Expression of thirty-six drug transporter genes in human intestine, liver, kidney, and organotypic cell lines

Cladophora glomerata Kützing extract exhibits antioxidant, anti-inflammation, and anti-nitrosative stress against impairment of renal organic anion transport in an in vivo study

BACKGROUND/OBJECTIVES

Cladophora glomerata extract (CGE), rich in polyphenols, was reported to exhibit antidiabetic and renoprotective effects by modulating the functions of protein kinases-mediated organic anion transporter 1 (Oat1) and 3 (Oat3) in rats with type 2 diabetes mellitus (T2DM). Nevertheless, the antioxidant effects of CGE on such renoprotection have not been investigated. This study examined the mechanisms involved in the antioxidant effects of CGE on renal organic anion transport function in an in vivo study.

MATERIALS/METHODS

Diabetes was induced in the rats through a high-fat diet combined with a single dose of 40 mg/kg body weight (BW) streptozotocin. Subsequently, normal-diet rats were supplemented with a vehicle or 1,000 mg/kg BW of CGE, while T2DM rats were supplemented with a vehicle, CGE, or 200 mg/kg BW of vitamin C for 12 weeks. The study evaluated the general characteristics of T2DM and renal oxidative stress markers. The renal organic transport function was assessed by measuring the para-aminohippurate (PAH) uptake using renal cortical slices and renal inflammatory cytokine expression in the normal diet (ND) and ND + CGE treated groups.

RESULTS

CGE supplementation significantly reduced hyperglycemia, hypertriglyceridemia, insulin resistance, and renal lipid peroxidation in T2DM rats. This was accompanied by the normalization of high expressions of renal glutathione peroxidase and nuclear factor kappa B by CGE and vitamin C. The renal anti-inflammation of CGE was evidenced by the reduction of tumor necrosis factor-1α and interleukin-1β. CGE directly blunted sodium nitroprusside-induced renal oxidative/nitrosative stresses and mediated the PAH uptake in the normally treated CGE in rats was particularly noteworthy. These data also correlated with reduced nitric oxide production, highlighting the potential of CGE as a therapeutic agent for managing T2DM-related renal complications.

CONCLUSION

These findings suggest that CGE has antidiabetic effects and directly prevents diabetic nephropathy through oxidative/nitrosative stress pathways.

Impact of liver diseases and pharmacological interactions on the transportome involved in hepatic drug disposition

The liver plays a pivotal role in drug disposition owing to the expression of transporters accounting for the uptake at the sinusoidal membrane and the efflux across the basolateral and canalicular membranes of hepatocytes of many different compounds. Moreover, intracellular mechanisms of phases I and II biotransformation generate, in general, inactive compounds that are more polar and easier to eliminate into bile or refluxed back toward the blood for their elimination by the kidneys, which becomes crucial when the biliary route is hampered. The set of transporters expressed at a given time, i.e., the so-called transportome, is encoded by genes belonging to two gene superfamilies named Solute Carriers (SLC) and ATP-Binding Cassette (ABC), which account mainly, but not exclusively, for the uptake and efflux of endogenous substances and xenobiotics, which include many different drugs. Besides the existence of genetic variants, which determines a marked interindividual heterogeneity regarding liver drug disposition among patients, prevalent diseases, such as cirrhosis, non-alcoholic steatohepatitis, primary sclerosing cholangitis, primary biliary cirrhosis, viral hepatitis, hepatocellular carcinoma, cholangiocarcinoma, and several cholestatic liver diseases, can alter the transportome and hence affect the pharmacokinetics of drugs used to treat these patients. Moreover, hepatic drug transporters are involved in many drug-drug interactions (DDI) that challenge the safety of using a combination of agents handled by these proteins. Updated information on these questions has been organized in this article by superfamilies and families of members of the transportome involved in hepatic drug disposition.

Molecular detection of lacrimal apparatus and ocular surface - related ABC transporter genes

The ocular system is in constant interaction with the environment and with numerous pathogens. The ATP-binding cassette (ABC) transporters represent one of the largest groups among the transmembrane proteins. Their relevance has been demonstrated for their defense function against biotic and abiotic stress factors, for metabolic processes in tumors and for their importance in the development of resistance to drugs. The aim of this study was to analyze which ABC transporters are expressed at the ocular surface and in the human lacrimal apparatus. Using RT-PCR, all ABC transporters known to date in humans were examined in tissue samples from human cornea, conjunctiva, meibomian glands and lacrimal glands. The RT-PCR analyses revealed the presence of all ABC transporters in the samples examined, although the results for some of the 48 transporters known in human and analyzed were different in the various tissues. The present results provide information on the expression of ABC transporters at the mRNA level on the ocular surface and in the lacrimal system. Their detection forms the basis for follow-up studies at the protein level, which will provide more information about their physiological significance at the ocular surface and in the lacrimal system and which may explain pathological effects such as drug resistance.

Evaluation of mAb 2C5-modified dendrimer-based micelles for the co-delivery of siRNA and chemotherapeutic drug in xenograft mice model

Combination therapy with small interfering RNA (siRNA) and chemotherapeutic drug is proven to be effective in downregulating cancer resistance proteins, such as P-glycoprotein (P-gp). These proteins are involved in multidrug resistance (MDR) of tumors. A targeted formulation capable of delivering siRNA and chemotherapeutic drug will not only downregulate P-gp but also increase the concentration of the chemotherapeutic drug at the site of tumor thereby increasing the therapeutic effect and lowering the systemic exposure. In this study, monoclonal antibody 2C5-modified dendrimer-based micelles were used to co-deliver siRNA and doxorubicin (DOX) to the tumor site in both male and female xenograft mouse model. The nucleosome-specific 2C5 antibody recognizes the cancer cells via the cell-surface bound nucleosomes. The ability of ability of the 2C5-modified formulation to affect the metastasis of highly aggressive triple negative breast cancer cell migration in (MDA-MB-231) was assessed by a wound healing. Further, the therapeutic efficacy of the formulation was assessed by measuring the tumor volume progression in which the 2C5-modified nanoparticle group had a similar tumor volume to the free drug group at the end of the study, although a 50% increase in DOX concentrations in blood was observed after the last dose of nanoparticle. The free drug group on the other hand showed body weight reduction as well as the visible irritation around the injection spot. The treatment group with 2C5-modified micelles has shown to be safe at the current dose of DOX and siRNA. Furthermore, the siRNA mediated P-gp downregualtion was studied using western blotting assay. We observed a 29% reduction of P-gp levels in both males and females with respect to the control (BHG). We also conclude that the dose of DOX and siRNA should be further optimized to have a better efficacy in a metastatic tumor model, which will be the subject of our future studies.

Knockout Transporter Cell Lines to Assess Substrate Potential Towards Efflux Transporters

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

Transporter Proteins as Therapeutic Drug Targets-With a Focus on SGLT2 Inhibitors

Membrane transporters interact not only with endogenous substrates but are also engaged in the transport of xenobiotics, including drugs. While the coordinated function of uptake (solute carrier family-SLC and SLCO) and efflux (ATP-binding cassette family-ABC, multidrug and toxic compound extrusion family-MATE) transporter system allows vectorial drug transport, efflux carriers alone achieve barrier functions. The modulation of transport functions was proved to be effective in the treatment strategies of various pathological states. Sodium-glucose cotransporter-2 (SGLT2) inhibitors are the drugs most widely applied in clinical practice, especially in the treatment of diabetes mellitus and heart failure. Sodium taurocholate co-transporting polypeptide (NTCP) serves as virus particles (HBV/HDV) carrier, and inhibition of its function is applied in the treatment of hepatitis B and hepatitis D by myrcludex B. Inherited cholestatic diseases, such as Alagille syndrome (ALGS) and progressive familial intrahepatic cholestasis (PFIC) can be treated by odevixibat and maralixibat, which inhibit activity of apical sodium-dependent bile salt transporter (ASBT). Probenecid can be considered to increase uric acid excretion in the urine mainly via the inhibition of urate transporter 1 (URAT1), and due to pharmacokinetic interactions involving organic anion transporters 1 and 3 (OAT1 and OAT3), it modifies renal excretion of penicillins or ciprofloxacin as well as nephrotoxicity of cidofovir. This review discusses clinically approved drugs that affect membrane/drug transporter function.

