Current
Topics in Medicinal Chemistry
ISSN: 1568-0266
Current Topics
in Medicinal Chemistry
Volume 7, Number 9, 2007
Contents
Carbonic Anhydrase Inhibitors
Guest Editor: Claudiu T. Supuran
Editorial Pp. 823-824
Carbonic Anhydrases as Drug Targets
– An Overview Pp. 825-833
Claudiu T. Supuran
[Abstract]
Metal Binding Functions in the Design of Carbonic
Anhydrase Inhibitors Pp. 835-848
Jean-Yves Winum, Andrea Scozzafava, Jean-Louis Montero
and Claudiu T. Supuran
[Abstract]
The Development of Topically Acting Carbonic Anhydrase
Inhibitors as Anti-glaucoma Agents Pp. 849-854
Francesco Mincione, Andrea Scozzafava and Claudiu T. Supuran
[Abstract]
Carbonic Anhydrase Inhibitors as Anticonvulsant Agents
Pp. 855-864
Anne Thiry, Jean-Michel Dogné, Claudiu T. Supuran
and Bernard Masereel
[Abstract]
Carbonic Anhydrase Inhibitors and the Management of
Cancer Pp. 865-878
Silvia Pastorekova, Juraj Kopacek and Jaromir Pastorek
[Abstract]
Antiobesity Carbonic Anhydrase Inhibitors
Pp. 879-884
Giuseppina De Simone and Claudiu T. Supuran
[Abstract]
Dual Carbonic Anhydrase – Cyclooxygenase-2 Inhibitors
Pp. 885-891
Jean-Michel Dogné, Anne Thiry, Domenico Pratico,
Bernard Masereel and Claudiu T. Supuran
[Abstract]
Characterization and Inhibition of the Recently Discovered
Carbonic Anhydrase Isoforms CA XIII, XIV and XV Pp.
893-899
Mika Hilvo, Claudiu T. Supuran and Seppo Parkkila
[Abstract]
Inhibition of the Archaeal β-Class
(Cab) and γ-Class
(Cam) Carbonic Anhydrases Pp. 901-908
Sabrina A. Zimmerman, James G. Ferry and Claudiu T. Supuran
[Abstract]
Malarial Parasite Carbonic Anhydrase and Its Inhibitors
Pp. 909-917
Jerapan Krungkrai, Sudaratana R. Krungkrai and Claudiu
T. Supuran
[Abstract]
Molecule
of Month
Abstracts
[Back to top]
Editorial
Carbonic anhydrases (CAs), the metalloenzymes that catalyze
the conversion between carbon dioxide and bicarbonate, continue
to be surprising targets, as many exciting new discoveries
related to them emerge constantly. This is indeed unprecedented
as these are quite “old” enzymes, which were discovered
in 1933, and thoroughly investigated since then as drug targets.
Furthermore, their inhibitors are in clinical use since the
50s. However, in the last years, a host of interesting reports
were made regarding the catalytic/inhibition mechanism as
well as isolation/characterization of new isozymes belonging
to this family, as well as of CAs of non-vertebrate origin.
The first paper in this issue of the Journal dedicated to
these enzymes and their inhibitors, represents an overview
of CAs as drug targets. In fact, among the 16 isoforms known
up to now in mammals, 12 catalytically active ones seem to
be appropriate for designing inhibitors with various therapeutic
applications (only CA III seems to remain an orphan target).
In addition, many carbonic anhydrases isolated from other
organisms were recently shown to be possible targets for the
drug design, such as the α-CAs
from Plasmodium falciparum and Helicobacter pylori,
the β-CAs
from Mycobacterium tuberculosis, Candida albicans,
Cryptococcus neoformans, etc. Work is in progress
in many laboratories for developing specific inhibitors targeting
these enzymes, that would lead to conceptually novel therapies.
An exhaustive review regarding the design of such inhibitors
possessing different metal-binding functions than the classical
sulfonamide one is then presented by Winum et al.
The last years saw many relevant developments in this field
with the report of several interesting classes of such derivatives,
among which the sulfamates, sulfamides, substituted sulfonamides/sulfamides,
etc., as well as a detailed X-ray crystallographic dscription
of their interactions with various pharmacologically relevant
isoforms.
