July 13, 2023
MDR3 assay development
The ABCB4/MDR3 efflux transporter – a phospholipid floppase – is almost exclusively expressed on the canalicular membrane of hepatocytes, where it is responsible for active export of phosphatidylcholine (PC) into the bile. Because of its essential role in bile formation, inhibition of MDR3 by drugs and their metabolites may be related to cholestasis and drug induced liver injury (DILI). Various studies also demonstrated the capability of MDR3 of recognizing and transporting MDR1 substrates, having potential implications for both hepatotoxic effects and drug-drug interactions (DDI). Solvo has developed a unique in vitro assay using Abcb1KO-MDCKII cells overexpressing MDR3 to assess transport inhibition. Meaningful inhibition was shown by multiple compounds with known DILI effects, reinforcing the potential role of MDR3 interactions in DILI. This assay can also be used for producing MDR3 interaction data to be incorporated in in silico models of hepatotoxicity.
The MDR3 transporter interaction assay is now available!
Preincubation effect on SLC inhibition
Uptake transport inhibition is a potential effect that may be relevant at multiple points of the drug development, from transporter inhibition as mechanism of action to drug-drug interaction assessment and regulatory investigation. Preincubation of cells with the test compound when assessing its potential to inhibit SLC transporters in vitro has been shown to affect assay outcomes. With preincubation, IC50 values may be more potent, and compounds that would have otherwise been seen as non-inhibitors can have a considerable inhibitory effect on substrate transport. This effect called potentiation of transporter inhibition by preincubation (PTIP) has been described in a collaborative publication by SOLVO and Novartis scientists in 2019 for the 8 SLCs required in DDI assessment, a publication also cited by the ICH M12 draft guidelines. A new 2023 paper from the same team at SOLVO now extended the PTIP investigation to a larger number of SLCs with PTIP observed for 21 out of 30 transporters across multiple SLC subfamilies. This effect thus seems independent of transporter structure and function and is likely at least partially driven by inhibitor characteristics; therefore, it cannot be fully ruled out for most transporters if the inhibitory nature of the compound is unknown. This new finding has implications for assay design and data interpretation not only in the case of regulatory DDI investigations but for all assays where uptake transport inhibition is tested.
Browse all of Solvo’s peer reviewed publications on our website.
New Metabolism Assay – UGT inhibition
The range of metabolism assays offered by Solvo is continuously expanding with the newest addition of UGT inhibition assessment to our portfolio. UGTs - UDP glucuronosyltransferase enzymes – are responsible for glucuronidation of their substrates to convert them into more polar glucuronide metabolites. Glucuronidation is a Phase II metabolic process, facilitating the excretion of xenobiotics, or their metabolites generated during phase I reactions, in urine and bile, and generally results in detoxification. To date, 17 human UGTs have been identified, of which, 7 have been described to play a role in the metabolism of certain drugs (UGT1A1, 1A3, 1A4, 1A6, 1A9, 2B7, and 2B15). Investigation of the inhibition of these UGT enzymes is recommended by the ICH M12 draft DDI guidelines in case a compound is undergoing glucuronidation or will likely be co-administered with drugs metabolized via direct glucuronidation. Solvo’s regulatory compliant UGT inhibition assay is available using recombinant UGT enzymes and human liver microsomes.
Solvo’s Meet the Experts webinar series continued in 2023 with 2 fantastic presentations from invited expert speakers with recordings available on our website:
Register now for our next webinar on 26th September: