Population PK analysis of chloroquine in a humanized mouse model of P.falciparum malaria
Berja Checa, Sandra (1,2*); Jauregizar, Nerea (2); Jiménez-Díaz, María-Belén (1); Díaz, Pablo (1); Lorenzo, Patricia (1); Sánchez, Rebeca (1); Gómez, Hazel (1); Salazar, Eider (1); Romero, Judith1; Popescu, Gabriela (1); López, Lara (1); Cristina Eguizabal (3,4) Angulo-Barturen, Iñigo (1)
1: The Art of Discovery 2: Pharmacology Department, Faculty of Medicine and Nursing, University of the Basque Country (UPV/EHU) 3: Cell Therapy, Stem Cells and Tissues Group, Biocruces Bizkaia Health Research Institute 4: Basque Centre for Blood Transfusion and Human Tissues
Objectives: Malaria is a life-threatening disease caused by protozoa of the genus Plasmodium which are spread to people through the bites of infected female Anopheles mosquitoes. Fixed-dose combinations of artemisinins are the only drugs recommended by the WHO for the treatment of uncomplicated malaria, however significant resistance has emerged against these agents. To counter this spread, new chloroquine analogs active against chloroquine-resistant parasites are being investigated as promising new antimalarials given its exquisite specificity for Plasmodium erythrocyte stages. To support these discovery programs, the humanized mouse model of human malaria caused by Plasmodium falciparum is a valid tool to predict the antimalarial efficacy of new drugs in humans. Research using humanized mice has advanced our knowledge and understanding of the pharmacokinetic profiles of antimalarial drugs and their therapeutic effect against P. falciparum. Furthermore, this tool allows us to observe behaviors of antimalarial drugs that are not easily perceived in humans such as the accumulation of CQ in infected erythrocytes [1,2]. The aim of this work was to develop a population pharmacokinetics model of chloroquine in a humanized mouse model infected with P. falciparum and investigate the relationship between model PK parameters and evolution of parasitaemia.
Methods: In the experimental model, human erythrocytes were engrafted into 60 immunodeficient female NODscidIL2Rgammanull (NSG) mice and, once a percentage > 50 % of human erythrocytes in peripheral blood was reached, they were infected with P. falciparum intravenously (PfalcHuMouse model). The pharmacological treatment started when the desired percentage of parasitaemia in mice was reached (which varied depending on the specific objective of each test between 1% and 10%). Single and repeated doses of chloroquine from 2.5 to 300 mg/kg were administered orally once daily for 1 to 6 days. Drug concentrations were measured in whole blood samples (30 µL) by LC-MS/MS. Drug concentration and parasitaemia data from all dosing schedules were simultaneously modelled using Phoenix® NLMETM 8.3 and FOCE method. The relationship between physiological or pathological covariates and parameter estimates were explored. The studied covariates were: age, bodyweight, mouse strain, concentration of parasitized erythrocytes, parasites elimination rate and concentration of human erythrocytes. Since the animals were examined at different occasions, the interoccasion variability in individual parameters was also evaluated. Model parameters, diagnostic plots and internal validation techniques (VPC and bootstrap) were evaluated for model performance.
Results:
Overall, 466 chloroquine concentration data were available and were successfully characterized by a 1-compartment model with linear elimination associated to an additive error model and exponential interindividual error. Of the covariables tested, concentration of parasitized erythrocytes significantly influenced volume of distribution. The typical parameter estimates were 2.87 h-1 for the absorption rate constant (Ka), 0.06 h-1 for the elimination rate constant (Ke) and 1360 mL for the volume of distribution. The volume of distribution was lower when the concentration of parasitized erythrocytes was higher.
Conclusions: Our results demonstrate that the PK of chloroquine in this model is highly dependent on the concentration of P. falciparum in peripheral blood, suggesting that this fact should be taken into account to understand and model the PK behavior of chloroquine. In future steps, the model will be adapted to simulate chloroquine human blood concentrations.
References:
[1] Cambie, G., Verdier, F., Gaudebout, C., Clavier, F., & Ginsburg, H. (1994). The pharmacokinetics of chloroquine in healthy and Plasmodium chabaudi-infected mice: implications for chronotherapy. Parasite, 1(3), 219–226. doi:10.1051/parasite/1994013219
[2] Ch'ng JH, Lee YQ, Gun SY, Chia WN, Chang ZW, Wong LK, Batty KT, Russell B, Nosten F, Renia L, Tan KS. Validation of a chloroquine-induced cell death mechanism for clinical use against malaria. Cell Death Dis. 2014 Jun 26;5(6):e1305. doi: 10.1038/cddis.2014.265.