Inhibitors of nucleoside transport. Structure-activity study using human erythrocytes

Abstract

The passage of nucleosides across the plasma membrane of erythrocytes is a membrane-mediated process which is strongly inhibited by derivatives of 9-beta-D-ribofuranosylpurine (1) with S, O, or N atoms at the purine 6 position bearing variously substituted arylalkyl groups. In this structure-activity study, nucleoside derivatives were compared in respect to their ability to inhibit a transport-dependent aspect of nucleoside metabolism in erythrocytes, the synthesis of inosine from external guanosine and hypoxanthine. 6-Benzylthio, 6-benzylamino, and 6-benzyloxy derivatives of 1 were inhibitory at 10(-5)-10(-6) M and the similarity of their activities suggested that alkylation of the transporter as the mechanism of transport inhibition was unlikely. The hydrophobicity of the 6-position substituents appeared to contribute importantly to inhibitory activity. Although replacement of the ribofuranose moiety by other sugars reduced inhibitory activity, compounds with 9-butyl groups were inhibitory. 6-[(2-Hydroxy-5-nitrobenzyl)thio] derivatives of 1 were the most potent of the inhibitors tested, being active at about 10(-7) M.

Transport of uridine in human red blood cells. Demonstration of a simple carrier-mediated process.

“…Crystals were collected after 20 h, and were subsequently washed with ether and petroleum ether and kept desiccated in vacuo at 4°C. The properties of the final products (IR, UV and visible spectra, melting points, and chromatography properties) are essentially similar to those published in a recent work (11).…”

Constrained NBMPR analogue synthesis, pharmacophore mapping and 3D-QSAR modeling of equilibrative nucleoside transporter 1 (ENT1) inhibitory activity

“…The training set used for developing 3D-QSAR models included 77 compounds and comprised a series of compounds with a high diversity in structure and a wide range of ENT1 inhibitory potencies as reported by Paul et al, 28 a series of tetrahydroisoquinoline conformationally constrained ENT1 inhibitors reported by us, 1 and a series of 5′-O, 8-cyclo conformationally constrained ENT1 inhibitors, reported in this study (see Table 1). The test set included 39 compounds with biological data taken from the literature.…”

“…The differences emphasize the remarkable regioselectivity of ENT1 among these tetrahydroisoquinoline NBMPR analogues with respect to the NO 2 substituent. 28,34 Compared to their less constrained counterparts compounds 2-5, the binding affinities of compounds 6-9 were significantly lower (see Table 4, K i values increased from the nanomolar range to the micromolar range except for compound 8). These results are interesting since compounds 6-9 were obtained by just forming a 5′-O, 8-linkage to block the free rotation of the N 9 -C 1′ glycosidic bond in compounds 2-5, respectively.…”

“…18,38,39,40 The hydrophobic function is mapped onto the N 6 -benzyl ring, and the two aromatic groups are mapped onto the purine system. The importance of hydrophobicity of the purine 6-position substituent was highlighted in the study of Paul et al 28 Compound 4 adopts an anti conformation, whereas compound 8 adopts a high-anti conformation due to the restriction imposed by the 5′-O, 8-linkage (see Figure 6). However, such a conformational shift is not large enough to prohibit compound 8 from mapping onto all the chemical features encoded in the pharmacophore, which is consistant with the results obtained from the flow cytometric assay showing that compound 8 was able to bind well to the ENT1 transporter with a K i values in the nanomolar range (K i = 18.89 nM, see Table 3).…”

Molecular cloning and functional characterization of inhibitor-sensitive (mENT1) and inhibitor-resistant (mENT2) equilibrative nucleoside transporters from mouse brain

“…It is noteworthy that the amino acid sequence between residues 99 and 231 is highly conserved between species (Figure 2), suggesting that differences in dipyridamole sensitivity may be due to discrete amino acid substitutions in this region. Structure-activity studies [19,34,38] have led to the hypothesis that interactions with discrete hydrophobic elements of the transporter are required for high-affinity binding of inhibitors to hENT1. Comparative hydropathy analysis showed that residues 50-67 of the first extracellular loop of hENT1 are significantly more hydrophobic than the corresponding residues in mENT1 and rENT1 ; indeed, this region is the only one that displays a marked difference in hydrophobicity among the species examined.…”