Intravenous RMP-7 Increases Delivery of Ganciclovir into Rat Brain Tumors and Enhances the Effects of Herpes Simplex Virus Thymidine Kinase Gene Therapy

Abstract

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.

Overview summary

We studied the effects of RMP-7 on ganciclovir (GCV)/herpes simplex virus thymidine kinase (HSV-tk) gene therapy in C6 gliomas. The bystander and cytocidal effects of GCV were shown in vitro. Rats bearing transduced (HSV-tk ⁺) or nontransduced (HSV-tk¯) intracerebral gliomas were treated for 7 days with intravenous infusions of GCV alone or with GCV and RMP-7 (2.5 μg/kg/day). At 100 mg/kg/day, GCV eradicated all HSV-tk¯ and HSV-tk ⁺ tumors. At 5 mg/kg/day, GCV reduced the growth of HSV-tk¯ gliomas by 42% (alone) and by 88% (with RMP-7). At 0.5 mg/kg/day, GCV plus RMP-7 enhanced the regression of HSV-tk ⁺ gliomas by 87% compared with GCV alone. Tumoral uptake of GCV was significantly (1.7 to 2.6-fold) increased by RMP-7. We conclude that RMP-7 could be an important adjunctive treatment for suicide gene therapy of brain tumors, while the RMP-7/GCV combination may have a significant antitumor effect in untransfected gliomas.