Showing papers in "Current Pharmaceutical Design in 1999"

An overview of cyclophosphamide development and clinical applications.

Abstract: In this overview of the pharmacology of the anticancer drug cyclophosphamide, a brief history of the development of this drug from the general class of nitrogen mustards is provided. The antitumor activity of cyclophosphamide and its isomer ifosfamide is discussed through considerations of metabolism, resistance, detoxification, and DNA cross-linking. Clinical uses in general chemotherapy, bone marrow transplantation and immunosuppression are presented. A review with 73 references.

Current trends in the development of nitric oxide donors.

Abstract: Nitric oxide (NO) is an important messenger molecule involved in many pathological and physiological processes within the mammalian body. Exogenous NO sources constitute a powerful way to supplement NO when the body can not generate enough for normal biological functions. In this article, general aspects on NO and NO donors are reviewed. Major focus is placed on recent developments of novel NO donors, NO releasing device(s) as well as innovative improvements to current NO donors. Finally, an outlook on future NO donor development is provided.

OXA-type beta-lactamases.

Abstract: The OXA-type (oxacillin-hydrolysing) enzymes are widespread and have been mostly described in Enterobacteriaceae and in P. aeruginosa. They usually confer resistance to amino- and ureidopenicillin and possess high-level hydrolytic activity against cloxacillin, oxacillin, and methicillin. Their activities are weakly inhibited by clavulanic acid but sodium chloride (NaCl) possesses a strong inhibition activity. Oxacillin-hydrolysing b-lactamases belong to Ambler class D and thus possess an active serine site as classes A and C b-lactamases. Overall amino-acid identities between class D and class A or class C b-lactamases is about 16%. Until now, 24 Ambler class D enzymes, named OXA-1 to OXA-22, AmpS and LCR-1, have been characterised, either by sequence and/or by biochemical analyses, but for none of them a three dimensional structure is yet available. While some oxacillinases present a significant degree of amino-acid identity (for example, OXA-1 and OXA-4; OXA-10 (PSE-2) derivatives; OXA-2 and OXA-3), most of them are only weakly related (20% to 30% amino-acid identity). Oxacillinases usually display a restricted-spectrum phenotype. However extension of their spectrum towards oxyimino cephalosporins and/or imipenem has recently been observed mostly as a consequence of point mutations in OXA-2 or OXA-10 derivatives. Their frequent plasmid- and/or integron-location provide them a mean for a wide diffusion.

Transferrin As A targeting ligand for liposomes and anticancer drugs.

Abstract: In cancer treatment, one of the approaches is targeting of the drug to tumor cells via receptor specific ligands. Transferrin (molecular weight 80,000) has been used as a ligand for delivering anticancer drugs or drug containing liposomes mostly due to the increased number of transferrin (trf) receptors found on tumor cells as compared to normal cells. Transferrin was linked to methotrexate (MTX) containing small unilamellar liposomes and its activity was compared to antitransferrin receptor antibody (7D-3) linked to MTX liposomes. In each of these conjugates, the method of coupling was the same and a disulphide linkage was formed between the ligand and MTX liposomes. No significant differences in the potency of 7D-3 conjugate or trf conjugate with MTX liposomes were observed in studies performed in vitro against various human tumor cell lines (Hela, KB and Colon). Trf was also linked to adriamycin via a schiff base which was formed by using glutaraldehyde. This conjugate was found to be effective in vitro against various human tumors (Lovo, HL-60, SW 403 and Hep2) and also in vivo against H-mesothelioma tumors. Transferrin receptor has also been used for gene delivery. Gene delivery to K562 haematopoietic leukaemic cells was achieved by using a transferrin-polycation (poly-L-lysine or protamine) conjugate. This review will cover the various important applications of transferrin based drug delivery formulations in the chemotherapy of cancer and the related work performed in our and other laboratories.

Brain inflammation in Alzheimer disease and the therapeutic implications.

Abstract: Immunohistochemical studies suggested the existence of a chronic inflammatory condition in affected regions of the brain in Alzheimer disease (AD). Since inflammation can be damaging to host tissue, it was hypothesized that antiinflammatory drugs might inhibit both the onset and the progression of AD. This hypothesis is supported by a number of epidemiological studies suggesting that the prevalence of AD in persons is reduced by 40 - 50% in persons using antiinflammatory drugs. In one small pilot trial in early AD, the nonsteroidal antiinflammatory drug indomethacin appeared to halt the progressive memory loss. Immunohistochemical and molecular biological studies on immune system components in AD brain are revealing the complexities of the innate immune reaction. This very complexity may offer points of therapeutic intervention for new types of antiinflammatory agents. The complement system, microglia and cytokines are key components. This review summarizes the present state of knowledge on the immune system elements found in AD brain.