Historically, in addition to their well-known role for the
development of diuretics, the CA inhibitors were mainly used
as antiglaucoma agents. The review by Mincione et al.
in this issue presents up-to-date data regarding the ophthalmologic
use of systemically- and topically-acting CA inhibitors, as
well as some drug design studies reported ultimately, which
substantially extended the current knowledge in obtaining
water-soluble such derivatives, potentially useful not only
in the treatment of glaucoma but also for the management of
macular degeneration.
CA inhibitors were also used as antiepileptic drugs, but with
less fortune. Indeed, the classical derivatives, acetazolamide
and methazolamide, showed reduced utility in the treatment
of seizure, as presented thoroughly in the review of Thiry
et al., regarding the anticonvulsants belonging to
this class of pharmacological agents. However, the last years
saw the discovery of many CA isoforms present in the brain
and a somehow better understanding of their role in this organ.
Furthermore, some newer antiepileptics, such as topiramate
and zonisamide also show substantial CA inhibitory activity,
although it is unclear to what extent this activity is essential
for their anticonvulsant effects, since these drugs possess
a complex mechanism of action.
Probably the most unexpected applications of the CA inhibitors
are those regarding the diagnosis and treatment of tumors.
This very important and dynamic research field is reviewed
in the excellent paper of Pastorekova et al., the
discoverer of the first tumor-associated CA isozyme, CA IX.
In several seminal papers from her group, it has recently
been demonstrated that CA IX (and probably also CA XII, the
other tumor-associated isozyme) is overexpressed in hypoxic
tumors being involved in tumor acidification processes which
lead to metastatic spread and non-responsiveness to chemotherapeutic
agents/radiation treatment. Furthermore, the same group demonstrated
that sulfonamide CA IX-selective inhibitors may revert these
processes, opening the way to conceptually novel anticancer
therapies and diagnostic tools based on CA IX inhibitors.
In the last years, there are also encouraging reports linking
CA inhibitors to novel antiobesity therapies, field reviewed
in a nice paper by De Simone et al. In fact two mitochondrial
CA isoforms, CA VA and CA VB are involved in lipogenesis and
their inhibition leads to diminished fatty acid biosynthesis.
De Simone’s group resolved the X-ray crystallographic
structures of many important, clinically used inhibitors with
various isozymes, and performed modelling studies regarding
their binding to targets which have not been crystallized
yet (such as the human CA VA/VB or the human CA IX). Such
data are extremely useful for the drug design of inhibitors
with various applications, not only as antiobesity agents,
but also as antitumor or antiglaucoma drugs.
Interesting links emerged ultimately also between some CA
inhibitors and inhibitors of cyclooxygenase 2 (COX-2), reviewed
in the excellent paper by Dogné et al. Indeed,
two of the clinically used COX-2 inhibitors, celecoxib and
valdecoxib, are also potent inhibitors of many physiologically
relevant CA isoforms. Thus, potentially important applications
for these dual enzyme inhibitors may be envisaged, although
the COX-2 class of pharmacological agents underwent a drastic
loss of importance after the recent withdrawal of Rofecoxib
(Vioxx) from clinical use.
Hilvo et al. present then a very interesting review
regarding the characterization and inhibition studies of the
last CA isozymes reported in vertebrates, i.e., CA XIII, XIV
and XV. Indeed, Parkkila’s group made seminal contributions
in this field during the last decades, and their discovery
of two of these isoforms (CA XIII and XV; CA XIV was reported
by Nishimori) is just another example of excellency in CA
research. Much is to be understood yet regarding the physiological
roles of some of these “late” isoforms and the
consequences of their inhbition or activation.
Ferry’s group reported the first γ-CA
some years ago, which constituted a revolutionary proof regarding
the ubiquity and important roles of these ancient enzymes
all over the phylogenetic tree of living organisms. Indeed,
this enzyme (Cam) was discovered in a methanogenic archaeon.
Subsequently, the same group investigated a very interesting
and relatively simple, monomeric β-CA
(Cab) from another archaeon. All these fascinating discoveries
as well as the first inhibition studies of these non-α-CAs
are extensively reviewed in a nice paper by Zimmerman et al.
in this issue. Indeed, as mentioned briefly above, CAs are
abundant in the genome of many prokaryotes, but research in
this field is still in its infancy. The important contribution
of Zimmerman et al. sheds some new light in this
novel field.
