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Jakobsen S, Nielsen CU. Exploring Amino Acid Transporters as Therapeutic Targets for Cancer: An Examination of Inhibitor Structures, Selectivity Issues, and Discovery Approaches. Pharmaceutics 2024; 16:197. [PMID: 38399253 PMCID: PMC10893028 DOI: 10.3390/pharmaceutics16020197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 01/18/2024] [Accepted: 01/28/2024] [Indexed: 02/25/2024] Open
Abstract
Amino acid transporters are abundant amongst the solute carrier family and have an important role in facilitating the transfer of amino acids across cell membranes. Because of their impact on cell nutrient distribution, they also appear to have an important role in the growth and development of cancer. Naturally, this has made amino acid transporters a novel target of interest for the development of new anticancer drugs. Many attempts have been made to develop inhibitors of amino acid transporters to slow down cancer cell growth, and some have even reached clinical trials. The purpose of this review is to help organize the available information on the efforts to discover amino acid transporter inhibitors by focusing on the amino acid transporters ASCT2 (SLC1A5), LAT1 (SLC7A5), xCT (SLC7A11), SNAT1 (SLC38A1), SNAT2 (SLC38A2), and PAT1 (SLC36A1). We discuss the function of the transporters, their implication in cancer, their known inhibitors, issues regarding selective inhibitors, and the efforts and strategies of discovering inhibitors. The goal is to encourage researchers to continue the search and development within the field of cancer treatment research targeting amino acid transporters.
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Affiliation(s)
- Sebastian Jakobsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense, Denmark
| | - Carsten Uhd Nielsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense, Denmark
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Rasmussen AD, Truchot N, Dyssegaard A, Fant P. Retinal and Systemic Toxicity of Vigabatrin Is Driven by the S-Enantiomer in the Long Evans Rat. Toxicol Pathol 2023; 51:126-134. [PMID: 37401471 DOI: 10.1177/01926233231179147] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/05/2023]
Abstract
In this study, we assessed the toxicity and toxicokinetics of racemic vigabatrin and its S- and R-enantiomers (vigabatrin consists of 50:50% of the two enantiomers) by administering doses of the three test articles to male Long Evans rats via oral gavage. The animals were housed under high-intensity light conditions and the study consisted of an escalating dose phase and a 21-day fixed-dose phase. Systemic toxicity of vigabatrin appears to be due to the Vig-S-enantiomer only, as increasing doses of Vig-S or Vig-RS caused body weight loss, decreased food consumption, and affected activity. Administration of the Vig-R-enantiomer did not cause any such effects. Systemic exposure to R- and S-enantiomers was approximately linear with dose. Compared to administration of the racemate, there appeared to be a tendency for animals to take up higher amounts of Vig-R and lower amounts of Vig-S when administered as enantiomer. Bilateral retinal atrophy was observed in the fixed-dose phase in rats receiving Vig-S (either alone or as part of Vig-RS) and was characterized by irregular thinning and disorganization of the outer nuclear layer and thinning of the photoreceptor layer. The administration of the R-enantiomer alone did not cause any microscopic retinal change.
