PROTACs* are emerged as a novel therapeutic option for treating previously untreatable diseases. However, traditional testing methods cannot accurately evaluate the pharmacokinetics properties of PROTACs. Drug developers seeking to push this exciting and important area of research forward urgently need unique pharmacokinetics evaluation systems for PROTAC molecules.
WuXi AppTec’s Drug Metabolism and Pharmacokinetics Service Department has established a pharmacokinetics evaluation system for PROTAC drugs based on PROTAC drug study experience. This unique evaluation system relies on our complete in vitro and in vivo pharmacokinetic studies platform combined with the technical principles and characteristics of PROTAC.
Solubility in different medium
Optimized in vitro permeability evaluation model
In vivo studies to evaluate the absorption
Customized method to investigate plasma protein binding
In vivo tissue distribution or QWBA
Multiple in vitro metabolic models
Explore metabolic transformation with metabolite identification
Investigate the excretion pathway with in vivo excretion experiments
Complete DDI assessment based on drug-metabolizing enzymes
Complete DDI assessment based on drug transporters
PROTACs have a large molecular weight and poor solubility, making it difficult to meet the Classical Lipinski's Rule of Five.
PROTAC drugs have poor permeability, which results in poor druggability for oral administration; the correlation between in vitro and in vivo permeability is poor, too.
Overexposure to PROTAC causes a 'hook effect', which renders the effective dose range difficult to control.
Neither the USFDA or ICH has formulated specific guidelines for PROTAC pharmacokinetic studies.
The metabolism of PROTAC involves a variety of metabolic mechanisms; thus, multiple in vitro metabolic models can be selected, and the metabolites are relatively complex.
The physicochemical properties (solubility, lipophilicity) are closely related to its absorption properties.
The therapeutic effect is related to its concentration in plasma and target tissues.
The selection of toxicological species is related to its similarity in metabolism, with extra attention to the linker cleavage metabolites.
It is necessary to select a suitable in vitro metabolic model and strategy to screen PROTAC molecules according to the metabolic characteristics.
The preclinical optimization of PROTAC drugs is mainly conducted via the cascade optimization of physicochemical and pharmacokinetic properties.
To characterize PROTAC molecules in vitro and in vivo. This includes physicochemical properties, permeability, protein binding, and drug interactions.
To improve the metabolic clearance and solubility of PROTAC. This stage involves screening PROTAC molecules with good oral absorption and relatively stable metabolism combined with the PK properties of oral administration.
To gain a deeper exposure-response relationship. This stage uses PROTAC molecules with strong efficacy and sufficient oral bioavailability for further PK/PD studies.
Customer First and Customer CentricWe have a specialized and dedicated service model. Each client will be connected to a dedicated study director who will provide comprehensive management services for the pharmacokinetic project from drug discovery to the clinical phase.
Extensive Experience and Short Turn-Around TimeWe have more than 8 years experience on PROTAC research, with the annual study of 1,000+ PROTAC molecules, a variety of mature solutions, and short experiment cycle.
Comprehensive Capabilities and High-Quality DeliveryWith a professional PROTAC study team and a complete range of instruments and equipment, WuXi AppTec DMPK is equipped with comprehensive PROTAC study and analysis capabilities to ensure the delivery of high-quality in vivo and in vitro data.
Customized Study DesignBased on flexible study concepts, we provide customized designs for pharmacokinetic study strategies for our customers' new molecules with rapid optimization and adjustment.
Cross-Department Cooperation and High EfficiencyCross-department organization and coordination to promote the smooth operation of the project, which shortens the research period.
BCRP (Breast Cancer Resistance protein) is an important ATP-binding cassette (ABC) transporter. BCRP is mainly expressed in the apical membrane of the intestinal epithelia, in the bile duct side of hepatocytes, and in the blood-brain barrier near the blood, which can have a significant impact on restricting the entry of BCRP substrates into intestinal epithelia, mediating drug biliary excretion and the blood-brain barrier. A client needed to evaluate the inhibition of BCRP by PROTAC molecules. Preliminary results showed that the molecule had no significant inhibition of BCRP (IC 50 > 100 μM). However, the PROTAC molecule was reported in the literature to inhibit BCRP, so the client sought assistance and explanation.
After receiving questions from the client, we evaluated the study methods and data. Based on what we know about PROTAC molecules, PROTAC generally has poor permeability. With the routine cell model the extracellular PROTAC concentration is high, while the concentration of drugs entering the cell may be very low. Therefore, we recommended the BCRP-expressing inside-out membrane vesicles model for the evaluation of BCRP inhibition. The transport direction of the BCRP-mediated substrates is from the outer membrane to the inner membrane, and thus PROTAC could directly bind to the BCRP transporter outside the membrane.
The vesicle method showed that the PROTAC molecule had a strong inhibitory effect on BCRP, which was consistent with the previous literature reports. Compared with conventional methods, which cannot obtain an inhibitory window, the vesicle method is more sensitive in the evaluation of efflux transporter inhibition. In addition to the BCRP transporter, the vesicle method was also recommended for the evaluation of the inhibition of other efflux transporters by PROTAC molecules.
 Cantrill C, Chaturvedi P, Rynn C, Petrig Schaffland J, Walter I, Wittwer MB.Fundamental aspects of DMPK optimization of targeted protein degraders.Drug Discov Today.2020 Jun; 25(6): 969 - 982. doi: 10.1016 / j.drudis .2020 .03 .012.Epub 2020 Apr 13. PMID: 32298797.
 Giacomini, Kathleen M.; Huang, Shiew - Mei; Tweedie, Donald J.; Benet, Leslie Z.; Brouwer, Kim L.R.; Chu, Xiaoyan; Dahlin, Amber; Evers, Raymond; Fischer, Volker; Hillgren, Kathleen M.(2010).Membrane transporters in drug development., 9(3), 215– 236.doi: 10.1038 / nrd3028.