Hypoxia-Inducible Factor Pathway Inhibition Resolves Tumor Hypoxia and Improves Local Tumor Control After Single-Dose Irradiation

Purpose: To study the effects of BAY-84-7296, a novel orally bioavailable inhibitor of mitochondrial complex I and hypoxia-inducible factor 1 (HIF-1) activity, on hypoxia, microenvironment, and radiation response of tumors. Methods and Materials: UT-SCC-5 and UT-SCC-14 human squamous cell carcinomas were transplanted subcutaneously in nude mice. When tumors reached 4 mm in diameter BAY-84-7296 (Bayer Pharma AG) or carrier was daily administered to the animals. At 7 mm tumors were either excised for Western blot and immunohistologic investigations or were irradiated with single doses. After irradiation animals were randomized to receive BAY-84-7296 maintenance or carrier. Local tumor control was evaluated 150 days after irradiation, and the dose to control 50% of tumors (TCD50) was calculated. Results: BAY-84-7296 decreased nuclear HIF-1 alpha expression. Daily administration of inhibitor for approximately 2 weeks resulted in a marked decrease of pimonidazole hypoxic fraction in UT-SCC-5 (0.5% vs 21%,