Inhibiting RRM2 to enhance the anticancer activity of chemotherapy.

RRM2, the small subunit of ribonucleotide reductase, is identified as a tumor promotor and therapeutic target. It is common to see the overexpression of RRM2 in chemo-resistant cancer cells and patients. RRM2 mediates the resistance of many chemotherapeutic drugs and could become the predictor for chemosensitivity and prognosis. Therefore, inhibition of RRM2 may be an effective means to enhance the anticancer activity of chemotherapy. This review tries to discuss the mechanisms of RRM2 overexpression and the role of RRM2 in resistance to chemotherapy. Additionally, we compile the studies on small interfering RNA targets RRM2, RRM2 inhibitors, kinase inhibitors, and other ways that could overcome the resistance of chemotherapy or exert synergistic anticancer activity with chemotherapy through the expression inhibition or the enzyme inactivation of RRM2.

Identification of osalmid metabolic profile and active metabolites with anti-tumor activity in human hepatocellular carcinoma cells.

BACKGROUNDS: Ribonucleotide reductase (RR) catalyzes the essential step in the formation of all four deoxynucleotides. Upregulated activity of RR plays an active role in tumor progression. As the regulatory subunit of RR, ribonucleotide reductase subunit M2 (RRM2) is regarded as one of the effective therapeutic targets for DNA replication-dependent diseases, such as cancers. Recent studies have revealed that osalmid significantly inhibits the activity of RRM2, but the metabolic profile of osalmid remains unknown. OBJECTIVE: The aim of this study was to clarify the metabolic profile including metabolites, isoenzymes and metabolic pathways of osalmid. The anti-human hepatocellular carcinoma activity and mechanism of metabolites were further investigated. MATERIALS AND METHODS: Ultra high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS) was used for identifying metabolites and for characterizing phase I and phase II metabolic pathways with recombinant enzymes or in human liver microsomes of osalmid. The eHiTS docking system was used for potential RRM2 inhibitor screening among metabolites. Cytotoxicity assays were performed for evaluating cell proliferation inhibitory activity of metabolites. Cell cycle assays and cell apoptosis assays were assessed by flow cytometry. Western blotting analysis of RRM2, cyclin D1, p21, p53, phosphorylated p53, Bcl-2 and Bax was performed to explore the anti-hepatocellular carcinoma mechanism of the active metabolites. RESULTS: Ten metabolites of osalmid were identified, and none of them have been reported previously. Hydroxylation, glucuronidation, sulfonation, acetylation and degradation were recognized as the main metabolic processes of osalmid. Isozymes of CYP1A2, CYP2C9, UGT1A1, UGT1A6, UGT1A9, UGT2B7 and UGT2B15 were involved in phase I and phase II metabolism of osalmid. Metabolites M7, M8 and M10 showed higher binding affinities with the RRM2 active site than osalmid. Metabolite M7 exhibited potent inhibitory activity to hepatocellular carcinoma cell lines by both competitive inhibition and down-regulation of RRM2. Moreover, M7 significantly induced cell cycle arrest and apoptosis by activating p53-related pathways. CONCLUSIONS: The metabolic profile of osalmid was identified. M7 significantly inhibited human hepatocellular carcinoma progression by inhibiting RRM2 activity. Furthermore, M7 induced cell cycle arrest and apoptosis by activating p53-related signaling pathways.

A novel multitarget kinase inhibitor BZG with potent anticancer activity in vitro and vivo enhances efficacy of sorafenib through PI3K pathways in hepatocellular carcinoma cells.

OBJECTIVES: BZG as a novel multitarget kinase inhibitor, has been proved to inhibit the proliferation of hepatocellular carcinoma (HCC) previously. In this study, we aimed at investigating the underlying mechanisms of BZG with and without sorafenib and evaluating their anti-tumor effects as well as whether BZG could inhibit the activation of phosphoinositide 3-kinase (PI3K)/AKT signaling which is associated with acquired resistance to sorafenib. METHODS: We evaluated the proliferation of HCC cells by CCK-8 assay and colony formation assay. Cell apoptosis was assessed by Hoechst 33342 staining assay and flow cytometry. Western blot was used to detect the critical enzymes in the PI3K pathways and the expression of p-ERK after BZG alone and combined with sorafenib treatments. Huh-7 hepatocellular carcinoma xenograft model was used to evaluate the anti-carcinoma effects of BZG alone and in combination in vivo. HE staining and TUNEL assay tested the necrosis of tumor tissue and apoptosis of tumor cells. RESULTS: BZG could inhibit the proliferation of HCC cells in a dose-dependent manner. The combination of BZG and sorafenib produced synergistic effects. PI3K and p-ERK pathway were involved in the anti-tumor functions of BZG alone and when combined with sorafenib. In addition, the combination treatment was seen to be more effective in inhibiting the expression of p-AKT, p-ERK and p-mTOR. Furthermore, Tumor necrosis and cell apoptosis were also observed in Huh-7 hepatocellular carcinoma xenograft models. CONCLUSIONS: BZG is an attractive agent for treating HCC. The effects of BZG and sorafenib's co-treatment on HCC are more effective than BZG or sorafenib alone.