Targeted agents for the treatment of advanced renal cell carcinoma

Renal cell carcinoma (RCC) is a highly treatment-resistant tumor type; however, advances in elucidating the molecular pathophysiology underlying RCC has led to the identification of promising targets for therapeutic intervention. In clear-cell RCC, mutations to the von Hippel-Lindau (VHL) gene results in the up regulation of many proteins necessary for tumor growth and survival, - such as vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and platelet derived growth factor (PDGF), which are involved in tumor-initiated angiogenesis. Carbonic anhydrase IX and signaling via the epidermal growth factor receptor (EGFR) are involved in tumor cell proliferation and are also up regulated by mutation in the VHL gene. The intracellular messenger pathways phosphoinositide 3-kinase (PI3K) and Raf/MEK/ERK act as convergence points for positive growth signaling; the Raf/MEK/ERK pathway is also implicated in apoptosis. Several agents in development target VEGF (bevacizumab), the VEGF receptor (PTK787, SU 11248, VEGF-trap, and BAY 43-9006), the PDGF receptor (SUI 1248 and BAY 43-9006), or the EGF receptor (gefitinib, cetuximab, ABX-EGF, and erlotinib). The intracellular Raf/MEK/ERK signaling cascade has been targeted at either the level of Raf (BAY 43-9006, ISIS 5132) or MEK (CI-1040, PD184352 and ARRY-142886), and PI3K signaling is disrupted by CCI-779. WX-G250 targets the G250 antigen, and PS-341 disrupts the 26S proteasome mediating the degradation of intracellular proteins. Given that multiple pathways contribute to tumor growth, anti-tumor activity may be increased by agents targeting multiple pathways, or by combining agents to allow horizontal or vertical inhibition of multiple pathways.