The development and use of vascular targeted therapy in ovarian cancer

Combination vascular-targeted therapies (VTTs) represent a promising approach for patients with platinum-resistant recurrent ovarian cancer (OC). VTTs include two mechanistically distinct classes of agents: anti-angiogenic agents (AAs) and vascular-disrupting agents (VDAs). AAs suppress growth of new tumor vasculature through inhibition of vascular endothelial growth factor (VEGF) and other pro-angiogenic molecules. Bevacizumab, a monoclonal antibody that binds to VEGF, has improved progression-free survival (PFS) when given with chemotherapy in patients with advanced OC. VDAs target the established tumor vascular network, inducing vessel occlusion, shutdown of circulation, and widespread necrosis within the tumor interior - a region often resistant to conventional chemotherapy and radiation. Tubulin-binding VDAs such as BNC105P, ombrabulin, and combretastatin A4-phosphate (CA4P) have been studied for the treatment of OC. These agents act by binding tubulin in the endothelial cells of tumor vessels, triggering cytoskeletal disruption, altering cellular shape, and destabilizing cell-cell junctions, which lead to increased vascular leakage and, ultimately, to disruption of blood flow. Fundamental differences between the vascular networks of tumors and those of normal tissues allow these agents to selectively reduce tumor circulation while having little effect on non-malignant tissues. Animal studies and clinical trials show enhanced efficacy when VDAs are combined with chemotherapy as well as AAs. The latter combination allows targeting of different aspects of the tumor vasculature, a strong rationale for combining these two drug classes into a single regimen. CA4P is the only VDA in active development for OC. In a phase II trial of patients with recurrent OC, CA4P added to bevacizumab improved PFS compared with bevacizumab alone. The phase II, placebo-controlled PAZOFOS trial (NCT02055690) is evaluating the effects of CA4P plus the anti-angiogenic agent pazopanib in recurrent OC. FOCUS, a phase II/III, placebo-controlled trial (NCT02641639), is currently evaluating CA4P plus bevacizumab and chemotherapy in platinum-resistant OC.