Using the Dynamic Well-Stirred Model to Extrapolate Hepatic Clearance of Organic Anion-Transporting Polypeptide Transporter Substrates without Assuming Albumin-Mediated Hepatic Drug Uptake

Extrapolating in vivo hepatic clearance from in vitro uptake data is a known challenge, especially for organic anion-transporting polypeptide transporter (OATP) substrates, and the well-stirred model (WSM) commonly yields systematic underpredictions for those anionic drugs, hypothetically due to "albumin-mediated hepatic drug uptake". In the present study, we demonstrate that the WSM incorporating the dynamic free fraction (f D), a measure of drug protein binding affinity, performs reasonably well in predicting hepatic clearance of OATP substrates. For a selection of anionic drugs, including atorvastatin, fluvastatin, pravastatin, rosuvastatin, pitavastatin, cerivastatin, and repaglinide, this dynamic well-stirred model (dWSM) correctly predicts hepatic plasma clearance within 2-fold error for six out of seven OATP substrates examined. The geometric mean of clearance ratios between the predicted and the observed values falls in the range of 1.21-1.38. As expected, the WSM with unbound fraction (f u) systematically underpredicts hepatic clearance with greater than 2-fold error for five out of seven drugs, and the geometric mean of clearance ratios between the predicted and the observed values is in the range of 0.20-0.29. The results suggest that, despite its simplicity, the dWSM operates well for transporter-mediated uptake clearance, and that clearance under-prediction of OATP substrates may not necessarily be associated with the chemical class of the anionic drugs, nor is it a result of albumin-mediated hepatic drug uptake as currently hypothesized. Instead, the superior prediction power of the dWSM confirms the utility of the dynamic free fraction in clearance prediction and the importance of drug plasma binding kinetics in hepatic uptake clearance. SIGNIFICANCE STATEMENT: The traditional well-stirred model (WSM) consistently underpredicts organin anion-transporting polypeptide transporter (OATP)-mediated hepatic uptake clearance, hypothetically due to the albumin-mediated hepatic drug uptake. In this manuscript, we apply the dynamic WSM to extrapolate hepatic clearance of the OATP substrates, and our results show significant improvements in clearance prediction without assuming albumin-mediated hepatic drug uptake.

A Historical Perspective on Uremia and Uremic Toxins

Uremia, also known as uremic syndrome, refers to the clinical symptoms in the final stage of renal failure. The definition of the term has changed over time due to an improved comprehension of the kidney's function and the advancement of dialysis technology. Here, we aim to present an overview of the various concepts that have developed regarding uremia throughout the years. We provide a comprehensive review of the historical progression starting from the early days of Kolff and his predecessors, continuing with the initial research conducted by Niwa et al., and culminating in the remote sensing hypothesis of Nigam. Additionally, we explore the subsequent investigation into the function of these toxins as signaling molecules in various somatic cells.

Targeted mutagenesis of negatively charged amino acids outlining the substrate translocation path within the human organic cation transporter 3

Recently published cryo-EM structures of human organic cation transporters of the SLC22 family revealed seven, sequentially arranged glutamic and aspartic acid residues, which may be relevant for interactions with positively charged substrates. We analyzed the functional consequences of removing those negative charges by creating D155N, E232Q, D382N, E390Q, E451Q, E459Q, and D478N mutants of OCT3. E232Q, E459Q, and D478N resulted in a lack of localization in the outer cell membrane and no relevant uptake activity. However, D155N and E451Q showed a substrate-specific loss of transport activity, whereas E390Q had no remaining activity despite correct membrane localization. In contrast, D382N showed almost wild-type-like uptake. D155 is located at the entrance to the substrate binding pocket and could, therefore be involved in guiding cationic substrates towards the inside of the binding pocket. For E390, we confirm its critical function for transporter function as it was recently shown for the corresponding position in OCT1. Interestingly, E451 seems to be located at the bottom of the binding pocket in the outward-open confirmation of the transporter. Substrate-specific loss of transport activity of the E451Q variant suggests an essential role in the transport cycle of specific substances as part of an opportunistic binding site. In general, our study highlights the impact of the cryo-EM structures in guiding mutagenesis studies to understand the molecular level of transporter-ligand interactions, and it also confirms the importance of testing multiple substrates in mutagenesis studies of polyspecific OCTs.

ABCG2 Transports the Flukicide Nitroxynil and Affects Its Biodistribution and Secretion into Milk

The ABCG2 transporter plays a key role in pharmacological and toxicological processes, affecting bioavailability, tissue accumulation and milk secretion of its substrates. This protein is expressed in several biological barriers acting as a protective mechanism against xenobiotic exposure by pumping out a broad range of compounds. However, its induced expression during lactation in alveolar cells of mammary gland represents a relevant route for active transport of unwanted chemicals into milk. This work aimed to characterize the involvement of ABCG2 in systemic exposure and milk secretion of the flukicide nitroxynil. Using MDCK-II cells overexpressing the transporter, we showed that nitroxynil is an in vitro substrate of different species variants of ABCG2. Moreover, using wild-type and Abcg2-/- mice, we showed that murine Abcg2 clearly affects plasma levels of nitroxynil. We also reported differences in nitroxynil accumulation in several tissues, with almost 2-fold higher concentration in kidney, small intestine and testis of Abcg2-/- mice. Finally, we proved that nitroxynil secretion into milk was also affected by Abcg2, with a 1.9-fold higher milk concentration in wild-type compared with Abcg2-/- mice. We conclude that ABCG2 significantly impacts nitroxynil biodistribution by regulating its passage across biological barriers.

Uric acid in health and disease: From physiological functions to pathogenic mechanisms

Owing to renal reabsorption and the loss of uricase activity, uric acid (UA) is strictly maintained at a higher physiological level in humans than in other mammals, which provides a survival advantage during evolution but increases susceptibility to certain diseases such as gout. Although monosodium urate (MSU) crystal precipitation has been detected in different tissues of patients as a trigger for disease, the pathological role of soluble UA remains controversial due to the lack of causality in the clinical setting. Abnormal elevation or reduction of UA levels has been linked to some of pathological status, also known as U-shaped association, implying that the physiological levels of UA regulated by multiple enzymes and transporters are crucial for the maintenance of health. In addition, the protective potential of UA has also been proposed in aging and some diseases. Therefore, the role of UA as a double-edged sword in humans is determined by its physiological or non-physiological levels. In this review, we summarize biosynthesis, membrane transport, and physiological functions of UA. Then, we discuss the pathological involvement of hyperuricemia and hypouricemia as well as the underlying mechanisms by which UA at abnormal levels regulates the onset and progression of diseases. Finally, pharmacological strategies for urate-lowering therapy (ULT) are introduced, and current challenges in UA study and future perspectives are also described.

Involvement of reactive oxygen species (ROS) in the hepatopancreatic cytotoxicity, oxidative stress, and apoptosis induced by microcystin-LR in Eriocheir sinensis

There is limited knowledge about the toxicity of Microcystin-LR (MC-LR) in crustaceans, despite its high toxicity to aquatic organisms. This research aimed to explore the effects of MC-LR on cytotoxicity, oxidative stress, and apoptosis in the hepatopancreas of Eriocheir sinensis, as well as elucidate the involvement of reactive oxygen species (ROS) and potential mechanisms of toxicity. In vivo and in vitro exposures of crabs to MC-LR and N-acetylcysteine (NAC) were performed, followed by assessments of cell morphology, viability, tissue pathology, biochemical indicators, gene expression, and hepatopancreatic transcriptome. Results revealed that MC-LR facilitated the entry of the MC-LR transporter oatp3a into hepatopancreatic cells, leading to upregulated expression of phase I detoxification enzyme genes (cyp4c, cyp2e1, and cyp3) and downregulated the phase II enzyme genes (gst1, gpx, gsr2, gclc, and nqo1), resulting in increased ROS levels and cytotoxic effects. MC-LR exhibited cytotoxicity, reducing cell viability and inducing abnormal nuclear morphology with a 48 h-IC50 value of approximately 120 μm. MC-LR exposure caused biochemical changes indicative of oxidative stress damage and evident hepatopancreatic lesions. Additionally, MC-LR exposure regulated the levels of bax and bcl-2 expression, activating caspase 3 and 6 to induce cell apoptosis. Intervention with NAC attenuated MC-LR-induced ROS production and associated toxic effects. Transcriptome analysis revealed enrichment of differentially expressed genes in pathways related to cytochrome P450-mediated xenobiotic metabolism and the FoxO signaling pathway. These findings shed light on the potential mechanisms underlying MC-LR toxicity and provide valuable references for further research and conservation efforts regarding the health of aquatic animals.

