腺嘌呤核苷三磷酸結合卡匣G2對五胺基酮戊酸光動力治療影響的研究

Abstract

口腔癌為台灣重要的疾病之一。目前對於口腔癌的治療，仍以手術切除為最快速且有效的方法。但是手術所造成的缺損，即使透過顏面重建手術，外觀仍會存留手術痕跡或疤痕。不僅可能影響病患的生理功能，也會造成心理的壓力。 近年來光動力治療(photodynamic therapy，PDT)在臨床上已有不錯的治療成效。經光動力治療後病灶的部位不會有明顯的組織缺損，對病患而言是一大福音。但是治療的時間較長，藥物的費用較高，以及因細胞特性與及生長環境的差異，光動力治療的成效也有不同。因此，如何加強對光動力較不敏感細胞的治療效果，縮短治療時間是研究光動力治療中很重要的方向。 五胺基酮戊酸(5-aminolevulinic acid，ALA)為光動力治療常使用的藥物。ALA被癌細胞吸收後，經過一連串的代謝路徑，最後會形成吡喀紫質九( protopophyrin IX，PpIX)。另外，許多研究指出位於細胞膜上的腺嘌呤核苷三磷酸結合卡匣G2 (ATP-binding cassette G2，ABCG2)可將細胞內的PpIX排出細胞外，使ALA-PDT效果下降。由此可知，癌細胞的ABCG2蛋白表現量會影響光動力治療的成效。此外，不同的細胞ABCG2蛋白表現量各不相同，生長環境中的糖分的多寡也會影響細胞ABCG2蛋白的表現。本篇研究主要探討不同口腔癌細胞株在微環境糖分改變情況下，癌細胞ABCG2蛋白表現的改變，並研究使用抗癌藥物或天然物質抑制ABCG2蛋白的表現後，是否強化光動力治療的成效。 本研究結果顯示，在SAS、OECM1、FaDu、HSC3四種口腔癌細胞株中，OECM1細胞表現的ABCG2蛋白最多。加入ALA後，PpIX累積量最少，經ALA-PDT治療後，細胞的存活率最高。本研究將SAS細胞培養在低糖(1.0g/L的DMEM)環境中，經30、60、90天後觀察， ABCG2的蛋白表現量會上升。加入ALA後， PpIX累積量變少，PDT後細胞存活率變高。利用ALDH測量也得知ABCG2蛋白較多的OECM1細胞和低糖培養90天的SAS細胞幹性(stemness)較強。OECM1細胞和低糖培養90天的SAS細胞分別加入不同劑量的gefitinib、EGCG、curcumin培養後，p-EGFR、EGFR、p-PI3K、p-Akt、Nrf2、ABCG2蛋白表現均被抑制，ABCG2蛋白表現變少。加入ALA後PpIX累積量上升，經ALA-PDT後，受照射細胞的存活率下降。 由研究結果得知，OECM1細胞和低糖培養90天的SAS細胞表現較多的ABCG2蛋白。gefitinib、EGCG及curcumin可透過EGFR細胞訊息傳導路徑調控Nrf2，抑制ABCG2生成，使PpIX累積量上升，增加ALA-PDT治療的效率。

Oral cancer is one of important diseases in Taiwan. Surgery is now the quickest and the most effective way to treat oral cancer. But the surgical defects after operation are not remediable even with reconstructive procedures. It not only interferes with patients’ physiological functions but also induces mental pressure to the patients. Recently, photodynamic therapy (PDT) has been successfully applied in a clinical treatment. The benefits of PDT are that it does not leave significant scars or surgical defects. However, PDT takes a long time, costs a lot of money and the effectiveness is different depending on the cell type and the environment in which they grow. Therefore, enhancing the efficiency of PDT and shortening the treatment period of the PDT- non-sensitive cells are issues that are yet to be resolved. 5-aminolevulinic acid (ALA) is a general drug for PDT. Protopophyrin IX (PpIX) are created through a series of metabolic pathways after ALA is absorbed by cancer cells. ATP-binding cassette G2 (ABCG2) are located on the cell membrane. It has been reported that ABCG2 protein expression in cancer cells will lower the efficacy of ALA-PDT, because ABCG2 transports PpIX from the intracellular to the extracellular region. The ABCG2 protein expression is dependent not only on the cell type, but also on the glucose concentration of the environment in which they grow. The aim of this study is to investigate whether or not potential anti-cancer drugs and natural substances could inhibit the expression of ABCG2 and enhance the efficacy of ALA-PDT in PDT- non-sensitive cells. The results showed that different oral cancer cell lines, such as SAS, OECM1, FaDu and HSC3 cells produced different expression of ABCG2. OECM1 cells expressed the highest levels of ABCG2, which resulted in the lowest levels of PpIX after administration of ALA and had the lowest sensitivity to ALA-PDT. When SAS cell line was cultured in low glucose medium (1.0g/L of DMEM) for varying periods, the level of ABCG2 expression became higher in a time dependent manner. The higher expression of ABCG2 attenuated the level of PpIX after administration of ALA, which reduced the sensitivity of SAS cells to ALA-PDT. On the other hand, OECM1 and SAS cells that were incubated in low glucose for 90 days had higher stemness measured by ALDH kit. The ABCG2 signal transduction proteins, such as p-EGFR, EGFR, p-PI3K, p-Akt, Nrf2 and ABCG2, were inhibited after administration of different doses of gefitinib, EGCG and curcumin. When ABCG2 expression was inhibited, PpIX would accumulate, therefore, enhancing the efficiency of ALA-PDT. In conclusion, PDT- non-sensitive cells like OECM1 and SAS cells cultured in low glucose for 90 days expressed higher level of ABCG2, which reduces the accumulation of PpIX. Gefitinib, EGCG and curcumin were capable of inhibiting ABCG2 expression through EGFR and Nrf2 related signaling pathways, which reduced PpIX accumulation and improved ALA-PDT efficacy.