H9N7OS: C. 57.1: H. 3.9: N. 13.2. Found: C.
57.2: H. 4.0: N. 17.3 %. lH NMR (MeOH-d4) d (ppm vs TMS) 7.20 (m. IH);
7.43 (m. IH): 7.85 (m. 3H): 8.26 (d, IH): 8.37 (s. IH); 8.56 (d. IH).
PCHH-H2O: Anal. Calcd for Cl3H11.5N3O2.25: C. 63.8; H. 4.3; N. 17.2.
Found: C. 63.6: H. 4.8: N. 16.4 %. lH NMR (MeOH-dJ 6 (ppm vs TMS) 6.88
(dd. 2H): 7.43 fm. 1H): 7.86 (m. 3H): 8.29 fd. IH): 8.36 (s. 1H): 8.55 (d. 1H).
PCAH-H2O: Anal. Calcd for C12H14N4O2: C. 60.5: H. 5.5: N. 21.7. Found:
C. 60.3: H. 5.5: N. 21.4 %. lH NMR (MeOH-d4) d (ppm vs TMS) 6.69 (dd. 2H):
7.39 (m. 1H): 7.74 (dd. 2H): 7.85 (td. 1H): 8.26 (d. 1H); 8.33 (s. 1H): 8.52 (d,
1H).
FIH: Anal. Calcd for C11H9N3O2: C. 61.4: R 4.2; N, 19.5. Found: C, 61.6;
H. 4.2: N. 19.4 %. 1H NMR (MeOHd4) (ppm vs TMS) 5 6.59 (dd. 1H); 7.00 (d,
1H): 7.69 (d. 1H): 7.86 (dd. 2H:): 8.26 (s. 1H): 8.73 (dd. 2H).
PCIH-2HCl-2.5H2O: Anal. Calcd. for C12H17Cl2N4O3.5: C. 41.9: H, 5.0; N,
16.3. Found: C. 41.6: H. 4.5: N. 16.0%. lH NMR (D2O). d (ppm vs TMS): 8.17
(t. 1H), 8.40 (d. 1H). 8.59 (d. 2H). 8.70 (s. 1H). 8.75 (t. 1H). 8.94 (d. 1H), 9.12
(d. 2H).
PCBH-HC1-1.5H2O: Anal. Calcd. for C13H19C1N3O2.3: C. 54.1: H, 5.2; N,
14.6. Found: C. 53.9: H. 4.8: N. 14.1%. 1H NMR (D2O). d (ppm vs TMS):
7.39-7.53 (m. 3H). 7.80 (d. 2H). 7.97 (t. 1H). 3.12 (d. 1H). 8 .32 (s. 1H). 8.55 (t.
1H). 8.69 (d. 1H).
PCBBH-HCl: Anal. Calcd. for C10H11ClN2O: C. 45.8: H. 3.3: N. 12.3.
Found: C. 45.2: H. 4.1. N. 13.3 % lH NMR (D2O). d (ppm vs TMS): 7.25 (m.
2H). 7.50 (d. 1H). 7.7-8.0 (m. 4H). 8.5 (s. 1H). 8.70 (d. 1H).
PCTH-HC1-H2O: Anal. Calcd. for C11H12ClN22S: C. 46.2: H. 4.2: N. 14.7.
Found: C. 45.6: H. 4.1. N. 14.3%. lH NMR (D2O). d (ppm vs TMS): 7.2 (m.
2H). 7.7-8.0 (m. 3H). 8.4-3.6(m. 2H). 8.50 (d. 1H).
PCHH-HCI: Anal. Calcd. for C12:H10ClN2O4: C. 49.8: H. 5.1: N. 13.4.
Found: C. 50.2: H. 4.9. N. 13.1%. lH NMR (D2O). d (ppm vs TMS): 6.60 (d.
2H). 7.60 (d. 2H). 7.91 (t. 1H). 8.01 (s. 1H). 8.43 (t. 1H). 8.59 (d. H).
PCAH-HCI: Anal. Calcd. for C13H16Cl2N4O3: C. 44.7: H. 5.2: N. 16.0.
Found: C. 44.7: H. 5.2. N. 15.9%. lH NMR (D2O). d (ppm vs TMS): 7.28 (d.
2H). 7.90 (d. 2H). 8.20 (t. 1H). 8.40 (s. 1H). 8.60 (t. 1H). 8.80 (d. 1H).
FIH-2HC1-H3O: Anal. Calcd. for C11HU13Cl2N2O2: C. 49.0: H. 4.5; N. 15.6.
Found: C. 49.2: H,. 4.5. N. 15.6%. lH NMR (D2O), d (ppm vs TMS): 6.64 (m.
