Uptake of temozolomide in a rat glioma model in the presence and absence of the angiogenesis inhibitor TNP-470.

The angiogenic phenotype is associated with hyperpermeable capillaries. Through treatment with angiogenesis inhibitors capillary permeability may be reduced, and it can be anticipated that cytotoxic agents coadministered may be adversely affected. The current investigation examined this possibility for the combination of TNP-470, an angiogenesis inhibitor, and temozolomide (TMZ), a DNA-alkylating agent with demonstrated activity in brain tumors. TNP-470 (30 mg/kg) was given s.c. on days 6, 8, 10, 12, and 14 following s.c. implantation of rat C6 glioma cells in Sprague-Dawley rats. On the 15th day following tumor implantation, control (no TNP-470) and treated rats received 40 mg/kg of TMZ intraarterially. Prior to dosing, a linear microdialysis probe was placed in the tumor to collect interstitial fluid. Plasma and interstitial fluid samples were collected for 8 h and measured for TMZ by a high-performance liquid chromatography assay. Pharmacokinetic parameters for TMZ were calculated by noncompartmental methods. Total systemic clearance (39.8 +/- 7 versus 44.2 +/- 14 ml min(-1) kg(-1)) and volume of distribution (5.4 +/- 2 versus 5.2 +/- 0.8 L kg(-1)) were not significantly different in control and TNP-470-treated animals. However, the mean TMZ area under the interstitial fluid concentration-time curve was reduced by 25% in the TNP-470-treated group compared to the control (5450 +/- 1892 versus 4120 +/- 1790 micrograms min ml(-1); P < 0.05). It appears that TNP-470 caused this reduction in the tumor uptake of TMZ by its pharmacodynamic action on the tumor vasculature. Since combination regimens using angiogenesis inhibitors and cytotoxic drugs will be needed to determine how such combinations can be used effectively. The current animal model, which utilized tumor microdialysis, can serve as a model to further analyze combination chemotherapy.