Inhibition of Vinca alkaloid-induced apoptosis by anthracyclines. (A) CEM leukemia cells were simultaneously stimulated with doxorubicin (doxo, 100 ng/mL) and VCR (300 ng/mL) for time periods indicated. *P < .05 (ANOVA). NS indicates not significant. (B) Corresponding data from panel A for 48-hour incubation time and simultaneous application were analyzed for a total of n = 20 combinations by median effect plots investigating a range of drug concentrations (doxorubicin 10, 30, 60, and 100 ng/mL; VCR 3, 10, 30, 100, and 300 ng/mL). fa indicates apoptotic fraction; fu, fraction of cells alive; and d, drug dosage. (C-E) Further n = 6 B-ALL and T-ALL (C), n = 7 acute myeloid leukemia (D), and n = 3 lymphoma cell lines (E) were stimulated with doxorubicin and VCR for 48 hours as in panel A. *P < .05 (ANOVA). NS indicates not significant. (F) Xenograft study of CEM leukemia cells subcutaneously implanted into NSG mice was performed as described in “Animal trial.” Mice were treated as shown in the treatment schedule with doxorubicin (0.3 mg/kg) and/or VCR (0.9 mg/kg) or placebo as shown. Tumor size was measured in 2 dimensions, and tumor volume was calculated. Statistical analysis using Mann-Whitney rank-sum test was performed comparing VCR and combinatorial treatment (doxorubicin + VCR) at each measurement point (*P < .01) and revealed that doxorubicin followed by VCR 1 day later significantly inhibited the effect of VCR alone. The 25th and 75th quartiles are shown. p indicates placebo; d, doxorubicin; and V, VCR.