Objectives Discoidin Domain Receptor 2 (DDR2) is a receptor tyrosine kinase which binds fibrillar collagen. Previous work from our lab demonstrated that DDR2 inhibition increases sensitivity to olaparib in homologous recombination (HR) proficient ovarian cancer. This study aimed to understand the mechanism of DDR2 inhibition increasing sensitivity to olaparib.

Methods Three DDR2-expressing human ovarian cancer cell lines, ES2, COV362, and PEO4, with short hairpin control and DDR2 knockdowns were used. The HR status after irradiation and DNA damage response after treatment with olaparib was determined using immunofluorescence. In vivo metabolomics analysis of ES2 tumors was performed after injection of U-13C-glucose tracer.

Results All cell lines had a 2-fold increase in RAD51 foci after irradiation indicating HR proficiency. DDR2 knockdown induced HR deficiency. To confirm that DDR2 regulated HR, DDR2 knockdown cells were rescued with DDR2 wild-type (DDR2-WT rescue) in order to re-express DDR2. DDR2-WT rescue cells were again HR proficient. On western, BRCA1 expression was decreased in cells without DDR2 expression through decreased activation of the PI3K pathway. Knockdown of DDR2 increased DNA damage and repair through non-homologous end-joining both at baseline and after treatment with olaparib. These findings reversed in DDR2-WT rescue cells. In vivo metabolomics analysis of tumors without DDR2 expression found decreased pentose phosphate pathway activation including decreased ribose-5-phsophate, an intermediate essential for DNA repair through nucleotide biosynthesis.

Conclusions DDR2 inactivation sensitizes HR proficient ovarian cancer cells to olaparib through induced HR deficiency and metabolic rewiring possibly leading to impaired DNA damage repair. Current experiments are underway to confirm metabolomics findings.