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. Author manuscript; available in PMC: 2019 Aug 23.
Published in final edited form as: J Med Chem. 2018 Aug 10;61(16):7358–7373. doi: 10.1021/acs.jmedchem.8b01007

Table 3.

Relative Exchange Efflux Rate, Uptake Inhibition of [3H]-Gabapentin, and IC50 Values in HEK-hLAT1 Cells for L and D Isomers of Endogenous LAT1 Substrates and Various Nonsubstrate Amino Acids

graphic file with name nihms-1042302-t0010.jpg
Compounda R” %L-Phe
Effluxb 		%
Inhibitionc 		IC50 ((μM)d
45
(Gly)		 H (achiral) 29 33 -
46
(L-Leu)		 (CH3)2CHCH2- 120 73 85 ± 21
46-D
(D-Leu)		 (CH3)2CHCH2- 100¯ 56 220 ± 47
47
(L-Ile)		 (S)-CH3CH2(CH3)CH- 93 - 140 ± 27
47-D
(D-Ile)		 (S)-CH3CH2(CH3)CH- 78 18 >3,000
48
(L-Met)		 CH3S(CH2)2- 89 - 170 ±23
48-D
(D-Met)		 CH3S(CH2)2 110 56 120 ±33
49
(L-Val)		 (CH3)2CH- 100 43 68 ±21
49
D (D-Val)		 (CH3)2CH- 41 11 >50,000
50
(L-Phe)		 PhCH2- 100 85 69 ±29
50-D
(D-Phe)		 PhCH2- 96 74 46 ±23
51
(L-Tyr)		 para-HOPhCH2- 96 68 68 ± 34
51-D
(D-Tyr)		 para-HOPhCH2- 85 35 380 ± 73
52
(L-Trp)		 graphic file with name nihms-1042302-t0011.jpg 59 79 160 ± 87
52-D
(D-Trp)		 graphic file with name nihms-1042302-t0012.jpg 81 29 380 ± 130
53
(L-His)		 graphic file with name nihms-1042302-t0013.jpg 140 92 20 ± 9
53-D
(D-His)		 graphic file with name nihms-1042302-t0014.jpg 78 33 460 ± 170
54
(L-Arg)		 NH2(NH)CNH(CH2)3- 28 49 -
55
(L-Lys)		 NH2(CH2)4- 33 −2.1 -
56
(L-Asp)		 HO2CCH2- 27 4.2 -
57
(L-Glu)		 HO2C(CH2)2- 27 −2.4 -
a

Cell assay data was obtained at least in triplicate (wells). Amino acids were purchased from commercial vendors. All compounds above are single enantiomers of L configuration, unless indicated otherwise. Most of these amino acids (except 54–57) were converted and tested as their HCl salts to improve water solubility.

b

Compounds were tested at 200 μM for their ability to cause efflux (fmol/min) of [3H]-gabapentin from preloaded HEK-hLAT1 cells. Efflux of [3H]-gabapentin was calculated at 3 min after adding test compound. %Efflux was normalized relative to L-Phe (50), which had an efflux rate of 2.7 ± 0.3 fmol/min, from an average of seven experiments.

c

Compounds were tested at 200 μM for their ability to inhibit uptake of [3H]-gabapentin into HEK-hLAT1 cells. Data is presented as % inhibition relative to background signal in the absence of a test compound.

d

For IC50 determinations, varying concentrations of each compound were added, from 0.1 to 500 μM. IC50 and standard deviation of each compound were calculated by Graphpad Prism version 5.0. %[3H]-gabapentin uptake at each concentration was normalized relative to % inhibition by BCH80,81 at 2 mM, which was set to 100% inhibition.