Abstract
Programmed death-ligand 1 (PD-L1) is an immune checkpoint molecule, that is overexpressed in non-small cell lung cancer (NSCLC) and has been associated with the response to anti-PD-1/PD-L1 immunotherapy. Z-guggulsterone (Z-GS), an active compound extracted from the gumresin of the Commiphora mukul tree, has been shown to have anti-tumor effects in NSCLC in our previous study. However, whether Z-GS could affect PD-L1 expression levels in tumor cells remains unknown. In this study, we verified the inhibitory effects of Z-GS on NSCLC cell viability and cell cycle progression in vitro, and mouse Lewis lung carcinoma (LLC) tumor growth in vivo. Notably, Z-GS treatment increased PD-L1 surface and mRNA expression levels, and gene transcription in NSCLC cells, in a dose- and time-dependent manner. Mechanistic experiments showed that the upregulation of PD-L1 was mediated, partly by farnesoid X receptor inhibition, and partly by the activation of the Akt and Erk1/2 signaling pathways in Z-GS-treated NSCLC cells. In vivo, Z-GS treatment dose-dependently increased PD-L1 expression levels in mouse LLC tumor models. Overall, our findings demonstrated a promoting role for Z-GS in PD-L1 expression in NSCLC and provided mechanistic insights, that may be used for further investigation into synergistic combined therapies.