PEPT1 is essential for the growth of pancreatic cancer cells: a viable drug target.

PEPT1 is a proton-coupled peptide transporter that is up-regulated in PDAC cell lines and PDXs, with little expression in the normal pancreas. However, the relevance of this up-regulation to cancer progression and the mechanism of up-regulation have not been investigated. Herein, we show that PEPT1 is not just up-regulated in a large panel of PDAC cell lines and PDXs but is also functional and transport-competent. PEPT2, another proton-coupled peptide transporter, is also overexpressed in PDAC cell lines and PDXs, but is not functional due to its intracellular localization. Using glibenclamide as a pharmacological inhibitor of PEPT1, we demonstrate in cell lines in vitro and mouse xenografts in vivo that inhibition of PEPT1 reduces the proliferation of the cancer cells. These findings are supported by genetic knockdown of PEPT1 with shRNA, wherein the absence of the transporter significantly attenuates the growth of cancer cells, both in vitro and in vivo, suggesting that PEPT1 is critical for the survival of cancer cells. We also establish that the tumor-derived lactic acid (Warburg effect) in the tumor microenvironment supports the transport function of PEPT1 in the maintenance of amino acid nutrition in cancer cells by inducing MMPs and DPPIV to generate peptide substrates for PEPT1 and by generating a H+ gradient across the plasma membrane to energize PEPT1. Taken collectively, these studies demonstrate a functional link between PEPT1 and extracellular protein breakdown in the tumor microenvironment as a key determinant of pancreatic cancer growth, thus identifying PEPT1 as a potential therapeutic target for PDAC.

Role of PEPT1in the transport of cinnabar in Caco-2 cells.

Cinnabar, a mercury-containing mineral medicine, has been used as an ingredient in Traditional Chinese Medicines for treatment of various diseases for thousands of years and is still widely used today. The toxicity of cinnabar is much less than other mercury-containing compounds. This study aimed to evaluate the possible role of oligopeptide transporter1 (PEPT1) in intestinal uptake of cinnabar. Thus, the Caco-2 cell model was employed to investigate the differential transport levels and the probable transporter involved in the transport of cinnabar, mercury sulfide (HgS) and mercury chloride (HgCl2). Cells were incubated with the same molar concentration of cinnabar, HgS or HgCl2 and then the inorganic mercury content of apical (AP), cellular and basolateral (BL) side of the cell was measured by ultra-high liquid chromatography-inductively coupled plasma mass spectrometry (UPLC-ICP/MS) after the treatment, respectively. Their transportation levels were also investigated when pH was changed to 5.5 in AP side to define the role of the H+ dependent transporter. Effects of cinnabar, HgS or HgCl2 on transporter mRNA and protein expression levels were assayed by RT-PCR and Western-blot method, respectively. The possible transporter involved in the transport was examined by siRNA silencing and chemical inhibition. The results showed that the levels of inorganic mercury in the BL side for cinnabar and HgS were 49.39% and 30.41% of that in HgCl2 group. The transport levels of cinnabar and HgCl2 were significantly increased when the pH was changed to 5.5 on the AP side as compared with the control group (pH 7.4). Cinnabar significantly decreased the mRNA and protein expression of PEPT1. Transport levels of cinnabar were significantly decreased by PEPT1-siRNA and chemical inhibition of PEPT1. The present study demonstrates that PEPT1 may be an important transporter in the entry of cinnabar into the intestinal epithelium, and intestinal transport levels of cinnabar and HgS was lower than that of HgCl2.

Apically targeted oral micelles exhibit highly efficient intestinal uptake and oral absorption.

