Targeting MET and vascular endothelial growth factor receptor signaling in castration-resistant prostate cancer.

Effective management of bone metastases in men with castration-resistant prostate cancer (CRPC) remains an important unmet medical need. MET and vascular endothelial growth factor receptor (VEGFR) are rational targets for intervention in CRPC. Clinical trials involving agents that inhibit one but not both pathways have reported modest activity and no improvement in overall survival. Cabozantinib is an oral multitargeted tyrosine kinase inhibitor that inhibits both MET and VEGFR-2. A phase II randomized discontinuation study involving subjects with CRPC demonstrated that cabozantinib therapy is associated with improvement in bone scans, bone turnover markers, and pain response, but with significant adverse events leading to dose reduction and treatment discontinuation. Lower doses of cabozantinib retain high levels of activity with less toxicity. Ongoing phase III clinical trials will define the role of cabozantinib in CRPC. We summarize the rationale for targeting MET and VEGFR pathways in CRPC and the clinical data available to date.