1H). 7.01 (d. 1H). 7.71 (s. 1H). 8.26 (s. 1H). 8.42 (d. 2H). 8.99 (d. 2H).
The chelators in their free base form were sparingly soluble in water
but are quite soluble in methanol and somewhat less so in ethanol. Upon
protonation of their basic groups, the aqueous solubility of all chelators is
dramatically increased. The hydrochloride salts of PCBBH-HCl and PCTH-
HCl exhibit the lowest aqueous solubility of the series, whereas the most
soluble chelators are PCIH-2HC1 and PCAH-2HC1 (both diprotic acids).
The 1H NMR spectra of the hydrochloride salts in water are quite
similar to those of the corresponding free bases (in methanol). Most
importantly, the imine singlet resonance is observed in all cases, which
indicates that the imine functional group remains intact upon formation of
the hydrochloride salt. Moreover, the protonated chelators do not exhibit
any noticeable imine hydrolysis over a period of a week in aqueous solution
as shown by NMR spectroscopy.
The degree of protonation was dependent on the number of basic
groups present. The isonicotinoyl. p-aminophenyl and 2-pyridyl groups all
underwent protonation. The imine X-atom (a potentially basic site) was not
protonated unless the adjacent heterocycle was itself non-basic (i.e. the furyl
group in FIH). Internal hydrogen bonding of the imine X-atom with the
protonated pyridinium group appears to explain the resistance of the imine to
protonation in these ligands.
Effect of the Chelators on Iron Release from Prelabelled cells and Iron
Uptake from Transferrin
The ability of the PCIH analogues to increase 39Fe release from SK-N-
MC cells was compared to "standard chelators" (DFO. PIH and 311) whose
activity has been previously documented in this cell line. The efflux of 39Fe
from SK-X-MC cells was examined after a 3 hr labelling period with 39Fe-Tf
(0.75 µM) followed by a 3 hr reincubation in the presence and absence of
DFO (100 µM) or the remainder of the ligands at 50 uM (Figure 2A). It ,
should be noted that DFO was screened at 100 µM in all experiments because
of its low Fe chelation efficacy in SK-N-MC cells. Chelators 311. PIH. PCTH.
PCBH and PCBBH showed similar activity resulting in the release of 40-42%
of cellular 39Fe. The mobilization of 39Fe by PCIH was similar to that of DFO
which released 19% of cellular 39Fe. In contrast. FIH. PCAH and PCHH did
not appreciably increase 39Fe mobilization over that observed for the control
medium (Figure 2A).
To determine the ability of the chelators to inhibit 39Fe uptake from
39Fe-Tf (0.75 µM). SK-N-MC cells were incubated for 3 hrs at 37ºC with 39Fe -
and either DFO (100 µM) or the other chelators (50 µM) (Figure 2B). Ligands
311. PIH. PCTH. PCBH and PCBBH showed much greater efficacy than DFO
at preventing 39Fe uptake from 39Fe-Tf (Figure 2B). decreasing it to 13-30% of
the control value respectively, whereas DFO reduced it to 91% of the control
(Figure 2B). In terms of the other chelators. PCIH was slightly more effective
than DFO. while FIH. PCAH and PCHH had no effect on 39Fe uptake from
39Fe-Tf. Considering these data, in both 39Fe uptake and 39Fe efflux studies,
three of the PCIH analogues, namely PCTH. PCBH and PCBBH. showed
activity that was greater than DFO and comparable to PIH and 311 (Figure 2A
and 2B).
To further investigate the efficacy of the most effective PCIH analogues
identified from the screening studies above, the efficacy of PIH. PCIH, PCTH,
PCBH and PCBBH at mobilizing 39Fe from SK-N-MC cells at a range of ligand
concentrations was compared (0.5-50µM; Figure 3A). The mobilization of
39Fe from SK-N-MC cells was examined after a 3 hr labelling period with 39Fe-
Tf (0.75µM) followed by a 3 hr reincubation in the presence and absence of
effective chelators (0.5-50µM: Figure 3A). The 39Fe release mediated by all
chelators was biphasic as a function of chelator concentration, with 39Fe
release beginning to plateau at a ligand concentration of 25 µM. It was
apparent that at chelator concentrations up to 10 µM. the most effective
chelatorsat mobilizing 39Fe were PCTH and PCBBH (Figure 3A). However, as
the ligand concentration was increased up to 25 and 50 µM. the activity of
PCTH and PCBBH became similar to PIH and PCBH. PCIH was the least
effective chelator at all concentrations (Figure 3A).
