SIRT6 Inhibition As a Novel Approach for Treating Acute Myeloid Leukemia

Currently available therapeutics against Acute Myeloid Leukemia (AML) have improved patient outcome. However, resistance develops even to novel therapies and patient overall survival remains low, especially for patients who are not eligible for allogeneic bone marrow transplantation. Therefore, there is an urgent need to overcome the biologic mechanisms underlying drug resistance in AML, to enhance the efficacy of existing treatments and to facilitate the design of novel approaches. Recently, our group has demonstrated that SIRT6, a NAD+-dependent histone deacetylase involved in genome maintenance, is frequently up-regulated in Multiple Myeloma and its targeting induces cancer cell killing (Cea M. et al, Blood 2016). Furthermore, gene expression analyses performed by our groups show that SIRT6 is also up-regulated in AML and confers poor prognosis in a series of 200 primary AML cases from our Hematology Clinic. Thus, these data suggested a role for SIRT6 in AML biology. High SIRT6 expression was typically observed in AML cell lines characterized by constitutive DNA damage and intense replicative stress. Likewise, primary AML cases exhibiting an intermediate-to-high chromosome instability (CIN) gene expression signature were also those with the highest SIRT6 expression, and worst prognosis. Subsequent studies demonstrated that SIRT6 silencing or its chemical inhibition, as observed in Multiple Myeloma exacerbates DNA damage in response to genotoxic agents, sensitizing AML cells to cytarabine (ARA-C) and idarubicin in vitro. Overall, enhancing genotoxic stress while concomitantly blocking DNA double-strand breaks (DSBs) repair response, may represent an innovative strategy to increase chemosensitivity of AML cells. Mechanistic studies revealed that SIRT6 acts as a genome guardian in AML cells by binding DNA damage sites and activating DNA-PKcs and CtIP by deacetylation, which in turn promotes DNA repair. Overall our data suggest that genomic instability is present in all hematologic malignancies including AML. Strategies aimed to shift the balance towards high DNA damage and reduced DNA repair by SIRT6 inhibition can decrease AML growth and may benefit patients with otherwise unfavorable outcomes.