In Vitro to In Vivo Extrapolation Linked to Physiologically Based Pharmacokinetic Models for Assessing the Brain Drug Disposition

Drug development for the central nervous system (CNS) is a complex endeavour with low success rates, as the structural complexity of the brain and specifically the blood-brain barrier (BBB) poses tremendous challenges. Several in vitro brain systems have been evaluated, but the ultimate use of these data in terms of translation to human brain concentration profiles remains to be fully developed. Thus, linking up in vitro-to-in vivo extrapolation (IVIVE) strategies to physiologically based pharmacokinetic (PBPK) models of brain is a useful effort that allows better prediction of drug concentrations in CNS components. Such models may overcome some known aspects of inter-species differences in CNS drug disposition. Required physiological (i.e. systems) parameters in the model are derived from quantitative values in each organ. However, due to the inability to directly measure brain concentrations in humans, compound-specific (drug) parameters are often obtained from in silico or in vitro studies. Such data are translated through IVIVE which could be also applied to preclinical in vivo observations. In such exercises, the limitations of the assays and inter-species differences should be adequately understood in order to verify these predictions with the observed concentration data. This report summarizes the state of IVIVE-PBPK-linked models and discusses shortcomings and areas of further research for better prediction of CNS drug disposition.

A crosscorrelation methodology for in vivo pharmacokinetic study by the trans-scale fluorescent system

Conventional single-organ-isolation-based pharmacokinetics study is short of time-course information and exists considerable inaccuracy due to the inter-individual differences and characteristic imparities between in vivo and ex vivo tissues/cells. The in vivo time-course and multi-organs study of model drugs in living subjects could afford precise spatio-temporal correlation. Herein, a revolutionized trans-dimensional fluorescence system was home built, with the macro-level detection part for simultaneous pharmacokinetic study in different organs, and one confocal imaging needle for micro-level visualizing cellular uptake of drugs with super-high resolution (0.472 μm). Correlating these simultaneous acquired trans-scale data, an innovative physiologically-based pharmacokinetics (PBPK) model was firstly created for predicting drug disposition in other species. Its accuracy and reliability was firmly supported by the high consistent predicted-data with the real-measured data in mice and in human, respectively. This study provides an innovative methodology and revolutionized instrument for in vivo real-time advancing assessment of druggability.

Pharmacokinetic Developability and Disposition Profiles of Bispecific Antibodies: A Case Study with Two Molecules

Bispecific antibodies (BsAb) that engage multiple pathways are a promising therapeutic strategy to improve and prolong the efficacy of biologics in complex diseases. In the early stages of discovery, BsAbs often exhibit a broad range of pharmacokinetic (PK) behavior. Optimization of the neonatal Fc receptor (FcRn) interactions and removal of undesirable physiochemical properties have been used to improve the ‘pharmacokinetic developability’ for various monoclonal antibody (mAb) therapeutics, yet there is a sparsity of such information for BsAbs. The present work evaluated the influence of FcRn interactions and inherent physiochemical properties on the PK of two related single chain variable fragment (scFv)-based BsAbs. Despite their close relation, the two BsAbs exhibit disparate PK in cynomolgus monkeys with BsAb-1 having an aberrant clearance of ~2 mL/h/kg and BsAb-2 displaying a an ~10-fold slower clearance (~0.2 mL/h/kg). Evaluation of the physiochemical characteristics of the molecules, including charge, non-specific binding, thermal stability, and hydrophobic properties, as well as FcRn interactions showed some differences. In-depth drug disposition results revealed that a substantial disparity in the complete release from FcRn at a neutral pH is a primary factor contributing to the rapid clearance of the BsAb-1 while other biophysical characteristics were largely comparable between molecules.

The role of pharmacogenetics in Efficacy and safety of protease inhibitor based therapy in human immunodeficiency virus type (HIV) infection.

Antiretroviral therapy has markedly reduced morbidity and mortality for persons living with human immunodeficiency virus (HIV). HIV can now be classified as a chronic disease; until a cure is found, patients are likely to require life-long therapy. However, despite these undoubted advances, there are many issues that need to be resolved, including the problems associated with long-term efficacy and toxicity. Moreover, pharmacotherapy of patients infected with HIV is challenging because a great number of comorbidities increase polypharmacy and the risk for drug-drug interactions. There is considerable interindividual variability in patient outcomes in terms of drug disposition, drug efficacy and adverse events. The basis of these differences is multifactorial, but host genetics are believed to play a significant part. HIV-infected population consists of ethnically diverse individuals on complex and potentially toxic antiretroviral regimens on a long-term basis. These individuals would benefit greatly from predictive tests that identify the most durable regimens. Pharmacogenetics holds that promise. Thus, detailed understanding of the metabolism and transport of antiretrovirals and the influence of genetics on these pathways is important. To this end, this review provides an up-to-date overview of the metabolism of antiHIV therapeutics of the protease inhibitors Lopinavir and Ritonavir and the impact of genetic variation in drug metabolism and transport on the treatment of HIV.

