Current Cancer Drug Targets - Volume 3, Issue 6, 2003

Solid tumors with areas of hypoxia are the most aggressive and difficult tumors to treat and are a major reason for treatment failure. Previous attempts to treat hypoxic tumors have been largely unsuccessful and new agents are needed. The cellular response to hypoxia is controlled by the hypoxia inducible factor-1 (HIF-1) transcription factor. HIF-1 consists of an oxygen regulated alpha subunit and a constitutively expressed beta subunit, which bind and translocate to the nucleus to activate transcription of a range of genes involved in increasing glycolysis, inhibition of apoptosis and promotion of angiogenesis and metastasis. The activity of the HIF-1 complex is primarily controlled by levels of the alpha subunit and a series of mechanisms exist to control activation of the HIF-1 pathway. HIF-1α is over-expressed in a large number of human tumors and its over-expression correlates with poor prognosis and treatment failure. HIF-1 is therefore an important target for cancer chemotherapy. This review summarizes the literature surrounding the control of HIF-1, its role in cancer and potential drugs to target the pathway for cancer therapy.

Colorectal cancer is the second most common cause of cancer-related mortality in the west. The high incidence and mortality make effective prevention an important public-health and economic issue. The regular intake of aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) has been associated with decreased incidence of certain types of cancer particularly those with an inflammatory component, and then are among the few agents known to be chemopreventive. Nitric oxide-releasing non-steroidal anti-inflammatory drugs (NO-NSAIDs) are new chemical entities obtained by adding a nitric oxide-releasing moiety to classical molecules. This new class of molecules has been demonstrated to be much more safe than NSAIDs due to their ability to reduce gastric toxicity. They could therefore represent an alternative to classical NSAIDs treatment. In this review, we sumarise the recent findings in the mechanisms and pathways involved in the antitumoral effects of both NSAIDs and NO-NSAIDs as well as the clinical trials performed with these compounds.

Angiogenesis is crucial for tumor development and progression, and antiangiogenetic therapy represents a promising approach for cancer treatment. Thus, the in-depth understanding of the molecular mechanism(s) regulating angiogenesis, together with the characterization of molecules expressed by endothelial cells and involved in distinct steps of the angiogenetic process, will greatly improve the design of new and more effective therapeutic strategies in human malignancies. Endoglin (CD105), a cell membrane glycoprotein predominantly expressed on cellular lineages within the vascular system, and over-expressed on proliferating endothelial cells, is involved in blood vessels development and represents a powerful marker of neovascularization. CD105 binds several factors of the Transforming Growth Factor (TGF)-β superfamily, a pleiotropic cytokine that regulates different cellular functions including proliferation, differentiation and migration. In human malignancies of different histotype, CD105 is highly expressed on endothelial cells of both peri- and intratumoral blood vessels, while it is weakly expressed or absent on neoplastic cells. This unique tissue distribution strongly suggests for a prognostic, diagnostic and therapeutic potential of CD105 in neoplastic diseases. In this review we will summarize the structural and functional features of CD105, as well as its tissue distribution in normal and neoplastic tissues. Furthermore, the practical implications of CD105 in human malignancies will also be discussed.

Mucin-type O-glycans are upregulated and aberrantly glycosylated in many carcinomas. O-glycan Core 1 (Galβ1-3GalNAcα-O-), also called Thomsen-Friedenreich disaccharide, is a cryptic structure overexpressed in cancer cells through modification of its glycosyltransferase profile. This molecule is a useful model for study of carbohydrate immunogenicity as well as a candidate for active specific immunotherapy of cancer patients. Several strategies are discussed for enhancing immune response to a particular region of carbohydrate: carbohydrate-protein conjugation, linkers, synthetic clustered sugars, chemical modifications, peptide / protein mimetics, and molecular rotation.

Tumor cells respond to growth signals by the activation of protein kinases, altered gene expression and significant modifications in substrate flow and re-distribution among biosynthetic pathways. This results in a proliferating phenotype with altered cellular function. These transformed cells exhibit unique anabolic characteristics, which includes increased and preferential utilization of glucose through the non-oxidative steps of the pentose cycle for nucleic acid synthesis but limited de novo fatty acid synthesis and TCA cycle glucose oxidation. This primarily non-oxidative anabolic profile reflects an undifferentiated highly proliferative aneuploid cell phenotype and serves as a reliable metabolic biomarker to determine cell proliferation rate and the level of cell transformation / differentiation in response to drug treatment. Novel drugs effective in particular cancers exert their anti-proliferative effects by inducing significant reversions of a few specific non-oxidative anabolic pathways. Here we present evidence that cell transformation of various mechanisms is sustained by a unique disproportional substrate distribution between the two branches of the pentose cycle for nucleic acid synthesis, glycolysis and the TCA cycle for fatty acid synthesis and glucose oxidation. This can be demonstrated by the broad labeling and unique specificity of [1,2-13C2]glucose to trace a large number of metabolites in the metabolome. Stable isotope-based dynamic metabolic profiles (SIDMAP) serve the drug discovery process by providing a powerful new tool that integrates the metabolome into a functional genomics approach to developing new drugs. It can be used in screening kinases and their metabolic targets, which can therefore be more efficiently characterized, speeding up and improving drug testing, approval and labeling processes by saving trial and error type study costs in drug testing.

Colorectal cancer is a leading cause of cancer death throughout the world. The high prevalence and mortality associated with colon cancer make effective prevention and treatment an important public health and economic concern. Among the few agents known to inhibit colorectal tumorigenesis are the nonsteroidal antiinflammatory drugs or NSAIDs, as well as newer agents such as celecoxib and rofecoxib. Both epidemiologic studies and investigations with animals show that these compounds possess marked anti-colorectal cancer properties. NSAIDS are widely known to be inhibitors of the cyclooxygenase (COX) enzymes, and it is thought that the chemopreventive effects of NSAIDs are at least in part due to this ability to inhibit COX. More recent studies, however, have suggested that NSAIDs may also exert anti-cancer effects through mechanisms independent of COX inhibition. COX-dependent and COX-independent mechanisms are not mutually exclusive and it is likely that both are involved in the biological activity of NSAIDs.