Damaraju Vijaya L, Bouffard David Y, Wong Clarence K W, Clarke Marilyn L, Mackey John R, Leblond Lorraine, Cass Carol E, Grey Mike, Gourdeau Henriette
Department of Oncology, University of Alberta, and Cross Cancer Institute, Edmonton, Alberta, Canada.
BMC Cancer. 2007 Jul 3;7:121. doi: 10.1186/1471-2407-7-121.
Gemcitabine, a deoxycytidine nucleoside analog, is the current standard chemotherapy used as first-line treatment for patients with locally advanced or metastatic cancer of the pancreas, and extends life survival by 5.7 months. Advanced pancreatic cancer thus remains a highly unmet medical need and new therapeutic agents are required for this patient population. Troxacitabine (Troxatyl) is the first unnatural L-nucleoside analog to show potent preclinical antitumor activity and is currently under clinical investigation. Troxacitabine was recently evaluated as a first-line therapy in 54 patients with advanced adenocarcinoma of the pancreas and gave comparable overall results to those reported with gemcitabine in recently published randomized trials.
The human pancreatic adenocarcinoma cell lines, AsPC-1, Capan-2, MIA PaCa-2 and Panc-1, were exposed to troxacitabine or gemcitabine alone or in combination, for 72 h, and the effects on cell growth were determined by electronic particle counting. Synergistic efficacy was determined by the isobologram and combination-index methods of Chou and Talalay. Mechanistic studies addressed incorporation of troxacitabine into DNA and intracellular levels of troxacitabine and gemcitabine metabolites. For in vivo studies, we evaluated the effect of both drugs, alone and in combination, on the growth of established human pancreatic (AsPC-1) tumors implanted subcutaneously in nude mice. Statistical analysis was calculated by a one-way ANOVA with Dunnett as a post-test and the two-tailed unpaired t test using GraphPad prism software.
Synergy, evaluated using the CalcuSyn Software, was observed in all four cell-lines at multiple drug concentrations resulting in combination indices under 0.7 at Fa of 0.5 (50% reduction of cell growth). The effects of drug exposures on troxacitabine and gemcitabine nucleotide pools were analyzed, and although gemcitabine reduced phosphorylation of troxacitabine when cells were exposed at equal drug concentrations, there was no effect on phosphorylated pools at drug combinations that were synergistic. The amount of troxacitabine incorporated into DNA was also not affected by the presence of gemcitabine. In vivo testing against a human pancreatic (AsPC-1) xenograft mouse tumor model indicated that both drugs were more than additive at well-tolerated doses and schedule. The biological basis for this synergy is unclear as we did not observe changes in apoptosis, DNA repair, troxacitabine incorporation into DNA or troxacitabine metabolism in the presence of gemcitabine.
These data, together with phase I clinical data showing tolerability of both agents when combined, suggest combination therapy with troxacitabine and gemcitabine warrants further evaluation in advanced pancreatic cancer patients.
吉西他滨是一种脱氧胞苷核苷类似物，是目前用于局部晚期或转移性胰腺癌患者一线治疗的标准化疗药物，可使生存期延长5.7个月。晚期胰腺癌因此仍然是一个未得到满足的重大医疗需求，该患者群体需要新的治疗药物。曲沙他滨（Troxatyl）是首个显示出强大临床前抗肿瘤活性的非天然L-核苷类似物，目前正处于临床研究阶段。曲沙他滨最近在54例晚期胰腺腺癌患者中被评估为一线治疗药物，总体结果与近期发表的随机试验中吉西他滨报道的结果相当。
将人胰腺腺癌细胞系AsPC-1、Capan-2、MIA PaCa-2和Panc-1单独或联合暴露于曲沙他滨或吉西他滨中72小时，通过电子粒子计数确定对细胞生长的影响。协同疗效通过Chou和Talalay的等效线图和联合指数方法确定。机制研究涉及曲沙他滨掺入DNA以及曲沙他滨和吉西他滨代谢物的细胞内水平。对于体内研究，我们评估了两种药物单独和联合对裸鼠皮下植入的人胰腺（AsPC-1）肿瘤生长的影响。使用GraphPad prism软件通过单向方差分析（ANOVA）并以Dunnett作为事后检验以及双尾非配对t检验进行统计分析。
使用CalcuSyn软件评估，在所有四种细胞系的多个药物浓度下均观察到协同作用，在Fa为0.5（细胞生长减少50%）时联合指数低于0.7。分析了药物暴露对曲沙他滨和吉西他滨核苷酸库的影响，尽管当细胞以相等药物浓度暴露时吉西他滨会降低曲沙他滨的磷酸化，但在具有协同作用的药物组合中对磷酸化库没有影响。曲沙他滨掺入DNA的量也不受吉西他滨存在的影响。针对人胰腺（AsPC-1）异种移植小鼠肿瘤模型的体内测试表明，在耐受性良好的剂量和给药方案下，两种药物的作用均超过相加作用。由于我们在吉西他滨存在的情况下未观察到细胞凋亡、DNA修复、曲沙他滨掺入DNA或曲沙他滨代谢的变化，这种协同作用的生物学基础尚不清楚。
这些数据，连同I期临床数据显示两种药物联合使用时具有耐受性，表明曲沙他滨和吉西他滨联合治疗值得在晚期胰腺癌患者中进一步评估。
