Abstract 4696: The LSD1 inhibitor INCB059872 is synergistic with ATRA in models of non-APL acute myelogenous leukemia

Acute myeloid leukemia (AML) is a disease characterized by the expansion of a hematopoietic stem cell like population caused in part by a block of myeloid differentiation. In AML, an altered epigenetic landscape, often arising from genetic lesions in epigenetic regulators, enforces an oncogenic expression profile and suppresses myeloid differentiation. Lysine specific demethylase 1 (LSD1) catalyzes the demethylation of lysine 4 and 9 of histone H3 through an FAD-dependent redox process. Aberrant LSD1 activity has been proposed to maintain oncogenic programs and prevent differentiation of multiple subtypes of AML. Intriguingly, recent studies indicate that LSD1 inhibition can reactivate an all-trans retinoic acid (ATRA)-dependent differentiation program in non-acute promyelocytic leukemia (APL) hematologic malignancies, a genetically heterogeneous group of blood cancers that normally respond poorly to ATRA therapy. In this study, we assessed the in vitro and in vivo effects of combining ATRA with INCB059872, a potent and selective FAD-directed LSD1 inhibitor, in non-APL AML models. As a single agent, INCB059872 induced differentiation of AML cells and when combined with ATRA, synergistically promoted differentiation as indicated by induction of CD86 and CD11b expression. In addition, the combination of INCB059872 and ATRA increased apoptosis in a panel of non-APL AML cell lines. Similarly, the combination significantly increased the fraction of CD86+CD11b+ cells and reduced cell viability in a panel of primary AML cells ex vivo. These effects in both human AML cell lines and human primary AML cells were observed across distinct FAB subtypes and genetic mutation profiles. Microarray profiling coupled with bioinformatic analysis of MV-4-11 cells demonstrated that the number of regulated genes related to differentiation and apoptotic pathways was markedly elevated in cells treated with the combination of LSD1 inhibition and ATRA relative to single agents. The synergistic increase in levels of myeloid lineage transcription factors GFI1, PU.1, CEBP and a decrease in levels of the oncogene c-MYC in the combination groups were validated by q-RT-PCR and western blot analyses. In vivo, the combination of INCB059872 and ATRA enhanced CD86 and CD11b induction and reduced tumor growth in the THP-1 xenograft model of AML compared with monotherapy. Similarly, oral administration of INCB059872 and ATRA in PDX mouse models markedly increased levels of CD11b+ cells in bone