A minority of Colorectal Cancer (CRC) patients with peritoneal metastases is eligible for cytoreductive surgery (CRS) followed by hyperthermic intraperitoneal chemotherapy (HIPEC). However, recurrence rates are high (~80%). We tested whether inhibitors of the DNA damage response (DDR) could prevent recurrence in an in vitro HIPEC model.

Peritoneal metastasis-derived organoids (PMDOs; n=10) were treated with inhibitors of ATR (berzosertib, ceralasertib, elimusertib), CHK1 (rabusertib), and WEE1 (adavosertib) alone, and in combination with MMC, oxaliplatin, or irinotecan. Western blotting was used to determine Chk1 phosphorylation and markers of DNA damage. Microscopy and ATP quantification were used to measure the effects of (combination) treatments on cell viability and recurrence/regrowth.

All PMDOs displayed rapid regrowth (recurrence) following single-drug chemotherapy treatment. Berzosertib inhibited chemotherapy-induced CHK1 phosphorylation, augmented DNA damage, and abrogated recurrence in all 10 MMC-treated PMDOs. The combination with oxaliplatin and irinotecan was less effective. In vitro HIPEC with MMC followed by ‘adjuvant’ treatment with any of the DDR inhibitors for 3 days completely prevented PMDO recurrence.

PMDOs can be completely eradicated if MMC treatment is followed by inhibition of ATR or other DDR kinases. DDR inhibitors may, therefore, have value in the adjuvant treatment of peritoneal metastases following CRS-HIPEC.