Current Pharmaceutical Design - Volume 13, Issue 27, 2007

Drug design based on the structure of specific enzymes playing a role in carcinogenesis, e.g. tyrosine kinases, has been successful at identifying novel effective anticancer drugs. In contrast, no success has been achieved in drug design attempts, in which transcription factors or DNA-transcription factor complexes involved in the pathogenesis of human neoplasms were targeted. This failure is likely to be due to the fact that the mechanism of transcription regulation is probably too complex and still too inadequately understood to be a suitable target for drug design. It seems plausible that the high selectivity of some human tumors to some DNA-interactive anticancer drugs, e.g. cisplatin, is related to an effect on the transcription of genes that are crucial for those tumors. In this article we propose that some natural products have evolutionarily evolved to exert highly specialized functions, including modulation of the transcriptional regulation of specific genes. We discuss in detail the marine natural product Yondelis (Trabectedin, ET-743) that is effective against some soft tissue sarcoma, possibly because it interferes with the aberrant transcription mechanism in these tumors. In addition we highlight the existing evidence that many different natural products are effective inhibitors of NF-kB, a transcription factor that plays a crucial role in inflammation and cancer, indicating that some of these compounds might possess antitumor properties. We propose that large-scale characterization of natural products acting as potential modulators of gene transcription is a realistic and attractive approach to discover compounds therapeutically effective against neoplastic diseases characterized by specific aberrations of transcriptional regulation.

Protein kinases are involved in many diseases like cancer, inflammation, cardiovascular disease, and diabetes. They have become attractive target classes for drug development, making kinase inhibitors as important class of therapeutics. The success of smallmolecule ATP-competitive kinase inhibitors such as Gleevec, Iressa, and Tarceva has attracted much attention in the recent past. Kinases make use of ATP for phosphorylation of a specific residue(s) on their protein substrates. More than 400 X-ray structures of about 70 different kinases are publicly available. These structures provide insights into selectivity and mechanisms of inhibition. However, prediction of binding specificity of kinase inhibitors based on structural information alone appears to be insufficient. Here, we will review these observations to gain insights into the rules that govern protein kinase inhibitor selectivity.

DNA Topoisomerase II (Top2) is an essential nuclear enzyme that regulates the topological state of the DNA, and a target of very effective anticancer drugs including anthracycline antibiotics. Even though several aspects of drug activity against Top2 are understood, the drug receptor site is not yet known. Several Top2 mutants have altered drug sensitivity and have provided information of structural features determining drug action. Here, we have revised the published crystal structures of eukaryotic and prokaryotic Top2s and relevant biochemical investigations of enzyme activity and anthracycline action. In particular, we have considered Top2 mutations conferring resistance to anthracyclines and related agents. Following a previous study (Moro et al, Biochemistry, 2004; 43: 7503-13), we have then re-built a molecular model of the entire enzyme in complex with DNA after the cleavage reaction, and used it to define the receptor site of anthracyclines. The results suggest a model wherein the drug specifically contacts the cleaved DNA as well as amino acid residues of the enzyme CAP-like domain. The findings can explain several established structure-activity relationships of antitumour anthracyclines, and provide a framework for further developments of effective Top2 poison.

The origin of activity differences between stereoisomers of anticancer platinum(II) complexes chelated with chiral diamine ligands has been almost exclusively explained by diastereoselective interactions with DNA. Although this model has been widely accepted in vitro and in vivo experiments showed some conflicting results, leading to the conclusion that other biomolecules might be responsible for this stereoselectivity as well. These compounds, called bionucleophiles, are in most instances amino acids or proteins present in biological fluids. As these chiral molecules are very reactive towards the platinum complexes, they may contribute to stereoselectivity, but also to resistance and toxicity. This review gives a general survey of chiral platinum(II) complexes and their interactions with DNA. The bionucleophiles which have been identified and the consequences of their reaction with platinum(II) complexes are discussed. Analytical techniques used to investigate interactions between established and potential chiral platinum drugs and bionucleophiles are presented.

