Contribution of organic cation transporter 2 (OCT2) to cisplatin-induced nephrotoxicity

Extracellular nucleotides from dying cells act as molecular signals to promote wound repair in renal tubular injury

Acute kidney injury (AKI) often correlates with poor prognosis and is followed by various severe unfavorable systemic outcomes. It is important to understand the pathophysiology of AKI for the development of novel therapeutic approaches toward promoting renal regeneration after injury. Recent studies have indicated that AKI-induced tubular cell death plays an active role in the onset of tissue regeneration; however, the mechanisms underlying renal tubular repair after injury have yet to be understood. In the present study, we explored molecules that might serve as "danger" signals in mediating tubular regeneration. Kidneys of rats systemically administered the nephrotoxicant cisplatin (to induce AKI) exhibited massive cell proliferation. The proportion of proliferating cells in the total cell distribution was highest in the outer stripe of the outer medulla coincided with where the tubular damage was the most severe in this study. This finding suggests that soluble factors may have been released from damaged cells to stimulate the proliferation of neighboring tubular epithelial cells. In elucidating the mechanism of dying cell-to-surviving cell communication using normal rat kidney NRK-52E epithelial cells, we found a significant increase in ATP levels in supernatants of these cells after the induction of cell death using ultraviolet irradiation. Furthermore, treatment of conditioned supernatants with apyrase or suramin, which inhibits purinergic signaling, resulted in significant decreases in cell proliferation and migration activities. These results demonstrate a novel role for extracellular nucleotides, probably as danger signals in aggravating tubular regeneration after AKI.

Multiple analytical approaches demonstrate a complex relationship of genetic and nongenetic factors with cisplatin- and carboplatin-induced nephrotoxicity in lung cancer patients

Background. Cisplatin and carboplatin cause nephrotoxicity by forming platinum-DNA adducts and lead to cell death. Methods. One-hundred and sixteen Taiwanese lung cancer patients who received cisplatin or carboplatin more than twice were recruited, and their genotypes were determined. The risk of renal dysfunction, injury to the kidney, failure of kidney function, loss of kidney function, and end-stage kidney disease (RIFLE) criteria were used to evaluate the occurrence of nephrotoxicity. A logistic regression, multiple regression with a classification and regression tree (CART), and the Framingham study risk score were used to analyze interactions between genetic and nongenetic factors in producing platinum-induced nephrotoxicity. Results. ERCC1 118C and TP53 72Arg polymorphisms were associated with increased risks of platinum-induced nephrotoxicity. Other risk factors found included the platinum type, baseline serum creatinine (Scr), coadministration of vinorelbine, and the number of chemotherapy cycles. The overall prediction rate of the CART was 82.7%, with a sensitivity of 0.630 and specificity of 0.896. The Framingham study risk prediction model contained 7 factors. Its prediction rate was 84.5%, with a sensitivity of 0.643 and specificity of 0.909. Conclusions. Genetic polymorphisms of ERCC1 and TP53 are risk factors for nephrotoxicity. The CART analysis may provide a clinically applicable model to predict the risk of cisplatin- and carboplatin-induced nephrotoxicity.

Organic cation transporter variation and response to smoking cessation therapies

INTRODUCTION

We evaluated chr6q25.3 organic cation transporter gene (SLC22A1, SLC22A2, SLC22A3) variation and response to smoking cessation therapies. The corresponding proteins are low-affinity transporters of choline, acetylcholine and monoamines, and smoking cessation pharmacotherapies expressed in multiple tissues.

METHODS

We selected 7 common polymorphisms for mega-regression analysis. We assessed additive model association of polymorphisms with 7-day point prevalence abstinence overall and by assigned pharmacotherapy at end of treatment and at 6 months among European-ancestry participants of 7 randomized controlled trials adjusted for demographic, population genetic, and trial covariates.

RESULTS

Initial results were obtained in 6 trials with 1,839 participants. Nominally statistically significant associations of 2 SLC22A2 polymorphisms were observed: (1) with rs316019 at 6 months, overall ([c.808T>G; p.Ser270Ala], OR = 1.306, 95% CI = 1.034-1.649, p = .025), and among those randomized to nicotine replacement therapy (NRT) (OR = 1.784, 95% CI = 1.072-2.970, p = .026); and (2) with rs316006 (c.1502-529A>T) among those randomized to varenicline (OR = 1.420, 95% CI = 1.038-1.944, p = .028, OR = 1.362, 95% CI = 1.001-1.853, p = .04) at end of treatment and 6 months. Individuals randomized to NRT from a seventh trial were genotyped for rs316019; rs316019 was associated with a nominally statistically significant effect on abstinence overall at 6 months among 2,233 participants (OR = 1.249, 95% CI = 1.007-1.550, p = .043).

CONCLUSIONS

The functional OCT2 Ser270Ala polymorphism is nominally statistically significantly associated with abstinence among European-ancestry treatment-seeking smokers after adjustments for pharmacotherapy, demographics, population genetics, and without adjustment for multiple testing of 7 SNPs. Replication of these preliminary findings in additional randomized controlled trials of smoking cessation therapies and from multiple continental populations would describe another pharmacogenetic role for SLC22A2/OCT2.

Complex disease-, gene-, and drug-drug interactions: impacts of renal function, CYP2D6 phenotype, and OCT2 activity on veliparib pharmacokinetics

PURPOSE

Veliparib, a poly (ADP-ribose) polymerase (PARP) inhibitor, undergoes renal excretion and liver metabolism. This study quantitatively assessed the interactions of veliparib with metabolizing enzyme (CYP2D6) and transporter (OCT2) in disease settings (renal impairment).

EXPERIMENTAL DESIGN

Veliparib in vitro metabolism was examined in human liver microsomes and recombinant enzymes carrying wild-type CYP2D6 or functional defect variants (CYP2D6*10 and *4). Plasma pharmacokinetics were evaluated in 27 patients with cancer. A parent-metabolite joint population model was developed to characterize veliparib and metabolite (M8) pharmacokinetics and to identify patient factors influencing veliparib disposition. A physiologically based pharmacokinetic model integrated with a mechanistic kidney module was developed to quantitatively predict the individual and combined effects of renal function, CYP2D6 phenotype, and OCT2 activity on veliparib pharmacokinetics.

