Jounaidi Y, Waxman D J
Division of Cell and Molecular Biology, Department of Biology, Boston University, Boston, MA 02215, USA.
Cancer Res. 2001 Jun 1;61(11):4437-44.
Transduction of tumor cells with a cyclophosphamide (CPA)-activating cytochrome P-450 (P450) gene provides the capacity for localized prodrug activation and greatly sensitizes solid tumors to CPA treatment in vivo. The therapeutic impact of this P450-based cancer gene therapy strategy can be substantially enhanced by cotransduction of P450 reductase, a rate-limiting component of P450-dependent intratumoral CPA activation. The present study examined the possibility of further improving P450/P450 reductase-based gene therapy by using a novel schedule of CPA administration, involving repeated CPA injection every 6 days and previously shown to have an antiangiogenic component. 9L gliosarcoma cells transduced with the CPA-activating enzyme couple P450 2B6/P450 reductase and grown s.c. in immunodeficient severe combined immunodeficient (scid) mice were repeatedly challenged with 140 mg/kg CPA every 6 days. Full tumor regression leading to eradication of six of eight tumors was observed when the tumor size at the time of initial drug treatment was approximately 400 mm(3) (approximately 1.5% of body weight). Little or no overt toxicity of the repeated CPA treatment regimen was observed. The same CPA schedule was much less effective in inducing regression of 9L tumors that were not transduced with P450/P450 reductase. Repeated CPA treatment of mice bearing large, late-stage P450/P450 reductase-transduced tumors (approximately 9-16% of body weight) resulted in major (> or =95%) regression in 15 of 16 tumors, with tumor eradication observed in 2 cases. Although CPA resistance was found to emerge in the population of P450/P450 reductase-transduced tumors, this resistance primarily involved a loss of expression of the transduced P450 and/or P450 reductase gene, rather than development of intrinsic cellular resistance to the activated form of CPA. These findings demonstrate that repeated CPA treatment on a 6 day schedule can be highly effective when combined with P450/P450 reductase gene therapy and suggest that repeated transduction of tumors with prodrug-activation genes may be necessary to achieve tumor eradication and a sustained therapeutic response.
用环磷酰胺（CPA）激活细胞色素P-450（P450）基因转导肿瘤细胞，可实现局部前药激活，并大大提高实体瘤对CPA体内治疗的敏感性。通过共转导P450还原酶（P450依赖性肿瘤内CPA激活的限速成分），基于P450的癌症基因治疗策略的治疗效果可得到显著增强。本研究探讨了通过采用一种新的CPA给药方案进一步改善基于P450/P450还原酶的基因治疗的可能性，该方案包括每6天重复注射CPA，且先前已证明具有抗血管生成成分。用CPA激活酶对P450 2B6/P450还原酶进行转导的9L胶质肉瘤细胞，在免疫缺陷的重度联合免疫缺陷（scid）小鼠体内皮下生长，每6天用140mg/kg CPA反复攻击。当初始药物治疗时肿瘤大小约为400mm³（约占体重的1.5%）时，观察到完全肿瘤消退，导致8个肿瘤中的6个被根除。重复CPA治疗方案几乎没有观察到明显毒性。相同的CPA方案在诱导未用P450/P450还原酶转导的9L肿瘤消退方面效果要差得多。对携带大型晚期P450/P450还原酶转导肿瘤（约占体重的9 - 16%）的小鼠进行重复CPA治疗，导致16个肿瘤中的15个出现主要（≥95%）消退，2例观察到肿瘤根除。尽管在P450/P450还原酶转导的肿瘤群体中发现出现了CPA耐药性，但这种耐药性主要涉及转导的P450和/或P450还原酶基因表达的丧失，而不是对激活形式的CPA产生内在细胞耐药性。这些发现表明，每6天进行一次重复CPA治疗与P450/P450还原酶基因治疗联合使用时可能非常有效，并表明用前药激活基因对肿瘤进行重复转导可能是实现肿瘤根除和持续治疗反应所必需的。