Further studies examined the effect of chelator concentrations (0.5-50
µM) on the uptake of 39Fe from 39Fe-Tf (0.75 µM) during a 3 hr incubation
(Figure 3B). Similar to the results found in the efflux studies above. PCTH
and PCBBH were the most effective chelators at preventing 39Fe uptake from
39Fe-Tf at ligand concentrations up to 10µM. while at concentrations from 25-
50 µM the activity of PIH. PCIH. PCTH and PCBH were similar (Figure 3B).
Again. PCIH was the least effective chelator at all concentrations examined.
To determine if there were any differences in Fe chelation efficacy of the
ligands between different cell types, the activity of the three most effective
PCIH analogues (PCTH. PCBH and PCBBH) were compared to DFO and 311
in BE-2 neuroblastoma cells. SK-N-MC neuroepithelioma cells and SK-Mel-28
melanoma cells (Tables 1 and 2). Examining the ability of the chelators to
mobilize 39Fe from cells prelabelled for 3 hrs with 39Fe-Tf (0.75 uM) and then
reincubated for 3 hrs. DFO(100 µM) had comparable activity to 311 and the 3
PCIH analogues (50µM) at mobilizing 39Fe from BE-2 cells (Table 1). In
contrast. DFO was far less effective than either 311 or the PCIH analogues at
mobilizing 39Fe from SK-N'-MC or SK-Mel-23 Cells (Table 1).
Table 1. The effect of DFO. 311, PCTH. PCBH, or PCBHH on 39Fe release
from BE-2 neuroblastoma cells, SK-N-MC neuroepithelioma cells, and SK-
Mel-28 melanoma cells. Cells were labeled for 3 h at 37°C with 39Fe-
transferrin (0.75 µM), washed, and then reincubated with the chelators for 3
h at 37°C. The chelators 311. PCTH. PCBH. and PCBBH were screened at 50
µM while DFO was examined at 100 µM. Results are Mean ± SD of three
determinations in a typical experiment.
Table 2. The effect of DFO. 311. PCTH. PCBH. or PCBBH on internalized
39Fe uptake from 39Fe-transferrin by BE-2 neuroblastoma cells, SK-N-MC
neuroepithelioma cells, and SK-Mel-28 melanoma cells. Cells were
incubated with the chelators and 39Fe-transferrin (0.75 µM) for 3 h at 37°C,
washed, and incubated for 30 min at 4°C with pronase (1 mg/ml) to separate
the internalized from the membrane-bound 39Fe. All chelators were screened
at a concentration of 50 µM except for DFO which was examined at 100 µM.
Results are mean ± SD (three determinations) from a typical experiment.
The effect of the chelators at preventing 39Fe uptake from 39Fe-Tf
(0.75µM) after a 3 hr incubation was also examined in the same cell lines
(Table 2). The most effective chelator at inhibiting 39Fe uptake from 39Fe-Tf
was 311. which reduced 39Fe uptake similarly in all 3 cell lines to 8-10% of
the control value. The three PCIH analogues showed less activity than 311
but were far more effective than DFO (Table 2). It is of interest to note that
DFO had little effect at inhibiting 39Fe uptake in both SK-N-MC
neuroepithelioma cells and SK-Mel-28 melanoma cells (100 and 98% of the
control, respectively), whereas it reduced internalised 39Fe uptake from 39Fe-
Tf to 42% of the control in the BE-2 cell line (Table 2). In contrast, the
activity of the 3 PCIH analogues were somewhat similar in all 3 cell lines,
reducing 39Fe uptake from 39Fe-Tf to 15-38% of the control. The only
exception to this was PCBBH. which was much less effective at reducing 39Fe
uptake in SK-Mel-28 cells than either SK-N-MC or BE-2 cells (Table 2).
Effect of the PCIH Analogues on Cellular Proliferation
The studies above have clearly demonstrated that PCBH. PCBBH and
PCTH have Fe chelation efficacy that is comparable to that of PIH or 311 and
greater than that found for DFO. Hence, it was decided to determine the
antiproliferative effects of the PCIH analogues compared to DFO. PIH, and
311 whose activity has been previously characterized. From Figure 4, it is
clear that all of the PCIH analogues have much less effect on proliferation
than chelator 311. which has been shown in previous studies to be potent at
inhibiting the growth of a wide range of neoplastic cell lines. As shown
previously, the ability of DFO to inhibit growth of SK-N-MC cells was far less
than that of 311 (IC30 DFO = 47 µM: IC30 311 = 2µM). Of the PCIH
analogues. PCBBH and PCBH had antiproliferative activity comparable to
that of DFO (IC70 PCBBH = 42 µM: IC50 PCBH = 50 µM). The remaining
PCIH analogues had little effect at inhibiting growth. It is of interest to note
that while PIH. PCTH. PCBH and PCBBH had comparable Fe chelation
activity to 311 in SK-X-MC cells (Figure 2. Tables 1 and 2). their ability to
inhibit proliferation was much less. These results concur with previous
studies which demonstrated that Fe chelation efficacy is not always well
correlated to the ability of a ligand to inhibit proliferation.
