Intravenous RMP-7 increases delivery of ganciclovir into rat brain tumors and enhances the effects of herpes simplex virus thymidine kinase gene therapy

Herpes simplex virus thymidine kinase (HSV-tk) gene therapy for brain tumors depends on ganciclovir (GCV) and its transport across the blood-brain tumor barrier (BBTB). We examined whether RMP-7, the bradykinin analog and potent BBTB permeabilizer, could enhance the efficacy of GCV treatment of brain tumors by increasing the BBTB delivery of GCV. In vitro, a significant bystander cytocidal effect of GCV was shown in mixed HSV-tk-transduced (HSV-tk⁺) and control vector-transduced (HSV-tk^-) C6 glioma cultures. A dose-dependent cytotoxic effect of GCV on untransformed C6 cells was also shown. In vivo, rats with 100% HSV-tk⁺ or 100% HSV-tk^- intracerebral C6 gliomas were treated for 7 days with intravenous infusions of GCV alone or with GCV and RMP-7 (2.5 μg/kg/day). The growth of HSV-tk⁺ and HSV-tk^- gliomas decreased with increasing doses of GCV. A high dosage (100 mg of GCV/kg/day) eradicated all HSV-tk^- and HSV-tk⁺ tumors. An intermediate dosage (5 mg of GCV/kg/day) reduced the growth of HSV-tk^- gliomas by 42% if given alone, and by 88% in combination with RMP-7. A low dosage (0.5 mg of GCV/kg/day) in combination with RMP-7 enhanced the regression of HSV-tk⁺ gliomas by 87% compared with GCV alone. Low-dose GCV was ineffective in HSV-tk^- tumors, RMP-7 increased [³H] GCV tumoral uptake by 2.6- and 1.7-fold in the tumor center and periphery, respectively. We conclude that RMP-7 could be an important adjunctive treatment for suicide gene therapy of brain tumors, while an RMP-7/GCV combination may also have a significant antitumor effect in untransfected gliomas.