Drug Design Reviews - Online (Discontinued) - Volume 1, Issue 4, 2004

Nitric oxide (NO) and nitrogen oxide species have been shown to be critical elements in most physiological functions in the cardiovascular system. The chemical unbalance of these species results in progression of disease. Until recent, most of the focus of nitrogen oxide chemistry has been on the effect NO and oxidized progenitors have on cardiovascular system. Recently, nitroxyl (HNO / NO-) the one electron reduced species of NO has been shown to have unique and possible pharmaceutically beneficial properties. These properties are often the opposite of those of NO and provide an interesting paradigm. This review will discuss novel and emerging aspects of HNO and NO unique effects in vivo and in vitro. Cardioprotective mechanisms such as acute or early preconditioning triggered by NO and nitroxyl will be analyzed. Preconditioning includes several primary signaling pathways that seem to converge on mitochondrial targets, leading to altered cell metabolism and inhibition of apoptosis. Brief ischemia leads to generation of agonists that bind to G protein-coupled receptors, and initiates a signaling cascade that involves activation of phosphoinositide-3-kinase, endothelial NO synthase, protein kinase C, mitogen-activated protein kinases, and other signaling pathways. Activation of these pathways along with generation of reactive oxygen species leads to alterations in the activity of mitochondrial proteins such as mitochondrial ATP-sensitive K+ channels, thus resulting in cardioprotection.

Protease-activated receptors (PARs), a family of G-protein-coupled seven-transmembrane-domain receptors, are activated by proteolytic unmasking of the N-terminal cryptic tethered ligand by certain serine proteases. Among four PAR family members cloned to date, PAR-1, PAR-2 and PAR-4 can also be activated through a non-enzymatic mechanism, which is achieved by direct binding of exogenously applied synthetic peptides based on the tethered ligand sequence, namely PARs-activating peptides, to the body of the receptor. Various peptide mimetics have been synthesized as agonists and / or antagonists for PARs with improved potency, selectivity and stability. The amidation of the C-terminal of PARs-activating peptides increases the potency and metabolic resistance, particularly in vivo . Substitution of the Nterminal serine residue of PAR-2-activating peptides with a furoyl group dramatically enhances both potency and metabolic resistance, providing the most potent PAR-2 agonist. Some peptide mimetics and / or non-peptide compounds have also been developed as antagonists for PAR-1 and PAR-4. PARs are widely distributed in the mammalian body, especially throughout the alimentary systems, and play various roles in physiological / pathophysiological conditions; i.e. modulation of salivary, gastric or pancreatic glandular exocrine secretion and gastrointestinal smooth muscle motility, gastric mucosal cytoprotection, suppression / facilitation of visceral pain and inflammation, etc. Thus, PARs are now considered novel therapeutic targets, and development of selective agonists and / or antagonists for PARs might provide novel strategy for clinical treatment of various diseases that are resistant to current therapeutics.

Despite improved treatments and early detection of breast cancer (BC), bone metastasis remains a clinical dilemma. The time interval between breast cancer cell (BCC) entry in the bone marrow (BM) and clinically apparent bone metastasis could be years, suggesting that the marrow might allow for quiescence of BCCs. This review discusses the molecular mechanism by which BCCs enter and integrate into the BM microenvironment long before the cancer is clinically detected. BCCs entering the BM can be subdivided based on the cells' locations within the BM: I) BCCs within the stromal compartment and close to the endosteum are defined as cells undergoing epithelial to mesenchymal to stromal transition (EMST), and II) Rapidly proliferating BCCs located within the central medullary region. The preprotachykinin- I (PPT-I) gene and genes for cognate receptors, neurokinin-1 subtypes (full-length and truncated) and NK-2, are linked to BC development, including early entry into the BM. NK receptors form a network with cytokines and other molecules to promote the survival and quiescence of BCCs. A central role of NK receptors in the early entry of BCC into the BM microenvironment is discussed. We propose that NK receptors and subtypes are potential targets for breast, and perhaps other endocrine-linked cancers, during different phases of the disease.

