The sulfated conjugate of biochanin A is a substrate of breast cancer resistant protein (ABCG2)

Comprehensive exploration of Biochanin A as an oncotherapeutics potential in the treatment of multivarious cancers with molecular insights

Cancer is considered a leading cause of mortality. This rising cancer death rate and several existing limitations like side effects, poor efficacies, and high cost of the present chemotherapeutic agents have increased the demand for more potent and alternative cancer treatments. This review elucidated a brief overview of Biochanin A (BCA) and its potentiality on various cancers with details of anticancer mechanism. According to our review, a number of studies including in silico, in vitro, pre-clinical, and clinical trials have tested to evaluate the efficacy of BCA. This compound is effective against 15 types of cancer, including breast, cervical, colorectal, gastric, glioblastoma, liver, lung, melanoma, oral, osteosarcoma, ovarian, pancreatic, pharynx, prostate, and umbilical vein cancer. The general anticancer activities of this compound are mediated via several molecular processes, including regulation of apoptosis, cell proliferation, metastasis and angiogenesis, signaling, enzymatic pathways, and other mechanisms. Targeting both therapeutic and oncogenic proteins, as well as different pathways, makes up the molecular mechanism underlying the anticancer action. Many signaling networks and their components, such as EFGR, PI3K/Akt/mTOR, MAPK, MMP-2, MMP-9, PARP, Caspase-3/8/9, Bax, Bcl2, PDL-1, NF-κB, TNF-α, IL-6, JAK, STAT3, VEGFR, VEGF, c-MY, Cyclin B1, D1, E1 and CDKs, Snail, and E-cadherin proteins, can be regulated in cancer cells by BCA. Such kind of anticancer properties of BCA could be a result of its correct structural chemistry. The use of BCA-based therapies as nano-carriers for the delivery of chemotherapeutic medicines has the potential to be very effective. This natural compound synergises with other natural compounds and standard drugs, including sorafenib, 5-fluorouracil, temozolomide, doxorubicin, apigenin, and genistein. Moreover, proper use of this compound can reverse multidrug resistance through numerous mechanisms. BCA has better drug-likeness and pharmacokinetic properties and is nontoxic (eye, liver, kidney, skin, cardio) in human bodies. As having a wide range of cancer-fighting mechanisms, synergistic effects, and good pharmacokinetic properties, BCA can be used as a supplementary food until standard drugs are available at pharma markets.

Tailoring Potential Natural Compounds for the Treatment of Luminal Breast Cancer

Breast cancer (BC) is the most diagnosed cancer worldwide, mainly affecting the epithelial cells from the mammary glands. When it expresses the estrogen receptor (ER), the tumor is called luminal BC, which is eligible for endocrine therapy with hormone signaling blockade. Hormone therapy is essential for the survival of patients, but therapeutic resistance has been shown to be worrying, significantly compromising the prognosis. In this context, the need to explore new compounds emerges, especially compounds of plant origin, since they are biologically active and particularly promising. Natural products are being continuously screened for treating cancer due to their chemical diversity, reduced toxicity, lower side effects, and low price. This review summarizes natural compounds for the treatment of luminal BC, emphasizing the activities of these compounds in ER-positive cells. Moreover, their potential as an alternative to endocrine resistance is explored, opening new opportunities for the design of optimized therapies.

Effects and mechanisms of dietary bioactive compounds on breast cancer prevention

Breast cancer (BC) is the most often diagnosed cancer among females globally and has become an increasing global health issue over the last decades. Despite the substantial improvement in screening methods for initial diagnosis, effective therapy remains lacking. Still, there has been high recurrence and disease progression after treatment of surgery, endocrine therapy, chemotherapy, and radiotherapy. Considering this view, there is a crucial requirement to develop safe, freely accessible, and effective anticancer therapy for BC. The dietary bioactive compounds as auspicious anticancer agents have been recognized to be active and their implications in the treatment of BC with negligible side effects. Hence, this review focused on various dietary bioactive compounds as potential therapeutic agents in the prevention and treatment of BC with the mechanisms of action. Bioactive compounds have chemo-preventive properties as they inhibit the proliferation of cancer cells, downregulate the expression of estrogen receptors, and cell cycle arrest by inducing apoptotic settings in tumor cells. Therapeutic drugs or natural compounds generally incorporate engineered nanoparticles with ideal sizes, shapes, and enhance their solubility, circulatory half-life, and biodistribution. All data of in vitro, in vivo, and clinical studies of dietary bioactive compounds and their impact on BC were collected from Science Direct, PubMed, and Google Scholar. The data of chemopreventive and anticancer activity of dietary bioactive compounds were collected and orchestrated in a suitable place in the review. These shreds of data will be extremely beneficial to recognize a series of additional diet-derived bioactive compounds to treat BC with the lowest side effects.

