Inhibition of CCT5-mediated asparagine biosynthesis and anti-PD-L1 produce synergistic antitumor effects in colorectal cancer.

Abnormal amino acid metabolism promotes tumor progression by inducing malignant behaviors in tumor cells and altering the immune landscape within the tumor microenvironment. However, the underlying mechanisms remain unclear. In this study, we constructed colorectal cancer (CRC) organoids and patient-derived tumor xenograft (PDX) models, performing multifaceted validation to confirm that T-complex protein 1 subunit epsilon (CCT5), mediates the biosynthesis of aspartate and enhances sensitivity to anti-PD-L1 immunotherapy. Mechanistically, CCT5 directly binds to asparagine synthetase (ASNS) and promotes the synthesis of aspartate (Asn). The Asn-mTORC1 axis facilitates tumor cell proliferation while upregulating PD-L1 expression, which leads to a reduction in the number of effector CD8(+) T cells. Treatment with l-asparaginase (ASNase) combined with anti-PD-L1 therapy effectively reverses the growth of CRC characterized by high CCT5 expression. In summary, we identify CCT5 as a potential biomarker to guide the combined use of ASNase and anti-PD-L1 antibodies in CRC treatment.