The Synthetic Oleanane Triterpenoids and the Histone Deacetylase Inhibitor Vorinostat Cooperate to Delay Tumor Development in a Transgenic Model of Estrogen Receptor -- Negative Breast Cancer

Breast cancer is the most common cancer and the second leading cause of cancer related deaths among women in the United States. There has been no change in the incidence of estrogen receptor-negative (ER-) breast cancer in over 30 years; hence, novel drugs are needed for the prevention and treatment of ER- breast cancer. Synthetic triterpenoids are a promising new class of compounds in a variety of preclinical cancer models. Although numerous studies have demonstrated the ability of the synthetic triterpenoids to inhibit proinflammatory mediators in primary peritoneal macrophages and the RAW 246.7 macrophage-like cell line, no studies have shown to date that the synthetic triterpenoids target tumor-associated macrophages (TAMs).;We tested the anti-neoplastic activity of the methyl ester derivative of the synthetic triterpenoid, 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO-Me), in a relevant model of ER-negative breast cancer, in which the polyoma-middle T (PyMT) oncoprotein drives carcinogenesis. The developing tumors recapitulate key features of the human disease including apprecible infiltration of TAMs. We show that CDDO-Me significantly delayed the initial development of tumors in PyMT mice while extending overall survival. Additionally, CDDO-Me significantly inhibited the infiltration of TAMs into mammary glands of PyMT mice along with levels of the chemokines chemokine (C-X-C motif) ligand 12 (CXCL12) and chemokine (C-C motif) ligand 2 (CCL2) in primary PyMT mammary tumor cells. We also found that CDDO-Me inhibited the secretion of matrix metalloproteinase 9 (MMP-9) along with levels of key breast cancer biomarkers in primary PyMT tumor cells.;In additional studies, we showed that CDDO-Me cooperated with the histone deacetylase inhibitor (HDI) Vorinostat (suberoylanilide hydroxamic acid; SAHA) to delay tumor development in the PyMT model. Additionally, the ethyl amide derivative of 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO-Ea), demonstrated the same cooperative effects in delaying tumor development in PyMT mice. Both CDDO-Me and CDDO-Ea also cooperated to inhibit proliferation in primary PyMT tumor cells and the de novo levels of nitric oxide (NO) in RAW 246.7 cells. We found that SAHA also inhibited the infiltration of TAMs by targeting different chemokines than CDDO-Me. While CDDO-Me targeted CXCL12 and CCL2, SAHA targeted the chemokine macrophage colony-stimulating factor (M-CSF). Both CDDO-Me and SAHA suppressed levels of secreted MMP-9 levels in primary PyMT mammary tumor cells. We also found that CDDO-Me and SAHA cooperated to suppress MMP-9 levels.