Abstract 1184: Characterization of novel STAT5 inhibitors to interfere with the oncogenic activities of STAT5 in hematopoietic diseases

Abstract

Abstract Activation of the transcription factor STAT5 is essential for the pathogenesis of acute myeloid leukemia (AML) containing the FLT3 internal tandem duplication (ITD). FLT3 ITD is a constitutively active tyrosine kinase (TK) that drives the activation of STAT5 leading to the growth and survival of AML cells. Although there has been some success in identifying TK inhibitors that block the function of FLT3 ITD, treatment options are still limited. This is mainly due to drug resistance development by mutations that allow for the continued activation of STATs. Since STAT5 represents a critical mediator of malignant cellular behavior and sits at the convergence point of many kinase pathways, the direct targeting of STAT5 may be an effective means of overcoming this resistance to TK inhibitors. First, we screened a library of potential STAT5 inhibitors for specific SH2 domain binders using a fluorescent polarization assay. Thereby, we identified small inhibitory molecules, called AC-3-019 and AC-4-130, that bind to the SH2 domain of STAT5, subsequently resulting in the disruption of the reciprocal STAT5-phosphopeptide interactions. They efficiently blocked kinase-mediated phosphorylation, dimer formation, nuclear translocation, DNA binding and STAT5 mediated target gene expression. Further, we observed a time- and dose-dependent impairment of proliferation, blocked cell cycle progression and increased apoptosis. Studies with human AML patient-derived samples similarly showed an induction of apoptotic cell death and decreased colony forming capabilities. A combinatorial drug screen revealed synergistic effects with TK inhibitors, as well as with drugs standardly used in the treatment of AML patients, e.g. Cytarabine. Finally, AC-3-019 and AC-4-130 significantly suppressed tumor growth in vivo without general toxicity in healthy organs. Overall, our findings indicate that AC-3-019 and AC-4-130 are potent and selective inhibitors of STAT5. These compounds provide lead structures for further chemical modifications and clinical development for the identification of compounds to improve existing therapies. Citation Format: Bettina Wingelhofer, Barbara Maurer, Elizabeth C. Heyes, Patricia Freund, Abbarna A. Cumaraswamy, Jisung Park, Stefan Kubicek, Peter Valent, Patrick T. Gunning, Richard Moriggl. Characterization of novel STAT5 inhibitors to interfere with the oncogenic activities of STAT5 in hematopoietic diseases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1184. doi:10.1158/1538-7445.AM2017-1184