Emerging roles of the ribonucleotide reductase M2 in colorectal cancer and ultraviolet-induced DNA damage repair

AIM:To investigate the roles of the ribonucleotide reductase M2 (RRM2) subunit in colorectal cancer (CRC) and ultraviolet (UV)-induced DNA damage repair. METHODS:Immunohistochemical staining of tissue microarray was performed to detect the expression of RRM2. Seven CRC cell lines were cultured and three human colon cancer cell lines, i.e., HCT116, SW480 and SW620, were used. Reverse transcription polymerase chain reaction and Western blotting were performed to determine the mRNA and protein expression levels of RRM2, respectively. Cell proliferation assay, cell cycle analysis were performed. Cell apoptosis was evaluated by double staining with fluorescein isothiocyanate-conjugated Annexin Ⅴ and propidium iodide (PI) usingAnnexin Ⅴ/PI apoptosis kit. The motility and invasion of CRC cells were assessed by the Transwell chamber assay. Cells were irradiated with a 254 nm UV-C lamp to detect the UV sensitivity after RRM2 depletion. RESULTS:Immunohistochemical staining revealed elevated RRM2 levels in CRC tissues. RRM2 overexpression was positively correlated with invasion depth (P < 0.05), poorly differentiated type (P = 0.0051), and tumor node metastasis stage (P = 0.0015). The expression of RRM2 in HCT116 cells was downregulated after transfection, and HCT116 cell proliferation was obviously suppressed compared to control groups (P < 0.05). In the invasion test, the number of cells that passed through the chambers in the RRM2-siRNA group was 81 ± 3, which was lower than that in the negative control (289 ± 7) and blank control groups (301 ± 7.2). These differences were statistically significant (P < 0.01). Our data suggest that RRM2 overexpression may be associated with CRC progression. RRM2 silencing by siRNA may inhibit the hyperplasia and invasiveness of CRC cells, suggesting that RRM2 may play an important role in the infiltration and metastasis of CRC, which is a potential therapeutic strategy in CRC. In addition, RRM2 depletion increased UV sensitivity. CONCLUSION:These findings suggest that RRM2 may be a facilitating factor in colorectal tumorigenesis and UV-induced DNA damage repair.

Screening of traditional Chinese medicine monomers as ribonucleotide reductase M2 inhibitors for tumor treatment

BACKGROUND Ribonucleotide reductase(RR)is a key enzyme in tumor proliferation,especially its subunit-RRM2.Although there are multiple therapeutics for tumors,they all have certain limitations.Given their advantages,traditional Chinese medicine(TCM)monomers have become an important source of anti-tumor drugs.Therefore,screening and analysis of TCM monomers with RRM2 inhibition can provide a reference for further anti-tumor drug development.AIM To screen and analyze potential anti-tumor TCM monomers with a good binding capacity to RRM2.METHODS The Gene Expression Profiling Interactive Analysis database was used to analyze the level of RRM2 gene expression in normal and tumor tissues as well as RRM2's effect on the overall survival rate of tumor patients.TCM monomers that potentially act on RRM2 were screened via literature mining.Using AutoDock software,the screened monomers were docked with the RRM2 protein.RESULTS The expression of RRM2 mRNA in multiple tumor tissues was significantly higher than that in normal tissues,and it was negatively correlated with the overall survival rate of patients with the majority of tumor types.Through literature mining,we discovered that berberine,ursolic acid,gambogic acid,cinobufagin,quercetin,daphnetin,and osalmide have inhibitory effects on RRM2.The results of molecular docking identified that the above TCM monomers have a strong binding capacity with RRM2 protein,which mainly interacted through hydrogen bonds and hydrophobic force.The main binding sites were Arg330,Tyr323,Ser263,and Met350.CONCLUSION RRM2 is an important tumor therapeutic target.The TCM monomers screened have a good binding capacity with the RRM2 protein.