Identification of Food-Derived Isoflavone Sulfates as Inhibition Markers for Intestinal Breast Cancer Resistance Proteins

Potential inhibition of the breast cancer resistance protein (BCRP), a drug efflux transporter, is a key issue during drug development, and the use of its physiologic substrates as biomarkers can be advantageous to assess inhibition. In this study, we aimed to identify BCRP substrates by an untargeted metabolomic approach. Mice were orally administered lapatinib to inhibit BCRP in vivo, and plasma samples were assessed by liquid chromatography/time of flight/mass spectrometry with all-ion fragmentation acquisition and quantified by liquid chromatography with tandem mass spectrometry. A differential metabolomic analysis was also performed for plasma from Bcrp ^-/- and wild-type mice. Plasma peaks of food-derived isoflavone metabolites, daidzein sulfate (DS), and genistein sulfate (GS) increased after lapatinib administration and in Bcrp ^-/- mice. Administration of lapatinib and another BCRP inhibitor febuxostat increased the area under the plasma concentration-time curve (AUC) of DS, GS, and equol sulfate (ES) by 3.6- and 1.8-, 5.6- and 4.1-, and 1.6- and 4.8-fold, respectively. BCRP inhibitors also increased the AUC and maximum plasma concentration of DS and ES after coadministration with each parent compound. After adding parent compounds to the apical side of induced pluripotent stem cell-derived small intestinal epithelial-like cells, DS, GS, and ES in the basal compartment significantly increased in the presence of lapatinib and febuxostat, suggesting the inhibition of intestinal BCRP. ATP-dependent uptake of DS and ES in BCRP-expressing membrane vesicles was reduced by both inhibitors, indicating inhibition of BCRP-mediated DS and ES transport. Thus, we propose the first evidence of surrogate markers for BCRP inhibition. SIGNIFICANCE STATEMENT: This study performed untargeted metabolomics to identify substrates of BCRP/ABCG2 to assess changes in its transport activity in vivo by BCRP/ABCG2 inhibitors. Food-derived isoflavone sulfates were identified as useful markers for evaluating changes in BCRP-mediated transport in the small intestine by its inhibitors.

Potential Herb-Drug Interactions in the Management of Age-Related Cognitive Dysfunction

Late-life mild cognitive impairment and dementia represent a significant burden on healthcare systems and a unique challenge to medicine due to the currently limited treatment options. Plant phytochemicals have been considered in alternative, or complementary, prevention and treatment strategies. Herbals are consumed as such, or as food supplements, whose consumption has recently increased. However, these products are not exempt from adverse effects and pharmacological interactions, presenting a special risk in aged, polymedicated individuals. Understanding pharmacokinetic and pharmacodynamic interactions is warranted to avoid undesirable adverse drug reactions, which may result in unwanted side-effects or therapeutic failure. The present study reviews the potential interactions between selected bioactive compounds (170) used by seniors for cognitive enhancement and representative drugs of 10 pharmacotherapeutic classes commonly prescribed to the middle-aged adults, often multimorbid and polymedicated, to anticipate and prevent risks arising from their co-administration. A literature review was conducted to identify mutual targets affected (inhibition/induction/substrate), the frequency of which was taken as a measure of potential interaction. Although a limited number of drugs were studied, from this work, interaction with other drugs affecting the same targets may be anticipated and prevented, constituting a valuable tool for healthcare professionals in clinical practice.

