Current Medicinal Chemistry - Volume 10, Issue 3, 2003

This work details recent advances in the science of estrogen receptor (ER) modulation, with emphasis on the discovery of novel ligands for the ER ligand binding domain (LBD). A detailed examination of structural studies of the ERs is presented with analysis of the impact of such works on contemporary ligand design and the molecular pharmacology of the ER. The various classes of ER modulators are discussed on the basis of stuctural similarities including selective estrogen receptor modulators (SERMs) and ‘pure’ nonsteroidal antiestrogens. Additionally we review the emergence of a novel selective class of modulator - which we have termed the selective estrogen receptor subtype modulators (SERSMs) and, in a departure from LBD strategies we examine the discovery of novel peptide inhibitors of the ER which inhibit transcriptional activiation of agonist liganded receptor through interaction with coactivator recruitment proteins, and offer unique insight to the mechanism of action of all classes of ER modulators. Through examination of patent and classical literature we present a thorough and informative cross-section of the contemporary state of the art in this exciting field of pharmaceutical research.

Fungal infections represent a serious problem for patients with immune systems compromized either by HIV infection, or administration of immunosuppressive drugs during cancer therapy and organ transplantation. High dissemination and proliferation rates of many pathogenic fungi along with their insusceptibility to common antimicrobial drugs urge implementation of efficient and reliable antifungal therapy. Up to date, polyene macrolide antibiotics proved to be the most effective antifungal agents due to their potent fungicidal activity, broad spectrum, and relatively low frequency of resistance among the fungal pathogens. However, polyene macrolides are rather toxic, causing such serious side effects as renal failure, hypokalemia and thrombophlebitis, especially upon intravenous administration. Current views on the biosynthesis of polyene macrolides, their mode of action and structure-function relationship, as well as strategies used to overcome the toxicity problem are discussed in this review. In addition, some of the new potential applications for polyene macrolides in therapy of prion diseases, HIV infection and cancer are highlighted.

The concept of Biological Activity Spectrum served as a basis for developing PASS (Prediction of Activity Spectra for Substances) software product. PASS predicts simultaneously more than 780 pharmacological effects and biochemical mechanisms based on the structural formula of a substance. It may be used for finding new targets (mechanisms) for known pharmaceuticals and for searching new biologically active substances. PASS prediction ability was evaluated by activity spectra prediction for 63 substances that are presented in the Molecule of the Month section of Prous Science (http: / / www.prous.com), belong to different chemical classes and reveal various types of biological activity. Mean accuracy of prediction turned out to be about 90%, therefore, it is reasonable to use PASS for finding and optimizing new lead compounds. A web-site with a new internet version of PASS is introduced into practice in December 2001 (http: / / www.ibmh.msk.su / PASS). On the site, one can find a detailed description of the PASS approach as well as some examples of its applications, and estimate the quality of prediction by submitting structures of substances with known activities.

ATP-sensitive K+ channels (KATP channels) regulate insulin secretion by coupling intracellular metabolic changes to excitability of the plasma membrane in pancreatic β-cells. The channels are closed when extracellular glucose levels are elevated due to enhanced feature. By contrast, cardiac-type KATP channels, which open in response to metabolic stress during cardiac ischemia, shorten action potential durations. This may contribute to the cardioprotection by decreasing Ca2+ influx through sarcolemma. By sensing intracellular ATP levels or ATP / ADP ratios, changes in activity of KATP channels convert metabolic information into membrane excitability. In addition to channel regulation by nucleotide concentrations, the channel activity is also dependent on the concentrations of membrane phospholipids, including phosphatidyl inositol-4,5-bisphosphate (PIP2). The levels of PIP2 in the membrane may determine the basal activity of the channels. This suggests that channel activity would be modulated by the pathway of receptor-coupled GTPbinding protein (G-protein) and phosphatidyl inositol phospholipase C (PI-PLC) stimulation, which brings about depletion of the membrane PIP2 pool. Thus, KATP channels not only provide interface of metabolic changes with electrical excitation, but also rapidly transmit extracellular signals through receptor-coupled Gprotein and PI-PLC pathway via PIP2 metabolism.

RNA interference (RNAi) as a protecting mechanism against invasion by foreign genes was first described in C. elegans and has subsequently been demonstrated in diverse eukaryotes such as insects, plants, fungi and vertebrates. RNAi is the mechanism of sequence-specific, post-transcriptional gene silencing initiated by double-stranded RNAs (dsRNA) homologous to the gene being suppressed. dsRNAs are processed by Dicer, a cellular ribonuclease III, to generate duplexes of about 21 nt with 3'-overhangs (small interfering RNA, siRNA) which mediate sequence-specific mRNA degradation. In mammalian cells siRNA molecules are capable of specifically silencing gene expression without induction of the unspecific interferon response pathway. Thus, siRNAs have become a new and powerful alternative to other genetic tools such as antisense oligonucleotides and ribozymes to analyze loss-of-function phenotypes. Application of siRNA duplexes to interfere with the expression of a specific gene requires knowledge of target accessibility, highly effective delivery of siRNAs into target cells and for some applications long-term siRNA expression. Effective strategies to deliver siRNAs to target cells in cell culture include transduction by physical or chemical transfection. An alternative strategy uses the endogenous expression of siRNAs by various Pol III promoter expression cassettes that allow transcription of functional siRNAs or their precursors. This review summarizes some genetic and biochemical aspects of RNAi, the delivery and application of siRNAs to target cells, the kinetics of RNAi and the utility of siRNAs as analytical and potential therapeutic tools.

Although cisplatin, cis-diamminedichloroplatinum(II), has been successfully used in the chemotherapy of cancer for more than 25 years, its biochemical mechanism of action is still unclear. The current accepted paradigm about cisplatin mechanism of action is that the drug induces its cytotoxic properties through binding to nuclear DNA and subsequent interference with normal transcription, and / or DNA replication mechanisms. If cisplatin-DNA adducts are not efficiently processed by cell machinery, cytotoxic processes eventually end up in cell death. However, before cisplatin enters the cell it may bind to phospholipids and phosphatidylserine in the cell membrane. In addition, in the cytoplasm many potential platinum-binding sites are also available, including RNA and sulfur-containing biomolecules. Moreover, there is much evidence suggesting that the cytotoxic effects induced by binding of cisplatin to non-DNA targets (especially proteins) may contribute to its biochemical mechanism of action. On the other hand, it has been found that several factors such as the dose of drug as well as the metabolic condition of the cell subjected to cisplatin aggression, may determine that cancer cells die through apoptosis or necrosis. In fact, it has recently been reported that both mechanisms of cell demise work in concert so that within a population of tumour cells there is a continuum of possible modes of cell death.