Our knowledge of drug transporter interactions continues to evolve. Recently, it has been shown that compound-specific transporter interactions can be influenced by pre-incubating with inhibitor prior to the addition and co-incubation with the transporter substrate. In fact, the latest draft US FDA guidance for in vitro metabolism- and transporter-mediated drug-drug interactions advises a 30 min pre-incubation with test compound prior to OATP1B1 and OATP1B3 inhibition assessment.
Our research at Cyprotex has further evaluated the effect of pre-incubation by analysing:
- different inhibitor pre-incubation times (15 min versus 30 min) for OATP1B1
- other transporters in polarised cell monolayers (i.e., P-gp in MDCK-MDR1 cells and BCRP in Caco-2 cells)
In agreement with literature and our previous findings (published AAPS abstracts from 2015 and 2016), we demonstrated that the inhibitory potency against OATP1B1 was enhanced with pre-incubation in the presence of inhibitor compared to a pre-incubation in vehicle-containing buffer alone. Furthermore, there was no statistical difference in the determined IC50 value from our standard 15 min pre-incubation period compared to a 30 min pre-incubation period. This finding is encouraging as reducing the pre-incubation time for the assay will be beneficial in terms of throughput and will limit the degradation of the test article if stability issues are expected.
With BCRP, there was no change in the inhibitory potential when pre-incubating with inhibitor versus pre-incubation in vehicle-containing buffer alone, suggestion pre-incubation is not required for the reference inhibitors tested. Conversely, the effect of pre-incubation on P-gp in MDCK-MDR1 cells was compound-specific with a significant effect only observed with elacridar (fold change 2.92; p≤0.001) suggesting that pre-incubation may be important for future screening of new chemical entities.
This research was presented at the AAPS Joint Workshop on Drug Transporters in ADME from April 16-18, 2018.