Novel drug transporter substrates identification: An innovative approach based on metabolomic profiling, in silico ligand screening and biological validation.

Solute carrier (SLC) transport proteins are fundamental for the translocation of endogenous compounds and drugs across membranes, thus playing a critical role in disease susceptibility and drug response. Because only a limited number of transporter substrates are currently known, the function of a large number of SLC transporters is elusive. Here, we describe the proof-of-concept of a novel strategy to identify SLC transporter substrates exemplarily for the proton-coupled peptide transporter (PEPT) 2 (SLC15A2) and multidrug and toxin extrusion (MATE) 1 transporter (SLC47A1), which are important renal transporters of drug reabsorption and excretion, respectively. By combining metabolomic profiling of mice with genetically-disrupted transporters, in silico ligand screening and in vitro transport studies for experimental validation, we identified nucleobases and nucleoside-derived anticancer and antiviral agents (flucytosine, cytarabine, gemcitabine, capecitabine) as novel drug substrates of the MATE1 transporter. Our data confirms the successful applicability of this new approach for the identification of transporter substrates in general, which may prove particularly relevant in drug research.

Investigation of endogenous compounds for assessing the drug interactions in the urinary excretion involving multidrug and toxin extrusion proteins.

PURPOSE: Multidrug and toxin extrusion proteins (MATEs) are multispecific organic cation transporters mediating the efflux of various cationic drugs into the urine. The present study aimed at identifying endogenous compounds in human plasma and urine specimens as biomarkers to evaluate drug interactions involving MATEs in the kidney without administration of their exogenous probe drugs. METHODS: An untargeted metabolomic analysis was performed using urine and plasma samples from healthy volunteers and mice treated with or without the potent MATE inhibitor, pyrimethamine. Plasma and urinary concentrations of candidate markers were measured using liquid chromatography-mass spectrometry. Transport activities were determined in MATE- or OCT2-expressing HEK293 cells. The deuterium-labeled compounds of candidates were administered to mice for pharmacokinetics study. RESULTS: Urinary excretion of eleven compounds including thiamine and carnitine was significantly lower in the pyrimethamine-treatment group in humans and mice, whereas no endogenous compound was noticeably accumulated in the plasma. The renal clearance of thiamine and carnitine was decreased by 70%-84% and 90%-94% (p < 0.05), respectively, in human. The specific uptake of thiamine was observed in MATE1-, MATE2-K- or OCT2-expressing HEK293 cells with Km of 3.5 ± 1.0, 3.9 ± 0.8 and 59.9 ± 6.7 µM, respectively. The renal clearance of carnitine-d 3 was decreased by 62% in mice treated with pyrimethamine. CONCLUSIONS: Our findings indicate that MATEs account for the efflux of thiamine and perhaps carnitine as well as drugs into the urine. The urinary excretion of thiamine is useful to detect drug interaction involving MATEs in the kidney.

The effect of ABCG2 genotype on the population pharmacokinetics of sunitinib in patients with renal cell carcinoma.

BACKGROUND: Sunitinib, a multitargeted tyrosine kinase inhibitor, offers favorable therapeutic outcomes to patients with advanced renal cell carcinoma. However, to maximize the clinical benefits, an effective therapeutic management strategy with dose optimization is essential. The objectives of this analysis were to describe the pharmacokinetics (PK) of sunitinib by a population PK approach and to quantitatively evaluate the effect of potential predictive factors including ABCG2 genotype on the PK of sunitinib. METHODS: Plasma concentration-time profiles at 3 consecutive days including a total of 245 sunitinib plasma concentrations were available from 19 Japanese patients with renal cell carcinoma. Blood samples were collected on days 2, 8, and 15 after the start of the therapy. Population PK analysis was performed using NONMEM 7.2. Body weight, gender, and genotype of ABCG2 421C>A were evaluated as potential covariates. Interoccasion variability (IOV) among the 3 sampling days was also assessed as a random effect parameter. RESULTS: The sunitinib PK profiles were best described by a 1-compartment model with first-order absorption. The ABCG2 421C>A genotype was identified as a significant covariate for the prediction of oral clearance (CL/F). No significant improvement in model fit was observed by including body weight and/or gender. A systematic difference in estimated population CL/F was observed between days 2 and 8, which was quantified as approximately 30% decrease over time. This difference was described as a covariate for CL/F in the model. IOV included as a random effect parameter significantly improved the model fit. CONCLUSIONS: This analysis provides a population PK model of sunitinib with the ABCG2 421C>A genotype as a predictive covariate for CL/F. It also suggests that IOV and change of CL/F over time need to be considered to predict the sunitinib PK more accurately. These findings will be implemented to optimize the pharmacotherapy of sunitinib.