15-Lipoxygenase and its inhibition: a novel therapeutic target for vascular disease.

Abstract: The disease process known as atherosclerosis is the leading cause of morbidity and mortality in the Western world. Current therapies have focused on treating the major risk factors identified to date including plasma lipid derangements, hypertension, clotting disorders, and diabetes. However, a significant number of individuals will be diagnosed with this malady in the apparent absence of known risk factors. Recent attention has turned toward treating the disease at the level of the vessel wall. In this review, we assess the relevancy of the oxygenating enzyme 15-lipoxygenase (15-LO) as a therapeutic target. In vitro studies suggest that this enzyme may be involved in processes that modify native LDL in such a way as to be avidly taken up by tissue macrophages. In support of this contention are reports demonstrating the colocalization of 15-LO with macrophage-rich arterial lesions and epitopes of modified LDL. Investigations using transgenic animals also suggest that the site of 15-LO expression may be an important factor in the development of the disease. The alteration of important cellular fatty acids may also generate intracellular signals that promote a pro-atherogenic phenotype in the absence of measurable changes in bulk lipid peroxidation. A limited number of studies have examined 15-LO inhibitors and those structural determinants necessary for inhibition of the enzyme. These include natural products and synthetic analogs. Structure activity relationships have been defined for a number of compounds including caffeic acid derivatives, propargyl ethers, and catechols. A novel, potent, specific inhibitor of 15-LO that lacks significant antioxidant activity was tested for its ability to inhibit atherosclerotic lesion formation in vivo. This benzothiopyranoindole virtually eliminated lesion formation in two animal models in the absence of significant changes in plasma lipids. Further, it prevented the progression of pre-established lesions in another study. Collectively, these data provide a strong scientific rationale for exploring the inhibition of 15-LO as a therapeutic strategy.

Regulation of inducible AmpC beta-lactamase expression among Enterobacteriaceae.

Abstract: AmpC ss-lactamases are active-site serine enzymes that are primarily cephalosporinases. In many gram negative organisms, including Enterobacter spp.,Citrobacter freundii, Serratia marcescens, Morganella morganii and Pseudomonas aeruginosa, the expression of chromosomal ampC genes is low but inducible in response to ss-lactams and other stimuli. The current working model for AmpC induction requires exposure of bacterial cells to ss-lactam drugs or other stimuli and is linked to the cell wall recycling pathway. Induction of ampC appears to involve several gene products associated with this pathway. These gene products include AmpR, AmpD, and AmpG. In addition, anhydro forms of cell wall precursor muropeptides are believed to act as cofactors for AmpC induction. These cofactors bind to the DNA binding protein, AmpR, and define the role of AmpR as activator. Recent debate has ensued in the literature as to the identification of the precursor muropeptide involved in the activation process. Two candidate muropeptides include 1,6-anhydro-N-acetylmuramic acid L-Ala-D-Glu-meso-diaminopimelic acid (anhydro-MurNAc-tripeptide) and anhydro-MurNAc-L-Ala-D-Glu-meso-diaminopimelic acid- D-Ala-D-Ala (pentapeptide). The intent of this review is to address the general mechanism involved in AmpC induction. In doing so, the genes and gene products required for the process of AmpC induction are described. In addition, we review the data addressing cell wall recycling as it relates to AmpC induction.

The chemistry of the metabolites of cyclophosphamide.

Abstract: This is primarily an overview of the spontaneous (non-enzymatic) chemistry of the metabolites of cyclophosphamide, viz., cis- and trans-4-hydroxycyclophosphamide, aldophosphamide (and its hydrate), iminophosphamide, phosphoramide mustard, acrolein, and chloroethylaziridine. A brief description of detoxification products obtained through enzyme catalyzed reactions appears. Included as the historical basis for the development of cyclophosphamide is the chemistry of nitrogen mustards. Among the topics covered are: perturbations to metabolite distributions and half-lives effected by buffer, structure, pH and nucleophiles; effects of pH on mechanism; alkylation versus P-N bond hydrolysis; the influence of nucleophiles on alkylation product distributions; the influence of substituents on alkylation rates; and preactivated forms of cyclophosphamide as metabolite precursors (4-hydroperoxycyclophosphamide and mafosfamide). A review with 66 references.

Antagonists selective for NMDA receptors containing the NR2B subunit.

