BH3 Profiling to define therapy resistance classes in neuroblastoma
The failure of cancer treatments to kill tumor cells, called therapy resistance, is responsible for most childhood cancer deaths. The precise mechanisms for this resistance are obscure, but most are thought to disrupt death signals that should be “turned on” when sufficient cell stress is encountered. A family of Bcl2-homology (BH) proteins are responsible for responding to chemotherapy- or radiation-induced stress to activate such a death signal. Accordingly, cancer cells typically alter their BH proteins to block these death signals, leading to resistance. Our initial work, funded through this Innovator Award, used a novel functional test to assess BH changes in neuroblastoma. We identified several neuroblastoma subtypes, differing only in their BH signaling, that can help triage Bcl2-antagonists (possible new cancer drugs) to the patients most likely to respond. Our results with highly lethal mouse xenograft models and the Bcl2-antagonist ABT-737 are remarkable. Most importantly, however, using rare sets of neuroblastoma cell lines from the same patients before and after relapse, we discovered a new paradigm for treatment resistance. Our results show that alterations in tumor cell mitochondria (an organelle responsible for energy and death signaling) is the root cause of therapy resistance. Our assays, using only cancer cell mitochondria, convincingly demonstrate that relapsed cells are less responsive to death signals at the very point at which apoptosis (cell death signals) should be activated. This renewal application is a natural extension to directly study the changes in mitochondrial functioning that lead to therapy resistance in the post-treatment relapse setting.