ARNT and malignant colon neoplasm: Whereas in the absence of PT-2385 both HIF- 1α and HIF-2α co-immunoprecipitated with HIF-1β, in cells treated with 100 μM PT-2385 only HIF-1α coprecipitated with HIF-1β confirming the specificity of the inhibitor [14] and importantly, indicating that concentrations above 50 μM of the inhibitor are required in colon cancer cells.