It will be important to determine whether sunitinibinduced apoptosis is mediated by PUMA or other BH3-only proteins in other solid tumors such as renal cancer and GISTs, and their potential role in the apoptotic responses to other VEGFR and PDGFR inhibitors. Reduced sensitivity to sunitinib was suggested to be linked to mutations in KIT or VEGFR/FDGFR or in other RTKs, as well as decreased expression of soluble VEGF receptors, which can suppress cell death or promote survival. In addition, inhibition of tumor angiogenesis or other components in the microenvironment might indirectly activate cell death pathways. The use of isogenic cell lines as we did here could be particularly useful in understanding drug targets and mechanisms. Despite the excitement in the development of agents targeting oncogenic kinases, clinical data demonstrate that most of these agents are generally efficacious only in a minor fraction of patients. One major change is to identify biomarkers to help patient selection and stratification. Our data showed that PUMA persists 24�C48 hours after sunitinib treatment. In contrast, inhibition of AKT/A 943931 dihydrochloride FoxO3a is more transient and recovers in hours, likely reflecting secondary and survival attempts in tumor cells following activation of apoptotic signaling. These findings potentially explain why upstream signaling molecules are less suitable as biomarkers, and suggest modulation of the mitochondrial death pathway might be a more useful readout for the overall therapeutic activity of anticancer agents. It may be particularly relevant to explore the regulation of Bcl-2 family members as they are rarely found mutated in solid tumors, and can be functionally achieved by ����BH3 profiling���� as demonstrated recently in leukemia patients following chemotherapy. Current biomarkers of sunitinib include plasma levels of VEGF, sVEGFR2, sVEGFR3, and sKIT. Interrogation of changes in PUMA and other Bcl- 2 family members using biopsies collected before and after treatment would certainly be possible as well as informative. Therefore, a combination of markers monitoring tumor microenvironment, angiogenesis, cell survival and death might ultimately prove more useful. Current treatment modalities provide limited benefits to patients with advanced colorectal cancer, and targeted agents might bring new hopes. A better understanding of their mechanisms of action and identification of biomarkers are expected to help guide their further development, clinical testing and use. Our work suggests that PUMA induction predicts the apoptotic responses to sunitinib in colon cancer cells, and 16,16-Dimethyl Prostaglandin E2 provides potential strategies for combination therapies. In preclinical models, small molecule BH3 mimetics synergize with a wide variety of anticancer agents, and generally have none-overlapping side effects with chemo-drugs or kinase inhibitors.