RESULTS

In vitro intrinsic clearance of CYP2D6.1 and CYP2D6.10 for veliparib metabolism were 0.055 and 0.017 μL/min/pmol CYP, respectively. Population mean values for veliparib oral clearance and M8 clearance were 13.3 and 8.6 L/h, respectively. Creatinine clearance was identified as the significant covariate on veliparib oral clearance. Moderate renal impairment, CYP2D6 poor metabolizer, and co-administration of OCT2 inhibitor (cimetidine) increased veliparib steady-state exposure by 80%, 20%, and 30%, respectively. These factors collectively led to >2-fold increase in veliparib exposure.

CONCLUSIONS

Renal function (creatinine clearance) is a significant predictor for veliparib exposure in patients with cancer. Although a single factor (i.e., renal impairment, CYP2D6 deficiency, and reduced OCT2 activity) shows a moderate impact, they collectively could result in a significant and potentially clinically relevant increase in veliparib exposure.

Magnesium protects against cisplatin-induced acute kidney injury by regulating platinum accumulation

Despite its success as a potent antineoplastic agent, ∼25% of patients receiving cisplatin experience acute kidney injury (AKI) and must discontinue therapy. Impaired magnesium homeostasis has been linked to cisplatin-mediated AKI, and because magnesium deficiency is widespread, we examined the effect of magnesium deficiency and replacement on cisplatin-induced AKI in physiologically relevant older female mice. Magnesium deficiency significantly increased cisplatin-associated weight loss and markers of renal damage (plasma blood urea nitrogen and creatinine), histological changes, inflammation, and renal cell apoptosis and modulated signaling pathways (e.g., ERK1/2, p53, and STAT3). Conversely, these damaging effects were reversed by magnesium. Magnesium deficiency alone significantly induced basal and cisplatin-mediated oxidative stress, whereas magnesium replacement attenuated these effects. Similar results were observed using cisplatin-treated LLC-PK1 renal epithelial cells exposed to various magnesium concentrations. Magnesium deficiency significantly amplified renal platinum accumulation, whereas magnesium replacement blocked the augmented platinum accumulation after magnesium deficiency. Increased renal platinum accumulation during magnesium deficiency was accompanied by reduced renal efflux transporter expression, which was reversed by magnesium replacement. These findings demonstrate the role of magnesium in regulating cisplatin-induced AKI by enhancing oxidative stress and thus promoting cisplatin-mediated damage. Additional in vitro experiments using ovarian, breast, and lung cancer cell lines showed that magnesium supplementation did not compromise cisplatin's chemotherapeutic efficacy. Finally, because no consistently successful therapy to prevent or treat cisplatin-mediated AKI is available for humans, these results support developing more conservative magnesium replacement guidelines for reducing cisplatin-induced AKI in cancer patients at risk for magnesium deficiency.

Cisplatin-induced renal injury is independently mediated by OCT2 and p53

PURPOSE

Tubular secretion of cisplatin is abolished in mice deficient for the organic cation transporters Oct1 and Oct2 (Oct1/2(-/-)mice), and these animals are protected from severe cisplatin-induced kidney damage. Since tubular necrosis is not completely absent in Oct1/2(-/-)mice, we hypothesized that alternate pathways are involved in the observed injury.

EXPERIMENTAL DESIGN

Studies were done in wild-type, Oct1/2(-/-), or p53-deficient animals, all on an FVB background, receiving cisplatin intraperitoneally at 15 mg/kg. Cisplatin metabolites were analyzed using mass spectrometry, and gene expression was assessed using Affymetrix microarrays and RT-PCR arrays.

RESULTS

KEGG pathway analyses on kidneys from mice exposed to cisplatin revealed that the most significantly altered genes were associated with the p53 signaling network, including Cdnk1a and Mdm2, in both wild-type (P = 2.40 × 10(-11)) and Oct1/2(-/-)mice (P = 1.92 × 10(-8)). This was confirmed by demonstrating that homozygosity for a p53-null allele partially reduced renal tubular damage, whereas loss of p53 in Oct1/2(-/-)mice (p53(-/-)/Oct1/2(-/-)) completely abolished nephrotoxicity. We found that pifithrin-α, an inhibitor of p53-dependent transcriptional activation, inhibits Oct2 and can mimic the lack of nephrotoxicity observed in p53(-/-)/Oct1/2(-/-)mice.

CONCLUSIONS

These findings indicate that (i) the p53 pathway plays a crucial role in the kidney in response to cisplatin treatment and (ii) clinical exploration of OCT2 inhibitors may not lead to complete nephroprotection unless the p53 pathway is simultaneously antagonized.

Role of solute carriers in response to anticancer drugs

Membrane transporters play critical roles in moving a variety of anticancer drugs across cancer cell membrane, thereby determining chemotherapy efficacy and/or toxicity. The retention of anticancer drugs in cancer cells is the result of net function of efflux and influx transporters. The ATP-binding cassette (ABC) transporters are mainly the efflux transporters expressing at cancer cells, conferring the chemo-resistance in various malignant tumors, which has been well documented over the past decades. However, the function of influx transporters, in particular the solute carriers (SLC) in cancer cells, has only been recently well recognized to have significant impact on cancer therapy. The SLC transporters not only directly bring anticancer agents into cancer cells but also serve as the uptake mediators of essential nutrients for tumor growth and survival. In this review, we concentrate on the interaction of SLC transporters with anticancer drugs and nutrients, and their impact on chemo-sensitivity or -resistance of cancer cells. The differential expression patterns of SLC transporters between normal and tumor tissues may be well utilized to achieve specific delivery of chemotherapeutic agents.

Role of solute carriers in response to anticancer drugs

Membrane transporters play critical roles in moving a variety of anticancer drugs across cancer cell membrane, thereby determining chemotherapy efficacy and/or toxicity. The retention of anticancer drugs in cancer cells is the result of net function of efflux and influx transporters. The ATP-binding cassette (ABC) transporters are mainly the efflux transporters expressing at cancer cells, conferring the chemo-resistance in various malignant tumors, which has been well documented over the past decades. However, the function of influx transporters, in particular the solute carriers (SLC) in cancer cells, has only been recently well recognized to have significant impact on cancer therapy. The SLC transporters not only directly bring anticancer agents into cancer cells but also serve as the uptake mediators of essential nutrients for tumor growth and survival. In this review, we concentrate on the interaction of SLC transporters with anticancer drugs and nutrients, and their impact on chemo-sensitivity or -resistance of cancer cells. The differential expression patterns of SLC transporters between normal and tumor tissues may be well utilized to achieve specific delivery of chemotherapeutic agents.

