(A) HMGBs inhibit cell proliferation. MCF-7 cells (3×104 cells/well in six-well tissue culture dishes) were cultured in the medium containing Ad5-wtHMGB1–3, Ad5-HMGB1–3 mutLXCXE, Ad5-HMGB4 mutLXCXD, or Ad5-lacZ (a control) at an MOI of 100 p.f.u./cell. At the indicated time points, the cells were counted with a hemocytometer. SEMs from 10 wells in three independent experiments were less than 10%. (B) HMGBs increase radiosensitivity. Exponentially growing MCF-7 and T-47D cells were infected with Ad5-wtHMGB1–4, Ad5-HMGB1–3 mutLXCXE, Ad5-HMGB4 mutLXCXD, or Ad5-lacZ (a control) at an MOI of 100 p.f.u./cell for 24 hours and then exposed to γ-ray irradiation at indicated doses. MTT survival assays were conducted for cell viability 24 hours after irradiation.