Current Medicinal Chemistry - Volume 13, Issue 16, 2006

Angiogenesis is important in the growth and progression of solid tumours. The main pro-angiogenic factor, namely vascular endothelial growth factor (VEGF), also known as vascular permeability factor, is a potent angiogenic cytokine that induces mitosis and also regulates the permeability of endothelial cells. The soluble isoform of VEGF is a dimeric glycoprotein of 36-46 kDa, induced by hypoxia and oncogenic mutation and it binds to two specific tyrosinekinase receptors: VEGF-1 (flt-1) and VEGF-2 (KDR/flk1). An increase in VEGF expression in tumour tissue or some blood compartments (i.e. serum or plasma) has been found in solid and haematological malignancies of various origins and is associated with metastasis formation and poor prognosis. Bevacizumab, a recombinant humanised monoclonal antibody developed against VEGF, binds to soluble VEGF, preventing receptor binding and inhibiting endothelial cell proliferation and vessel formation. Pre-clinical and clinical studies have shown that bevacizumab alone or in combination with a cytotoxic agent decreases tumour growth and increases median survival time and time to tumour progression. Bevacizumab is the first anti-angiogenetic treatment approved by the American Food and Drug Administration in the first-line treatment of metastatic colorectal cancer. It has shown preliminary evidence of efficacy for breast, non-small-cell lung, pancreatic, prostate, head and neck and renal cancer as well as haematological malignancies. Common toxicities associated with bevacizumab include hypertension, proteinuria, bleeding episodes and thrombotic events. This review summarises the critical role of VEGF and discusses the data available on bevacizumab, from the humanisation of its parent murine monoclonal antibody (mAb) A.4.6.1 to its use in cancer clinical trials.

Conventional cancer chemotherapy is seriously limited by the multidrug resistance (MDR) commonly exhibited by tumour cells. One mechanism by which a living cell can achieve multiple resistances is via the active efflux of a broad range of anticancer drugs through the cellular membrane by MDR proteins. Such drugs are exported in both ATP-dependent and -independent manners, and can occur despite considerable concentration gradients. To the ATPdependent group belongs the ATP-binding cassette (ABC) transporter family, which includes P-gp, MRP, BCRP, etc. Another protein related to MDR, though not belonging to the ABC transporter family, is lung resistance-related protein (LRP). All of these proteins are involved in diverse physiological processes, and are responsible for the uptake and efflux of a multitude of substances from cancer cells. Many inhibitors of MDR transporters have been identified over the years. Firstly, MDR drugs were not specifically developed for inhibiting MDR; in fact, they had other pharmacological properties, as well as a relatively low affinity for MDR transporters. They included compounds of diverse structure and function, such as verapamil and cyclosporine, and caused side effects. Secondly, the new drugs were more inhibitor-specific, in terms of MDR transport, and were designed to reduce such side effects (e.g., R-verapamil, dexniguldipine, etc.). Unfortunately, they displayed poor response in clinical studies. Recently, new compounds obtained from drug development programs conducted by the pharmaceutical industry are characterized by a high affinity to MDR transporters and are efficient at nanomolar concentrations. Some of these compounds (e.g., MS-209) are currently under clinical trials for specific forms of advanced cancers. We aim to provide an overview of the properties associated with those mammalian MDR transporters known to mediate significant transport of relevant drugs in cancer treatments. We also summarize recent advances concerning resistance to cancer drug therapies with respect to the function and overexpression of ABC and LRP multidrug transporters.

