Organoids from colorectal peritoneal metastases as a platform for improving hyperthermic intraperitoneal chemotherapy

Background: Patients with peritoneal metastases from colorectal cancer have a poor prognosis. If the intraperitoneal tumour load is limited, patients may be eligible for cytoreductive surgery followed by hyperthermic intraperitoneal chemotherapy (HIPEC). This treatment has improved overall survival, but recurrence rates are high. The aim of this study was to create a preclinical platform for the development of more effective intraperitoneal chemotherapy strategies. Methods: Using organoid technology, five tumour cultures were generated from malignant ascites and resected peritoneal metastases. These were used in an in vitro HIPEC model to assess sensitivity to mitomycin C (MMC) and oxaliplatin, the drugs used most commonly in HIPEC. The model was also used to test a rational combination treatment involving MMC and inhibitors of the checkpoint kinase ATR. Results: MMC was more effective in eliminating peritoneal metastasis-derived organoids than oxaliplatin at clinically relevant concentrations. However, the drug concentrations required to eliminate 50 per cent of the tumour cells (IC50) were higher than the median clinical dose in two of five organoid lines for MMC, and all five lines for oxaliplatin, indicating a general resistance to monotherapy. ATR inhibition increased the sensitivity of all peritoneal metastasis-derived organoids to MMC, as the IC50 decreased 2.6-12.4-fold to well below concentrations commonly attained in clinical practice. Live-cell imaging and flow cytometric analysis showed that ATR inhibition did not release cells from MMC-induced cell cycle arrest, but caused increased replication stress and accelerated cell death. Conclusion: Peritoneal metastasis-derived organoids can be used to evaluate existing HIPEC regimens on an individual-patient level and for development of more effective treatment strategies.