Current Medicinal Chemistry - Volume 8, Issue 13, 2001

ThiS review starts from a brief introduction followed by the list of commercial antimalarial drug. According to the nature of chemical entities, these drugs have been divided into the following categories- Quinolines, pyrimidines, amidinies, guanidines, sulfonamides, sulfones, acridines, antibiotics and sesquiterpene lactones. The site of action and status of the antimalarial drugs have been described against each category. A brief description of reasons behind the search of a new antimalarilal drug have been discussed. Finally, the review deals the well known biochemical target sites such as folate metabolism, pyrimidine metabolism and polyamines for the designing of antimalarial drugs. The detail description of the newly discovered biochemical target sites, alpha tublin and DNA topoisomerases, have been highlighted. In the conclusion section, we have discussed the future strategies for the chemotherapy of malaria.

Virtually all the compounds that are currently used, or under advanced clinical trial, for the treatment of HIV infections, belong to one of the following classes: (i) nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs): i.e., zidovudine (AZT), didanosine (ddI), zalcitabine (ddC), stavudine (d4T), lamivudine (3TC), abacavir (ABC), emtricitabine [(-)FTC], tenofovir (PMPA) disoproxil fumarate (ii) non-nucleoside reverse transcriptase inhibitors (NNRTIs): i.e., nevirapine, delavirdine, efavirenz, emivirine (MKC- 442) and (iii) protease inhibitors (PIs): i.e., saquinavir, ritonavir, indinavir, nelfinavir, amprenavir, and lopinavir. In addition to the reverse transcriptase and protease step, various other events in the HIV replicative cycle are potential targets for chemotherapeutic intervention: (i) viral adsorption, through binding to the viral envelope glycoprotein gp120 (polysulfates, polysulfonates, polyoxometalates, zintevir, negatively charged albumins, cosalane analogues) (ii) viral entry, through blockade of the viral coreceptors CXCR4 and CCR5 [bicyclams (i.e. AMD3100), polyphemusins (T22), TAK-779, MIP-1α LD78β isoform] (iii) virus-cell fusion, through binding to the viral glycoprotein gp41 [T-20 (DP-178), T-1249 (DP-107), siamycins, betulinic acid derivatives] (iv) viral assembly and disassembly, through NCp7 zinc finger-targeted agents [2,2'-dithiobisbenzamides (DIBAs), azadicarbonamide (ADA) and NCp7 peptide mimics] (v) proviral DNA integration, through integrase inhibitors such as L-chicoric acid and diketo acids (i.e. L-731,988) (vi) viral mRNA transcription, through inhibitors of the transcription (transactivation) process (fluoroquinolone K-12, Streptomyces product EM2487, temacrazine, CGP64222). Also, in recent years new NRTIs, NNRTIs and PIs have been developed that possess respectively improved metabolic characteristics (i.e. phosphoramidate and cyclosaligenyl pronucleotides of d4T), or increased activity against NNRTI-resistant HIV strains [second generation NNRTIs, such as capravirine and the novel quinoxaline, quinazolinone, phenylethylthiazolylthiourea (PETT) and emivirine (MKC-442) analogues], or, as in the case of PIs, a different, non-peptidic scaffold [i.e. cyclic urea (DMP 450), 4-hydroxy-2-pyrone (tipranavir)]. Given the multitude of molecular targets with which anti-HIV agents can interact, one should be cautious in extrapolating from cell-free enzymatic assays to the mode of action of these agents in intact cells. A number of compounds (i.e. zintevir and L-chicoric acid, on the one hand and CGP64222 on the other hand) have recently been found to interact with virus-cell binding and viral entry in contrast to their proposed modes of action targeted at the integrase and transactivation process, respectively.

The role of topological indices in drug development research is updated. A series of definitions in the fields of topological indices and drug discovery technologies are introduced. In all cases where it is possible the IUPAC recommendations for terms used in medicinal chemistry and in computational drug design are used. Recent advances on the use of topological indices in the lead discovery process are reviewed making emphasis on two approaches: combined use of connectivity and charge indices and TOSS- MODE approach. Studies of similarity / dissimilarity and rational combinatorial library design are also updated. The use of these descriptors in lead optimization process is critically analyzed. Topological indices QSAR, the problem of 2D QSAR versus 3D QSAR, strategies of orthogonalization and the use of linear combination and semiempirical connectivity indices are also described. The main directions of progress for these indices in QSAR and drug research are analyzed with examples of application of novel statistical techniques, such as artificial neural networks, genetic algorithms and partial least squares. Future outlooks of development in this area of research are also given.

Src homology 2 (SH2) domains are protein modules that mediate intracellular protein-protein interactions in signal transduction pathways. The specific association of an SH2 domain with a phosphotyrosine-containing sequence of another protein induces a cascade of molecular interactions that effect a wide range of cellular processes. Alterations in these signaling pathways have been associated with the development and progression of a broad range of pathologies. Because of the regulatory role of SH2 domains in these signal transduction pathways, specific SH2 domains can be ideal targets for intervention with therapeutic agents in many different disease indications (e.g. cancer, osteoporosis, disorders of the immune and cardiovascular systems). Among the SH2 domains pursued as drug discovery targets in the last few years are those of Grb2, Src, Lck and ZAP-70. This review focuses on contributions in the design and synthesis of antagonists of these particular SH2 domains. Specific examples have been selected to illustrate how structure-based design approaches have been used to progress in this area of research.

