Combined inhibition of JAK2-STAT3 and SMO-GLI1/tGLI1 pathways suppresses breast cancer stem cells, tumor growth, and metastasis.

Triple-negative breast cancer (TNBC) and HER2-positive breast cancer are particularly aggressive and associated with unfavorable prognosis. TNBC lacks effective treatments. HER2-positive tumors have treatment options but often acquire resistance to HER2-targeted therapy after initial response. To address these challenges, we determined whether novel combinations of JAK2-STAT3 and SMO-GLI1/tGLI1 inhibitors synergistically target TNBC and HER2 breast cancer since these two pathways are concurrently activated in both tumor types and enriched in metastatic tumors. Herein, we show that novel combinations of JAK2 inhibitors (ruxolitinib and pacritinib) with SMO inhibitors (vismodegib and sonidegib) synergistically inhibited in vitro growth of TNBC and HER2-positive trastuzumab-resistant BT474-TtzmR cells. Synergy was also observed against breast cancer stem cells. To determine if the combination is efficacious in inhibiting metastasis, we treated mice with intracardially inoculated TNBC cells and found the combination to inhibit lung and liver metastases, and prolong host survival without toxicity. The combination inhibited orthotopic growth, VEGF-A expression, and tumor vasculature of both TNBC and HER2-positive trastuzumab-refractory breast cancer. Lung metastasis of orthotopic BT474-TtzmR xenografts was suppressed by the combination. Together, our results indicated that dual targeting of JAK2 and SMO resulted in synergistic suppression of breast cancer growth and metastasis, thereby supporting future clinical testing.