Abstract
Multiple clinical trials have shown that monoclonal antibodies (mAbs) against programmed death-ligand 1 (PD-1/PD-L1) can benefit patients with lung cancer by increasing their progression-free survival and overall survival. However, a significant proportion of patients do not respond to anti-PD-1/PD-L1 mAbs. In the present study, we investigated whether galectin (Gal)-3 inhibitors can enhance the antitumor effect of PD-L1 blockade. Using the NSCLC-derived cell line A549, we examined the expression of Gal-3 in lung cancer cells under hypoxic conditions and investigated the regulatory effect of Gal-3 on PD-L1 expression, which is mediated by the STAT3 pathway. We also explored whether Gal-3 inhibition can facilitate the cytotoxic effect of T cells induced by PD-L1 blockade. The effects of combined use of a Gal-3 inhibitor and PD-L1 blockade on tumor growth and T-cell function were also investigated, and we found that hypoxia increased the expression and secretion of Gal-3 by lung cancer cells. Gal-3 increased PD-L1 expression via the upregulation of STAT3 phosphorylation, and administration of a Gal-3 inhibitor enhanced the effect of PD-L1 blockade on the cytotoxic activity of T cells against cancer cells in vitro. In a mouse xenograft model, the combination of a Gal-3 inhibitor and PD-L1 blockade synergistically suppressed tumor growth. Furthermore, the administration of a Gal-3 inhibitor enhanced T-cell infiltration and granzyme B release in tumors. Collectively, our results show that Gal-3 increases PD-L1 expression in lung cancer cells and that the administration of a Gal-3 inhibitor as an adjuvant enhanced the antitumor activity of PD-L1 blockade.