At the same level of importance is the report of Krungkrai
et al. regarding the presence of several α-CAs
in the protozoa causing malaria, belonging to the genus Plasmodium.
In several seminal papers, this group reported the cloning,
characterization and inhibition studies of one of these enzymes,
showing it to be a druggable target. The last paper in this
issue is just an excellent review of this work, potentially
leading to novel antimalarial drugs.
Over the last 20 years I was personally involved with many
of these projects, and several others related to CA inhibitors
or activators. This is indeed rewarding, since I remember
colleagues prognosticating that this was a dead field already
in the early 90s. These excellent ten review articles in this
issue of Curr. Top. Med. Chem. represent the proof
(if that was necessary) that this was not the case. The data
presented throughout these papers clearly show that CAs and
their inhibitors may play an essential role in the development
of new therapeutic approaches against a multitude of disorders
in addition to the classical ones for which such agents were
and are still used clinically. Furthermore, some drug design
studies of CA inhibitors may represent useful paradigms for
developing agents against more complicated targets.
I am particularly grateful to the Editor-in-Chief, Dr. Allen
Reitz (Johnson & Johnson) for inviting me to prepare this
issue of the journal dedicated to CA inhibitors, and to all
the scientists who dedicated much time and energy to produce
these nice articles which will be helpful to all the members
of the scientific community working in the drug design field.
Claudiu T. Supuran
Università degli Studi di Firenze,
Laboratorio di Chimica Bioinorganica,
Rm. 188, Via della Lastruccia 3,
I-50019 Sesto Fiorentino (Firenze),
Italy
[Back to top]
Carbonic Anhydrases as Drug Targets – An
Overview
Claudiu T. Supuran
At least 15 different α-carbonic
anhydrase (CA, EC 4.2.1.1) isoforms were isolated in mammals,
where these zinc enzymes play crucial physiological roles.
Some of these isozymes are cytosolic (CA I, CA II, CA III,
CA VII, CA XIII), others are membrane-bound (CA IV, CA IX,
CA XII, CA XIV and CA XV), CA VA and CA VB are mitochondrial,
and CA VI is secreted in saliva and milk. Three acatalytic
forms are also known, the CA related proteins (CARP), CARP
VIII, CARP X and CARP XI. Representatives of the β
- δ-CA
family are highly abundant in plants, diatoms, eubacteria
and archaea. These enzymes are very efficient catalysts for
the reversible hydration of carbon dioxide to bicarbonate,
but at least the α-CAs
possess a high versatility, being able to catalyze different
other hydrolytic processes The catalytic mechanism of the
α-CAs
is understood in detail: the active site consists of a Zn(II)
ion co-ordinated by three histidine residues and a water molecule/hydroxide
ion. The latter is the active species, acting as a potent
nucleophile. For β-
and γ-CAs,
the zinc hydroxide mechanism is valid too, although at least
some β-class
enzymes do not have water directly coordinated to the metal
ion. CAs are inhibited primarily by two classes of compounds:
the metal complexing anions (such as cyanide, cyanate, thiocyanate,
azide, hydrogensulfide, etc) and the sulfonamides/sulfamates/sulfamides
possessing the general formula RXSO2NH2
(R = aryl; hetaryl; perhaloalkyl; X = nothing, O or NH). Several
important physiological and physio-pathological functions
are played by the CA isozymes present in organisms all over
the phylogenetic tree, related to respiration and transport
of CO2/bicarbonate between
metabolizing tissues and the lungs, pH and CO2
homeostasis, electrolyte secretion in a variety of tissues/organs,
biosynthetic reactions, such as the gluconeogenesis and ureagenesis
among others (in animals), CO2
fixation (in plants and algae), etc. The presence of these
ubiquitous enzymes in so many tissues and in so different
isoforms, represents an attractive goal for the design of
inhibitors with biomedical applications. Indeed, CA inhibitors
are clinically used as antiglaucoma drugs, some other compounds
being developed as antitumor agents/diagnostic tools for tumors,
antiobesity agents, anticonvulsants, and antimicrobials/antifungals
(inhibitors targeting CAs from pathogenic organisms such as
Helicobacter pylori, Mycobacterium tuberculosis, Plasmodium
falciparum, Candida albicans, etc).
