Abstract C246: SH-4-54, a novel small-molecule inhibitor of STAT3, demonstrates significant anti-tumor activity against multiple myeloma.

Abstract Aberrant STAT3 signaling is prevalent in hematologic malignancies such as Multiple Myeloma (MM) and is recognized as a master regulator of tumor processes such as survival, angiogenesis, and drug resistance. Significant efforts have therefore focused on therapeutic targeting of STAT3 as an anti-cancer strategy. Based on rational structure-based design, we present pre-clinical findings for a newly developed small molecule STAT3 inhibitor, SH-4-54. SH-4-54 was designed to block the SH2 domain of STAT3 by mimicking its native phosphopeptide binding sequence and in turn prevent phosphorylation (activation) and disrupt transcriptionally active STAT3:STAT3 dimerization. SH-4-54 has been shown to have a KD for STAT3 protein of 300 nM by surface plasmon resonance and inhibits STAT3 SH2 domain-phosphopeptide interactions as assessed by a fluorescence polarization assay. The anti-MM activity of SH-4-54 was assessed using MTT assays against a panel of molecularly heterogeneous human myeloma cell lines (HMCLs), revealing potent and broad effects on cell viability with 10/15 HMCLs displaying IC50 values < 10 μM. Moreover, SH-4-54 induced apoptotic responses in HMCLs as evidenced by increased Annexin V staining. Promising results were observed for the effects of SH-4-54 on primary patient-derived myeloma cells. Using flow cytometric analysis of CD138 as a marker of myeloma cells and Annexin V staining, SH-4-54 was found to significantly reduce the percentage of CD138+/Annexin V negative, viable myeloma cells, while displaying little to no toxicity against the non-malignant (CD138−) cell fraction. Supporting the predicted molecular mechanisms of SH-4-54 activity, immunoblot analysis revealed that SH-4-54 inhibits constitutive STAT3 phosphorylation, but does not alter STAT3 protein levels. Furthermore, using HMCLs engineered to express a STAT3-driven luciferase reporter construct, SH-4-54 was found to significantly reduce STAT3 transcriptional activity, and consistently induce a reduction in proteins that encode STAT3 target genes such as c-Myc. Taken together, our results highlight the promising therapeutic potential of SH-4-54 and support the continued development of targeted therapies for MM with a focus on aberrant STAT signaling. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C246. Citation Format: Zhi Hua Li, Sina Haftchenary, Danielle Croucher, Patrick T. Gunning, Suzanne Trudel. SH-4-54, a novel small-molecule inhibitor of STAT3, demonstrates significant anti-tumor activity against multiple myeloma. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C246.