Mary M. Mullen

Multiomic Characterization of Pre- and Post-Neoadjuvant Chemotherapy–Treated Ovarian Cancer Reveals Mediators of Tumorigenesis and Chemotherapy Response

Abstract High-grade serous ovarian cancer (HGSC) accounts for more than 200,000 deaths each year. Despite recent advances in treating HGSC with neoadjuvant chemotherapy, the majority of patients ultimately develop chemotherapy resistance. HGSC is characterized by TP53 mutations and widespread copy-number alterations and occurs frequently in the setting of deleterious germline BRCA1/2 variations, but many cases lack putative driver mutations. In this study, we performed whole-exome, whole-genome, and whole-transcriptome sequencing along with mass spectrometry to characterize the molecular landscape of HGSC in 22 paired samples obtained before and after neoadjuvant chemotherapy. Responsiveness to chemotherapy was determined for each patient. Evidence at the DNA, RNA, and protein level revealed numerous defects in cell–cell and cell–matrix interactions, as well as disruption of cell polarity and cytoskeletal regulation in HGSC, indicating that defects in epithelial integrity were present in the majority of patients with HGSC. Nonresponsive HGSC harbored subclones with putative survival mutations. Additionally, ineffective nonsense-mediated decay resulted in the persistence of transcripts with frameshift mutations that were translated into aberrant proteins detectable in HGSC samples. Together, these findings suggest that HGSC may arise through defects in the maintenance of epithelial integrity that lead to the shedding of malignant cells throughout the peritoneum, and the presence of resistant subclones prior to chemotherapy may decrease the chemosensitivity of patients. Significance: Comprehensive longitudinal characterization of ovarian cancer identifies pathways that promote tumorigenesis and provides insights into regulators of chemotherapy response, which could help develop strategies to improve outcomes for patients.

DDR2 Confers Ferroptosis Resistance to Cancer-Associated Fibroblasts and Attenuates PARPi Sensitivity of Ovarian Tumor Cells

Abstract In ovarian cancer, resistance to conventional treatments has prompted the search for alternative targets and/or cells within the tumor microenvironment that could enhance tumor cell death. Ferroptosis, an iron-dependent, lipid peroxide–triggered form of cell death, is one such pathway. Cancer-associated fibroblasts (CAF) are key stromal cells in the ovarian tumor microenvironment that can affect therapeutic responses. Using various genetic approaches, we generated multiple DDR2-expressing and DDR2-deficient human ovarian tumor and mouse breast tumor CAFs. We found that DDR2 expression in CAFs protects these cells from ferroptosis by regulating the xCT–GSH–GPX4 antioxidant pathway and cellular iron metabolism. Specifically, DDR2 regulates xCT expression through noncanonical p62-dependent NRF2 activation and the labile iron pool by controlling ferritinophagy. CAFs secrete factors, in a DDR2-dependent manner, that provide protection to ovarian tumor cells against olaparib-induced cell death, a clinically relevant PARP inhibitor (PARPi). Finally, we found that high expression of DDR2 in the stromal cells of human ovarian tumors is associated with poor response to PARPi in clinical trials. These findings suggest that ferroptotic regulation by DDR2 in ovarian tumor CAFs could affect therapeutic sensitivity and resistance to PARPi. Implications: The action of the collagen receptor tyrosine kinase DDR2 in CAFs confers PARPi protection to ovarian tumor cells by protecting CAFs from ferroptosis.

Stromal DDR2 Promotes Ovarian Cancer Metastasis through Regulation of Metabolism and Secretion of Extracellular Matrix Proteins

Abstract Ovarian cancer is the leading cause of gynecologic cancer–related deaths. The propensity for metastasis within the peritoneal cavity is a driving factor for the poor outcomes associated with this disease, but there is currently no effective therapy targeting metastasis. In this study, we investigate the contribution of stromal cells to ovarian cancer metastasis and identify normal stromal cell expression of the collagen receptor, discoidin domain receptor 2 (DDR2), that acts to facilitate ovarian cancer metastasis. In vivo, global genetic inactivation of Ddr2 impairs the ability of Ddr2-expressing syngeneic ovarian cancer cells to spread throughout the peritoneal cavity. Specifically, DDR2 expression in mesothelial cells lining the peritoneal cavity facilitates tumor cell attachment and clearance. Subsequently, omentum fibroblast expression of DDR2 promotes tumor cell invasion. Mechanistically, we find DDR2-expressing fibroblasts are more energetically active, such that DDR2 regulates glycolysis through AKT/SNAI1 leading to suppressed fructose-1,6-bisphosphatase and increased hexokinase activity, a key glycolytic enzyme. Upon inhibition of DDR2, we find decreased protein synthesis and secretion. Consequently, when DDR2 is inhibited, there is reduction in secreted extracellular matrix proteins important for metastasis. Specifically, we find that fibroblast DDR2 inhibition leads to decreased secretion of the collagen crosslinker, LOXL2. Adding back LOXL2 to DDR2 deficient fibroblasts rescues the ability of tumor cells to invade. Overall, our results suggest that stromal cell expression of DDR2 is an important mediator of ovarian cancer metastasis. Implications: DDR2 is highly expressed by stromal cells in ovarian cancer that can mediate metastasis and is a potential therapeutic target in ovarian cancer.

RAD51 Foci as a Biomarker Predictive of Platinum Chemotherapy Response in Ovarian Cancer

Abstract Purpose: To determine the ability of RAD51 foci to predict platinum chemotherapy response in high-grade serous ovarian cancer (HGSOC) patient-derived samples. Experimental Design: RAD51 and γH2AX nuclear foci were evaluated by immunofluorescence in HGSOC patient-derived cell lines (n = 5), organoids (n = 11), and formalin-fixed, paraffin-embedded tumor samples (discovery n = 31, validation n = 148). Samples were defined as RAD51-High if >10% of geminin-positive cells had ≥5 RAD51 foci. Associations between RAD51 scores, platinum chemotherapy response, and survival were evaluated. Results: RAD51 scores correlated with in vitro response to platinum chemotherapy in established and primary ovarian cancer cell lines (Pearson r = 0.96, P = 0.01). Organoids from platinum-nonresponsive tumors had significantly higher RAD51 scores than those from platinum-responsive tumors (P < 0.001). In a discovery cohort, RAD51-Low tumors were more likely to have a pathologic complete response (RR, 5.28; P < 0.001) and to be platinum-sensitive (RR, ∞; P = 0.05). The RAD51 score was predictive of chemotherapy response score [AUC, 0.90; 95% confidence interval (CI), 0.78–1.0; P < 0.001). A novel automatic quantification system accurately reflected the manual assay (92%). In a validation cohort, RAD51-Low tumors were more likely to be platinum-sensitive (RR, ∞; P < 0.001) than RAD51-High tumors. Moreover, RAD51-Low status predicted platinum sensitivity with 100% positive predictive value and was associated with better progression-free (HR, 0.53; 95% CI, 0.33–0.85; P < 0.001) and overall survival (HR, 0.43; 95% CI, 0.25–0.75; P = 0.003) than RAD51-High status. Conclusions: RAD51 foci are a robust marker of platinum chemotherapy response and survival in ovarian cancer. The utility of RAD51 foci as a predictive biomarker for HGSOC should be tested in clinical trials.