INTRODUCTION: Polymeric micelles (PMs) hold promise for improving solubility and oral absorption of poorly soluble drugs. Unfortunately, the oral absorption of PMs is also limited by intestinal epithelium. To improve the oral delivery efficiency of micelles, transporter-mediated micelles could enhance the transport efficiency across the epithelial barrier, and they have attracted more attention. METHODS: Peptide transporter 1 (PepT1)-mediated micelles (Val-PMs/Phe-PMs) were designed by grafting valine (or phenylalanine) onto the surface of curcumin (Cur)-loaded-D-α-tocopheryl polyethylene glycol 1000 succinate micelles (TP-PMs). The oral absorption mechanism and oral bioavailability were further investigated in vitro and in vivo. RESULTS: The cellular study showed that Val-PMs/Phe-PMs had a high PepT1 affinity, resulting in a higher drug uptake and transcellular transport than TP-PMs. In rats, Val-PMs/Phe-PMs exhibited higher intestinal accumulation in the apical side of the intestinal epithelium than TP-PMs, promoting drug diffusion across epithelial barrier. The oral bioavailability of Cur was significantly improved by Val-PMs/Phe-PMs, which was about 10.50- and 3.40-fold greater than that of Cur-Sol and TP-PMs, respectively. CONCLUSION: PepT-1-mediated micelles, using PepT1 as a target on intestinal epithelium, have unique functions with intestine and prove promising for oral delivery of poorly water-soluble drugs.

Sodium caprate enables the blood pressure-lowering effect of Ile-Pro-Pro and Leu-Lys-Pro in spontaneously hypertensive rats by indirectly overcoming PepT1 inhibition.

The tripeptides, Ile-Pro-Pro (IPP) and Leu-Lys-Pro (LKP), inhibit angiotensin-converting enzyme (ACE) resulting in lowered blood pressure. Our hypothesis was that the medium chain fatty acid permeation enhancer, sodium caprate (C10), may prevent the decrease in permeability of the tripeptides when PepT1 is inhibited by glycyl-sarcosine (Gly-Sar), a situation that may occur in the presence of food hydrolysates. Using Caco-2 monolayers and isolated rat jejunal tissue, the apparent permeability coefficients (Papp) of [3H]-IPP and [3H]-LKP were assessed in the presence of Gly-Sar with and without C10. Gly-Sar decreased the Papp of both tripeptides across monolayers and isolated jejunal tissue, but C10 restored it. C10 likely increased the paracellular permeability of the tripeptides, as indicated by immunofluorescence changes in tight junction proteins in Caco-2 monolayers accompanied by a concentration-dependent decrease in transepithelial electrical resistance (TEER). [3H]-IPP and [3H]-LKP were orally-gavaged to normal rats with Gly-Sar, C10, or with a mixture. Plasma levels of both peptides were reduced by Gly-Sar to less than half that of the levels detected in its absence, but were restored when C10 was co-administered. In spontaneously hypertensive rats (SHRs), unlabelled IPP and LKP lowered blood pressure when delivered either by i.v. or oral routes. Oral gavage of Gly-Sar reduced the hypotensive action of peptides in SHRs, but the effect was restored in the presence of C10. In conclusion, there was a reduction in the hypotensive effects of IPP and LKP in SHRs when intestinal PepT1 was inhibited by Gly-Sar, but C10 may circumvent this by enhancing paracellular permeability.

Physiological and therapeutic regulation of glucose homeostasis by upper small intestinal PepT1-mediated protein sensing.

High protein feeding improves glucose homeostasis in rodents and humans with diabetes, but the mechanisms that underlie this improvement remain elusive. Here we show that acute administration of casein hydrolysate directly into the upper small intestine increases glucose tolerance and inhibits glucose production in rats, independently of changes in plasma amino acids, insulin levels, and food intake. Inhibition of upper small intestinal peptide transporter 1 (PepT1), the primary oligopeptide transporter in the small intestine, reverses the preabsorptive ability of upper small intestinal casein infusion to increase glucose tolerance and suppress glucose production. The glucoregulatory role of PepT1 in the upper small intestine of healthy rats is further demonstrated by glucose homeostasis disruption following high protein feeding when PepT1 is inhibited. PepT1-mediated protein-sensing mechanisms also improve glucose homeostasis in models of early-onset insulin resistance and obesity. We demonstrate that preabsorptive upper small intestinal protein-sensing mechanisms mediated by PepT1 have beneficial effects on whole-body glucose homeostasis.