Effect of the Chelators on 3H-Thymidine. 3H-Leucine or 3H-Uridine
Incorporation
The effect of the chelators on 'H-thymidine. 3H-leucine or 3H-uridine
incorporation in to SK-N'-MC cells was examined to obtain further
information on the possible mechanisms of action of these ligands (Table 3).
In these experiments, the effect of PCIH analogues have been compared to
DFO and 311. as the antiproliferative activity of these latter compounds has
been previously characterized using SK-N-MC Cells. The PCIH analogues
with the greatest Fe chelation efficacy, namely PCBBH. PCTH and PCBH,
reduced 3H-thymidine incorporation to 33%. 64% and 72% of the control
respectively, which was far less than the inhibition observed with 311 (0.1%
of the control) and similar to that found with PIH (5 2% of the control).
Interestingly, three chelators that showed little Fe chelation efficacy, namely
FIH. PCAH and PCHH (Figure 2) caused a considerable decrease in 3H-
thymidine incorporation to 11-17% of the control value (Table 3).
Table 3. The effect of the chelators on 3H-thymidine. 3H-leucine. or 3H-
uridine incorporation into SK-N-MC neuroepithelioma cells. Cells were
incubated for 20 hr at 37°C with either DFO (100 µM) or the other chelators
(50 µM). Following this, either 3H-thymidine. 3H-leucine. or 3H-uridine (1
µCi/mL) were added and the cells incubated for an additional 2 h at 37°C (see
Methods for details). Results are Mean ± SD (4-5 determinations) from a
typical experiment of 2-4 experiments performed.
Examining the effect of the chelators at inhibiting 3H-leucine and 3H-
uridine incorporation (Table 3). again the most effective chelator was 311.
which reduced their incorporation to 2% and 5% of the control value
respectively. In contrast. PCBH. PCBBH and PCTH. were far less active than
311 at inhibiting 3H-leucine and 3H-uridine incorporation, reducing it to 16-
47% of the control (Table 3). DFO was also less effective than 311 at
inhibiting 3H-leucine and 3H-uridine incorporation, reducing it to 9% and
34% of the control respectively. The 3 PCIH analogues that caused a
considerable decrease in 3H-thymidine incorporation (FIH. PCAH and PCHH)
did not inhibit 3H-leucine and 3H-uridine incorporation to the same extent,
reducing it to between 40-30% of the control value (Table 3).
The Effect of Chelators on the RNA-Binding Activity of the Iron Regulatory
Proteins (IRPs)
An important effect of intracellular Fe depletion using DFO is the
activation of RNA-binding activity of the iron regulatory proteins (IRP's)
(Hentze et al.. 1996. Proc. Natl. Acad. Sci. USA 93 8175-82). While the effect
of DFO on the RNA-binding activity of this protein has been well
characterized, little is known concerning the effect of other Fe chelators such
as the PCIH analogues. The present inventors examined the effect of a 20 hr
incubation with 311. PIH and the PCIH analogues (25 µM) on IRP-RNA
binding activity in SK-N-MC cells. In all experiments. DFO (100 µM) was
used as a positive control to deplete cells of Fe and increase IRP-RNA binding
activity. In contrast, ferric ammonium citrate (FAC: 100 .ug/ml) was used to
donate Fe to cells and reduce IRP-RNA binding. Examining Figure 5. it is
clear that only one major IRP-IRE band is present, which is due to the fact
that human IRP1-IRE and IRP2-IRE complexes co-migrate in non-denaturing
polyacrylamide gels (Chitambar et al. 1995. Cancer Res. 55 4361-66). As
expected, there was an increase in IRP-RNA binding activity following a 20
hr incubation with DFO. whereas after a 20 hr incubation with the Fe donor
FAC. there was an appreciable decrease in IRP-RNA binding activity
compared to the control (Figure 5). In comparison to the control, there was a
marked increase in IRP-RNA binding activity after treatment of cells with
311. PCTH. PCBH and PCBBH (Figure 5). which most likely reflects their
high Fe chelation efficacy (Figures 2 and 3). Surprisingly. PIH and PCIH had
little effect on IRP-RNA binding activity, whereas FIH. PCAH and PCHH
decreased IRP-RNA binding compared to the control (Figure 5). Addition of
ß-mercaptoethanol to the cell lysates demonstrated that there was no change
in the total amount of IRP-RNA binding activity after incubation with the
chelators (date not shown).
