STAT5 inhibitor Pimozide as a probable therapeutic option in overcoming Ponatinib resistance in K562 leukemic cells.

Signal Transducer and Activator of Transcription 5 (STAT5) is a transcription factor that plays a key role in neoplasia, triggered by the fusion oncogene BCR-ABL1; it is not only an essential protein for the pathogenesis of chronic myeloid leukemia (CML), but also its overexpression is associated with drug resistance developed toward various generations of Tyrosine Kinase Inhibitors (TKIs); these are still accepted as gold standard therapeutics for the treatment of CML. In this study, it was investigated whether suppression of STAT5 via a "STAT5 inhibitor" Pimozide resulted in any regain of chemosensitivity to third-generation TKI Ponatinib. Accordingly, the experimental work was designed on both parental CML cell line K562WT and its 1 nM Ponatinib-resistant counterpart, indicated as K562-Pon1. Based on the experimental results, Pimozide was more effective in resistant cells compared to wild-type cells for inducing apoptosis and block cell arrest. Combination therapy of Pimozide and Ponatinib demonstrated that STAT5 was a significant protein for regaining chemosensitivity to Ponatinib when its expression was suppressed both at mRNA and protein level. In conclusion, we consider that STAT5 inhibitor Pimozide can be a good alternative or combination therapy with TKIs for patients suffering from chemotherapeutic drug resistance. Communicated by Ramaswamy H. Sarma.