Abstract: In the late 1980s, a new class of N-methyl-D-aspartate (NMDA) receptor antagonists, exemplified by the phenylethanolamine ifenprodil (1), was identified. Initially, the mechanism of action of ifenprodil was a mystery as it was not a competitive antagonist at the glutamate or glycine (co-agonist) binding sites, nor was it a blocker of the calcium ion channel associated with the NMDA receptor. Early studies with a novel polyamine binding site associated with the NMDA receptor and functional studies in various brain regions suggested a unique and selective activity profile for 1. However, it was not until the NMDA receptor subunits were identified and expressed that ifenprodil was shown to be a selective antagonist for a subset of NMDA receptors containing the NR2B subunit. The wide range of potential therapeutic targets for NMDA antagonists coupled with the hope that NR2B selective agents might possess an improved clinical safety profile compared to non-selective compounds has supported an aggressive effort to develop the structure-activity relationships (SAR) of NR2B selective antagonists. This SAR and the basic physiology of the NMDA receptor form the basis of this review.

A pharmacological review of competitive inhibitors and substrates of high-affinity, sodium-dependent glutamate transport in the central nervous system.

Abstract: The acidic amino acid L-glutamate acts as both a primary excitatory neurotransmitter and a potential neurotoxin within the mammalian central nervous system. Functionally juxtaposed between these neurophysiological and pathological actions are an assorted group of integral membrane transporter proteins that rapidly and efficiently sequester glutamate into cellular and subcellular compartments. While multiple systems exist that are capable of mediating the uptake of L-glutamate, the high-affinity, sodium-dependent transporters have emerged as the most prominent players in the CNS with respect to terminating the excitatory signal, recycling the transmitter, and regulating extracellular levels of glutamate below those which could induce excitotoxic pathology. The focus of the present review is on the pharmacological specificity of these sodium-dependent transporters and, more specifically, on the competitive inhibitors that have been used to delineate the chemical requirements for binding and translocation. Analogues of glutamate that are conformationally constrained as a consequence of either the addition of substituents to the carbon backbone of glutamate or aspartate (e.g., beta-hydroxyaspartate or methylglutamate derivatives) or the incorporation of ring systems (e.g., (carboxycyclopropyl)glycines, aminocyclobutane dicarboxylates, or pyrrolidine dicarboxylates), have been especially valuable in these efforts. In this review, a particular emphasis is placed on the identification of analogues that exhibit preferential activity among the recently cloned transporter subtypes and on the differentiation of substrates from non-transportable inhibitors.

Aldehyde dehydrogenase-mediated cellular relative insensitivity to the oxazaphosphorines.

Abstract: As judged by findings in preclinical models, determinants of cellular sensitivity to cyclophosphamide and other oxazaphosphorines include two cytosolic aldehyde dehydrogenases, viz., ALDH1A1 and ALDH3A1. Each catalyzes the detoxification of the oxazaphosphorines; thus, cellular sensitivity to these agents decreases as cellular levels of ALDH1A1 and/or ALDH3A1 increase. Of particular clinical relevance may be that stable sublines, relatively insensitive to the oxazaphosphorines due to elevated ALDH1A1 or ALDH3A1 levels, emerged when cultured human tumor cells were exposed only once to a high concentration of one of these agents for 30 to 60 minutes. Whether differences in cellular levels of either enzyme accounts for the clinically-encountered uneven therapeutic effectiveness of the oxazaphosphorines remains to be determined. However, it has already been established that measurable levels of these enzymes are found in some, but not all, tumor types, and that in those tumor types where measurable levels are present, e.g., infiltrating ductal carcinomas of the breast, they vary widely from patient to patient. Potentially useful clinical strategies that might be pursued if it turns out that ALDH1A1 and/or ALDH3A1 are, indeed, clinically operative determinants of cellular sensitivity to the oxazaphosphorines include 1) individualizing cancer chemotherapeutic regimens based, at least in part, on the levels of these enzymes in the malignancy of interest, and 2) sensitizing tumor cells that express relatively large amounts of ALDH1A1 and/or ALDH3A1 to the oxazaphosphorines by preventing the synthesis of these enzymes, e.g., with antisense RNA, or by introducing an agent that directly inhibits the catalytic action of the operative enzyme. Further, the fact that ALDH1A1 and ALDH3A1 are determinants of cellular sensitivity to the oxazaphosphorines provides the rationale for the investigation of two additional strategies with clinical potential, viz., decreasing the sensitivity of vulnerable and essential normal cells, e.g., pluripotent hematopoietic cells, to the oxazaphosphorines by selectively transferring into them the genetic information that encodes 1) ALDH1A1 or ALDH3A1, or 2) a signaling factor, the presence of which would directly or indirectly, stably upregulate the expression of these enzymes.

