MODULATION OF 5-FU PHARMACOLOGY BY PALA & DIPYRIDAMOLE

虽然5-FU是治疗结直肠癌最有效的药物， 癌症，反应率（10-20%）相当低;因此，结肠肿瘤 最初或随后对该药剂具有抗性。 5-Fu 体外耐药性与细胞内高水平的尿苷有关 核苷酸（DUMP和UTP），它们与5-FU代谢物竞争靶点 位点（TMP合酶，RNA），并通过 去磷酸化和跨膜流出。 一种额外的机制， 对5-FU的耐药性是通过以下方式增强预形成尿苷（Urd）的利用： 肿瘤细胞通过嘧啶补救途径。 拟议的临床和实验室研究的目标是增加 通过克服这些耐药机制， PALA（阻断从头嘧啶合成），从而降低细胞内 竞争核苷酸、DUMP和UTP以及双嘧达莫（DP）的池， 阻断核苷转运，从而阻断嘧啶补救途径。 DP可通过阻止FU-1的细胞外排进一步增强5-FU的作用。 核苷（DFURD FdUrd），从而使它们被重新合成代谢为 活性代谢物FUTP和FdUMP。 技术转移的第一个领域是从先前的实验室观察到 实际的临床应用将涉及使用PALA来降低肿瘤 单元UTP和DUMP水平。 最初的第一阶段试验将确定最低的 具有接近最大可量化生化效应的PALA剂量， 也就是说，降低血浆Urd并抑制WBC ATCase活性至少6 天 一项与PALA + DP同时进行的I期试验将发现 DP通过阻断血浆补救来增强PALA的作用 核苷，Dthd和Urd。 在确定了“最佳低剂量的 为了进行有效的生化调节，5-FU的MTD将是 测定 这些同时进行的I期研究之后， 比较PALA/5-FU与DP/PALA/5-FU的随机（2项同时进行）II期试验， 未接受治疗的晚期结直肠癌患者。 预期 每组的缓解范围（CR+PR）至少为30- 40%。 将对选定患者的新鲜手术标本进行检查， 确定DUMP和UTP的内在库，并评估TMP合酶活性， 在治疗前辨别这些参数在人类肿瘤中的范围。 在最低点给予5-FU后，将获得额外的活检 PALA + DP治疗后的血浆Urd。 这将决定范围 获得的FdUMP合并物、DUMP的蓄积和 TMP合酶作为DUMP/FdUMP比率的函数。 这些细胞研究 将有助于整合临床试验的结果， 建立一个数据库，用于未来的临床设计 调查方法。 缓解患者在疾病缓解时的肿瘤标本再活检 急性加重将阐明药物可能的生化机制， 阻力 由I期实验室确定的最佳剂量和时间表 和临床观察结果将在第二阶段方案中进行测试， 未接受治疗的晚期结直肠癌患者。 继续实验室 将在整个II期试验期间继续监测。 这些结果和 经验 将这些技术用于临床样本将具有适用性 对其他5-FU敏感的人类肿瘤，如乳腺、头颈部， 卵巢癌

Although 5-FU is the most effective drug for the treatment of colorectal carcinoma, response rates (10-20%) are quite low; therefore, colon tumors are either initially or subsequently resistant to this agent. 5-FU resistance in vitro has been linked to high intracellular levels of uridine nucleotides (DUMP and UTP), which compete with 5-FU metabolites for target site (TMP synthase, RNA), and to rapid elimination of FdUMP via dephosphorylation and transmembrane efflux. An additional mechanism of resistance to 5-FU is enhanced utilization of preformed uridine (Urd) by tumor cells via the pyrimidine salvage pathway. The goal of the proposed clinical and laboratory studies is to increase response rates to FU therapy by overcoming these resistance mechanisms with PALA (blocks de novo pyrimidine synthesis), and thus lowers intracellular pools of competing nucleotides, DUMP and UTP, and dipyridamole (DP) which blocks nucleoside transport and thus blocks the pyrimidine salvage pathway. DP may further enhance 5-FU action by preventing cellular efflux of FU- nucleosides (DFURD FdUrd) and thus allow them to be re-anabolized to athe active metabolites FUTP and FdUMP. The first area of technology transfer from prior laboratory observations to practical clinical application will involve the use of PALA to lower tumor cell UTP and DUMP levels. Initial Phase I trials will determine the lowest dose of PALA which has a near-maximum quantifiable biochemical effect, i.e., lowers plasma Urd and inhibits WBC ATCase activity for at least 6 days. A concurrent Phase I trial with PALA + DP will discern the ability of DP to enhance PALA's effects by blocking salvage from plasma nucleosides, Dthd and Urd. Having determined the "optimal low dose of PALA" for effective biochemical modulation, the MTD of 5-FU will then be determined. These concurrent Phase I studies will be followed by a randomized (2 concurrent) Phase II trials of PALA/5-FU vs. DP/PALA/5-FU in untreated patients with advanced colorectal carcinoma. The expected response range (CR+PR) for each arm is at least 30-40%. Fresh surgical specimens from selected patients will be examined to determine intrinsic pools of DUMP & UTP and assess TMP synthase activity to discern the range of these parameters in human tumors before therapy. Additional biopsies will be obtained after 5-FU administration at the nadir of plasma Urd following PALA + DP treatment. This will determine the range of attained FdUMP pools, the accumulation of DUMP, and the inhibition of TMP synthase as a function of the DUMP/FdUMP ratio. These cellular studies will be useful in integrating the results of the clinical trial and will establish a data base for use in the design of future clinical investigative approaches. Re-biopsy of tumor specimens in responding patients at athe time of disease exacerbation will elucidate possible biochemical mechanisms of drug resistance. The optimal dosages and schedule as determined by the Phase I laboratory and clinical observations will be tested in a Phase II protocol in untreated patients with advanced colorectal cancer. Continued laboratory monitoring will continue throughout this Phase II trial. These results and experience in the use of these techniques with clinical samples will have applicability to other 5-FU-sensitive human neoplasms such as breast, head and neck and ovarian cancer.