LIN28/let-7/PD-L1 Pathway as a Target for Cancer Immunotherapy.

The immunocheckpoint protein PD-1/PD-L1 is considered a promising target for cancer immunotherapeutics. However, the objective response rate using antibodies that block the interaction between PD-1 and PD-L1 was less than 40%, and the mechanism underlying regulation of PD-1/PD-L1 expression is poorly understood. In this study, we identified the miRNA let-7 that posttranscriptionally suppresses PD-L1 expression. LIN28, an RNA binding protein upregulated in most cancer cells, inhibits the biogenesis of let-7, thus promoting PD-L1 expression. Therefore, inhibition of LIN28 may be a strategy to prevent immune evasion of cancer cells. We found that treatment with a LIN28 inhibitor, the small compound C1632, increases let-7 and suppresses PD-L1 expression, leading to reactivation of antitumor immunity in vitro and in vivo In addition, C1632 also displayed the capacity to inhibit cancer cell proliferation and tumor growth in mice. Altogether, these findings identified LIN28/let-7 as a target for PD-L1-mediated immunotherapeutics and reveal the potential of C1632 and its derivatives as promising oncotherapeutic agents. ©2019 American Association for Cancer Research.