Recent advances with the CRF1 receptor: design of small molecule inhibitors, receptor subtypes and clinical indications.

Abstract: Corticotropin-releasing factor (CRF) has been widely implicated as playing a major role in modulating the endocrine, autonomic, behavioral and immune responses to stress. The recent cloning of multiple receptors for CRF as well as the discovery of non-peptide receptor antagonists for CRF receptors have begun a new era of CRF study. Presently, there are five distinct targets for CRF with unique cDNA sequences, pharmacology and localization. These fall into three distinct classes, encoded by three different genes and have been termed the CRF1 and CRF2 receptors (belonging to the superfamily of G-protein coupled receptors) and the CRF-binding protein. The CRF2 receptor exists as three splice variants of the same gene and have been designated CRF2a CRF2b and CRF2g. The pharmacology and localization of all of these proteins in brain has been well established. The CRF1 receptor subtype is localized primarily to cortical and cerebellar regions while the CRF2a receptor is localized to subcortical regions including the lateral septum, and paraventricular and ventromedial nuclei of the hypothalamus. The CRF2b receptor is primarily localized to heart, skeletal muscle and in the brain, to cerebral arterioles and choroid plexus. The CRF2g receptor has most recently been identified in human amygdala. Expression of these receptors in mammalian cell lines has made possible the identification of non-peptide, high affinity, selective receptor antagonists. While the natural mammalian ligands oCRF and r/hCRF have high affinity for the CRF1 receptor subtype, they have lower affinity for the CRF2 receptor family making them ineffective labels for CRF2 receptors. [125I]Sauvagine has been characterized as a high affinity ligand for both the CRF1 and the CRF2 receptor subtypes and has been used in both radioligand binding and receptor autoradiographic studies as a tool to aid in the discovery of selective small molecule receptor antagonists. A number of non-peptide CRF1 receptor antagonists that can specifically and selectively block the CRF1 receptor subtype have recently been identified. Compounds such as CP 154,526 (12), NBI 27914 (129) and Antalarmin (154) inhibit CRF-stimulation of cAMP or CRF-stimulated ACTH release from cultured rat anterior pituitary cells. Furthermore, when administered peripherally, these compounds compete for ex vivo [125I]sauvagine binding to CRF1 receptors in brain sections demonstrating their ability to cross the blood-brain-barrier. In in vivo studies, peripheral administration of these compounds attenuate stress-induced elevations in plasma ACTH levels in rats demonstrating that CRF1 receptors can be blocked in the periphery. Furthermore, peripherally administered CRF1 receptor antagonists have also been demonstrated to inhibit CRF-induced seizure activity. These data clearly demonstrate that non-peptide CRF1 receptor antagonists, when administered systemically, can specifically block central CRF1 receptors and provide tools that can be used to determine the role of CRF1 receptors in various neuropsychiatric and neurodegenerative disorders. In addition, these molecules will prove useful in the discovery and development of potential orally active therapeutics for these disorders.

The dolastatins, a family of promising antineoplastic agents.

Abstract: The dolastatins and some related compounds are antineoplastic pseudopeptides isolated from the sea hare Dolabella auricularia by the groups of G. R. Pettit and K. Yamada. Several groups including ours have contributed to the development of synthetic routes to most of these compounds. We recently described the synthesis of dolatrienoic acid, the lipidic component of dolastatin 14. Among all these metabolites, dolastatin 10 and dolastatin 15 exhibit the most promising antiproliferative properties and are currently under evaluation in clinical trials. These antimitotic agents seem to exert their activity by interacting with tubulin and inducing apoptosis. Research in this domain could greatly benefit from the recent elucidation of the atomic structure of tubulin. However, other targets cannot be excluded. Elucidation of the structure-activity relationships is an important step in the development of therapeutic agents. Parallel to the studies developed by other groups, our approach to exploring structural requirements for the antineoplastic activity of these compounds involved the determination of their preferred conformations in solution. Our study showed that dolastatin 10 exists in two different conformations corresponding to a cis-trans isomerization of a central amide bond. Such a situation was not demonstrated in the case of dolastatin 15. In view of elucidating the biological relevance of these findings, we elaborated hybrid molecules constituted of parts of both compounds. We also synthesized a cyclic analogue of dolastatin 10 which locked this compound in its cis conformation. Our results as well as those of others could be interpreted in terms of an existing structural model.

