O6‐methylguanine DNA methyltransferase repairs platinum‐DNA adducts following cisplatin treatment and predicts prognoses of nasopharyngeal carcinoma

Cisplatin (CDDP) is an important anti‐cancer drug commonly used in various human cancers, including nasopharyngeal carcinoma (NPC). How to overcome the drug resistance of CDDP provides opportunities to improve clinical outcomes of NPC. O⁶‐methylguanine–DNA methyltransferase (MGMT) has been well‐characterized to be a therapeutic determinant of O⁶‐alkylguanine alkylating drugs. However, the underlying mechanism and clinical relevance between MGMT and CDDP remain poorly defined in NPC. In this study, we showed that MGMT‐proficient cells were highly resistant to the cytotoxic effects of CDDP as compared to MGMT‐deficient cells. Further studies showed that the platinum level of DNA after CDDP exposure was significantly lower in MGMT‐proficient cells than in MGMT‐deficient cells. Host cell reactivation assay revealed that MGMT protected NPC cells from CDDP‐induced DNA damage by enhancing DNA repair capacity. Importantly, we demonstrated for the first time that MGMT protein directly bound to CDDP‐induced DNA damages. Subsequently, CDDP‐bound MGMT protein became ubiquitinated and was degraded through ubiquitin‐mediated proteasome system. We further analyzed the relationship between MGMT expression and clinical survivals in a cohort of 83 NPC patients. NPC patients who received CDDP‐based concurrent chemoradiotherapy (CCRT), with high MGMT expression level, exhibited shorter progression‐free survival (PFS; p = 0.022) and overall survival (OS; p = 0.015), than patients with low MGMT expression level. Furthermore, high MGMT expression level remained to be an independent prognostic factor for worse PFS (p = 0.01, hazard ratio 2.23) and OS (p = 0.018, hazard ratio 2.14). Our findings suggest that MGMT protein is important to determine the efficacy of CDDP in NPC.     

Pomegranate extract inhibits migration and invasion of oral cancer cells by downregulating matrix metalloproteinase‐2/9 and epithelial‐mesenchymal transition

Discovering drug candidates for the modulation of metastasis is of great importance in inhibiting oral cancer malignancy. Although most pomegranate extract applications aim at the antiproliferation of cancer cells, its antimetastatic effects remain unclear, especially for oral cancer cells. The aim of this study is to evaluate the change of two main metastasis characters, migration and invasion of oral cancer cells. Further, we want to explore the molecular mechanisms of action of pomegranate extract (POMx) at low cytotoxic concentration. We found that POMx ranged from 0 to 50 μg/mL showing low cytotoxicity to oral cancer cells. In the case of oral cancer HSC‐3 and Ca9‐22 cells, POMx inhibits wound healing migration, transwell migration, and matrix gel invasion. Mechanistically, POMx downregulates matrix metalloproteinase (MMP)‐2 and MMP‐9 activities and expressions as well as epithelial‐mesenchymal transition (EMT) signaling. POMx upregulates extracellular signal‐regulated kinases 1/2 (ERK1/2), but not c‐Jun N‐terminal kinase (JNK) and p38 expression. Addition of ERK1/2 inhibitor (PD98059) significantly recovered the POMx‐suppressed transwell migration and MMP‐2/?9 activities in HSC‐3 cells. Taken together, these findings suggest to further test low cytotoxic concentrations of POMx as a potential antimetastatic therapy against oral cancer cells.