Targeting CDK4 in TGS-B Inactivated Gastrointestinal Cancers

最近的研究表明，TGF-B通过在细胞周期的G1期阻断细胞周期进程来抑制细胞增殖，因此被认为是一种肿瘤抑制蛋白。大多数人类癌症似乎已经失去了对TGF-B的生长抑制反应。我们的初步研究表明，TGF-B信号失活的前肠癌表达高水平的细胞周期蛋白D1和CDK4水平，这表明这些蛋白的表达失调可能有助于这些肿瘤的发展。黄酮吡醇是一种成熟的Cdk抑制剂，用于某些癌症的治疗方案，已知可以抑制大多数已知的Cdk，特别是CDKs 7, 8和9，在临床试验中被认为是该药物引起毒副作用的主要原因。根据这些观察结果，我们筛选了一个具有CDK-4特异性抑制作用的激酶抑制剂化合物库，并分离出两个具有CDK4抑制活性的新分子（ON55290和ON27900）。在这项应用中，我们建议进行临床前研究，以测试这些分子在胃肠道癌症治疗中的有效性。该建议的目的是：

Recent studies have shown that TGF-B inhibits cell proliferation by blocking cell cycle progression at the G1 phase of the cell cycle and hence, is thought to function as a tumor suppressor protein. Most human cancers appear to have lost their growth-inhibitory response to TGF-B. Our preliminary studies show that foregut cancers with inactivation of TGF-B signaling express high levels of cyclin D1 and CDK4 levels, suggesting that the deregulated expression of these proteins may contribute to the development of these tumors. Flavopiridol, an established Cdk inhibitor used in treatment protocols for certain cancers, is known to inhibit most known CDKs especially against CDKs 7, 8 and 9, is thought to be largely responsible for the toxic side effects caused by this drug in clinical trials. In light of these observations, we have screened a compound library of kinase inhibitors for CDK-4 specific inhibition and isolated two novel molecules (ON55290 and ON27900) which exhibit CDK4 inhibitory activity. In this application, we propose to carry out pre-clinical studies to test the usefulness of these molecules in gastrointestinal cancer therapy. The aims of the proposal are: 1. To further validate the role of CDK4 in Elf+/-, Elf+/-:Smad3+/- tumor model system through evaluation of tumor incidence in CDK4+/V El+/- : CDK4+/-: Elf/Elf[+]-Smad4[+/-] and CDK4[+/-]; Elf¿/Elf+:Smad4+/- mice. 2. (a) To expand the chemical library in an effort to understand the structure-activity relationship (SAR) of CDK4 inhibitors and (b) to conduct a detailed kinetic analysis of CDK4 inhibition by ON55290 and ON27900 to gain critical information on the mechanisms by which these compounds elicit their inhibitory effects on CDK4. 3. To determine the molecular mechanisms by which ON55290 and ON27900 bring about growth arrest and death of human gastrointestinal cancer cells. 4. To assess the safety and pharmacokinetics of the candidate drug in animal models of gastrointestinal cancers that develop in the TGF-f3 inactivated state.