Modulation of Rad51, ERCC1, and thymidine phosphorylase by emodin result in synergistic cytotoxic effect in combination with capecitabine.

Thymidine phosphorylase (TP) is the rate-limiting enzyme for the activation of capecitabine (pro-drug of fluorouracil), and as a useful predictor of tumor response to capecitabine-based chemotherapy. Overexpression of Rad51 and ERCC1 induce resistance to chemotherapeutic agents. Emodin, one of the main bioactive anthraquinone derivatives in the roots and rhizomes of numerous plants, possesses potent antitumor effects. Accordingly, we aimed to explore the molecular mechanism of emodin enhances the capecitabine-induced cytotoxicity through controlling Rad51, ERCC1, and TP expression in human non-small cell lung cancer (NSCLC). The results show that capecitabine increases the phosphorylation of MKK1/2-ERK1/2 and protein levels of Rad51 and ERCC1 through enhancing the protein stability. Depletion of endogenous Rad51 or ERCC1 expression by specific small interfering RNA transfection significantly increases capecitabine-induced cell death and growth inhibition. Emodin enhances the capecitabine-induced cytotoxic effects through ERK1/2 inactivation and decreasing the Rad51 and ERCC1 protein levels induced by capecitabine. Enhancement of ERK1/2 signaling by constitutively active MKK1/2 (MKK1/2-CA) results in increasing Rad51 and ERCC1 protein levels and cell viability in NSCLC cell lines treated with emodin and capecitabine. Interestingly, emodin enhances TP mRNA and protein expression in capecitabine treated NSCLC cell lines, and depletion of the TP expression decreases the cytotoxic effects induced by capecitabine and emodin. We conclude that enhancing the cytotoxicity to capecitabine by emodin is mediated by down-regulation the expression of Rad51 and ERCC1 and up-regulation TP expression.

Analysis of the changes in bacterial types and drug sensitivity profiles of mycobacterial strains in Guangzhou over the last twelve years / 中华预防医学杂志

<p><b>OBJECTIVE</b>To improve evidence-based care in the management of tuberculosis, we retrospectively analyzed the bacterial types and drug sensitivity test results of mycobacteria in Guangzhou over the past twelve years (from July 1998 to March 2010).</p><p><b>METHODS</b>Over these twelve years, a total of 14 095 mycobacterial strains isolated from different samples were subjected to type identification and drug sensitivity tests according to the Standard Protocols of Laboratory Diagnostics for Tuberculosis by the Chinese Antituberculosis Association. Chi-square test was performed for statistical analyses for comparisons between groups.</p><p><b>RESULTS</b>Of 14 095 strains of mycobacteria isolated, 10 844 strains (76.84%) were MTB, and 3251 strains (23.16%) were non-tuberculosis mycobacteria (NTM). Compared with the result of the fourth national survey of tuberculosis epidemiology, which showed 11.1% of NTM, the one of our study was significantly different (χ(2) = 69.79, P < 0.001). Drug sensitivity tests of MTB showed tolerance rates of 28.99% (2729/9413), 21.75% (2047/9413), 17.45% (1643/9413) and 11.53% (1085/9413) against isoniazid, rifampin, streptomycin and ethambutol, respectively.</p><p><b>CONCLUSION</b>An increasing trend was observed in MTB drug tolerance against streptomycin, rifampin and isoniazid, whereas more and more NTM strains were isolated in recent years. These findings are worthy of note for clinicians.</p>

Down-regulation of Rad51 expression overcomes drug resistance to gemcitabine in human non-small-cell lung cancer cells.

Gemcitabine (2',2'-difluorodeoxycytidine), a deoxycytidine analog, and erlotinib, an epidermal growth factor receptor-tyrosine kinase inhibitor, are used clinically to treat patients with non-small-cell lung cancer (NSCLC). However, the molecular mechanisms for the drug resistance of gemcitabine in NSCLC cells are poorly understood. In this study, we used constructs containing human Rad51 cDNA or specific Rad51 small interfering RNA (siRNA) to examine the role of Rad51 in chemoresistance of gemcitabine in three different human NSCLC cell lines. Exposure of human NSCLC cell lines to gemcitabine increased the phosphorylation levels of mitogen-activated protein kinase kinase (MKK) 1/2-extracellular signal-regulated kinase (ERK) 1/2 and AKT in a time- and dose-dependent manner, which was accompanied by an induction of Rad51 mRNA and protein expression. Gemcitabine increased the expression of Rad51 by increasing its mRNA and protein stability. Blockage of ERK1/2 or AKT activation by 1,4-diamino-2,3-dicyano-1,4-bis(methylthio)butadiene (U0126; MKK1/2 inhibitor) or 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002; phosphatidyl inositol 3-kinase inhibitor), respectively, decreased the gemcitabine-induced Rad51 expression. Gemcitabine-induced cytotoxicity was significantly increased using siRNA depletion of Rad51 or blockage of ERK1/2 and AKT activation. Erlotinib enhanced the gemcitabine-induced cytotoxicity via the inactivation of ERK1/2 and AKT and the down-regulation of Rad51. Enforced expression of constitutively active MKK1/2 or AKT recovered cell viability and Rad51 protein levels that were decreased by the combination of erlotinib and gemcitabine. Suppression of Rad51 expression or the inactivation of ERK1/2 or AKT signaling may be considered potential therapeutic modalities for gemcitabine-resistant lung cancer.