Prodrug approaches to the improved delivery of peptide drugs.

Abstract: Undesirable pharmaceutical and biopharmaceutical properties, which include low water solubility, poor stability, and low permeability through biological membrane barriers, often hinder the clinical development of biologically active peptides. Finding solutions to these problems is a contemporary issue in developing clinically the vast number of biologically active peptides as drugs. In recent years, significant progress has been made in developing prodrug approaches for the improvement of the water solubility, stability, and membrane permeability of peptides. For improving water solubility, the focus has been on the bioreversible introduction of ionizable functional groups to peptides, which helps to increase the polarity and thus water solubility of the peptide drugs. For improving stability, efforts have focused on stabilizing peptides against exopeptidase-mediated hydrolysis by bioreversibly masking the terminal carboxyl and/or amino groups. For improving permeability through biological barriers, recent efforts have focused on both improving the lipophilicity of a peptide in order to facilitate its passive permeation through biological membranes and conjugation of a peptide to a carrier which allows for the active transport of the peptide-carrier conjugate. Many of the prodrug systems developed recently have the potential to be used clinically for the delivery of peptide drugs to the desired site of action.

Current progress in the chemistry, medicinal chemistry and drug design of artemisinin based antimalarials.

Abstract: This review covers developments in relation to artemisinin-based antimalarial agents. Topics covered include a brief introduction to the history and treatment of malaria, and more recently, drug resistant malaria; the discovery of the naturally occurring novel peroxidic antimalarial artemisinin; artemisinin biosynthesis, metabolism and biotransformations; the diversity of proposed mechanisms of action; pharmacokinetics; the insight into structure-toxicity relationships; the total syntheses and the progress made in the syntheses of its analogs; and, ultimately the contribution of these efforts towards rational drug design in order to access potent, non-toxic antimalarial drugs based on artemisinin.

Interleukin-8 : An autocrine inflammatory mediator

Abstract: Interleukin-8 (IL-8), a pro-inflammatory chemokine, induces trafficking of neutrophils across the vascular wall. The release of IL-8 is triggered by inflammatory signals from a large variety of cells. The diversity in the cellular source indicates pleiotropy of its functions. IL-8 plays a key role in host defense mechanism through its effects on neutrophil activation, but a continued presence of IL-8 in circulation in response to inflammatory conditions may lead to a variable degree of tissue damage. Like most of the peptide hormones or mediators, IL-8 transmits its signals through distinct cell surface receptors. The membrane spanning heptahelical IL-8 receptor is coupled with the effector enzyme(s) through the intermediacy of heterotrimeric GTP-binding regulatory proteins. A growing number of studies demonstrated regulation of IL-8 activity by pertussis toxin treatment, implying a role of pertussis toxin sensitive G proteins (Gi), in IL-8 induced effects. IL-8 induced activation of G-protein results in activation of phospholipase C b2 (PLCb2). This enzyme catalyzes the hydrolysis of membrane phosphoinositides to yield diacylglycerol (DAG) and inositol 1,4,5 trisphosphate (IP3), which in turn activates protein kinase C (PKC) and mobilizes the intracellular Ca2+, respectively. Neutrophils activation of phospholipase D (PLD) and superoxide generation in response to IL-8 have also been demonstrated. Furthermore, IL-8-mediated activation of mitogen activating protein kinase (MAPK) and tyrosine phosphorylation of cellular proteins have been observed. It appears that the signalling pathways induced by IL-8 are subject to fine modulations by the demand and presence of IL-8. The presence of IL-8 in various pathophysiological condition implies that blockade of its actions could be exploited for therapeutic purposes.

SHV-type beta-lactamases.

Abstract: The group of plasmid-mediated SHV b-lactamases includes SHV-1 and at least twenty-three variants, most of which possess extended-spectrum (ES) activity against the newer broad-spectrum cephalosporins. Their likely ancestor is a chromosomal penicillinase of Klebsiella pneumoniae. SHV enzymes belong to the molecular class A of serine b-lactamases and share extensive functional and structural similarity with TEM b-lactamases. The three-dimensional structure of the SHV-1 b-lactamase possesses an active site wider than that of TEM-1 b-lactamase by 0.7 to 1.2 A. This results in subtle, yet important, differences in the positioning of critical active-site residues. SHV-1 b-lactamase behaves as a typical penicillinase hydrolyzing penicillins and early generation cephalosporins. SHV-1 b-lactamase has spread, via plasmids, to virtually all enterobacterial species but is encountered mostly in K. pneumoniae. ES SHV b-lactamases are found with increasing frequency in K. pneumoniae and other enterobacterial isolates and are now considered the most prevalent ES b-lactamases. These ES SHV b-lactamases confer a wide spectrum of resistance to b-lactams, including the new generation cephalosporins and monobactams, and are usually encoded by self-transmissible multi-resistant plasmids that are highly mobile. Extension of the hydrolytic spectrum of ES SHV enzymes to include oximino-b-lactams is seen as a result of substitutions of critical amino acid residues that alter the properties of the active site. These mutational changes, however, result in diminished hydrolytic activity against penicillins and an increased susceptibility to mechanism-based inhibitors. Understanding the substrate evolution, properties and modes of spread of these clinically important b-lactamases can help in formulating effective antibiotic policies and developing new antimicrobial agents.

