2013-08-012024-05-18https://scholars.lib.ntu.edu.tw/handle/123456789/699587滅糖敏(metformin)為一種双胍類 (biguanide)之口服第一線降血糖藥物，適合用於第二 型成人之糖尿病人，尤其適合用於肥胖與腎功能正常之病人。其降血糖之機轉為減少肝 臟之糖質新生作用，與增加肌肉對葡萄糖之攝取。近年的研究發現，滅糖敏可以在體外 的細胞培養中，抑制包括乳癌、攝護腺癌、大腸癌、胰臟癌的增生。此外，滅糖敏可以 抑制香煙致癌物所誘導肺癌腫瘤之增長現象。肺癌的高死亡率在於早期肺癌沒有症狀， 一旦有嚴重的咳嗽、咳血、胸痛及呼吸困難時，已經是第三或第四期，錯失手術切除的 時機，預後效果自然不佳，五年存活率只有 5-10%。有高達~85%肺癌是屬於非小細胞 肺癌，其分類包括腺癌，肺泡細胞癌，及扁平細胞癌。一般而言，接受化療的肺癌病人 平均只有八個月的存活期，效果十分有限，這與癌細胞對化學治療產生抗藥性有關。最 新肺癌的治療方法是標靶藥物治療，主要的藥物為表皮生長因子受體(EGFR)抑制劑， 例如:艾瑞莎，其作用機轉為佔據表皮生長因子受體上的ATP結合處，使表皮生長因子 受體不會被外來的生長因子活化，進而抑制下游調控細胞生長、分化，及存活的 extracellular signal-regulated kinase 1/2 (ERK1/2) 激酶訊號，達到抑制或殺死癌細胞的目 的。但是標靶藥物主要對肺腺癌與肺泡細胞癌才有較好的療效，至於扁平細胞肺癌則標 靶藥物的療效不佳。我們先前的研究指出肺癌細胞內核酸代謝酵素 thymidine phosphorylase (TP)的過量表現會對化療藥物順鉑失去敏感性。有趣地，我們初步研究發 現滅糖敏能使肺癌細胞內 TP蛋白質與mRNA表現量下降，伴隨向下調節 MEK1/2-ERK1/2 訊號路徑。轉錄子signal transducers and activators of transcription (STATs)抑制劑能協力降低滅糖敏所誘導tp mRNA的向下調節。此外，滅糖敏已經被證 實可以殺死乳癌細胞，增強化療藥物doxorubicin的效果。因此，在肺癌的治療上，滅糖 敏是否能藉由調控核酸代謝酵素TP的表現，進而加強化療藥物順鉑與標靶藥物艾瑞莎 的效果，仍有待進一步的研究。因此，計畫第一年我們將分析滅糖敏如何抑制 MEK1/2-ERK1/2 訊號路徑，上游分子EGFR的失活是否參與其中。以及滅糖敏如何調 控轉錄子Sp1與STATs活性，進而向下調節TP的表現。計畫第二年我們將探討 分析滅糖敏是否能直接或間接影響TP的酵素活性，進而破壞核酸代謝平衡。滅 糖敏所向下調控 TP的表現在增加肺癌細胞對化療與標靶藥物敏感性及抑制癌細 胞生長之角色。在未來的肺癌治療上，新一代的標靶藥物之研發，固然扮演一個十分重 要的角色，但是因為新藥的研發不易，因此現有藥物若能被發現有抗癌之效果而有新的 應用，同時又有極佳的藥物安全性與藥物動力學的結果，在未來的肺癌研究與治療上， 也會扮演一個很重要的角色。本計畫的研究成果將可提供滅糖敏作為克服化療與標把 藥物抗藥性的最新細胞體外研究報告，日後做為臨床試驗的重要依據。Metformin, a widely used and well tolerated antidiabetic agent, exerts remarkable antitumoral effects on cancer cells and mouse models. Currently, a number of clinical trials examining the use of metformin as a cancer therapy are underway including studies in breast, prostate, colon, and pancreatic cancer patients. Metformin is able to reduce overall tumor burden in a tobacco carcinogen-induced model of lung cancer. However, its effect on lung cancer, particularly on non-small cell lung cancer (NSCLC) viability and the detailed molecular mechanism involved are still unknown. Lung cancer remains a high-incidence, high-mortality malignancy, and approximately 85% are NSCLC, which including adenocarcinoma, bronchioloalveolar carcinoma, and squamous cell carcinoma. Most cases are already in an advanced stage when first diagnosed and thus cannot benefit from surgery. Platinum-based therapy remains the standard of care for the first-line treatment of patients with advanced NSCLC. On the other hand, gefitinib (IressaR) is selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) in the treatment of NSCLC, that blocks growth factor-mediated cell proliferation and extracellular signal-regulated kinases 1/2 (ERK1/2) signaling activation. Our previous studies have indicated that up-regulation of thymidine phosphorylase (TP), is an enzyme of the pyrimidine salvage pathway, expression is correlated decreasing drugs sensitivity of chemotherapeutic drug cisplatin to NSCLC cell lines. Interestingly, our preliminary results showed that metformin down-regulated the protein and mRNA expression of TP in a MKK1/2-ERK1/2 inactivation manner. Signal transducers and activators of transcription 3 (STAT3) inhibitors further decreased cellular tp mRNA expression in metformin-treated human lung cancer cells. Moreover, metformin synergistic enhances the chemotherapeutic drug doxorubicin-induced cytotoxic effects in breast cancer. However, the roles of TP in metformin enhancing cisplatin or gefitinib induced cytotoxic effect, proliferation inhibition, and mutagenesis in NSCLC is unclear. Therefore, first year, we will plan to explore how metformin inactivate MKK1/2-ERK1/2 signals and down-regulate TP expression in different types of NSCLC. Whether metformin decreased cellular TP expression was through the effect on transcription factor Sp1 and STAT3. Second year, we will determine whether metformin could directly or indirectly affect the catalytic activity of TP. How does metformin affect the chemotherapeutic drug (cisplatin) and EGFR-TKI (gefitinib) induced TP mRNA and protein expression? Could metformin enhance the sensitivity to cisplatin or gefitinib through increasing apoptosis, mutagenicity, and enhancing dNTP imbalance in NSCLC, due to decrease of the TP expression? The final goal of this project is to understand the how metformin modulate TP expression and its role in regulating metformin and chemotherapeutic drugs or EGFR-TKIs induced synergistic cytotoxicity in NSCLC cell lines. The findings prompt prospective investigations using metformin combined with chemotherapeutic drugs or EGFR-TKIs to optimize and improve clinical outcomes in lung cancer treatment. The clinical safety, well characterized pharmacodynamic profile, and low cost of metformin make it an ideal candidate for development as an anticancer agent for NSCLC. In conclusion, suppression of TP expression by metformin maybe a novel therapeutic modality in overcoming drug resistance of chemotherapeutic drugs or EGFR-TKIs in NSCLC.