Design and synthesis of combretastatin A-1 analogs, small molecule vascular disrupting agents, and bioreductive triggers as potential therapeutic agents for the treatment of cancer.
Access changed 3/18/13.
Cancer is the second leading cause of death in the United States with over 550,000 deaths in 2009 and a devastating 7.9 million deaths worldwide in 2007. Vascular disrupting agents (VDAs) represent a novel method developed for the treatment of cancer. VDAs, such as combretastatin A1 phosphate (CA1P, Oxi4503) and combretastatin A4 phosphate (CA4P, ZybrestatTM, fosbretabulin), after undergoing phosphate cleavage by non-specific phosphatase enzymes, selectively bind to the colchicine site on tubulin, disrupting tubulin polymerization. The integrity of the microtubules that form the cytoskeleton of the endothelial cells that line the tumor vasculature is altered, causing tumor vasculature occlusion and collapse, thus preventing nutrients and oxygen from reaching the tumor. This leads to severe tumor hypoxia, tumor perfusion regression and tumor necrosis. A series of anticancer agents were designed to incorporate a VDA or cytotoxic agent linked to a bioreductive drug to form a bioreductive prodrug conjugate. When the bioreductive portion of the molecular conjugate is reduced, the linkage between the VDA and the bioreductive drug is broken, releasing the VDA in its active form to act upon the tumor vasculature. The reduced bioreductive drug becomes a chemotherapeutic agent that can damage the tumor cells. CA1 is a potent inhibitor of tubulin polymerization and it has been shown that CA1 undergoes a second mechanism of action against tumors. CA1 incorporates an ortho diphenolic moiety that can be oxidized to form an ortho quinone that can damage DNA. To further elucidate the biological mechanism of action of CA1, a synthetic methodology was developed to incorporate a radioisotope at a metabolically stable position. In addition, a total synthesis was designed to prepare each of the combretastatin A1 monophosphates in regioisomeric pure form.