beta-Lactamases of increasing clinical importance.

Abstract: Resistance to b-lactam-containing antimicrobial agents continues to increase, frequently due to the presence of b-lactamases in Gram-negative bacteria. Over the past twenty-five years broad-spectrum enzymes such as TEM- and SHV-variants and the metallo-b-lactamases have become more prolific. As a result of the ability of plasmids to continue to acquire additional resistance determinants, many of the b-lactamase-producing Gram-negative pathogens have become multi-drug resistant. In combination with decreased permeability, the organisms can become virtually untreatable with current therapies. The major groups of b-lactamases that pose the most serious therapeutic problems include the extended-spectrum b-lactamases, the plasmid-mediated cephalosporinases, the inhibitor-resistant TEM- or SHV-derived b-lactamases and the carbapenem-hydrolyzing b-lactamases. Those enzymes that can be transferred on mobile elements are the most serious of the newer b-lactamases, and include enzymes in each of the four groups outlined above.

Polyoxins and nikkomycins: progress in synthetic and biological studies.

Abstract: Polyoxins and nikkomycins are naturally-occurring peptidyl nucleoside antibiotics. As inhibitors of chitin synthetase, they exhibit antifungal activity, but lack antibacterial activity. Since they also lack mammalian toxicity, they represent potentially useful models for the development of effective agents for the treatment of opportunistic fungal infections. Direct clinical application of the natural peptidyl nucleosides is compromised by their attenuated in vivo activity, apparently due to their hydrolytic lability and inefficient fungal cell wall permeability. Thus, extensive efforts have focused on syntheses of natural peptidyl nucleosides, their components and analogs in anticipation of establishing useful structure-activity-relationships (SAR) for the development of new antifungal agents. A comprehensive and critical review of the synthetic effort and subsequent biological studies reveals that while much has been accomplished, ideal antifungal agents have not yet been developed from the natural peptidyl nucleoside leads. The need for continued study of agents with novel modes of action is emphasized by the realization that other structurally varied antifungal agents currently used clinically have limitations and often severe side effects, including nephrotoxicity.

Recent advances in matrix metalloproteinase inhibitors research.

Abstract: Excess MMP proteolytic activity has been associated with a wide variety of pathological conditions such as arthritis, cancer and heart failure. The potential utility of MMP inhibitors as therapeutic interventions in these diverse and important disease states has led to an intense effort toward the development of such inhibitors. The first generation of compounds were peptide-like broad spectrum inhibitors, active against a broad range of MMPs. However, the induction of musculoskeletal side effects seen in clinical trials with these agents has emphasized the need for a better understanding of the role that each of the MMPs plays in normal tissue turnover and disease progression. Advances in our ability to engineer and synthesize selective inhibitors as well as the discovery of small molecule, non-peptidic inhibitors has spurred an intense effort to identify potent and bioavailable second generation compounds. There are now several such compounds targeted against various subsets of the MMPs in clinical development. This review will focus on the design and structure activity relationships of these second generation compounds.

Inhibitors of 17alpha-hydroxylase/17,20-lyase (CYP17): potential agents for the treatment of prostate cancer.

Abstract: Prostate cancer (PCa) is now the most prevalent cancer in men in the U.S.A. and Europe. At present the major treatment options include surgical or medical castration. These strategies depend on the abolition of the production of testosterone by the testes. However, as these procedures do not affect adrenal androgen production, they are frequently combined with androgen receptor antagonist to block their action. Inhibition of the key enzyme which catalyzes the biosynthesis of androgens from pregnane precursors, 17alpha-hydroxylase/17,20-lyase (hereafter referred to as CYP17 ) could prevent androgen biosynthesis from both sources. Thus total blockade of androgen production by CYP17 inhibitors may provide effective treatment of prostate cancer patients. Indeed, this strategy is now an area of intense interest within research institutions and the pharmaceutical industry. This review highlights development in the design and evaluation of both steroidal and non-steroidal CYP17 inhibitors since 1965. Major emphasis is given to the potent CYP17 inhibitors and those which may show clinical promise. The review could function as a comprehensive working reference of research accomplishment in the field and what problems remain to be tackled in the future.