Olive (Olea europaea L.) Seed as New Source of Cholesterol-Lowering Bioactive Peptides: Elucidation of Their Mechanism of Action in HepG2 Cells and Their Trans-Epithelial Transport in Differentiated Caco-2 Cells

The production of olive oil has important economic repercussions in Mediterranean countries but also a considerable impact on the environment. This production generates enormous quantities of waste and by-products, which can be exploited as new raw materials to obtain innovative ingredients and therefore make the olive production more sustainable. In a previous study, we decided to foster olive seeds by generating two protein hydrolysates using food-grade enzymes, alcalase (AH) and papain (PH). These hydrolysates have shown, both in vitro and at the cellular level, antioxidant and antidiabetic activities, being able to inhibit the activity of the DPP-IV enzyme and modulate the secretion of GLP-1. Given the multifunctional behavior of peptides, both hydrolysates displayed dual hypocholesterolemic activity, inhibiting the activity of HMGCoAR and impairing the PPI of PCSK9/LDLR, with an IC50 equal to 0.61 mg/mL and 0.31 mg/mL for AH and PH, respectively. Furthermore, both samples restored LDLR protein levels on the membrane of human hepatic HepG2 cells, increasing the uptake of LDL from the extracellular environment. Since intestinal bioavailability is a key component of bioactive peptides, the second objective of this work is to evaluate the capacity of AH and PH peptides to be transported by differentiated human intestinal Caco-2 cells. The peptides transported by intestinal cells have been analyzed using mass spectrometry analysis, identifying a mixture of stable peptides that may represent new ingredients with multifunctional qualities for the development of nutraceuticals and functional foods to delay the onset of metabolic syndrome, promoting the principles of environmental sustainability.

Significance of Organic Anion Transporter 2 and Organic Cation Transporter 2 in Creatinine Clearance: Mechanistic Evaluation Using Freshly Prepared Human Primary Renal Proximal Tubule Cells

Creatinine, a clinical marker for kidney function, is predominantly cleared by glomerular filtration, with active tubular secretion contributing to about 30% of its renal clearance. Recent studies suggested the potential involvement of organic anion transporter (OAT)2, in addition to the previously known organic cation transporter (OCT)2-mediated basolateral uptake, in creatinine active secretion. Here we characterized the transport mechanisms of creatinine using transfected human embryonic kidney (HEK)293 cells and freshly prepared human primary renal proximal tubule epithelial cells (hPTCs). Creatinine showed transport by OAT2 in transfected HEK293 cells. In addition, both creatinine and metformin showed transport by OCT2 and multidrug and toxin extrusion pump (MATE)1 and MATE2K, while penciclovir was selective for OAT2. Time-dependent cell accumulation was observed for creatinine and metformin in hPTCs. Their accumulation was increased by pyrimethamine but inhibited by decynium-22, likely due to differential inhibition of OCT2 versus MATEs. Additionally, indomethacin (an OAT2 inhibitor) reduced penciclovir uptake (∼75%) in hPTCs illustrating functional OAT2 activity. However, no modulation of creatinine and metformin cell accumulation was apparent with indomethacin. Creatinine transport characteristics in the presence of inhibitors approached those of metformin, an OCT2/MATE substrate, but were distinct from those of penciclovir, an OAT2-selective substrate. Moreover, indomethacin showed no significant effect on the basolateral-to-apical transport and net secretion of creatinine across hPTC monolayers. Collectively, the functional studies suggest OCT2 as the primary basolateral uptake mechanism and that OAT2 has a minimal role, in creatinine renal secretion. Our results highlight the utility of hPTCs to enable the functional assessment of renal transport mechanisms. SIGNIFICANCE STATEMENT: Our results obtained with primary hPTCs indicate that OCT2/MATE (vs. OAT2) play a major role in the active renal secretion of creatinine. Quantitative pharmacokinetic models should therefore focus on OCT2/MATE when describing serum creatinine and creatinine clearance modulation by inhibitor drugs and genotype- or disease-related activity changes. The present study highlights the utility of freshly isolated hPTCs to support solute carrier phenotyping to enable the functional assessment of renal transport mechanisms.

Recent Advances in the Gastrointestinal Complex in Vitro Model for ADME Studies

Intestinal absorption is a complex process involving the permeability of the epithelial barrier, efflux transporter activity, and intestinal metabolism. Identifying the key factors that govern intestinal absorption for each investigational drug is crucial. To assess and predict intestinal absorption in humans, it is necessary to leverage appropriate in vitro systems. Traditionally, Caco-2 monolayer systems and intestinal Ussing chamber studies have been considered the 'gold standard' for studying intestinal absorption. However, these methods have limitations that hinder their universal use in drug discovery and development. Recently, there has been an increasing number of reports on complex in vitro models (CIVMs) using human intestinal organoids derived from intestinal tissue specimens or iPSC-derived enterocytes plated on 2D or 3D in microphysiological systems. These CIVMs provide a more physiologically relevant representation of key ADME-related proteins compared to conventional in vitro methods. They hold great promise for use in drug discovery and development due to their ability to replicate the expressions and functions of these proteins. This review highlights recent advances in gut CIVMs employing intestinal organoid model systems compared to conventional methods. It is important to note that each CIVM should be tailored to the investigational drug properties and research questions at hand.

Stereoselective Inhibition of High- and Low-Affinity Organic Cation Transporters

Many drugs have chiral centers and are therapeutically applied as racemates. Thus, the stereoselectivity in their interactions with membrane transporters needs to be addressed. Here, we studied stereoselectivity in inhibiting organic cation transporters (OCTs) 1, 2, and 3 and the high-affinity monoamine transporters (MATs) NET and SERT. Selectivity by the inhibition of 35 pairs of enantiomers significantly varied among the three closely related OCTs. OCT1 inhibition was nonselective in almost all cases, whereas OCT2 was stereoselectively inhibited by 45% of the analyzed drugs. However, the stereoselectivity of the OCT2 was only moderate with the highest selectivity observed for pramipexole. The (R)-enantiomer inhibited OCT2 4-fold more than the (S)-enantiomer. OCT3 showed the greatest stereoselectivity in its inhibition. (R)-Tolterodine and (S)-zolmitriptan inhibited OCT3 11-fold and 25-fold more than their respective counterparts. Interestingly, in most cases, the pharmacodynamically active enantiomer was also the stronger OCT inhibitor. In addition, stereoselectivity in the OCT inhibition appeared not to depend on the transported substrate. For high-affinity MATs, our data confirmed the stereoselective inhibition of NET and SERT by several antidepressants. However, the stereoselectivity measured here was generally lower than that reported in the literature. Unexpectedly, the high-affinity MATs were not significantly more stereoselectively inhibited than the polyspecific OCTs. Combining our in vitro OCT inhibition data with available stereoselective pharmacokinetic analyses revealed different risks of drug-drug interactions, especially at OCT2. For the tricyclic antidepressant doxepine, only the (E)-isomer showed an increased risk of drug-drug interactions according to guidelines from regulatory authorities for renal transporters. However, most chiral drugs show only minor stereoselectivity in the inhibition of OCTs in vitro, which is unlikely to translate into clinical consequences.

The substrate and inhibitor binding mechanism of polyspecific transporter OAT1 revealed by high-resolution cryo-EM

Organic anion transporters (OATs) of the SLC22 family have crucial roles in the transport of organic anions, including metabolites and therapeutic drugs, and in transporter-mediated drug-drug interactions. In the kidneys, OATs facilitate the elimination of metabolic waste products and xenobiotics. However, their transport activities can lead to the accumulation of certain toxic compounds within cells, causing kidney damage. Moreover, OATs are important drug targets, because their inhibition modulates the elimination or retention of substrates linked to diseases. Despite extensive research on OATs, the molecular basis of their substrate and inhibitor binding remains poorly understood. Here we report the cryo-EM structures of rat OAT1 (also known as SLC22A6) and its complexes with para-aminohippuric acid and probenecid at 2.1, 2.8 and 2.9 Å resolution, respectively. Our findings reveal a highly conserved substrate binding mechanism for SLC22 transporters, wherein four aromatic residues form a cage to accommodate the polyspecific binding of diverse compounds.

The shape of our gut: Dissecting its impact on drug absorption in a 3D bioprinted intestinal model

The small intestine is a complex organ with a characteristic architecture and a major site for drug and nutrient absorption. The three-dimensional (3D) topography organized in finger-like protrusions called villi increases surface area remarkably, granting a more efficient absorption process. The intestinal mucosa, where this process occurs, is a multilayered and multicell-type tissue barrier. In vitro intestinal models are routinely used to study different physiological and pathological processes in the gut, including compound absorption. Still, standard models are typically two-dimensional (2D) and represent only the epithelial barrier, lacking the cues offered by the 3D architecture and the stromal components present in vivo, often leading to inaccurate results. In this work, we studied the impact of the 3D architecture of the gut on drug transport using a bioprinted 3D model of the intestinal mucosa containing both the epithelial and the stromal compartments. Human intestinal fibroblasts were embedded in a previously optimized hydrogel bioink, and enterocytes and goblet cells were seeded on top to mimic the intestinal mucosa. The embedded fibroblasts thrived inside the hydrogel, remodeling the surrounding extracellular matrix. The epithelial cells fully covered the hydrogel scaffolds and formed a uniform cell layer with barrier properties close to in vivo. In particular, the villus-like model revealed overall increased permeability compared to a flat counterpart composed by the same hydrogel and cells. In addition, the efflux activity of the P-glycoprotein (P-gp) transporter was significantly reduced in the villus-like scaffold compared to a flat model, and the genetic expression of other drugs transporters was, in general, more relevant in the villus-like model. Globally, this study corroborates that the presence of the 3D architecture promotes a more physiological differentiation of the epithelial barrier, providing more accurate data on drug absorbance measurements.

