Figure 1

Acquired resistance upon long-term 4-HPR exposure. (A, left) R cell lines were continuously exposed to different 4-HPR concentrations (0.5, 3, 5, and 10 μM; cell lines named R0.5, R3, R5, and R10, respectively) and resistance verified by comparison to 48 h drug-withdrawn R cells. Data are the average ± SD of three independent experiments performed in quadruplicates, n = 12. (A, right) Parental CCRF-CEM cells and developed R cell lines were exposed to 10 μM 4-HPR and viability estimated after 48 h of drug exposure. (n = 12). **P < 0.01; ANOVA plus Tamhane post-hoc analysis. (B) Comparative cell proliferation was determined by BrdU labeling as specified in Materials and Methods. Data are average ± SD of four independent experiments. *P < 0.05; Kruskal Wallis and Mann-Whitney test for pair-wise comparison.