Mechanisms of resistance to the toxicity of cyclophosphamide.

Abstract: Resistance to cyclophosphamide therapy continues to be a major reason for treatment failure. This chapter covers some of the mechanisms implicated in resistance to the toxic and mutagenic effects of cyclophosphamide therapy in the laboratory and clinic. Since resistance is likely to be the result of a number of interrelating factors, this chapter evaluates the contribution of both glutathione and DNA repair processes to cyclophosphamide resistance. Glutathione appears to be involved directly in the detoxification of cyclophosphamide and metabolites and may play a more indirect role in other processes. The ability of the cell to repair cyclophosphamide-induced DNA lesions, possibly through nucleotide excision repair or other processes, may be a key contributor to drug resistance. Interestingly, the presence of the repair enzyme, O6-alkylguanine-DNA alkyltransferase, long thought to be involved with resistance to methylating and chloroethylating agents, may also contribute to resistance to the cytotoxic and mutagenic effects of cyclophosphamide.

Strategies and progress towards the ideal orally active thrombin inhibitor.

Abstract: Thrombin plays a key role in the control of thrombus formation, for which reason its inhibition has become a target for new antithrombotics. Important issues in the profile of the ideal thrombin inhibitor are: potency, selectivity, oral bioavailability, half-life in the circulatory system and safety. Although many potent direct inhibitors of thrombin have been discovered, most of these inhibitors lack sufficient oral bioavailability. This is often associated with the presence of highly basic functionalities such as guanidine or amidine. These basic functionalities in the P1 moiety are preferred by thrombin and are present in the first generation of thrombin inhibitors. Recently, several orally active direct thrombin inhibitors have been disclosed. Most of these inhibitors originate from leads of the first generation. Two major optimization strategies could be identified to further improve these leads: A: maintain the highly basic P1 moiety and compensate its negative effects, and B: reduce the basicity of the P1 moiety and compensate for the decrease in inhibitory activity. The progress made using these strategies is evaluated. In addition, screening large sets of compounds yielded new structures that provide useful starting points for optimization. The optimization strategy used to convert leads from screening into potent orally active thrombin inhibitors is also be evaluated.

Cadmium therapeutic agents.

Abstract: Pollution of the environment with toxic metals has increased dramatically since the beginning of the industrial revolution. Cadmium is of particular concern because it accumulates in the human body with a half-life exceeding 10 years and has been linked with a number of health problems including renal tubular dysfunction, pulmonary emphysema, significant kidney damage, and possibly osteoporosis. Moreover, in 1993 the International Agency for Research on Cancer (IARC) classified cadmium and compounds containing cadmium as human carcinogens. The field of cadmium intoxication therapy has seen increases in interest due to its poignant toxicity in both humans and animals. Preliminary attempts to combat acute cadmium poisoning included the use of the chelating agents ethylenediaminetetraacetic acid (EDTA) and British anti-Lewisite (BAL). This review will focus on the chemistry, biology, and effectiveness of cadmium intoxication therapy to date. The toxicokinetics of cadmium mammals will be discussed briefly to understand the extent and severity of overexposure. An overview of cadmium chelation therapy will be given with an emphasis on the measurable effectiveness of each and significant structure activity relationships. Cadmium intoxication therapy will be reviewed by their indicated routes of action: direct (chelation and antagonism), indirect (induction), and symptom alleviation. The methods by which cadmium therapeutics are evaluated (in vivo, in vitro) are to be discussed. An evaluation of the clinical potential for promising therapeutics will be given.

Drugs acting on DNA topoisomerases: recent advances and future perspectives.

Abstract: DNA-topoisomerases, a family of DNA-processing enzymes, represent the pharmacological target of major clinically useful chemotherapeutic agents. These drugs essentially act by trapping a topoisomerase-DNA cleavable complex, an intermediate in the enzyme s catalytic cycle. Research activity in this field continues to grow exponentially, resulting in a wealth of new information on the functional role and the biochemical and structural properties of the enzymes. In addition, the drug pharmacophores have been further characterized, along with their sequence preferences, and key interactions with the target macromolecules are being unveiled. This review will discuss the recent advances in elucidating the mode of action of DNA-topoisomerases and of topoisomerase-targeted anticancer agents.