The Concise Guide to PHARMACOLOGY 2023/24: Transporters.

The Concise Guide to PHARMACOLOGY 2023/24 is the sixth in this series of biennial publications. The Concise Guide provides concise overviews, mostly in tabular format, of the key properties of approximately 1800 drug targets, and over 6000 interactions with about 3900 ligands. There is an emphasis on selective pharmacology (where available), plus links to the open access knowledgebase source of drug targets and their ligands (https://www.guidetopharmacology.org/), which provides more detailed views of target and ligand properties. Although the Concise Guide constitutes almost 500 pages, the material presented is substantially reduced compared to information and links presented on the website. It provides a permanent, citable, point-in-time record that will survive database updates. The full contents of this section can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.16182. Transporters are one of the six major pharmacological targets into which the Guide is divided, with the others being: G protein-coupled receptors, ion channels, nuclear hormone receptors, catalytic receptors and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. The landscape format of the Concise Guide is designed to facilitate comparison of related targets from material contemporary to mid-2023, and supersedes data presented in the 2021/22, 2019/20, 2017/18, 2015/16 and 2013/14 Concise Guides and previous Guides to Receptors and Channels. It is produced in close conjunction with the Nomenclature and Standards Committee of the International Union of Basic and Clinical Pharmacology (NC-IUPHAR), therefore, providing official IUPHAR classification and nomenclature for human drug targets, where appropriate.

Developmental expression of renal organic anion transporters in rat kidney and its effect on renal secretion of phenolsulfonphthalein.

Organic anion transporters (OAT1 and OAT3) and multidrug resistance-associated proteins (MRP2 and MRP4) play important roles in anionic drug secretion in renal proximal tubules. Changes in the expression of such transporters are considered to affect the tubular secretion of anionic drugs. The purpose of this study was to elucidate the developmental changes in the expression of OAT1, OAT3, MRP2, and MRP4 and their effects on the tubular secretion of drugs. The mRNA level of each transporter was measured by real-time PCR, and the protein expression was evaluated by Western blotting and immunohistochemical analysis. In addition, the tubular secretion of phenolsulfonphthalein (PSP) in infant (postnatal day 14) and adult rats was estimated based on in vivo clearance study. The protein expression of organic anion transporters were very low at postnatal day 0 and gradually increased with age. In postnatal day 14 rats, the expression of OAT1 and OAT3 seemed to be at almost mature levels, while MRP2 and MRP4 seemed to be at immature levels. Immunohistochemical analysis in the kidney of postnatal day 0 rats revealed OATs on the basolateral membrane and MRPs on the brush-border membrane. At postnatal day 0, the distribution of these transporters was restricted to the inner cortical region, while after postnatal day 14, it was identical to that in adult kidney. An in vivo clearance study revealed that the tubular secretion of PSP was significantly lower in postnatal day 14 rats than adult rats. These results indicate that age-dependent changes in organic anion transporter expression affect the tubular secretion of anionic drugs in pediatric patients.

Significance of trough monitoring for tacrolimus blood concentration and calcineurin activity in adult patients undergoing primary living-donor liver transplantation.

