Authenticity and drug resistance in a panel of acute lymphoblastic leukaemia cell lines

Abstract

Cell lines are important models for drug resistance in acute lymphoblastic leukaemia (ALL), but are often criticised as being unrepresentative of primary disease. There are also doubts regarding the authenticity of many lines. We have characterised a panel of ALL cell lines for growth and drug resistance and compared data with that published for primary patient specimens. In contrast to the convention that cell lines are highly proliferative, those established in our laboratory grow at rates similar to estimates of leukaemic cells in vivo (doubling time 53-442 h). Authenticity was confirmed by genetic fingerprinting, which also demonstrated the potential stability of long-term cultures. In vitro glucocorticoid resistance correlated well with that measured ex vivo, but all lines were significantly more sensitive to vincristine than primary specimens. Sensitivity to methotrexate was inversely correlated to that of glucocorticoids and L-asparaginase, indicating possible reciprocity in resistance mechanisms. A cell line identified as highly methotrexate resistant (IC50 > 8000-fold higher than other lines) was derived from a patient receiving escalating doses of the drug, indicating in vivo selection of resistance as a cause of relapse. Many of these lines are suitable as models to study naturally occurring resistance phenotypes in paediatric ALL.

Figure 1

Drug resistance profile of ALL cell lines. IC₅₀ values for T-ALL (open, n=15) vs B-lineage ALL (shaded, n=7) cell lines. Boxes indicate medians and inter-quartile range, whiskers indicate 10th and 90th percentiles and dots indicate outliers; values are calculated as log₂ molarity (μM) for all drugs, except ASP which is given as log₂ IU ml⁻¹.

Figure 2

Comparison of resistance profiles in patients and cell lines. Data indicate total IC₅₀ ranges determined from published studies of diagnosis (PD) and relapse (PR) patient specimens, and from cell lines derived from diagnosis (CLD) and relapse (CLR) specimens in the present study. Median values from individual studies are indicated as tick marks. Median values from the single study of MPRED resistance in patient specimens are indicated as crosses. Data represent combined T and B lineages; values are μg ml⁻¹ for all drugs, except ASP which is given as IU ml⁻¹.

Figure 3

Resistance profiles of MPRED, DEX, ASP and MTX in T-ALL cell lines. Delta IC₅₀ scores (Log₂ IC₅₀ – median Log₂ IC₅₀) were calculated for each drug and cell lines plotted from left to right according to their Delta IC₅₀ rank for MPRED.