Effects of Chrysin and Its Major Conjugated Metabolites Chrysin-7-Sulfate and Chrysin-7-Glucuronide on Cytochrome P450 Enzymes and on OATP, P-gp, BCRP, and MRP2 Transporters

Chrysin is an abundant flavonoid in nature, and it is also contained by several dietary supplements. Chrysin is highly biotransformed in the body, during which conjugated metabolites chrysin-7-sulfate and chrysin-7-glucuronide are formed. These conjugates appear at considerably higher concentrations in the circulation than the parent compound. Based on previous studies, chrysin can interact with biotransformation enzymes and transporters; however, the interactions of its metabolites have been barely examined. In this in vitro study, the effects of chrysin, chrysin-7-sulfate, and chrysin-7-glucuronide on cytochrome P450 enzymes (2C9, 2C19, 3A4, and 2D6) as well as on organic anion-transporting polypeptides (OATPs; 1A2, 1B1, 1B3, and 2B1) and ATP binding cassette [P-glycoprotein, multidrug resistance-associated protein 2, and breast cancer resistance protein (BCRP)] transporters were investigated. Our observations revealed that chrysin conjugates are strong inhibitors of certain biotransformation enzymes (e.g., CYP2C9) and transporters (e.g., OATP1B1, OATP1B3, OATP2B1, and BCRP) examined. Therefore, the simultaneous administration of chrysin-containing dietary supplements with medications needs to be carefully considered due to the possible development of pharmacokinetic interactions. SIGNIFICANCE STATEMENT: Chrysin-7-sulfate and chrysin-7-glucuronide are the major metabolites of flavonoid chrysin. In this study, we examined the effects of chrysin and its conjugates on cytochrome P450 enzymes and on organic anion-transporting polypeptides and ATP binding cassette transporters (P-glycoprotein, breast cancer resistance protein, and multidrug resistance-associated protein 2). Our results demonstrate that chrysin and/or its conjugates can significantly inhibit some of these proteins. Since chrysin is also contained by dietary supplements, high intake of chrysin may interrupt the transport and/or the biotransformation of drugs.

Placental BCRP/ABCG2 Transporter Prevents Fetal Exposure to the Estrogenic Mycotoxin Zearalenone

In the placenta, the breast cancer resistance protein (BCRP)/ABCG2 efflux transporter limits the maternal-to-fetal transfer of drugs and chemicals. Previous research has pointed to the estrogenic mycotoxin zearalenone as a potential substrate for BCRP. Here, we sought to assess the role of the BCRP transporter in the transplacental disposition of zearalenone during pregnancy. In vitro transwell transport assays employing BCRP/Bcrp-transfected Madine-Darby canine kidney cells and BeWo trophoblasts with reduced BCRP expression were used to characterize the impact of BCRP on the bidirectional transport of zearalenone. In both models, the presence of BCRP protein increased the basolateral-to-apical transport and reduced the apical-to-basolateral transport of zearalenone over a 2-h period. In vivo pharmacokinetic analyses were then performed using pregnant wild-type and Bcrp-/- mice after a single tail vein injection of zearalenone. Zearalenone and its metabolite α-zearalenol were detectable in serum, placentas, and fetuses from all animals, and β-zearalenol was detected in serum and fetuses, but not placentas. There were no significant differences in the maternal serum concentrations of any analytes between the two genotypes. In Bcrp-/- mice, the free fetal concentrations of zearalenone, α-zearalenol, and β-zearalenol were increased by 115%, 84%, and 150%, respectively, when compared with wild-type mice. Concentrations of free zearalenone and α-zearalenol were elevated 145% and 78% in Bcrp-/- placentas, respectively, when compared with wild-type placentas. Taken together, these data indicate that the placental BCRP transporter functions to reduce the fetal accumulation of zearalenone, which may impact susceptibility to developmental toxicities associated with in utero zearalenone exposure.

Breast Cancer Resistance Protein and Multidrug Resistance Protein 2 Determine the Disposition of Esculetin-7-O-Glucuronide and 4-Methylesculetin-7-O-Glucuronide

