?帕替尼(Lapatinib)為?胺酸激?抑制劑(Tyrosine Kinase Inhibitor)，於2007 ?由美國食品藥物 管?局核准為治?晚期或轉移性乳癌之標靶藥物，可抑制第一型(EGFR)與第二型(HER2)之上皮 細胞生長因子受體之活化。大約20-30％之乳癌患者具有第二型上皮細胞生長因子受體過?活化 之現象，因此lapatinib 可有效的延緩該型乳癌病患之病程發展。然而，?床上發現，使用lapatinib 治?約6-12 個月後，患者即有抗藥性的情形產生，而其中之分子機制目前尚未全然?解。許多 文獻指出乳癌組織具有?質性的HER2 表現，在HER2 大?表現之腫瘤組織中仍存在些許低 HER2 表現之癌細胞，在此種?態下，lapatinib 雖然可有效的?死高HER2 表現之乳癌細胞，低 HER2 表現之癌細胞可能?受?帕替尼影響，進而成為癌症?發之?源。因此，本研究的主軸在 於探討HER2 ?質性表現對lapatinib 抗癌效果的影響。初步結果發現在高 HER2 表現的細胞株 中，存在少許的HER2 ?表現的癌細胞，並在給予lapatinib 之後，此群細胞的比?明顯增多。 此外將?表現HER2 的人?乳腺癌細胞株MDA-MB-231 長期給予lapatinib 之後，?但?影響該 細胞之生長速?，反而會增強其移動(Migration)及入侵(Invasion)的能?。因此，本研究計畫第一 ?將先以細胞株模式?探討HER2 ?質性表現是否的確影響lapatinib 的抗癌效果，並同時建? 抗藥細胞株配合動物模式，?研究在長期給予lapatinib 後，是否除??影響?表現HER2 細胞 的生長速?外，?增加其轉移的機?。我們初步結果亦發現EGFR 與 cyclooxygenase-2 (COX-2) 的表現增加可能與lapatinib 所增強的癌細胞爬?與侵入作用有關，因此在第二?的工作內容將 同時以細胞株及動物模式?探討EGFR 與COX-2 於lapaitnib 所促進的腫瘤?發與轉移過程中所 扮演的角色，測試合併使用COX-2 抑制劑是否可?低此轉移作用，同時並研究lapatinib 增加 EGFR 表現的分子機制。另外，我們目前的結果顯示，EGFR 在?需要其?胺酸蛋白激?活性的 ?態下，即可透過穩定COX-2 mRNA ?增加其蛋白表現?，因此第三?將探討EGFR 如何以蛋 白激?非依賴性的特性?調控COX-2 的表現，?解其分子機制。藉由此研究成果，應可?解? 質性HER2 表現對於lapatinib 抗癌效果的影響，藉由探討低HER2 表現癌細胞於形成lapatinib 抗性並產生?發與轉移的過程中所扮演之角色，並研究其分子機制，以發展出適合的合併?法， 或許可?低乳癌病人產生?發與轉移的機?。
Lapatinib, a dual EGFR/HER2 tyrosine kinase inhibitor, has been shown to improve the survival rate of patients with advanced HER2-positive breast cancers. However, the anti-tumoral effects and survival benefit from lapatinib treatment is limited ultimately due to the development of therapeutic resistance that typically occurs within 12 months of starting therapy. The factors that confer primary or acquired resistance to lapatinib are not well characterized. Although lapatinib can effectively eliminate HER2-positive cells, the minor subpopulation of HER2-negative cells within the HER2-heterogeneous tumors may escape the attack by lapatinib and be the seeds of the recurrent and metastatic lapatinib-resistant tumors. Our preliminary data showed that the existence of HER2-negative cells in two HER2-overexpressing breast cancer cell lines, and that treatment with lapatinib increased the percentile of HER2-negative subpopulation. To further address whether lapatinib has any off-target effect on HER2-negative cells, we chronically treated HER2-negative MDA-MB-231 breast cancer cells with lapatinib and unexpectedly found that the lapatinib-selected MDA-MB-231 (231/Lap) clones have higher migration and invasion abilities without altering their proliferation rates. Therefore, in the first year of this proposal, the impact of heterogeneous HER2 expression on the therapeutic efficacy of lapatinib will be addressed. To mimic the clinical scenario, the pro-metastatic effect of lapatinib in HER2-negative breast cancer cells will be confirmed by establishing lapatinib-resistant clones from HER2-heterogeneous cell lines in the first year. The enhanced migration of 231/Lap clones may involve increased EGFR and cyclooxygenase-2 (COX-2) overexpression. In the second year, the involvement of EGFR and COX-2 in the enhanced metastasis in vitro and in vivo will be studied, and the molecular mechanisms underlying the lapatinib-increased EGFR expression will also be investigated. Moreover, our preliminary data revealed that the increased EGFR may further mediate COX-2 expression independent of its tyrosine kinase activity via stabilizing COX-2 mRNA level. The kinase-independent role of EGFR in the regulation of lapatinib-induced COX-2 expression will be explored in the third year. The results from this proposal would help us to understand the target(EGFR/HER2)-independent molecular mechanisms for acquired resistance to lapatinib therapy, and would also be helpful to develop combination therapy to reduce tumor recurrence and metastasis.