Antiseptic resistance of staphylococci is caused by multidrug transporter proteins represented by QacA / QacB and Smr / QacC which mediate efflux of drugs via electrochemical proton gradient across the cytoplasmic membrane. Smr / QacC is a member of small multidrug resistance (SMR) family which consists of approximately 110 amino acids and contains four predicted transmembrane segments. SMR family includes various antiseptic resistance proteins which have been found in staphylococci as well as in other bacterial species. Phylogenetically, SMR family proteins are classified into two major clusters, genogroup 1 and genogroup 2, which are mostly found in Gram-positive cocci and Gram-negative bacteria, respectively. Although amino acid sequences of SMR family are divergent among different genotypes, several amino acids in transmembrane regions are highly conserved and considered to be directly associated with a process of drug transport through the bacterial cytoplasmic membrane. The Smr / QacC which is encoded by smr is genetically well conserved in staphylococci. However, genomic diversity is found outside the ORF of smr gene and three types of smr gene cassette (Types 1, 2, and 3) which is a structural unit containing smr and terminal direct repeats (DRs) have been discriminated. Although antiseptic resistance levels of Staphylococcus aureus having smr in each of the three types of cassettes were generally similar, higher copy numbers were detected for type 2 cassette-smr than type 1 cassettesmr in our recent study, suggesting that expression level of smr might be different depending on the type of smr gene cassette. Further study of genomic structure and diversity of smr gene will contribute to prevent spread of antiseptic resistance in staphylococci and development of novel antiseptic substances.

Apoptosis has fundamental significance in both normal tissue homeostasis and pathophysiological processes such as wound healing, inflammation, and fibrosis. Failure to clear unwanted cells by apoptosis will prolong inflammation due to the release of their toxic contents. In contrast, excessive apoptosis may cause diseases. Examination of lung biopsies from patients with idiopathic pulmonary fibrosis and animal models of lung fibrosis have found apoptotic cells associated with fibrotic lesions. Transforming growth factor-β1 (TGF-β1) has important roles in lung fibrosis and has the potential to induce apoptosis of lung epithelial cells in vitro and in vivo . Administration of TGF-β1 could enhance Fasmediated epithelial cell apoptosis and lung injury via caspase-3 activation, and caspase inhibitors can prevent the development of fibrosis. Recent progress in understanding the mechanisms of lung fibrosis and regulation of apoptosis in various cell types in lung tissue leads us to expect that inhibitors of apoptosis can prevent subsequent increases in collagen levels and may also be useful as novel therapeutic agents in controlling undesirable fibrosis. In this review, the role of apoptosis in the pathogenesis and resolution of fibrotic lesions will be summarized and highlighted, with more detailed discussion on regulation and signal transduction pathway of apoptosis in lung fibrosis.

Echinococcus granulosus and Echinococcus multilocularis are cestode parasites, of which the metacestode (larval) stages cause the diseases cystic echinococcosis (CE) and alveolar echinococcosis (AE), respectively. These two species represent an important medical and veterinary health concern with considerable economic impact. The metacestodes are basically fluid-filled vesicles. Their surface consists of an acellular carbohydrate-rich laminated layer, which is synthesised by the germinal layer situated on the inner surface. Metacestodes of E. granulosus are characerised by expansive growth, while the hallmarks of E. multilocularis metacestodes are tumour like, exogenous proliferation and infiltration of neighbouring sites. The potentially unlimited increase of the parasite mass causes compression of neighbouring tissue, which eventually results in disease. Total surgical removal of the parasitic mass is still considered the gold standard treatment for human echinococcosis. Benzimidazoles (albendazole, mebendazole), given either alone, or combined with praziquantel in the case of CE, are presently used for the treatment of non-surgical cases and as a supplementary treatment prior and post-surgery. Chemotherapy, employing those drugs, has been successful in many cases, especially in human CE and has clearly improved the life span and the living conditions of many individuals, by effectively stopping the growth of the parasite. However, failures in drug treatments, most notably in human AE, have been reported, either related to severe side effects such as liver toxicity, typically leading to discontinuation of treatment or to progressive disease despite benzimidazole treatment. In addition, in AE, benzimidazoles do not appear to be parasiticidal in vivo, and the parasite may resume growth after discontinuation of treatment. Thus, improved therapeutic tools are needed in order to optimize treatment. In vivo studies have primarily focussed on the identification of novel compounds with anti-parasitic activity, on the kinetics of drug uptake and metabolic changes imposed upon the parasite, while most studies employing animal models have focussed mainly on comparing the activities of different benzimidazole derivatives, and on different formulations and modes of application. In this paper, we will provide an overview on the current treatment of echinococcosis and we will discuss the mechanisms of drug activities, possible reasons for failure of drugs to act on those parasites, and the efforts on obtaining better anti-parasitic compounds.

