BCL-2 is a key pro-survival protein that is highly expressed in many leukemias and lymphomas. ABT-199 (venetoclax) is a small molecule inhibitor of BCL-2 that has demonstrated impressive responses in chronic lymphocytic leukemia (CLL) leading to FDA approval for second line treatment of patients with 17p deletion. However, other hematologic malignancies are less responsive to ABT-199 as a single agent, suggesting that combinations of targeted therapies may be required to elicit more promising responses. We have investigated the potential of combining ABT-199 with HMG-CoA reductase (HMGCR) inhibitors (statins), which have known anti-cancer potential in hematologic malignancies. Using multiple chemically distinct statin compounds, we observed profound synergistic induction of apoptosis when combined with ABT-199 in both human diffuse large B cell lymphoma (DLBCL) as well as acute myeloid leukemia (AML) cell lines. This synergy was also seen in primary murine B lymphoma cells over-expressing MYC and BCL-2. Importantly, addition of exogenous mevalonate completely rescued cells from the combination, confirming on-target efficacy of HMGCR inhibition. Using BH3 profiling, we found that simvastatin significantly primed lymphoma cells for undergoing apoptosis (termed mitochondrial priming). Notably, the degree of priming correlated with its ability to synergize with ABT-199, suggesting that BH3 profiling may be used to predict patient responses. The combination did not synergize to kill normal human peripheral blood mononuclear cells from healthy donors, suggesting that statins may selectively prime cancer cells for apoptosis. Mechanistic studies support the hypothesis that statins synergize with ABT-199 by suppressing protein prenylation, particularly protein geranylgeranylation. In support, the addition of exogenous geranylgeranyl pyrophosphate (GGPP) completely rescued cells from the effects of simvastatin. Furthermore, selective inhibition of protein geranylgeranyl transferase (GGT) increased priming and was sufficient to recapitulate the effects of simvastatin in combination with ABT-199. Statins and GGT inhibitors increased the mitochondrial abundance of a subset of BH3-only pro-apoptotic proteins. Lastly, we have identified Rap1A de-prenylation as a marker of pharmacodynamic response to statins in vivo. Thus, this project highlights a novel combination for use in aggressive lymphomas, establishes its efficacy and tolerability using preclinical models, and provides proof-of-concept to warrant investigation of its clinical potential.
Letai:AbbVie: Consultancy, Research Funding; Astra-Zeneca: Consultancy, Research Funding; Tetralogic: Consultancy, Research Funding.
Asterisk with author names denotes non-ASH members.