SLCO Family Research Articles

Distinguishing Molecular Properties of OAT, OATP, and MRP Drug Substrates by Machine Learning.

The movement of organic anionic drugs across cell membranes is partly governed by interactions with SLC and ABC transporters in the intestine, liver, kidney, blood-brain barrier, placenta, breast, and other tissues. Major transporters involved include organic anion transporters (OATs, SLC22 family), organic anion transporting polypeptides (OATPs, SLCO family), and multidrug resistance proteins (MRPs, ABCC family). However, the sets of molecular properties of drugs that are necessary for interactions with OATs (OAT1, OAT3) vs. OATPs (OATP1B1, OATP1B3) vs. MRPs (MRP2, MRP4) are not well-understood. Defining these molecular properties is necessary for a better understanding of drug and metabolite handling across the gut-liver-kidney axis, gut-brain axis, and other multi-organ axes. It is also useful for tissue targeting of small molecule drugs and predicting drug-drug interactions and drug-metabolite interactions. Here, we curated a database of drugs shown to interact with these transporters in vitro and used chemoinformatic approaches to describe their molecular properties. We then sought to define sets of molecular properties that distinguish drugs interacting with OATs, OATPs, and MRPs in binary classifications using machine learning and artificial intelligence approaches. We identified sets of key molecular properties (e.g., rotatable bond count, lipophilicity, number of ringed structures) for classifying OATs vs. MRPs and OATs vs. OATPs. However, sets of molecular properties differentiating OATP vs. MRP substrates were less evident, as drugs interacting with MRP2 and MRP4 do not form a tight group owing to differing hydrophobicity and molecular complexity for interactions with the two transporters. If the results also hold for endogenous metabolites, they may deepen our knowledge of organ crosstalk, as described in the Remote Sensing and Signaling Theory. The results also provide a molecular basis for understanding how small organic molecules differentially interact with OATs, OATPs, and MRPs.

SLCO family of organic anion transporting polypeptides in GtoPdb v.2023.1

The SLCO superfamily is comprised of the organic anion transporting polypeptides (OATPs). The 11 human OATPs are divided into 6 families and ten subfamilies based on amino acid identity. These proteins are located on the plasma membrane of cells throughout the body. They have 12 TM domains and intracellular termini, with multiple putative glycosylation sites. OATPs mediate the sodium-independent uptake of a wide range of amphiphilic substrates, including many drugs and toxins. Due to the multispecificity of these proteins, this guide lists classes of substrates and inhibitors for each family member. More comprehensive lists of substrates, inhibitors, and their relative affinities may be found in the review articles listed below.

Highlights of This Issue

Factors influencing the efficacy of abiraterone in suppressing tumor growth in castration-resistant prostate cancer (CRPC) are not well understood. Based on its steroidal structure, Mostaghel and colleagues hypothesized that abiraterone may be transported by the SLCO family of androgen transporters. In vitro, prostate cancer cells expressing SLCO2B1 showed higher abiraterone uptake when compared with controls. In a neoadjuvant trial of abiraterone prior to prostatectomy, genetic variation in SLCO2B1 was associated with tissue abiraterone levels and rates of minimal residual disease. These data suggest variation in SLCO genes may serve as predictors of response to abiraterone treatment in men with CRPC.KRAS mutation was reported as a contributor to acquired cetuximab resistance in metastatic colorectal cancer. To explore whether other mutations in genes downstream of EGFR confer acquired resistance to cetuximab-based therapy, Xu and colleagues designed a strategy to identify low-frequency candidate mutations that are associated with acquired cetuximab resistance by sequencing circulating tumor DNA taken from patient plasma samples obtained before and during treatment. Five novel mutations in exon 19 and hotspot PIK3CA mutations were identified, which contribute to acquired cetuximab resistance. The role of PIK3CA mutations in acquired cetuximab resistance appears to be comparable with that of KRAS mutations.In patients treated with pembrolizumab, tumor burden increase of less than 20% from baseline during therapy was noted in 55% of the patients and was associated with longer overall survival, proposing a practical prognostic marker that may objectively guide treatment decisions. Pseudoprogression was noted in 4 among 107 patients (4%), including one patient without measurable tumor burden at baseline, which is indicative of a need for increased attention to nonmeasurable tumor burden in the context of immunotherapy.Reliable and reproducible methods for detecting PD-L1 expression in tumors is crucial for identifying patients who respond to anti-PD-1 therapy. The PD-L1 IHC 22C3 pharmDx is a companion diagnostic developed by Dako to identify non-small cell lung cancer patients who are likely to derive benefit from treatment with pembrolizumab. Using this assay, Cooper and colleagues investigated the inter- and intra-observer reproducibility of pathologists' assessment of PD-L1 staining and the impact of training on reproducibility. They demonstrated good agreement at both 1% and 50% cut-points. A one-hour training session had minimal impact on the reproducibility.