Effect of the PCIH Analogues on the Expression of Genes involved in the Cell
Cycle.
Treatment of cells with high concentrations of DFO (150 µM) or much
lower concentrations of 311 (2.5-5µM) resulted in an increase in the
expression of the p53-responsive genes VVAF1 (wild-type activating gene 1)
and GADD45 (growth arrest and DNA damage gene: (Darnell et al.. 1994.
Blood 94 731-792). VVAF-1 is a potent universal inhibitor of cyclin-
dependent kinases and can induce a G1/S arrest and possibly a G2/M arrest.
GADD45 is induced upon DNA damage and can arrest the cell cycle and is
also involved in DNA nucleotide excision repair. While it is known that
DFO. 311 and other Fe chelators can cause cell arrest, little is understood
concerning the changes in gene expression that may play a role in inhibiting
the cell cycle. In the present study, incubation with 311 (25 µM) and to a
lesser extent DFO (100 µM), caused an increase in the levels of both WAF1
and GADD45 mRNA in SK-N-MC cells (Figure 6). Of the PCIH analogues,
only PCBBH markedly increased the level of GADD45 mRNA but not WAF1
mRNA. This latter effect corresponds to the greater anti-proliferative activity
of PCBBH relative to the other PCIH analogues.
Effect of the PCIH Analogues on Mitochondrial Iron Mobilization in
Reticulocytes
In this investigation Fe chelation efficacy of PCIH analogues was
studied using the only well characterised model of mitochondrial Fe
overload, that is reticulocytes loaded with mitochondrial non-heme 39Fe. In
all studies. PIH was used as the reference compound as this chelator has
been characterized in previous studies to effectively deplete the non-heme
mitochondrial Fe pool.
In initial studies the effect of reincubation time on 39Fe release from
Fe-loaded reticulocytes was assessed (Figure 7). In these experiments, cells
were labelled with 39Fe-Tf for 1 h at 37ºC. washed, and then reincubated for
up to 240 min in the presence and absence of the chelators (200 µM). Of the
eight compounds examined. PCIH was the most effective at increasing
cellular 39Fe release as a function of incubation time (Figure 7). Indeed. PCIH
was more effective than PIH during incubation periods from 15-120 min. but
had similar activity after a 240 min reincubation. The high activity of PCIH
is evident after only 15 min incubation with 39Fe-loaded reticulocytes, at
which point the compound had mobilized 21 ± 1 % (3 determinations) of
cellular 39Fe (Figure 7). The amount of 39Fe released by PCIH after 15 min
was more than that mobilized by PCBBH. PCAH. PCHH. and FIH after 240
min of incubation viz. 17%. 15%. 6%. and 4% respectively. Examination of
the ethanol-soluble intracellular 39Fe after incubation with the chelators
revealed that this only increased in the presence of FIH (Figure 8). suggesting
the possible accumulation of its 39Fe complex within the cell.
In further studies, the effect of chelator concentration was assessed on
39Fe mobilization from 39Fe-loaded reticulocytes. In these experiments, the
cells were labelled with 39Fe-Tf for 1 h at 37ºC. washed, and then reincubated
for 1 h at 37ºC in the presence and absence of the chelators (Figure 9). Again,
PCIH was the most active compound. At a concentration of 200 µM. PCIH
released 31 ± 1 % (3 determinations) of cellular 39Fe compared to PIH that
mobilized 18 ± 1% (3 determinations). The compound PCTH had similar Fe
chelation efficacy as PIH. while the remaining ligands were substantially less
efficient. As described previously. DFO even at high concentrations up to 5
mM had little effect on mobilizing 39Fe, having activity similar to that
observed with control medium. As reported using the SK-N'-MC
neuroepithelioma cell line, both FIH and PCHH showed very low activity at
mobilizing intracellular 39Fe (Figure 9). As shown in Figure 8. an increase in
ethanol-soluble intracellular 39Fe was only observed with FIH and this
increased as the concentration increased up to 200 µM.
CONCLUSION'S
The present inventors have synthesized and screened a number of
aroylhydrazone ligands based upon 2-pyridylcarboxaldehyde isonicotinoyl
hydrazone (PCIH). Three of these chelators, namely PCBH. PCBBH and
PCTH. showed Fe chelation activity that was greater than DFO and
comparable to that of PIH and 311. In addition, the antiproliferative activity
of these chelators was far less than that found for analogue 311. an
aroylhydrazone ligand previously shown to possess high cytotoxic activity.
