5-Methoxyflavone inhibits the proliferation of lung adenocarcinoma cells through PI3K/AKT/GSK3β/β-catenin/Cyclin D1 signaling and attenuates chemoresistance and PD-L1 expression.

5-Methoxyflavone, a natural flavonoid compound, has been shown to exhibit pro-apoptotic effects in certain types of cancer. However, its function in lung adenocarcinoma (LUAD) is not known. This study is designed to investigate the anti-tumor effect of 5-methoxyflavone on LUAD. In vitro and in vivo experiments were performed to examine the impact of 5-methoxyflavone on the proliferation of LUAD cells. The target and biological activities of 5-methoxyflavone against LUAD were predicted by bioinformatics analysis. The effect of 5-methoxyflavone on cisplatin resistance was assessed by MTT and RT-qPCR. The programmed death-ligand 1 (PD-L1) expression was determined by western blot and immunofluorescence. 5-Methoxyflavone significantly inhibited the proliferation of LUAD cells by inducing G0/G1-phase arrest. Moreover, it suppressed tumor growth in a xenograft mouse model without causing organ toxicity. Mechanistic studies revealed that 5-methoxyflavone induced proteasomal degradation of cyclin D1 through inactivation of phosphoinositide 3-kinase/protein kinase B/glycogen synthase kinase-3β (PI3K/AKT/GSK3β) signaling. The addition of the AKT activator SC79 or the GSK3β inhibitor SB216763 reversed the reduction of cyclin D1 expression. Furthermore, 5-methoxyflavone might decrease the transcriptional level of cyclin D1 via downregulation of β-catenin expression (substrate of GSK3β). A combination of 5-methoxyflavone and cisplatin acted synergistically to overcome cisplatin resistance and reduced mRNA expression of resistant-associated genes in LUAD cells. Remarkably, 5-methoxyflavone hindered phosphorylation activation of STAT3, thus inhibiting PD-L1 expression in LUAD cells. In summary, we elucidated the anti-proliferative, chemo-sensitizing, and immunomodulatory effects of 5-methoxyflavone against LUAD, providing a potential new drug for the treatment of LUAD.