Transgenic expression of the human MRP2 transporter reduces cisplatin accumulation and nephrotoxicity in Mrp2-null mice

The chemotherapeutic drug cisplatin is actively transported into proximal tubules, leading to acute renal injury. Previous studies suggest that the multidrug resistance-associated protein 2 (Mrp2) transporter may efflux cisplatin conjugates from cells. We sought to determine whether the absence of Mrp2 alters the accumulation and toxicity of platinum in the kidneys of mice and whether transgenic expression of the human MRP2 gene could protect against cisplatin injury in vivo. Plasma, kidneys, and livers from vehicle- and cisplatin-treated wild-type and Mrp2-null mice were collected for quantification of platinum and toxicity. By 24 hours, twofold higher concentrations of platinum were detected in the kidneys and livers of Mrp2-null mice compared with wild types. Enhanced platinum concentrations in Mrp2-null mice were observed in DNA and cytosolic fractions of the kidneys. Four days after cisplatin treatment, more extensive proximal tubule injury was observed in Mrp2-null mice compared with wild-type mice. Kidneys from naive Mrp2-null mice had elevated glutathione S-transferase mRNA levels, which could increase the formation of cisplatin-glutathione conjugates that may be metabolized to toxic thiol intermediates. Transgenic expression of the human MRP2 gene in Mrp2-null mice reduced the accumulation and nephrotoxicity of cisplatin to levels observed in wild-type mice. These data suggest that deficiency in Mrp2 lowers platinum excretion and increases susceptibility to kidney injury, which can be rescued by the human MRP2 ortholog.

Digging up the human genome: current progress in deciphering adverse drug reactions

Adverse drug reactions (ADRs) are a major clinical problem. In addition to their clinical impact on human health, there is an enormous cost associated with ADRs in health care and pharmaceutical industry. Increasing studies revealed that genetic variants can determine the susceptibility of individuals to ADRs. The development of modern genomic technologies has led to a tremendous advancement of improving the drug safety and efficacy and minimizing the ADRs. This review will discuss the pharmacogenomic techniques used to unveil the determinants of ADRs and summarize the current progresses concerning the identification of biomarkers for ADRs, with a focus on genetic variants for genes encoding drug-metabolizing enzymes, drug-transporter proteins, and human leukocyte antigen (HLA). The knowledge gained from these cutting-edge findings will form the basis for better prediction and management for ADRs, ultimately making the medicine personalized.

Renal circadian clock regulates the dosing-time dependency of cisplatin-induced nephrotoxicity in mice

Cisplatin, cis-diamminedichloro-platinum (CDDP), is a widely used anticancer agent, the clinical applications of which have been limited by severe nephrotoxicity. Although dosing time-dependent differences in CDDP-induced nephrotoxicity have been reported in both humans and laboratory animals, the underlying mechanism remains unknown. In the present study, we investigated the molecular mechanism for the dosing-time dependency of the nephrotoxic effect of CDDP in mice. CDDP-induced nephrotoxicity was significantly attenuated by injecting CDDP at times of the day when its renal clearance was enhanced. The dosing-time dependency of the nephrotoxic effect was parallel to that of CDDP incorporation into renal DNA. Two types of transporters, organic cation transporter 2 (OCT2, encoded by Slc22a2) and multidrug and toxin extrusion 1 (MATE1, encoded by Slc47a1), are responsible for the renal excretion of CDDP. The expression of OCT2, but not MATE1, exhibited a significant time-dependent oscillation in the kidneys of mice. The circadian expression of OCT2 was closely related to the dosing-time dependency of CDDP incorporation into renal DNA. Molecular components of the circadian clock regulated the renal expression of Slc22a2 mRNA by mediating peroxisome proliferator-activated receptor-α, which resulted in rhythmic oscillations in OCT2 protein levels. These findings indicate a clock-regulated mechanism of dosing time-dependent changes in CDDP-induced nephrotoxicity and also suggest a molecular link between the circadian clock and renal xenobiotic excretion.

Solute carrier transporter and drug-related nephrotoxicity: the impact of proximal tubule cell models for preclinical research

INTRODUCTION

The final excretion step of several drugs is facilitated by membrane transporters of the Solute carrier (SLC) family expressed in the proximal tubules of the kidney. Membrane transporters contribute substantially to the pharmacokinetic profile of drugs and play important roles in drug-induced nephrotoxicity. Different cell models have been applied as tools for the assessment of nephrotoxic effects caused by drugs.

AREAS COVERED

This review gives an overview over clinically relevant SLC transporters involved in the renal elimination of drug agents and their specific role in drug-induced nephrotoxicity. Most widely applied cell models are described and their advantages and limitations are outlined.

EXPERT OPINION

In vitro cell culture models (e.g., continuous and primary renal cell lines, polarized cell monolayers) represent valuable tools for early assessment of the nephrotoxic potential of drugs. Since SLC transporters contribute to drug excretion in a large part, in vitro cell culture models might be very helpful to study transport pathways and/or potential drug-drug interactions at an early stage of the drug development process to predict nephrotoxic effects.

Renal transport of organic anions and cations

Organic anions and cations (OAs and OCs, respectively) comprise an extraordinarily diverse array of compounds of physiological, pharmacological, and toxicological importance. The kidney, primarily the renal proximal tubule, plays a critical role in regulating the plasma concentrations of these organic electrolytes and in clearing the body of potentially toxic xenobiotics agents, a process that involves active, transepithelial secretion. This transepithelial transport involves separate entry and exit steps at the basolateral and luminal aspects of renal tubular cells. Basolateral and luminal OA and OC transport reflects the concerted activity of a suite of separate proteins arranged in parallel in each pole of proximal tubule cells. The cloning of multiple members of several distinct transport families, the subsequent characterization of their activity, and their subcellular localization within distinct regions of the kidney, now allows the development of models describing the molecular basis of the renal secretion of OAs and OCs. New information on naturally occurring genetic variation of many of these processes provides insight into the basis of observed variability of drug efficacy and unwanted drug-drug interactions in human populations. The present review examines recent work on these issues.

Uptake carriers and oncology drug safety

Members of the solute carrier (SLC) family of transporters are responsible for the cellular influx of a broad range of endogenous compounds and xenobiotics in multiple tissues. Many of these transporters are highly expressed in the gastrointestinal tract, liver, and kidney and are considered to be of particular importance in governing drug absorption, elimination, and cellular sensitivity of specific organs to a wide variety of oncology drugs. Although the majority of studies on the interaction of oncology drugs with SLC have been restricted to the use of exploratory in vitro model systems, emerging evidence suggests that several SLCs, including OCT2 and OATP1B1, contribute to clinically important phenotypes associated with those agents. Recent literature has indicated that modulation of SLC activity may result in drug-drug interactions, and genetic polymorphisms in SLC genes have been described that can affect the handling of substrates. Alteration of SLC function by either of these mechanisms has been demonstrated to contribute to interindividual variability in the pharmacokinetics and toxicity associated with several oncology drugs. In this report, we provide an update on this rapidly emerging field.