These properties suggest that these three PCIH analogues would be more
appropriate for the treatment of Fe-loading diseases rather than as anti-
proliferative agents against cancer.
It was attempted to synthesize ligands with high anti-proliferative
activity by condensing 2-pyridylcarboxaldehyde with a range of acid
hydrazides previously used in the synthesis of the PIH analogues. The 2-
pyridylcarboxaldehyde moiety was examined because when it is condensed
with thiosemicarbazide to form the relevant thiosemicarbazone. this ligand
has potent anti-proliferative activity. In fact, this latter group of a-N-
heterocyclic carboxaldehyde thiosemicarbazones have been described as the
most effective ribonucleotide reductase inhibitors yet identified. The present
results demonstrate that the PCIH analogues show little anti-proliferative
activity being far less effective than 311. These data may indicate that in
contrast to the 2-pyridylcarboxaldehyde moiety, the thiosemicarbazide
component of the 2-pyridylcarboxaldehyde thiosemicarbazones may be
important for antiproliferative activity.
All of the PCIH analogues examined in the present investigation,
except FIH. have the same potential Fe ligating sites, namely the carbonyl
oxygen, aldimine nitrogen and 2-pyridyl nitrogen (Figure 1). It is of interest,
however, that the biological activity of these ligands can be markedly
influenced by the nature of the substituents placed distal to the Fe-binding
site. For example, both PCHH and PCAH display very poor Fe chelation
activity, while PCTH. PCBBH and PCBH show very high efficacy (Figures 2A.
2B). Since lipophilicity is an important criterion for the membrane
permeability and Fe chelation efficacy of ligands. it may be that the
increased hydrophilicity of PCHH and PCAH (due to the presence of a
hydroxyl and amino group respectively) could prevent the access of these
chelators to intracellular Fe pools. While PCAH. PCHH and FIH showed
little ability to mobilize 39Fe and inhibit 39Fe uptake from 39Fe-Tf. it was of
interest that these chelators were more effective than the other PCIH
analogues at inhibiting 3H-thymidine incorporation (Table 3). Considering
this, it is possible that FIH. PCAH and PCHH may be relatively more efficient
at inhibiting ribonucleotide reductase, a crucial Fe-containing enzyme that is
involved in the conversion of ribonucleotides into deoxyribonucleotides for
DNA synthesis.
One advantage of the PCIH analogues according to the present
invention in comparison to the PIH analogues was their higher solubility in
aqueous solutions. While lipophilicity is an important property for
membrane permeability, the solubility of a chelator in water is also an
important factor in terms of its practical and clinical use. Hence, for a
chelator to be employed as a useful therapeutic agent, an appropriate balance
between solubility in aqueous solutions and the ability to permeate biological
membranes must be reached. For several of the PCIH analogues, this appears
to have been achieved.
The effect of DFO at increasing the RXA-binding activity of the IRPs
has been well characterized. Little is known, however, concerning the effect
of other Fe chelators. The fact that 311. PCTH. PCBH and PCBBH all
increased IRP-RXA binding activity in a similar way to DFO (Figure 5) may
suggest that these ligands act on the same or a similar intracellular pool of
Fe. In contrast to expectations. PIH and PCIH had no effect at increasing IRP-
RNA binding activity despite the fact that these chelators were highly
effective at mobilizing 39Fe from cells and preventing 39Fe uptake from 38Fe-Tf
(Figures 2 and 3). Higher concentrations of PIH did increase IRP-RNA
binding activity, however, suggesting that a concentration effect may be
involved. It is also of interest to note that FIH. PCAH and PCHH inhibited
IRP-RNA binding activity to a level comparable to that found after incubation
with FAC (Figure 5). Considering these results, it can be speculated that
PCAH. PCHH and FIH may disturb the intracellular distribution of Fe. such
that there is an increase in the Fe pool sensed by the IRPs.
While ability of Fe chelators to inhibit the cell cycle at GvS is well
known, very little is understood about the changes in gene expression that
may play a role in this process. In a previous study using neuroblastoma cell
lines and K562 cells, the present inventors demonstrated that incubation
with DFO (150 µM) or 311 (2.5-5 µM) resulted in a marked increase in the
expression of WAF1 and GADD45. two molecules that play key roles in
inducing cell cycle arrest at GvS. In the present study, it has been confirmed
these results using DFO and 311 and have shown that of the PCIH analogues,
only PCBBH increased the expression of GADD45 RNA (Figure 6). The
ability of a chelator to increase the expression of molecules involved in
inhibiting the cell cycle is not an appropriate characteristic of a compound to
be used of treating Fe overload.
