Differential effects of nitric oxide on blood-brain barrier integrity and cerebral blood flow in intracerebral C6 gliomas.
ABSTRACT Nitric oxide (NO) signaling in tumors and endothelial cells regulates vascular permeability and blood flow and therefore influences tumor uptake and response to therapeutic compounds. As delivery and efficacy of chemotherapy is impaired in CNS neoplasms due to a partially intact blood-brain barrier (BBB), we studied the effects of NO released by the short-acting NO donor disodium 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate methanolate (PROLI/NO) on BBB integrity and blood flow in C6 gliomas using [¹⁴C]-aminoisobutyric acid (AIB) and [¹⁴C]-iodoantipyrine quantitative autoradiography. PROLI/NO selectively increased intratumoral uptake of [¹⁴C]AIB and [¹⁴C]sucrose when given as a 3-minute intracarotid infusion or a 15-minute i.v. infusion (AIB: tumor, K₁ = 68.7 ± 3.2 vs 24.9 ± 0.9 µL g⁻¹ min⁻¹, P < .0001; sucrose, K₁ = 16.9 ± 0.9 vs 11.5 ± 0.9 µL g⁻¹ min⁻¹, P = .0007). This effect was achieved without significant changes in cerebral and tumor blood flow or arterial blood pressure, which indicates that the effect on vascular permeability is independent of changes in vascular tone induced by NO. This effect was mediated by activation of the NO/3',5'-cyclic guanosine monophosphate (cGMP) pathway, as it was blocked by guanylate cyclase inhibition by LY83583 and reproduced by the delivery of 8-bromoguanosine 5'-monophosphate or inhibition of cGMP degradation by the phosphodiesterase inhibitor zaprinast. Inhibition of inducible NO synthase by aminoguanidine or cyclooxygenase inhibition by indometacin or dexamethasone did not reduce the blood-tumor barrier (BTB) response to PROLI/NO. PROLI/NO, and perhaps other NO-donating compounds, can be used to selectively increase BTB permeability in gliomas through the NO/cGMP pathway at doses that do not cause unwanted vasodilatory changes in blood flow and that do not affect the systemic circulation.