Quantitative insight into the design of compounds recognized by the L-type amino acid transporter 1 (LAT1).

L-Type amino acid transporter 1 (LAT1) is a transmembrane protein expressed abundantly at the blood-brain barrier (BBB), where it ensures the transport of hydrophobic acids from the blood to the brain. Due to its unique substrate specificity and high expression at the BBB, LAT1 is an intriguing target for carrier-mediated transport of drugs into the brain. In this study, a comparative molecular field analysis (CoMFA) model with considerable statistical quality (Q(2) =0.53, R(2) =0.75, Q(2) SE=0.77, R(2) SE=0.57) and good external predictivity (CCC=0.91) was generated. The model was used to guide the synthesis of eight new prodrugs whose affinity for LAT1 was tested by using an in situ rat brain perfusion technique. This resulted in the creation of a novel LAT1 prodrug with L-tryptophan as the promoiety; it also provided a better understanding of the molecular features of LAT1-targeted high-affinity prodrugs, as well as their promoiety and parent drug. The results obtained will be beneficial in the rational design of novel LAT1-binding prodrugs and other compounds that bind to LAT1.

Design, synthesis and brain uptake of LAT1-targeted amino acid prodrugs of dopamine.

PURPOSE: Drug delivery to the brain is impeded by the blood-brain barrier (BBB). Here, we attempted to enhance the brain uptake of cationic dopamine by utilizing the large amino acid transporter 1 (LAT1) at the BBB by prodrug approach. METHODS: Three amino acid prodrugs of dopamine were synthesized and their prodrug properties were examined in vitro. Their LAT1-binding and BBB-permeation were studied using the in situ rat brain perfusion technique. The brain uptake after intravenous administration and the dopamine-releasing ability in the rat striatum after intraperitoneal administration were also determined for the most promising prodrug. RESULTS: All prodrugs underwent adequate cleavage in rat tissue homogenates. The prodrug with phenylalanine derivative as the promoiety had both higher affinity for LAT1 and better brain uptake properties than those with an alkyl amino acid - mimicking promoiety. The phenylalanine prodrug was taken up into the brain after intravenous injection but after intraperitoneal injection the prodrug did not elevate striatal dopamine concentrations above those achieved by corresponding L-dopa treatment. CONCLUSIONS: These results indicate that attachment of phenylalanine to a cationic drug via an amide bond from the meta-position of its aromatic ring could be highly applicable in prodrug design for LAT1-mediated CNS-delivery of not only anionic but also cationic polar drugs.

Structure-activity relationship study of compounds binding to large amino acid transporter 1 (LAT1) based on pharmacophore modeling and in situ rat brain perfusion.

Large neutral amino acid transporter 1 (LAT1) is predominantly expressed at the blood-brain barrier and it has a major role in transporting neutral amino acids into the brain. LAT1 has the potential to function as a drug carrier for improved drug brain delivery which makes it an intriguing target protein for central nervous system disorders, e.g., Alzheimer's disease, Parkinson's disease and brain tumors. In this study, a 3D pharmacophore was generated for a set of LAT1 substrates whose binding affinities were studied using competitive inhibition of the brain uptake of [¹4C]-L-leucine with an in situ rat brain perfusion method. The pharmacophore highlights the most important molecular features shared by efficient LAT1-binding compounds and elucidates their 3D-arrangement in detail. This clarifies the structure-activity relationships of LAT1 substrates and provides insights for making a binding hypothesis. The results can be further applied in the design of novel efficient LAT1 substrates.

Large amino acid transporter 1 (LAT1) prodrugs of valproic acid: new prodrug design ideas for central nervous system delivery.

Central nervous system (CNS) drug delivery is a major challenge in drug development because the blood-brain barrier (BBB) efficiently restricts the entry of drug molecules into the CNS at sufficient amounts. The brain uptake of poorly penetrating drugs could be improved by utilizing the transporters at the BBB with a prodrug approach. In this study, we designed four phenylalanine derivatives of valproic acid and studied their ability to utilize a large amino acid transporter 1 (LAT1) in CNS delivery with an aim to show that the meta-substituted phenylalanine prodrugs bind to LAT1 with a higher affinity compared with the affinity of the para-substituted derivatives. All of the prodrugs crossed the BBB carrier mediatedly via LAT1 in in situ rat brain perfusion. For the first time, we introduced a novel meta-substituted phenylalanine analogue promoiety which improved the LAT1 affinity 10-fold and more importantly the rat brain uptake of the prodrug 2-fold compared with those of the para-substituted derivatives. Therefore, we have characterized a new prodrug design idea for CNS drug delivery utilizing a transporter-mediated prodrug approach.

[Prodrug technology in the development of medicinal agents]. / Aihiolääketeknologia lääkekehityksessä.

Medicinal agents acetosalicylic acid, lansoprazole, simvastatin, clopidogrel and oseltamivir are known prodrugs. Prodrugs are pharmacologically inactive medicine molecules, from which the active drug is released in the body through a chemical or enzymatic reaction. This mechanism can be used to solve pharmaceutical and pharmacokinetic problems restricting the use of medicinal agents, without altering the pharmacological effects of the agent that ends up in the site of action. Of the medicinal agents currently on the market, as many as one out of ten is a prodrug.