Considering this, and the fact that PCBBH was the most effective
ligand at inhibiting proliferation. PCTH and PCBH appear to be preferable
candidate chelators for the treatment of Fe-loading diseases.
In the present work, all of the PCIH analogues showed far less anti-
proliferative activity than 311 (see Figure 4).. despite the high Fe chelation
efficacy of some of these compounds, e.g. PCBBH. PCBH and PCTH (Figures
2 and 3). The present inventors have shown that when the Fe complex of
311 is prepared, it prevents its antiproliferative activity and also its ability to
increase the expression of GADD45 and WAFl rnRNA. These results,
together with its high Fe chelation efficacy, suggests that 311 inhibits growth
by depleting intracellular Fe pools.
Several studies have suggested that Friedreich's ataxia may be caused
bv an accumulation of Fe in the mitochondrion. If this latter disease is
caused by mitochondrial Fe overload, possible treatment regimes could
include Fe chelation therapy. DFO effectively depletes cytosolic Fe pools,
but is unknown whether it can chelate mitochondrial Fe. In contrast,
previous studies have shown that aroylhydrazone chelators, such as PIH, can
remove Fe from the mitochondrion.
It will also be apparent that the PCIH analogues according to the
present invention may also include these compounds in their free base form
as well as their hydrochloride salts and the synthesis of the bases and salts is
discussed hereinafter.
At present, there is no treatment for FA which is a severe crippling
neurological condition. The exciting finding that mitochondrial Fe
accumulation may play an important role in its pathogenesis suggests that a
possible therapeutic intervention may be Fe chelation therapy. This study
identifies some of the PCIH class of chelators as highly effective ligands for
mobilizing mitochondrial non-heme Fe from reticulocytes. This latter model
was implemented as it is the only well characterized system of mitochondrial
Fe overload in cells. The ability of PCIH and PCTH to mobilize mitochondria
Fe pools overcomes the disadvantage of DFO that cannot effectively deplete
Fe from this compartment. These studies complement the work
demonstrating the high chelation efficacy and low toxicity of the PCIH group
of ligands in the SK-N-MC neuroepithelioma cell line. Indeed, some of these
compounds were far more efficient than DFO at increasing Fe mobilization
from cells and preventing Fe uptake from Tf.
The PCIH class of chelators were specifically designed based upon
studies on a wide range of compounds of the PIH class. From these studies,
structural features necessary for high Fe chelation efficacy and low toxicity
were chosen to optimise the use of these ligands as agents to treat Fe-
overload disease. Indeed, the design strategy has been very successful, as it
has resulted in chelators that show higher activity than the parent compound
PIH.
The strategy to design new chelators derived from PIH was based upon
the advantageous properties of this compound. These are: (a) oral
effectiveness: (b) near optimal hydrophilic-lipophilic balance: (c) high
specificity and selectivity for Fe; (d) predominantly neutral at physiological
pH: (e) economical and simple to synthesize: and (f) high chelation efficacy
both in vitro and in vivo.
The reason for the ability of some of the PCIH ligands to mobilize
mitochondrial Fe may be their much higher lipophilicity in comparison to
DFO. Indeed, to permeate the mitochondrion and chelate Fe. three lipid
membranes need to be transversed. viz.. the plasma membrane and the inner
and outer mitochondrial membranes. Accordingly, a lipophilic chelator that
rapidly permeates membranes and targets mitochondrial Fe will be far more
effective than a hydrophilic compound such as DFO. This may be an
important property of the analogue, since the Fe-loading in FA is not
pronounced as that found in untreated ß-thalassemia. Hence, only very short
durations of therapy may be possible or necessary in order to prevent overall
body Fe depletion. Under these conditions specific targeting of
mitochondrial Fe pools could be an important property.
It will be appreciated by persons skilled in the art that numerous
variations and/or modifications may be made to the invention as shown in
the specific embodiments without departing from the spirit or scope of the
invention as broadly described. The present embodiments are. therefore, to
be considered in all respects as illustrative and not restrictive.
WE CLAIM:
1. A 2-pyridylcarboxaldehyde isonicotinoyl hydrazone (PCIH) analogue suitable
for use as an in vivo iron chelator, the PCIH analogue having Formula 1:
Formula 1
wherein R2 is either OH or H, such that when R2 is OH, R1 is phenyl, pyridine, furan
or thiophene ring optionally with alkyl, halo, nitro, amine or hydroxyl attached to any of
the vacant positions on the ring; isomers thereof or salts thereof; or when R2 is H, Rl is
thiophene, phenol or 2-, 3- or 4- bromophenyl optionally substituted with alkyl, halo,
nitro, or amine attached to any of the vacant positions on the ring; or salts thereof.