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Affiliation(s)
| | - Nathalie Truchot
- Charles River Laboratories France Safety Assessment, Saint-Germain-Nuelles, France
| | | | - Pierluigi Fant
- Charles River Laboratories France Safety Assessment, Saint-Germain-Nuelles, France
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ACE2 and gut amino acid transport. Clin Sci (Lond) 2020; 134:2823-2833. [PMID: 33140827 DOI: 10.1042/cs20200477] [Citation(s) in RCA: 58] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Revised: 10/13/2020] [Accepted: 10/15/2020] [Indexed: 12/22/2022]
Abstract
ACE2 is a type I membrane protein with extracellular carboxypeptidase activity displaying a broad tissue distribution with highest expression levels at the brush border membrane (BBM) of small intestine enterocytes and a lower expression in stomach and colon. In small intestinal mucosa, ACE2 mRNA expression appears to increase with age and to display higher levels in patients taking ACE-inhibitors (ACE-I). There, ACE2 protein heterodimerizes with the neutral amino acid transporter Broad neutral Amino acid Transporter 1 (B0AT1) (SLC6A19) or the imino acid transporter Sodium-dependent Imino Transporter 1 (SIT1) (SLC6A20), associations that are required for the surface expression of these transport proteins. These heterodimers can form quaternary structures able to function as binding sites for SARS-CoV-2 spike glycoproteins. The heterodimerization of the carboxypeptidase ACE2 with B0AT1 is suggested to favor the direct supply of substrate amino acids to the transporter, but whether this association impacts the ability of ACE2 to mediate viral infection is not known. B0AT1 mutations cause Hartnup disorder, a condition characterized by neutral aminoaciduria and, in some cases, pellagra-like symptoms, such as photosensitive rash, diarrhea, and cerebellar ataxia. Correspondingly, the lack of ACE2 and the concurrent absence of B0AT1 expression in small intestine causes a decrease in l-tryptophan absorption, niacin deficiency, decreased intestinal antimicrobial peptide production, and increased susceptibility to inflammatory bowel disease (IBD) in mice. Thus, the abundant expression of ACE2 in small intestine and its association with amino acid transporters appears to play a crucial role for the digestion of peptides and the absorption of amino acids and, thereby, for the maintenance of structural and functional gut integrity.
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Nielsen CU, Pedersen M, Müller S, Kæstel T, Bjerg M, Ulaganathan N, Nielsen S, Carlsen KL, Nøhr MK, Holm R. Inhibitory Effects of 17-α-Ethinyl-Estradiol and 17-β-Estradiol on Transport Via the Intestinal Proton-Coupled Amino Acid Transporter (PAT1) Investigated In Vitro and In Vivo. J Pharm Sci 2020; 110:354-364. [PMID: 32835702 DOI: 10.1016/j.xphs.2020.08.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Revised: 08/12/2020] [Accepted: 08/18/2020] [Indexed: 11/24/2022]
Abstract
The proton-coupled amino acid transporter, PAT1, is known to be responsible for intestinal absorption drug substances such as gaboxadol and vigabatrin. The aim of the present study was to investigate, if 17-α-ethinyl-estradiol (E-E2) and 17-β-estradiol (E) inhibit PAT1-mediated intestinal absorption of proline and taurine in vitro in Caco-2 cells and in vivo using Sprague-Dawley rats to assess the potential for taurine-drug interactions. E and E-E2 inhibited the PAT1-mediated uptake of proline and taurine in Caco-2 cells with IC50 values of 10.0-50.0 μM without major effect on other solute carriers such as the taurine transporter (TauT), di/tri-peptide transporter (PEPT1), and serotonin transporter (SERT1). In PAT1-expressing oocytes E and E-E2 were non-translocated inhibitors. In Caco-2 cells, E and E-E2 lowered the maximal uptake capacity of PAT1 in a non-competitive manner. Likewise, the transepithelial permeability of proline and taurine was reduced in presence of E and E-E2. In male Sprague Dawley rats pre-dosed with E-E2 a decreased maximal plasma concentration (Cmax) of taurine and increased the time (tmax) to reach this was indicated, suggesting the possibility for an in vivo effect on the absorption of PAT1 substrates. In conclusion, 17-α-ethinyl-estradiol and 17-β-estradiol were identified as non-translocated and non-competitive inhibitors of PAT1.
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Affiliation(s)
- Carsten Uhd Nielsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark.