PURPOSE: Tacrolimus pharmacokinetics and calcineurin activity in peripheral blood mononuclear cells (PBMCs) were investigated in adult patients undergoing primary living-donor liver transplantation (LDLT) in order to clarify the significance of monitoring the tacrolimus blood trough concentration during the early post-transplantation period. METHODS: Fourteen patients were enrolled in this study, and time-course data following the oral administration of a conventional tacrolimus formulation twice daily were obtained at 1 and 3 weeks post-transplantation. The concentration of tacrolimus in whole blood and calcineurin activity in PBMCs were measured. RESULTS: The apparent clearance of tacrolimus significantly increased at 3 weeks versus 1 week post-transplantation, although the trough concentration did not significantly differ at these time points. The concentration at each sampling time, except at 1 h post-dose, correlated well with the area under the concentration-time curve from 0 to 12 h (AUC(0-12)). Neither the concentration at the trough time point nor AUC(0-12) was correlated with the area under the calcineurin activity-time curve from 0 to 12 h; however, calcineurin activity at the trough time point was strongly correlated with the latter (r (2) > 0.92). CONCLUSIONS: Based on these results, trough concentration monitoring can be considered an appropriate procedure for routine tacrolimus dosage adjustment in adult LDLT patients. Monitoring of calcineurin activity at the trough time point was also found to be potentially useful for predicting the immunological status of the patient during the tacrolimus dosing interval.

Recent advances in structural biology of peptide transporters.

Peptide transporters localized at brush-border membranes of intestinal and renal epithelial cells mediate the membrane transport of di- and tripeptides, and play important roles in protein absorption and the conservation of peptide-bound amino nitrogen. Peptide-like drugs that show structural similarities to di- and tripeptides are also recognized by peptide transporters. The energy for transport of small peptides and peptide-like drugs is provided by the proton gradient across the cell membrane. Since the cloning of H(+)/peptide cotransporter (PEPT1, SLC15A1), there have been advances in the molecular biology, biochemistry, biophysics and structural determination of PEPT1. By integrating these advances, much effort has been made to understand the relationship between structure and function. In silico experimental strategies are classified as (1) construction of kinetic models, (2) computer modeling of PEPT1 structure and (3) homology modeling of PEPT1 with crystal structures of bacterial transporters. The hypotheses regarding the structure-function relationship produced by these strategies have been confirmed by in vitro mutagenesis including cysteine-scanning mutagenesis. Recently, the crystal structure of PepT(So), a functionally similar prokaryotic homolog of the mammalian peptide transporters from Shewanella oneidensis, was classified, and the previous hypotheses regarding the structure-function relationship of PEPT1 have been re-evaluated. This review highlights the recent advances in our knowledge of the structural biology of PEPT1.

Maternal riboflavin deficiency, resulting in transient neonatal-onset glutaric aciduria Type 2, is caused by a microdeletion in the riboflavin transporter gene GPR172B.

Riboflavin, or vitamin B2, is a precursor to flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) molecules, required in biological oxidation-reduction reactions. We previously reported a case of a newborn female who had clinical and biochemical features of multiple acyl-CoA dehydrogenation deficiency (MADD), which was corrected by riboflavin supplementation. The mother was then found to be persistently riboflavin deficient, suggesting that a possible genetic defect in riboflavin transport in the mother was the cause of the transient MADD seen in the infant. Two recently-identified riboflavin transporters G protein-coupled receptor 172B (GPR172B or RFT1) and riboflavin transporter 2 (C20orf54 or RFT2) were screened for mutations. Two missense sequence variations, c.209A>G [p.Q70R] and c.886G>A [p.V296M] were found in GPR172B. In vitro functional studies of both missense variations showed that riboflavin transport was unaffected by these variations. Quantitative real-time PCR revealed a de novo deletion in GPR172B spanning exons 2 and 3 in one allele from the mother. We postulate that haploinsufficiency of this riboflavin transporter causes mild riboflavin deficiency, and when coupled with nutritional riboflavin deficiency in pregnancy, resulted in the transient riboflavin-responsive disease seen in her newborn infant. This is the first report of a genetic defect in riboflavin transport in humans.

Effects of metabolic acidosis on expression levels of renal drug transporters.

