臺灣博碩士論文加值系統

脂肪酸合成酶 (fatty acid synthase, FAS) 為一個270 kDa，具有七個催化活性的巨大酵素複合體。在脂肪酸合成的代謝路徑上扮演十分重要的角色；其主使著由malonyl-coA轉為palmitate的主要催化反應並進一步促成長鏈脂肪酸之合成。近幾年發現，在眾多人類腫瘤細胞中具有高度表現的脂肪酸合成酶；包含乳癌細胞、攝護腺癌細胞、大腸直腸癌細胞及肺癌細胞。本篇研究對象為人類攝護腺癌（LNCaP）中高度表現的脂肪酸合成酶，嘗試以FAS作為抑制腫瘤增生之標的。

據研究表示，對比攝護腺癌細胞及正常細胞，脂肪酸合成酶若同時於蛋白質及mRNA層次有高達四倍以上的過度表現（overexpression）時，其復發機率與病理分級上皆偏高；另一方面，在高度表現脂肪酸合成酶的攝護腺癌病患中，發生骨轉移之潛在危險性也較高。本篇研究應用脂肪酸合成酶之抑制劑(C75)，針對FAS於攝護腺癌細胞之高表現作抑制效應評估。在細胞實驗中，可見脂肪酸合成酶之抑制劑隨時間對細胞具有相當程度的毒殺效應;分析其對於細胞週期之影響，C75造成大量細胞停頓於G1期，而使進入合成期之細胞銳減。近一步，我們以雙報導基因(tk-luc)建立LNCaP/ tk-luc人類攝護腺癌小鼠模式；利用雙報導基因之影像系統，作為治療效益之評估平台。在單次給予C75 30 mg/kg/week及分次給予15 mgx2/kg/week的兩治療組別中，皆可見腫瘤生長受到明顯抑制，且動物體重的變異並不顯著。在非侵入式生物冷光影像及加碼閃爍攝影術中，對比給予5% DMSO的控制組老鼠，亦可見顯著的腫瘤生長抑制。應用同ㄧ活體實驗平台，給予針對FAS mRNA的特異小片段核酸干擾素siRNA(1.4 mg/kg/
once two days)亦可見顯著抑制效應；在兩週的療程裡，siRNA之療效更優於FAS抑制劑C75。

攝護腺癌細胞較一般癌症細胞不同，其對於脂肪之能量需求較醣解作用大。本篇研究旨在阻斷其主能量來源，以達到抑制腫瘤生長之目的。脂肪酸合成酶之抑制劑C75，不僅在細胞實驗中對細胞具毒殺效應；應用於動物模式時亦可見腫瘤增生之受限。本研究以先進靈敏之多種非侵入式分子基因影像，預見以脂肪酸合成酶於攝護腺癌標的治療之將來。

Fatty acid synthase (FAS), with ability of de novo fatty acid synthesis, is highly expressed in most human cancers, including prostate carcinoma. FAS is overexpressed at both mRNA and protein levels in prostate carcinoma associated with a 4-fold risk of disease recurrence and higher stage. The high-level FAS expression in patients with prostate cancers was also found with high risk in bone metastases. As a novel potential therapeutic target, inhibition of FAS could arrest cell cycle and trigger apoptosis rapidly, implying the reliance of cancer cell survival on FAS activity. In this study, we used the FAS inhibitor, C75, manifest the inhibition effect of endogenous fatty acid metabolism in a human prostate carcinoma LNCaP/tk-luc cells both in vitro and in vivo. Multimodalities of molecular imaging were used to demonstrate the inhibition effects of FAS in a LNCaP-tk/luc bearing mouse model, which constitutively expresses herpes simplex virus type-1 thymidine kinase (HSV1-tk) and luciferase (luc) genes. Bioluminescent imaging (BLI) and nuclear imaging (gamma scintigraphy, PET and autoradiography) were used to monitor tumor progression and metastasis spreading.

LNCaP-tk/luc cells were implanted subcutaneously into NOD/SCID mice. Animals were i.p. injected with high-dose C75 (total 120 mg/kg, i.e. 30 mg/kg once a week or 15 mg/kg twice a week for 4 weeks) or FAS sequence-specific siRNA (1.4 mg/kg/once two days). The results showed that the intensity levels of BLI from in vivo and ex vivo post treatments were well correlated to the tumor growth inhibition, and were further confirmed by histopathology. In conclusion, the targeted therapy using enzyme inhibitor, such as C75, or siRNA for mRNA knockdown of specific protein could be explored using reporter genes combined with multimodalities of molecular imaging.

1.Abstract -------------------------------- p.3
2.Abstract in Chinese --------------------- p.4
3.Study Aim ------------------------------ p.5
4.Introduction --------------------------- p.6
5.Materials and Methods ------------------- p.13
6.Results --------------------------------- p.21
7.Discussion ------------------------------ p.28
8.Conclusions------------------------------- p.32
9.References ------------------------------ p.33
10.Figures -------------------------------- p.37

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