2. The PCIH analogue as claimed in claim 1, wherein Rl is hydrophobic.
3. The PCIH analogue as claimed in claim 1 selected from the group consisting of
2-pyridylcarboxaldehyde m-bromobenzoyl hydrazone (PCBBH), 2-
pyridylcarboxaldehyde p-hydroxybenzoyl hydrazone (PCHH), 2-pyridylcarboxaldehyde
2-thiophenecarboxyl hydrazone (PCTH) and salts thereof.
4. A pharmaceutical composition suitable for use as an iron chelator comprising a
therapeutically effective amount of at least one 2-pyridylcarboxaldehyde isonicotinoyl
hydrazone (PCIH) analogue having Formula 1:
wherein R2 is either OH or H, such that when R2 is OH, R1 is phenyl, pyridine, furan
or thiophene ring optionally with alkyl, halo, nitro, amine or hydroxyl attached to any of
the vacant positions on the ring; isomers thereof or salts thereof; or when R2 is H, Rl is
thiophene, phenol or 2-, 3- or 4- bromophenyl optionally substituted with alkyl, halo,
nitro, or amine attached to any of the vacant positions on the ring; or salts thereof;
together with a pharmaceutically suitable carrier or diluent.
5. The pharmaceutical composition as claimed in claim 4 wherein R1 is
hydrophobic.
6. The pharmaceutical composition as claimed in claim 4 wherein the 2-
pyridylcarboxaldehyde isonicotinoyl hydrazone (PCIH) analogue is selected from the
group consisting of 2-pyridylcarboxaldehyde 2-thiophenecarboxyl hydrazone (PCTH),
2-pyridylcarboxaldehyde m-bromobenzoyl hydrazone (PCBBH), 2-
pyridylcarboxaldehyde p-hydroxybenzoyl hydrazone (PCHH), and salts thereof.
7. The pharmaceutical composition as claimed in any one of claims 4 to 6
formulated for subcutaneous or intravenous injection, oral administration, inhalation,
transdermal application, or rectal administration.
8. A composition comprising 2-pyridylcarboxaldehyde isonicotinoyl hydrazone
(PCIH) analogue suitable for iron chelation therapy, the PCIH analogue having Formula
I:
wherein R1 is an aromatic or heterocyclic group and R2 is either H or OH; isomers
thereof or salts thereof.
9. A composition comprising 2-pyridylcarboxaldehyde isonicotinoyl hydrazone
(PCIH) analogue suitable for iron overload disease, the PCIH analogue having Formula
1:
Formula 1
wherein R1 is an aromatic or heterocyclic group and R2 is either H or OH; isomers
thereof or salts thereof.
10. The composition as claimed in claim 9, wherein the iron overload disease is ?-
thalassemia or Friedreich's ataxia.
There is disclosed a 2-pyridylcarboxaldehyde isonicotinoyl hydrazone (PCIH)
analogue suitable for use as an in vivo iron chelator, the PCIH analogue having
Formula 1:
Formula 1
wherein R2 is either OH or H, such that when R2 is OH, R1 is phenyl, pyridine, furan
or thiophene ring optionally with alkyl, halo, nitro, amine or hydroxyl attached to any of
the vacant positions on the ring; isomers thereof or salts thereof; or when R2 is H, R1 is
thiophene, phenol or 2-, 3- or 4- bromophenyl optionally substituted with alkyl, halo,
nitro, or amine attached to any of the vacant positions on the ring; or salts thereof.
A pharmaceutical composition containing a 2-pyridylcarboxaldehyde
isonicotinoyl hydrazone (PCIH) analogue is also disclosed.

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Patent Number 222753
Indian Patent Application Number IN/PCT/2002/286/KOL
PG Journal Number 34/2008
Publication Date 22-Aug-2008
Grant Date 21-Aug-2008
Date of Filing 26-Feb-2002
Name of Patentee THE UNIVERSITY OF QUEENSLAND
Applicant Address ST.LUCIA, BRISBANE, QUEENSLAND
Inventors:
# Inventor's Name Inventor's Address
1 RICHARDSON DES 6/04 HIGHFIELD ROAD, QUAKERS HILL, NEW SOUTH WALES 2763
2 BERNHARDT PAUL VINCENT 56 MORNINGVIEW STREET, CHAPEL HILL, QUEENSLAND 4069
3 BECKER ERIKA MICHELLE 10 BECKFORD STREET, MOOROOKA, QUEENSLAND 4069
PCT International Classification Number A61K 31/4402,31/444
PCT International Application Number PCT/AU00/01050
PCT International Filing date 2000-09-04
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 PQ2624 1999-09-02 Australia