Abstract 2032: Combination of epigenetic regulation via LSD1 inhibition with signal transduction inhibitors significantly enhances anti-tumor activity in models of hematologic malignancies

Combinatorial therapeutic strategies have achieved improved response rates and durability of responses in several malignancies either by selectively targeting distinct and non-overlapping oncogenic signaling pathways (e.g. PARP and phosphoinositide 3-kinase (PI3K) inhibition in subsets of breast and ovarian cancers), or alternatively, inhibiting distinct nodal points of regulation in common oncogenic signaling pathways (e.g BRaf and MEK inhibition in subsets of melanoma). Recent data suggest that deregulated epigenetic modifications may be just as significant as genetic mutations in driving cancer development and growth by inhibition of tumor suppressor activity and activation of oncogenic pathways. We therefore hypothesized that an epigenetic regulator could potentiate the efficacy of a protein kinase inhibitor to result in robust tumor growth inhibition. We previously reported that the potent and selective LSD1 inhibitor INCB059872 potently inhibited tumor growth in multiple tumor xenograft models of AML and SCLC as a single agent and in a combination with standard of care of agents. In this study, we explored the anti-tumor effect of combining INCB059872 and various signal transduction pathway inhibitors, including the PIM kinase inhibitor INCB053914, the JAK1/2 inhibitor ruxolitinib, or the PI3K delta-selective inhibitor INCB050465 in models of human hematologic malignancies. Each of these therapeutic combinations significantly inhibited tumor growth in the Molm-16 human AML xenograft model. Mechanistic studies suggested that MYC expression levels were downregulated by these combinations both in vitro and in vivo. Treatment with INCB059872 alone or in combination with signal transduction kinase inhibitors significantly downregulated cytokines levels, particularly IL-10, sCD40L, and MCP-1 in Molm-16 tumors. These data suggest that the combination of an LSD1 inhibitor and signal transduction inhibitor can co-regulate key tumor intrinsic and extrinsic pathways involved in paracrine or autocrine signaling in AML. In addition to the improved efficacy observed in AML models, the combination of INCB059872 with the PI3Kdelta inhibitor INCB050465 enhanced tumor growth inhibition in the Will-2 xenograft model (GCB subtype, double hit lymphoma), whereas the activity of these single agents were modest in this particular subtype of lymphoma. Additional mechanistic studies are ongoing to further understand the molecular bases of these observations. Taken together, these data suggest that targeting distinct epigenetic and oncogenic signaling pathways may potentiate anti-tumor efficacy and overcome intrinsic resistance mechanisms in specific hematologic malignancies. Citation Format: Sang Hyun Lee, Matthew Stubbs, Ashish Juvekar, Melody Diamond, Antony Chadderton, Robert Collins, Xiaoming Wen, Holly Koblish, Chunhong He, Liangxing Wu, Richard Wynn, Andrew Combs, Chu-Biao Xue, Wenqing Yao, Gregory Hollis, Reid Huber, Peggy Scherle, Bruce Ruggeri. Combination of epigenetic regulation via LSD1 inhibition with signal transduction inhibitors significantly enhances anti-tumor activity in models of hematologic malignancies [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 2032. doi:10.1158/1538-7445.AM2017-2032