Targeting of STAT5 using the small molecule topotecan hydrochloride suppresses acute myeloid leukemia progression

Acute myeloid leukemia (AML) is a common type of acute leukemia in adults and relapse is one of the main reasons for treatment failure. FLT3-ITD mutations are associated with poor prognosis, short disease-free progression survival and high relapse rates in patients with AML. STAT5 is activated by FLT3-ITD and drives the pathogenesis of AML. STAT5 activation is usually a hallmark of hematologic malignancies and occurs in ~70% of patients with AML. Moreover, STAT5 is a key molecule which regulates hematopoiesis, and its high expression is closely associated with drug resistance, thus direct targeting of STAT5 for AML is of great clinical value. The present study introduces a new small-molecule inhibitor that targets STAT5, presenting a promising approach for AML therapy. A high throughput fluorescence polarization (FP) screening system for STAT5 was designed and established, and used to screen an existing compound library to obtain the highly active small molecule inhibitor, topotecan hydrochloride. Topotecan hydrochloride was demonstrated to be an effective inhibitor of STAT5 by molecular docking prediction and cellular thermal shift assay. Topotecan hydrochloride bound to STAT5, inhibiting its dimerization, phosphorylation and transcription of specific target genes. The compound exhibits cellular activity at the nanomolar level and significantly inhibits the proliferation of human AML cell lines and FLT3-ITD(+) AML cells. Furthermore, topotecan hydrochloride has the potential to exert an anti-tumor effect in vivo. Overall, topotecan hydrochloride offers a new opportunity for the treatment of AML and other hematologic malignancies by directly targeting STAT5.