Esculetin (ET)-7-O-glucuronide (ET-G) and 4-methylesculetin (4-ME)-7-O-glucuronide (4-ME-G) are the main glucuronide of ET and 4-ME, respectively. The disposition mediated by efflux transporters for glucuronide has significant influence on the pharmacokinetic profile and efficacy of bioactive compounds. In the current study, transporter gene knockout mice and Caco-2 cells were used to explore the effects of breast cancer resistance protein (BCRP) and multidrug resistance-associated protein 2 (MRP2) on the disposition of ET-G and 4-ME-G. After oral or i.v. administration of ET and 4-ME, the area under the plasma concentration-time curve from time 0 to the last data point or infinity values of ET, 4-ME, and their glucuronides (ET-G and 4-ME-G) were remarkably and significantly increased in most Bcrp1^-/- and Mrp2^-/- mice compared with those in wild-type FVB mice (P < 0.05). These results were accompanied with a significant increase of maximum plasma concentration values (P < 0.05). In Caco-2 monolayers, the efflux and clearance rates of ET-G and 4-ME-G were markedly reduced by the BCRP inhibitor Ko143 and MRP2 inhibitor MK571 on the apical side (P < 0.05). In an intestinal perfusion study, the excretion of ET-G was significantly decreased in perfusate and increased in plasma in Bcrp1^-/- mice compared with those in wild-type FVB mice (P < 0.05). The 4-ME-G concentration was also decreased in the bile in transporter gene knockout mice. ET and 4-ME showed good permeability in both Caco-2 monolayers [apparent permeability (P_app ) ≥ 0.59 × 10^-5 cm/s] and duodenum (P_app ≥ 1.81). In conclusion, BCRP and MRP2 are involved in excreting ET-G and 4-ME-G. ET and 4-ME are most likely absorbed via passive diffusion in the intestines.

An update on polyphenol disposition via coupled metabolic pathways

INTRODUCTION

Polyphenols, which are widely distributed in plants and the human diets, are known to have numerous biological activities. However, the low bioavailability of polyphenols is mediated by coupled metabolic pathways. Areas covered: The key role of the interplay between drug metabolic enzymes (DMEs) and efflux transporters (ETs), nuclear receptors (NRs), and intestinal microflora in the disposition of polyphenols is summarized. Expert opinion: ETs are shown to act as a 'revolving door', facilitating and/or controlling cellular polyphenol glucuronide/sulfate excretion. Elucidating the mechanisms underlying the glucuronidation/sulfation-transport interplay and structure-activity relationships (SAR) of glucuronide/sulfate efflux by an ET is important. Some new physiologically based pharmacokinetic (PBPK) models could be developed to predict the interplay between glucuronides/sulfates and ETs. Additionally, the combined actions of uridine-5'-diphosphate glucuronosyltransferases, ETs, and intestinal microflora/enterocyte-derived β-glucuronidase enable triple recycling (local, enteric, and enterohepatic recycling), thereby increasing the residence time of polyphenols and their glucuronides in the local intestine and liver. Further studies are necessary to explore these recycling mechanisms and interactions between polyphenols and the intestinal microbiota. Since NRs govern the inducible expression of target genes that encode DMEs and ETs. Determination of the regulation mechanism mediated by NRs using transgenic and knockout animals is still needed.

Glucuronidation: driving factors and their impact on glucuronide disposition

Glucuronidation is a well-recognized phase II metabolic pathway for a variety of chemicals including drugs and endogenous substances. Although it is usually the secondary metabolic pathway for a compound preceded by phase I hydroxylation, glucuronidation alone could serve as the dominant metabolic pathway for many compounds, including some with high aqueous solubility. Glucuronidation involves the metabolism of parent compound by UDP-glucuronosyltransferases (UGTs) into hydrophilic and negatively charged glucuronides that cannot exit the cell without the aid of efflux transporters. Therefore, elimination of parent compound via glucuronidation in a metabolic active cell is controlled by two driving forces: the formation of glucuronides by UGT enzymes and the (polarized) excretion of these glucuronides by efflux transporters located on the cell surfaces in various drug disposition organs. Contrary to the common assumption that the glucuronides reaching the systemic circulation were destined for urinary excretion, recent evidences suggest that hepatocytes are capable of highly efficient biliary clearance of the gut-generated glucuronides. Furthermore, the biliary- and enteric-eliminated glucuronides participate into recycling schemes involving intestinal microbes, which often prolong their local and systemic exposure, albeit at low systemic concentrations. Taken together, these recent research advances indicate that although UGT determines the rate and extent of glucuronide generation, the efflux and uptake transporters determine the distribution of these glucuronides into blood and then to various organs for elimination. Recycling schemes impact the apparent plasma half-life of parent compounds and their glucuronides that reach intestinal lumen, in addition to prolonging their gut and colon exposure.

Design of inhibitors of BCRP/ABCG2

BCRP/ABCG2, a second member of ABC transporter subclass G, has been shown to be overexpressed in several solid tumors, acute myelogenous leukemia and chronic myeloid leukemia. A variety of chemically unrelated anticancer drugs have been found to be transported by ABCG2 leading to their lower intracellular accumulation and hence causing chemoresistance. Until now several efforts have been taken to identify potent and selective inhibitors of ABCG2. Recent studies carried out to deign BCRP inhibitors have been able to point out the effect of the substitution pattern in compound scaffolds on the potency, selectivity and cytotoxicity of ABCG2 inhibitors.