PURPOSE: In the renal proximal tubular cells, various transporters play important roles in the secretion and reabsorption of drugs. When metabolic acidosis is induced, a number of adaptive changes occur in the kidney. The purpose of this study was to clarify the changes of drug transporters under the acidosis and the effects of these changes on urinary drug excretion. METHODS: Wistar/ST rats were given 1.5% NH4Cl in tap water for 48 h to induce the acidosis. Pharmacokinetics of PSP or metformin was evaluated. In addition, expression levels of drug transporters were examined by Western Blotting. RESULTS: The renal clearance of PSP was markedly decreased, whereas the creatinine clearance and renal clearance of metformin were unchanged. Furthermore, Western blots indicated that the protein expression level of organic anion transporter (OAT) 3 was decreased. In contrast to OAT3 levels, OAT1 and organic cation transporter (OCT) 2 levels were unaffected. An immunohistochemical analysis showed that the OAT3 protein in the proximal tubules was localized in the basolateral membrane both of the normal and the acidosis rats. CONCLUSION: The decrease of renal excretion of anionic drugs during metabolic acidosis might be partly due to a reduction in the level of OAT3 protein.

Human NPC1L1 expression is positively regulated by PPARα.

PURPOSE: Niemann-Pick C1-like 1 (NPC1L1), a pharmacological target of ezetimibe, is responsible for cholesterol absorption in enterocytes and hepatocytes. In the present study, the involvement of peroxisome proliferator-activated receptor α (PPARα) and its cofactor, PPARγ coactivator 1α (PGC1α) in the transcriptional regulation of human NPC1L1 was analyzed. METHODS: Reporter gene assays and electrophoretic mobility shift assays (EMSAs) were performed with the 5'-flanking region of the human NPC1L1 gene and the effect of siPPARα was examined. RESULTS: PPARα-mediated transactivation was observed with human NPC1L1 promoter constructs. Detailed analyses using deletion- and mutated-promoter constructs revealed the presence of a functional PPARα-response element (PPRE) upstream of the human NPC1L1 gene (-846/-834), a direct binding of PPARα and RXRα to which was confirmed by EMSAs. Moreover, PPARα-specific knockdown resulted in a significant decrease in the endogenous expression of NPC1L1 mRNA and protein in human-derived HepG2 cells. Furthermore, cotransfection of PGC1α stimulated the SREBP2/HNF4α- and PPARα/RXRα-mediated activation of the human NPC1L1 promoter. CONCLUSIONS: We found that PPARα positively regulates human NPC1L1 transcription via direct binding to a PPRE. Additionally, PGC1α stimulates the SREBP2/HNF4α- and PPARα/RXRα-mediated transactivation of human NPC1L1. These findings may provide new insights into the close relationship of glucose, fatty acids and cholesterol homeostasis.

Tacrolimus therapy as an alternative to thiopurines for maintaining remission in patients with refractory ulcerative colitis.

BACKGROUND: Although the efficacy of tacrolimus for inducing remission of refractory ulcerative colitis (UC) is established, its efficacy for maintaining remission of UC has not been evaluated. AIM: The aim of this study was to evaluate the efficacy of tacrolimus compared with thiopurines for maintaining remission in patients with refractory UC. METHODS: Twenty-four UC patients treated with tacrolimus and 34 treated with thiopurines to maintain remission were enrolled as the tacrolimus group and the thiopurine group, respectively. In the tacrolimus group, 82.8% of the patients were treated with tacrolimus for induction of the remission, whereas 70% of the patients in the thiopurine group were induced remission with either corticosteroid or cytapheresis. Proportions of patients who kept steroid-free remission between the tacrolimus and the thiopurine groups were compared. Maintenance of remission using tacrolimus or thiopurines was defined as no need for other therapies other than aminosalicylates without relapse for at least 3 months. Secondarily, to determine whether the response to thiopurines affects the long-term efficacy of tacrolimus maintenance therapy, the overall cumulative relapse-free survival based on the Kaplan-Meier method was estimated in thiopurine-naive or thiopurine-intolerant patients and thiopurine-refractory ones in the tacrolimus group. RESULTS: Remission was successfully maintained in 17 patients (70.8%) of the tacrolimus group, and 28 patients (82.4%) of the thiopurine group. The overall cumulative relapse-free survival of thiopurine-naive or thiopurine-intolerant patients in the tacrolimus group was similar to that in the thiopurine group, and significantly higher than that of thiopurine-refractory patients in the tacrolimus group. CONCLUSION: Maintenance therapy with tacrolimus for patients with UC could be considered an alternative to thiopurine therapy.

