Metabolic plasticity underlying resistance to anti-PD1 retifanlimab and the arginase inhibitor CB-1158, in microsatellite-stable colorectal cancer patient-derived organoids co-cultured with tumor-infiltrating lymphocytes

Aim Cancer immunotherapies show low activity in metastatic microsatellite-stable (MSS) colorectal cancer (CCR) patients. Arginase 1 inhibitors have shown activity in pre-clinical animal models associated with PD-1 inhibitors but failed in clinical trials. Therefore, we evaluated this combination, in co-cultures of metastatic MSS CCR patient-derived organoids (PDOs) and expanded autologous tumor-infiltrating lymphocytes (TILs). Methods We established a platform with co-cultures of metastatic MSS PDOs and expanded TILs and perform transcriptomics and metabolomic analysis to evaluate the efficacy of retifanlimab (PD-1 inhibitor), CB-1158 (arginase inhibitor), and their combination. Results T-cell PDOs recognition was observed in co-cultures versus T cells alone. CB-1158, retifanlimab and CB-1158 plus retifanlimab failed to increase T-cell PDOs recognition and T-cell cytotoxic effects. Treatment with CB-1158-arginase inhibitor resulted in decrease of ornithine production, with respect to untreated co-cultures. Glutamine and histidine consumption, that are precursors of ornithine synthesis, increased upon CB-1158 to guarantee polyamines synthesis. Arginine and citrulline exchange fluxes did not change, confirming that CB-1158 inhibited arginase activity in PDOs. Combined analysis of transcriptomics and metabolomics data, revealed an intrinsic urea-cycle dysregulation metabolic program and a glutamine-dependent polyamines synthesis, that differs from murine colorectal cancer cell models used to test immune checkpoint blockade therapies and sustains an immune-suppressive arginase-independent model. Conclusions These results provide a putative metabolic mechanism that contributes to resistance to both monotherapy and combination therapy, with Arginase 1 and PD-1 inhibitors and explain the poor clinical activity in clinical trials. Clinical trial number Not applicable.