The EZH2 inhibitor tazemetostat (EPZ-6438) is currently being evaluated in phase 2 clinical trials for the treatment of non-Hodgkin’s Lymphoma (NHL). EZH2 inhibitors have shown anti-proliferative effects in multiple preclinical models of NHL and objective clinical responses have been reported in patients with B-cell lymphomas in phase 1 and phase 2 studies of tazemetostat. Mounting evidence suggests that EZH2 is an important regulator of B cell differentiation, both in normal B-cells and in B-cell lymphoma, and may be an important mediator of cell fate in B-cell malignancies in the clinic. Consistent with its essential role in regulating B cell differentiation, recent studies have also shown a dependence on EZH2 activity in multiple myeloma (MM), a disease arising from terminally-differentiated B-cell lymphocyte plasmablasts. Frequent genetic alterations of epigenetic modulators are observed in MM, pointing towards an important role in the initiation and maintenance of this disease. Dysregulation of the H3K27 methyltransferase EZH2, its corresponding histone demethylase UTX and the H3K36 methyltransferase WHSC1 in MM suggest that disruption of the balance of histone methylation may be fundamental to MM pathogenesis in a subset of cases. Indeed, inhibition of EZH2 alone has shown potent anti-proliferative effects both in in vitro and in vivo preclinical models of MM. Here, we describe the effects of small molecule EZH2 inhibitors as monotherapy and in combination with standard of care agents in preclinical models of MM. Tazemetostat selectively inhibits intracellular H3K27 methylation in MM cell lines and elicits a robust anti-proliferative effect in 14-day assays. Following demonstration of single agent activity, we then investigated potential for combinatorial activity of tazemetostat with first and second line therapies for multiple myeloma as well as other non-approved but emerging therapies. Synergistic anti-proliferative activity was observed when tazemetostat was combined with glucocorticoid receptor agonists (dexamethasone, prednisolone), small molecule immune system modulators (lenalidomide, pomalidomide) and proteasome inhibitors (bortezomib, ixazomib) when cells were primed with tazemetostat for seven days prior to the addition of the standard of care drugs. Combination activity was also observed with an alternate treatment schedule where cells were co-treated with tazemetostat along with the combination partner for seven days. Studies with selected therapeutic modalities were expanded into in vivo xenograft models to further evaluate monotherapy and combination activity of EZH2 inhibitors in MM.

Citation Format: Allison E. Drew, Vinny Motwani, John E. Campbell, Cuyue Tang, Jesse J. Smith, Richard Chesworth, Robert A. Copeland, Alejandra Raimondi, Scott Ribich. Activity of the EZH2 inhibitor tazemetostat as a monotherapy and in combination with multiple myeloma therapies in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5060. doi:10.1158/1538-7445.AM2017-5060