Inhibitory effects of vandetanib on creatinine transport via renal organic cation transporter OCT2.

Vandetanib (ZD6474, Zactima®, Caprelsa®) is a newly developed dual tyrosine kinase inhibitor of vascular endothelial growth factor and epidermal growth factor receptor. Recently, several reports have indicated the interaction of vandetanib with tyrosine kinase inhibitors and transporters. However, these characteristics of vandetanib remain unclear. We examined the interaction of vandetanib with the human organic cation transporter 2 (hOCT2) stably expressed in human embryonic kidney (HEK) 293 cells. The specific uptake of vandetanib was not observed in hOCT2-expressing HEK293 cells. Vandetanib inhibited the uptake of creatinine mediated by hOCT2 in a dose-dependent manner. The IC50 value for vandetanib inhibition of creatinine uptake by hOCT2 was 3.7 ± 1.0 µM (average ± SE of three separate experiments). The IC50 value of cimetidine and trimethoprim for hOCT2 were 100 ± 13.5 and 52.1 ± 8.0 µM, respectively. Vandetanib showed markedly higher affinity for hOCT2 than cimetidine and trimethoprim. These results suggest that hOCT2 may play a crucial role in elevating the serum creatinine levels, as well as increasing the risk of renal impairment during vandetanib administration.

THE CONCISE GUIDE TO PHARMACOLOGY 2021/22: Transporters.

The Concise Guide to PHARMACOLOGY 2021/22 is the fifth in this series of biennial publications. The Concise Guide provides concise overviews, mostly in tabular format, of the key properties of nearly 1900 human drug targets with an emphasis on selective pharmacology (where available), plus links to the open access knowledgebase source of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. Although the Concise Guide constitutes over 500 pages, the material presented is substantially reduced compared to information and links presented on the website. It provides a permanent, citable, point-in-time record that will survive database updates. The full contents of this section can be found at http://onlinelibrary.wiley.com/doi/bph.15543. Transporters are one of the six major pharmacological targets into which the Guide is divided, with the others being: G protein-coupled receptors, ion channels, nuclear hormone receptors, catalytic receptors and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. The landscape format of the Concise Guide is designed to facilitate comparison of related targets from material contemporary to mid-2021, and supersedes data presented in the 2019/20, 2017/18, 2015/16 and 2013/14 Concise Guides and previous Guides to Receptors and Channels. It is produced in close conjunction with the Nomenclature and Standards Committee of the International Union of Basic and Clinical Pharmacology (NC-IUPHAR), therefore, providing official IUPHAR classification and nomenclature for human drug targets, where appropriate.

Impact of Cyclin B2 and Cell division cycle 2 on tubular hyperplasia in progressive chronic renal failure rats.

To clarify the specific molecular events of progressive tubular damage in chronic renal failure (CRF), we conducted microarray analyses using isolated proximal tubules from subtotally nephrectomized (Nx) rats as a model of CRF. Our results clearly demonstrated time-dependent changes in gene expression profiles localized to proximal tubules. The expression of mitosis-specific genes Cyclin B2 and Cell division cycle 2 (Cdc2) was significantly and selectively increased in the proximal tubules during the compensated period but decreased to basal level in the end-stage period. Administration of everolimus, a potent inhibitor of mammalian target of rapamycin, markedly reduced compensatory hypertrophy and hyperplasia of epithelial cells, which was accompanied by complete abolishment of the expression of Cyclin B2 and Cdc2 enhancement; renal function was then severely decreased. Treatment with the Cdc2 inhibitor 2-cyanoethyl alsterpaullone clearly decreased epithelial cell hyperplasia, based on staining of phosphorylated histone H3 and Ki-67, while hypertrophy was not inhibited. In conclusion, we have demonstrated roles of Cyclin B2 and Cdc2 in the epithelial hyperplasia in response to Nx. These results advance the knowledge of the contribution of cell cycle regulators, especially M phase, in pathophysiology of tubular restoration and/or degeneration, and these two molecules are suggested to be a marker for the proliferation of proximal tubular cells in CRF.