Klotho has dual protective effects on cisplatin-induced acute kidney injury

Klotho protects the kidney from ischemia-reperfusion injury, but its effect on nephrotoxins is unknown. Here we determined whether Klotho protects the kidney from cisplatin toxicity. Cisplatin increased plasma creatinine and induced tubular injury, which were exaggerated in Klotho haplosufficient (Kl/+) and ameliorated in transgenic Klotho overexpressing (Tg-Kl) mice. Neutrophil gelatinase-associated lipocalin and active caspase-3 protein and the number of apoptotic cells in the kidney were higher in Kl/+ and lower in Tg-Kl compared with wild-type mice. Klotho suppressed basolateral uptake of cisplatin by the normal rat kidney cell line (NRK), an effect similar to cimetidine, a known inhibitor of organic cation transport (OCT). A decrease in cell surface and total OCT2 protein and OCT activity by Klotho was mimicked by β-glucuronidase. The Klotho effect was attenuated by β-glucuronidase inhibition. On the other hand, OCT2 mRNA was reduced by Klotho but not by β-glucuronidase. Moreover, cimetidine inhibited OCT activity but not OCT2 expression. Unlike cimetidine, Klotho reduced cisplatin-induced apoptosis from either the basolateral or apical side and even when added after NRK cells were already loaded with cisplatin. Thus, Klotho protects the kidney against cisplatin nephrotoxicity by reduction of basolateral uptake of cisplatin by OCT2 and a direct anti-apoptotic effect independent of cisplatin uptake. Klotho may be a useful agent to prevent and treat cisplatin-induced nephrotoxicity.

An update on oxidative stress-mediated organ pathophysiology

Exposure to environmental pollutants and drugs can result in pathophysiological situations in the body. Research in this area is essential as the knowledge on cellular survival and death would help in designing effective therapeutic strategies that are needed for the maintenance of the normal physiological functions of the body. In this regard, naturally occurring bio-molecules can be considered as potential therapeutic targets as they are normally available in commonly consumed foodstuffs and are thought to have minimum side effects. This review article describes the detailed mechanisms of oxidative stress-mediated organ pathophysiology and the ultimate fate of the cells either to survive or to undergo necrotic or apoptotic death. The mechanisms underlying the beneficial role of a number of naturally occurring bioactive molecules in oxidative stress-mediated organ pathophysiology have also been included in the review. The review provides useful information about the recent progress in understanding the mechanism(s) of various types of organ pathophysiology, the complex cross-talk between these pathways, as well as their modulation in stressed conditions. Additionally, it suggests possible therapeutic applications of a number of naturally occurring bioactive molecules in conditions involving oxidative stress.

Absence of effect of SLC22A2 genotype on cisplatin-induced nephrotoxicity in oesophageal cancer patients receiving cisplatin and 5-fluorouracil: report of results discordant with those of earlier studies

WHAT IS KNOWN AND OBJECTIVE

Cancer patients treated with cisplatin chemotherapy frequently experience drug-induced nephrotoxicity. Clinical studies using a single chemotherapeutic regimen or large sample sizes for patients with the SLC22A2 808T allele have not been reported. Here, we examined 95 patients with oesophageal cancer who received 5-fluorouracil and cisplatin (FP) to determine whether nephrotoxicity was affected by SLC22A2 808G>T polymorphism.

METHODS

The change rate of the estimated glomerular filtration rate (eGFR) was used for the evaluation of cisplatin-induced nephrotoxicity and calculated for each patient according to the following formula: change rate = (prechemotherapy value - post-chemotherapy value)/prechemotherapy value. Genotyping of SLC22A2 808G>T was carried out using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method.

RESULTS

The eGFR after FP chemotherapy was significantly lower than that before chemotherapy, and the mean difference in eGFR was 25·7 mL/min (P < 0·01). There was no significant difference in the mean change rate of the eGFR following FP chemotherapy between the SLC22A2 808GG genotype (n = 70) and the 808GT+TT genotypes (n = 25) (27·9% and 27·8%, respectively). In multiple regression analyses, the change rate of eGFR following FP chemotherapy was associated with the eGFR value prior to chemotherapy (P = 0·04).

WHAT IS NEW AND CONCLUSION

In FP chemotherapy for oesophageal cancers, cisplatin-induced nephrotoxicity seems to be unaffected by the SLC22A2 808G>T polymorphism. The eGFR prior to chemotherapy might be an important risk factor for cisplatin-induced nephrotoxicity. Our present study was estimated with a single chemotherapeutic regimen, eGFR, and was calculated using serum creatinine, age and the sex of the patient and sample sizes of 25 patients with SLC22A2 808T allele. However, further examinations with a larger sample size to corroborate the study results might be necessary.

The SLC22 family with transporters of organic cations, anions and zwitterions

The SLC22 family contains 13 functionally characterized human plasma membrane proteins each with 12 predicted α-helical transmembrane domains. The family comprises organic cation transporters (OCTs), organic zwitterion/cation transporters (OCTNs), and organic anion transporters (OATs). The transporters operate as (1) uniporters which mediate facilitated diffusion (OCTs, OCTNs), (2) anion exchangers (OATs), and (3) Na(+)/zwitterion cotransporters (OCTNs). They participate in small intestinal absorption and hepatic and renal excretion of drugs, xenobiotics and endogenous compounds and perform homeostatic functions in brain and heart. Important endogeneous substrates include monoamine neurotransmitters, l-carnitine, α-ketoglutarate, cAMP, cGMP, prostaglandins, and urate. It has been shown that mutations of the SLC22 genes encoding these transporters cause specific diseases like primary systemic carnitine deficiency and idiopathic renal hypouricemia and are correlated with diseases such as Crohn's disease and gout. Drug-drug interactions at individual transporters may change pharmacokinetics and toxicities of drugs.

