No abstract

Etoposide (VP-16), a topoisomerase II inhibitor, is an effective anti-cancer drug used for the treatment of non-smallcell lung cancer (NSCLC). Resveratrol is a naturally occurring polyphenolic compound that has been proved to have anti-cancer activity. XRCC1 is an important scaffold protein involved in base excision repair that is regulated by ERK1/2 and AKT signals and plays an important role in the development of lung cancer. However, the role of ERK1/2 and AKT-mediated XRCC1 expression in etoposide treatment alone or combined with resveratrol-induced cytotoxicity in NSCLC cells has not been identified. In this study, etoposide treatment increased XRCC1 mRNA and protein expression through AKT and ERK1/2 activation in two NSCLC cells, H1703 and H1975. Knockdown of XRCC1 in NSCLC cells by transfection of XRCC1 siRNA or inactivation of ERK1/2 and AKT resulted in enhancing cytotoxicity and cell growth inhibition induced by etoposide. Resveratrol inhibited the expression of XRCC1 and enhanced the etoposide-induced cell death and anti-proliferation effect in NSCLC cells. Furthermore, transfection with constitutive active MKK1 or AKT vectors could rescue the XRCC1 protein level and also the cell survival suppressed by co-treatment with etoposide and resveratrol. These findings suggested that down-regulation of XRCC1 expression by resveratrol can enhance the chemosensitivity of etoposide in NSCLC cells.Lung cancer, the leading cause of cancer death in the world, is classified as non-small-cell lung cancer (NSCLC) and small-cell lung cancer [1]. NSCLC accounts for 85% of lung cancer cases, and despite aggressive radio-and/or chemotherapy, fewer than 20% of patients reach a 5-year survival. This poor treatment outcome is due to the primary or acquired drug resistance of NSCLC cells to present cytotoxic therapeutic agents [2,3].Etoposide is an epipodophyllotoxin employed in the therapy of a wide spectrum of cancers [4][5][6]. In vitro studies have shown that etoposide increases topoisomerase II-mediated DNA breakage primarily by inhibiting the ability of the enzyme to religate cleaved nucleic acid molecules [7]. XRCC1 (X-ray repair cross-complementing group 1) is a key mediator of base excision repair (BER). Deficiency of XRCC1 in mice results in embryonic lethality [8,9]. XRCC1 interacts with enzymatic factors such as polyadenosine diphosphate (ADP)-ribose polymerase, DNA ligase III and DNA polymerase b to facilitate efficient repair of DNA single-strand breaks (SSBs) [10]. Down-regulation of XRCC1 expression in human breast cancer cell lines resulted in decreased SSB repair capacity and hypersensitivity to methyl methane sulphonate (MMS) [11]. A previous study has shown that the PI3K-AKT pathway regulates the basal expression of XRCC1 in non-irradiated cells, and MKK1/2-ERK1/2 is essential for the induction of XRCC1 after exposure to radiation [12]. However, whether ERK1/2 and AKT signals involve in regulating XRCC1 expression upon etoposide treatment and its role in the etoposide-induced cytotoxicity in NSCL...

No abstract

No abstract

No abstract

No abstract

No abstract

Tamoxifen is a triphenylethylene nonsteroidal antiestrogen used worldwide as an adjuvant chemotherapeutic agent in the treatment of breast cancer. However, the molecular mechanism of tamoxifen also could induce cytotoxicity in non-small cell lung cancer (NSCLC) cells have not been proved. In this study, tamoxifen treatment inhibited cell survival in two NSCLC cells, H520 and H1975. Treatment with tamoxifen decreased TP mRNA and protein levels in an AKT inactivation-dependent manner. Furthermore, expression of constitutively active AKT (AKT-CA) vectors significantly rescued the decreased TP protein and mRNA levels in tamoxifen-treated NSCLC cells. In contrast, a combination of PI3K inhibitors (LY294002 or wortmannin) further decreased the TP expression and cell viability induced by tamoxifen. Moreover, knocking down TP expression by transfection with small interfering RNA of TP enhanced the cytotoxicity and growth inhibition of tamoxifen. Erlotinib (Tarceva, OSI-774), an orally available inhibitor of epidermal growth factor receptor (EGFR) tyrosine kinase, is approved for clinical use in the NSCLC therapy. Compared to each single treatment, the combining tamoxifen with erlotinib resulted in a synergistically inhibited the cell viability and cell growth, accompanied with the reduction of phospho-AKT, phosph-ERK1/2, and TP protein levels. An enhancement of AKT or ERK1/2 activation by transfecting the cancer cells with constitutively active AKT or MKK1/2 expression vectors significantly restored the two drugs combination-reduced TP protein levels as well as cell viability. Taken together, our results suggest that the down-modulation of AKT and ERK1/2-mediated TP expression by erlotinib represents a key factor in enhancing the cytotoxic effects of tamoxifen in NSCLC cells. Citation Format: Yun-Wei Lin, Hsien-Chun Chiu, Jhan-Jhang Syu, Yun-Ting Jian, Chien-Yu Chen. Enhancement of thymidine phosphorylase downregulation by erlotinib enhances cytotoxicity affected by tamoxifen in human non-small cell lung cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr A33. doi: 10.1158/1557-3125.RASONC14-A33