LLL12B, a Novel Small-Molecule STAT3 Inhibitor, Induces Apoptosis and Suppresses Cell Migration and Tumor Growth in Triple-Negative Breast Cancer Cells.

Persistent STAT3 signaling plays a pivotal role in human tumor malignancy, including triple-negative breast cancer (TNBC). There are few treatment options currently available for TNBC; thus, given its importance to cancer, STAT3 is a potential cancer therapeutic target and is the focus of drug discovery efforts. In this study, we tested a novel orally bioavailable small-molecule STAT3 inhibitor, LLL12B, in human MDA-MB-231, SUM159, and murine 4T1 TNBC cell lines. TNBC cells frequently expressed persistent STAT3 phosphorylation and their cell viability was sensitive to STAT3 knockdown by siRNA. LLL12B selectively inhibited the IL-6-mediated induction of STAT3 phosphorylation, but had little effect on the IFN-γ-mediated induction of STAT1 phosphorylation nor the EGF-mediated induction of ERK phosphorylation. In addition, targeting STAT3 with LLL12B induced apoptosis, reduced colony formation ability, and inhibited cell migration in TNBC cells. Furthermore, LLL12B suppressed the tumor growth of the MDA-MB-231 TNBC cells in a mammary fat pad mouse tumor model in vivo. Together, our findings support the concept that targeting persistent STAT3 signaling using the novel small-molecule LLL12B is a potential approach for TNBC therapy.