Evaluation of In Vitro Metabolism- and Transporter-Based Drug Interactions with Sunscreen Active Ingredients.

PURPOSE: The aim of this study was to examine the ability of sunscreen active ingredients to inhibit in vitro drug metabolism via cytochrome P450 (CYP) enzymes and drug uptake transporters. METHODS: Metabolism assays with human liver microsomes were conducted for CYP2C9, CYP2D6 and CYP3A4 using probe substrates warfarin, bufuralol and midazolam, respectively. Uptake transporter assays with transfected cell lines were conducted for OAT3, OCT2 and OATP1B1 with probe substrates estrone-3-sulfate, metformin and rosuvastatin, respectively. Six sunscreen active ingredients, avobenzone, enzacamene, oxybenzone, octinoxate, trolamine, and homosalate, were evaluated up to their aqueous solubility limits in the assays. RESULTS: None of the sunscreen active ingredients inhibited CYP2D6 or CYP3A4 activities in the microsomes at concentration ranges up to tenfold higher than their known clinical total plasma levels. Only enzacamene, oxybenzone and trolamine were found to be inhibitory to CYP2C9 activity with IC50 values of 14.76, 22.46 and 154.7 µM, respectively. Avobenzone, enzacamene, homosalate and octinoxate were not inhibitory to the uptake transporters at the evaluated concentrations. Oxybenzone was inhibitory to OAT3 and OCT2 with IC50 values of 39.93 and 42.77 µM, respectively. Trolamine also inhibited uptake in OAT3 and OCT2 transfected cells with IC50 values of 448.1 and 1376 µM, respectively. CONCLUSIONS: Although enzacamene, oxybenzone and trolamine inhibited CYP2C9 and the renal transporters OAT3 and OCT2 in vitro, their IC50 values exceeded total plasma levels found in clinical studies. Therefore, it is unlikely that these sunscreen active ingredients in sunscreen products will inhibit the metabolism or transport of co-administered drugs in consumers.

Knockout Transporter Cell Lines to Assess Substrate Potential Towards Efflux Transporters.

P-glycoprotein (P-gp), breast cancer resistance protein (BCRP) and multidrug resistance transporter 2 (MRP2) are efflux transporters involved in the absorption, excretion, and distribution of drugs. Bidirectional cell assays are recognized models for evaluating the potential of new drugs as substrates or inhibitors of efflux transporters. However, the assays are complicated by a lack of selective substrates and/or inhibitors, as well simultaneous expression of several efflux transporters in cell lines used in efflux models. This project aims to evaluate an in vitro efflux cell assay employing model substrates and inhibitors of P-gp, BCRP and MRP2 with knockout (KO) cell lines. The efflux ratios (ER) of P-gp (digoxin, paclitaxel), BCRP (prazosin, rosuvastatin), MRP2 (etoposide, olmesartan) and mixed (methotrexate, mitoxantrone) substrates were determined in wild-type C2BBe1 and KO cells. For digoxin and paclitaxel, the ER decreased to less than 2 in the cell lines lacking P-gp expression. The ER decreased to less than 3 for prazosin and less than 2 for rosuvastatin in the cell lines lacking BCRP expression. For etoposide and olmesartan, the ER decreased to less than 2 in the cell lines lacking MRP2 expression. The ER of methotrexate and mitoxantrone decreased in single- and double-KO cells without BCRP and MRP2 expression. These results show that KO cell lines have the potential to better interpret complex drug-transporter interactions without depending upon multi-targeted inhibitors or overlapping substrates. For drugs that are substrates of multiple transporters, the single- and double-KO cells may be used to assess their affinities for the different transporters.

Application of transporter assays for drug discovery and development: an update of the literature.

INTRODUCTION: Determining whether a new drug is a substrate, inhibitor or inducer of efflux or uptake membrane transporters has become a routine process during drug discovery and development. In vitro assays are utilized to establish whether a new drug has the potential to be an object (substrate) or precipitant (inhibitor, inducer) in transporter-mediated clinical drug-drug interactions. The findings from these in vitro experiments are then used to determine whether further in vivo drug interaction studies are necessary for a new drug. AREAS COVERED: This article provides an update on in vitro transporter assays, focusing on new uses of transfected cells, time-dependent inhibition, transporter induction, and complex model systems. EXPERT OPINION: The newer in vitro assays add to the toolbox in defining new drugs as transporter substrates, inhibitors, or inducers. Complex models such as spheroids, organoids, and microphysiological systems require standardization and further research with model transporter substrates and inhibitors. In drug discovery, the more traditional transporter assays may be employed as substrate and inhibitor screening assays. In drug development, more complex cell models can be employed in later drug development to better understand how transporter(s) are involved in the absorption, distribution, and excretion of new drugs.