Marine Natural Products with Activities against Prostate Cancer: Recent Discoveries

Prostate cancer is the most common cancer in men, with over 52,000 new cases diagnosed every year. Diagnostics and early treatment are potentially hindered by variations in screening protocols, still largely reliant on serum levels of acid phosphatase and prostate-specific antigen, with tumour diagnosis and grading relying on histopathological examination. Current treatment interventions vary in terms of efficacy, cost and severity of side effects, and relapse can be aggressive and resistant to the current standard of care. For these reasons, the scientific community is looking for new chemotherapeutic agents. This review reports compounds and extracts derived from marine organisms as a potential source of new drugs against prostate cancer. Whilst there are several marine-derived compounds against other cancers, such as multiple myeloma, leukemia, breast and lung cancer, already available in the market, the presently collated findings show how the marine environment can be considered to hold potential as a new drug source for prostate cancer, as well. This review presents information on compounds presently in clinical trials, as well as new compounds/extracts that may enter trials in the future. We summarise information regarding mechanisms of action and active concentrations.

ScFvs as Allosteric Inhibitors of VEGFR-2: Novel Tools to Harness VEGF Signaling

Vascular Endothelial Growth Factor Receptor 2 (VEGFR-2) is the main mediator of angiogenic signaling in endothelial cells and a primary responder to VEGF. VEGF dependent VEGFR-2 activation regulates endothelial cell migration and proliferation, as well as vessel permeability. VEGF is presented as an antiparallel homodimer, and its binding to VEGFR-2 brings two receptors in close proximity. Downstream signaling is triggered by receptor dimerization, kinase activation, and receptor internalization. Our aim was to further investigate allosteric inhibition using binders targeting extracellular subdomains 4⁻7 of VEGFR-2 as an alternative to existing anti-angiogenic therapies, which rely on neutralizing VEGF or blocking of the ligand-binding site on the receptor. We applied phage display technology to produce single chain antibody fragments (scFvs) targeting VEGFR-2. Selected antibody fragments were characterized using biophysical and biological assays. We characterized several antibody fragments, which exert their inhibitory effect of VEGFR-2 independent of ligand binding. These reagents led to rapid clearance of VEGFR-2 from the cell surface without kinase activation, followed by an increase in intracellular receptor-positive vesicles, suggesting receptor internalization. Our highly specific VEGFR-2 binders thus represent novel tools for anti-angiogenic therapy and diagnostic applications.

Inhibition of arachidonic acid metabolism and its implication on cell proliferation and tumour-angiogenesis

Arachidonic acid (AA) and its metabolites have recently generated a heightened interest due to growing evidence of their significant role in cancer biology. Thus, inhibitors of the AA cascade, first and foremost COX inhibitors, which have originally been of interest in the treatment of inflammatory conditions and certain types of cardiovascular disease, are now attracting attention as an arsenal against cancer. An increasing number of investigations support their role in cancer chemoprevention, although the precise molecular mechanisms that link levels of AA, and its metabolites, with cancer progression have still to be elucidated. This article provides an overview of the AA cascade and focuses on the roles of its inhibitors and their implication in cancer treatment. In particular, emphasis is placed on the inhibition of cell proliferation and neo-angiogenesis through inhibition of the enzymes COX-2, 5-LOX and CYP450. Downstream effects of inhibition of AA metabolites are analysed and the molecular mechanisms of action of a selected number of inhibitors of catalytic pathways reviewed. Lastly, the benefits of dietary omega-3 fatty acids and their mechanisms of action leading to reduced cancer risk and impeded cancer cell growth are mentioned. Finally, a proposal is put forward, suggesting a novel and integrated approach in viewing the molecular mechanisms and complex interactions responsible for the involvement of AA metabolites in carcinogenesis and the protective effects of omega-3 fatty acids in inflammation and tumour prevention.