Neonicotinoid pesticides poorly interact with human drug transporters

Combined in silico and in vitro approaches to identify P-glycoprotein-inhibiting pesticides

The P-glycoprotein (P-gp) efflux pump plays a major role in xenobiotic detoxification. The inhibition of its activity by environmental contaminants remains however rather little characterised. The present study was designed to develop a combination of different approaches to identify P-gp inhibitors among a large number of pesticides using in silico and in vitro models. First, the prediction performance of four web tools was evaluated alone or in combination using a set of recently marketed drugs. The best combination of web tools-AdmetSAR2.0/PgpRules/pkCSM-was next used to predict P-gp activity inhibition by 762 pesticides. Among the 187 pesticides predicted to be P-gp inhibitors, 11 were tested in vitro for their ability to inhibit the efflux of reference substrates (rhodamine 123 and Hoechst 33342) in P-gp overexpressing MCF7R cells and to inhibit the efflux of the reference substrate rhodamine 123 in the Caco-2 cell monolayer. In MCF7R cell assays, ivermectin B1a, emamectin B1 benzoate, spinosad, dimethomorph and tralkoxydim inhibited P-gp activity; ivermectin B1a, emamectin B1 benzoate and spinosad were determined to be stronger inhibitors (half-maximal inhibitory concentration [IC50 ] of 3 ± 1, 5 ± 1 and 7 ± 1 µM, respectively) than dimethomorph and tralkoxydim (IC50 of 102 ± 7 and 88 ± 7 µM, respectively). Ivermectin B1a, emamectin B1 benzoate, spinosad and dimethomorph also inhibited P-gp activity in Caco-2 cell monolayer assays, with dimethomorph being a weaker P-gp inhibitor. These combined approaches could be used to identify P-gp inhibitors among food contaminants, but need to be optimised and adapted for high-throughput screening.

Interactions of organophosphate flame retardants with human drug transporters

Organophosphate flame retardants (OPFRs) are environmental pollutants of increasing interest, widely distributed in the environment and exerting possible deleterious effects towards the human health. The present study investigates in vitro their possible interactions with human drug transporters, which are targets for environmental chemicals and actors of their toxicokinetics. Some OPFRs, i.e., tris(2-butoxyethyl) phosphate (TBOEP), tris(1,3-dichloroisopropyl) phosphate (TDCPP), tri-o-cresyl phosphate (TOCP) and triphenyl phosphate (TPHP), were found to inhibit activities of some transporters, such as organic anion transporter 3 (OAT3), organic anion transporting polypeptide (OATP) 1B1, OATP1B3, organic cation transporter 2 (OCT2) or breast cancer resistance protein (BCRP). These effects were concentration-dependent, with IC50 values ranging from 6.1 µM (for TDCPP-mediated inhibition of OCT2) to 51.4 µM (for TOCP-mediated inhibition of BCRP). OPFRs also blocked the transporter-dependent membrane passage of endogenous substrates, notably that of hormones. OAT3 however failed to transport TBOEP and TPHP. OPFRs additionally repressed mRNA expressions of some transporters in cultured human hepatic HepaRG cells, especially those of OAT2 and OCT1 in response to TOCP, with IC50 values of 2.3 µM and 2.5 µM, respectively. These data therefore add OPFRs to the expanding list of pollutants interacting with drug transporters, even if OPFR concentrations required to impact transporters, in the 2-50 µM range, are rather higher than those observed in humans environmentally or dietarily exposed to these chemicals.

Transporter-mediated Natural Product-Drug Interactions

The increasing use of natural products in clinical practice has raised great concerns about the potential natural product-drug interactions (NDIs). Drug transporters mediate the transmembrane passage of a broad range of drugs, and thus are important determinants for drug pharmacokinetics and pharmacodynamics. Generally, transporters can be divided into ATP binding cassette (ABC) family and solute carrier (SLC) family. Numerous natural products have been identified as inhibitors, substrates, inducers, and/or activators of drug transporters. This review article aims to provide a comprehensive summary of the recent progress on the research of NDIs, focusing on the main drug transporters, such as P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), organic anion transporter 1 and 3 (OAT1/OAT3), organic anion-transporting polypeptide 1B1 and 1B3 (OATP1B1/OATP1B3), organic cation transporter 2 (OCT2), multidrug and toxin extrusion protein 1 and 2-K (MATE1/MATE2-K). Additionally, the challenges and strategies of studying NDIs are also discussed.

