PU.1 and MYC transcriptional network defines synergistic drug responses to KIT and LSD1 inhibition in acute myeloid leukemia

Activating mutations in the KIT tyrosine receptor kinase confer an adverse prognosis for patients with acute myeloid leukemia (AML). Outside of bone marrow transplantation, treatment options are limited. Here we demonstrate combined KIT and LSD1 inhibition produces synergistic cell death against KIT mutant AML cells. This combination suppresses MYC expression to drive cell cycle exit and apoptosis. This decreased MYC expression results from a loss of PU.1 binding at downstream MYC enhancers. The drug combination also inactivates PI3K/AKT/GSK3a/b signaling to decrease MYC protein abundance. KIT-mutant AML cells rapidly adapt to KIT inhibitor monotherapy by restoring PI3K/AKT activity, but cannot when treated with combined KIT and LSD1 inhibitor. In addition, we validate MYC suppression as a mechanism of synergy in KIT-mutant AML patient samples. Collectively, this work provides rational for a clinical trial to assess the efficacy of KIT and LSD1 inhibition in patients with KIT-mutant AML. Statement of significance Effective treatment options for AML are limited. We describe the synergistic response to combined KIT and LSD1 inhibition in KIT-mutant AML and identify key biomarkers of drug response. The specificity and efficacy of this combination in cell lines and patient samples provides rationale for investigation in early phase clinical trials. ### Competing Interest Statement B.J.D. has potential competing interests as follows: SAB: Aileron Therapeutics, Therapy Architects (ALLCRON), Cepheid, Vivid Biosciences, Celgene, RUNX1 Research Program, EnLiven Therapeutics, Gilead Sciences (inactive), Monojul (inactive); SAB & Stock: Aptose Biosciences, Blueprint Medicines, Iterion Therapeutics, Third Coast Therapeutics, GRAIL (SAB inactive); Scientific Founder: MolecularMD (inactive, acquired by ICON); Board of Directors & Stock: Amgen; Board of Directors: Burroughs Wellcome Fund, CureOne; Joint Steering Committee: Beat AML LLS; Founder: VB Therapeutics; Clinical Trial Funding: Novartis, Bristol-Myers Squibb, Pfizer; Royalties from Patent 6958335 (Novartis exclusive license) and OHSU and Dana-Farber Cancer Institute (one Merck exclusive license). J.E.M.-- SAB: Ionis pharmaceuticals. The other authors do not have conflicts of interest, financial or otherwise.