Targeting PI3K and mTORC2 in metastatic renal cell carcinoma: New strategies for overcoming resistance to VEGFR and mTORC1 inhibitors

With the advent of molecularly targeted agents, treatment of metastatic renal cell carcinoma (mRCC) has improved significantly. Agents targeting the vascular endothelial growth factor receptor (VEGFR) and the mammalian target of rapamycin complex 1 (mTORC1) are more effective and less toxic than previous standards of care involving cytotoxic and cytokine therapies. Unfortunately, many patients relapse following treatment with VEGFR and mTORC1 inhibitors as a result of acquired resistance mechanisms, which are thought to lead to the reestablishment of tumor vasculature. Specifically, the loss of negative feedback loops caused by inhibition of mTORC1 leads to upregulation of downstream effectors of the phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway and subsequent activation of hypoxia-inducible factor, an activator of angiogenesis. De novo resistance involving activated PI3K signaling has also been observed. These observations have led to the development of novel agents targeting PI3K, mTORC1/2 and PI3K/mTORC1/2, which have demonstrated antitumor activity in preclinical models of RCC. Several agents--BKM120, BEZ235 and GDC-0980--are being investigated in clinical trials in patients with metastatic/advanced RCC, and similar agents are being tested in patients with solid tumors. The future success of mRCC treatment will likely involve a combination of agents targeting the multiple pathways involved in angiogenesis, including VEGFR, PI3K and mTORC1/2.