The tumor promoter cysteinyl leukotriene receptor 1 regulates PD-L1 expression in colon cancer cells via the Wnt/β-catenin signaling axis.

Immunotherapy targeting programmed death-ligand 1 (PD-L1) or PD-1 in solid tumors has been shown to be clinically beneficial. However, in colorectal cancer (CRC), only a subset of patients benefit from PD-1/PD-L1 treatment. Previously, we showed that high cysteinyl leukotriene receptor 1 (CysLTR) levels are associated with poor prognosis in CRC patients. Recently, we have revealed the role of the tumor promoter CysLTR in drug resistance and stemness in colon cancer (CC) cells. Here, we show the role of the CysLTR/Wnt/β-catenin signaling axis in the regulation of PD-L1 using both in vitro and in vivo preclinical model systems. Interestingly, we found that both endogenous and IFNγ-induced PD-L1 expression in CC cells is mediated through upregulation of CysLTR, which enhances Wnt/β-catenin signaling. Therapeutic targeting of CysLTR with its antagonist montelukast (Mo), as well as CRISPR/Cas9-mediated or doxycycline-inducible functional absence of CysLTR, negatively regulated PD-L1 expression in CC cells. Interestingly, an anti-PD-L1 neutralizing antibody exhibited stronger effects together with the CysLTR antagonist in cells (Apc or CTNNB1) with either endogenous or IFNγ-induced PD-L1 expression. Additionally, mice treated with Mo showed depletion of PD-L1 mRNA and protein. Moreover, in CC cells with combined treatment of a Wnt inhibitor and an anti-PD-L1 antibody was effective only in β-catenin-dependent (APC) context. Finally, analysis of public dataset showed positive correlations between the PD-L1 and CysLTR mRNA levels. These results elucidate a previously underappreciated CysLTR/Wnt/β-catenin signaling pathway in the context of PD-L1 inhibition in CC, which might be considered for improving the efficacy of anti-PD-L1 therapy in CC patients. Video Abstract.