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      L-Type amino acid transporter 1 as a target for drug delivery

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          Abstract

          Our growing understanding of membrane transporters and their substrate specificity has opened a new avenue in the field of targeted drug delivery. The L-type amino acid transporter 1 (LAT1) has been one of the most extensively investigated transporters for delivering drugs across biological barriers. The transporter is predominantly expressed in cerebral cortex, blood-brain barrier, blood-retina barrier, testis, placenta, bone marrow and several types of cancer. Its physiological function is to mediate Na + and pH independent exchange of essential amino acids: leucine, phenylalanine, etc. Several drugs and prodrugs designed as LAT1 substrates have been developed to improve targeted delivery into the brain and cancer cells. Thus, the anti-parkinsonian drug, L-Dopa, the anti-cancer drug, melphalan and the anti-epileptic drug gabapentin, all used in clinical practice, utilize LAT1 to reach their target site. These examples provide supporting evidence for the utility of the LAT1-mediated targeted delivery of the (pro)drug. This review comprehensively summarizes recent advances in LAT1-mediated targeted drug delivery. In addition, the use of LAT1 is critically evaluated and limitations of the approach are discussed.

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          Most cited references91

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          CATs and HATs: the SLC7 family of amino acid transporters.

          The SLC7 family is divided into two subgroups, the cationic amino acid transporters (the CAT family, SLC7A1-4) and the glycoprotein-associated amino acid transporters (the gpaAT family, SLC7A5-11), also called light chains or catalytic chains of the hetero(di)meric amino acid transporters (HAT). The associated glycoproteins (heavy chains) 4F2hc (CD98) or rBAT (D2, NBAT) form the SLC3 family. Members of the CAT family transport essentially cationic amino acids by facilitated diffusion with differential trans-stimulation by intracellular substrates. In some cells, they may regulate the rate of NO synthesis by controlling the uptake of l-arginine as the substrate for nitric oxide synthase (NOS). The heterodimeric amino acid transporters are, in contrast, quite diverse in terms of substrate selectivity and function (mostly) as obligatory exchangers. Their selectivity ranges from large neutral amino acids (system L) to small neutral amino acids (ala, ser, cys-preferring, system asc), negatively charged amino acid (system x(c)(-)) and cationic amino acids plus neutral amino acids (system y(+)L and b(0,+)-like). Cotransport of Na(+) is observed only for the y(+)L transporters when they carry neutral amino acids. Mutations in b(0,+)-like and y(+)L transporters lead to the hereditary diseases cystinuria and lysinuric protein intolerance (LPI), respectively.
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            Amino acid transporters revisited: New views in health and disease

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              Boron neutron capture therapy of cancer: current status and future prospects.

              Boron neutron capture therapy (BNCT) is based on the nuclear reaction that occurs when boron-10 is irradiated with low-energy thermal neutrons to yield high linear energy transfer alpha particles and recoiling lithium-7 nuclei. Clinical interest in BNCT has focused primarily on the treatment of high-grade gliomas and either cutaneous primaries or cerebral metastases of melanoma, most recently, head and neck and liver cancer. Neutron sources for BNCT currently are limited to nuclear reactors and these are available in the United States, Japan, several European countries, and Argentina. Accelerators also can be used to produce epithermal neutrons and these are being developed in several countries, but none are currently being used for BNCT. Two boron drugs have been used clinically, sodium borocaptate (Na(2)B(12)H(11)SH) and a dihydroxyboryl derivative of phenylalanine called boronophenylalanine. The major challenge in the development of boron delivery agents has been the requirement for selective tumor targeting to achieve boron concentrations ( approximately 20 microg/g tumor) sufficient to deliver therapeutic doses of radiation to the tumor with minimal normal tissue toxicity. Over the past 20 years, other classes of boron-containing compounds have been designed and synthesized that include boron-containing amino acids, biochemical precursors of nucleic acids, DNA-binding molecules, and porphyrin derivatives. High molecular weight delivery agents include monoclonal antibodies and their fragments, which can recognize a tumor-associated epitope, such as epidermal growth factor, and liposomes. However, it is unlikely that any single agent will target all or even most of the tumor cells, and most likely, combinations of agents will be required and their delivery will have to be optimized. Current or recently completed clinical trials have been carried out in Japan, Europe, and the United States. The vast majority of patients have had high-grade gliomas. Treatment has consisted first of "debulking" surgery to remove as much of the tumor as possible, followed by BNCT at varying times after surgery. Sodium borocaptate and boronophenylalanine administered i.v. have been used as the boron delivery agents. The best survival data from these studies are at least comparable with those obtained by current standard therapy for glioblastoma multiforme, and the safety of the procedure has been established. Critical issues that must be addressed include the need for more selective and effective boron delivery agents, the development of methods to provide semiquantitative estimates of tumor boron content before treatment, improvements in clinical implementation of BNCT, and a need for randomized clinical trials with an unequivocal demonstration of therapeutic efficacy. If these issues are adequately addressed, then BNCT could move forward as a treatment modality.
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                Author and article information

                Contributors
                elena.puris@uni-heidelberg.de
                Journal
                Pharm Res
                Pharm. Res
                Pharmaceutical Research
                Springer US (New York )
                0724-8741
                1573-904X
                6 May 2020
                6 May 2020
                2020
                : 37
                : 5
                : 88
                Affiliations
                [1 ]GRID grid.9668.1, ISNI 0000 0001 0726 2490, School of Pharmacy, , University of Eastern Finland, ; P.O. Box 1627, FI-70211 Kuopio, Finland
                [2 ]GRID grid.7700.0, ISNI 0000 0001 2190 4373, Institute of Pharmacy and Molecular Biotechnology, , Ruprecht-Karls-University, ; 69120 Heidelberg, Germany
                Author information
                http://orcid.org/0000-0002-1769-389X
                Article
                2826
                10.1007/s11095-020-02826-8
                7203094
                32377929
                b890040a-fa2d-4a71-a790-2a27f4429f46
                © The Author(s) 2020

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 4 March 2020
                : 15 April 2020
                Funding
                Funded by: Academy of Finland
                Award ID: 294227, 307057
                Award Recipient :
                Funded by: FundRef http://dx.doi.org/10.13039/501100005440, Keski-Suomen Rahasto;
                Funded by: FundRef http://dx.doi.org/10.13039/100008969, Alfred Kordelinin Säätiö;
                Funded by: FundRef http://dx.doi.org/10.13039/100007753, Itä-Suomen Yliopisto;
                Categories
                Expert Review
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                © Springer Science+Business Media, LLC, part of Springer Nature 2020

                Pharmacology & Pharmaceutical medicine
                drug delivery systems,l-type amino acid transporter 1,membrane transporter,targeting

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