Over the last decades distinct members of the G Protein-Coupled Receptor (GPCR) family emerged as prominent drug targets within pharmaceutical research, since approximately 60 percent of marketed prescription drugs act by selectively addressing representatives of that class of transmembrane signal transduction systems. It is noteworthy that the majority of GPCR-targeted drugs elicit their biological activity by selective agonism or antagonism of biogenic monoamine receptors, while the development status of peptide-binding GPCR-adressing compounds is still in its infancy.Exemplified on selected medicinal chemistry projects, this review will focus on the opportunities of therapeutic intervention into a broad spectrum of disease processes through agonizing or antagonizing the functions of peptide-binding GPCRs. In this context, a brief overview of GPCR-mediated signal transduction pathways will be given in order to emphasize the biomedical relevance of a controlled modulation of receptor function. Modern trends on lead finding and optimization strategies for peptide-binding GPCR-targeted low-molecular weight compounds will be highlighted on the basis of current research programs conducted in the areas of angiotensin II, endothelin, bradykinin, neurokinin, neuropeptide Y, LHRH, C5a antagonists, and somatostatin agonists, respectively. Special emphasis will be laid on the elaboration and utilization of structural rationales on the potential drug candidates, thus facilitating more detailed insights into the underlying molecular recognition event.

The prevention of anthracycline cardiotoxicity is particularly important in children who can be expected to survive for decades after cancer chemotherapy with these agents. The rapid increase in clinical toxicity at doses greater than 550 mg / m² of doxoru- bicin (DOX) has made this dose the limiting one in order to avoid DOX-induced cardiac failure. However, arbitrary dose limitation is inadequate because of variability of individual tolerance. Decreasing myocardial concentrations of anthracyclines (ANT) and their metabolites and schedule modification of administration can reduce anthracycline cardiotoxicity. Anthracycline structural analogues such as epirubicin, idarubicin and mitoxantrone have been used in clinical practice. In addition, the liposomal ANT, which can be incorporated into a variety of liposomal preparations, are a new class of agents that may permit more specific organ targeting of ANT, thereby producing less cardiac toxicity. Much interest has focused on the administration of ANT in conjunction with another agent that will selectively attenuate the cardiotoxicity. As is known, the ANT chelate iron and the DOX-iron complex catalyzes the formation of extremely reactive hydroxyl radicals. Many agents, such as dexrazoxane (DEX), able to remove iron from DOX, have been investigated as anthracycline cardioprotectors. Clinical trials of DEX have been conducted in children and significant short-term cardioprotection with no evidence of interference with antitumor activity has been demonstrated. Whether long-term cardiac toxicity will also be avoided in surviving patients has not yet been determined.

The physiological VDR ligand, 1α,25-dihydroxyvitamin D3, acts upon a wide variety of tissues and cells, both related to and unrelated to calcium and phosphate Homeostasis. The noncalcemic actions of natural and synthetic VDR ligands are exemplified by their potent anti-proliferative, prodifferentiative and immunomodulatory activities. As a result, a VDR ligand is an approved drug for the topical treatment of psoriasis. A plethora of actions of 1α,25-dihydroxyvitamin D3 in various systems have suggested wide clinical applications of VDR ligands in such diverse disease states as inflammation (rheumatoid arthritis, psoriatic arthritis), dermatological indications (psoriasis, photoaging and skin rejuvenation), osteoporosis, cancers (breast, prostate, colon, leukemia and myelodysplastic syndrome) and autoimmune diseases (multiple sclerosis, type I diabetes and systemic lupus erythematosus). VDR ligands have shown therapeutic potential in limited human clinical trials as well as in animal models of these diseases. Some of the VDR ligands have shown not only potent preventive but also therapeutic anabolic activities in animal models of osteoporosis. However, the use of VDR in above mentioned indications as well as in oral therapy for psoriasis and even topical therapy for severe psoriasis is hampered by its associated toxicity, namely hypercalcemia. New VDR ligands have been synthesized which exhibit greater specificity by retaining desirable properties, but with reduced calcemic potential. The discovery of novel vitamin D3 analogs along with an increased understanding of the biological functions and mechanisms of action of VDR are likely to result in improved treatments for responsive indications.

Marine natural products, form a field of scientific endeavour, that has recently grown considerably. The isolation, biological evaluation, chemical properties and synthetic elaborations of products of marine organisms have attracted the attention of organic chemists, medicinal chemists, biologists and pharmacists. In this context a structurally and biologically highly interesting class is represented by the marine natural products containing an indole moiety in a pure substituted form or in an anella- ted form. The present review summarizes primarily the actual results concerning these products as new pharmacologically attractive lead compounds for drug design. The chemistry, biological evaluation and synthetic aspects are discussed. The spectrum of compounds represented comprises simply substituted indoles, peptidic products, dimeric indoles, anellated indoles and a variety of carbazoles. Most of them exhibit significant cytotoxicities.