J. Biol. Chem., Vol. 263, Issue 19, 9285-9291, Jul, 1988
Acyclovir transport into human erythrocytes
WB Mahony, BA Domin, RT McConnell and TP Zimmerman
Experimental Therapy Department, Wellcome Research Laboratories, Research Triangle Park, North Carolina 27709.
The mechanism of transport of the antiviral agent acyclovir (ACV) into
human erythrocytes has been investigated. Initial velocities of ACV influx
were determined with an "inhibitor-stop" assay that used papaverine to
inhibit ACV influx rapidly and completely. ACV influx was nonconcentrative
and appeared to be rate-saturable with a Km of 260 +/- 20 microM (n = 8).
However, two lines of evidence indicate that ACV permeates the erythrocyte
membrane by means other than the nucleoside transport system: 1) potent
inhibitors (1.0 microM) of nucleoside transport (dipyridamole,
6-[(4-nitrobenzyl)thio]-9-beta-D- ribofuranosylpurine, and dilazep) had
little (less than 8% inhibition) or no effect upon the influx of 5.0 microM
ACV; and 2) a 100-fold molar excess of several purine and pyrimidine
nucleosides had no inhibitory effect upon the influx of 1.0 microM ACV.
However, ACV transport was inhibited competitively by adenine (Ki = 9.5
microM), guanine (Ki = 25 microM), and hypoxanthine (Ki = 180 microM).
Conversely, ACV was a competitive inhibitor (Ki = 240-280 microM) of the
transport of adenine (Km = 13 microM), guanine (Km = 37 microM), and
hypoxanthine (Km = 180 microM). Desciclovir and ganciclovir, two compounds
related structurally to ACV, were also found to be competitive inhibitors
of acyclovir influx (Ki = 1.7 and 1.5 mM, respectively). These results
indicate that ACV enters human erythrocytes chiefly via the same nucleobase
carrier that transports adenine, guanine, and hypoxanthine.