5,7-Dihydroxy-4'-methoxyisoflavone induces apoptosis by inhibiting the ERK and Akt pathways in human osteosarcoma cells

Phytoestrogens are known to prevent tumor progression by inhibiting proliferation and inducing apoptosis in cancer cells. In this study we determine the effect of 5,7-dihydroxy-4'-methoxyisoflavone, a phytoestrogen, on proliferation and apoptosis in the human osteosarcoma (OS) cell line U2OS. 5,7-Dihydroxy-4'-methoxyisoflavone dose-dependently inhibited proliferation in U2OS cells, which was accompanied by an increase of early apoptotic cells. However, 5,7-dihydroxy-4'-methoxyisoflavone had little effect on the growth and apoptosis of normal human skin fibroblast (HSF) cells. This may indicate that 5,7-dihydroxy-4'-methoxyisoflavone can selectively inhibit the proliferation of cancerous cells. Meanwhile, 5,7-dihydroxy-4'-methoxyisoflavone decreased the protein levels of phosphorylated ERK and Akt. Inactivation of these pathways was confirmed by upregulation of Bax expression and downregulation of Bcl-2 expression. Phosphorylated Akt protein levels were decreased in HSF cells only at a high concentration (80 μM) of 5,7-dihydroxy-4'-methoxyisoflavone. Together, we suggest that 5,7-dihydroxy-4'-methoxyisoflavone promotes cell death of human OS cells U2OS by induction of apoptosis, which is associated with the inhibition of ERK and Akt signaling. Thus, 5,7-dihydroxy-4'-methoxyisoflavone may have less toxicity compared to normal tissue and could be a potential therapy for OS.

Interaction of Isoflavones with the BCRP/ABCG2 Drug Transporter

This review will provide a comprehensive overview of the interactions between dietary isoflavones and the ATP-binding cassette (ABC) G2 efflux transporter, which is also named the breast cancer resistance protein (BCRP). Expressed in a variety of organs including the liver, kidneys, intestine, and placenta, BCRP mediates the disposition and excretion of numerous endogenous chemicals and xenobiotics. Isoflavones are a class of naturallyoccurring compounds that are found at high concentrations in commonly consumed foods and dietary supplements. A number of isoflavones, including genistein and daidzein and their metabolites, interact with BCRP as substrates, inhibitors, and/or modulators of gene expression. To date, a variety of model systems have been employed to study the ability of isoflavones to serve as substrates and inhibitors of BCRP; these include whole cells, inverted plasma membrane vesicles, in situ organ perfusion, as well as in vivo rodent and sheep models. Evidence suggests that BCRP plays a role in mediating the disposition of isoflavones and in particular, their conjugated forms. Furthermore, as inhibitors, these compounds may aid in reversing multidrug resistance and sensitizing cancer cells to chemotherapeutic drugs. This review will also highlight the consequences of altered BCRP expression and/or function on the pharmacokinetics and toxicity of chemicals following isoflavone exposure.

The molecular basis for the pharmacokinetics and pharmacodynamics of curcumin and its metabolites in relation to cancer

This review addresses the oncopharmacological properties of curcumin at the molecular level. First, the interactions between curcumin and its molecular targets are addressed on the basis of curcumin's distinct chemical properties, which include H-bond donating and accepting capacity of the β-dicarbonyl moiety and the phenylic hydroxyl groups, H-bond accepting capacity of the methoxy ethers, multivalent metal and nonmetal cation binding properties, high partition coefficient, rotamerization around multiple C-C bonds, and the ability to act as a Michael acceptor. Next, the in vitro chemical stability of curcumin is elaborated in the context of its susceptibility to photochemical and chemical modification and degradation (e.g., alkaline hydrolysis). Specific modification and degradatory pathways are provided, which mainly entail radical-based intermediates, and the in vitro catabolites are identified. The implications of curcumin's (photo)chemical instability are addressed in light of pharmaceutical curcumin preparations, the use of curcumin analogues, and implementation of nanoparticulate drug delivery systems. Furthermore, the pharmacokinetics of curcumin and its most important degradation products are detailed in light of curcumin's poor bioavailability. Particular emphasis is placed on xenobiotic phase I and II metabolism as well as excretion of curcumin in the intestines (first pass), the liver (second pass), and other organs in addition to the pharmacokinetics of curcumin metabolites and their systemic clearance. Lastly, a summary is provided of the clinical pharmacodynamics of curcumin followed by a detailed account of curcumin's direct molecular targets, whereby the phenotypical/biological changes induced in cancer cells upon completion of the curcumin-triggered signaling cascade(s) are addressed in the framework of the hallmarks of cancer. The direct molecular targets include the ErbB family of receptors, protein kinase C, enzymes involved in prostaglandin synthesis, vitamin D receptor, and DNA.

