THE ANTINEOPLASTIC ROLE OF STAT5 INHIBITION IN BCRABL1-POSITIVE CELLS EXPOSED TO PIMOZIDE ALONE AND IN COMBINATION WITH DASATINIB AND PONATINIB

EVEN though the last decades have seen the success of the targeted treatments for BCRABL1-positive Chronic Myeloid Leukemia (CML), with the outstanding achievement of placing selected patients into the so called treatment-free remission, a minor part of these subjects face TKI resistance and/or intolerance. Resistance is a challenging point in the clinical management of CML, occurring in approximately 10–20% of CML cases, due to several mechanisms, among which point mutations of the BCR‐ABL kinase domain, BCRABL overexpression or alternative splicing, sub-efficient plasma concentration of the inhibitor and abnormal drug efflux/influx. The Signal Transducer and Activators of Transcription (STAT) proteins are a family of transcription factors commonly involved in multiple intracellular tasks and pathways, among which survival and proliferation. The STAT family is made up of seven factors, each one with a specific role. In particular, STAT3 and STAT5 (A and B) are strictly involved in cell survival and proliferation and thus are commonly implied in the pathogenesis of many neoplasms. STAT5 is of peculiar interest for its critical role in cellular differentiation, adipogenesis, oncogenesis, immune function and is known to be constitutively activated after the BCRABL1 effect in CML cells. STAT5 expression has been strictly linked to BCRABL1 mutations and disease progression to accelerated and blast phase and may thus represent a significant target to overcome resistance to TKI in CML. In 2011, Nelson et al. evidenced the effect of STAT5 inhibition exerted by a Pimozide, a commonly used neuroleptic drug. As far as we know, literature reports experiments involving STAT5 inhibitors in association with BCRABL inhibition only with first generation inhibitor imatinib. There is no news about the association between STAT5 inhibitors and newer generations of TKIs. The aim of this study is to explore the antineoplastic role of the STAT5 inhibitor Pimozide in association with 2nd and 3rd generation TKIs, dasatinib and ponatinib respectively, and to identify the cytotoxic in vitro concentrations. For the purpose of the study, K562 cell line was used to simulate the frame of a classical Chronic Myeloid Leukemia disease. The cytotoxic effect was evaluated by the Trypan blue dye exclusion test. K562 cell lines were exposed to pimozide alone and in association with ponatinib and dasatinib at different concentrations to explore the drugs association effect and the in vitro cytotoxic concentrations. Pimozide showed a synergic effect when associated with ponatinib and dasatinib in survival inhibition of K562 cell lines. This results are of note and pave the way for a possible in vivo associations. Moreover, an extension of the present study is evaluating the cytotoxic effect on CML leukemic stem cells (LSC), aiming at revealing whether STAT5 inhibition may determine a more profound effect on CML disease and may overcome the LSC escape mechanisms on which TKIs are not active.