Loss of claudin-4 reduces DNA damage repair and increases sensitivity to PARP inhibitors (228)

Abstract

Objectives: Claudin-4 is aberrantly expressed in nearly 70% of all ovarian cancer tumors, and increased claudin-4 expression conveys a worse overall survival. Poly (ADP-ribose) polymerase (PARP) inhibitors are a therapeutic option for patients with ovarian cancer. PARP inhibitors exploit deficiencies in DNA damage repair (e.g., BRCA-mutation) by inducing replication stress and DNA damage. This study aimed to define the relationship between claudin-4 expression and response to PARP inhibitors. Results: Elevated claudin-4 mRNA expression is associated with ovarian cancer, DNA damage repair pathways, and resistance to platinum-based chemotherapies and PARP inhibitors. Claudin-4 knockdown significantly sensitized ovarian cancer cells to PARP inhibitors. Specifically, loss of claudin-4 reduced the 50% inhibitory concentration (IC50) of olaparib by 70% (IC50 - 378 nM to 88 nM) and rucaparib by 85% (IC50 - 189 nM to 27.5 nM). Furthermore, loss of claudin-4 expression sensitized ovarian cancer cells to several FDA-approved chemotherapies that induce DNA damage. Claudin-4 downregulation resulted in the decrease of several DNA damage repair effectors, including 53BP1 and XRCC1. Claudin-4/53BP1/XRCC1 expression was mainly confined to the tumor cells. Claudin-4 knockdown did not change homology-directed repair but reduced both non-homologous end-joining activity by 41% (p<0.001) and 53BP1 foci formation by an average of 50% (p<0.05). In the TCGA, lower claudin-4 expression correlated to increased mutational burden (Claudin-4 “High”, 45.2 mutations vs Claudin-4 “Low” 134.6 mutations; p<0.01). In 15 primary ovarian cancer tumors (12 high-grade serous, one low-grade serous, one mucinous, and one granulosa cell), “low”/null claudin-4 expressing tumors had a significant reduction in Ki67 after PARP inhibitor treatment alone (p<0.01). In contrast, “High” claudin-4 tumors only had significantly reduced Ki67 in the claudin-4 inhibitor alone (p<0.0001) and in the CMP/olaparib combination (p<0.0001). Conclusions: Claudin-4 is related to non-homologous end-joining DNA damage repair and 53BP1 foci formation. Claudin-4 inhibition in “high” claudin-4 tumors sensitized tumors to PARP inhibition. Claudin-4 expression in high-grade ovarian cancer tumors could potentially serve as both a marker of PARP inhibitor response and a target to improve PARP inhibitor response. Objectives: Claudin-4 is aberrantly expressed in nearly 70% of all ovarian cancer tumors, and increased claudin-4 expression conveys a worse overall survival. Poly (ADP-ribose) polymerase (PARP) inhibitors are a therapeutic option for patients with ovarian cancer. PARP inhibitors exploit deficiencies in DNA damage repair (e.g., BRCA-mutation) by inducing replication stress and DNA damage. This study aimed to define the relationship between claudin-4 expression and response to PARP inhibitors. Results: Elevated claudin-4 mRNA expression is associated with ovarian cancer, DNA damage repair pathways, and resistance to platinum-based chemotherapies and PARP inhibitors. Claudin-4 knockdown significantly sensitized ovarian cancer cells to PARP inhibitors. Specifically, loss of claudin-4 reduced the 50% inhibitory concentration (IC50) of olaparib by 70% (IC50 - 378 nM to 88 nM) and rucaparib by 85% (IC50 - 189 nM to 27.5 nM). Furthermore, loss of claudin-4 expression sensitized ovarian cancer cells to several FDA-approved chemotherapies that induce DNA damage. Claudin-4 downregulation resulted in the decrease of several DNA damage repair effectors, including 53BP1 and XRCC1. Claudin-4/53BP1/XRCC1 expression was mainly confined to the tumor cells. Claudin-4 knockdown did not change homology-directed repair but reduced both non-homologous end-joining activity by 41% (p<0.001) and 53BP1 foci formation by an average of 50% (p<0.05). In the TCGA, lower claudin-4 expression correlated to increased mutational burden (Claudin-4 “High”, 45.2 mutations vs Claudin-4 “Low” 134.6 mutations; p<0.01). In 15 primary ovarian cancer tumors (12 high-grade serous, one low-grade serous, one mucinous, and one granulosa cell), “low”/null claudin-4 expressing tumors had a significant reduction in Ki67 after PARP inhibitor treatment alone (p<0.01). In contrast, “High” claudin-4 tumors only had significantly reduced Ki67 in the claudin-4 inhibitor alone (p<0.0001) and in the CMP/olaparib combination (p<0.0001). Conclusions: Claudin-4 is related to non-homologous end-joining DNA damage repair and 53BP1 foci formation. Claudin-4 inhibition in “high” claudin-4 tumors sensitized tumors to PARP inhibition. Claudin-4 expression in high-grade ovarian cancer tumors could potentially serve as both a marker of PARP inhibitor response and a target to improve PARP inhibitor response.