Quantitative Consideration of Clinical Increases in Serum Creatinine Caused by Renal Transporter Inhibition

Creatinine is a common biomarker of renal function and is secreted in the renal tubular cells via drug transporters, such as organic cation transporter 2 and multidrug and toxin extrusion (MATE) 1/2-K. To differentiate between drug-induced acute kidney injury (AKI) and drug interactions through the renal transporter, it has been examined whether these transporter inhibitions quantitatively explained increases in serum creatinine (SCr) at their clinically relevant concentrations using drugs without any changes in renal function. For such renal transporter inhibitors and recently approved tyrosine kinase inhibitors (TKIs), this mini-review describes clinical increases in SCr and inhibitory potentials against the renal transporters. Most cases of SCr elevations can be explained by considering the renal transporter inhibitions based on unbound maximum plasma concentrations, except for drugs associated with obvious changes in renal function. SCr increases for cobicistat, dolutegravir, and dronedarone, and some TKIs were significantly underestimated, and these underestimations were suggested to be associated with low plasma unbound fractions. Sensitivity analysis of SCr elevations regarding inhibitory potentials of MATE1/2-K demonstrated that typical inhibitors such as cimetidine, DX-619, pyrimethamine, and trimethoprim could give false interpretations of AKI according to the criteria based on relative or absolute levels of SCr elevations. Recent progress and current challenges of physiologically-based pharmacokinetics modeling for creatinine disposition were also summarized. Although it should be noted for the potential impact of in vitro assay designs on clinical translatability of transporter inhibitions data, mechanistic approaches could support decision-making in clinical development to differentiate between AKI and creatinine-drug interactions. SIGNIFICANCE STATEMENT: Serum creatinine (SCr) is widely used as an indicator of kidney function, but it increases due to inhibitions of renal transporters, such as multidrug and toxin extrusion protein 1/2-K despite no functional changes in the kidney. Such SCr elevations were quantitatively explained by renal transporter inhibitions except for some drugs with high protein binding. The present analysis demonstrated that clinically relevant inhibitors of the renal transporters could cause SCr elevations above levels corresponding to acute kidney injury criteria.

Quantitative Prediction of Intestinal Absorption of Drugs from In Vitro Study: Utilization of Differentiated Intestinal Epithelial Cells Derived from Intestinal Stem Cells at Crypts

Prediction of intestinal absorption of drugs in humans is one of the critical elements in the development process for oral drugs. However, it remains challenging, because intestinal absorption of drugs is influenced by multiple factors, including the function of various metabolic enzymes and transporters, and large species differences in drug bioavailability hinder the prediction of human bioavailability directly from in vivo animal experiments. For the screening of intestinal absorption properties of drugs, a transcellular transport assay with Caco-2 cells is still routinely used by pharmaceutical companies because of its convenience, but the predictability of the fraction of the oral dose that goes to the portal vein of metabolic enzyme/transporter substrate drugs was not always good because the cellular expression of metabolic enzymes and transporters is different from that in the human intestine. Recently, various novel in vitro experimental systems have been proposed such as the use of human-derived intestinal samples, transcellular transport assay with induced pluripotent stem-derived enterocyte-like cells, or differentiated intestinal epithelial cells derived from intestinal stem cells at crypts. Crypt-derived differentiated epithelial cells have an excellent potential to characterize species differences and regional differences in intestinal absorption of drugs because a unified protocol can be used for the proliferation of intestinal stem cells and their differentiation into intestinal absorptive epithelial cells regardless of the animal species and the gene expression pattern of differentiated cells is maintained at the site of original crypts. The advantages and disadvantages of novel in vitro experimental systems for characterizing intestinal absorption of drugs are also discussed. SIGNIFICANCE STATEMENT: Among novel in vitro tools for the prediction of human intestinal absorption of drugs, crypt-derived differentiated epithelial cells have many advantages. Cultured intestinal stem cells are rapidly proliferated and easily differentiated into intestinal absorptive epithelial cells simply by changing the culture media. A unified protocol can be used for the establishment of intestinal stem cell culture from preclinical species and humans. Region-specific gene expression at the collection site of crypts can be reproduced in differentiated cells.

Validation of Freshly Isolated Rat Renal Cells as a Tool for Preclinical Assessment of Radiolabeled Receptor-Specific Peptide Uptake in the Kidney

The synthetic analogs of regulatory peptides radiolabeled with adequate radionuclides are perspective tools in nuclear medicine. However, undesirable uptake and retention in the kidney limit their application. Specific in vitro methods are used to evaluate undesirable renal accumulation. Therefore, we investigated the usefulness of freshly isolated rat renal cells for evaluating renal cellular uptake of receptor-specific peptide analogs. Special attention was given to megalin as this transport system is an important contributor to the active renal uptake of the peptides. Freshly isolated renal cells were obtained from native rat kidneys by the collagenase method. Compounds with known accumulation in renal cells were used to verify the viability of cellular transport systems. Megalin expressions in isolated rat renal cells were compared to two other potential renal cell models by Western blotting. Specific tubular cell markers were used to confirm the presence of proximal tubular cells expressing megalin in isolated rat renal cell preparations by immunohistochemistry. Colocalization experiments on isolated rat kidney cells confirmed the presence of proximal tubular cells bearing megalin in preparations. The applicability of the method was tested by an accumulation study with several analogs of somatostatin and gastrin labeled with indium-111 or lutetium-177. Therefore, isolated rat renal cells may be an effective screening tool for in vitro analyses of renal uptake and comparative renal accumulation studies of radiolabeled peptides or other radiolabeled compounds with potential nephrotoxicity.

Exploring the effect of polyamines on NK cell function in colorectal cancer process based on glycolysis

Natural killer (NK) cells are lymphocytes with important anti-tumour functions. Cellular metabolism is dynamically regulated in NK cells and strongly influences their responses. Myc is a key regulator of immune cell activity and function, but little is known about how Myc controls NK cell activation and function. In this study, we found that c-Myc is involved in the regulation of NK cell immune activity. In the development of colon cancer, the energy generation disorder of tumor cells promotes the plunder of polyamines of NK cells by tumor cells, resulting in the inhibition of NK cell c-Myc. After inhibition of c-Myc, glycolysis of NK cells was impaired, resulting in decreased killing activity. There are three main types of polyamines: putrescine (Put), spermidine (Spd) and spermine (Spm). We found that the NK cells could reverse the inhibition state of c-Myc and glycolysis energy supply disorder and recover the killing activity of NK cells after giving certain spermidine. These results suggest that polyamine content and glycolysis supply under the regulation of c-Myc play a crucial role in the immune activity of NK cells.

Transcriptional Regulation of Liver-Type OATP1B3 (Lt-OATP1B3) and Cancer-Type OATP1B3 (Ct-OATP1B3) Studied in Hepatocyte-Derived and Colon Cancer-Derived Cell Lines

Due to alternative splicing, the SLCO1B3 gene encodes two protein variants; the hepatic uptake transporter liver-type OATP1B3 (Lt-OATP1B3) and the cancer-type OATP1B3 (Ct-OATP1B3) expressed in several cancerous tissues. There is limited information about the cell type-specific transcriptional regulation of both variants and about transcription factors regulating this differential expression. Therefore, we cloned DNA fragments from the promoter regions of the Lt-SLCO1B3 and the Ct-SLCO1B3 gene and investigated their luciferase activity in hepatocellular and colorectal cancer cell lines. Both promoters showed differences in their luciferase activity depending on the used cell lines. We identified the first 100 bp upstream of the transcriptional start site as the core promoter region of the Ct-SLCO1B3 gene. In silico predicted binding sites for the transcription factors ZKSCAN3, SOX9 and HNF1α localized within these fragments were further analyzed. The mutagenesis of the ZKSCAN3 binding site reduced the luciferase activity of the Ct-SLCO1B3 reporter gene construct in the colorectal cancer cell lines DLD1 and T84 to 29.9% and 14.3%, respectively. In contrast, using the liver-derived Hep3B cells, 71.6% residual activity could be measured. This indicates that the transcription factors ZKSCAN3 and SOX9 are important for the cell type-specific transcriptional regulation of the Ct-SLCO1B3 gene.