Ondansetron can enhance cisplatin-induced nephrotoxicity via inhibition of multiple toxin and extrusion proteins (MATEs)

The nephrotoxicity limits the clinical application of cisplatin. Human organic cation transporter 2 (OCT2) and multidrug and toxin extrusion proteins (MATEs) work in concert in the elimination of cationic drugs such as cisplatin from the kidney. We hypothesized that co-administration of ondansetron would have an effect on cisplatin nephrotoxicity by altering the function of cisplatin transporters. The inhibitory potencies of ondansetron on metformin accumulation mediated by OCT2 and MATEs were determined in the stable HEK-293 cells expressing these transporters. The effects of ondansetron on drug disposition in vivo were examined by conducting the pharmacokinetics of metformin, a classical substrate for OCTs and MATEs, in wild-type and Mate1-/- mice. The nephrotoxicity was assessed in the wild-type and Mate1-/- mice received cisplatin with and without ondansetron. Both MATEs, including human MATE1, human MATE2-K, and mouse Mate1, and OCT2 (human and mouse) were subject to ondansetron inhibition, with much greater potencies by ondansetron on MATEs. Ondansetron significantly increased tissue accumulation and pharmacokinetic exposure of metformin in wild-type but not in Mate1-/- mice. Moreover, ondansetron treatment significantly enhanced renal accumulation of cisplatin and cisplatin-induced nephrotoxicity which were indicated by increased levels of biochemical and molecular biomarkers and more severe pathohistological changes in mice. Similar increases in nephrotoxicity were caused by genetic deficiency of MATE function in mice. Therefore, the potent inhibition of MATEs by ondansetron enhances the nephrotoxicity associated with cisplatin treatment in mice. Potential nephrotoxic effects of combining the chemotherapeutic cisplatin and the antiemetic 5-hydroxytryptamine-3 (5-HT3) receptor antagonists, such as ondansetron, should be investigated in patients.

Effect of oral administration of magnesium on Cisplatin-induced nephrotoxicity in normal and streptozocin-induced diabetic rats

Background

Cisplatin (CP) therapy as the most common potent chemotherapeutic process is accompanied by nephrotoxicity. The diabetic state may protect rat kidney against this toxicity, and magnesium (Mg) on the other hand may reduce the glucose level in diabetic animals.

Objectives

Current study was planned to investigate the effect of oral administration of magnesium supplementation on CP-induced nephrotoxicity in normal and Streptozocin (STZ)-induced diabetic rats.

Materials and Methods

Male Wistar rats were divided into seven groups and underwent two experiment protocols. As protocol 1, group 1 was considered as the sham group. Group 2 (CP group) received CP (2 mg/kg/d) for five consecutive days. Group 3 (CP + Mg group) received magnesium sulphate (MgSO4, 10 g/L added to the drinking water) for 10 days and then treated with CP from sixth day. As protocol 2, animals received a single dose of STZ (65 mg/kg i.p.). Three days after diabetes induction, animals were divided into four groups; Groups 4 (D group), 5 (D + CP group), and 7 (D + Mg + CP group) followed the same manner as groups 1 to 3, respectively; and group 6 (D + Mg group) was treated with MgSO4 alone for 10 days. Finally, blood samples were obtained, and all animals were killed for kidney tissue investigation.

Results

CP administration in normoglycemic rats significantly elevated the serum levels of blood urea nitrogen (BUN) and creatinine (Cr) (P < 0.05). However, coadministration of CP and Mg statistically increased the serum levels of BUN and Cr in both normoglycemic and diabetic animals when compared to the rats treated with CP alone (P < 0.05), while the serum level of Mg was significantly increased in nondiabetic groups (P < 0.05). No significant changes were observed in serum and kidney levels of nitrite; as well as the testis weight between all normoglycemic groups, whereas Mg decreased kidney levels of nitrite in diabetic groups when accompanied by CP (P < 0.05). The kidney and serum levels of malondialdehyde (MDA) enhanced significantly in nondiabetic rats treated with Mg and CP (P < 0.05). Kidney tissue damage score (KTDS), kidney weight, and body weight loss were significantly different among normoglycemic groups (P < 0.05), and Mg promoted the KTDS in diabetic animals treated with CP.

Conclusions

Oral Mg supplementation did not protect the CP induced nephrotoxicity in diabetic rats.

Conjunctive therapy of cisplatin with the OCT2 inhibitor cimetidine: influence on antitumor efficacy and systemic clearance

The organic cation transporter 2 (OCT2) regulates uptake of cisplatin in proximal tubules, and inhibition of OCT2 protects against severe cisplatin-induced nephrotoxicity. However, it remains uncertain whether potent OCT2 inhibitors, such as cimetidine, can influence the antitumor properties and/or disposition of cisplatin. Using an array of preclinical assays, we found that cimetidine had no effect on the uptake and cytotoxicity of cisplatin in ovarian cancer cells with high OCT2 mRNA levels (IGROV-1 cells). Moreover, the antitumor efficacy of cisplatin in mice bearing luciferase-tagged IGROV-1 xenografts was unaffected by cimetidine (P = 0.39). Data obtained in 18 patients receiving cisplatin (100 mg/m(2)) in a randomized crossover fashion with or without cimetidine (800 mg × 2) revealed that cimetidine did not alter exposure to unbound cisplatin, a marker of antitumor efficacy (4.37 vs. 4.38 µg·h/ml; P = 0.86). These results support the future clinical exploration of OCT2 inhibitors as specific modifiers of cisplatin-induced nephrotoxicity.

Increasing cGMP-dependent protein kinase I activity attenuates cisplatin-induced kidney injury through protection of mitochondria function

Cisplatin is widely used to treat malignancies. However, its major limitation is the development of dose-dependent nephrotoxicity. The precise mechanisms of cisplatin-induced kidney damage remain unclear, and the renoprotective agents during cisplatin treatment are still lacking. Here, we demonstrated that the expression and activity of cGMP-dependent protein kinase-I (PKG-I) were reduced in cisplatin-treated renal tubular cells in vitro as well as in the kidney tissues from cisplatin-treated mice in vivo. Increasing PKG activity by both pharmacological and genetic approaches attenuated cisplatin-induced kidney cell apoptosis in vitro. This was accompanied by decreased Bax/Bcl2 ratio, caspase 3 activity, and cytochrome c release. Cisplatin-induced mitochondria membrane potential loss in the tubular cells was also prevented by increased PKG activity. All of these data suggest a protective effect of PKG on mitochondria function in renal tubular cells. Importantly, increasing PKG activity pharmacologically or genetically diminished cisplatin-induced tubular damage and preserved renal function during cisplatin treatment in vivo. Mitochondria structural and functional damage in the kidney from cisplatin-treated mice was inhibited by increased PKG activity. In addition, increasing PKG activity enhanced ciaplatin-induced cell death in several cancer cell lines. Taken together, these results suggest that increasing PKG activity may be a novel option for renoprotection during cisplatin-based chemotherapy.