Dosimetry estimates of normal organs and tumors are presented for 34 lung cancer patients after administration of 111In-CC49 tracer / 90Y-CC49 + / - adjuvant EDTA or DTPA chelator, or paclitaxel chemotherapy. Data were obtained from quantitation of serial gamma camera images and blood radioactivity. Radiation dose estimates were calculated by Medical Internal Radiation Dose (MIRD) formalism using lesion or organ dimensions obtained from CT images. The pharmacokinetics and dosimetry of the serum and whole body after a single IV administration of 90Y-CC49 were similar to that reported in multiple studies of 131I-CC49 (serum T1 / 2 45 + / - 15h), with a ∼2-fold range between the shortest and longest circulation time. Normal organs including liver, lung and kidney had ranges from 5-7 fold between the lowest and highest radiation dose while tumors had the widest range of 10 fold. Using specific liver masses for 20 patients resulted in dose estimates 0.5-1.7x that derived with the mass of a standard reference man model. Whole body radiation dose per unit of injected activity (cGy / mCi) was relatively consistent among 33 patients, varying between 2.0 and 2.6 with a mean of 2.4 despite modest but significant differences with chemotherapy or chelator. Paclitaxel in conjunction with the 90Y-CC49 resulted in a modest increase in whole body cGy / mCi but effects for other parameters measured were not statistically significant. The adjuvant use of EDTA or DTPA as a chelator for unbound radioactive metal resulted in small, although significant decreases, in whole body T1 / 2, and cGy / mCi for the whole body, lung and liver but did not significantly change plasma pharmacokinetics.

The discovery and development of camptothecin and its various analogues illustrates a number of interesting points concerning the rational development of therapeutic drugs and the implementation of promising compounds into the therapeutic setting. The unique pentacyclic structure (rings A-E) of camptothecins is essential for anti-tumour activity. This basic structure contains an α-hydroxy-δ-lactone system in ring E and an unsaturated pyridone moiety in ring D. The lactone E-ring of camptothecins hydrolyses reversibly to the carboxylate form in aqueous solutions and this ring-opening is a critical determinant of activity. The spectacular early failure of camptothecin in the clinical setting, due to the use of the inactive carboxylate form, highlights the need for extensive studies on structure-activity relationships before drugs are tested in patient populations. Following the elucidation of the molecular target of camptothecins there was renewed interest in developing more water-soluble derivatives of camptothecin that still retained anti-tumour activity. Two of these derivatives, CPT-11 and topotecan, have shown promising activity against a wide range of tumours and are now being used in the clinical setting.

Myristoyl-CoA:protein N-myristoyltransferase (NMT) is an enzyme that catalyzes the attachment of myristate to the N-terminus of a number of cellular proteins of signal transduction pathways which may be involved in oncogenesis, in secondary cellular signaling and in infectivity of retroviruses. NMT expression and activity have been found to be elevated in cancers of the stomach, colon and gallbladder as well as in some leukemia cell lines. NMT is proposed as a novel molecular target for anticancer drug design. There is a rapidly expanding body of synthetic chemical and endogenous NMT inhibitors and this review discusses the design and characterization of some inhibitors from our laboratory.