Inhibition of mammary tumor cell growth by T-oligo and ionizing radiation. (a) Mammary tumor cells isolated from MMT mice were cultured with T-oligo at the concentration of 10, 20, 30 and 40 μM for 24 hours. Tumor cells cultured with control-oligo at the concentration of 40 μM or medium alone were used as control. On Day 2, the cells were exposed to 3 Gy IR. The cells were then collected at indicated time after radiation and counted in triplicates. (b) MMT tumor cells were cultured with T-oligo or control-oligo at a concentration of 40 μM for 24 hours and then irradiated with indicated dose of IR or mock irradiated (0 Gy). Seventy-two hours after IR, the cells were counted using a particle counter in triplicates. Statistical significance from three independent experiments was determined by one-way ANOVA. (c) Surviving fraction. The tumor cells were cultured in 10 cm tissue culture plates and pretreated with T-oligo or control-oligo at a concentration of 40 μM for 24 hours, and then irradiated with indicated doses. After two-weeks culture, the tumor colonies were fixed and stained with 0.5% crystal violet. The colonies were counted with a cut-off of 50 viable cells. Surviving fractions were calculated by the number of colonies divided as the number of seeded cells × plating efficiency.