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，有效率(10%-20%)相当低；因此，结肠肿瘤 最初或随后对该制剂产生抗药性。5-FU 体外耐药性与细胞内高水平的尿苷有关 与5-FU代谢产物竞争靶点的核苷酸(DUMP和UTP) 位点(TMP合成酶，RNA)，并通过 去磷酸化和跨膜外排。一种额外的机制， 预先形成的尿苷(URD)的利用增强了对5-FU的耐药性 肿瘤细胞通过嘧啶挽救途径。 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来提高FU治疗的应答率 Pala(阻止从头合成嘧啶)，从而降低细胞内 相互竞争的核苷酸池，Dump和UTP，以及双嘧达莫(DP) 阻断核苷转运，从而阻断嘧啶抢救途径。 DP可能通过阻止5-FU的细胞外流进一步增强5-FU的作用。 核苷(DFURD FdUrd)，从而允许它们被重新合成到AAT 活性代谢产物FUTP和FdUMP。 技术转让的第一个领域是从先前的实验室观察到 实际的临床应用将包括使用PALA来降低肿瘤 单元UTP和转储级别。最初的第一阶段试验将确定最低的 具有近乎最大可量化生化效应的PALA剂量， 即降低血浆URD并抑制WBC ATCase活性至少6 几天。与PALA+DP同时进行的I期试验将识别 DP阻断血浆挽救作用增强PALA的作用 核苷、Dthd和Urd。在确定了“最佳低剂量的 为了有效的生化调节，5-FU的MTD将被 下定决心。这些同时进行的第一阶段研究之后将会有一个 PALA/5-FU与DP/PALA/5-FU的随机(2个并行)II期临床试验 未经治疗的晚期结直肠癌患者。预期中的 每支手臂的反应范围(CR+PR)至少为30-40%。 来自选定患者的新鲜手术样本将被检查以 确定转储和UTP的内部池并评估TMP合成酶活性 在治疗前辨别这些参数在人类肿瘤中的范围。 在最低点注射5-FU后，将获得额外的活组织检查 PALA+DP治疗后血浆URD的变化。这将确定范围 已获得的FdUMP池、转储的积累和对 TMP合成酶作为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，并将 建立用于未来临床设计的数据库 调查方法。 有反应的患者在发病时对肿瘤标本进行再次活检 病情加重将阐明药物可能的生化机制 抵抗。 一期实验室确定的最佳剂量和方案 临床观察将在#年的第二阶段方案中进行测试 未经治疗的晚期结直肠癌患者。后续实验室 监测将在整个第二阶段试验期间继续进行。这些结果和 有以下经验 这些技术在临床样本中的使用将具有适用性。 对其他5-FU敏感的人类肿瘤，如乳房、头颈部和 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.