Heterozygous variants of multidrug and toxin extrusions (MATE1 and MATE2-K) have little influence on the disposition of metformin in diabetic patients.

Multidrug and toxin extrusions (MATE1/SLC47A1 and MATE2-K/SLC47A2) play important roles in the renal excretion of metformin. We have previously identified the nonsynonymous MATE variants with functional defects at low allelic frequencies. The purpose of this study was to evaluate the effects of heterozygous MATE variants on the disposition of metformin in mice and humans. Pharmacokinetic parameters of metformin in Mate1(+ or -) heterozygous mice were comparable with those in Mate1(+ or +) wild-type mice. Among 48 Japanese diabetic patients, seven patients carried heterozygous MATE variant and no patient carried homozygous MATE variant. There was no significant difference in oral clearance of metformin with or without heterozygous MATE variants. In addition, creatinine clearance, but not heterozygous MATE variants, significantly improved the model fit of metformin clearance by statistical analysis using the nonlinear mixed-effects modeling program. In conclusion, heterozygous MATE variants could not influence the disposition of metformin in diabetic patients.

Topical insulin-like growth factor 1 treatment using gelatin hydrogels for glucocorticoid-resistant sudden sensorineural hearing loss: a prospective clinical trial.

BACKGROUND: Sudden sensorineural hearing loss (SSHL) is a common condition in which patients lose the hearing in one ear within 3 days. Systemic glucocorticoid treatments have been used as standard therapy for SSHL; however, about 20% of patients do not respond. We tested the safety and efficacy of topical insulin-like growth factor 1 (IGF1) application using gelatin hydrogels as a treatment for SSHL. METHODS: Patients with SSHL that showed no recovery to systemic glucocorticoid administration were recruited. We applied gelatin hydrogels, impregnated with recombinant human IGF1, into the middle ear. The primary outcome measure was the proportion of patients showing hearing improvement 12 weeks after the test treatment. The secondary outcome measures were the proportion of patients showing improvement at 24 weeks and the incidence of adverse events. The null hypothesis was that 33% of patients would show hearing improvement, as was reported for a historical control after hyperbaric oxygen therapy. RESULTS: In total, 25 patients received the test treatment at a median of 23 days (range 15-32) after the onset of SSHL, between 2007 and 2009. At 12 weeks after the test treatment, 48% (95% CI 28% to 69%; P = 0.086) of patients showed hearing improvement, and the proportion increased to 56% (95% CI 35% to 76%; P = 0.015) at 24 weeks. No serious adverse events were observed. CONCLUSIONS: Topical IGF1 application using gelatin hydrogels is well tolerated and may be efficacious for hearing recovery in patients with SSHL that is resistant to systemic glucocorticoids.

Reduced renal clearance of a zwitterionic substrate cephalexin in MATE1-deficient mice.

Multidrug and toxin extrusion 1 (MATE1/solute carrier 47A1) mediates the transport of not only organic cations but also zwitterions such as cephalexin. However, the contribution of MATE1 to tubular secretion of cephalexin in vivo has not been elucidated. In the present study, we carried out transport experiments of cephalexin via MATE1 and performed pharmacokinetic analyses of cephalexin in Mate1 knockout [Mate1(-/-)] mice. Cephalexin uptake by human MATE1-expressing human embryonic kidney 293 cells exhibited saturable kinetics (K(m) = 5.9 +/- 0.5 mM) and a bell-shaped pH profile with a maximum at pH 7.0. We confirmed that mouse MATE1 also transported cephalexin. After a single intravenous administration of cephalexin (5 mg/kg), Mate1(-/-) mice showed higher plasma concentrations of cephalexin than wild-type [Mate1(+/+)] mice. The urinary excretion of cephalexin for 60 min was significantly reduced, and the renal concentration was markedly increased in Mate1(-/-) mice compared with Mate1(+/+) mice. The renal clearance of cephalexin in Mate1(-/-) mice was approximately 60% of that in Mate1(+/+) mice and seemed to be near the creatinine clearance. In contrast, there were no significant differences between both mice in the pharmacokinetics of anionic cefazolin, which is not a substrate for MATE1. In this study, we demonstrated that MATE1 is responsible for renal tubular secretion of a zwitterionic substrate cephalexin in vivo.