[Back to top]
Metal Binding Functions in the Design of Carbonic
Anhydrase Inhibitors
Jean-Yves Winum, Andrea Scozzafava, Jean-Louis Montero
and Claudiu T. Supuran
The carbonic anhydrases (CAs, EC 4.2.1.1) are zinc containing
metalloenzymes which catalyse efficiently the reversible hydration
of carbon dioxide to bicarbonate with discharge of a proton,
playing important physiological and physiopathological functions.
To date, 16 different carbonic anhydrase isoforms have been
described in higher vertebrates, including humans, and some
of them have been considered as important targets for inhibitors
with therapeutic applications. The catalytic and structural
role of zinc in these enzyme are understood in great detail,
and this provided molecular basis for the design of potent
inhibitors, some of which possessing important clinical applications
mainly as topically acting anti-glaucoma drugs, anticancer
or antiobesity agents. The metal binding function is a critically
important factor in the development of isozyme-specific and
organ-selective inhibitors. Discovery of compounds that possess
zinc binding function different from that of the classical
one (sulfonamide type) is in constant progress and can offer
opportunities for developing novel pharmacological agents.
In the present review we will discuss the different zinc binding
function reported in the literature up to now in the design
of carbonic anhydrase inhibitors.
[Back to top]
The Development of Topically Acting Carbonic Anhydrase
Inhibitors as Anti-glaucoma Agents
Francesco Mincione, Andrea Scozzafava and Claudiu T. Supuran
Carbonic anhydrase inhibitors (CAIs) such as acetazolamide,
methazolamide, ethoxzolamide and dichlorophenamide were and
still are widely used systemic antiglaucoma drugs. Their mechanism
of action consists in inhibition of CA isozymes present in
ciliary processes of the eye (such as CA II, IV and XII),
with the consequent reduction of bicarbonate and aqueous humour
secretion, and of elevated intraocular pressure (IOP) characteristic
of this disease. Since CA II/IV/XII are present in many other
tissues/organs, generally, systemic CAIs possess undesired
side effects such as numbness and tingling of extremities;
metallic taste; depression; fatigue; malaise; weight loss;
decreased libido; gastrointestinal irritation; metabolic acidosis;
renal calculi and transient myopia. In order to avoid these
undesired side effects, recently, topically effective CAIs
have been developed. Two drugs are available clinically: dorzolamide
and brinzolamide. Both these drugs are applied topically as
water solutions/suspensions, alone or in combination with
other agents (such as β-blockers,
prostaglandin derivatives, etc) and produce a consistent and
prolonged reduction of IOP. Furthermore, recent reports show
both the systemically as well as topically acting sulfonamide
CAIs to be effective in the treatment of macular oedema and
other macular degeneration diseases, for which pharmacological
treatment was unavailable up to now. Much research is in act
in the search of even more effective topically acting CAIs,
free of the inconveniences and side effects of the presently
available drugs. For achieving this goal, a recently reported
strategy, the tail approach, was extensively applied for the
synthesis of large numbers of derivatives possessing various
physico-chemical properties. Many such new sulfonamides showed
promising antiglaucoma activity in animal models of the disease.
[Back to top]
Carbonic Anhydrase Inhibitors as Anticonvulsant Agents
Anne Thiry, Jean-Michel Dogné, Claudiu T. Supuran
and Bernard Masereel
Seizures is one of the most common neurological disorders
in clinical medicine. Triggering mechanisms by which seizures
form remain unclear, but are related to a rapid change in
ionic composition, including an increase of intracellular
potassium concentration and pH shifts within the brain. pH
buffering of extra- and intracellular spaces is mainly carried
out by the CO2 / HCO3-
buffer, the equilibration of the two species being assured
by the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1). Some
carbonic anhydrase inhibitors (CAIs) are used as anticonvulsants
in the treatment of epilepsy. In this review, we will describe
the link between CA and seizures on the basis of several putative
mechanisms. Several CA isozymes have been pointed out for
their contribution to epileptiform activity. An overview of
the CA isozyme expression in the brain and of their specifics
roles is also discussed. This article reviews the research
achievements published on CA inhibitors, clinically used as
anticonvulsant and those under development.