P-Glycoprotein and Organic Anion Transporter Polypeptide 1B/Breast Cancer Resistance Protein Drug Transporter Activity in Pregnant Women Living With HIV

This study evaluates the influence of pregnancy and HIV infection in conjunction with the use of raltegravir, lamivudine, and tenofovir disoproxil fumarate (combined antiretroviral therapy [cART]) on intestinal P-glycoprotein (P-gp) and hepatic organic anion transporter polypeptide (OATP) 1B1/1B3 and/or breast cancer resistance protein (BCRP) drug transporter activity using rosuvastatin (OATP1B/BCRP) and fexofenadine (P-gp) probes. Single oral doses of 5-mg rosuvastatin and 60-mg fexofenadine were administered to women living with HIV under cART in the third trimester of gestation (n = 15) and postpartum period (n = 10). A control group of 12 healthy nonpregnant women also was investigated. Pharmacokinetic parameters were estimated by using a noncompartmental method and evaluated by t test (P < .05). The rosuvastatin area under the plasma concentration-time curve from time 0 to the last quantifiable concentration (AUC_0-last ) value was higher in the third trimester of pregnancy (19.5 [95%CI, 16.8-22.3] ng • h/mL] when compared to postpartum (13.3 [95%CI, 9.3-17.5] ng • h/mL), while the fexofenadine AUC_0-last values did not differ between the third trimester of pregnancy (738.0 [95%CI, 611.4-864.6] ng • h/mL) and postpartum period (874.9 [95%CI, 408.2-1342.0] ng• h/mL). The rosuvastatin AUC_0-last values did not differ between healthy nonpregnant women (13.8 [95%CI, 10.0-17.6] ng • h/mL) and women living with HIV in the postpartum period (13.3 [95%CI, 9.3-17.5] ng • h/mL), and the fexofenadine AUC_0-last values did not differ between the 2 investigated groups (603.6 [95%CI, 467.5-739.7] ng • h/mL vs 874.9 [95%CI, 408.2-1342.0] ng • h/mL). It is suggested that gestation inhibits the hepatic OATP1B1/1B3 and/or BCRP activity but does not alter intestinal P-gp activity. The influence of HIV infection in conjunction with use of cART on OATP1B/BCRP and intestinal P-gp activity was not observed.

Evaluation of ABCG2-mediated extra-renal urate excretion in hemodialysis patients

Two-thirds of urate is excreted via the renal pathway and the remaining one-third via the extra-renal pathway, the latter mainly via the intestine in healthy individuals. ABCG2, a urate exporter, is expressed in various tissues including the kidney and intestine, and its dysfunction leads to hyperuricemia and gout. ABCG2 is regarded as being responsible for most of the extra-renal urate excretion. However, the extra-renal urate excretion capacity via ABCG2 remains undefined in end-stage kidney diseases. Therefore, we evaluated the capacity of extra-renal ABCG2 using 123 anuric hemodialysis patients whose urate excretion depended on only the extra-renal pathway. ABCG2 function in each participant was estimated based on ABCG2 dysfunctional variants. We computed the uric acid pool (Pool_UA) from bodyweight and serum urate level (SUA) using previously reported radio-isotopic data, and we analyzed the association between ABCG2 function and the Pool_UA. SUA and Pool_UA increased significantly with ABCG2 dysfunction, and extra-renal ABCG2 could excrete up to approximately 60% of the daily uric acid turnover in hemodialysis patients. Our findings indicate that the extra-renal urate excretion capacity can expand with renal function decline and highlight that the extra-renal pathway is particularly important in the uric acid homeostasis for patients with renal dysfunction.

Pharmacodynamic Modeling to Evaluate the Impact of Cimetidine, an OCT2 Inhibitor, on the Anticancer Effects of Cisplatin

Despite potent anticancer activity, the clinical utilization of cisplatin is limited due to nephrotoxicity. As Organic Cation Transporter 2 (OCT2) has been shown to be one of the key transporters involved in the uptake of cisplatin into renal proximal tubules, OCT2 inhibitors such as cimetidine have been explored to suppress cisplatin-induced nephrotoxicity. Nonetheless, the impact of OCT2 inhibition or cimetidine on the anti-cancer effects of cisplatin has not been extensively examined. The main objective of the present study was to quantitatively characterize the anticancer effects of cisplatin and cimetidine and determine their nature of interactions in two cancer cell lines, OCT2-negative hepatocellular carcinoma (HCC) cell line, Huh7, and OCT2-positive breast cancer cell line, MDA-MB-468. First, we determined the static concentration-response curves of cisplatin and cimetidine as single agents. Next, with the help of three-dimensional (3D) response surface analyses and a competitive interaction model, we determined their nature of interactions at static concentrations to be modestly synergistic or additive in Huh7 and antagonistic in MDA-MB-468. These results were consistent with the cell-level pharmacodynamic (PD) modeling analysis which leveraged the time-course effects of drugs as single agents and drug combinations. Our developed PD model can be further used to design future preclinical studies to further investigate the cisplatin and cimetidine combinations in different in vitro and in vivo cancer models.

Polymorphisms in solute carrier genes (SLC19A1, SLCO1B1, and SLCO1B3) predicts survival and toxicity in North Indian lung cancer patients undergoing platinum-based doublet chemotherapy

WHAT IS KNOWN AND OBJECTIVE

Solute Carrier (SLC) transporters are known mediators of drug disposition that facilitate the influx of substrates and various chemotherapeutic agents into cells. Polymorphisms in the SLC19A1, SLCO1B1, and SLCO1B3 gene influence the prognosis in the cancer patients, but little is known about their role in lung cancer in Asians. So, the current study aims to investigate the polymorphisms in SLC19A1, SLCO1B1, and SLCO1B3 genes in Northern Indian lung cancer patients.

METHODS

Patients with lung cancer who had a confirmed histology and cytology diagnosis were enrolled in the study. SLC polymorphisms were assessed by Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) for variations in SLC19A1 (G⁸⁰ A), SLCO1B1 (A³⁸⁸ G, T⁵²¹ C), and SLCO1B3 (A^1683-5676 G).

RESULTS AND DISCUSSION

Our results showed that mutant genotype for SLC19A1 G⁸⁰ A polymorphism had higher median survival time (MST) compared to wild genotype. ADCC patients with mutant genotype showed better survival compared to wild genotype for SLC19A1 G⁸⁰ A. SCLC patients G⁸⁰ A polymorphism showed increased survival in patients with mutant genotype (p = 0.04). In SLCO1B3, A^1683-5676 G patients carrying heterozygous alleles and administered with platinum and docetaxel showed inferior survival (p = 0.006). In T⁵²¹ C variant, patients with carrier genotype had reduced chances of developing anaemia (p = 0.04). Patients with SLC19A1 and SLCO1B3 variants showed lower incidence of thrombocytopenia and nephrotoxicity.

WHAT IS NEW AND CONCLUSION

Our findings imply that Solute Carrier gene polymorphisms modulate the overall survival in lung cancer patients undergoing platin-based doublet chemotherapy, also these polymorphisms have a modifying impact on the associated adverse events/toxicity.

Involvement of Transporters in Intestinal Drug-Drug Interactions of Oral Targeted Anticancer Drugs Assessed by Changes in Drug Absorption Time

(1) Background: Oral targeted anticancer drugs are victims of presystemic pharmacokinetic drug−drug interactions (DDI). Identification of the nature of these DDIs, i.e., enzyme-based or/and transporter-based, is challenging, since most of these drugs are substrates of intestinal and/or hepatic cytochrome P-450 enzymes and of intestinal membrane transporters. (2) Methods: Variations in mean absorption time (MAT) between DDIs and control period (MAT ratios < 0.77 or >1.30) have been proposed to implicate transporters in DDIs at the intestinal level. This methodology has been applied to a large set of oral targeted anticancer drugs (n = 54, involved in 77 DDI studies), from DDI studies available either in the international literature and/or in publicly accessible FDA files. (3) Results: Significant variations in MAT were evidenced in 33 DDI studies, 12 of which could be explained by modulation of an efflux transporter. In 21 DDI studies, modulation of efflux transporters could not explain the MAT variation, suggesting a possible relevant role of influx transporters in the intestinal absorption. (4) Conclusions: This methodology allows one to suggest the involvement of intestinal transporters in DDIs, and should be used in conjunction with in vitro methodologies to help understanding the origin of DDIs.

