• 作者： 方剛
• 作者服務機構： 臺灣師範大學生物系
• 中文摘要： 癌症是國人最大致命病症之一。這類細胞皆表現有高密度之上皮生長因子受體（Epidermal growth factor receptor;EGFR）。EGFR是由1,186個胺基酸所組成，它的碳端位於細胞質部份具有磷酸化的功能。而自腫瘤細胞自身分泌之第一類轉形生長因子（transforming growth factor-α; TGF-α）與自身EGFR緊密結合之後，造成受體自體磷酸化，接著引發細胞內連續訊號傳遞的發生，進而促使細胞增生，而受質TGF-α則由EGFR攜入細胞，最後在溶體中被解離。 本文利用TGF-α這項特性，將之與蓖麻毒素A（ricin A）結合所形成共軛毒素，由EGFR攜入細胞質後，使蓖麻毒素A結合ribosome失去效用，而抑制腫瘤細胞的生長。由於蓖麻毒素的另外一部份蓖麻毒素B被TGF-α所取代，這種方式所製造共軛毒素的專一性較蓖麻毒素本身增加，也會使共軛毒素對其它非相關組織的毒性得以相對減低。以共價連結方式所製備此共軛物是直接將 TGF-α與蓖麻毒素A以化學雙硫鍵方式結合，再以親和色層分析純化之後，分別觀察純化後共軛毒素對癌細胞的毒性（cytotoxicity）。實驗結果顯示純化的TGF-α與蓖麻毒素A共軛毒素對含大量EGFR的人類上皮癌細胞A431，有顯著抑制生長的效應，其I（方程式無法摘錄）約在（方程式無法摘錄）M。其次是含相當高EGFR的人類腦轉移肺癌鱗細胞H226Br有略微但不若A431細胞為顯著的抑制效應。其它如H226，H460等含較低EGFR的人類肺癌細胞則無反應，而正常肺組織細胞MRC-5也無反應，顯示毒性的效應與EGFR表現相關。由於TGF-α價格高昂，而且純化共軛毒素回收率低，雖然由初步結果顯示此共軛毒素具胞殺性，為使這份結果有更進一步意義，應發展以基因工程方式製作大量合成TGF-α蓖麻毒素A共軛毒素，以為將來作更進一步深入的研究。
• 英文摘要： The inhibitory effect of human epidermoid cancer cells A431 caused by conjugate toxin containingtransforming growth factor (TGF-α) and ricin A was studied. TGF-α is a protein with 50 amino acids thatspecifically binds and stimulates phosphorylation of cell surface epidermal growth factor receptor (EGFR)and, subsequently, triggers cell proliferation. TGF-α as a ligand for EGFR is internalized upon binding anddecomposed within lysosome. Lectin ricin is contained in the castor bean plant. The lectin consists of twosubunits, ricin A and B. Toxic ricin A binds to ribosome and inhibits protein synthesis of target cells. Inview of the abundance of EGFR in human cancer cells, the receptor-mediated endocytosis with the conjugatetoxin composed of TGF-α and ricin A was synthesized, purified and tested for growth inhibition in bothnormal and tumor cells. The cytotoxicity of the conjugate was studied within the range of (方程式無法摘錄) and (方程式無法摘錄) M and I (方程式無法摘錄) was foundto be (方程式無法摘錄) M for human A431 epidermoid cells that over-express EGFR. Compared to A431 cells, the brainmetastatic variant of human Non-Small Cell Lung Cancer (NSCLC) H226Br squamous cells showed a re-duced inhibitory effect. On the other hand, no inhibitory effect was found with other NSCLC cells studiedand normal human lung cells because of the fewer available EGF binding sites on the surface of the cells.These results indicated that the amount of the available EGFR contributes to the cytotoxic effect on humancancer cells, thereby demonstrating involvement of the receptor-mediated endocytosis of the conjugate. Theresult from (方程式無法摘錄) EGF-mediated competition assay further demonstrated the specific inhibitionactivity conferred by TGF-α and ricin A conjugation. Due to poor recovery of the chemical conjugation,modification in the form of a recombinant toxin is needed for further in-depth studies.
• 中文關鍵字： human cancer cells; ricin A; Transforming Growth factor-α; Toxin
• 英文關鍵字： --