Application of pharmacokinetic/pharmacodynamic and stochastic modelling to 6-mercaptopurine micronucleus induction in mouse bone marrow erythrocytes

This study investigates the kinetics of bone marrow micronucleated polychromatic erythrocytes and some mechanistic aspects of micronuclei induction using mathematical models. Female mice were administered a single intraperitoneal injection of the purine antagonist 6-mercaptopurine at 50 mg kg(-1). The time course evolution of the drug concentrations in the plasma and the micronucleated polychromatic erythrocyte kinetic rate in bone marrow were observed. Two mathematical models were developed for this study. The first model was built from a simultaneous pharmacokinetic/pharmacodynamic approach, but was invalidated after comparing its predictions to experimental data. The second model was a stochastic model based on some biological hypotheses involved in micronuclei induction. This model predicted a wavy kinetic rate of micronucleated polychromatic erythrocytes that was confirmed by a second data set obtained from a specifically built experimental design. The biological hypotheses were then discussed. It turned out from this work that mathematical modelling could be used as a tool to explore the cellular mechanisms of toxicity of the compound: for instance, the assumptions that 6-mercaptopurine induced micronuclei mainly in cells entering the S phase, and not only during the last cell cycle but during one of the earlier cycles preceding the extrusion of the main nucleus, were confirmed. Moreover, the use of the stochastic model would help to schedule more accurately the bone marrow or blood harvesting times in the in vivo rodent micronucleus test.