Overexpression of catalytic subunit M2 in patients with ovarian cancer

Background The formation and growth of tumors are related to the synthesis of the DNA. The enzyme ribonucleotide reductase （RR） is an enzyme that regulates the total rate of DNA synthesis and thus plays a pivotal role in cell growth. Catalytic subunit M2 （RRM2） is the main unit modulating the ribonucleotide reductase enzymatic activity. This study aimed to investigate the expression of RRM2 mRNA and protein in patients with ovarian cancer and its relevance to diagnosis and clinical outcome of the patients. Methods RRM2 mRNA levels and protein expression were detected in 98 ovarian specimens with immunohistochemistry and real-time quantitative polymerase chain reaction （PCR）. Expression of the RRM2 protein and correlation of the RRM2 gene expression with clinical pathological features were analyzed. The Kaplan-Meier test was used for evaluating RRM2 expression and time to progression and survival. The Cox proportional model was used to analyze the risk factors in prognosis of patients. Results Positive RRM2 immunostaining was found in 43 of 62 （69.4%） patients with epithelial ovarian cancer, 10 of 15 （66.7%） patients with borderline neoplasm, 4 of 15 （26.7%） patients with benign growths, and none of the normal group. The RRM2 mRNA levels were significantly over expressed in epithelial ovarian cancer （1.722＋0.639） and borderline ovarian neoplasms （1.365＋0.615）, compared to the normal group （0.678＋0.446） and benign group （0.828_＋0.545）. Patients with ovarian caner in clinical FIGO-stages Ill-IV presented higher RRM2 gene expression than those in clinical FIGO-stages I-I1. Furthermore, the survival of patients with low RRM2 mRNA level was significantly better than patients with high levels （P 〈0.05）. By Cox proportional risk model analysis, the risk of mortality of patients with high level expression of RRM2 mRNA was 2.553 times greater than those with low expression. Conclusion RRM2 expression closely correlates with the development of ovarian tumor and may serve as a novel predictive marker for diagnosis and prognosis of the disease.

Development of gemcitabine-resistant patient-derived xenograft models of pancreatic ductal adenocarcinoma

Aim:Gemcitabine is a frontline agent for locally-advanced and metastatic pancreatic ductal adenocarcinoma(PDAC),but neither gemcitabine alone nor in combination produces durable remissions of this tumor type.We developed three PDAC patient-derived xenograft(PDX)models with gemcitabine resistance(gemR)acquired in vivo,with which to identify mechanisms of resistance relevant to drug exposure in vivo and to evaluate novel therapies.Methods:Mice bearing independently-derived PDXs received 100 mg/kg gemcitabine once or twice weekly.Tumors initially responded,but regrew on treatment and were designated gemR.We used immunohistochemistry to compare expression of proteins previously associated with gemcitabine resistance[ribonucleotide reductase subunit M1(RRM1),RRM2,human concentrative nucleoside transporter 1(hCNT1),human equilibrative nucleoside transporter 1(hENT1),cytidine deaminase(CDA),and deoxycytidine kinase(dCK)]in gemR and respective gemcitabine-naïve parental tumors.Results:Parental and gemR tumors did not differ in tumor cell morphology,amount of tumor-associated stroma,or expression of stem cell markers.No consistent pattern of expression of the six gemR marker proteins was observed among the models.Increases in RRM1 and CDA were consistent with in vitro-derived gemR models.However,rather than the expected decreases of hCNT1,hENT1,and dCK,gemR tumors expressed no change in or higher levels of these gemR marker proteins than parental tumors.Conclusion:These models are the first PDAC PDX models with gemcitabine resistance acquired in vivo.The data indicate that mechanisms identified in models with resistance acquired in vitro are unlikely to be the predominant mechanisms when resistance is acquired in vivo.Ongoing work focuses on characterizing unidentified mechanisms of gemR and on identifying agents with anti-tumor efficacy in these gemR models。