SLCO1B3 screening in colorectal cancer patients using High-Resolution Melting Analysis method and immunohistochemistry.

Personalized medicine has made some major advances in colorectal cancer, but new biomarkers still remain a hot issue as an emerging tool with potential prognostic and therapeutic potential. We investigated for SLCO1B3 gene alterations and protein expression in colorectal cancer, using the novel high-resolution melting analysis technique and immunohistochemistry. Formalin-fixed paraffin-embedded tumor samples from 30 colorectal cancer patients were used. The screening for gene alterations was done by high-resolution melting analysis for all exons of SLCO1B3 gene. Organic anion-transporting polypeptide 1B3 protein expression was assessed by immunohistochemistry using the monoclonal mouse MDQ antibody. High level of polymorphism was observed in the SLCO1B3 gene. We identified three previously reported polymorphisms in exons 7, 12, and 14, 699G>A, 1557A>G, and 1833G>A, respectively. In the exon 5, one variant seems to correspond to an as yet unknown SLCO family member. The immunohistochemical study revealed that organic anion-transporting polypeptide 1B3 was expressed in 27/30 samples. Of great interest, the three samples, which were immunohistochemically negative, all appeared to accommodate mutations which lead to either early stop codons or other conformations of the tertiary protein structures affecting the antibody-epitope binding. The results of this study are of much interest as high-resolution melting analysis proved to be a reliable and rapid genotyping/scanning method for mutation detection of SLCO1B3 gene.

Interaction of human organic anion transporter polypeptides 1B1 and1B3 with antineoplastic compounds.

Antineoplastic compounds are used in the treatment of a variety of cancers. The effectiveness of an antineoplastic compound to exert its activity is largely dependent on transport proteins involved in the entry of the compound into the cells, and those which drive it out of the cell. Organic anion transporting polypeptide 1B1 (OATP1B1) and organic anion transporting polypeptide 1B3 (OATP1B3), belonging to the SLCO family of proteins, are specifically expressed in the sinusoidal membranes of the liver, and are known to interact with a variety of drugs. The present study deals with the interaction of these proteins with antineoplastic compounds routinely used in cancer chemotherapy. The proteins OATP1B1 and OATP1B3 were functionally characterized in stably transfected human embryonic kidney cells using [(3)H] labeled estrone 3-sulfate and [(3)H] labeled cholecystokinin octapeptide (CCK-8) as substrates, respectively. Substrate uptake experiments performed in the presence of antineoplastic compounds showed that vinblastine and paclitaxel strongly interacted with the OATP1B1 with Ki values of 10.2μM and 0.84μM, respectively. OATP1B3 showed highly significant interactions with a variety of antineoplastic compounds including chlorambucil, mitoxantrone, vinblastine, vincristine, paclitaxel and etoposide, with Ki values of 40.6μM, 3.2μM, 15.9μM, 30.6μM, 1.8μM and 13.5μM, respectively. We report several novel interactions of the transporter proteins OATP1B1 and OATP1B3 highlighting the need to investigate their role in drug-drug interactions and cancer chemotherapy.

Estimation of the Effect ofSlco1B1Polymorphisms on Lopinavir Plasma Concentration in HIV-Infected Adults

