RESUMO
Cisplatin plus 5-fluorouracil (PF) is used as the standard neoadjuvant chemotherapy (also called preoperative chemotherapy) in the treatment of tongue squamous cell carcinoma (TSCC). Although PF chemotherapy reduces the distant metastasis of TSCC, the five-year survival rate has not significantly improved. In recent years, components considered in traditional Chinese medicine have been researched as adjuvant drugs for radiotherapy and chemotherapy. Plumbagin (PB) is a quinone component isolated from Plumbago zeylanica L. Notably, PB demonstrates numerous anticancer properties. In order to examine the chemosensitization effect of PB on PF and its associated mechanisms, in vitro experiments using TSCC Cal27 and cisplatin (CDDP)-resistant Cal27/CDDP cells were carried out in the present study, and the results were subsequently verified using nude mice xenografts. Results of the present study demonstrated that PB enhanced the anticancer effects of PF on the proliferation, migration, and invasion of Cal27 and Cal27/CDDP cells. Cell cycle assays demonstrated that both Cal27 and Cal27/CDDP cells were arrested in the S phase following the combined treatment of PF and PB. Moreover, the PF and PB combination group induced higher levels of apoptosis in Cal27 and Cal27/CDDP cells compared with the group treated with PF alone. In addition, the results of the present study demonstrated that combined PB and PF inhibited the PI3K/AKT/mTOR/p70S6K pathway in TSCC cells. Moreover, the weight and volumes of tumors in nude mice were reduced following treatment with a combination of PF and PB. Results of the present study also demonstrated that the expression levels of Ki67 were markedly reduced in the combined treatment group compared with the group treated with PF alone. In summary, the results of the present study demonstrated that PB enhanced the PF sensitivity of TSCC through induction of S-phase arrest and apoptosis via the PI3K/AKT/mTOR/p70S6K pathway.
RESUMO
OBJECTIVES: To evaluate the inhibitory effect and mechanism of plumbagin (PLB) against drug-resistant tongue squamous cell carcinoma (TSCC), and whether its antitumour effect is not affected by tumour drug resistance. METHODS: TSCC sensitive CAL27 cells and drug-resistant CAL27/RE cells were used to study the cytotoxicity and mechanism of PLB in vitro, including CCK-8 analysis, colony formation, DAPI staining, flow cytometry assay, transmission electron microscopy, western blotting assay, autophagy, apoptosis and ROS fluorescent probes. BALB/c nude mice xenograft models were used to study the growth inhibitory effect of PLB in vivo. KEY FINDINGS: The results showed that the cell viability and proliferation inhibition and apoptosis induction abilities of PLB on drug-resistant cells were more obvious than that on sensitive cells. And PLB induced protective autophagy in TSCC cells. Mechanistically, PLB induced apoptosis and autophagy by generating reactive oxygen species to mediate JNK and AKT/mTOR pathways. Finally, the growth inhibitory effect of PLB against drug-resistant TSCC was also confirmed in vivo. CONCLUSIONS: PLB will be a promising anticancer agent to overcome drug-resistant TSCC without being affected by its drug resistance properties.