Oct-4（亦稱Oct3/4, Oct-3 或 POU5F1）的全名是POU homeodomain protein octamer binding protein 4，是胚胎的轉錄因子，會表現在生殖細胞與胚胎幹細胞中，一般的正常體組織不會表現Oct-4。最近的研究發現Oct-4 會表現在臨床膀胱癌組織與膀胱癌細胞中，Oct-4於膀胱癌治療中似乎可以作為一個治療標的。文獻報導在缺氧調控下，穩定的累積缺氧誘發因子2α (hypoxia-inducible factor 2α, HIF-2α) ，而不是缺氧誘發因子1α (HIF-1α)，會連接到Oct-4的啟動子，接著誘發下游 Oct-4 蛋白質的表現量增加。我們實驗室之前的研究中建構了一段 9倍的Oct-4 response elements (9xORE) 所驅動的溶瘤腺病毒 (oncolytic adenovirus)，能夠選擇性的毒殺Oct-4過量表現的 小鼠MBT-2 膀胱癌細胞，而正常細胞則不受影響。因此在本研究中，我們利用一段帶有9倍 ORE加上6倍 hypoxia response element (HRE)所驅動的溶瘤腺病毒，研究它對腫瘤的影響。首先我們先確定在膀胱癌細胞株中，缺氧調控能夠誘發HIF-2α與Oct-4 表現量增加；以冷光報導測定(luciferase reporter assay)，不論是有氧或是缺氧，我們發現9xORE-6xHRE相較於單獨的9xORE 或 6xHRE具有加成活化冷光報導基因的效果。缺氧時，使用由9xORE-6xHRE 驅動的E1B 55 kD基因剔除溶瘤腺病毒Ad.LCY 對於膀胱癌細胞的毒殺是具有較好的效率，也提供了更好的選擇性。Ad.LCY 在NOD/SCID小鼠模式和C3H/HeN 小鼠模式中，展現了減緩腫瘤形成與延長存活時間的能力。經由免疫組織染色的實驗，我們首度發現少量的臨床膀胱癌組織與膀胱癌細胞中有CD133蛋白質的表現，這暗示我們膀胱癌幹細胞(cancer stem cell) 有可能存在。綜合來說，我們的研究結果顯示 Ad.LCY由 9xORE-6xHRE驅動的溶瘤腺病毒在對於膀胱癌的治療上，可以作為一個具有潛力的方法。

The POU homeodomain protein octamer binding protein 4 (Oct-4), also known as Oct3/4, Oct-3, and POU5F1) is an embryonic transcription factor expressed in germ and embryonic stem cells, but not in normal somatic tissues. It has been shown recently that the expression of Oct-4 is higher in bladder cancer than in normal genitourinary tissues, and that Oct-4 may be exploited as a therapeutic target for bladder cancer therapy. It has also been demonstrated that hypoxia-inducible factor -2α, but not HIF-1α, binds to the Oct-4 promoter and induces Oct-4 expression under hypoxic conditions. Our previous study has shown that 9 copies of Oct-4 response elements (ORE)-driven oncolytic adenovirus selectively killed Oct-4-overexpressing MBT-2 bladder cancer, but not normal cells. In this study, we generated a novel oncolytic adenovirus, designated Ad.LCY, under the control of 9 copies of ORE combined with 6 copies of hypoxia response element (HRE) and studied its antitumor activity. First, we showed that the protein levels of HIF-1α, HIF-2α and Oct-4 were upregulated in both murine MBT-2 and human TCCSUP bladder cancer cells under hypoxic conditions. In a reporter assay, we also found that the 9xORE-HRE promoter exerted higher hypoxia-inducible transcriptional activity than ORE or HRE alone in bladder cancer. The cytolytic effect of Ad.LCY on bladder cancer was more evident under hypoxic than under normoxic conditions. Furthermore, Ad.LCY had antitumor effects on tumor growth and survival in NOD/SCID and C3H/HeN mice bearing TCCSUP and MBT-2 tumors, respectively. CD133-positive cells were detected in TCCSUP bladder cancer cells and clinical tumor tissues, but not in the normal bladder tissues by immunohistochemical staining, suggesting that cancer stem cells exist in bladder cancer. Taken together, our results suggest that Ad.LCY, a 9xORE-6xHRE-driven oncolytic adenovirus, may have therapeutic potential for the treatment of bladder cancer.

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