Boningmycin induces AMPK-mediated endoplasmic reticulum-associated degradation of PD-L1 protein in human cancer cells.

Anti-PD-1/PD-L1 monoclonal antibodies have displayed remarkable clinical benefits and revolutionized the treatment of multiple tumor types, but the low response rates and immune-related adverse events limit their application, which promoting the development of small molecule agents to improve the efficacy of PD-1/PD-L1 blockade therapy. Boningmycin (BON), a new small molecule belonging to bleomycin (BLM) family, exhibits potent anticancer activity in vitro and in vivo, as well as negligible lung toxicity, thereby can be an alternative of BLM. However, understandings about the anticancer mechanism of BLM-related compounds are extremely rare, it remains unclear if they affect PD-L1 level in a manner similar to that of other antitumor drugs. In this study, we discover that BON significantly reduces PD-L1 protein level in NCI-H460 and HT-1080 cells. Meanwhile, BON decreases the protein level of PD-L1 in a tumor xenograft model of NCI-H460 cells. Nevertheless, the mRNA level is not influenced after BON exposure. Furthermore, BON-induced PD-L1 reduction is proteasome- dependent. By using specific inhibitors and RNA interference technology, we confirm that the decline of PD-L1 protein by BON is mediated by AMPK-activated endoplasmic reticulum-associated degradation pathway, which is like to the action of metformin. Last but not the least, BON has synergism on gefitinib in vitro and in vivo. In conclusion, it is the first report demonstrating that BON decreases PD-L1 protein level through AMPK-mediated endoplasmic reticulum-associated degradation pathway. These findings will benefit the clinical transformation of BON and aid in the elucidation of molecular mechanism of BLM-related compounds.

Nrf2 mediates the resistance of human A549 and HepG2 cancer cells to boningmycin, a new antitumor antibiotic, in vitro through regulation of glutathione levels.

NF-E2-related factor 2 (Nrf2) is a transcription factor and a pivotal factor in the induction of the cell defense system. Recent reports show that Nrf2 plays critical roles in tumor heterogeneity and drug resistance. In the present study we investigated whether and how Nrf2 mediated the resistance of human cancer cells to boningmycin (BON), a new antitumor antibiotic of the bleomycin family. We showed that in the expression levels of Nrf2 in human non-small lung cancer A549 cells were much higher than those in human hepatoblastoma HepG2 cells, and their resistance to BON was opposite to Nrf2 expression (the IC50values of BON in A549 cells and HepG2 cells were 5.97 and 0.61 µmol/L, respectively). Similar results were observed with the anticancer agent cisdiamminedichloroplatinum (DDP), which was used as a positive control. In A549 cells, Nrf2 mRNA knockdown significantly increased their susceptibilities to BON and DDP. An enhanced resistance to BON and DDP was observed in HepG2 cells after overexpression of the wild-type Nrf2 protein. Treatment with a specific Nrf2 inhibitor, luteolin, significantly sensitized A549 cells to BON and DDP and increased BON- or DDP-induced apoptosis. The total levels of glutathione (GSH), the final product of the Nrf2 signaling pathway, were much higher in A549 cells than those in HepG2 cells. Supplementation of GSH in HepG2 cells significantly decreased their susceptibility to BON and DDP, wheras depleting GSH with the specific inhibitor L-buthionine sulfoximine in A549 cells significantly increased their susceptibility to BON and DDP. Our results demonstrate that Nrf2 mediates the resistance to BON through regulating glutathione levels in A549 cells and HepG2 cells.

Effect of boningmycin on expression of capsid protein L1 and serum immune factors in cervical HPV infection patients / 中国生化药物杂志

Objective To investigate the effect of boningmycin on expression of capsid protein L1 and serum immune factors in cervical HPV infection patients.Methods 60 patients with cervical HPV infection were divided into experimental group and control group, 30 cases in each group.The control group were given recombinant human interferon α2b suppository, 100 000 IU, once every other day, and the experiment group were given boningmycin 300 mg intramuscular injection,once every other day.Treatment of 10 times for a course,2 consecutive courses After treatment, the HPV capsid protein L1, serum TNF-α, IL-2, IFN-αand HPV were compared.Results Compared with control group after treatment, the percentage of HPV capsid protein L1 increased ( P <0.05 ) , serum TNF-α, IFN-αlevels increased ( P <0.05 ) , IL-2 decreased ( P <0.05 ) , and HPV positive rate decreased( P <0.05 ).Conclusion Boningmycin could reduce the percentage of capsid protein L1 in patients with cervical human papilloma virus infection, elevate serum TNF-αand IFN-αlevels, reduce the level of IL-2 and HPV positive rate.