THYMIDYLATE SYNTHASE INHIBITORS IN HEAD AND NECK CANCER

胸苷酸合酶(TS)是从头合成过程中的一个重要酶 因为它是细胞增殖的关键酶， 它已成为肿瘤治疗药物开发的重要靶点。 虽然5-氟尿嘧啶和甲氨蝶呤是药物治疗的有效药物。 头颈部鳞状细胞癌的治疗 颈部，缺乏治疗选择性和耐药性仍然是主要的 使用这些药物进行治疗的障碍。最近，抗代谢药物 它们是基于叶酸的特异性TS抑制剂；D1694， AG331和AG337。这些药物目前处于不同的临床阶段。 结直肠癌的临床活动性评估。 这项研究的总体目标是发展基本知识， 生化和分子机制的临床评价 抗代谢药物TS的体内治疗选择性 为了实现这一目标，分化程度较低的人类 咽鳞状细胞癌(FADU)和分化良好的人表皮样癌 宫颈癌(A253)细胞株将用于实现 以下是具体目标：1)确定治疗的选择性 TS抑制剂是一种时序依赖假说：观察到胃肠道毒性 在临床和模型系统中使用单一静脉注射。ZD1694的推送可以 通过分次剂量或连续静脉注射改变。输液。很有可能 药物的峰值血药浓度对观察到的 组织特异性毒性，即以胃肠道为剂量限制 毒性。实体瘤中细胞很少，处于S期，单个 药物剂量可能不会有那么好的疗效。因此，SCC细胞系将用于 以确定最佳剂量-时间表关系的裸鼠 最大治疗指数。2)评价血浆dThd和 组织胸腺挽救通路在TS治疗选择性中的作用 DThyd磷酸化酶、干扰素和潘生丁的抑制剂作用 将对(DP)进行评估。假设：小鼠血浆中dThyd水平较高 (约1微摩尔)具有活性组织dThyd激酶补救作用 途径降低从头合成胸苷的治疗潜力 抑制剂。DThyd磷酸化酶降低血浆dThyd的作用 DP对核苷转运的抑制和dThyd的激活 干扰素对正常人(骨骼)胸腺苷酸池的磷酸化作用 将对骨髓)和肿瘤组织进行评估。3)生化和生物化学鉴定 与药物治疗选择性相关的分子决定因素。 假设：TS的高度和持续抑制(&gt；95%，至少 3细胞倍增时间)是诱导的基本前提 不可逆的G1/S阻滞，P53上调(野生型)和高水平 肿瘤组织中持续的DNA损伤。4)确定是否缺少 抗肿瘤活性与肿瘤耐药性的形成有关 假设：对D1694的耐药性与减少有关 叶多聚谷氨酸合成酶及TS改变的AG331和AG337 导致TS抑制程度和持续时间的降低。与 在使用这些新代理的模型系统中获得的知识，选择性 头颈癌患者可设计和验证治疗方法 和其他实体肿瘤恶性肿瘤。

Thymidylate synthase (TS) is an essential enzyme in the de novo synthesis of thymidylate and because it is a critical enzyme for cell proliferation, it has been an important target for drug development in cancer therapy. Although 5-fluorouracil and methotrexate are active agents in the treatment of patients with squamous cell carcinoma (SCC) of the head and neck, lack of therapeutic selectivity and resistance remain major obstacles to curative therapy with these agents. Recently, antimetabolites which are folate-based specific TS inhibitors became available; D1694, AG331 and AG337. These agents are now at various stages of clinical evaluation with demonstrated clinical activity in colorectal cancer. Overall goal of this research is to develop basic knowledge that can be evaluated clinically concerning the biochemical and molecular mechanisms associated with in vivo therapeutic selectivity of antimetabolites TS inhibitors in SCC tumors.To achieve this goal, less-differentiated human SCC of the pharynx (FaDu), and well-differentiated human epidermoid carcinoma of the neck (A253) cell lines will be used to achieve the following specific aims:1)to establish that the therapeutic selectivity of TS inhibitors is schedule dependent Hypothesis: G.I. toxicity observed clinically and in model system with a single i.v. push of ZD1694 can be altered by fractionated doses or by continuous i.v. infusion. It is likely that peak plasma concentration of the drug contributes to the observed tissue specific toxicity, namely gastrointestinal as the dose limiting toxicity. With few cells in solid tumors which are in S-phase, a single drug dose may be less therapeutic. Thus SCC cell lines will be used in nude mice to define the optimal dose-schedule relationship associated with maximum therapeutic index. 2)to evaluate the role of plasma dThd and tissue dthyd salvage pathway in the therapeutic selectivity of TS inhibitors The role of dThyd phosphorylase, interferon and dipyridamole (DP) will be evaluated. Hypothesis: High plasma level dThyd in mice (approximately 1 micromole) with active tissue dThyd kinase salvage pathway reduce the therapeutic potential of de novo thymidylate synthesis inhibitors. The effects of reducing plasma dThyd by dThyd phosphorylase, inhibition of nucleoside transport by DP, and activation of dThyd phosphorylase by interferon on thymidylate pools in normal (G.I., bone marrow) and tumor tissues will be assessed. 3)to identify biochemical and molecular determinants associated with drug therapeutic selectivity. Hypothesis: high degree and sustained inhibition of TS (>95%, for at least 3 cell doubling time) are essential prerequisites for inducting irreversible G1/S block, upregulation of p53 (wild) and high level and sustained DNA damage in tumor tissue. 4)to determine if the lack of antitumor activity is associated with development of tumor drug resistance Hypothesis: Resistance to D1694 is associated with decreased folypolyglutamate synthase and to AG331 and AG337 with altered TS resulting in a decrease in degree and duration of TS inhibition. With the knowledge gained in model system with these new agents, selective treatment may be designed and verified in patients with head & neck cancer and other solid tumor malignancies.