gms | German Medical Science

Objective: Chemoresistance to temozolomide (TMZ) and insufficient drug delivery into intracranial neoplasms impair the efficacy of glioma therapy. JS-K, a diazeniumdiolate activated to release high levels of NO by glutathione-S-transferase (GST) enzymes, inhibits tumor cell growth in vitro and in vivo and has chemosensitizing effects. The objective was to evaluate concomitant therapy of JS-K and TMZ in vitro and in vivo.

Methods: U87 cells were grown in a standardized manner to 80% confluence. Cells were exposed to JS-K (5–25 μM) and TMZ (1–150 μM) alone or a combination for 24 h. Cell viability was assessed after 24, 48 and 72 h by MTT assay.

Nude rats (n=10/group) were inoculated with 5x10⁵ U87 cells into the right striatum. Treatment with JS-K (5mg/kg s.c.), TMZ (3mg/kg i.p.), or with a combination was performed 3x/week starting on day 8. MRI scans were performed on 4 rats per group on day 8 and 15 using T2 weighted images, dynamic contrast enhanced MRI (DCE-MRI) and diffusion weighted imaging (DWI) to assess tumor size, perfusion and vessel permeability. The apparent diffusion coefficient (ADC) was calculated to determine cell density. Tumor volume was calculated on MRI. Statistical analysis was performed by t-test and Kaplan Meier survival statistics.

Results: Concomitant incubation of U87 with JS-K and TMZ increased the cytotoxic effect of TMZ significantly in a dose-dependent manner in vitro. Combinations of 15-25 μM JS-K with TMZ concentrations between 20 and 100 μM lead to a 1.8 to 22.4-fold reduction in cell viability compared to TMZ alone.

Treatment of rats harboring U87 gliomas with JS-K and/or TMZ did not result in a survival benefit in any of the groups using this dosing regimen with a mean survival of 22±2 days (p>0.05). Tumor volume was not significantly different but the change in tumor growth between day 8 and day 15 was smallest in the TMZ group (p=0.088). Although DCE-MRI showed no significant differences in tumor perfusion and permeability, ADC values were significantly reduced in the JS-K group compared to untreated controls (p=0.02).

Conclusions: The potent chemosensitizing effect of JS-K to TMZ in U87 glioma cells in vitro could not be reproduced in vivo. As insufficient delivery into the tumor after s.c. injection might account for this, future studies will investigate JS-K effects on proliferation, perfusion and permeability in a survival study with serial MRI imaging using i.v. delivery and different dosing regimens.