Abstract
Bcl-2 family proteins regulate mitochondrial apoptosis downstream of diverse stressors. Cancer cells frequently deregulate Bcl-2 proteins leading to chemoresistance. We have optimized a platform for solid tumors in which Bcl-2 family resistance patterns are inferred. Functional mitochondria were isolated from neuroblastoma (NB) cell lines, exposed to distinct BH3-domain peptides, and assayed for cytochrome c release. Such BH3 profiles revealed three patterns of cytochrome c response. A subset had a dominant NoxaBH3 response implying Mcl1 dependence. These cells were more sensitive to small molecules that antagonize Mcl1 (AT-101) than those that antagonize Bcl-2, Bcl-xL and Bcl-w (ABT-737). A second subset had a dominant BikBH3 response, implying a Bcl-xL/-w dependence, and was exquisitely sensitive to ABT-737 (IC(50) <200 nM). Finally, most NB cell lines derived at relapse were relatively resistant to pro-death BH3 peptides and Bcl-2 antagonists. Our findings define heterogeneity for apoptosis resistance in NB, help triage emerging Bcl-2 antagonists for clinical use, and provide a platform for studies to characterize post-therapy resistance mechanisms for NB and other solid tumors.