Stereoselectivity in the Membrane Transport of Phenylethylamine Derivatives by Human Monoamine Transporters and Organic Cation Transporters 1, 2, and 3

Stereoselectivity is well known and very pronounced in drug metabolism and receptor binding. However, much less is known about stereoselectivity in drug membrane transport. Here, we characterized the stereoselective cell uptake of chiral phenylethylamine derivatives by human monoamine transporters (NET, DAT, and SERT) and organic cation transporters (OCT1, OCT2, and OCT3). Stereoselectivity differed extensively between closely related transporters. High-affinity monoamine transporters (MATs) showed up to 2.4-fold stereoselective uptake of norepinephrine and epinephrine as well as of numerous analogs. While NET and DAT preferentially transported (S)-norepinephrine, SERT preferred the (R)-enantiomer. In contrast, NET and DAT showed higher transport for (R)-epinephrine and SERT for (S)-epinephrine. Generally, MAT stereoselectivity was lower than expected from their high affinity to several catecholamines and from the high stereoselectivity of some inhibitors used as antidepressants. Additionally, the OCTs differed strongly in their stereoselectivity. While OCT1 showed almost no stereoselective uptake, OCT2 was characterized by a roughly 2-fold preference for most (R)-enantiomers of the phenylethylamines. In contrast, OCT3 transported norphenylephrine and phenylephrine with 3.9-fold and 3.3-fold preference for their (R)-enantiomers, respectively, while the para-hydroxylated octopamine and synephrine showed no stereoselective OCT3 transport. Altogether, our data demonstrate that stereoselectivity is highly transporter-to-substrate specific and highly diverse even between homologous transporters.

Substrates and Inhibitors of the Organic Cation Transporter 3 and Comparison with OCT1 and OCT2

Organic cation transporters (OCTs) 1, 2, and 3 facilitate cellular uptake of structurally diverse endogenous and exogenous substances. However, their substrate and inhibitor specificity are not fully understood. We performed a broad in vitro screening for OCT3 substrates and inhibitors, allowing us to compare the substrate spectra and to study the relationship between transport and inhibition of transport. Generally, substrates were smaller and more hydrophilic than OCT3 inhibitors. The best model-based predictor of transport was the positive charge, while the best predictor of inhibition was the aromatic ring count. OCT3 inhibition was well correlated between different model substrates. Substrates of OCT3 were mainly weak inhibitors, and the best inhibitors were not substrates. As tested with 264 substances, OCT3 transport had significantly more overlap with OCT2 than OCT1. Our data further substantiate that specificity of OCT transport varies with minor substitutions rather than with the general scaffolds of substrates.

Altered Bioavailability and Pharmacokinetics in Crohn's Disease: Capturing Systems Parameters for PBPK to Assist with Predicting the Fate of Orally Administered Drugs

Backgrond and Objective

Crohn’s disease (CD) is a chronic inflammatory bowel disease that affects a wide age range. Hence, CD patients receive a variety of drugs over their life beyond those used for CD itself. The changes to the integrity of the intestine and its drug metabolising enzymes and transporters (DMETs) can alter the oral bioavailability of drugs. However, there are other changes in systems parameters determining the fate of drugs in CD, and understanding these is essential for dose adjustment in patients with CD.

Methods

The current analysis gathered all the available clinical data on the kinetics of drugs in CD (by March 2021), focusing on orally administered small molecule drugs. A meta-analysis of the systems parameters affecting oral drug pharmacokinetics was conducted. The systems information gathered on intestine, liver and blood proteins and other physiological parameters was incorporated into a physiologically based pharmacokinetic (PBPK) platform to create a virtual population of CD patients, with a view for guiding dose adjustment in the absence of clinical data in CD.

Results

There were no uniform trends in the reported changes in reported oral bioavailability. The nature of the drug as well as the formulation affected the direction and magnitude of variation in kinetics in CD patients relative to healthy volunteers. Even for the same drug, the reported changes in exposure varied, possibly due to a lack of distinction between the activity states of CD. The highest alteration was seen with S-verapamil and midazolam, 8.7- and 5.3-fold greater exposure, respectively, in active CD patients relative to healthy volunteers. Only one report was available on liver DMETs in CD, and indicated reduced CYP3A4 activity. In a number of reports, mRNA expression of DMETs in the ileum and colon of CD patients was measured, focussing on P-glycoprotein (p-gp) transporter and CYP3A4 enzyme, and showed contradictory results. No data were available on protein expression in duodenum and jejunum despite their dominant role in oral drug absorption.

Conclusion

There are currently inadequate dedicated clinical or quantitative proteomic studies in CD to enable predictive PBPK models with high confidence and adequate verification. The PBPK models for CD with the available systems parameters were able to capture the major physiological influencers and the gaps to be filled by future research. Quantification of DMETs in the intestine and the liver in CD is warranted, alongside well-defined clinical drug disposition studies with a number of index drugs as biomarkers of changes in DMETs in these patients, to avoid large-scale dedicated studies for every drug to determine the effects of disease on the drug’s metabolism and disposition and the consequential safety and therapeutic concerns.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40262-022-01169-4.

Co-Delivery of siRNA and Chemotherapeutic Drug Using 2C5 Antibody-Targeted Dendrimer-Based Mixed Micelles for Multidrug Resistant Cancers

Multidrug resistance (MDR) observed in tumors significantly hinders the efficacy of chemotherapy. Downregulation of efflux proteins, such as P-glycoprotein (P-gp), using small interfering RNA (siRNA) can be an effective way to minimize the resistance in tumors. In this study, monoclonal antibody 2C5 (mAb 2C5)-PEG_7k-DOPE conjugates were post-inserted into the mixed dendrimer micelles containing generation 4 (G4) polyamidoamine (PAMAM)-PEG_2k-DOPE and PEG_5k-DOPE. The inherent amphiphilic nature of DOPE conjugates causes the copolymers to self-assemble to form a micelle, which can encapsulate hydrophobic chemotherapeutic drugs in its core. The siRNA electrostatically binds to the cationic charges on the G4 PAMAM dendrimer. The tumor-specific mAb 2C5 on the surface of these nano-preparations resulted in improved tumor targeting. This active targeting to tumors can cause increase in the drug and siRNA accumulation at the tumor site, and thereby minimizing the off-target effects. The micelles were shown to have higher cellular association and effectiveness in vitro. The immunomicelle preparation was also tested for cytotoxicity in breast (MDA-MB-231) and ovarian (SKOV-3TR) MDR cancer cell lines.

The Mechanism of Action of Biguanides: New Answers to a Complex Question

Biguanides are a family of antidiabetic drugs with documented anticancer properties in preclinical and clinical settings. Despite intensive investigation, how they exert their therapeutic effects is still debated. Many studies support the hypothesis that biguanides inhibit mitochondrial complex I, inducing energy stress and activating compensatory responses mediated by energy sensors. However, a major concern related to this “complex” model is that the therapeutic concentrations of biguanides found in the blood and tissues are much lower than the doses required to inhibit complex I, suggesting the involvement of additional mechanisms. This comprehensive review illustrates the current knowledge of pharmacokinetics, receptors, sensors, intracellular alterations, and the mechanism of action of biguanides in diabetes and cancer. The conditions of usage and variables affecting the response to these drugs, the effect on the immune system and microbiota, as well as the results from the most relevant clinical trials in cancer are also discussed.

Multidrug Resistance in Cancer: Understanding Molecular Mechanisms, Immunoprevention and Therapeutic Approaches

Cancer is one of the leading causes of death worldwide. Several treatments are available for cancer treatment, but many treatment methods are ineffective against multidrug-resistant cancer. Multidrug resistance (MDR) represents a major obstacle to effective therapeutic interventions against cancer. This review describes the known MDR mechanisms in cancer cells and discusses ongoing laboratory approaches and novel therapeutic strategies that aim to inhibit, circumvent, or reverse MDR development in various cancer types. In this review, we discuss both intrinsic and acquired drug resistance, in addition to highlighting hypoxia- and autophagy-mediated drug resistance mechanisms. Several factors, including individual genetic differences, such as mutations, altered epigenetics, enhanced drug efflux, cell death inhibition, and various other molecular and cellular mechanisms, are responsible for the development of resistance against anticancer agents. Drug resistance can also depend on cellular autophagic and hypoxic status. The expression of drug-resistant genes and the regulatory mechanisms that determine drug resistance are also discussed. Methods to circumvent MDR, including immunoprevention, the use of microparticles and nanomedicine might result in better strategies for fighting cancer.

Significance of the Vitamin D Receptor on Crosstalk with Nuclear Receptors and Regulation of Enzymes and Transporters

The vitamin D receptor (VDR), in addition to other nuclear receptors, the pregnane X receptor (PXR) and constitutive androstane receptor (CAR), is involved in the regulation of enzymes, transporters and receptors, and therefore intimately affects drug disposition, tissue health, and the handling of endogenous and exogenous compounds. This review examines the role of 1α,25-dihydroxyvitamin D₃ or calcitriol, the natural VDR ligand, on activation of the VDR and its crosstalk with other nuclear receptors towards the regulation of enzymes and transporters, notably many of the cytochrome P450s including CYP3A4 and sulfotransferase 2A1 (SULT2A1) as well as cholesterol 7α-hydroxylase (CYP7A1). Moreover, the VDR upregulates the intestinal channel, TRPV6, for calcium absorption, LDL receptor-related protein 1 (LRP1) and receptor for advanced glycation end products (RAGE) in brain for β-amyloid peptide efflux and influx, the sodium phosphate transporters (NaP_i), the apical sodium-dependent bile acid transporter (ASBT) and organic solute transporters (OSTα-OSTβ) for bile acid absorption and efflux, respectively, the renal organic anion transporter 3 (OAT3) and several of the ATP-binding cassette protein transporters-the multidrug resistance protein 1 (MDR1) and the multidrug resistance-associated proteins (MRPs). Hence, the role of the VDR is increasingly being recognized for its therapeutic potential and pharmacologic activity, giving rise to drug-drug interactions (DDI). Therapeutically, ligand-activated VDR shows anti-inflammatory effects towards the suppression of inflammatory mediators, improves cognition by upregulating amyloid-beta (Aβ) peptide clearance in brain, and maintains phosphate, calcium, and parathyroid hormone (PTH) balance and kidney function and bone health, demonstrating the crucial roles of the VDR in disease progression and treatment of diseases.

