Antioxidant Treatment Promotes Prostate Epithelial Proliferation in <em>Nkx3.1</em> Mutant Mice

Discordant results in preclinical and clinical trials have raised questions over the effectiveness of antioxidants in prostate cancer chemoprevention. Results from the large-scale Selenium and Vitamin E Cancer Prevention Trial (SELECT) showed that antioxidants failed to prevent, and in some cases promoted, prostate cancer formation in men without a history of the disease. One possible explanation for these alarming results is the notion that the effects of antioxidant treatment on the prostate are modified by specific, intrinsic genetic risk factors, causing some men to respond negatively to antioxidant treatment. Loss of expression of the homeobox transcription factor NKX3.1 in the prostate is frequently associated with human prostate cancer. Nkx3.1 mutant mice display prostatic hyperplasia and dysplasia and are used as a model of the early stages of prostate cancer initiation. While the mechanisms by which Nkx3.1 loss promotes prostate tumorigenicity are not completely understood, published data have suggested that elevated reactive oxygen species (ROS) associated with Nkx3.1 loss may be a causative factor. Here we have tested this hypothesis by treating Nkx3.1 mutant mice with the antioxidant N-acetylcysteine (NAC) for 13 weeks post-weaning. Surprisingly, while NAC treatment decreased ROS levels in Nkx3.1 mutant mouse prostates, it failed to reduce prostatic epithelial hyperplasia/dysplasia. Rather, NAC treatment increased epithelial cell proliferation and promoted the expression of a pro-proliferative gene signature. These results show that ROS do not promote proliferation in the Nkx3.1-null prostate, but instead inhibit proliferation, suggesting that antioxidant treatment may encourage prostate epithelial cell proliferation early in prostate tumorigenesis. Our findings provide new insight that may help explain the increased prostate cancer risk observed with vitamin E treatment in the SELECT trial and emphasize the need for preclinical studies using accurate models of cancer.临床前研究与临床试验结果不一致，引发了学界对抗氧化剂用于前列腺癌化学预防的有效性质疑。大型硒与维生素E癌症预防试验（SELECT）结果显示，对于无前列腺癌病史的男性，抗氧化剂不仅未能预防前列腺癌，在部分受试者中甚至可能促进肿瘤发生。针对这一令人警惕的结果，一种可能的解释是：抗氧化治疗对前列腺的影响会受到特定内在遗传风险因素的调控，导致部分男性对抗氧化剂治疗产生负面反应。前列腺组织中同源盒转录因子NKX3.1（homeobox transcription factor NKX3.1）的表达缺失，常与人类前列腺癌相关。NKX3.1突变小鼠会出现前列腺增生与异型增生，被用作前列腺癌发生早期阶段的研究模型。尽管NKX3.1缺失促进前列腺肿瘤发生的具体机制尚未完全阐明，但已有研究数据表明，与NKX3.1缺失相关的活性氧（reactive oxygen species, ROS）水平升高可能是关键致病因素。本研究通过在NKX3.1突变小鼠断奶后13周给予抗氧化剂N-乙酰半胱氨酸（N-acetylcysteine, NAC）处理，对这一假说进行了验证。令人意外的是，尽管NAC处理成功降低了NKX3.1突变小鼠前列腺组织中的ROS水平，但并未减轻前列腺上皮增生/异型增生程度。相反，NAC处理反而上调了上皮细胞增殖活性，并增强了促增殖基因特征的表达。上述结果表明，ROS在NKX3.1缺失的前列腺组织中并未促进细胞增殖，反而起到了抑制增殖的作用，这提示抗氧化治疗可能在前列腺肿瘤发生早期促进前列腺上皮细胞增殖。本研究的发现为解释SELECT试验中维生素E治疗相关前列腺癌风险升高的现象提供了新的视角，同时也强调了采用精准癌症模型开展临床前研究的必要性。