Effect of ProVP16-I and -II on MDR-1—transfected Molt-3 cells. Molt-3 cells were transfected with pMDR-IRESpuro and empty pIRESpuro to generate Molt-3/MDR-1 and Molt-3/Mock control. Resistance of Molt-3/MDR-1 cells against VP16, doxorubicin, vinblastin, and paclitaxel was calculated from IC₅₀ concentrations according to IC₅₀ Molt-3/MDR-1 ÷ IC_50Molt-3 (n = 3) and results compared with effects observed with ProVP16-I and -II. Results obtained with Molt-3/Mock cells were calculated according to IC₅₀ Molt-3/Mock ÷ IC_50Molt-3 (n = 3). Differential findings between Molt-3/MDR-1 and Molt-3/Mock cells obtained with VP16, doxorubicin, vinblastin, and paclitaxel were statistically significant (P < .001) in contrast to ProVP16-I and -II (P > .10).