Metabolic conjugation reduces in vitro toxicity of the flavonoid nevadensin

The present study focuses on the association between metabolic capacity and toxicity of the natural occurring flavonoid nevadensin in vitro. Human colon (HT29), liver (HepG2) and bone marrow (KG1) carcinoma cells were used and strong cell line dependent differences in toxic effect strength were found. HepG2 and KG1 cells were more sensitive against nevadensin treatment in comparison to HT29 cells. High resolution mass spectrometry experiments showed that nevadensin is rapidly glucuronidated in HT29 cells, whereas KG1 cells do not metabolize nevadensin, thus glucuronidation was supposed to be a crucial metabolic pathway in vitro. To proof this suggestion, nevadensin glucuronides were isolated from pig liver microsomes und structurally elucidated via NMR spectroscopy. In HepG2 cells a cellular enrichment of nevadensin itself as well as nevadensin-7-O-glucuronide was determined by tandem mass spectrometry. A proteomic screening of uridine 5'-diphospho (UDP)-glucuronosyltransferase (UGT) in HT29 and HepG2 cells provided first hints that the isoforms UGT1A6 and UGT1A1 are responsible for nevadensin glucuronidation. Additionally, nevadensin was found to be a potent SULT inhibitor in HepG2 cells. In sum, the present study clearly illustrates the importance of obtaining detailed information about metabolic competence of cell lines which should be considered in the evaluation of toxic endpoints.

Transepithelial delivery of insulin conjugated with phospholipid-mimicking polymers via biomembrane fusion-mediated transcellular pathways

Epithelial barriers that seal cell gaps by forming tight junctions to prevent the free permeation of nutrients, electrolytes, and drugs, are essential for maintaining homeostasis in multicellular organisms. The development of nanocarriers that can permeate epithelial tissues without compromising barrier function is key for establishing a safe and efficient drug delivery system (DDS). Previously, we have demonstrated that a water-soluble phospholipid-mimicking random copolymer, poly(2-methacryloyloxyethyl phosphorylcholine₃₀-random-n‑butyl methacrylate₇₀) (PMB30W), enters the cytoplasm of live cells by passive diffusion manners, without damaging the cell membranes. The internalization mechanism was confirmed to be amphiphilicity-induced membrane fusion. In the present study, we demonstrated energy-independent permeation of PMB30W through the model epithelial barriers of Madin-Darby canine kidney (MDCK) cell monolayers in vitro. The polymer penetrated epithelial MDCK monolayers via transcellular pathways without breaching the barrier functions. This was confirmed by our unique assay that can monitor the leakage of the proton as the smallest indicator across the epithelial barriers. Moreover, energy-independent transepithelial permeation was achieved when insulin was chemically conjugated with the phospholipid-mimicking nanocarrier. The bioactivity of insulin as a growth factor was found to be maintained even after translocation. These fundamental findings may aid the establishment of transepithelial DDS with advanced drug efficiency and safety. STATEMENT OF SIGNIFICANCE: A nanocarrier that can freely permeate epithelial tissues without compromising barrier function is key for successful DDS. Existing strategies mainly rely on paracellular transport associated with tight junction breakdown or transcellular transport via transporter recognition-mediated active uptake. These approaches raise concerns about efficiency and safety. In this study, we performed non-endocytic permeation of phospholipid-mimicking polymers through the model epithelial barriers in vitro. The polymer penetrated via transcytotic pathways without breaching the barriers of biomembrane and tight junction. Moreover, transepithelial permeation occurred when insulin was covalently attached to the nanocarrier. The bioactivity of insulin was maintained even after translocation. The biomimetic design of nanocarrier may realize safe and efficient transepithelial DDS.

Relationships between Inhibition, Transport and Enhanced Transport via the Organic Cation Transporter 1

The organic cation transporter 1 (OCT1, SLC22A1) transports a large number of structurally diverse endogenous and exogenous substrates. There are numerous known competitive and non-competitive inhibitors of OCT1, but there are no studies systematically analyzing the relationship between transport, stimulation, and inhibition. Here, we tested in vitro OCT1 inhibition by OCT1 substrates and transport of OCT1 inhibitors under uniform analytical conditions. Beyond inhibition testing with two model substrates, we tested nine additional OCT1 substrates for their mutual inhibition. Inhibition of ASP⁺ uptake by most OCT1 substrates was weak. The model substrate sumatriptan, with its moderately stronger inhibitability, was used to confirm this. Interestingly, OCT1 substrates exhibiting stronger OCT1 inhibition were mainly biaromatic β-agonistic drugs, such as dobutamine, fenoterol, ractopamine and ritodrine. Biaromatic organic cations were both, strong inhibitors and good substrates, but many OCT1 substrates showed little pairwise inhibition. Surprisingly, sumatriptan did significantly enhance dobutamine uptake. This effect was concentration dependent and additional experiments indicated that efflux inhibition may be one of the underlying mechanisms. Our data suggests, that OCT1 substrates are mainly weak OCT1 inhibitors and among those inhibiting well, noncompetitive inhibition could be responsible. Weak competitive inhibition confirms that OCT1 inhibition screenings poorly predict OCT1 substrates. Additionally, we showed that the OCT1 substrate sumatriptan can enhance uptake of some other OCT1 substrates. OCT1 transport stimulation was already observed earlier but is still poorly understood. Low OCT1 uptake inhibition and strong OCT1 efflux inhibition could be mechanisms exploitable for enhancing transport.

Toward Xeno-Free Differentiation of Human Induced Pluripotent Stem Cell-Derived Small Intestinal Epithelial Cells

The small intestinal epithelium has an important role in nutrition, but also in drug absorption and metabolism. There are a few two-dimensional (2D) patient-derived induced pluripotent stem cell (iPSC)-based intestinal models enabling easy evaluation of transcellular transport. It is known that animal-derived components induce variation in the experimental outcomes. Therefore, we aimed to refine the differentiation protocol by using animal-free components. More specifically, we compared maturation of 2D-cultured iPCSs toward small intestinal epithelial cells when cultured either with or without serum, and either on Geltrex or on animal-free, recombinant laminin-based substrata. Differentiation status was characterized by qPCR, immunofluorescence imaging, and functionality assays. Our data suggest that differentiation toward definitive endoderm is more efficient without serum. Both collagen- and recombinant laminin-based coating supported differentiation of definitive endoderm, posterior definitive endoderm, and small intestinal epithelial cells from iPS-cells equally well. Small intestinal epithelial cells differentiated on recombinant laminin exhibited slightly more enterocyte specific cellular functionality than cells differentiated on Geltrex. Our data suggest that functional small intestinal epithelial cells can be generated from iPSCs in serum-free method on xeno-free substrata. This method is easily converted to an entirely xeno-free method.

In Vitro Evaluation of P-gp-Mediated Drug-Drug Interactions Using the RPTEC/TERT1 Human Renal Cell Model

BACKGROUND AND OBJECTIVES

In vitro evaluation of the P-glycoprotein (P-gp) inhibitory potential is an important issue when predicting clinically relevant drug-drug interactions (DDIs). Located within all physiological barriers, including intestine, liver, and kidneys, P-gp plays a major role in the pharmacokinetics of various therapeutic classes. However, few data are available about DDIs involving renal transporters during the active tubular secretion of drugs. In this context, the present study was designed to investigate the application of the human renal cell line RPTEC/TERT1 to study drug interactions mediated by P-gp.

METHODS

The P-gp inhibitory potentials of a panel of drugs were first determined by measuring the intracellular accumulation of rhodamine 123 in RPTEC/TERT1 cells. Then four drugs were selected to assess the half-maximal inhibitor concentration (IC50) values by measuring the intracellular accumulation of two P-gp-substrate drugs, apixaban and rivaroxaban. Finally, according to the FDA guidelines, the [I₁]/IC50 ratio was calculated for each combination of drugs to assess the clinical relevance of the DDIs.

