Structure-Based Screen Identifies a Potent Small Molecule Inhibitor of Stat5a/b with Therapeutic Potential for Prostate Cancer and Chronic Myeloid Leukemia

Abstract

Bypassing tyrosine kinases responsible for Stat5a/b phosphorylation would be advantageous for therapy development for Stat5a/b-regulated cancers. Here, we sought to identify small-molecule inhibitors of Stat5a/b for lead optimization and therapy development for prostate cancer (PC) and Bcr-Abl-driven leukemias. In silico screening of chemical structure databases combined with medicinal chemistry was used for identification of a panel of small-molecule inhibitors to block SH2-domain-mediated docking of Stat5a/b to the receptor-kinase complex and subsequent phosphorylation and dimerization. We tested the efficacy of the lead-compound, IST5-002, in experimental models and patient samples of two known Stat5a/b-driven cancers, prostate cancer (PC) and chronic myeloid leukemia (CML). The lead compound Inhibitor of Stat5-002 (IST5-002) prevented both Jak2 and Bcr-Abl-mediated phosphorylation and dimerization of Stat5a/b, and selectively inhibited transcriptional activity of Stat5a (IC50 1.5 μM) and Stat5b (IC50 3.5 μM). IST5-002 suppressed nuclear translocation of Stat5a/b, binding to DNA and Stat5a/b target gene expression. IST5-002 induced extensive apoptosis of PC cells, impaired growth of PC xenograft tumors and induced cell death in patient-derived PCs when tested ex vivo in explant organ cultures. Importantly, IST5-002 induced robust apoptotic death not only of imatinib-sensitive but also imatinib-resistant chronic myeloid leukemia (CML) cell lines and primary CML cells from patients. IST5-002 provides a lead structure for further chemical modifications for clinical development for Stat5a/b-driven solid tumors and hematological malignancies.

Targeting STAT5 or STAT5-Regulated Pathways Suppresses Leukemogenesis of Ph+ Acute Lymphoblastic Leukemia

“…Based on these findings, we assessed the reliance of Phþ ALL cells on STAT5 activity by ex vivo and in vivo assays using IST5-002, a small molecule inhibitor of STAT5A/B tyrosine phosphorylation and dimerization, recently identified through structure-based in silico screening of compounds binding to the STAT5 SH2 domain (31).…”

“…In silico screening of chemical structure databases has recently identified IST5-002 as a candidate small molecule inhibitor of STAT5 (31). Such activity was confirmed based on its ability to suppress JAK2 and BCR-ABL1-mediated STAT5 phosphorylation, STAT5A/B dimerization, and to inhibit the transcriptional activity of STAT5A and STAT5B (31).…”

Direct Targeting Options for STAT3 and STAT5 in Cancer

“…In 2015, Liao et al conducted a large scale structure-based virtual screening campaign for STAT5A/B inhibitors [99]. Using a STAT3 based homology model of STAT5, the authors docked 30 million compounds to the dimerization interface on the SH2 domain [65].…”

Preclinical Models of Prostate Cancer: Patient-Derived Xenografts, Organoids, and Other Explant Models

“…Although varied techniques have been reported that include full submersion of the tissue, the use of various scaffolds or supports is more effective where tissues are kept in contact with the media on agar or other metal grids made of titanium (McMahon et al 1972) or stainless steel (Nevalainen et al 1993). The grid approach was used to yield novel information such as the role of Jak2/Stat5a signaling to induce epithelial-to-mesenchymal transition and stemlike properties in prostate cancer (Gu et al 2013;Liao et al 2015;Talati et al 2015). With the development of bioengineered scaffolds to support and seed human cells for tissue regeneration, it is likely that these grid supports will lead to further advances as discussed below.…”