Healing of myocardial infarcts depends on an inflammatory cascade that ultimately results in clearance of dead cells and matrix debris and formation of a scar. Myocardial necrosis activates complement, Nuclear Factor (NF)-kB and Toll-like Receptor (TLR)-dependent pathways, and generates free radicals, triggering an inflammatory response. Chemokines and cytokines are markedly induced in the infarct and mediate recruitment and activation of neutrophils and mononuclear cells. Extravasation of platelets and plasma proteins, such as fibrinogen and fibronectin, results in formation of a clot, consisting of platelets embedded in a mesh of crosslinked fibrin. This provisional matrix provides a scaffold for migration of cells into the infarct. Monocytes differentiate into macrophages and secrete fibrogenic and angiogenic growth factors inducing formation of granulation tissue, containing myofibroblasts and neovessels. Repression of proinflammatory cytokine and chemokine synthesis, mediated in part through Transforming Growth Factor (TGF)-β and Interleukin (IL)-10, is critical for resolution of the inflammatory infiltrate and transition to fibrous tissue deposition. Infarct myofibroblasts deposit extracellular matrix proteins and a collagen-based scar is formed. As the wound matures, fibroblasts undergo apoptosis and neovessels regress, resulting in formation of a scar with a low cellular content containing dense, cross-linked collagen. The pathologic and structural changes associated with infarct healing directly influence ventricular remodeling and affect prognosis in patients with myocardial infarction. Understanding the mechanisms involved in the regulation of the post-infarction inflammatory response, and the spatial and temporal parameters of wound healing is necessary in order to identify specific molecular targets for therapeutic intervention.

Transglutaminases (TGases) are enzymes which catalyze the cross linking of a glutaminyl residue of a protein/peptide substrate to a lysyl residue of a protein/peptide co-substrate with the formation of an N-gamma-(epsilon- L-glutamyl)-L-lysine [GGEL] cross link (isopeptidic bond) and the concomitant release of ammonia. Such cross-linked proteins are often highly insoluble. The TGases are closely related enzymes and can also catalyze other important reactions for cell life. Recently, several findings concerning the relationships between the biochemical activities of the TGases and the basic molecular mechanisms responsible for some human diseases, have been reported. For example, some neurodegenerative diseases, such as Alzheimer's disease (AD), Huntington's disease (HD), Parkinson’s disease (PD), supranuclear palsy, etc., are characterized in part by aberrant cerebral TGase activity and by increased cross-linked proteins in affected brains. Our article describes the biochemistry and the physio-pathological roles of the TGase enzymes, with particular reference to human pathologies in which the molecular mechanism of disease can be due to biochemical activities of the tissue TGase enzyme (tTGase, type 2), such as in a very common human disease, Celiac Disease (CD), and also in certain neuropsychiatric disorders.

Alzheimer disease (AD) and Creutzfeldt-Jakob disease (CJD) are sporadic and genetic neurodegenerative conditions characterized by brain accumulation and deposition of protein aggregates. In AD, the key pathogenic event is linked to the formation of a 4-kDa amyloid β (Aβ) peptide, generated by sequential cleavages of the amyloid precursor protein (APP). In CJD and other prion diseases, the process is initiated by conformational changes of the cellular prion protein, or PrPC, into a β-sheet rich isoform, named PrPsc, which acquires protease-resistance and detergent insolubility. Once generated, Aβ and PrPsc are highly prone to misassembly under thermodynamically favourable oligomeric forms and protofibril/fibril structures. The variety of physicochemical states exhibited by Aβ and PrPsc is accounted for by distinct molecular forms with different amino and/or carboxyl termini and alternative conformations. Unlike Aβ, PrPsc is also infectious, and this feature poses public health concerns, as in the case of iatrogenic and variant CJD (vCJD). Several lines of evidence suggest that Aβ and PrPsc are the main factors responsible for death of selected neuronal populations in brains of AD and prion disease's victims. Therefore, in addition to symptomatic treatment of dementia, therapeutic efforts are currently aimed at testing the efficacy of disease-modifying, anti-amyloid therapies. Experimental and clinical therapeutic interventions include passive and active immunization against amyloidogenic peptides, non immunological strategies, as well as drugs enhancing the nonamyloidogenic protein processing. In this review, we focus on molecular mechanisms of AD and prion diseases, and on novel treatment approaches.

