Regiospecific and conformationally restrained analogs of melphalan and dl-2-NAM-7 and their affinities for the large neutral amino acid transporter (system LAT1) of the blood–brain barrier

Abstract

Regiospecific and conformationally restrained analogs of melphalan and DL-2-NAM-7 have been synthesized and their affinities for the large neutral amino acid transporter (LAT1) of the blood–brain barrier have been determined to assess their potential for accessing the CNS via facilitated transport. Several analogs had Ki values in the range 2.1–8.5 μM with greater affinities than that of either L-phenylalanine (Ki = 11 μM) or melphalan (Ki = 55 μM), but lower than DL-2-NAM-7 (Ki = 0.08 μM). The results indicate that regiospecific positioning of the mustard moiety on the aromatic ring in these analogs is very important for optimal affinity for the large neutral amino acid transporter, and that conformational restriction of the DL-2-NAM-7 molecule in benzonorbornane and indane analogs leads to 25- to 60-fold loss, respectively, in affinity.

Targeting L-type amino acid transporter 1 for anticancer therapy: clinical impact from diagnostics to therapeutics

“…Specifically, LAT1 allows anticancer drugs to overcome BBB without disruption of its integrity. For example, melphalan, a chemotherapeutic drug, has a moderately low affinity to LAT1 as a L-phenylalanine derivative (K m = 90~150 mM), showing poor brain penetration [80]. However, Matharu et al reported the enhanced anticancer effect of the melphalan analog, phenylglycine-mustard, due to the improvement of their affinity for LAT1 [80].…”

“…For example, melphalan, a chemotherapeutic drug, has a moderately low affinity to LAT1 as a L-phenylalanine derivative (K m = 90~150 mM), showing poor brain penetration [80]. However, Matharu et al reported the enhanced anticancer effect of the melphalan analog, phenylglycine-mustard, due to the improvement of their affinity for LAT1 [80]. In addition, Li et al reported O,N-carboxymethyl chitosanGly-Gly-melphalan conjugates as prodrugs for melphalan presented good cathepsin X-sensitivity, lower toxicity and improved drug release pattern [81].…”

“…Several substrates are well known for the transport through LAT1. By the conjugation of LAT1 substrate on the anticancer drugs in market, their affinity for LAT1 could be improved [80]. LAT1 targeted drugs are constructed in a relatively simple way compared to new drug development processes.…”

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

“…As a result, the BBB penetration of D,L-NAM in rats was more than 20 times greater than that of melphalan after in situ brain perfusion (87). In another study, several isomers (C-6 and C-8) of D,L-NAM (C-7 isomer) were synthetized in order to improve the affinity of the agent (88). However, when investigated using in situ rat brain perfusion, it was found that all compounds had lower affinity to LAT1 as compared to D,L-NAM.…”

Insights into the Structure, Function, and Ligand Discovery of the Large Neutral Amino Acid Transporter 1, LAT1

“…Moreover, the transfer of the amino acid group in compound 9 from C-2 to C-1 in compound 12 diminished LAT1 affinity by over three orders of magnitude ( K i = 730 μM). Later, Matharu et al [ 98 ] assessed the LAT1 affinities of more rigid analogs, compounds 13 – 16 , through competitive l -[ 14 C]-leucine uptake inhibition using the in situ rat brain perfusion technique. The results indicated that a restriction of the conformational flexibility of the scaffold 6 appeared to be detrimental to LAT1 binding, since the indane analog 15 and the bicyclo analog 16 had 60 and 25 times less affinity, respectively, for LAT1 than compound 9 , but an approximately matched affinity to compound 7 .…”