TASK ORDER TITLE: MICROBIAL METABOLITE MIMICRY, A NANO-DRUG FOR COLON CANCER PREVENTIONPREVENT PRECLINICAL DRUG DEVELOPMENT PROGRAM: PRECLINICAL EFF

大约75%的结直肠癌（CRC）病例是散发性的（发生在没有遗传倾向的患者中），这表明环境和生活方式的影响。由于饮食塑造了肠道微生物群，WD诱导的肠道生态失调和相关的致癌代谢产物，如次级胆汁酸脱氧胆酸（DCA），已被认为在CRC的发展中发挥关键作用。肠道微生物组的生态失调导致膳食营养代谢物的合成减少，特别是短链脂肪酸（SCFA）。事实上，将WD诱导的肠道生态失调与肥胖、炎症性肠病（IBD）和CRC风险增加联系起来的因素之一是SCFA合成水平降低。以肠道生态失调为靶点的化学预防策略可以推进CRC预防领域的发展。有效的药物将被口服递送以减轻由WD诱导的生态失调，从而预防肥胖人群中的CRC。 纤维的细菌发酵导致SCFA的产生，包括丁酸（BU）、丙酸和戊酸。在细胞外，SCFA通过G蛋白偶联受体（GPCR）介导的信号传导途径在免疫细胞、脂肪组织和其他器官部位发挥功能。在细胞内，BU和其他SCFA显示出组蛋白脱乙酰酶（HDAC）抑制特性，导致在肠道中活化视黄醇脱氢酶1A（ALDH 1A）并增强视黄醇转化为全反式视黄酸（RA），这调节免疫细胞的肠道归巢。已经表明，WD喂养的小鼠具有降低的BU浓度以及bcoA的拷贝数，bcoA是在肠道细菌中发现的产生BU的基因。 RA和HDAC抑制剂（HDACi）如BU的组合可能是抗肿瘤的，如我们先前的研究所表明的，其显示类维生素A和HDACi的组合可以诱导结肠癌细胞的凋亡。为了在临床前CRC模型中进一步测试这种方法，已经合成了名为BURA的纳米颗粒“基于RA的HDACi”（美国专利申请号17/522，405;国际公开号WO 2020/232399 Al）。 RA本身通常不具有凋亡癌细胞杀伤作用，然而，当RA与HDACi组合使用时，注意到对培养细胞的凋亡作用。治疗策略是使用亲水性聚乙烯醇（PVA）作为赋形剂共同递送BU和疏水性RA。PVA被证明可以提高稳定性和生物利用度，以及产生口服药物的持续释放，以治疗胃肠道疾病，如疟疾和炎症性肠病。所得纳米药物形成两亲性聚合物，其中BU和RA聚集并包封，从而在纳米颗粒的中心受到保护，其中亲水部分暴露以增加溶解度。以这种方式，游离药物BU和RA将通过遇到破坏共价键的内源性酯酶而一起释放。

Approximately 75% of colorectal cancer (CRC) cases are sporadic (occurring in patients not genetically predisposed to CRC), suggesting environmental and lifestyle influences. Because diet shapes the gut microbiota, WD-induced gut dysbiosis and related carcinogenic metabolites, such as the secondary bile acid deoxycholic acid (DCA), have been suggested to play a critical role in the CRC development. Dysbiosis of the gut microbiome leads to reduced synthesis of dietary nutrient metabolites, in particular short-chain fatty acids (SCFAs). Indeed, one of the factors linking the WD-induced gut dysbiosis and increased risk of obesity, inflammatory bowel disease (IBD), and CRC is the reduced level of SCFA synthesis. Gut dysbiosis-targeted chemoprevention strategy could advance the field of CRC prevention. An effective drug would be orally delivered to mitigate the dysbiosis induced by a WD, thereby preventing CRC in obese populations. Bacterial fermentation of fiber results in the production of SCFAs, including butyrate (BU), propionate, and valerate. Extracellularly, SCFAs exert functions through G-protein coupled receptor (GPCR)-mediated signaling pathways in the immune cells, adipose tissue, and other organ sites. Intracellularly, BU and other SCFAs show histone deacetylase (HDAC) inhibitory properties, resulting in the activation of retinaldehyde dehydrogenase 1A (ALDH1A) and the enhanced conversion of retinaldehyde into all-trans retinoic acid (RA) in the gut, which regulates the gut homing of immune cells. It has been shown that WD-fed mice have a reduced concentration of BU as well as the copy number of the bcoA, which is a BU-producing gene found in the intestinal bacteria. It is possible that a combination of RA and HDAC inhibitor (HDACi), such as BU, may be anti-tumorigenic, as has been suggested by our previous studies, that showed a combination of a retinoid and a HDACi can induce apoptosis of colon cancer cells. In order to further test this approach in preclinical CRC models, a nanoparticle “RA-based HDACi” named BURA has been synthesized (US Patent Application No. 17/522,405; International Publication No. WO 2020/232399 A1). By itself, RA does not typically have an apoptotic cancer cell killing effect, however, an apoptotic effect on cultured cells was noted when RA was used in combination with a HDACi. The treatment strategy is to co-deliver BU and hydrophobic RA using hydrophilic polyvinyl alcohol (PVA), as an excipient. PVA is proven to improve stability, and bioavailability, as well as generate the sustained release of oral drugs to treat gastrointestinal diseases such as malaria and inflammatory bowel disease. The resulting nanodrug forms an amphiphilic polymer in which BU and RA are aggregated and encapsulated, and thereby protected in the center of a nanoparticle with hydrophilic moieties exposed to increase solubility. In this way, the free drugs BU and RA will be released together by encountering endogenous esterase that breaks the covalent bonds.