Alkyltransferase Inhibitors for Cancer Chemotherapy

描述（由申请人提供）：人O 6-烷基鸟嘌呤-DNA烷基转移酶（hAGT）是肿瘤细胞对某些治疗性甲基化和氯乙基化试剂杀伤产生抗性的主要原因。O 6-苄基鸟嘌呤（BG）灭活hAGT已被证明在细胞培养中使人肿瘤对这些烷化剂敏感，并提高对裸鼠中人肿瘤异种移植物的治疗指数。BG的临床试验表明，由于缺乏足够的效力和肿瘤特异性以及容易产生对BG具有抗性的hAGT突变体，该药剂仅在有限的情况下才会成功。因此，需要更有效和特异性的抑制剂。本课题的主要目的有三：（1）研究2-氨基-O_4-苄基蝶啶类化合物对hAGT的失活机制。我们已经表明，这些化合物中的一些，包括O 4-苄基叶酸（BF）是hAGT的有效灭活剂。在这个目标中，分子建模，晶体学，定点诱变和强大的选择技术，以获得信息突变体将被用来了解这些化合物的BG的活性改善的基础上，失活的原因是干扰的DNA的存在，并改善这类化合物的设计。(2)研究叶酸转运与BF抑制细胞AGT和克服AGT介导的烷化剂耐药性的能力之间的关系。这些研究将跟进我们的初步研究，这些研究表明，BF在具有高水平叶酸转运的肿瘤细胞系中更有效地灭活AGT。(3)初步结果还表明，BG或O 6-苄基-2 '-脱氧鸟苷的其它叶酸衍生物和含有多个BG残基的寡脱氧核苷酸也具有提供改进的AGT抑制剂的性质。该目的的最终目标是通过进一步研究和适当修饰这些化合物，可以制备满足增加溶解度、增加针对BG抗性突变体的效力和肿瘤特异性的期望目标的AGT灭活剂。对抗癌药物的耐药性的发展是限制这些药物成功的主要因素。这些实验提供了一种逆转对用于这种治疗的烷化剂的抗性的众所周知的来源的方法。因此，它们将增加这些药剂产生治疗反应的可能性。

DESCRIPTION (provided by applicant): Human O6-alkylguanine-DNA alkyltransferase (hAGT) is a major cause of resistance of tumor cells to killing by certain therapeutic methylating and chloroethylating agents. Inactivation of hAGT by O6-benzylguanine (BG) has been shown to sensitize human tumors to these alkylating agents in cell culture and to improve the therapeutic index against human tumor xenografts in nude mice. Clinical trials with BG indicate that this agent will be successful only in limited situations due to the lack of adequate potency and tumor specificity and the facile production of mutants of hAGT resistant to BG. Therefore, more potent and specific inhibitors are needed. The proposal has 3 specific aims to develop such compounds: (1) To understand the mechanism of the inactivation of hAGT by 2-amino- O4-benzylpteridine derivatives. We have shown that some of these compounds including O4-benzylfolic acid (BF) are potent inactivators of hAGT. In this aim, molecular modelling, crystallography, site-directed mutagenesis and powerful selection techniques to obtain informative mutants will be used to understand the basis for the improved activity of these compounds over BG, the reason that the inactivation is interfered with by the presence of DNA and to improve design of this class of compounds. (2) To investigate the relationship between folate transport and the ability of BF to inactivate cellular AGT and overcome AGT-mediated resistance to alkylating agents. These studies will follow up our preliminary studies that have shown that BF is much more effective at inactivating AGT in tumor cell lines that have high levels of folate transport. (3) Preliminary results also indicate that other folate derivatives of BG or O6-benzyl-2'-deoxyguanosine and oligodeoxynucleotides containing multiple BG residues also have properties that would provide improved AGT inhibitors. The ultimate goal of this aim is that by further study and appropriate modifications of these compounds, AGT inactivators can be made that fill the desired goals of increased solubility, increased potency against BG resistant mutants and tumor specificity. The development of resistance to anticancer agents is a major factor in limiting the success of these drugs. These experiments provide a means to reverse a well know source of resistance to alkylating agents that are used in such therapy. As such, they will increase the likelihood that these agents will produce therapeutic responses.