Soy, red clover, and isoflavones and breast cancer: a systematic review

BACKGROUND

Soy and red clover isoflavones are controversial due to purported estrogenic activity and possible effects on breast cancer. We conducted a systematic review of soy and red clover for efficacy in improving menopausal symptoms in women with breast cancer, and for potential impact on risk of breast cancer incidence or recurrence.

METHODS

We searched MEDLINE, Embase, the Cochrane Library, and AMED from inception to March 2013 for human interventional or observational data pertaining to the safety and efficacy of soy and red clover isoflavones in patients with or at risk of breast cancer.

RESULTS

Of 4179 records, we included a total of 131 articles: 40 RCTs, 11 uncontrolled trials, and 80 observational studies. Five RCTs reported on the efficacy of soy for hot flashes, showing no significant reductions in hot flashes compared to placebo. There is lack of evidence showing harm from use of soy with respect to risk of breast cancer or recurrence, based on long term observational data. Soy intake consistent with that of a traditional Japanese diet (2-3 servings daily, containing 25-50mg isoflavones) may be protective against breast cancer and recurrence. Human trials show that soy does not increase circulating estradiol or affect estrogen-responsive target tissues. Prospective data of soy use in women taking tamoxifen does not indicate increased risk of recurrence. Evidence on red clover is limited, however existing studies suggest that it may not possess breast cancer-promoting effects.

CONCLUSION

Soy consumption may be associated with reduced risk of breast cancer incidence, recurrence, and mortality. Soy does not have estrogenic effects in humans. Soy intake consistent with a traditional Japanese diet appears safe for breast cancer survivors. While there is no clear evidence of harm, better evidence confirming safety is required before use of high dose (≥ 100 mg) isoflavones can be recommended for breast cancer patients.

The effects of flavonoids on the ABC transporters: consequences for the pharmacokinetics of substrate drugs

INTRODUCTION

The flavonoids are a large group of dietary plant compounds with suggested health benefits. There is accumulating evidence that many of these flavonoids can interact with the major drug transporters (and metabolizing enzymes) in the body, leading to alterations in the pharmacokinetics of substrate drugs, and thus their efficacy and toxicity.

AREAS COVERED

This review summarizes and updates the reported in vitro and in vivo interactions between common dietary flavonoids and the major drug-effluxing ABC transporters; these include P-glycoprotein, breast cancer resistance protein and multidrug resistance proteins 1 and 2. In contrast to previous reviews, the ADME of flavonoids are considered, along with their glycosides and Phase II conjugates. The authors also consider their possible interactions with the ABC transporters in the oral absorption, distribution into pharmacological sanctuaries and excretion of substrate drugs. Electronic databases, including PubMed, Scopus and Google Scholar were searched to identify appropriate in vitro and in vivo ABC transporter-flavonoid interactions, particularly within the last 10 years.

EXPERT OPINION

Caution is advised when taking flavonoid-containing supplements or herbal remedies concurrently with drugs. Further clinical studies are warranted to explore the impact of flavonoids and their metabolites on the pharmacokinetics, efficacy and toxicity of drugs.

Endocrine and metabolic regulation of renal drug transporters

Renal xenobiotic transporters are important determinants of urinary secretion and reabsorption of chemicals. In addition to glomerular filtration, these processes are key to the overall renal clearance of a diverse array of drugs and toxins. Alterations in kidney transporter levels and function can influence the efficacy and toxicity of chemicals. Studies in experimental animals have revealed distinct patterns of renal transporter expression in response to sex hormones, pregnancy, and growth hormone. Likewise, a number of disease states including diabetes, obesity, and cholestasis alter the expression of kidney transporters. The goal of this review is to provide an overview of the major xenobiotic transporters expressed in the kidneys and an understanding of metabolic conditions and hormonal factors that regulate their expression and function.