Quantitative Models for Growth Inhibition of Human Leukemia Cells by Antitumor Anthracycline Derivatives¹

A batch elution method with hydroxylapatite was developed to assay DNA damage by a set of antitumor anthracycline derivatives and was standardized with respect to the kinetics of unwinding, size of the alkaline unwinding unit, and fidelity of selective elution of single and double-stranded DNA. The method was applied to a study of a set of 10 antitumor anthracycline derivatives which inhibit growth of CCRF-CEM human leukemia cells over a range of potencies exceeding four orders of magnitude. The derivatives, including Adriamycin, daunorubicin, and carminomycin, vary in structure at C-4 and C-13, with substitutions at C-14 and N and stereochemical differences at C-4′, In a static model (fixed drug concentrations and incubation times), the potency [1/ID₃₇ (concentration of agent that inhibits cell growth by 37%)] of nine of the ten derivatives may be expressed as functions of DNA damage (n), inhibition of thymidine incorporation (l), and drug retention (r): ID₃₇ = K_a(r/l·n)^k_b, with a coefficient of correlation of >0.99. A kinetic model with 4-demethoxydaunorubicin (varying concentrations and incubation times) was also described. Following initial uptake and a period of rapid loss after cells are washed free of excess drug, the change in agent concentration in the cells follows first-order kinetics. The cell index (cell number after 50 hr in drug-free growth medium/cell number after initial 2-hr exposure with drug) may be expressed linearly in terms of the kinetics of drug loss (coefficient of correlation, >0.98), or as functions of 1/n (coefficient of correlation, >0.958), 1/l·n (coefficient of correlation, >0.963), or r/l·n (coefficient of correlation, >0.963). These studies may be used to define a class of similarly acting anthracycline agents and to give some insight into the mechanism of action of the agents that fall within the class.