In mothers who later develop breast cancer, having breast-fed a child may reduce the risk of cancer recurrence.

Decitabine, a cancer therapeutic that inhibits DNA methylation, produces variable antitumor response rates in patients with solid tumors that might be leveraged clinically with identification of a predictive biomarker. In this study, we profiled the response of human ovarian, melanoma, and breast cancer cells treated with decitabine, finding that RAS/MEK/ERK pathway activation and DNMT1 expression correlated with cytotoxic activity. Further, we showed that KRAS genomic status predicted decitabine sensitivity in low-grade and high-grade serous ovarian cancer cells. Pretreatment with decitabine decreased the cytotoxic activity of MEK inhibitors in KRAS-mutant ovarian cancer cells, with reciprocal downregulation of DNMT1 and MEK/ERK phosphorylation. In parallel with these responses, decitabine also upregulated the proapoptotic BCL-2 family member BNIP3, which is known to be regulated by MEK and ERK, and heightened the activity of proapoptotic small-molecule navitoclax, a BCL-2 family inhibitor. In a xenograft model of KRAS-mutant ovarian cancer, combining decitabine and navitoclax heightened antitumor activity beyond administration of either compound alone. Our results define the RAS/MEK/DNMT1 pathway as a determinant of sensitivity to DNA methyltransferase inhibition, specifically implicating KRAS status as a biomarker of drug response in ovarian cancer. Cancer Res; 75(14); 1–10. ©2015 AACR.

Decitabine, a cancer therapeutic that inhibits DNA methylation, has elicited moderate to low response rates in patients with solid tumors. Despite efforts to identify responders based on DNA methylation, a marker for decitabine activity has yet to be determined. Here, we profiled the response of ovarian, melanoma, and breast cancer cell lines to decitabine after treatment for nine days. We found that activation of the RAS/MEK/ERK pathway and DNMT1 expression correlate with decitabine activity. We further showed that KRAS genomic status predicts sensitivity to decitabine in low and high-grade serous ovarian cancer cell lines. We demonstrated that pre-treatment with decitabine decreases activity of MEK inhibitors in KRAS-mutant ovarian cancer cell lines and showed reciprocal regulation of DNMT1 protein level and phosphorylation of MEK and ERK using small-molecule probes targeted to MEK and decitabine, respectively. We observed that decitabine upregulates BNIP3, a pro-apoptotic BCL-2 family member that is regulated by MEK and ERK, and increases activity of navitoclax, a BCL-2 family inhibitor, in KRAS-mutant ovarian cancer cell lines. Finally, we demonstrated that the combination of decitabine and navitoclax greatly decreases tumor burden in a KRAS-mutant ovarian cell line-derived xenograft model. Our results correlate activation of the RAS/MEK/DNMT1 pathway with sensitivity to the DNA methyltransferase inhibitor, decitabine, and implicate KRAS genomic status as a biomarker for sensitivity in ovarian cancer.

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic malignancies. PDAC builds a tumor microenvironment that plays critical roles in tumor progression and metastasis. However, the relationship between chemotherapy and modulation of PDAC-induced tumor microenvironment remains poorly understood. In this study, we report a role of chemotherapy-derived inflammatory response in the enrichment of PDAC microenvironment with immunosuppressive myeloid cells. Granulocyte macrophage colony-stimulating factor (GM-CSF) is a major cytokine associated with oncogenic KRAS in PDAC cells. GM-CSF production was significantly enhanced in various PDAC cell lines or PDAC tumor tissues from patients after treatment with chemotherapy, which induced the differentiation of monocytes into myeloid-derived suppressor cells (MDSC). Furthermore, blockade of GM-CSF with monoclonal antibodies helped to restore T-cell proliferation when cocultured with monocytes stimulated with tumor supernatants. GM-CSF expression was also observed in primary tumors and correlated with poor prognosis in PDAC patients. Together, these results describe a role of GM-CSF in the modification of chemotherapy-treated PDAC microenvironment and suggest that the targeting of GM-CSF may benefit PDAC patients’ refractory to current anticancer regimens by defeating MDSC-mediated immune escape. Cancer Res; 75(13); 1–12. ©2015 AACR.

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic malignancies. PDAC builds a tumor microenvironment that plays critical roles in tumor progression and metastasis. However, the relationship between chemotherapy and modulation of PDAC-induced tumor microenvironment remains poorly understood. In this study, we report a role of chemotherapy-derived inflammatory response in the enrichment of PDAC microenvironment with immunosuppressive myeloid cells. GM-CSF is a major cytokine associated with oncogenic KRAS in PDAC cells. GM-CSF production was significantly enhanced in various PDAC cell lines or PDAC tumor tissues from patients after treatment with chemotherapy, which induced the differentiation of monocytes into myeloid derived suppressor cells (MDSCs). Furthermore, blockade of GM-CSF with monoclonal antibodies helped to restore T cell proliferation when co-cultured with monocytes stimulated with tumor supernatants. GM-CSF expression was also observed in primary tumors and correlated with poor prognosis in PDAC patients. Together, these results describe a role of GM-CSF in the modification of chemotherapy-treated PDAC microenvironment, and suggest that the targeting of GM-CSF may benefit PDAC patients’ refractory to current anticancer regimens by defeating MDSCs-mediated immune escape.