Clinical observations of AML expressing mutant RUNX1 and pre-clinical studies of RUNX1-targeted novel therapy of AML.

Abstract

7030 Background: Runt-related transcription factor 1 ( RUNX1) is critically involved in normal and malignant hematopoiesis. Somatic mutations in RUNX1 occur in ~10% of AML, especially in older patients with history of radiation or antecedent hematologic disorder. Presence of mRUNX1 is reported to confer relative resistance to therapy and poorer prognosis in AML, and there are no mRUNX1-targeted or specific therapies available. Methods: We retrospectively analyzed outcomes of 94 mRUNX1 and 444 wild-type RUNX1 AML patients treated at our institution from 9/2013 to 12/2016. We also determined the pre-clinical efficacy of a targeted therapy against cultured and primary AML cells expressing mRUNX1. Results: 67% of mRUNX1 patients were > 65 years of age. Co-occurring mutations with mRUNX1 were ASXL1 (33%), N/KRAS (20%), FLT3 (20%), IDH2 (18%), IDH1 (13%) and TET2 (10%). In patients > 65 years treated with hypomethylating agent-based therapy, the presence or absence of mRUNX1 did not impact response rate (42% vs 46% CR/CRp, p = 0.67), median event-free survival (3.4 vs 4.7 mo, p = 0.82) or overall survival (11.5 vs 9.3 mo, p = 0.97). In mRUNX1 expressing AML OCI-AML5 and MonoMac1 cells, knockdown of RUNX1 by shRNA repressed its targets, e.g., MYC and PU.1, inhibited growth and induced apoptosis. Ex vivo knockdown of RUNX1 abrogated in vivo leukemia initiation by OCI-AML5 cells. After engraftment, inducible shRNA-mediated in vivo knockdown of RUNX1 restored survival of immune-depleted NSG mice engrafted with OCI-AML5 cells. RUNX1 transcription is driven by a super enhancer occupied by the bromodomain extraterminal protein (BETP), BRD4. Accordingly, BRD4 knockdown by shRNA or treatment with the BRD4-inhibitor OTX015 depleted RUNX1 and its targets, and induced apoptosis of AML cells. Treatment of OCI-AML5 cell-engrafted NSG mice with OTX015 (50 mg/Kg/day X 5, for 3 wks) reduced AML burden and improved survival (p < 0.01). Co-treatment with the BETi and BCL2 inhibitor venetoclax or CDK4/6 antagonist palbociclib or decitabine synergistically induced apoptosis of OCI-AML5 and primary AML blasts. Conclusions: These findings highlight a novel, promising, BETP antagonist-based therapy of AML expressing mtRUNX1.