Suppression of mammary tumorigenesis by a Gemini vitamin D analog and a synthetic truterpenoid

Breast cancer is a heterogeneous disease categorized into multiple subtypes, including luminal, HER2-positive and basal-like subtypes, which exhibit distinct gene signatures and clinical outcomes. Basal-like breast cancer has the worst prognosis among these subtypes and has no clinically approved targeted therapy. While HER2-targeting therapy with a humanized HER2 monoclonal antibody markedly improved the prognosis of HER2-positive breast cancer, the de novo and acquired resistance against the antibody has emerged as a new challenge for patients with HER2-positive breast cancer. MCF10 cell lines, a human breast cancer progression model representing the basal-like breast cancer subtype, were employed to identify key proteins involved in different stages of mammary tumorigenesis. Increased levels of IGF-IR, cyclin D1 and c-Myc were associated with HRAS-driven transformation. Higher levels of pErk, pAkt, STAT3 and Pak4 contribute to tumorigenicity in vivo, whereas CD44, HER2, COX-2 and Smad4 may be involved in the breast cancer progression. The MCF10DCIS.com cells, one of the MCF10 cell lines, highly express a breast cancer stem cell marker, CD44. A Gemini vitamin D analog BXL0124 markedly repressed the CD44 protein level and the growth of MCF10DCIS.com xenograft tumors. CD44 overexpression was correlated with invasive phenotype in MCF10DCIS.com cells, and the repression of CD44 by BXL0124 contributed to the inhibition of cell invasion. STAT3, which interacts directly with CD44, was identified as a key downstream signaling molecule affected by BXL0124 in MCF10DCIS.com cells. The CD44 knockdown study supported the critical role of CD44-STAT3 signaling in the invasive potential of MCF10DCIS.com cells in vitro and in vivo. The anti-cancer effects of BXL0124 and a synthetic triterpenoid CDDO-Im on HER2-positive breast cancer were tested in MMTV-HER2/neu transgenic mice. BXL0124, CDDO-Im and their combination delayed the development of mammary tumors and markedly inhibited the activation of HER2 and EGFR as well as their downstream molecules, such as Erk, Src and c-Myc in MMTV-HER2/neu mammary tumors. In conclusion, we demonstrated therapeutic potential of Gemini vitamin D analog BXL0124 targeting CD44-STAT3 signaling in basal-like breast cancer. In addition, we found anti-cancer activities of BXL0124 and CDDO-Im in HER2-positive breast cancer and potentially additive effects of their combination.Ph. D.Includes bibliographical referencesby Jae Young S