Andrea Scozzafava

Carbonic anhydrase inhibitors and their therapeutic potential

Carbonic anhydrases (CAs, EC 4.2.1.1) are wide-spread zinc enzymes, present in archaeo- and eubacteria, algae, green plants and animals. Within these organisms CAs are encoded by three distinct, evolutionarily unrelated gene families: the α-CA, the β-CA and the γ-CA families, respectively. These enzymes are very efficient catalysts for the reversible hydration of CO2 to bicarbonate; the α-CAs possess high versatility, being able to catalyse other hydrolytic processes. It is not known whether other reactions catalysed by CAs (than the hydration of CO2/dehydration of HCO-) may have physiological relevance in systems where these enzymes are present. CAs are inhibited primarily by two main classes of compounds: the metal complexing inorganic anions (e.g., cyanide, cyanate, thiocyanate, azide, hydrogensulphide etc.) and the unsubstituted sulphonamides possessing the general formula RSO2NH2 (R = aryl; hetaryl; perhaloalkyl). The first type of inhibitor was important for understanding in detail the catalytic and inhibitory mechanisms, whereas the second led to the development of several classes of pharmacological agents. Inhibitors of both types directly bind to the metal ion within the enzyme active site, either by substituting the zinc-bound H-, or adding to the co-ordination sphere, leading thus to pentaco-ordinated Zn(II). Sulphonamide CA inhibitors (CAIs) are useful as diuretics, or in the treatment and prevention of a variety of diseases such as glaucoma, epilepsy, congestive heart failure, mountain sickness, gastric and duodenal ulcers, neurological disorders and osteoporosis among others, as well as diagnostic tools. Their applications are due to the wide distribution of the different α-CA isozymes (14 are presently known) in higher vertebrates, where they play important physiological functions related to respiration and transport of CO2/HCO3 between metabolising tissues and the lungs, pH and CO2 homeostasis, electrolyte secretion in a variety of tissues/organs, and biosynthetic reactions, such as gluconeogenesis and ureagenesis, among others. CA activators have recently been described and their mechanism of action at molecular level elucidated. Such agents might be useful for developing therapies for the CA deficiency syndrome.

Applications of carbonic anhydrase inhibitors and activators in therapy

Inhibitors and activators of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1) have a large number of applications in therapy. Many types of such new derivatives have been reported recently, together with their potential applications as antiglaucoma, anticancer and anti-osteoporosis agents or for the management of a variety of neurological disorders, among others. Furthermore, some CA isozymes seem to be valuable markers of tumour progression in a variety of tissues and organs. The CA activators, although not clinically exploited up to now, seem to constitute a new revolutionary approach for the treatment of Alzheimers disease and other neurodegenerative disorders in need of memory therapy. Recent progress in all these areas, as well as in the characterisation of new such enzymes/isozymes isolated in many organisms/tissues and their detailed catalytic/inhibition mechanisms are, reviewed in the present paper.

Bacterial proteases: current therapeutic use and future prospects for the development of new antibiotics

Proteases of the serine-, cysteine- and metallo- type are widely spread in many pathogenic bacteria, where they play critical functions related to colonisation and evasion of host immune defences, acquisition of nutrients for growth and proliferation, facilitation of dissemination, or tissue damage during infection. Since all the antibiotics currently used clinically share a common mechanism of action, i.e., inhibition of bacterial cell wall biosynthesis, resistance to these pharmacological agents represents a serious medical problem, which might be resolved by using a new generation of antibiotics with a different mechanism of action. Bacterial protease inhibitors constitute an interesting possibility, due to the fact that many specific and ubiquitous proteases have recently been characterised in some detail in both Gram-positive and Gram-negative pathogens. Unfortunately, at this moment few potent, specific inhibitors for such bacterial proteases have been reported, except for signal peptidase, clostripain, Clostridium histolyticum collagenase, botulinum neurotoxin and tetanus neurotoxin inhibitors (but such protease inhibitors are not used clinically for the moment). No inhibitors of the critically important and ubiquitous AAA proteases, degP or sortase have been reported, although such compounds would presumably constitute a new class of highly effective antibiotics. On the other hand, several bacterial proteases, such as the Clostridium histolyticum collagenase, or the botulinum neurotoxin A possess therapeutic applications per se for the treatment of some diseases or for the preparation of vaccines. This review presents the state of the art in the design of such enzyme inhibitors with potential therapeutic applications, as well as recent advances in the use of some of these proteases in therapy.

Small molecule antagonists of chemokine receptors as emerging anti-HIV agents

HIV entry into the cell involves the presence of at least two chemokine coreceptors, the CCR5 and CXCR4 receptors. Much research by the major drug companies has ultimately been directed to the development of small molecule chemokine antagonists that inhibit virus entry into the cell and in this way constitute novel antiviral medications. The scientific and patent literature of this highly dynamic field has been reviewed, showing that a large number of highly effective lead molecules have recently been identified, and at least one compound (the bicyclam AMD3100) has entered clinical trials as a new anti-HIV pharmacological agent. An effective chemokine antagonist with antiviral properties combined with the presently available classes of antivirals (nucleoside and non-nucleoside reverse transcriptase inhibitors (NRTIs and NNRTIs) and/or protease inhibitors (PIs)) may act synergistically in the treatment of the HIV infection, explaining the tremendous research efforts in this field.