CASK, which belongs to the family of membrane-associated guanylate kinase (MAGUK) proteins, is recognized as a multidomain scaffolding protein highly expressed in the mammalian nervous system. MAGUK proteins generally target to neuronal synapses and regulate trafficking, targeting, and signaling of ion channels. However, CASK is a unique MAGUK protein in several respects. It not only plays a role in synaptic protein targeting but also contributes to neural development and regulation of gene expression. Several CASK-interacting proteins have been identified from yeast two-hybrid screening and biochemical isolation. These proteins, whose interactions with CASK are reviewed here, include the Parkinson's disease molecule parkin, the adhesion molecule neurexin, syndecans, calcium channel proteins, the cytoplasmic adaptor protein Mint1, Veli/mLIN-7/MALS, SAP97, caskin and CIP98, transcription factor Tbr-1, and nucleosome assembly protein CINAP. More important, CASK may form different complexes with different binding partners and perform different functions. Among these interactions, CASK, Tbr-1, and CINAP can form a transcriptional complex regulating gene expression. Reelin and NMDAR subunit 2b (NR2b) genes have been identified as Tbr-1 target genes. Reelin is critical for neural development. NR2b is an important subunit of NMDAR, which plays important roles in neural function and neurological diseases. Regulation of reelin and NR2b expression suggests the potential roles of the Tbr-1-CASK-CINAP complex in neural activity, development, and disease. The functions of these CASK protein complexes are also discussed in detail in this review.

Crystallographic structures of wild-type and mutant NOS isoforms complexed with substrate, intermediate, inhibitor, cofactor, and cofactor analogs are currently available. However, because of the high level of amino-acid conservation and the consequent similarity in dimeric quaternary structure as well as in the active site of NOS isoforms, structure-based isoform-selective inhibitor design is still a very challenging task. Nevertheless, the comprehension of the structural determinants for selectivity among the isoforms is fundamental for the design of further potent and more selective inhibitors. Computational techniques, based on the knowledge of the tridimensional structure of the isozymes, have been already applied to understand the significant isoform selectivity shown by some compounds. Collectively these structure-based approaches, in combination with SAR studies, have been able to explain the structural reasons of this selectivity.

The majority of the anti-inflammatory drugs routinely used nowadays are COX (cyclo-oxygenase) inhibitors. The important role of this enzyme, once known as prostanglandin synthase, in inflammation came a consequence of the discovery by the Nobel prize winner John Vane with his path-breaking discovery that aspirin and similar drugs exert their action by blocking the biosynthesis of the prostaglandin group of lipid mediators. (John R. Vane, Nobel Lecture, December 8, 1982 and references cited therein) In the last five years it has become clear that there are two such enzymes involved. One of the "cyclo-oxygenases", called COX1 is responsible for making prostaglandins, which among other things, protect the stomach and kidney from damage. It is now clear that inhibition of COX1 accounts for the unwanted side effects of aspirin-like drugs such as gastric irritation and renal damage. The other enzyme, COX2, is induced by inflammatory stimuli and it is prostaglandins made by this enzyme that contribute to the inflammation in diseases such as rheumatoid arthritis. However, concerning inflammation-related targets, one should not limit the interest to COX and PLA2 enzymes. In recent years, it has steadily become more clear, that modulation in the expression of genes underlies most cellular responses, and inflammation is certainly not an exception in this sense. It does not come as surprise that molecules showing ability to interfere with factors involved in the modulation of genes expression, such as NF-kB, have also to be considered potential anti-inflammatory agents. Also in this respect, marine natural products (MNP) have brought a collection of novel molecular entities displaying ability to target COX1/COX2, NF-kB or acting through molecular mechanisms yet-to-be-discovered. Following, the marine natural products accounted for within this review will be grouped on the basis of their bio-molecular targets. Chemical synthesis of particular relevant molecules will be also discussed, especially in those cases where the natural products can be considered as lead compounds for the development of simplified derivatives or analogues of potential pharmaceutical interest.