Hsien-Chun Chiu

Metformin-mediated downregulation of p38 mitogen-activated protein kinase-dependent excision repair cross-complementing 1 decreases DNA repair capacity and sensitizes human lung cancer cells to paclitaxel

Metformin, an extensively used and well-tolerated drug for treating individuals with type 2 diabetes, has recently gained significant attention as an anticancer drug. On the other hand, paclitaxel (Taxol) is a new antineoplastic drug that has shown promise in the treatment of non-small cell lung cancer (NSCLC). High expression levels of excision repair cross-complementary 1 (ERCC1) in cancers have been positively associated with the DNA repair capacity and a poor prognosis in NSCLC patients treated with platinum-containing chemotherapy. In this current study, paclitaxel was found to increase phosphorylation of mitogen-activated protein kinase (MAPK) kinase 3/6 (MKK3/6)-p38 MAPK as well as protein and mRNA levels of ERCC1 in H1650 and H1703 cells. Moreover, paclitaxel-induced ERCC1 protein and mRNA levels significantly decreased via the downregulation of p38 activity by either a p38 MAPK inhibitor SB202190 or p38 knockdown with specific small interfering RNA (siRNA). Specific inhibition of ERCC1 with siRNA was found to enhance the paclitaxel-induced cytotoxic effect and growth inhibition. Furthermore, metformin was able to not only decrease the paclitaxel-induced p38 MAPK-mediated ERCC1 expression, but also augment the cytotoxic effect induced by paclitaxel. Finally, expression of constitutive activate MKK6 or HA-p38 MAPK vectors in lung cancer cells was able to abrogate ERCC1 downregulation by metformin and paclitaxel as well as cell viability and DNA repair capacity. Overall, our results suggest that inhibition of the p38 MAPK signaling by metformin coupled with paclitaxel therapy in human NSCLC cells may be a clinically useful combination, which however will require further validation.

Tamoxifen enhances erlotinib-induced cytotoxicity through down-regulating AKT-mediated thymidine phosphorylase expression in human non-small-cell lung cancer cells

Tamoxifen is a triphenylethylene nonsteroidal estrogen receptor (ER) antagonist used worldwide as an adjuvant hormone therapeutic agent in the treatment of breast cancer. However, the molecular mechanism of tamoxifen-induced cytotoxicity in non-small cell lung cancer (NSCLC) cells has not been identified. Thymidine phosphorylase (TP) is an enzyme of the pyrimidine salvage pathway which is upregulated in cancers. In this study, tamoxifen treatment inhibited cell survival in two NSCLC cells, H520 and H1975. Treatment with tamoxifen decreased TP mRNA and protein levels through AKT inactivation. 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, combination treatment with PI3K inhibitors (LY294002 or wortmannin) and tamoxifen further decreased the TP expression and cell viability of NSCLC cells. Knocking down TP expression by transfection with small interfering RNA of TP enhanced the cytotoxicity and cell growth inhibition of tamoxifen. Erlotinib (Tarceva, OSI-774), an orally available small molecular inhibitor of epidermal growth factor receptor (EGFR) tyrosine kinase, is approved for clinical treatment of NSCLC. Compared to a single agent alone, tamoxifen combined with erlotinib resulted in cytotoxicity and cell growth inhibition synergistically in NSCLC cells, accompanied with reduced activation of phospho-AKT and phospho-ERK1/2, and reduced TP protein levels. These findings may have implications for the rational design of future drug regimens incorporating tamoxifen and erlotinib for the treatment of NSCLC.

Metformin Induces Cytotoxicity by Down‐Regulating Thymidine Phosphorylase and Excision Repair Cross‐Complementation 1 Expression in Non‐Small Cell Lung Cancer Cells

Metformin is an antidiabetic drug recently shown to inhibit cancer cell proliferation and growth, although the involved molecular mechanisms have not been elucidated. In many cancer cells, high expression of thymidine phosphorylase (TP) and Excision repair cross‐complementation 1 (ERCC1) is associated with poor prognosis. We used A549 and H1975 human non‐small cell lung cancer (NSCLC) cell lines to investigate the role of TP and ERCC1 expression in metformin‐induced cytotoxicity. Metformin treatment decreased cellular TP and ERCC1 protein and mRNA levels by down‐regulating phosphorylated MEK1/2‐ERK1/2 protein levels in a dose‐ and time‐dependent manner. The enforced expression of the constitutively active MEK1 (MEK1‐CA) vectors significantly restored cellular TP and ERCC1 protein levels and cell viability. Specific inhibition of TP and ERCC1 expression by siRNA enhanced the metformin‐induced cytotoxicity and growth inhibition. Arachidin‐1, an antioxidant stilbenoid, further decreased TP and ERCC1 expression and augmented metformins cytotoxic effect, which was abrogated in lung cancer cells transfected with MEK1/2‐CA expression vector. In conclusion, metformin induces cytotoxicity by down‐regulating TP and ERCC1 expression in NSCLC cells.