Oxaliplatin-induced neurotoxicity is dependent on the organic cation transporter OCT2

Oxaliplatin is an integral component of colorectal cancer therapy, but its clinical use is associated with a dose-limiting peripheral neurotoxicity. We found that the organic cation transporter 2 (OCT2) is expressed on dorsal root ganglia cells within the nervous system where oxaliplatin is known to accumulate. Cellular uptake of oxaliplatin was increased by 16- to 35-fold in cells overexpressing mouse Oct2 or human OCT2, and this process was associated with increased DNA platination and oxaliplatin-induced cytotoxicity. Furthermore, genetic or pharmacologic knockout of Oct2 protected mice from hypersensitivity to cold or mechanical-induced allodynia, which are established tests to assess acute oxaliplatin-induced neurotoxicity. These findings provide a rationale for the development of targeted approaches to mitigate this debilitating toxicity.

Modulation of OATP1B-type transporter function alters cellular uptake and disposition of platinum chemotherapeutics

Expression of the human organic anion transporting polypeptides OATP1B1 and OATP1B3 has been previously believed to be restricted to hepatocytes. Here we show that the gene encoding OATP1B3, but not OATP1B1, is abundantly expressed in multiple human solid tumors that include hepatocellular, lung, and ovarian carcinomas. Surprisingly, OATP1B3 gene expression in a panel of 60 human tumor cell lines was linked with sensitivity to multiple cytotoxic agents, including the platinum anticancer drugs cisplatin, carboplatin, and oxaliplatin. In addition, overexpression of OATP1B3 in mammalian cells increased cellular accumulation of platinum agents and decreased cell survival. In mice with a targeted disruption of the ortholog transporter Oatp1b2, the liver-to-plasma ratio of cisplatin was significantly reduced compared with wild-type mice, without concurrent changes in expression profiles of other transporter genes. Our findings indicate an unexpected role for tumoral and host OATP1B-type carriers in the toxicity and disposition of platinum anticancer drugs, and may provide a foundation for understanding the extensive interindividual pharmacodynamic variability seen with these drugs in patients.

The role of inherited TPMT and COMT genetic variation in cisplatin-induced ototoxicity in children with cancer

Ototoxicity is a debilitating side effect of platinating agents with substantial interpatient variability. We sought to evaluate the association of thiopurine S-methyltransferase (TPMT) and catechol O-methyltransferase (COMT) genetic variations with cisplatin-related hearing damage in the context of frontline pediatric cancer treatment protocols. In 213 children from the St. Jude Medulloblastoma-96 and -03 protocols, hearing loss was related to younger age (P = 0.013) and craniospinal irradiation (P = 0.001), but did not differ by TPMT or COMT variants. Results were similar in an independent cohort of 41 children from solid-tumor frontline protocols. Functional hearing loss or hair cell damage was not different in TPMT knockout vs. wild-type mice following cisplatin treatment, and neither TPMT nor COMT variant was associated with cisplatin cytotoxicity in lymphoblastoid cell lines. In conclusion, our results indicated that TPMT or COMT genetic variation was not related to cisplatin ototoxicity in children with cancer and did not influence cisplatin-induced hearing damage in laboratory models.

Transporters and drug-drug interactions: important determinants of drug disposition and effects

Uptake and efflux transporters determine plasma and tissue concentrations of a broad variety of drugs. They are localized in organs such as small intestine, liver, and kidney, which are critical for drug absorption and elimination. Moreover, they can be found in important blood-tissue barriers such as the blood-brain barrier. Inhibition or induction of drug transporters by coadministered drugs can alter pharmacokinetics and pharmacodynamics of the victim drugs. This review will summarize in particular clinically observed drug-drug interactions attributable to inhibition or induction of intestinal export transporters [P-glycoprotein (P-gp), breast cancer resistance protein (BCRP)], to inhibition of hepatic uptake transporters [organic anion transporting polypeptides (OATPs)], or to inhibition of transporter-mediated [organic anion transporters (OATs), organic cation transporter 2 (OCT2), multidrug and toxin extrusion proteins (MATEs), P-gp] renal secretion of xenobiotics. Available data on the impact of nutrition on transport processes as well as genotype-dependent, transporter-mediated drug-drug interactions will be discussed. We will also present and discuss data on the variable extent to which information on the impact of transporters on drug disposition is included in summaries of product characteristics of selected countries (SPCs). Further work is required regarding a better understanding of the role of the drug metabolism-drug transport interplay for drug-drug interactions and on the extrapolation of in vitro findings to the in vivo (human) situation.

Protective effect of CV247 against cisplatin nephrotoxicity in rats

CV247 (CV), an aqueous mixture of copper (Cu) and manganese (Mn) gluconates, vitamin C and sodium salicylate increased the antitumour effects of cisplatin (CDPP; cis-diamminedichloroplatinum) in vitro. We hypothesized that the antioxidant and cyclooxygenase-2 (COX-2; prostaglandin-endoperoxide synthase 2) inhibitory components of CV can protect the kidneys from CDPP nephrotoxicity in rats. CDPP (6.5 mg/kg, intraperitoneally) slightly elevated serum creatinine (Crea) and blood urea nitrogen (BUN) 12 days after treatment. Kidney histology demonstrated extensive tubular epithelial damage and COX-2 immunoreactivity increased 14 days after treatment. A large amount of platinum (Pt) accumulated in the kidney of CDPP-treated rats. Furthermore, CDPP decreased renal iron (Fe), molybdenum (Mo), zinc (Zn), Cu and Mn concentrations and increased plasma Fe and Cu concentrations. CDPP elevated plasma free radical concentration. Treatment with CV alone for 14 days (twice 3 ml/kg/day orally) did not influence these parameters. Chronic CV administration after CDPP reduced renal histological damage and slightly decreased COX-2 immunoreactivity, while failed to prevent the increase in Crea and BUN levels. Blood free radical concentration was reduced, that is, CV improved redox homeostasis. CV restored plasma Fe and renal Fe, Mo and Zn, while decreased Pt and elevated Cu and Mn concentrations in the kidney. Besides the known synergistic antitumour effects with CDPP, CV partially protected the kidneys from CDPP nephrotoxicity probably through its antioxidant effect.