[Back to top]
Carbonic Anhydrase Inhibitors and the Management of
Cancer
Silvia Pastorekova, Juraj Kopacek and Jaromir Pastorek
Recent progress in understanding the role of catalytically
active carbonic anhydrases in tumors has opened new possibilities
for diagnostic and/or therapeutic applications of carbonic
anhydrase inhibitors selectively blocking the enzyme activity
of cancer-related isoforms, namely CA IX and CA XII. Different
classes of inhibitors have been investigated in order to evaluate
their usefulness as in vivo imaging tools, as modulators
of intratumoral pH that influences uptake of conventional
chemotherapeutics, or as drugs impeding survival of tumor
cells exposed to physiological stresses including hypoxia
and acidosis. Here we summarize the most important data related
to expression, regulation and functional aspects of cancer-related
carbonic anhydrases and discuss advances in synthesis and
preclinical studies of isozyme-selective and highly efficient
carbonic anhydrase inhibitors.
[Back to top]
Antiobesity Carbonic Anhydrase Inhibitors
Giuseppina De Simone and Claudiu T. Supuran
Few pharmacological approaches for the treatment of obesity
exist at this time, and most of them are unsatisfactory, whereas
this disease is widespread both in the developed and developing
world. Novel effective approaches are needed for the development
of antiobesity agents possessing different mechanisms of action.
A possible new approach for the treatment and prophylaxis
of obesity is based on the inhibition of carbonic anhydrases
(CAs, EC 4.2.1.1), enzymes involved in several steps of de
novo lipogenesis, both in the mitochondria and the cytosol
of cells. Topiramate and zonisamide are two antiepileptic
drugs that were shown to induce persistent weight loss in
obese patients, but their mechanism of action is largely unknown.
We demonstrated strong CA inhibitory properties for these
two drugs, by means of kinetic studies in solution and X-ray
crystallography, against several physiologically relevant
isoforms, such as CA II, VA and VB. It has been proved that
topiramate also inhibits lipogenesis in adipocytes, similarly
to other sulfonamide CA inhibitors investigated earlier. A
large number of new sulfonamides have been synthesized and
assayed as possible inhibitors of CA isoforms involved in
lipogenesis. This is the beginning of a very new and promising
approach for the treatment of obesity, with the hope that
new compounds showing this property will be soon developed
and available for clinical use.
[Back to top]
Dual Carbonic Anhydrase – Cyclooxygenase-2 Inhibitors
Jean-Michel Dogné, Anne Thiry, Domenico Pratico,
Bernard Masereel and Claudiu T. Supuran
Cyclooxygenase is a key enzyme responsible for metabolisation
of arachidonic acid into prostaglandins and thromboxane. This
enzyme is the target of non steroidal anti-inflammatory drugs
(NSAIDs), used against inflammation and pain. The inducible
COX-2 was associated with inflammatory conditions, whereas
the constitutive form (COX-1) was responsible for the beneficial
effects of the PGs. This observation led to the development
of COX-2 inhibitors or “coxibs” of which rofecoxib
(Vioxx®) characterized by a methylsulfone moiety
and the sulfonamides celecoxib (Celebrex®)
and valdecoxib (Bextra®). Initially described
as COX-2 “selective” inhibitors, recent reports
revealed a nanomolar inhibition activity of the sulfonamide
COX-2 inhibitors for several carbonic anhydrase (CA) isoforms,
confirmed by X-ray crystal structures for the adducts of celecoxib
and valdecoxib with isozyme CA II. This dual activity may
help to explain differences in clinical observation between
sulfonamide and methylsulfone COX-2 inhibitors. Moreover,
the inhibition of CA isozymes, critical for the development
and invasion of cancer cells, such as CA II, IX and XII, may
constitute an important mechanism of antitumor action of such
sulfonamide compounds.
