gms | German Medical Science

Objective: Nitric oxide has potent dose-dependent growth-inhibitory and chemosensitizing effects in tumors. The nitric oxide (NO)-donor PABA/NO (O₂-(2,4-dinitro-5-(N-methyl-N-4-carboxyphenylamino) phenyl] 1-N,N-dimethylamino)diazen-1-ium-1,2-diolate) selectively releases NO after enzymatic activation by the glutathione S-transferase (GST-π) which is overexpressed in malignant glioma cells and contributes to chemoresistance.

Methods: We evaluated the growth-inhibitory effect of PABA/NO alone (2-100 µM) and in combination with imatinib (Glivec^®, 10-30 µM) and carboplatin (25-500 µM) in U87 cells. Fibroblasts were tested as non-neoplastic controls. Viability was assessed by MTT assay after incubation for 24h, and 48 & 72h after drug removal. Statistical analysis was performed by ANOVA and post-hoc tests.

Results: PABA/NO had a dose-dependent cytotoxic effect in U87 cells with an IC₅₀ of 45 µM (p<0.0001). Imatinib as monotherapy was not effective in U87 cells. However, concomitant incubation of U87 with doses of PABA/NO and imatinib which did not have a significant cytotoxic effect alone induced a significant increase in cell death indicating a chemosensitizing effect of PABA/NO (p<0.0001). A dose-dependent cytotoxic effect was observed after carboplatin exposure (IC₅₀ 150 µM) which could be increased in combination with PABA/NO doses ≥25 µM (p=0.008). Fibroblasts were significantly less affected by PABA/NO (p=0.0016) than U87 cells. GST-π expression was confirmed by immunocytochemistry.

Conclusions: PABA/NO has potent cytotoxic and chemosensitizing effects in U87 glioma cells. Current research activities focus on studying the intracellular pathways involved in the effect of the NO donor and on safety and efficacy in an intracranial U87 tumor model.