Ligands for the benzodiazepine binding site--a survey.

Abstract: Gamma-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian Central Nervous System (CNS). GABA participates in the regulation of neuronal excitability through interaction with specific membrane proteins (the GABAA receptors). The binding of GABA to these postsynaptic receptors, results in an opening of a chloride channel integrated in the receptor which allows the entry of Cl- and consequently leads to hyperpolarization of the recipient cell. The action of GABA is allosterically modulated by a wide variety of chemical entities which interact with distinct binding sites at the GABAA receptor complex. One of the most thoroughly investigated modulatory site is the benzodiazepine binding site. The benzodiazepines constitute a well-known class of therapeutics displaying hypnotic, anxiolytic and anticonvulsant effects. Their usefulness, however, is limited by a broad range of side effects comprising sedation, ataxia, amnesia, alcohol and barbiturate potentiation, tolerance development and abuse potential. Consequently, there has been an intensive search for modulatory agents with an improved profile, and a diversity of chemical entities distinct from the benzodiazepines, but with GABA modulatory effects have been identified. The existence of endogenous ligands for the GABAA receptor complex beside GABA has often been described, but their role in the regulation of GABA action is still a matter of controversy. The progress of molecular biology during the last decade has contributed enormously to the understanding of benzodiazepine receptor pharmacology. A total of 14 GABAA receptor subunits have been cloned from mammalian brain and have been expressed/co-expressed in stable cell lines. These transfected cells constitute an important tool in the characterization of subtype selective ligands. In spite of the rapidly expanding knowledge of the molecular and pharmacological mechanisms involved in GABA/benzodiazepine related CNS disorders, the identification of clinically selective acting drugs is still to come.

Advances in non-peptide glucagon receptor antagonists.

Abstract: This review deals with glucagon receptor antagonism as a possible treatm ent of Type 2 diabetes. The role of glucagon in animal models has been studied by glucagon antibodies as model antagonists. Depending upon the animal model studied, selective glucagon deficiency produced by immunone utralisation suggests that glucagon plays a modest (rats) to substantial (rabbits) role in the maintenance of euglycaemia and is an important dia betogenic factor. These data strongly suggest that glucagon antagonism may be a beneficial and safe therapeutic approach for the treatment of T ype 2 diabetes. Further, the progress on non-peptide glucagon receptor antagonists is reviewed with special focus on the different classes of g lucagon receptor antagonists published, namely quinoxalines /pyrrolo[1,2 -a]quinoxalines, mercaptobenzimidazoles, 2-pyridyl-3,5-diarylpyrroles, q uinoline hydrazones, 4-phenylpyridines, and alkylidene hydrazides.

Class B beta-lactamases: the importance of being metallic.

Abstract: The structural and functional features of class B b-lactamases, which are metal-dependent, are reviewed in this article. Enzymes from different bacterial strains exhibit a common fold and sequence similarity in their active sites. However, the protein scaffold fine tunes the metal binding affinity and substrate selectivity. In this way, some metallo-b-lactamases seem to be functional with only one Zn(II) equivalent per enzyme, whereas others require a binuclear active site. The sequence similarity leads to a subdivision of these enzymes into three subclasses. The substrate specificities are rather broad, except for enzymes belonging to subclass B2. Some inhibitors have been designed and tested, but none of them is able to exhibit a broad spectrum against these enzymes.

ACTH and its role in immune-neuroendocrine functions. A comparative study.

Abstract: Adrenocorticotropic hormone (ACTH) belongs to the melanocortine group of related peptides which share a common precursor, the pro-opiomelanocortin (POMC). Melanocortin expresses its functional effects by the stimulation of specific G-protein coupled receptors. To date, five receptor subtypes have been cloned. The POMC gene has been highly conserved during evolution, and ACTH has been found in different cells from invertebrates to vertebrates to vertebrates, including man. With regards the immune system, the presence of melanocortin receptors and the production of ACTH have been reported in invertebrate and vertebrate immuno-competent cells. Among its various physiological effects, ATCH has been shown to play a central role in immmune responses, such as chemotaxis and phagocytosis, in lower and higher forms of life. Moreover, ACTH is a key actor in stress response, and the complex cascade of events observed in vertebrates is reproduced and concentrated in intvertebrate immunocytes. On the basis of the present findings, ACTH should be considered an important immuno-regulator, forming part of the complex mosaic of relationships between the immune and neuroendocrine system which appears to have been substantially maintained over the course of evolution.