A re-evaluation of the role of hCTR1, the human high-affinity copper transporter, in platinum-drug entry into human cells

Cisplatin (cDDP) is an anticancer drug used in a number of malignancies, including testicular, ovarian, cervical, bladder, lung, head, and neck cancers. Its use is limited by the development of resistance, often rationalized via effects on cellular uptake. It has been claimed that human copper transporter 1 (hCTR1), the human high-affinity copper transporter, is the major entry pathway for cDDP and related drugs via a mechanism that mimics copper. This is an unexpected property of hCTR1, a highly selective copper (I) transporter. We compared the uptake rates of copper with cDDP (and several analogs) into human embryonic kidney 293 cells overexpressing wild-type or mutant hCTR1, mouse embryonic fibroblasts that do or do not express CTR1, and human ovarian tumor cells that are sensitive or resistant to cDDP. We have also compared the effects of extracellular copper, which causes regulatory endocytosis of hCTR1, to those of cDDP. We confirm the correlation between higher hCTR1 levels and higher platinum drug uptake in tumor cells sensitive to the drug. However, we show that hCTR1 is not the major entry route of platinum drugs, and that the copper transporter is not internalized in response to extracellular drug. Our data suggest the major entry pathway for platinum drugs is not saturable at relevant concentrations and not protein-mediated. Clinical trials have been initiated that depend upon regulating membrane levels of hCTR1. If reduced drug uptake is a major factor in resistance, hCTR1 is unlikely to be a productive target in attempts to enhance efficacy, although the proteins involved in copper homeostasis may play a role.

Association of genetic variation in the organic cation transporters OCT1, OCT2 and multidrug and toxin extrusion 1 transporter protein genes with the gastrointestinal side effects and lower BMI in metformin-treated type 2 diabetes patients

OBJECTIVE

Metformin is the most widely used oral antidiabetic drug for the treatment of type 2 diabetes (T2D). So far, the number of polymorphisms in SLC22A1, SLC22A2, and SLC47A1 genes coding for organic cation transporter 1 (OCT1), OCT2, and multidrug and toxin extrusion transporter 1 (MATE1) metformin transporters have been described in association with the efficacy of metformin. However, there is no information on the influence of genetic variations within these genes on the side effects of metformin. In this study, we assessed whether five single-nucleotide polymorphisms and two indel polymorphisms are associated with the side effects of metformin in patients with T2D.

METHODS

Seven polymorphisms in OCT1, OCT2, and MATE1 genes were compared between 53 T2D patients with side effects of metformin and 193 metformin users without symptoms of metformin intolerance.

RESULTS

We found a statistically significant association between the A allele of the rs628031 (P=0.012, odds ratio=0.389, confidence interval 95% [0.186-0.815]) as well as 8 bp insertion (rs36056065) in the OCT1 gene (P=0.002, odds ratio=0.405, confidence interval 95% [0.226-0.724]) and the presence of the side effects of metformin.

CONCLUSION

Two genetic variations in OCT1 that are in strong linkage disequilibrium may predispose toward an increased prevalence of the side effects of metformin in patients with T2D.

SLC22A2 is associated with tubular creatinine secretion and bias of estimated GFR in renal transplantation

Genome-wide association studies reported SLC22A2 variants to be associated with serum creatinine. As SLC22A2 encodes the organic cation transporter 2 (OCT2), the association might be due to an effect on tubular creatinine handling. To test this hypothesis we studied the association of SLC22A2 polymorphisms with phenotypes of net tubular creatinine secretion: fractional creatinine excretion (FEcreat) and bias of estimated glomerular filtration rate (eGFR). We also studied the association with end-stage renal disease (ESRD) and graft failure (GF) in renal transplant recipients. SLC22A2 single nucleotide polymorphisms (SNPs), rs3127573 and rs316009, were genotyped in 1,142 ESRD patients receiving renal transplantation and 1,186 kidney donors as controls. GFR was measured with (125)I-iothalamate clearance. Creatinine clearance was also assessed. FEcreat was calculated from the simultaneous clearances of creatinine and (125)I-iothalamate. Donor rs316009 was associated with FEcreat (beta -0.053, P = 0.024) and with estimated [modification of diet in renal disease (MDRD) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI)] but not measured GFR. In line with this, donor rs316009 was associated with bias of the MDRD and CKD-EPI but not the Cockroft-Gault equation. Both SNPs were associated with ESRD: odds ratios [95% CI] 1.39 [1.16-1.67], P = 0.00065, and 1.23 [1.02-1.48], P = 0.042, for rs3127573 and rs316009, respectively. Neither SNP was associated with GF. Thus, SLC22A2 is associated with phenotypes of net tubular creatinine secretion and ESRD.

Membrane transporters as mediators of Cisplatin effects and side effects

Transporters are important mediators of specific cellular uptake and thus, not only for effects, but also for side effects, metabolism, and excretion of many drugs such as cisplatin. Cisplatin is a potent cytostatic drug, whose use is limited by its severe acute and chronic nephro-, oto-, and peripheral neurotoxicity. For this reason, other platinum derivatives, such as carboplatin and oxaliplatin, with less toxicity but still with antitumoral action have been developed. Several transporters, which are expressed on the cell membranes, have been associated with cisplatin transport across the plasma membrane and across the cell: the copper transporter 1 (Ctr1), the copper transporter 2 (Ctr2), the P-type copper-transporting ATPases ATP7A and ATP7B, the organic cation transporter 2 (OCT2), and the multidrug extrusion transporter 1 (MATE1). Some of these transporters are also able to accept other platinum derivatives as substrate. Since membrane transporters display a specific tissue distribution, they can be important molecules that mediate the entry of platinum derivatives in target and also nontarget cells possibly mediating specific effects and side effects of the chemotherapeutic drug. This paper summarizes the literature on toxicities of cisplatin compared to that of carboplatin and oxaliplatin and the interaction of these platinum derivatives with membrane transporters.

The effect of novel promoter variants in MATE1 and MATE2 on the pharmacokinetics and pharmacodynamics of metformin

Interindividual variation in response to metformin, first-line therapy for type 2 diabetes, is substantial. Given that transporters are determinants of metformin pharmacokinetics, we examined the effects of promoter variants in both multidrug and toxin extrusion protein 1 (MATE1) (g.-66T → C, rs2252281) and MATE2 (g.-130G → A, rs12943590) on variation in metformin disposition and response. The pharmacokinetics and glucose-lowering effects of metformin were assessed in healthy volunteers (n = 57) receiving metformin. The renal and secretory clearances of metformin were higher (22% and 26%, respectively) in carriers of variant MATE2 who were also MATE1 reference (P < 0.05). Both MATE genotypes were associated with altered post-metformin glucose tolerance, with variant carriers of MATE1 and MATE2 having an enhanced (P < 0.01) and reduced (P < 0.05) response, respectively. Consistent with these results, patients with diabetes (n = 145) carrying the MATE1 variant showed enhanced metformin response. These findings suggest that promoter variants of MATE1 and MATE2 are important determinants of metformin disposition and response in healthy volunteers and diabetic patients.

