Predicting Pharmacokinetic-pharmacodynamic Correlation In Parkinson Primate Model Using ¹⁸F-fallypride Positron Emission Tomography

Objective: 8 Parkinson primate models were developed with MPTP to evaluate the binding potential(BP) of D2 receptor after different dosages chronic treatment with ropinirole. PET study was employed to evaluate the effectivity of ropinirole, and a PK-PD model was developed for the concentration-BP relationship.Method:(1) Establishment of method:Use 18F-Fallypride as the imaging agent, 100 min continuously scaning was carryed out on 5 healthy cynomolgus monkeys with the micro-Pet used only for huge animals.Processing the results of scanning every 10 min points, drawing BP-time curve, then the stability time of static scanning was determined.Then, 1 mg / kg ropinirole was taken by healthy cynomolgus monkey and static scanning before and 1, 2, 4, 6, 8 h after administration were taken to observe ropinirole binding behavior in brain, thus to determine the scanning time of efficacy evaluation.Finally, a UPLC-MS/MS method for the determination of plasma concentration of ropinirole in cynomolgus monkeys was developed.(2) Establishment and evaluation of Parkinson primate model: 8 healthy cynomolgus monkeys were treated with MPTP to develop Parkinson models. Moter activity, parkinsonian primate rating scale and a PET study with 18F-Fallypride were taken to evaluate the model. And the correlation between BP and parkinsonian primate rating scale was analysised.(3) Efficacy and safety of ropinirole in PD monkeys:Evaluation of the effectiveness includes: Moter activity, parkinsonian primate rating scale and a PET study with 18F-Fallypride was evaluated after continuous administration(three times daily) of ropinirole in different doses(1.0, 0.5, 0.2(1.5 mg / kg)) for 21 days.A new evaluation index of ropinirole efficacy was established by PET study.Safety evaluation includes blood pressure, heart rateblood routine, blood biochemistry,urine routine examination. Correlation between BP valuea and safety indexes was analysed.(4) Pharmacokinetic study of ropinirole in cynomolgus monkey and its correlation study with pharmacodynemics and safety indexes.:Blood samples were collected after 7 days contineous administration of ropinirole.The time of sample collection was before and 0.5, 0.75, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8 h after administration.UPLC-MS / MS method was used to determin the blood concentration of ropinirole and pharmacokinetic parameters was calculated with the Winnonlin software.The correlation between pharmacokinetic parameters and efficacy was found by linear regression analysis. And the correaltion between pharmacokinetic parameters and safety indexes was evaluated by ROC curve analysis. Based on the above studies, a PK-PD model was established using Winnonlin software to analyse ropinirole pharmacokinetic parameters and BP of the dopamine D2 receptor in cynomolgus monkeys.Results:(1) Establishment of method:The suitable static scanning time was determined as 40-50 min after 18F-Fallypride was injected. And the appropriate scan time to evaluate efficacy of ropinirole was 1.75 h after administration. UPLC-MS / MS method has been approved to be linear within the range of 20, 50, 100, 200, 500, 1000, 2000, 5000 pg·m L-1(r2>0.99). Good precision and accuracy were foune, and the matrix effect and stability met the requirements of biological sample analysis as well.(2)Establishment and evaluation of Parkinson primate model:Cynomolgus monkey were rendered parkinsonian by repetitive systemic administration of MPTP. The animals progressively developed a syndrome characterized by hypokinesia, bradykinesia as well as balance and fine motor skill disturbances. The rating scale of PD model was approximately 8~10. The mean reduction of moter activity was around 70 ± 20%. At the same time, BP reduced almost 54 ± 13%. The BP change was highly related to the change rating score and moter activity, thus it was proved to be a good evaluating indexes.(3) Efficacy and safety of ropinirole in PD monkeys:It was found that the BP of D2 receptor increased, which is highly correlated with motor activity and parkinsonian primate rating scale, in dose reduction. It maybe relate to the accumulation effect of BP. According to the result of linear-regression analysis between the change of rating score and BP, we speculate that ropinirole start to take effect while the improvement of BP was 14% and moderate effect occurred while the improvement of BP was 14-24%. It can be very effective while the improvement of BP beyound 33%.Hypotensive effect, decreation of heart rate and mental symptom were observed during the safety estimation. Blood routine, urine routine and blood biochemical examination were not unusual.The anomaly reduction of heart rate and blood pressure were observed while NO.3and NO.7 monkeys taken 0.5 mg/kg and 1.0 mg/kg ropinirole. And aberrant behavior was observed in NO.8 monkey which demonstrated the dose was too high.(4)Pharmacokinamic of ropinirole in PD monkey:Ropinirole eliminated rapidly in plasma after administration. Pharmacokinetic parameters of 4 dose levels analyzed by non-compartmental model were as follows respectively: eliminationhalf-life(t1/2): 1.45、1.48±0.14、1.7±0.44、1.85±0.35 h, volume of distribution(Vz): 219.55、311.02±264.34、304.86±180.08、415.53±233.78 L·kg-1, clearence(Cl): 105.17、142.35±111.73、123.36±77.52、127.77±89.88 L·h-1·kg-1. While NO.8monkey was excluded, linear pharmacokinetics of ropinile was observed from 0.2 to 1.5mg/kg.(5) Correlations study of pharmacokinetic with pharmacodynamic and safety of ropinirole in cynomolgus monkey.According to the correlation study of pharmacokinetic and pharmacodynamic parameters, we suspected that, ropinirole come into effect while Cmax reach 1.21 ng/m L,and it works a lot while the Cmax reach 2.25 ng/m L. And we found that side effects would occur while Cmax beyound 2.68 ng·m L-1 through ROC analysis.Based on the correaltion studies, one-compartment model with first-order elimination assuming a maximum BP model was applied to the PK-PD analysis. The model was steady and effective.Conclusion: PET study was more objective than motor activity and rating scale on the aspect of evaluating ropinirole pharmacodynamic. The PK-PD model demonstrated the correlation between pharmacokinetic and pharmacodynamic of ropinirole, which canprovide a brand new technolog platform for objective and direct evaluation of anti-Parkinson drug treatment for clinics. We hope to predict pharmacodynamic and safety index on the basis of concentrations of ropinirole in plasma.