| | - Maria Pedersen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Stefanie Müller
- Department of Pharmacy, Faculty of Health and Medical Sciences, Universitetsparken 2, DK-2100 Copenhagen, Denmark
| | - Thea Kæstel
- Department of Pharmacy, Faculty of Health and Medical Sciences, Universitetsparken 2, DK-2100 Copenhagen, Denmark
| | - Maria Bjerg
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Nithiya Ulaganathan
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Salli Nielsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Krestine Lundgaard Carlsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Martha Kampp Nøhr
- Department of Pharmacy, Faculty of Health and Medical Sciences, Universitetsparken 2, DK-2100 Copenhagen, Denmark
| | - René Holm
- Drug Product Development, Janssen R&D, Johnson & Johnson, Turnhoutseweg 30, 2340 Beerse, Belgium; Department of Science and Environment, Roskilde University, 4000 Roskilde, Denmark
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Police A, Shankar VK, Murthy SN. Role of Taurine Transporter in the Retinal Uptake of Vigabatrin. AAPS PharmSciTech 2020; 21:196. [PMID: 32666325 DOI: 10.1208/s12249-020-01736-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2020] [Accepted: 06/20/2020] [Indexed: 12/18/2022] Open
Abstract
Vigabatrin (VGB) is a first-line drug used for treatment of infantile spasms. On therapeutic dose, VGB accumulates in the retina causing permanent peripheral visual field constriction. The mechanism involved in retinal accumulation of VGB is ambiguous. In the present study, mechanism of VGB transport into retina was evaluated. VGB uptake into retina was studied in vitro using human adult retinal pigment epithelial (ARPE-19) cells as a model for outer blood retinal barrier. The VGB cell uptake studies demonstrated saturation kinetics with Km value of 13.1 mM and uptake was significantly increased at pH 7.4 and hyperosmolar conditions indicating involvement of carrier-mediated Na+-Cl--dependent transporter. In the presence of taurine transporter (TauT) substrates (taurine and GABA) and inhibitor guanidinoethyl sulfonate (GES), the uptake of VGB decreased significantly demonstrating contribution of TauT. The VGB retinal levels in rats were decreased by 1.5- and 1.3-folds on chronic administration of GES and taurine, respectively. In conclusion, this study demonstrated the TauT involvement in VGB uptake and accumulation in retina.
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O'Shea JP, Holm R, O'Driscoll CM, Griffin BT. Food for thought: formulating away the food effect - a PEARRL review. ACTA ACUST UNITED AC 2018; 71:510-535. [PMID: 29956330 DOI: 10.1111/jphp.12957] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Accepted: 06/03/2018] [Indexed: 12/14/2022]
Abstract
OBJECTIVES Co-ingestion of oral dosage forms with meals can cause substantial changes in bioavailability relative to the fasted state. Food-mediated effects on bioavailability can have significant consequences in drug development, regulatory and clinical settings. To date, the primary focus of research has focused on the ability to mechanistically understand the causes and predict the occurrence of these effects. KEY FINDINGS The current review describes the mechanisms underpinning the occurrence of food effects, sheds new insights on the relative frequency for newly licensed medicines and describes the various methods by which they can be overcome. Analysis of oral medicines licensed by either the EMA or FDA since 2010 revealed that over 40% display significant food effects. Due to altered bioavailability, these medicines are often required to be dosed, rather restrictively, in either the fed or the fasted state, which can hinder clinical usefulness. SUMMARY There are clinical and commercial advantages to predicting the presence of food effects early in the drug development process, in order to mitigate this risk of variable food effect bioavailability. Formulation approaches aimed at reducing variable food-dependent bioavailability, through the use of bio-enabling formulations, are an essential tool in addressing this challenge and the latest state of the art in this field are summarised here.
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Affiliation(s)
| | - René Holm
- Drug Product Development, Janssen Research and Development, Johnson and Johnson, Beerse, Belgium
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Nielsen CU, Bjerg M, Ulaganathan N, Holm R. Oral and intravenous pharmacokinetics of taurine in sprague-dawley rats: the influence of dose and the possible involvement of the proton-coupled amino acid transporter, PAT1, in oral taurine absorption. Physiol Rep 2017; 5:5/19/e13467. [PMID: 29038364 PMCID: PMC5641942 DOI: 10.14814/phy2.13467] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2017] [Revised: 08/30/2017] [Accepted: 09/10/2017] [Indexed: 11/24/2022] Open
Abstract
Taurine is involved in various physiological processes, and one of the most abundant amino acids in human. The aim was to investigate the mechanism for intestinal absorption of taurine in vivo using also in vitro mechanistic studies. Taurine absorption was measured in male Sprague‐Dawley rats at 10–997 mg/kg and 1–30 mg/kg for oral and intravenous administration, respectively. Oral absorption was measured in the presence of substrates for the proton‐coupled amino acid transporter, PAT1, that is, 200 mg/kg proline (Pro) and sarcosine (Sar), and in the presence of 2‐Amino‐2‐norbornanecarboxylic acid (BCH) (200 mg/kg). BCH is not an inhibitor of PAT1 or the taurine transporter, TauT, hence it was included as a negative control. In vitro studies investigating the transport mechanism of taurine were conducted in human intestinal Caco‐2 cells. The pharmacokinetic investigations showed that intestinal taurine absorption was not saturable at the investigated doses, but that the time (tmax) to reach the maximal plasma concentration (Cmax) increased with dose. Furthermore, Sar and Pro, but not BCH, decreased taurine Cmax. In vitro it was clearly shown that PAT1 mediated the cellular uptake of taurine and thereby facilitated the transepithelial taurine transport, which could be inhibited by Pro and Sar, but not BCH. In vivo and in vitro results suggest that taurine absorption from the intestine is caused by PAT1.