Differential in vitro interactions of the Janus kinase inhibitor ruxolitinib with human SLC drug transporters

Interactions of the Janus kinase (JAK) inhibitor ruxolitinib with solute carriers (SLCs) remain incompletely characterised. The present study was therefore designed to investigate this issue.The interactions of ruxolitinib with SLCs were analysed using transporter-overexpressing human embryonic kidney HEK293 cells. Substrate accumulation was detected by spectrofluorimetry, liquid chromatography coupled to tandem mass spectrometry or scintillation counting.Ruxolitinib was found to potently inhibit the activities of organic anion transporter 3 (OAT3), organic cation transporter 2 (OCT2), multidrug and toxin extrusion 1 (MATE1) and MATE2-K (half maximal inhibitory concentration (IC₅₀) < 10 µM). It blocked OAT1, OAT4, OATP1B1, OATP1B3, OATP2B1 and OCT3, but in a weaker manner (IC₅₀ > 10 µM), whereas OCT1 was not impacted. No time-dependent inhibition was highlighted. When applying the US Food and Drug Administration (FDA) criteria for transporters-related drug-drug interaction risk, OCT2 and MATE2-K, unlike MATE1 and OAT3, were predicted to be in vivo inhibited by ruxolitinib. Cellular uptake studies additionally indicated that ruxolitinib is a substrate for MATE1 and MATE2-K, but not for OAT3 and OCT2.Ruxolitinib in vitro blocked activities of most of SLC transporters. Only OCT2 and MATE-2K may be however clinically inhibited by the JAK inhibitor, with the caution for OCT2 that in vitro inhibition data were generated with an FDA-non recommended fluorescent substrate. Ruxolitinib MATEs-mediated transport may additionally deserve attention for its possible pharmacological consequences in MATE-positive cells.

Study on the binding mechanism of thiamethoxam with three model proteins:spectroscopic studies and theoretical simulations

As a top-selling neonicotinoid insecticide widely used in the field, thiamethoxam is an environmental pollutant because of the accumulation in ecosystem and has also been reported that it has potential risks to the health of mammals even humans. In order to understand the binding mechanism of thiamethoxam with biological receptors, spectroscopic techniques and theoretical simulations was used to explore the specific interactions between thiamethoxam and proteins. Interestingly, the results indicated that hydrophobic interaction as the main driving force, thiamethoxam formed a single binding site complex with proteins spontaneously, resulting in a decrease in the esterase-like activity of human serum albumin. The results of computer simulation showed that there were hydrophobic, electrostatic and hydrogen bonding interactions between thiamethoxam and receptors. The results of experiment and computer simulation were mutually confirmed, so a model was established for the interaction between the two which uncovered the structural characteristics of the binding site. This research provided new insights for the structure optimization of thiamethoxam, as well as gave an effective reference for evaluating the risk of thiamethoxam systemically in the future.

Differential interactions of carbamate pesticides with drug transporters

Pesticides are now recognised to interact with drug transporters, but only few data are available on this issue for carbamate pesticides, a widely used class of agrochemicals, to which humans are highly exposed. The present study was therefore designed to determine whether four representative carbamate pesticides, i.e. the insecticides aminocarb and carbofuran, the herbicide chlorpropham and the fungicide propamocarb, may impair activities of main drug transporters implicated in pharmacokinetics. The interactions of carbamates with solute carrier and ATP-binding cassette transporters were investigated using cultured transporter-overexpressing cells, reference substrates and spectrofluorimetry-, liquid chomatography/tandem mass spectrometry- or radioactivity-based methods. Aminocarb and carbofuran exerted no or minimal effects on transporter activities, whereas chlorpropham inhibited BCRP and OAT3 activities and propamocarb decreased those of OCT1 and OCT2, but cis-stimulated that of MATE2-K. Such alterations of transporters however required chlorpropham/propamocarb concentrations in the 5-50 µM range, likely not relevant to environmental exposure. Trans-stimulation assays and propamocarb accumulation experiments additionally suggested that propamocarb is not a substrate for OCT1, OCT2 and MATE2-K. These data indicate that some carbamate pesticides can interact in vitro with some drug transporters, but only when used at concentrations higher than those expected to occur in environmentally exposed humans.