Chemical Modulation of the Human Oligopeptide Transporter 1, hPepT1.

In humans, peptides derived from dietary proteins and peptide-like drugs are transported via the proton-dependent oligopeptide transporter hPepT1 (SLC15A1). hPepT1 is located across the apical membranes of the small intestine and kidney, where it serves as a high-capacity low-affinity transporter of a broad range of di- and tripeptides. hPepT1 is also overexpressed in the colon of inflammatory bowel disease (IBD) patients, where it mediates the transport of harmful peptides of bacterial origin. Therefore, hPepT1 is a drug target for prodrug substrates interacting with intracellular proteins or inhibitors blocking the transport of toxic bacterial products. In this study, we construct multiple structural models of hPepT1 representing different conformational states that occur during transport and inhibition. We then identify and characterize five ligands of hPepT1 using computational methods, such as virtual screening and QM-polarized ligand docking (QPLD), and experimental testing with uptake kinetic measurements and electrophysiological assays. Our results improve our understanding of the substrate and inhibitor specificity of hPepT1. Furthermore, the newly discovered ligands exhibit unique chemotypes, providing a framework for developing tool compounds with optimal intestinal absorption as well as future IBD therapeutics against this emerging drug target.

Inhibitory Potency of Marketed Drugs for Ulcerative Colitis and Crohn's Disease on PEPT1.

We investigate the inhibitory effect of marketed drugs for treatment of inflammatory bowel disease (IBD) such as ulcerative colitis (UC) and Crohn's disease (CD) on the uptake transporters of peptide transporter 1 (PEPT1), which are up-regulated under the inflamed condition. The uptake transport of glycylsarcosine, a typical substrate for PEPT1, was reduced to 60% only by 5-aminosalicylate at the clinically relevant concentration among tested marketed drugs in PEPT1 transfected HEK293 cell lines. These findings suggest that the inhibition of PEPT1, which were up-regulated in inflamed or non-inflamed site on UC and CD patients, contribute to the clinical effect of commercially available drugs for IBD patients through the inhibition of uptake of antigenic proinflammatory oligopeptides such as formyl-methionine (Met)-leucine (Leu)-phenylalanine (Phe) via PEPT1.

Tenapanor administration and the activity of the H+ -coupled transporter PepT1 in healthy volunteers.

AIM: Tenapanor (RDX5791/AZD1722), an inhibitor of gastrointestinal Na+ /H+ exchanger NHE3, is being evaluated for the treatment of patients with constipation-predominant irritable bowel syndrome and the treatment of hyperphosphataemia in patients with chronic kidney disease on dialysis. By reducing intestinal H+ secretion, inhibition of NHE3 by tenapanor could indirectly affect H+ -coupled transporter activity, leading to drug-drug interactions. We investigated the effect of tenapanor on the activity of the H+ -coupled peptide transporter PepT1 via assessment of the pharmacokinetics of cefadroxil - a compound transported by PepT1 - in healthy volunteers. METHODS: In this open-label, two-period crossover, phase 1 study (NCT02140281), 28 volunteers received in random order: a single dose of cefadroxil 500 mg for 1 day; and tenapanor 15 mg twice daily over 4 days followed by single doses of both cefadroxil 500 mg and tenapanor 15 mg on day 5. There was a 4-day washout between treatment periods. RESULTS: Cefadroxil exposure was similar when administered alone or in combination with tenapanor {geometric least-squares mean ratios [(cefadroxil + tenapanor)/cefadroxil] (90% confidence interval): area under the concentration-time curve 93.3 (90.6-96.0)%; maximum concentration in plasma 95.9 (89.8-103)%}. Tenapanor treatment caused a softening of stool consistency and an increase in stool frequency, consistent with its expected pharmacodynamic effect. No safety concerns were identified and tenapanor was not detected in plasma. CONCLUSIONS: These results suggest that tenapanor 15 mg twice daily does not have a clinically relevant impact on the activity of the H+ -coupled transporter PepT1 in humans. This may guide future research on drug-drug interactions involving NHE3 inhibitors.