apeutic Discovery Kinase Inhibitors Downregulate Ther T 3 Tyr 705 Phosphorylation

ownload g a cell-based high-throughput screen designed to detect small chemical compounds that inhibit cell h and survival, we identified three structurally related compounds, 21A8, 21H7, and 65D4, with differactivity on cancer versus normal cells. Introduction of structural modifications yielded compound , which inhibits the proliferation of prostate cancer cell lines with IC50s of 0.6 to 0.9 μmol/L, with no y on normal human peripheral blood mononuclear cells up to 40 μmol/L. Screening of 261 recombinant s and subsequent analysis revealed that M-110 is a selective inhibitor of the PIM kinase family, with ence for PIM-3. The prostate cancer cell line DU-145 and the pancreatic cancer cell line MiaPaCa2 tutively express activated STAT3 (pSTAT3). Treatment of DU-145 cells with M-110 or with a strucunrelated PIM inhibitor, SGI-1776, significantly reduces pSTAT3 expression without affecting the sion of STAT3. Furthermore, treatment of DU-145 cells with M-110 attenuates the interleukin-6– ed increase in pSTAT3. To determine which of the three PIM kinases is most likely to inhibit sion of pSTAT3, we used PIM-1–, PIM-2–, or PIM-3–specific siRNA and showed that knockdown -3, but not of PIM-1 or PIM-2, in DU-145 cells results in a significant downregulation of pSTAT3. hosphorylation of STAT5 on Tyr694 in 22Rv1 cells is not affected by M-110 or SGI-1776, suggesting icity for pSTAT3. These results identify a novel role for PIM-3 kinase as a positive regulator of specif STAT3 signaling and suggest that PIM-3 inhibitors cause growth inhibition of cancer cells by downregulating the expression of pSTAT3. Mol Cancer Ther; 9(9); 2478–87. ©2010 AACR.