Representative images of CXCR4 overexpression in subcutaneous tumor tissue, showing similar CXCR4 levels among compared groups (N=5/group; Buffer, T22-GFP-H6-FdU, T22-GFP-H6 and free oligo-FdU) before treatment (upper panels). Representative images of DNA double-strand break induction and caspase 3 activation (measured with anti-ɣH2AX or anti-cleaved caspase 3 by IHC) 5h post-administration (middle panels). Apoptotic induction (Hoescht staining, 24h post-administration, lower panels). Note the higher number of cells positive for DSBs, Caspase 3 activation and apoptosis induction in the T22-GFP-H6-FdU as compared to free oligo-FdU. Black or white arrows indicate dead cells. Quantitation of the number of cells containing DSBs or active Caspase-3 in IHC-stained tumor sections 5h post-treatment and the number of condensated or disaggregated nuclei (by Hoescht staining) 24h post-treatment in tumor sections of 10 high-powder fields (400x magnification) using the Cell D software. (N=50; 10 tumor fields/mice; 5 mice/group). Data expressed as mean±s.e.m. 