Efficacy of 25-hydroxyvitamin D3 in colon cancer chemoprevention

描述(由申请人提供)：维生素D在预防结直肠癌(CRC)中的作用得到了广泛的认可。流行病学证据表明，维生素D(饮食摄入量和阳光暴晒)与患结肠癌的风险呈负相关。同样，血浆中25-羟基维生素D3[25(OH)D3]水平的降低已被证明与女性远端结肠息肉形成的增加有关。实验证据发现，用维生素D的活性代谢物1，25-二羟基维生素D3治疗动物，可以减轻结肠癌的负担。然而，1，25(OH)2D3会引起高钙血症。有鉴于此，人们已经合成了许多维生素D的类似物。然而，这些类似物中只有一小部分成功地用于预防和治疗结肠癌。本实验室合成了一种新的维生素D类似物--1a-羟基-24-乙基-胆钙化醇[1cc(OH)D5]。初步结果表明，在无毒水平上，该制剂可显著减少致癌物偶氮甲烷(AOM)所致小鼠畸形隐窝病灶(ACF)的形成85%。最近，人们观察到结肠上皮细胞中存在1a-羟基酶，它需要将无毒的25(OH)D3转化为1，25(OH)2D3-。这表明25(OH)D3本身可能是一种潜在的化学预防药物。最后，维生素D受体(VDR)的作用仍有待充分阐明。我们的初步数据表明，维生素D在结直肠癌化学预防活性中的作用需要VDR的表达，而VDR的上调可能会改变这种突变(3Jcatenin)。因此，我们假设25(OH)D3将作为结肠化学预防药物，其作用主要通过VDR介导。我们的具体目标是：(1)确定25(OH)D3在抑制AOM诱导的ACF和CF-1小鼠腺癌发展中的剂量效应；(1B)评价25(OH)D3、1a(OH)D5和1，25(OH)2D3在结肠癌发生中的相对疗效。为此，将使用AOM诱导的CRC模型；(2)评估VDR、1a(OH)酶和24-羟基酶在ACF和CRC进展中的作用。在这些研究中，将使用AOM诱导的VDR敲除致癌模型和它们的野生型对应模型来评估对25(OH)D3的反应性；以及(3)研究VDR在WNT/(3-catenin)信号通路中的中介作用及其与维生素D作用的关系。这些研究将为使用25(OH)D3预防结肠癌的发生提供理论依据。

DESCRIPTION (provided by applicant): The role of vitamin D in colorectal cancer (CRC) prevention is well recognized. Epidemiological evidence demonstrates an inverse relationship between vitamin D, both dietary intake and exposure to sunlight, and risk of developing colon cancer. Similarly, decreased plasma levels of 25-hydroxyvitamin D3 [25(OH)D3] have been shown to correlate with increased polyp formation in distal colons of women. Experimental evidence has found that treatment of animals with the active metabolite of vitamin D, 1,25-dihydroxyvitamin D3, reduces colon tumor burden. However, 1,25(OH)2D3 causes hypercalcemia. In view of this numerous analogs of vitamin D have been synthesized. Yet only a handful of these analogs have been successfully used for the prevention and therapy of colon cancer. In our laboratory we synthesized a novel vitamin D analog, 1a-hydroxy-24-ethyl-cholecalciferol [1cc(OH)D5]. The preliminary results showed that this agent at non-toxic levels significantly decreases the formation of aberrant crypt foci (ACF) by 85% in mice exposed to the carcinogen azoxymethane (AOM). Recently, it has been observed that 1a-hydroxylase, required to convert non-toxic 25(OH)D3 to 1,25(OH)2D3- is present in colonic epithelial cells. This suggests that 25(OH)D3 alone may serve as potential chemopreventive agent. Finally, the role of vitamin D receptor (VDR) remains to be fully elucidated. Our preliminary data indicates that vitamin D's role in CRC chemopreventive activity requires VDR expression, and that aberrant (3Jcatenin may be modified by up- regulation of VDR. Thus, we hypothesize that 25(OH)D3 will serve as a colon chemopreventive agent with its actions mediated primarily via VDR. Our specific aims are to: (1 A) Determine the dose response of 25(OH)D3 in suppressing the development of AOM-induced ACF and adenocarcinomas in CF-1 mice; (1B) Evaluate the relative efficacy of 25(OH)D3, 1a(OH)D5, and 1,25(OH)2D3 in colon carcinogenesis. For this aim the AOM-induced CRC model will be used; (2) Assess the role VDR, 1a(OH)ase, and 24-hydroxylase in ACF and CRC progression. For these studies an AOM-induced carcinogenesis model using VDR knockout and their wild-type counterparts will be used to evaluate the responsiveness to 25(OH)D3; and (3) Investigate the mediating role of VDR in the wnt/(3-catenin signaling pathway and its relation to vitamin D actions. The studies will provide a rationale for using 25(OH)D3 for the prevention of colon carcinogenesis.