BCL-2 Inhibitors, Present and Future

The members of the B-cell leukemia/lymphoma-2 (BCL-2) family of proteins are key regulators of the intrinsic apoptotic pathway; dysregulation of this pathway leads to pathologic survival of cancer cells. B-cell leukemia/lymphoma-2 had long been viewed as a promising target for the treatment of several hematologic malignancies, specifically chronic lymphocytic leukemia (CLL), yet for many years the development of a drug to successfully target this protein remained elusive. The approval of the BCL-2 inhibitor venetoclax for relapsed/refractory del(17p) CLL in 2016 represented the culmination of decades of molecular and clinical research and has paved the way for new combination therapy regimens in CLL, including the venetoclax + rituximab regimen approved for relapsed/refractory CLL in 2018 and the venetoclax + obinutuzumab regimen approved for frontline CLL treatment in 2019. Here, we provide an overview of the mechanism of action of BCL-2 inhibition, the role of this approach in the current treatment paradigm of CLL, and an in-depth focus on the clinical trials in CLL involving venetoclax. Additionally, we review key areas of active research including the integration of minimal residual disease as a marker of clinical efficacy in current clinical trials as well as the emergence of venetoclax resistance mechanisms and potential strategies to overcome this resistance. Given the success of venetoclax in the clinical setting thus far, it is likely that BCL-2 inhibition will take on an increasingly important role in the treatment of CLL going forward.