Metformin treatment Overcomes ATRA-Resistance in Acute Promyelocytic Leukemia and Increases FOXO3A Expression

Introduction:FOXO3A is a transcription factor shown to be involved in all-trans retinoic acid (ATRA)-induced granulocytic differentiation and apoptosis in acute promyelocytic leukemia (APL). Its biological activity may be significantly enhanced upon metformin, raising the possibility that ATRA and Metformin may act synergistically; which could be useful to overcome ATRA resistance. Despite progress in APL treatment, approximately 10-15% of patients will relapse after treatment with ATRA and anthracyclines and frequently present with ATRA resistance. Relapsed patients respond well to arsenic trioxide (ATO) treatment, but the cost of ATO is a significant barrier in many countries. Aims: Here, we investigated the effects of in vitro treatment with ATRA plus metformin in APL cell lines and primary blasts, and quantified FOXO3A expression and correlated its levels with treatment outcome in a cohort of patients enrolled in the International Consortium on Acute Leukemia (ICAPL2006) study. Finally, we evaluated the effect of induced overexpression of FOXO3A gene in regards to cell viability and proliferation. Methods: Primary leukemic blasts from hCG-PMLRARα transgenic mice (TM; n=4) and APL patients (age, 25-47y; n=4) were treated with metformin alone (5mM/ 10mM) or in combination with ATRA (1µM) and evaluated for cell viability. In addition, 106 patients (age, 18-82y) with newly diagnosed APL enrolled in the ICAPL2006 study were included. As controls, eight samples of bone marrow mononuclear cells (BMMC) from healthy volunteers (age, 18-60y) were analyzed. To validate our data, FOXO3A transcript levels from an independent cohort was used (31 patients from Amazonia!, Probe n. 204131_s_at, and five normal BMMC samples included in the same databank). NB4/NB4R2 (ATRA-resistant) cell lines were transduced with FOXO3A or empty vector (control). After synchronization using double thymidine block, transduced cells were submitted to proliferation and cell cycle assays. For dose-response curves, cells were treated with graded concentrations of ATRA, ATO and metformin. For the apoptosis analysis, cells were treated with ATRA (1µM), metformin (5mM) and combination for 24, 48 and 72 hours. The granulocytic differentiation in response to ATRA treatment was evaluated based on the CD11b surface levels. Results: In primary cells (from TM/APL patients) a 2-fold reduction in viable cells was observed after metformin and metformin plus ATRA treatment (P Disclosures Tallman:BioSight: Other: Advisory board; Daiichi-Sankyo: Other: Advisory board; ADC Therapeutics: Research Funding; AROG: Research Funding; AbbVie: Research Funding; Cellerant: Research Funding; Orsenix: Other: Advisory board. Ganser:Novartis: Membership on an entity9s Board of Directors or advisory committees. Lowenberg:Editorial Board "European Oncology & Haematology": Membership on an entity9s Board of Directors or advisory committees; Royal Academy of Sciences and Arts, The Netherlands: Membership on an entity9s Board of Directors or advisory committees; Supervisory Board, National Comprehensive Cancer Center (IKNL), Netherlands: Membership on an entity9s Board of Directors or advisory committees; Clear Creek Bio Ltd: Consultancy, Honoraria; international Scientific Advisory Board, Institute Gustave Roussy, Paris: Membership on an entity9s Board of Directors or advisory committees; Chairman Scientific Committee and Member Executive Committee, European School of Hematology (ESH, Paris, France): Membership on an entity9s Board of Directors or advisory committees; Elected member, Royal Academy of Sciences and Arts, The Netherlands: Membership on an entity9s Board of Directors or advisory committees; Editorial Board "The Netherlands Journal of Medicine": Membership on an entity9s Board of Directors or advisory committees; Editorial Board "International Journal of Hematology": Membership on an entity9s Board of Directors or advisory committees; "Up-to-Date", section editor leukemia: Membership on an entity9s Board of Directors or advisory committees; Agios Pharmaceuticals: Membership on an entity9s Board of Directors or advisory committees; Astex: Consultancy; Chairman, Leukemia Cooperative Trial Group HOVON (Netherlands): Membership on an entity9s Board of Directors or advisory committees; Celgene: Membership on an entity9s Board of Directors or advisory committees.