Small Molecule STAT5-SH2 Domain Inhibitors Exhibit Potent Antileukemia Activity

Abstract

A growing body of evidence shows that Signal Transducer and Activator of Transcription 5 (STAT5) protein, a key member of the STAT family of signaling proteins, plays a pivotal role in the progression of many human cancers, including acute myeloid leukemia and prostate cancer. Unlike STAT3, where significant medicinal effort has been expended to identify potent direct inhibitors, Stat5 has been poorly investigated as a molecular therapeutic target. Thus, in an effort to identify direct inhibitors of STAT5 protein, we conducted an in vitro screen of a focused library of SH2 domain binding salicylic acid-containing inhibitors (∼150) against STAT5, as well as against STAT3 and STAT1 proteins for SH2 domain selectivity. We herein report the identification of several potent (K(i) < 5 μM) and STAT5 selective (>3-fold specificity for STAT5 cf. STAT1 and STAT3) inhibitors, BP-1-107, BP-1-108, SF-1-087, and SF-1-088. Lead agents, evaluated in K562 and MV-4-11 human leukemia cells, showed potent induction of apoptosis (IC(50)'s ∼ 20 μM) which correlated with potent and selective suppression of STAT5 phosphorylation, as well as inhibition of STAT5 target genes cyclin D1, cyclin D2, C-MYC, and MCL-1. Moreover, lead agent BP-1-108 showed negligible cytotoxic effects in normal bone marrow cells not expressing activated STAT5 protein. Inhibitors identified in this study represent some of the most potent direct small molecule, nonphosphorylated inhibitors of STAT5 to date.

Emerging therapeutic targets in myeloproliferative neoplasms and peripheral T-cell leukemia and lymphomas

“…To date, inhibition of STAT function has been attempted through several approaches, including N-terminal domain binders [131], oligonucleotides targeting the DNA binding domain [132], and most effectively through use of small molecule compounds that bind the SH 2 domain to block STAT phosphorylation, dimerization, nuclear transport, and target gene expression [133–135]. …”

“…More recently, a number of promising covalent STAT3/5 SH 2 domain-binding inhibitors have been described [8,133,134,152]. These compounds exhibit potent and selective binding activity for STAT3/5 by effectively disrupting phosphopeptide interactions.…”

Co-operating STAT5 and AKT signaling pathways in chronic myeloid leukemia and mastocytosis: possible new targets of therapy

“…Small molecules targeting STAT5 or AKT may indeed be effective in these malignancies, especially in TKIs-resistant patients. However, inhibitors available today, such as pimozide or BP-1-108 for STAT5, 10,11 or perifosine for AKT, During KIT phosphorylation on specific tyrosines, the resulting phosphotyrosine (PT) residues become docking sites for signal transduction molecules. Activated KIT also catalyzes the phosphorylation of substrate proteins and triggers multiple signal transduction pathways.…”

“…Small molecules targeting STAT5 or AKT may indeed be effective in these malignancies, especially in TKIs-resistant patients. However, inhibitors available today, such as pimozide or BP-1-108 for STAT5, 10,11 or perifosine for AKT,12 are neither specific nor potent enough to be applicable in clinical practice. Therefore, it seems important to develop compounds that specifically and potently target STAT5 and AKT.…”

The oncogenic FIP1L1-PDGFRαfusion protein displays skewed signaling properties compared to its wild-type PDGFRαcounterpart

“…Most recently, inhibitors that specifically target the SH2 domain of STAT5 have been developed and successfully tested for antileukemic activities in BCR-ABL and FLT3 ITD-expressing cell lines. 58 In the F/PDGFRa system, STAT5-SH2 domain inhibitors would not abrogate STAT5 phosphorylation, but impair the dimerization of phosphorylated STAT5. This implicates that direct STAT5-mediated transcriptional responses would be affected.…”