RESULTS

The data showed that drugs which are known P-gp inhibitors, including cyclosporin A, ketoconazole, and verapamil, caused great increases in rhodamine 123 retention, whereas noninhibitors did not affect the intracellular accumulation of the P-gp substrate. The determined IC50 values were in accordance with the inhibition profiles observed in the rhodamine 123 accumulation assays, confirming the reliability of the RPTEC/TERT1 model.

CONCLUSIONS

Taken together, the data demonstrate the feasibility of the application of the RPTEC/TERT1 model for evaluating the P-gp inhibitory potentials of drugs and consequently predicting renal drug interactions.

All layers matter: Innovative three-dimensional epithelium-stroma-endothelium intestinal model for reliable permeability outcomes

Drug development is an ever-growing field, increasingly requesting reliable in vitro tools to speed up early screening phases, reducing the need for animal experiments. In oral delivery, understanding the absorption pattern of a new drug in the small intestine is paramount. Classical two-dimensional (2D) in vitro models are generally too simplistic and do not accurately represent native tissues. The main goal of this work was to develop an advanced three-dimensional (3D) in vitro intestinal model to test absorption in a more reliable manner, by better mimicking the native environment. The 3D model is composed of a collagen-based stromal layer with embedded fibroblasts mimicking the intestinal lamina propria and providing support for the epithelium, composed of enterocytes and mucus-secreting cells. An endothelial layer, surrogating the absorptive capillary network, is also present. The cellular crosstalk between the different cells present in the model is unveiled, disclosing key players, namely those involved in the contraction of collagen by fibroblasts. The developed 3D model presents lower levels of P-glycoprotein (P-gp) and Multidrug Resistance Protein 2 (MRP2) efflux transporters, which are normally overexpressed in traditional Caco-2 models, and are paramount in the absorption of many compounds. This, allied with transepithelial electrical resistance (TEER) values closer to physiological ranges, leads to improved and more reliable permeability outcomes, which are observed when comparing our results with in vivo data.

Urate transport in health and disease

Circulation of urate levels is determined by the balance between urate production and excretion, homeostasis regulated by the function of urate transporters in key epithelial tissues and cell types. Our understanding of these physiological processes and identification of the genes encoding the urate transporters has advanced significantly, leading to a greater ability to predict risk for urate-associated diseases and identify new therapeutics that directly target urate transport. Here, we review the identified urate transporters and their organization and function in the renal tubule, the intestinal enterocytes, and other important cell types to provide a fuller understanding of the complicated process of urate homeostasis and its role in human diseases. Furthermore, we review the genetic tools that provide an unbiased catalyst for transporter identification as well as discuss the role of transporters in determining the observed significant gender differences in urate-associated disease risk.

Current Trends and Research Topics Regarding Intestinal Organoids: An Overview Based on Bibliometrics

Currently, research on intestinal diseases is mainly based on animal models and cell lines in monolayers. However, these models have drawbacks that limit scientific advances in this field. Three-dimensional (3D) culture systems named organoids are emerging as a reliable research tool for recapitulating the human intestinal epithelium and represent a unique platform for patient-specific drug testing. Intestinal organoids (IOs) are crypt–villus structures that can be derived from adult intestinal stem cells (ISCs), embryonic stem cells (ESCs), or induced pluripotent stem cells (iPSCs) and have the potential to serve as a platform for individualized medicine and research. However, this emerging field has not been bibliometric summarized to date. Here, we performed a bibliometric analysis of the Web of Science Core Collection (WoSCC) database to evaluate 5,379 publications concerning the use of organoids; the studies were divided into four clusters associated with the current situation and future directions for the application of IOs. Based on the results of our bibliometric analysis of IO applications, we systematically summarized the latest advances and analyzed the limitations and prospects.

Transporter-mediated drug-drug interactions: advancement in models, analytical tools, and regulatory perspective

Drug-drug interactions mediated by transporters are a serious clinical concern hence a tremendous amount of work has been done on the characterization of the transporter-mediated proteins in humans and animals. The underlying mechanism for the transporter-mediated drug-drug interaction is the induction or inhibition of the transporter which is involved in the cellular uptake and efflux of drugs. Transporter of the brain, liver, kidney, and intestine are major determinants that alter the absorption, distribution, metabolism, excretion profile of drugs, and considerably influence the pharmacokinetic profile of drugs. As a consequence, transporter proteins may affect the therapeutic activity and safety of drugs. However, mounting evidence suggests that many drugs change the activity and/or expression of the transporter protein. Accordingly, evaluation of drug interaction during the drug development process is an integral part of risk assessment and regulatory requirements. Therefore, this review will highlight the clinical significance of the transporter, their role in disease, possible cause underlying the drug-drug interactions using analytical tools, and update on the regulatory requirement. The recent in-silico approaches which emphasize the advancement in the discovery of drug-drug interactions are also highlighted in this review. Besides, we discuss several endogenous biomarkers that have shown to act as substrates for many transporters, which could be potent determinants to find the drug-drug interactions mediated by transporters. Transporter-mediated drug-drug interactions are taken into consideration in the drug approval process therefore we also provided the extrapolated decision trees from in-vitro to in-vivo, which may trigger the follow-up to clinical studies.

Current Understanding of the Intestinal Absorption of Nucleobases and Analogs

It has long been suggested that a Na⁺-dependent carrier-mediated transport system is involved in the absorption of nucleobases and analogs, including some drugs currently in therapeutic use, for their uptake at the brush border membrane of epithelial cells in the small intestine, mainly based on studies in non-primate experimental animals. The presence of this transport system was indeed proved by the recent identification of sodium-dependent nucleobase transporter 1 (SNBT1/Slc23a4) as its molecular entity in rats. However, this transporter has been found to be genetically deficient in humans and higher primates. Aware of this deficiency, we need to revisit the issue of the absorption of these compounds in the human small intestine so that we can understand the mechanisms and gain information to assure the more rational use and development of drugs analogous to nucleobases. Here, we review the current understanding of the intestinal absorption of nucleobases and analogs. This includes recent knowledge about the efflux transport of those compounds across the basolateral membrane when exiting epithelial cells, following brush border uptake, in order to complete the overall absorption process; the facilitative transporters of equilibrative nucleoside transporter 1 (ENT1/SLC29A1) and equilibrative nucleobase transporter 1 (ENBT1/SLC43A3) may be involved in that in many animal species, including human and rat, without any major species differences.

Potential Applications of Chitosan-Based Nanomaterials to Surpass the Gastrointestinal Physiological Obstacles and Enhance the Intestinal Drug Absorption

The small intestine provides the major site for the absorption of numerous orally administered drugs. However, before reaching to the systemic circulation to exert beneficial pharmacological activities, the oral drug delivery is hindered by poor absorption/metabolic instability of the drugs in gastrointestinal (GI) tract and the presence of the mucus layer overlying intestinal epithelium. Therefore, a polymeric drug delivery system has emerged as a robust approach to enhance oral drug bioavailability and intestinal drug absorption. Chitosan, a cationic polymer derived from chitin, and its derivatives have received remarkable attention to serve as a promising drug carrier, chiefly owing to their versatile, biocompatible, biodegradable, and non-toxic properties. Several types of chitosan-based drug delivery systems have been developed, including chemical modification, conjugates, capsules, and hybrids. They have been shown to be effective in improving intestinal assimilation of several types of drugs, e.g., antidiabetic, anticancer, antimicrobial, and anti-inflammatory drugs. In this review, the physiological challenges affecting intestinal drug absorption and the effects of chitosan on those parameters impacting on oral bioavailability are summarized. More appreciably, types of chitosan-based nanomaterials enhancing intestinal drug absorption and their mechanisms, as well as potential applications in diabetes, cancers, infections, and inflammation, are highlighted. The future perspective of chitosan applications is also discussed.

In vitro models replicating the human intestinal epithelium for absorption and metabolism studies: A systematic review

Absorption, distribution, metabolism and excretion (ADME) studies represent a fundamental step in the early stages of drug discovery. In particular, the absorption of orally administered drugs, which occurs at the intestinal level, has gained attention since poor oral bioavailability often led to failures for new drug approval. In this context, several in vitro preclinical models have been recently developed and optimized to better resemble human physiology in the lab and serve as an animal alternative to accomplish the 3Rs principles. However, numerous models are ineffective in recapitulating the key features of the human small intestine epithelium and lack of prediction potential for drug absorption and metabolism during the preclinical stage. In this review, we provide an overview of in vitro models aimed at mimicking the intestinal barrier for pharmaceutical screening. After briefly describing how the human small intestine works, we present i) conventional 2D synthetic and cell-based systems, ii) 3D models replicating the main features of the intestinal architecture, iii) micro-physiological systems (MPSs) reproducing the dynamic stimuli to which cells are exposed in the native microenvironment. In this review, we will highlight the benefits and drawbacks of the leading intestinal models used for drug absorption and metabolism studies.