Associations between ABCC2 polymorphisms and cisplatin disposition and efficacy

ABCC2 (MRP2, cMOAT) expression has been implicated in cisplatin resistance in vitro. In mice, cisplatin disposition and toxicity were unaffected by Abcc2 knockout (Abcc2−/−). Moreover, in cancer patients (n = 237), cisplatin pharmacokinetics (P > 0.12) and efficacy (P > 0.41) were not associated with seven of the single-nucleotide polymorphisms (SNPs) in ABCC2. These SNPs were also not correlated with ABCC2 expression in the NCI60 panel (P > 0.26) or with cisplatin-induced cytotoxicity (P = 0.21). These findings highlight the importance of verifying drug-transporter interactions with in vitro tests in humans.

The Role of Magnesium Supplementation in Cisplatin-induced Nephrotoxicity in a Rat Model: No Nephroprotectant Effect

OBJECTIVES

Cisplatin (CP) is used as the commonest drug to treat solid tumors. It is accompanied by a nephrotoxicity side effect. The main objective of this study is to investigate the protective role of magnesium (Mg) supplementation in CP-induced nephrotoxicity in a rat model.

METHODS

Twenty-nine Wistar rats were randomly assigned to four groups (1-4). Groups 1-3 received 20, 80, and 200 mg/kg magnesium sulfate respectively, for 10 days, but on day 3, a single dose of CP (7 mg/kg, i.p.) was also injected. Group 4 (positive control group) received the same regimen of Groups 1-3 except saline instead magnesium sulfate. One week after CP administration, blood samples were obtained and all animals were killed for kidney histopathological investigations.

RESULTS

All CP-treated animals lost weight, and the percentage of weight loss in Group 1 (low dose Mg sulfate treated) was significantly higher compared with the positive control group (Group 4, P < 0.05). The increase in blood urea nitrogen (BUN) and creatinine (Cr) levels in serum in Group 1 were more than those in other groups (P < 0.05). No statistical differences were observed in serum magnesium, nitrite, and total protein levels among the groups. The kidney tissue damage in Groups 1-3 was not significantly different when compared with Group 4. Moreover, the kidney and testis weights in Group 1 were significantly greater than those in the positive control group (P < 0.05).

CONCLUSION

Regarding the BUN and Cr levels in the serum, kidneys weight, and the histopathological study, the low dose of Mg supplementation intensifies kidney toxicity and renal dysfunction in CP-induced nephrotoxicity in the rat model. However, the protective role of Mg with moderate and high doses is not certain.

Drug-induced oxidative stress and toxicity

Reactive oxygen species (ROS) are a byproduct of normal metabolism and have roles in cell signaling and homeostasis. Species include oxygen radicals and reactive nonradicals. Mechanisms exist that regulate cellular levels of ROS, as their reactive nature may otherwise cause damage to key cellular components including DNA, protein, and lipid. When the cellular antioxidant capacity is exceeded, oxidative stress can result. Pleiotropic deleterious effects of oxidative stress are observed in numerous disease states and are also implicated in a variety of drug-induced toxicities. In this paper, we examine the nature of ROS-induced damage on key cellular targets of oxidative stress. We also review evidence implicating ROS in clinically relevant, drug-related side effects including doxorubicin-induced cardiac damage, azidothymidine-induced myopathy, and cisplatin-induced ototoxicity.

Effects of genetic variants in SLC22A2 organic cation transporter 2 and SLC47A1 multidrug and toxin extrusion 1 transporter on cisplatin-induced adverse events

BACKGROUND

Susceptibility to cisplatin (CDDP) nephrotoxicity is known to vary between individuals, but the basis of this variation has not been fully elucidated. In the kidney, CDDP is taken up into the renal proximal tubular cells mainly via SLC22A2 organic cation transporter 2 (OCT2) and secreted into lumen via other transporters including SLC47A1 multidrug and toxin extrusion 1 (MATE1). Here, we explore the effect of single-nucleotide polymorphisms (SNPs) at 808G>T in OCT2 and at rs2289669 G>A in MATE1 on CDDP-induced adverse events.

METHODS

Fifty-three patients who had been treated with CDDP were enrolled. The plasma concentration of CDDP was measured on days 4 and 7 after treatment. The grade of hematology and nephrotoxicity was evaluated by Common Terminology Criteria for Adverse Events.

RESULTS

In the first treatment cycle, serum creatinine (SCr) levels in the patients with OCT2 808GG and 808GT were increased by 1.43- and 1.19-fold, respectively. In the total treatment cycles, 12 patients (27 %) with 808GG experienced over grade 2 SCr elevation, whereas those with 808GT did not show any apparent nephrotoxicity. The hematological toxicity and plasma concentrations of CDDP showed no difference between patients in both groups. The rs2289669 G>A SNP in MATE1 was not associated with adverse effects and disposition of CDDP.

CONCLUSION

The 808G>T SNP in OCT2 ameliorated CDDP-induced nephrotoxicity without alteration of disposition, whereas the rs2289669 G>A SNP in MATE1 had no effect on CDDP toxicity.

Impact of drug transporter pharmacogenomics on pharmacokinetic and pharmacodynamic variability - considerations for drug development

INTRODUCTION

Drug transporter proteins are expressed on the cell membrane, regulating substrate exposure in systemic circulation and/or peripheral tissues. Genetic polymorphism of drug transporter genes encoding these proteins could alter the functional activity and/or protein expression, having effects on absorption, distribution, metabolism and excretion (ADME), efficacy and adverse effects.

AREAS COVERED

The authors provide the reader with an overview of the pharmacogenetics (PGx) of 12 membrane transporters. The clinical literature is summarized as to the quantitative significance on pharmacokinetics (PK) and implications on pharmacodynamics (PD) and adverse effects, due to transporter influence on intracellular drug concentrations.

EXPERT OPINION

Unlike polymorphisms for cytochrome P450s (CYPs) resulting in large magnitude of PK variation, genetic mutations for membrane transporters are typically less than threefold alteration in systemic PK for drugs with a few exceptions. However, substantially greater changes in intracellular drug levels may result. We are aware of 1880 exome variants in 12 of the best-studied transporters to date, and nearly 40% of these change the amino acid. However, the functional consequences of most of these variants remain to be determined, and have only been empirically evaluated for a handful. To the extent that genetic polymorphisms impact ADME, it is a variable that will contribute to ethnic differences due to substantial frequency differences for the known variants.