Inhibition of p38 MAPK-dependent MutS homologue-2 (MSH2) expression by metformin enhances gefitinib-induced cytotoxicity in human squamous lung cancer cells

OBJECTIVES Gefitinib, a quinazoline-derived tyrosine kinase inhibitor, has anti-tumor activity in vivo and in vitro. Human MutS homologue-2 (MSH2) plays a central role in promoting genetic stability by correcting DNA replication errors. The present study investigated the effects of p38 mitogen-activated protein kinase (MAPK) signal on gefitinib-induced MSH2 expression in two human non-small cell lung squamous cancer cell lines. MATERIALS AND METHODS After the gefitinib treatment, the expressions of MSH2 mRNA were determined by real-time PCR and RT-PCR analysis. Protein levels of MSH2, phospho-MKK3/6, phospho-p38 MAPK were determined by Western blot analysis. We used specific MSH2, and p38 MAPK small interfering RNA to examine the role of p38 MAPK-MSH2 signal in regulating the chemosensitivity of gefitinib. Cell viability was assessed by MTS assay, trypan blue exclusion, and colony-forming ability assay. RESULTS Exposure of gefitinib increased MSH2 protein and mRNA levels, which was accompanied by MKK3/6-p38 MAPK activation in H520 and H1703 cells. Moreover, blocking p38 MAPK activation by SB202190 significantly decreased gefitinib-induced MSH2 expression by increasing mRNA and protein instability. In contrast, enhancing p38 activation using constitutively active MKK6 (MKK6E) increased MSH2 protein and mRNA levels. Specific inhibition of MSH2 expression by siRNA enhanced gefitinib-induced cytotoxicity. Metformin, an anti-diabetic drug, might reduce cancer risk. In human lung squamous cancer cells, metformin decreased gefitinib-induced MSH2 expression and augmented the cytotoxic effect and growth inhibition by gefitinib. Transient expression of MKK6E or HA-p38 MAPK vector could abrogate metformin and gefitinib-induced synergistic cytotoxic effect in H520 and H1703 cells. CONCLUSION Together, down-regulation of MSH2 expression can be a possible strategy to enhance the sensitivity of gefitinib to human lung squamous cancer cells.

Down-regulation of MSH2 expression by Hsp90 inhibition enhances cytotoxicity affected by tamoxifen in human lung cancer cells

The anti-estrogen tamoxifen has been used worldwide as an adjuvant hormone therapeutic agent in the treatment of breast cancer. However, the molecular mechanism of tamoxifen-induced cytotoxicity in non-small cell lung cancer (NSCLC) cells has not been identified. Human MutS homolog 2 (MSH2), a crucial element of the highly conserved DNA mismatch repair system, and expression of MSH2 have been down-regulated by Hsp90 function inhibition in human lung cancer. Therefore, in this study, we examined whether MSH2 plays a role in the tamoxifen and Hsp90 inhibitor-induced cytotoxic effect on NSCLC cells. The results showed that treatment with tamoxifen increased MSH2 mRNA and protein levels. The combination treatment with PI3K inhibitors (LY294002 or wortmannin) or knockdown AKT expression by specific small interfering RNA could decrease tamoxifen-induced MSH2 expression. Both knocking down MSH2 expression and co-treatment of PI3K inhibitors enhanced the cytotoxicity and cell growth inhibition of tamoxifen. Compared to a single agent alone, tamoxifen combined with an Hsp90 inhibitor resulted in cytotoxicity and cell growth inhibition synergistically in NSCLC cells, accompanied with reduced MSH2 expression. These findings may have implications for the rational design of future drug regimens incorporating tamoxifen and Hsp90 inhibitors for the treatment of NSCLC.

Down-regulation of MSH2 expression by an Hsp90 inhibitor enhances pemetrexed-induced cytotoxicity in human non-small-cell lung cancer cells.