The organic anion transporting polypeptides (OATP)/SLCO family represents an important class of hepatic drug uptake transporters that mediate the sodium independent transport of a diverse range of amphipathic organic compounds, including the protease inhibitors. The SLCO1B1 521T>C (rs4149056) single nucleotide polymorphism (SNP) has been consistently associated with reduced transport activity in vivo, and we previously showed an association of this polymorphism with lopinavir plasma concentrations. The aim of this study was to develop a population pharmacokinetic (PK) model to quantify the impact of 521T>C. A population PK analysis was performed with 594 plasma samples from 375 patients receiving lopinavir/ritonavir. Non-linear mixed effects modelling was applied to explore the effects of SLCO1B1 521T>C and patient demographics. Simulations of the lopinavir concentration profile were performed with different dosing regimens considering the different alleles. A one-compartment model with first-order absorption best described the data. Population clearance was 5.67 l/h with inter-patient variability of 37%. Body weight was the only demographic factor influencing clearance, which increased 0.5 l/h for every 10 kg increase. Homozygosity for the C allele was associated with a 37% lower clearance, and 14% for heterozygosity, which were statistically significant. These data show an association between SLCO1B1 521T>C and lopinavir clearance. The association is likely to be mediated through reduced uptake by hepatocytes leading to higher plasma concentrations of lopinavir. Further studies are now required to confirm the association and to assess the influence of other polymorphisms in the SLCO family on lopinavir PK.

Overview of SLC22A and SLCO Families of Drug Uptake Transporters in the Context of Cancer Treatments

The effectiveness of many anticancer agents is dependent on their disposition to the intracellular space of cancerous tissue. Accumulation of anticancer drugs at their sites of action can be altered by both uptake and efflux transport proteins, however the majority of research on the disposition of anticancer drugs has focused on drug efflux transporters and their ability to confer multidrug resistance. Here we review the roles of uptake transporters of the SLC22A and SLCO families in the context of cancer therapy. The many first-line anticancer drugs that are substrates of organic cation transporters (OCTs) organic cation/carnitine transporters (OCTNs) and organic anion- transporting polypeptides (OATPs) are summarized. In addition, where data is available a comparison of the localization of drug uptake transporters in healthy and cancerous tissues is provided. Expression of drug uptake transporters increases the sensitivity of cancer cell lines to anticancer substrates. Furthermore, early observational studies have suggested a causal link between drug uptake transporter expression and positive outcome in some cancers. Quantification of drug transporters by mass spectrometry will provide an essential technique for generation of expression data during future observational clinical studies. Screening of drug uptake transporter expression in primary tumors may help differentiate between susceptible and resistant cancers prior to therapy.

HIV protease inhibitors are substrates for OATP1A2, OATP1B1 and OATP1B3 and lopinavir plasma concentrations are influenced by SLCO1B1 polymorphisms

OATP1B1 and OATP1B3 are major hepatic drug transporters whilst OATP1A2 is mainly located in the brain but is also located in liver and several other organs. These transporters affect the distribution and clearance of many endobiotics and xenobiotics and have been reported to have functional single nucleotide polymorphisms (SNPs). We have assessed the substrate specificities of these transporters for a panel of antiretrovirals and investigated the effects of SNPs within these transporters on the pharmacokinetics of lopinavir. SLCO1A2, SLCO1B1 and SLCO1B3 were cloned, verified and used to generate cRNA for use in the Xenopuslaevis oocyte transport system. Using the oocyte system, antiretrovirals were tested for their substrate specificities. Plasma samples (n=349) from the Liverpool therapeutic drug monitoring registry were genotyped for SNPs in SLCO1A2, SLCO1B1 and SLCO1B3 and associations between SNPs and lopinavir plasma concentrations were analysed. Antiretroviral protease inhibitors, but not non-nucleoside reverse transcriptase inhibitors, are substrates for OATP1A2, OATP1B1 and OATP1B3. Furthermore, ritonavir was not an inhibitor of OATP1B1. The 521T>C polymorphism in SLCO1B1 was significantly associated with higher lopinavir plasma concentrations. No associations were observed with functional variants of SLCO1A2 and SLCO1B3. These data add to our understanding of the factors that contribute to variability in plasma concentrations of protease inhibitors. Further studies are now required to confirm the association of SLCO1B1 521T>C with lopinavir plasma concentrations and to assess the influence of other polymorphisms in the SLCO family.

