R115777 diminishes UCN-01–induced ERK1/2 activation in association with an increase in γH2A.X expression/foci formation and a dramatic induction of apoptosis induced by UCN-01 in vivo. (A) Following the experiments described in Figure 6, tumors were excised after the final dose, and subjected to immunohistochemistry for ERK1/2 phosphorylation and Ki67 expression, as well as TUNEL staining. indicates nuclear staining of phospho-ERK1/2 in tumor cells. M indicates muscle. (B) Alternatively, tumor tissue sections were stained with Alexa Fluor 488–conjugated γH2A.X antibodies to monitor γH2A.X expression and nuclear foci formation. Arrows indicate cells with γH2A.X foci. Results are representative of 3 separate sets of tumor sections.