Elevated heat shock protein 90 (Hsp90) expression has been linked to poor prognosis in patients with non-small cell lung cancer (NSCLC). The multitargeted antifolate pemetrexed has demonstrated certain clinical activities against NSCLC. However, the efficacy of the combination of pemtrexed and Hsp90 inhibitor to prolong the survival of patients with NSCLC still remains unclear. Human MutS homolog 2 (MSH2), a crucial element of the highly conserved DNA mismatch repair system, and defects or polymorphisms of MSH2 have been found in lung cancer. In this study, we evaluated the effects of pemetrexed on NSCLC cell lines (H520 and H1703) and found that treatment with this drug at 20-50 µM increased the MSH2 mRNA and protein levels in a MKK3/6-p38 MAPK signal activation-dependent manner. Furthermore, the knockdown of MSH2 expression by transfection with small interfering RNA of MSH2 or the blockage of p38 MAPK activation by SB202190 enhanced the cytotoxicity of pemetrexed. Combining the drug treatment with an Hsp90 inhibitor resulted in an enhanced pemetrexed-induced cytotoxic effect, accompanied with the reduction of MSH2 protein and mRNA levels. The expression of constitutively active MKK6 (MKK6E) or HA-p38 MAPK vectors significantly rescued the decreased p38 MAPK activity, and restored the MSH2 protein levels and cell survival in NSCLC cells co-treated with pemetrexed and Hsp90 inhibitor. In this study, we have demonstrated that down-regulation of the MKK3/6-p38 MAPK signal with the subsequent reduction of MSH2 enhanced the cytotoxic effect of pemetrexed in H520 and H1703 cells. The results suggest a potential future benefit of combining pemetrexed and the Hsp90 inhibitor to treat lung cancer.

Abstract A33: Enhancement of thymidine phosphorylase downregulation by erlotinib enhances cytotoxicity affected by tamoxifen in human non-small cell lung cancer cells

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

Abstract 1283: Role of ERCC1 in metformin enhancing paclitaxel-induced cytotoxicity.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Metformin, an extensively used and well-tolerated drug for treating individuals with type 2 diabetes, has recently gained significant attention as an anticancer drug. On the other hand, paclitaxel (taxol) is a new antineoplastic drug that has shown promise in the treatment of non-small cell lung cancer (NSCLC). High expression levels of excision repair cross-complementary 1 (ERCC1) in cancers have been positively associated with the DNA repair capacity and a poor prognosis in NSCLC patients treated with platinum-containing chemotherapy. In this current study, paclitaxel was found to increase phosphorylation of mitogen-activated protein kinase (MAPK) kinase 3/6 (MKK3/6)-p38 MAPK as well as protein and mRNA levels of ERCC1 in H1650 and H1703 cells. Moreover, paclitaxel-induced ERCC1 protein and mRNA levels significantly decreased via the downregulation of p38 activity by either a p38 MAPK inhibitor SB202190 or p38 knockdown with specific small interfering RNA (siRNA). Specific inhibition of ERCC1 with siRNA was found to enhance the paclitaxel-induced cytotoxic effect and growth inhibition. Furthermore, metformin was able to not only decrease the paclitaxel-induced p38 MAPK-mediated ERCC1 expression, but also augment the cytotoxic effect induced by paclitaxel. Finally, expression of constitutive activate MKK6 or HA-p38 MAPK vectors in lung cancer cells was able to abrogate ERCC1 downregulation by metformin and paclitaxel as well as cell viability and DNA repair capacity. Overall, our results suggest that inhibition of the p38 MAPK signaling by metformin coupled with paclitaxel therapy in human NSCLC cells may be a clinically useful combination, which however will require further validation. Citation Format: Yun-Wei Lin, Sheng-Chieh Tseng, Yu-Ching Huang, Hsien-Chun Chiu, Huang-Jen Chen, Shao-Hsing Weng, Yi-Jhen Huang, Ting-Yu Wo. Role of ERCC1 in metformin enhancing paclitaxel-induced cytotoxicity. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1283. doi:10.1158/1538-7445.AM2013-1283

Abstract 1301: Metformin induces cytotoxicity by TP and ERCC1 decrease.

Metformin is an anti-diabetic drug recently shown to inhibit cancer cell proliferation and growth, although the involved molecular mechanisms have not been elucidated. In many cancer cells, highly expression of thymidine phosphorylase (TP) and ERCC1 are associated with poor prognosis. We used A549 and H1975 huamn non-small cell lung cancer (NSCLC) cell lines to investigate the role of TP and ERCC1 expression in metformin-induced cytotoxicity. Metformin treatment decreased cellular TP and ERCC1 protein and mRNA levels by down-regulating phosphorylated MEK1/2-ERK1/2 protein levels in a dose- and time-dependent manner. The enforced expression of the constitutively active MEK1 (MEK1-CA) vectors significantly restored cellular TP and ERCC1 protein levels and cells viability. Specific inhibition of TP and ERCC1 expression by siRNA enhanced the metformin-induced cytotoxicity and growth inhibition. In conclusion, metformin induces cytotoxicity by down-regulating TP and ERCC1 expression in NSCLC cells. Citation Format: Yun-Wei Lin, Yu-Ching Huang, Sheng-Chieh Tseng, Hsien-Chun Chiu, Huang-Jen Chen, Yi-Jhen Huang, Ting-Yu Wo, Shao-Hsing Weng, Jen-Chung Ko. Metformin induces cytotoxicity by TP and ERCC1 decrease. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1301. doi:10.1158/1538-7445.AM2013-1301