Abstract
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 (CysLT1R) levels are associated with poor prognosis in CRC patients. Recently, we have revealed the role of the tumor promoter CysLT1R in drug resistance and stemness in colon cancer (CC) cells. Here, we show the role of the CysLT1R/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 CysLT1R, which enhances Wnt/β-catenin signaling. Therapeutic targeting of CysLT1R with its antagonist montelukast (Mo), as well as CRISPR/Cas9-mediated or doxycycline-inducible functional absence of CysLT1R, negatively regulated PD-L1 expression in CC cells. Interestingly, an anti-PD-L1 neutralizing antibody exhibited stronger effects together with the CysLT1R antagonist in cells (Apcmut or CTNNB1mut) 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 (APCmut) context. Finally, analysis of public dataset showed positive correlations between the PD-L1 and CysLT1R mRNA levels. These results elucidate a previously underappreciated CysLT1R/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.