Division of Surgical Oncology, Massachusetts General Hospital Cancer Center and Harvard Medical School, Boston, MA, USA.
Cancer Gene Ther. 2012 Mar;19(3):160-70. doi: 10.1038/cgt.2011.70. Epub 2011 Nov 11.
Yeast cytosine deaminase (yCD) is a well-characterized prodrug/enzyme system that converts 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU), and has been combined with oncolytic viruses. However, in vivo studies of the interactions between 5-FC bioactivation and viral replication have not been previously reported, nor have the kinetics of transgene expression and the pharmacokinetics of 5-FC and 5-FU. We constructed a replication-conditional Herpes simplex virus 1 (HSV-1) expressing yCD and examined cytotoxicity when 5-FC was initiated at different times after viral infection, and observed that earlier 5-FC administration led to greater cytotoxicity than later 5-FC administration in vitro and in vivo. In animal models, 12 days of 5-FC administration was superior to 6 days, but dosing beyond 12 days did not further enhance efficacy. Consistent with the dosing-schedule results, both viral genomic DNA copy number and viral titers were observed to peak on Day 3 after viral injection and gradually decrease thereafter. The virus is replication-conditional and was detected in tumors for as long as 2 weeks after viral injection. The maximum relative extent of yCD conversion of 5-FC to 5-FU in tumors was observed on Day 6 after viral injection and it decreased progressively thereafter. The observation that 5-FU generation within tumors did not lead to appreciable levels of systemic 5-FU (<10 ng ml⁻¹) is important and has not been previously reported. The approaches used in these studies of the relationship between the viral replication kinetics, transgene expression, prodrug administration and anti-tumor efficacy are useful in the design of clinical trials of armed, oncolytic viruses.
酵母胞嘧啶脱氨酶（yCD）是一种经过充分研究的前药/酶系统，可将 5-氟胞嘧啶（5-FC）转化为 5-氟尿嘧啶（5-FU），并与溶瘤病毒结合使用。然而，之前尚未报道过 5-FC 生物活化与病毒复制之间相互作用的体内研究，也没有报告过转基因表达的动力学和 5-FC 和 5-FU 的药代动力学。我们构建了表达 yCD 的复制条件性单纯疱疹病毒 1（HSV-1），并在病毒感染后不同时间开始使用 5-FC 时观察到细胞毒性，结果表明，与后期相比，早期给予 5-FC 可导致体外和体内更大的细胞毒性。在动物模型中，12 天的 5-FC 给药优于 6 天，但剂量超过 12 天不会进一步提高疗效。与给药方案结果一致，病毒基因组 DNA 拷贝数和病毒滴度均在病毒注射后第 3 天达到峰值，此后逐渐下降。该病毒是复制条件性的，在病毒注射后长达 2 周内均可在肿瘤中检测到。在病毒注射后第 6 天观察到肿瘤中 yCD 将 5-FC 转化为 5-FU 的最大相对程度，此后逐渐降低。在肿瘤内生成 5-FU 并未导致系统 5-FU 水平（<10ngml⁻¹）明显升高，这一观察结果很重要，之前尚未报道过。这些研究中使用的方法，用于研究病毒复制动力学、转基因表达、前药给药和抗肿瘤疗效之间的关系，对于武装溶瘤病毒临床试验的设计非常有用。
