维生素D和抗菌肽在预防胃癌、逆转胃癌耐药中的作用及机理

Vitamin D has been widely used for bone health in humans. However, its deficiency is also associated with a heightened risk for gastrointestinal cancers. It predicts poor clinical outcomes in gastric cancer patients. All these findings suggest that vitamin D may be useful for chemoprevention of gastric cancer and may synergize with cytotoxic agents for chemotherapy. Nevertheless, vitamin D could induce CYP24A1 (a vitamin D catabolizing enzyme) in tumor cells and this may thereby limit its tumor-suppressing function. It is therefore imperative to dissect vitamin D signaling in tumor suppression in order to identify novel therapeutic targets. Herein, we found that cathelicidin, a vitamin D-inducible pleiotropic peptide in cancer cells, is involved in the tumor suppressing action of vitamin D. Furthermore administration of exogenous cathelicidin delivered by bioengineered Lactococcus lactis to the gastric epithelium strongly suppressed tumor growth in an orthotopic model of gastric cancer. To ascertain the key involvement of cathelicidin, we propose the chemopreventive effects of vitamin D to be assessed in a carcinogen and salt-induced model of gastric cancer by using wild type and cathelicidin-knockout mice. The function of cathelicidin as the mediator of vitamin D-dependent tumor suppression will also be evaluated by functional studies in cathelicidin-knockout gastric cancer cells. Moreover, the chemopreventive effect of exogenous cathelicidin delivered by bioengineered L. lactis will be determined. Finally, the therapeutic application of vitamin D and the transformed cathelicidin in probiotic alone or in combination with chemotherapeutic agents will be assessed in an orthotopic model of gastric cancer. We expect that vitamin D and cathelicidin could corroborate to achieve potent chemopreventive action in a carcinogen-induced gastric cancer as well as to produce therapeutic effect in established orthotopic gastric tumor animal models. Our previous study also showed that cathelicidin was effective against different types of drug-resistant cancer cells. It is suggested that both agents are also useful for gastric tumors with drug-resistant cancer cells. This additional therapeutic action is unique and different from other classical anticancer drugs. Data derived from this study will open up new avenues for the use of vitamin D to induce endogenous cathelicidin and the transformed probiotic to deliver exogenous cathelicidin to the targeted site for the prevention and treatment of gastric cancer.

维生素D（VD）是一种廉价安全的预防、治疗骨类疾病药物。已有研究发现VD缺乏可导致消化道癌发病率增加，胃癌患者预后较差，提示VD具有预防、治疗胃癌的潜力。然而，VD在癌细胞中可激活其分解酶而抑制其抗癌活性，因此，明晰VD的抑癌信号路径、甄选新的治疗靶标是亟需解决的问题。我们初步发现：1）VD在胃癌中可能通过抗菌肽发挥抑癌功能；2）口服我们构建的抗菌肽分泌型益生菌，可将抗菌肽运送至胃上皮组织并发挥抑癌效应；3）该抗菌肽下调耐药基因表达，抑制耐药胃癌细胞生长。综上所述，本课题将采用抗菌肽敲除型小鼠进一步验证抗菌肽是否参与VD的抑癌信号通路，研究抗菌肽预防胃癌的效果。同时，明确VD和抗菌肽逆转胃癌耐药的分子机制，分析VD、抗菌肽与常规胃癌化疗药物之间的协同效应。通过VD诱导内源性抗菌肽/益生菌补充外源性抗菌肽在预防、治疗胃癌及逆转耐药性方面的基础研究，为研发经济、安全的抗胃癌药物提供理论指导。

胃癌是一种发病率和死亡率都极高的恶性肿瘤。手术切除结合化疗药物对晚期胃癌患者的治疗效果不佳，且胃癌耐药也是治疗中的一大难题。有研究显示，维生素D（VD）缺乏可加快胃癌的发生、发展，与更差的预后有关，而补充VD或增加内源性VD可降低患肠胃癌的风险。此外VD还能诱导胃癌细胞凋亡和周期阻滞，显示出抗胃癌作用。VD诱导产生的抗菌肽也显示出对恶性肿瘤的调控作用，还能抑制多药耐药肿瘤细胞株的生长。因此本研究验证VD是否通过调控抗菌肽来发挥抑制胃癌的作用，VD和抗菌肽能否逆转胃癌耐药性，以及研究抗菌肽分泌型乳酸乳球菌在胃癌预防中的作用。我们的研究结果显示，CAMP基因并不是VD发挥抑制胃癌作用的关键基因；VD和抗菌肽对耐药胃癌细胞有一定的抑制作用，奥沙利铂联合VD治疗增强了抗癌药物的抗胃癌效果，但并未逆转耐药细胞的耐药性，提示VD和抗菌肽作为抗耐药细胞联合用药潜力不大。VD和抗菌肽能维持小鼠肠道微生物的多样性及丰富度，降低肠道内病原菌，增加有益菌的含量，显示VD及抗菌肽可能用于调控肠道菌群，治疗某些因肠道菌群失调而导致的疾病。