Identification and comparative functional characterization of a new human riboflavin transporter hRFT3 expressed in the brain.

We isolated cDNA coding a new human riboflavin transporter (hRFT)3, which exhibits 86.7 and 44.1% amino acid identity with hRFT1 and hRFT2, respectively. It was predicted to have 10 putative membrane-spanning domains. The functional characteristics of hRFT3 were examined and compared with those of its isoforms, hRFT1 and hRFT2. Real-time PCR revealed that hRFT3 mRNA was strongly expressed in the brain and salivary gland. hRFT1 mRNA was strongly expressed in the placenta and small intestine, whereas hRFT2 mRNA was most abundantly expressed in the testis and strongly in the small intestine and prostate. hRFT-mediated uptake of [3H]riboflavin was evaluated using human embryonic kidney 293 cells transiently transfected with the cDNA coding each hRFT. The apparent Michaelis-Menten constants of hRFT1, hRFT2, and hRFT3 for riboflavin were 1.38, 0.98, and 0.33 micromol/L, respectively. The hRFT-mediated [3H]riboflavin uptake was independent of extracellular Na+ and Cl(-). Specific uptake of [3H]riboflavin by hRFT2, but not hRFT1 and hRFT3, decreased as extracellular pH was changed from 5.4 to 8.4. The substrate specificities of the hRFT family were similar. hRFT-mediated uptake of [3H]riboflavin was inhibited by some riboflavin analogs, but not D-ribose, organic ions, or other vitamins. The newly isolated hRFT3 may play an important role in brain riboflavin homeostasis. Its amino acid sequence and functional characteristics are similar to those of hRFT1, but not hRFT2.

Efficacy and safety of infliximab as rescue therapy for ulcerative colitis refractory to tacrolimus.

BACKGROUND AND AIM: Little is known about the efficacy and safety of infliximab for ulcerative colitis refractory to tacrolimus. The aim of this study was to evaluate the efficacy and safety of infliximab in the induction of remission in ulcerative colitis patients with persistent symptoms despite tacrolimus therapy. METHODS: We report a retrospective, observational, single-center case series of 12 consecutively enrolled patients with ulcerative colitis refractory to tacrolimus that received infliximab therapy for the induction of remission. Eight patients received a single infusion of infliximab, and four received two or more infusions. Median follow-up duration was 16.0 months (range, 1.6-41.4 months). The clinical response was evaluated based on a modified Truelove-Witts severity index. RESULTS: Six patients (50.0%) achieved clinical remission within 30 days. Overall cumulative colectomy-free survival was estimated to be 58.3% at 41.4 months. Adverse events included an elevation of liver enzymes (1/12; 8.3%) and a mild infusion reaction (1/12; 8.3%). No mortality occurred. CONCLUSIONS: Infliximab can induce remission in patients with ulcerative colitis who do not tolerate or respond to tacrolimus therapy.

Tolerable sorafenib therapy for a renal cell carcinoma patient with hemodialysis: a case study.

Sorafenib (Nexavar(®)) has been approved for the treatment of advanced renal cell carcinoma (RCC) and hepatocellular carcinoma. There is little information on the dosage adjustment of sorafenib for patients with end-stage renal failure. Herein, we have examined the effect of hemodialysis on the pharmacokinetics of sorafenib and its major active metabolite, M-2, and assessed sorafenib-related toxicity throughout the therapy. The patient was a 54-year-old man who was diagnosed with advanced RCC. Pharmacokinetic analysis was carried out on days 9 and 183. The patient had stable disease on day 77 and showed progression on day 181. He has received about 6 months of continuous treatment with sorafenib 800 mg/day without any clinically relevant toxicity. The pharmacokinetic parameters of sorafenib such as C (max) and AUC(0-12) on day 183 were in the range of the reference values reported in patients with normal renal function. Our results suggest that sorafenib administered at a dose of 400 mg twice per day was well tolerated, at least for 6 months, for a patient undergoing hemodialysis.