Modulation of cerebrovascular LAT1 for brain delivery of amino acid-containing anticancer agents

Abstract

The blood-brain barrier (BBB) restricts brain transport for many therapeutic agents. Strategies to improve brain uptake of potential central nervous system therapeutics are needed. This research demonstrates that drug transport via the cerebrovascular large, neutral amino acid transporter (LAT) can be modulated to potentially improve brain drug delivery. We have created two novel drug delivery systems for amino acid-containing agents, BTDS and TDDS. BTDS possesses high recognition for cerebrovascular LAT while TDDS is not recognized by LAT, thereby demonstrating modulation of BBB transport. An in situ rat brain perfusion was utilized to examine cerebrovascular interactions as well as to determine brain uptake parameters. Radiotracer [14C]-L-Leu, an endogenous LAT ligand, was used to probe for cerebrovascular LAT expression. TDDS did not significantly inhibit [14C]-L-Leu brain uptake, suggesting that these agents are not transported into brain via LAT. Quantitative brain uptake of TDDS by UV-HPLC demonstrated rapid brain uptake. Additionally, evidence of TDDS brain uptake was provided using ESI-based mass spectrometry. In contrast, BTDS significantly inhibited [14C]-L-Leu PA product (down to 8--36% of control), to show high recognition for cerebrovascular LAT. Cerebrovascular LAT Ki determination for IBM-BTDS yielded 11.3 +/- 2.8 muM in parietal cortex of rat brain, which is similar to the high affinity values observed for endogenous ligands, L-Leu and L-Phe. Additionally, the LAT1 isoform was shown to be functionally predominantly at the cerebrovasculature. This work demonstrates that chemical alterations on amino acid-based compounds to form drug delivery systems modulate cerebrovascular LAT-mediated BBB transport. This research can potentially lead to therapeutically and pharmaceutically usefully brain drug delivery systems for the effective treatment of various CNS disorders and diseases.