Stereoselectivity in the Membrane Transport of Phenylethylamine Derivatives by Human Monoamine Transporters and Organic Cation Transporters 1, 2, and 3

Abstract

Stereoselectivity is well known and very pronounced in drug metabolism and receptor binding. However, much less is known about stereoselectivity in drug membrane transport. Here, we characterized the stereoselective cell uptake of chiral phenylethylamine derivatives by human monoamine transporters (NET, DAT, and SERT) and organic cation transporters (OCT1, OCT2, and OCT3). Stereoselectivity differed extensively between closely related transporters. High-affinity monoamine transporters (MATs) showed up to 2.4-fold stereoselective uptake of norepinephrine and epinephrine as well as of numerous analogs. While NET and DAT preferentially transported (S)-norepinephrine, SERT preferred the (R)-enantiomer. In contrast, NET and DAT showed higher transport for (R)-epinephrine and SERT for (S)-epinephrine. Generally, MAT stereoselectivity was lower than expected from their high affinity to several catecholamines and from the high stereoselectivity of some inhibitors used as antidepressants. Additionally, the OCTs differed strongly in their stereoselectivity. While OCT1 showed almost no stereoselective uptake, OCT2 was characterized by a roughly 2-fold preference for most (R)-enantiomers of the phenylethylamines. In contrast, OCT3 transported norphenylephrine and phenylephrine with 3.9-fold and 3.3-fold preference for their (R)-enantiomers, respectively, while the para-hydroxylated octopamine and synephrine showed no stereoselective OCT3 transport. Altogether, our data demonstrate that stereoselectivity is highly transporter-to-substrate specific and highly diverse even between homologous transporters.

Stereoselective Inhibition of High- and Low-Affinity Organic Cation Transporters

“…The trend of higher stereoselectivity in OCT2 and −3 inhibition compared to OCT1 aligns with previous studies on stereoselective OCT transport demonstrating that OCT2 and OCT3 act more stereoselectively than OCT1. , Recent structural data based on cryogenic electron microscopy (cryo-EM) have confirmed a fundamentally similar substrate binding cavities of all three OCTs. , Nevertheless, there were also more than 10 amino acids that differ between the three transporters and may therefore be responsible for substrate- and stereoselectivity. The long-known polyspecificity of OCTs was reflected for OCT1 by an orthosteric and opportunistic ligand binding site .…”

Stereoselectivity in Cell Uptake by SLC22 Organic Cation Transporters 1, 2, and 3

“…Generally, their stereoselectivity is much higher than that of OCT1, which is in accordance with previous reports. 26,28 With none of the substrates, there was absolutely zero transport for one of the enantiomers and a relevant transport for the other enantiomer, but as illustrated in Figures 2 and 3, particularly terbutaline and zolmitriptan transport by OCT3 was highly enantioselective.…”

“…Overview of stereoselectivity of SLC22 organic cation transporters. V max ratios are shown for all OCT substrates in ascending order where data on stereoselective transport kinetics were available. , Data are presented as the v max ratio of the higher transported enantiomer over the other. Substrates investigated in this study are highlighted by dark filling, whereas data taken from the literature are indicated by lighter fillings.…”

“…Both classes are composed almost completely of chiral molecules. In earlier studies, stereoselectivity in the transport by OCTs has only been investigated for (anti)­adrenergic drugs as well as for chiral phenylethylamines which are structurally related to adrenergic drugs. − For a more comprehensive characterization, we extended this series by investigating the cellular uptake of additional (anti)­adrenergic substrates but also included several anticholinergic substances among other OCT substrates (Figure B). All substances are known OCT substrates, but stereoselectivity in their transport was unknown.…”

“…Overview of stereoselectivity of SLC22 organic cation transporters. V max ratios are shown for all OCT substrates in ascending order where data on stereoselective transport kinetics were available 26,28. Data are presented as the v max ratio of the higher transported enantiomer over the other.…”