Reading mitochondrial apoptotic signaling to identify active cancer therapeutics

Summary I am an oncologist and cancer biologist supervising a laboratory focused on identifying therapies that selectively induce apoptosis in cancer cells. My initial contributions to the apoptosis field came with separating certain pro-death BCL-2 family BH3-only proteins into “sensitizers” and “activators” based on pro-apoptotic function. This finding drove my interest in the possibilities of inhibiting BCL-2 function with drugs that mimicked the BH3 domain of pro-apoptotic proteins. I designed the first mouse model that demonstrated that loss of BCL-2 function by itself could be sufficient to drive a cancer into remission. Following this, I designed a tool called BH3 profiling – exposing mitochondria to synthetic oligo-peptides based on the amphipathic alpha- helical BH3 domains of proapoptotic proteins and measuring mitochondrial outer membrane permeabilization (MOMP). By using certain selectively-interacting BH3 peptides, I could use BH3 profiling to identify cells that were especially sensitive to BH3 inhibition. I used BH3 profiling to help launch clinical trial programs of the BCL-2 inhibitor venetoclax in several diseases. Most successful among these so far have been programs in chronic lymphocytic leukemia and acute myelogenous leukemia, the former of which has already yielded FDA approvals. Using different BH3 peptides, BH3 profiling can measure overall apoptotic priming, or proximity to the threshold of apoptosis. We used this aspect to demonstrate that differential apoptotic priming is perhaps the most significant determinant of successful chemotherapy treatment. Moreover, differential apoptotic priming is the main reason that there is a therapeutic index for conventional chemotherapy – most non-malignant somatic cells are far less primed for apoptosis than chemosensitive cancer cells. Building on this finding, we asked whether we could identify drugs that could enhance apoptotic priming selectively in cancer cells. We found that we could measure increased apoptotic priming within hours of exposing cancer cells to effective drugs using dynamic BH3 profiling (DBP). Increased priming is measured as increased sensitivity of mitochondria in treated cells to BH3 peptides compared to untreated controls. Over the past few years, we have found that an increased priming by a drug in DBP is an excellent predictor of in vivo activity in human and mouse models, in solid and liquid tumors. An important advantage of DBP over most other ex vivo drug sensitivity strategies is that DBP requires no more than 24 hours of ex vivo culture. This overcomes the major obstacle to the general application of such strategies, since many cancers cannot adapt to long-term ex vivo culture, and if they do, they are phenotypically altered so as to degrade the information they can provide. We are exploring DBP as a discovery tool and predictive biomarker in many liquid and solid tumors. Moreover, we are using it as a tool to identify drugs that can make target tumor cells more sensitive to immuno-oncology therapies.