The critical role of angiogenesis in tumor development and progression has long been appreciated. The elucidation of the mechanisms of tumor angiogenesis and the emergence of anticancer drugs targeting the tumor vasculature has been a breakthrough in the treatment of several tumors in the last few years. Several novel molecules are being developed that target different aspects of angiogenesis. This review outlines the principle of anti-angiogenic therapies, illustrates the main mechanisms and complexity of growth signals involved in tumor angiogenesis, its interactions with hypoxia, stroma and tumor microenvironment. It provides a comprehensive review of clinical results obtained with anti-angiogenic agents (VEGF/VEGFR signaling inhibitors, direct angiogenesis inhibitors, vascular disrupting agents) and finally discusses the differences of the several approaches and their limitations due to the emergence of resistance.

Conventional therapy for non-small cell lung cancer (NSCLC) has reached a plateau in increasing patient survival and overall prognosis still remains dismal. Advances in the knowledge of molecular events governing oncogenesis has led to a number of novel agents targeting specific pathways critical for tumour growth and survival. In the present paper we have thoroughly reviewed the existing evidence of novel agents currently studied in clinical trials, focusing on epidermal growth factor receptor family inhibitors, angiogenesis inhibitors, cyclooxygenase-2 inhibitors, Bcl-2 targeted agents, protein kinase C inhibitors, proteasome inhibitors, farnesyl transferase inhibitors and retinoids. Although erlotinib monotherapy in the second or third line setting and bevacizumab combined with conventional chemotherapy as a frontline therapy manage to prolong the life of patients with NSCLC, there is still much to be learned about the proper design of clinical trials and the selection of patient population enrolled in them. Multi-targeted therapy still remains the most attractive avenue for future treatment strategies.

Non-enzymatic modification of proteins by reducing sugars, a process that is also known as Maillard reaction, leads to the formation of advanced glycation end products (AGEs) in vivo. It is now well established that formation and accumulation of AGEs progress during normal aging, and at an extremely accelerated rate under diabetes, thus being implicated in various types of AGE-related disorders such as diabetic vascular complications, neurodegenerative diseases and cancers. Further, there is accumulating evidence that AGEs and their receptor RAGE interaction elicits oxidative stress generation and subsequently alters gene expression in various types of cells. In addition, digested food-derived AGEs are found to play an important role in the pathogenesis of the AGE-related disorders as well. Indeed, restriction of diet-derived AGEs not only blocks the progression of atherosclerosis and renal injury, but also improves insulin resistance in animal models. AGE-poor diets reduce serum levels of inflammatory biomarkers in patients with diabetes or chronic renal failure. These observations suggest that the restriction of food-derived AGEs or the inhibition of absorption of dietary AGEs may be a novel target for therapeutic intervention in the AGE-related disorders. In this paper, we review the pathological role of food-derived AGEs in various types of disorders and discuss the potential utility of oral adsorbent that inhibits the absorption of AGEs in these devastating diseases.

The quest towards achieving a better understanding of underlying mechanisms by which genetic factors contribute to human disease has gathered considerable momentum, most notably due to the drafting of the complete human genome sequence. This has in turn accelerated research into identifying genes responsible for a plethora of genetic, infectious and metabolic diseases with the vision that therapies can then be developed. Although achieving a therapeutic intervention by gene delivery is perfectly feasible, the practical approach to achieving such a goal, at least in vivo, has proved far more challenging. Employing viruses as gene vectors has to-date proven to be the most effective method of delivery however concerns have emerged about both the short and long-term risks they pose. These fears being confirmed by incidents which led to the tragic deaths of subjects believed to have been triggered by adeno- & retroviral vectors used in clinical trials. This prompted many in the field to turn their research focus towards developing non-viral vectors deemed not only to be safer (non-immunogenic) than their viral counterparts but with a greater gene loading capacity. Polycationic dendrimers (PCDs) as vectors for this purpose have attracted significant interest due to their ease of synthesis, versatility and tolerability. This review will explore the physicochemical parameters crucial to PCD-mediated gene delivery and highlight some innovative strategies designed to maximise transfection efficacy and facilitate tissue-targeting of these elaborate macromolecules.