Using vitamin D glucuronide pro-drugs to prevent/treat colon cancer

描述（由申请人提供）：结肠癌细胞的生长，无论是在体外还是在体内，已被证明是由维生素D的活性激素形式，1，25-二羟基维生素D3抑制。不幸的是，有效治疗体内结肠肿瘤所需的1，25-二羟维生素D3剂量也会刺激维生素对钙稳态的经典作用，导致危及生命的高钙血症。我们的初步数据表明，与公认的教条相反，口服或皮下注射给药的1，25-二羟基维生素D3实际上很少到达结肠以改变靶基因的转录。我们通过合成1，25-二羟基维生素D3的前药形式来解决这些问题。该前药能够将大量的激素直接递送至结肠，而不会显著增加1，25-二羟基维生素D3的血液浓度，从而降低高钙反应的风险。这是通过将葡糖苷酸与激素结合在一个使其具有生物学活性并对哺乳动物消化酶具有抗性的连接中来实现的。然而，当到达下肠道时，由常驻细菌群体产生的葡糖苷酸酶将葡糖苷酸裂解并释放活性激素。目前的提案将确定使用葡糖苷酸前药系统将1，25-二羟基维生素D3靶向递送至下肠道是否可以减缓或预防结直肠肿瘤的发展，而不会诱导全身性高钙毒性。慢性炎症有助于癌变的发展;患有溃疡性结肠炎和克罗恩病的人患结肠癌的风险增加。目的1将确定维生素D葡糖苷酸前体药物在炎症相关致癌小鼠模型中预防或限制氧化偶氮甲烷/葡聚糖硫酸钠诱导的结肠肿瘤形成和大小的有效性。最初与家族性结肠癌相关的腺瘤性结肠息肉病（Apc）基因突变也已在人类结肠肿瘤的优势中被确定。目的2将确定葡糖苷酸在ApcMin/+小鼠中预防或限制结肠肿瘤形成和大小的作用，ApcMin/+小鼠携带小鼠Apc基因突变，并作为散发性人结肠癌模型。使用1，25-二羟基维生素D3或其类似物治疗结肠癌的先前研究受到高钙血症的发展和到达结肠的亚治疗量的限制。目前建议的优势在于能够将高浓度的1，25-二羟基维生素D3直接靶向递送至结肠，因此可以在没有高钙血症的情况下评估其对结肠癌发生的影响。

DESCRIPTION (provided by applicant): Growth of colon cancer cells, both in vitro and in vivo, has been shown to be inhibited by the active hormonal form of vitamin D, 1,25-dihydroxyvitamin D3. Unfortunately, doses of 1,25-dihydroxyvitamin D3 required to effectively treat colon tumors in vivo also stimulate the vitamin's classic effects on calcium homeostasis, resulting in the development of life-threatening hypercalcemia. Our preliminary data indicate, contrary to accepted dogma, very little 1,25-dihydroxyvitamin D3 administered either orally or injected subcutaneously actually reaches the colon to alter the transcription of target genes. We have approached these problems by synthesizing a pro-drug form of 1,25-dihydroxyvitamin D3. The pro-drug is capable of delivering high amounts of the hormone directly to the colon without substantially increasing blood concentrations of 1,25-dihydroxyvitamin D3, thus reducing the risk of a hypercalcemic response. This was achieved by conjugating a glucuronide to the hormone in a ¿-linkage that renders it biologically inactive and resistant to mammalian digestive enzymes. Upon reaching the lower intestinal tract, however, ¿-glucuronidase enzymes produced by resident bacterial populations cleave off the glucuronide and release the active hormone. The current proposal will determine whether using the glucuronide pro-drug system to target delivery of 1,25-dihydroxyvitamin D3 to the lower intestinal tract can slow or prevent the development of colorectal tumors without inducing systemic hypercalcemic toxicity. Chronic inflammation contributes to the development of carcinogenesis; people suffering from ulcerative colitis and Crohn's disease have an increased risk of developing colon cancer. Aim 1 will determine the efficacy of the vitamin D glucuronide pro-drug in preventing or limiting the formation and size of colon tumors induced by azoxymethane/dextran sodium sulfate in a mouse model of inflammation-associated carcinogenesis. Mutations in the adenomatous polyposis coli (Apc) gene, originally linked to familial forms of colon cancer, have also been identified in the preponderance of human colon tumors. Aim 2 will determine the effects of the glucuronide in preventing or limiting the formation and size of colon tumors in ApcMin/+ mice that carry a mutation in the mouse Apc gene and serve as a model of sporadic human colon cancer. Prior studies using 1,25-dihydroxyvitamin D3 or its analogs in the treatment of colon cancer have been limited by the development of hypercalcemia and sub-therapeutic amounts reaching the colon. The strength of the current proposal is the ability to target delivery of high concentrations of 1,25- dihydroxyvitamin D3 directly to the colon so its effects on colon carcinogenesis can be assessed in the absence of hypercalcemia.