Transporters can play a key role in the absorption, distribution, metabolism, and excretion of drugs. Understanding these contributions early in drug discovery allows for more accurate projection of the clinical pharmacokinetics. One method to assess the impact of transporters in vivo involves co‐dosing specific inhibitors. The objective of the present study was to optimize the dose and route of administration of a P‐glycoprotein (P‐gp) inhibitor, valspodar (PSC833), and a dual P‐gp/breast cancer resistance protein (BCRP) inhibitor, elacridar (GF120918), by assessing the transporters’ impact on brain penetration and absorption. A dual‐infusion strategy was implemented to allow for flexibility with dose formulation. The chemical inhibitor was dosed intravenously via the femoral artery, and a cassette of known substrates was infused via the jugular vein. Valspodar or elacridar was administered as 4.5‐hour constant infusions over a range of doses. To assess the degree of inhibition, the resulting ratios of brain and plasma concentrations, Kp's, of the known substrates were compared to the vehicle control. These data demonstrated that doses greater than 0.9 mg/hr/kg valspodar and 8.9 mg/hr/kg elacridar were sufficient to inhibit P‐gp‐ and BCRP‐mediated efflux at the blood‐brain barrier in rats without any tolerability issues. Confirmation of BBB restriction by efflux transporters in preclinical species allows for subsequent prediction in humans based upon the proteomic expression at rodent and human BBB. Overall, the approach can also be applied to inhibition of efflux at other tissues (gut absorption, liver clearance) or can be extended to other transporters of interest using alternate inhibitors.

In drug discovery, the extent of brain penetration as measured by free brain/plasma concentration ratio (K p,uu) is normally determined from one experiment following constant intravenous (IV) infusion, and PK parameters including clearance (CL), volume of distribution at steady-state (V SS), and effective half-life (t 1/2,eff) are determined from another experiment after a single IV-bolus injection. The objective of the present study was to develop and verify a method to simultaneously determine K p,uu and PK parameters from a single intravenous infusion experiment. In this study, 9 compounds (atenolol, loperamide, minoxidil, NFPS, sulpiride, and 4 proprietary compounds) were intravenously infused for 4 h at 1 mg/kg or 24 h at 1 or 6 mg/kg or bolus injection at 1 mg/kg. Plasma samples were serially collected and brain and CSF samples were collected at the end of infusion. The PK parameters were obtained using noncompartmental (NCA) and compartmental analyses. The K p,uu ,brain values of those compounds increased up to 2.86-fold from 4 h to 24 h. The CL calculated from infusion rate vs. steady-state concentration from the 24 h infusion studies was more consistent with the CL from the IV bolus studies than that from 4 h infusion studies (CL average fold-of-difference 1.19~1.44 vs. 2.10). The compartmental analysis using 1-and 2-compartment models demonstrated better performance than NCA regardless of study design. In addition, V ss and t 1/2,eff could be accurately obtained by 1-compartment analysis within 2-fold difference. In conclusion, both K p,uu,brain and PK parameters can be successfully estimated from a 24 h IV-infusion study design.

Bioanalysis, a key supporting function for generating data for pre-clinical and clinical studies in drug development, is under the regulation of local agencies as well as global organizations to ensure the data integrity and quality in submission. As major regulatory agencies and organizations, the US Food and Drug Administration, the European Medicines Agency and the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use have been updating their industry guidance for bioanalytical method validation, to keep up with the development new modalities, technologies and regulations. This article summarizes the recent updates and any clarifications and controversies triggered by those updates. Perspectives and recommendations are given based on our own experience as well as commonly accepted practice in the bioanalytical community.

No abstract

No abstract

No abstract