[Back to top]
Characterization and Inhibition of the Recently Discovered
Carbonic Anhydrase Isoforms CA XIII, XIV and XV
Mika Hilvo, Claudiu T. Supuran and Seppo Parkkila
The carbonic anhydrase (CA) protein family consists of twelve
active isozymes in humans and thirteen in most other mammals.
The most recently discovered members of this family include
cytosolic CA XIII and membrane-bound CAs XIV and XV. In this
article we will review the characterization and inhibition
profiles of these isozymes. CA XIII is expressed in the kidney
as well as in the gastrointestinal and reproductive tracts,
and therefore it may have a role in various physiological
processes. The inhibition studies with CA XIII have shown
that this isozyme can be inhibited efficiently with some sulfonamide
inhibitors, while it is resistant to inhibition with chloride
and bicarbonate ions. CA XIV is a membrane-bound enzyme that
is expressed in numerous organs such as the brain, kidney,
eye, liver and epididymis, where it has a role in the regulation
of acid-base balance. The inhibitory properties of CA XIV
have been studied, but no specific inhibitors have been found
for this isozyme. The membrane-bound CA XV is an exceptional
member of this protein family, because it is expressed in
numerous species but absent in humans and chimpanzees. A detailed
biochemical characterization of this isozyme is under way
in our laboratories.
[Back to top]
Inhibition of the Archaeal β-Class
(Cab) and γ-Class
(Cam) Carbonic Anhydrases
Sabrina A. Zimmerman, James G. Ferry and Claudiu T. Supuran
Five independently evolved classes (α-,
β-,
γ-,
δ-,ζ-)
of carbonic anhydrases facilitate the reversible hydration
of carbon dioxide to bicarbonate of which the α-class
is the most extensively studied. Detailed inhibition studies
of the α-class
with the two main classes of inhibitors, sulfonamides and
metal-complexing anions, revealed many inhibitors that are
used as therapeutic agents to prevent and treat many diseases.
Recent inhibitor studies of the archaeal β-class
(Cab) and the γ-class
(Cam) carbonic anhydrases show differences in inhibition response
to sulfonamides and metal-complexing anions, when compared
to the α-class
carbonic anhydrases. In addition, inhibition between Cab and
Cam differ. These inhibition patterns are consistent with
the idea that although, α-,
β-,
and γ-class
carbonic anhydrases participate in the same two-step isomechanism,
diverse active site architecture among these classes predicts
variations on the catalytic mechanism. These inhibitor studies
of the archaeal β-
and γ-class
carbonic anhydrases give insight to new applications of current
day carbonic anhydrase inhibitors, as well as direct research
to develop new compounds that may be specific inhibitors of
prokaryotic carbonic anhydrases.
[Back to top]
Malarial Parasite Carbonic Anhydrase and Its Inhibitors
Jerapan Krungkrai, Sudaratana R. Krungkrai and Claudiu
T. Supuran
Plasmodium falciparum is responsible for the majority
of life-threatening cases of human malaria. The global emergence
of drug-resistant malarial parasites necessitates identification
and characterization of novel drug targets. At present, carbonic
anhydrase (CA) genes are identified in limited numbers of
protozoa and helminthes parasites, however, they are demonstrated
in at least 4 Plasmodium species. The CA gene of
P. falciparum encodes an α-carbonic
anhydrase enzyme possessing catalytic properties distinct
of that of the human host enzymes. A small library of aromatic
sulfonamides, most of which were Schiff’s bases derived
from sulfanilamide/homosulfanilamide/4-aminoethylbenzenesulfonamide
and substituted-aromatic aldehydes, or ureido-substituted
sulfonamides are good inhibitors of P. falciparum
enzyme. The 4-(3,4-dichlorophenylureido-ethyl)-benzenesulfonamide
is the most effective antimalarial activity against growth
of P. falciparum in vitro. The nature of
the groups substituting the aromatic-ureido- or aromatic-azomethine
fragment of the molecule and the length of the parent sulfonamide
(i.e., from sulfanilamide to 4-aminoethylbenzenesulfonamide)
from which the Schiff’s base obtained, are the critical
parameters for the CA inhibitory activities of these aromatic
sulfonamide derivatives, both against the malarial as well
as human enzymes. Thus, the sulfonamide CA inhibitors may
have the potential for the development of novel antimalarial
drugs.
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