An Adaptive Biosystems Engineering Approach towards Modeling the Soluble-to-Insoluble Phase Transition of Clofazimine

Clofazimine (CFZ) is a weakly basic, small-molecule antibiotic used for the treatment of mycobacterial infections including leprosy and multidrug-resistant tuberculosis. Upon prolonged oral administration, CFZ precipitates and accumulates within macrophages throughout the host. To model the pharmacokinetics of CFZ, the volume of distribution (Vd) was considered as a varying parameter that increases with continuous drug loading. Fitting the time-dependent change in drug mass and concentration data obtained from CFZ-treated mice, we performed a quantitative analysis of the systemic disposition of the drug over a 20-week treatment period. The pharmacokinetics data were fitted using various classical compartmental models sampling serum and spleen concentration data into separate matrices. The models were constructed in NONMEM together with linear and nonlinear sigmoidal expansion functions to the spleen compartment to capture the phase transition in Vd. The different modeling approaches were compared by Akaike information criteria, observed and predicted concentration correlations, and graphically. Using the composite analysis of the modeling predictions, adaptive fractional CFZ sequestration, Vd and half-life were evaluated. When compared to standard compartmental models, an adaptive Vd model yielded a more accurate data fit of the drug concentrations in both the serum and spleen. Including a nonlinear sigmoidal equation into compartmental models captures the phase transition of drugs such as CFZ, greatly improving the prediction of population pharmacokinetics and yielding further insight into the mechanisms of drug disposition.

Impact of Genetic Polymorphisms at the Promoter area of IL-10 Gene on Tacrolimus Level in Jordanian Renal Transplantation Recipients

Background Tacrolimus is a widely used immunosuppressant that prevents the solid organ transplant rejection. The pharmacokinetics of Tacrolimus show considerable variability. interleukin-10 (IL-10), in the host’s immune response after transplantation contributes to the variable CYP3A-dependent drug disposition of Tacrolimus. In current study, our aim is to evaluate the impact of single nucleotide polymorphisms (SNP) in the promoter region of of IL-10 on Tacrolimus dose requirements and the Dose Adjusted Concentration (DAC) of Tacrolimus among kidney transplantation recipients. Methods Blood levels of Tacrolimus were measured using Micorparticle Enzyme Immunoassay (MEIA) for six months post-transplantation. Genotyping analysis was utilized using specific Polymerase Chain Reaction (PCR) followed by sequencing methods for 98 Jordanian kidney transplant recipients. Results Genotyping frequencies of IL-10 (-592) were (CC/CA/AA: 38, 46.7, 15.2%); IL-10 (-819) were (CC/CT/TT: 40.4, 44.1, 15.1%); and IL-10 (-1082) were (AA/AG/GG: 42.6, 44.7, 12.8%). The impact of IL-10 (-1082) on Tacrolimus DAC was gender dependent. Men carrying at least one A allele had significantly lower DAC than men carrying GG genotyping only in the first month post-transplantation [88.2±32.1 vs. 117.5±22.5 ng/ml per mg/kg/day, p=0.04].. Conclusion Our current study showed that the interaction between gender and IL-10 -1082 affects Tacrolimus DAC in Jordanian kidney transplantation recipients during the first month post-transplantation.

Effect of CYP3A4, CYP3A5, MDR1 and POR Genetic Polymorphisms in Immunosuppressive Treatment in Chilean Kidney Transplanted Patients

Cyclosporine (CsA) and tacrolimus (TAC) are immunosuppressant drugs characterized by a narrow therapeutic range and high pharmacokinetic variability. The effect of polymorphisms in genes related to the metabolism and transport of these drugs, namely CYP3A4, CYP3A5, MDR1 and POR genes, has been evaluated in diverse populations. However, the impact of these polymorphisms on drug disposition is not well established in Latin American populations. Using TaqMan® probes, we determined the allelic frequency of seven variants in CYP3A4, CYP3A5, MDR1 and POR in 139 Chilean renal transplant recipients, of which 89 were treated with CsA and 50 with TAC. We tested associations between variants and trough and/or 2-hour concentrations, normalized by dose (C0/D and C2/D) at specific time points post-transplant. We found that CYP3A5*3/*3 carriers required lower doses of TAC. In TAC treated patients, most CYP3A5*3/*3 carriers presented higher C0/D and a high proportion of patients with C0 levels outside the therapeutic range relative to other genotypes. These results reinforce the value of considering CYP3A5 genotypes alongside therapeutic drug monitoring for TAC treated Chilean kidney recipients.