Primary ALL tumors resistant to IR can be sensitized by targeted inhibition of prosurvival pathways. (A) Induction of IR-induced apoptosis measured by annexin V⁺/PI⁺ staining 24 hours after treatment with 20 μM UO126, 500 nM rapamycin, 30 μM LY294002, and 30 μM AG1024 in 4 apoptosis-resistant ALLs not previously included in the microarray experiments. The means and standard deviations from 3 experiments are shown as well as P values for each inhibitor relative to no treatment. The figure shows that the 4 patients with apoptosis-resistant ALL have individual patterns of response to inhibition of different prosurvival signals prior to IR. ALL 111 became IR sensitive after addition of PI-3 kinase inhibitor LY294002 only. ALL 141 showed an increase in IR-induced apoptosis after preincubation with IGFR inhibitor AG1024 only. ALL 102 and 106 are both IR sensitive following exposure to all inhibitors except rapamycin. (B) Western blotting showing post-IR–induced apoptosis after 8 hours of incubation with PI-3 inhibitor LY294002 in ALL 111 or IGFR inhibitor AG1024 in ALL 141 as measured by cleavage of PARP1 and appearance of the cleaved caspase-3. Both leukemias exhibit reduction in IR-induced phosphorylation of Akt in the presence of the respective inhibitors.