Most discovery projects focus on developing orally administered drugs that are primarily absorbed across the intestinal mucosa. Therefore, it is imperative to select an appropriate in vitro permeability study model in drug development that provides reliable data and accurately predicts human absorption. In addition to artificial membrane models such as PAMPA and simulated model systems, the data supplied by cell-based permeability models are more instructive for optimizing lead compounds . The permeability data obtained from these assays has many factors, including aqueous solubility, cell partitioning, influx/efflux transport, and tight junction modulability, making it helpful in estimating oral bioavailability and total biological distribution. Factors also include estimating permeation into the central nervous system (CNS) or blood-brain barrier (BBB).
Transporters are a group of carrier proteins that influence drugs' pharmacokinetics, pharmacodynamics, and toxicological properties. Drug-related transporters in humans mainly contain two types of transporter super-families. These are ATP-binding cassette (ABC) transporters and solute carrier (SLC) transporters. Transporters can affect the absorption, distribution, elimination, and other in vivo processes of drugs, affecting the efficacy and safety of drugs and playing an essential role in drug-drug interactions (DDIs) . Usually, in vitro testing is the first step in assessing transporter-mediated DDIs.
The WuXi AppTec in vitro permeability and transporter platform provides 4 models to evaluate the permeability of drugs. Combined with the needs of different stages in drug development, different solutions are customized for sponsors to meet the requirements of high-throughput screening, mechanistic research, and application. PAMPA is a non-cell-based model suitable for high-throughput screening  , mainly used to assess passive transcellular transport of compounds in the early stage of drug development. In addition, three cell-based models are provided for permeability assessment: wild-type MDCK II cells, MDR1-MDCK II cells (MDCK II cells transfected with the human MDR1 gene encoding for the efflux transporter, P-glycoprotein (P-gp)), and Caco-2 cells. Compared with the PAMPA model, cell-based models comprehensively monitor the facilitated diffusion and the active transport processes during absorption, thus providing more reliable data to support the permeability assessment In Vitro . Details of the models are shown in the table below:
WuXi AppTec's in vitro permeability and transporter platform provides various in vitro permeability and transporter platform provides various in vitro models for assessing transporter-mediated DDIs. We can evaluate substrates or inhibitors of specific transporters using three types of cell-based models. These include human embryonic kidney cells (HEK 293 cells) stably transfected with transporter genes such as human OATP1B1, OATP1B3, OATP2B1, OAT1, OAT3, OCT1, OCT2, MATE1, MATE2-K, PEPT1, PEPT2 and NTCP for DDI studies with SLC transporters; MDR1 MDCK I and MDR1-MDCK II cells specifically expressing P-gp, and Caco-2 cells expressing efflux transporters such as P-gp and BCRP for DDI studies with ABC transporters P-gp and BCRP . MDR1-MDCK I cells can better predict P-gp substrates at the blood-brain barrier in vivo and are mainly used in central nervous system-related drug development. In addition, we provide the vesicles models for ABC transporters BSEP and MRP2 and establish a model for the comprehensive assessment of hepatic uptake using primary hepatocytes. Details of the models are in below.
WuXi AppTec's In Vitro permeability and transporter platform pays excellent attention to the reproducibility of the system and the consistency with In Vitro data or literature data. For example, the validation of a Caco-2 permeability test was carried out with 29 commercial drugs. This validation experiment had been repeated three times in triplicate each time. The results were reproducible, and the Papp (A-B) values of these 29 model drugs correlated very well with the human absorption data (R2 of 0.93) (Figure 1). In addition, the verification of system reproducibility was performed once every year, and the data correlation was greater than 0.9 between years. For example, the correlation R2 of Papp (A-B) values for 18 model drugs tested from 2016 to 2020 was 0.98 (Figure 2).