Potentiation of radiation-induced regrowth delay by isosorbide dinitrate in FSaII murine tumors.

Oxygen deficiency in tumors reduces the efficacy of nonsurgical treatment modalities such as conventional radiotherapy and chemotherapy. Since tumor perfusion is directly affected by the vascular resistance to flow of vessels feeding the tumor, vasodilator drugs might be a way to increase tumor blood flow and oxygenation. The effects of nitric oxide (NO) donor administration on tumor oxygenation, perfusion and radiation sensitivity were studied in the FSaII tumor model. Local tumor oxygenation was measured using electron paramagnetic resonance oximetry and a fiberoptic probe, OxyLite. We concomitantly measured the modulation of tumor blood flow by laser Doppler flowmetry. We determined FSaII tumor regrowth delay after isosorbide dinitrate administration and irradiation compared to carbogen breathing before irradiation and with X-rays alone. Administration of the NO donor improved the FSaII tumor pO(2) concomitant with an increase in tumor blood flow. We also demonstrated an increase in FSaII tumor radiation sensitivity after isosorbide dinitrate administration, which was similar to the effect of carbogen breathing in the same tumor model. Administration of isosorbide dinitrate could be considered in terms of improvement in tumor blood flow and a possible concomitant increase in accessibility of chemosensitizing agents to the tumor, particularly in terms of modification of the tumor response to irradiation.