Interaction of the Multikinase Inhibitors Sorafenib and Sunitinib with Solute Carriers and ATP-Binding Cassette Transporters

To compare side-by-side the uptake of sorafenib and sunitinib in vitro by human uptake solute carriers of the SLC22A and SLCO families, the transport by and inhibition of efflux ATP-binding cassette (ABC) transporters, and the role of ABCB1 in the plasma pharmacokinetics and brain penetration of these agents. Uptake of [(3)H]sorafenib or [(3)H]sunitinib was assessed in Xenopus laevis oocytes or mammalian cells transfected with cDNAs coding for human OATP1A2, OATP1B1, OATP1B3, OCT1, OAT2, OAT3, OCTN1, or OCTN2. Efflux and inhibition experiments were conducted in cells transfected with human ABCB1, ABCG2, ABCC2, or ABCC4. In vivo pharmacokinetic studies were done in knockout mice lacking Abcb1-type transporters. Intracellular uptake was not appreciably affected by any of the studied solute carriers and was minute relative to the respective prototypical substrates. Sorafenib and sunitinib showed concentration-dependent (1 and 10 micromol/L), low to moderate affinity for ABCB1 but were not affected by the other ABC transporters. Both agents inhibited all tested ABC transporters. The absence of Abcb1 had no affect on plasma pharmacokinetics, but brain penetration was moderately increased by 1.9- and 2.9-fold for sorafenib and sunitinib, respectively, in knockout animals versus controls. Unlike other tyrosine kinase inhibitors, sorafenib and sunitinib do not appear to rely on active transport to enter the cell nor are they high-affinity substrates for ABC efflux transporters. Based on these characteristics, these two drugs may be less susceptible to transporter-mediated alterations in systemic exposure and transporter-related resistance mechanisms.

Profiling SLCO and SLC22 genes in the NCI-60 cancer cell lines to identify drug uptake transporters

Molecular and pharmacologic profiling of the NCI-60 cell panel offers the possibility of identifying pathways involved in drug resistance or sensitivity. Of these, decreased uptake of anticancer drugs mediated by efflux transporters represents one of the best studied mechanisms. Previous studies have also shown that uptake transporters can influence cytotoxicity by altering the cellular uptake of anticancer drugs. Using quantitative real-time PCR, we measured the mRNA expression of two solute carrier (SLC) families, the organic cation/zwitterion transporters (SLC22 family) and the organic anion transporters (SLCO family), totaling 23 genes in normal tissues and the NCI-60 cell panel. By correlating the mRNA expression pattern of the SLCO and SLC22 family member gene products with the growth-inhibitory profiles of 1,429 anticancer drugs and drug candidate compounds tested on the NCI-60 cell lines, we identified SLC proteins that are likely to play a dominant role in drug sensitivity. To substantiate some of the SLC-drug pairs for which the SLC member was predicted to be sensitizing, follow-up experiments were performed using engineered and characterized cell lines overexpressing SLC22A4 (OCTN1). As predicted by the statistical correlations, expression of SLC22A4 resulted in increased cellular uptake and heightened sensitivity to mitoxantrone and doxorubicin. Our results indicate that the gene expression database can be used to identify SLCO and SLC22 family members that confer sensitivity to cancer cells.

The complexities of hepatic drug transport: current knowledge and emerging concepts.

Recently, hepatic transport processes have been recognized as important determinants of drug disposition. Therefore, it is not surprising that characterization of the hepatic transport and biliary excretion properties of potential drug candidates is an important part of the drug development process. Such information also is useful in understanding alterations in the hepatobiliary disposition of compounds due to drug interactions or disease states. Basolateral transport systems are responsible for translocating molecules across the sinusoidal membrane, whereas active canalicular transport systems are responsible for the biliary excretion of drugs and metabolites. Several transport proteins involved in basolateral transport have been identified including the Na(+)-taurocholate co-transporting polypeptide [NTCP (SLC10A1)], organic anion transporting polypeptides [OATPs (SLCO family)], multidrug resistance-associated proteins [MRPs (ABCC family)], and organic anion and cation transporters [OATs, OCTs (SLC22A family)]. Canalicular transport is mediated predominantly via P-glycoprotein (ABCB1), MRP2 (ABCC2), the bile salt export pump [BSEP (ABCB11)], and the breast cancer resistance protein [BCRP (ABCG2)]. This review summarizes current knowledge regarding these hepatic basolateral and apical transport proteins in terms of substrate specificity, regulation by nuclear hormone receptors and intracellular signaling pathways, genetic differences, and role in drug interactions. Transport knockout models and other systems available for hepatobiliary transport studies also are discussed. This overview of hepatobiliary drug transport summarizes knowledge to date in this rapidly growing field and emphasizes the importance of understanding these fundamental processes in hepatic drug disposition.