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Affiliation(s)
- Carsten Uhd Nielsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense M, Denmark
| | - Maria Bjerg
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense M, Denmark
| | - Nithiya Ulaganathan
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense M, Denmark
| | - René Holm
- Pharmaceutical Science and CMC Biologics, H. Lundbeck A/S, Valby, Denmark
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Kuentz M, Holm R, Elder DP. Methodology of oral formulation selection in the pharmaceutical industry. Eur J Pharm Sci 2016; 87:136-63. [DOI: 10.1016/j.ejps.2015.12.008] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Revised: 11/24/2015] [Accepted: 12/06/2015] [Indexed: 12/30/2022]
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Rasmussen RN, Lagunas C, Plum J, Holm R, Nielsen CU. Interaction of GABA-mimetics with the taurine transporter (TauT, Slc6a6) in hyperosmotic treated Caco-2, LLC-PK1 and rat renal SKPT cells. Eur J Pharm Sci 2015; 82:138-46. [PMID: 26631583 DOI: 10.1016/j.ejps.2015.11.020] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Revised: 11/11/2015] [Accepted: 11/25/2015] [Indexed: 10/22/2022]
Abstract
The aim of the present study was to investigate if basic GABA-mimetics interact with the taurine transporter (TauT, Slc6a6), and to find a suitable cell based model that is robust towards extracellular changes in osmolality during uptake studies. Taurine uptake was measured in human Caco-2 cells, porcine LLC-PK1 cells, and rat SKPT cells using radiolabelled taurine. Hyperosmotic conditions were obtained by incubation with raffinose (final osmolality of 500mOsm) for 24h prior to the uptake experiments. Expression of the taurine transporter, TauT, was investigated at the mRNA level by real-time PCR. Uptake of the GABA-mimetics gaboxadol and vigabatrin was investigated in SKPT cells, and quantified by liquid scintillation or HPLC-MS/MS analysis, respectively. The uptake rate of [(3)H]-taurine was Na(+) and Cl(-) and concentration dependent with taurine with an apparent Vmax of 6.3±1.6pmolcm(-2)min(-1) and a Km of 24.9±15.0μM. β-alanine, nipecotic acid, gaboxadol, GABA, vigabatrin, δ-ALA and guvacine inhibited the taurine uptake rate in a concentration dependent manner. The order of affinity for TauT was β-alanine>GABA>nipecotic acid>guvacine>δ-ALA>vigabatrin>gaboxadol with IC50-values of 0.04, 1.07, 2.02, 4.19, 4.94, 31.4 and 39.9mM, respectively. In conclusion, GABA mimetics inhibited taurine uptake in hyperosmotic rat renal SKPT cells. SKPT cells, which seem to be a useful model for investigating taurine transport in the short-term presence of high concentrations of osmolytes. Furthermore, analogues of β-alanine appear to have higher affinities for TauT than GABA-analogues.
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Affiliation(s)
- Rune Nørgaard Rasmussen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK 5230 Odense M, Denmark
| | - Candela Lagunas
- Drug Transporters in ADME, Department of Pharmacy, Faculty of Health and Medical Sciences, Universitetsparken 2, DK 2100, Copenhagen, Denmark
| | - Jakob Plum
- Drug Transporters in ADME, Department of Pharmacy, Faculty of Health and Medical Sciences, Universitetsparken 2, DK 2100, Copenhagen, Denmark
| | - René Holm
- Pharmaceutical Science and CMC Biologics, H. Lundbeck A/S, DK 2500, Valby, Denmark
| | - Carsten Uhd Nielsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK 5230 Odense M, Denmark.
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