Loss of tumor forming ability in mammary tumor cells treated with T-oligo and radiation. (a, b) Mammary tumor cells were cultured in medium containing 40 μM T-oligo, control-oligo, or no additive. After 24 hours of culture, the tumor cells from each group were collected, counted, placed in the 50 ml polypropylene tube on ice and then irradiated with 0 or 3 Gy, respectively. Then 1 × 106 tumor cells from each group with or without irradiation were injected subcutaneously into right or left flanks of syngeneic wild-type mice (n = 4/group). Mice (n = 4/group) injected with tumor cells cultured with medium alone and/or that received radiation alone were used as controls. Tumor size was measured with calipers every other day for 30 days and tumor volume was calculated using the formula: tumor volume = (longer diameter × shorter diameter2)/2. The average tumor volume was calculated and presented at indicated days after tumor inoculation. The tumor incidence was indicated as the numbers of tumor-bearing mice/total numbers of mice in each group in the graph. Statistical significance was determined by one-way ANOVA. (c) Sections of tumors from mice inoculated with tumor cells treated in vitro with T-oligo or control-oligo followed by 0 or 3 Gy radiation were stained for apoptosis via TUNEL assay and then photographed at 40× magnification. (d) The cells stained brown are apoptotic. The apoptotic cells were counted in three to five randomly selected fields at 40× magnification. The percentage of apoptotic cells among all tumor cells is graphed and statistical significance was determined by X2-test.