Chemoprevention of Pancreatic Cancer by Capsaicin

描述（由申请人提供）：胰腺癌仍然是美国癌症相关死亡的第四大原因，诊断后的中位生存期不到6个月。它是最具侵袭性的人类恶性肿瘤之一，预后极差，因此提供了一个实验和临床挑战。辣椒素对胰腺癌疗效的详细临床前评估的基本原理源于我们体外和异种移植研究的可靠初步数据。我们发现人胰腺癌细胞系AsPC-1和BxPC-3对辣椒素的生长抑制高度敏感。有趣的是，辣椒素对来源于正常人胰腺或永生化正常人胰腺导管上皮（HPDE-6）细胞的腺泡细胞的活力影响最小。这些结果特别令人鼓舞，因为选择性杀死癌细胞是一种潜在的癌症预防或治疗药物的理想特征。我们的研究结果还表明，辣椒素的生长抑制作用与(i)细胞内活性氧（ROS）水平升高，（ii） bax表达增加，（iii）导致线粒体去极化，细胞色素c和AIF的释放，survivin的下调和caspase-3级联的激活有关，最终诱导AsPC-1和BxPC-3细胞凋亡，而在腺泡细胞中则没有。此外，我们发现辣椒素显著降低胰腺癌细胞中的谷胱甘肽和硫氧还蛋白水平，并激活JNK，这反映了辣椒化合物引发的细胞内氧化还原的有效改变。此外，我们发现口服辣椒素可显著延缓裸鼠AsPC-1胰腺肿瘤异种移植物的生长，但无明显毒性。辣椒素处理小鼠的肿瘤表现为Bax表达增加，细胞质细胞色素c增加，caspase-3断裂，有丝分裂活性降低，细胞凋亡增加。我们的研究结果还表明，辣椒素增强了吉西他滨对胰腺癌细胞的生长抑制作用。基于这些有希望的数据，我们假设辣椒素可以有效地延缓胰腺癌的发生，并通过诱导和调节氧化应激导致JNK激活和线粒体凋亡死亡途径，对这种肿瘤类型发挥有效的抗癌作用。为了验证这一假设，我们将：(1)阐明辣椒素触发胰腺癌细胞氧化应激的机制；(2)研究辣椒素诱导氧化失衡时丝裂原和应激调节信号转导通路的激活；(3)确定辣椒素对线粒体死亡通路激活的影响；(4)研究辣椒素对裸胸腺小鼠和KrasG12D转基因小鼠胰腺上皮内瘤变（PanINs）模型的预防和治疗作用及其生物利用度和药代动力学。该项目的成功完成将支持辣椒素在胰腺癌化学预防中的开发和临床应用。公共卫生相关性：这项转化研究是在胰腺癌细胞中使用辣椒素进行临床前研究，辣椒素是辣椒的一种活性成分。我们已经提供了大量的初步数据来支持辣椒素对癌细胞有选择性，对正常细胞没有毒性。我们建议在培养和动物模型中确定其分子机制。

DESCRIPTION (provided by applicant): Pancreatic cancer remains the fourth leading cause of cancer-related death in the United States with a median survival of less than 6 months following diagnosis. It is one of the most aggressive human malignancies with extremely poor prognosis, thus offering an experimental and clinical challenge. Rationale for a detailed pre-clinical evaluation of capsaicin for its efficacy against pancreatic cancer stems from our solid preliminary data from in vitro and xenograft studies. We showed that human pancreatic cancer cell lines AsPC-1 and BxPC-3 are highly sensitive to growth inhibition by capsaicin. Interestingly, the viability of acinar cells derived from normal human pancreas or immortalized normal human pancreatic ductal epithelial (HPDE-6) cells were minimally affected by capsaicin. These results are particularly encouraging because selective killing of cancer cells is a desirable characteristic of a potential cancer preventive or therapeutic agent. Our results also showed that growth inhibitory effect of capsaicin is associated with the (i) elevated levels of intracellular reactive oxygen species (ROS), (ii) increased expression of bax, (iii) leading to mitochondrial depolarization, release of cytochrome c and AIF, down regulation of survivin, and activation of caspase-3 cascade that eventually induces apoptosis in both AsPC-1 and BxPC-3 cells but not in acinar cells. In addition, we found that capsaicin significantly reduces glutathione and thioredoxin levels and activated JNK in pancreatic cancer cells, reflecting the potent alterations in intracellular redox triggered by the chili compound. Furthermore, we found that orally feeding capsaicin significantly retard the growth of AsPC-1 pancreatic tumor xenograft in nude mice with no discernible toxicity. Tumors obtained from capsaicin treated mice exhibited increased Bax expression, cytoplasmic cytochrome c, cleavage of caspase-3, reduced mitototic activity and increased apoptosis. Our results also showed that capsaicin enhances the growth suppressive effects of gemcitabine in pancreatic cancer cells. Building on these promising data, we hypothesize that capsaicin can effectively retard pancreatic carcinogenesis, and also exert potent anticancer effects against this tumor type, through a differential induction and modulation of oxidative stress leading to JNK activation and mitochondrial death pathway of apoptosis. To test this hypothesis we will: (1) Elucidate the mechanisms by which capsaicin triggers oxidative stress in pancreatic cancer cells, (2) Investigate the activation of mitogen- and stress-regulated signal transduction pathways in response to the oxidative imbalance induced by capsaicin, (3) Determine the effect of capsaicin on the activation of mitochondrial death pathway, and (4) Investigate the preventive and therapeutic effect of capsaicin in athymic nude mice and KrasG12D transgenic mice models of pancreatic intraepithelial neoplasia (PanINs) respectively and its bioavailability and pharmacokinetics. Successful completion of this project will support the development and clinical application of capsaicin for the chemoprevention of pancreatic cancer. PUBLIC HEALTH RELEVANCE: This translational research is to perform preclinical studies in pancreatic cancer cells using capsaicin, an active ingredient of chili pepper. We have provided lot of preliminary data to support that capsaicin is selective to cancer cells and is not toxic to normal cells. We propose to determine its molecular mechanism in culture and in the animal model.