| pA2 online © Copyright 2004 The British Pharmacological Society |
114P
GKT, University of London Winter Meeting December 2003 |
|
Effects
of quinoline-based drugs on transport mediated by multidrug resistance
associated proteins in human erythrocytes |
|
Print abstractMultidrug resistant-associated proteins (MRPs) mediate ATP-dependent transport of a wide range of compounds across membranes (Borst et al., 2002) including those of red blood cells. One of the most potent inhibitors of MRP-mediated transport is the LTD4 receptor antagonist MK-571, a quinoline derivative (Jedlitschky et al., 1996). Another quinoline-based compound, IAAQ photolabels MRP1 and both chloroquine and MK-571 inhibit this labeling (Vezmar et al., 1998). Thus it is possible that quinolines interact with MRPs.
Quinoline-based drugs are widely used to treat malaria. It is possible that these drugs are effluxed from infected red cells by MRPs. This would reduce drug concentrations and thus their effectiveness inside the parasite. We here investigate the effects of various quinolines on MRP-mediated transport.
We have already shown that transport of 3µM DNP-SG into inside-out membrane vesicles prepared from freshly drawn human erythrocytes is mediated primarily by MRP1 and that of cGMP has properties indistinguishable from those of MRP4 (Klokouzas et al., 2003). We here report the effects of quinolines on, uptake of 3 µM DNP-SG or 3.3 µM cGMP using the same preparations. Various quinolines were added to the buffer solution just before the vesicles and transport was followed for 15 min (cGMP) or 30 min (DNP-SG) at 37°C. The inhibition curves (uptake as a % of control vs. inhibitor concentration) have been fitted (unweighted least squares, Kaleidagraph, Macintosh v 3.6) using the equation for two components of uptake, one subject to simple competitive inhibition the other non-inhibitable. These data show that quinolines interact, though with low affinity, with both MRP1-mediated DNP-SG transport (A) and the MRP4-like transport of cGMP (B) and thus may be candidate substrates for MRPs.
A)
| Quinolines |
IC50
(µM) %
|
non-inhibitable
|
| MK-571 |
0.42
± 0.03
|
-0.3±
1.4
|
| Mefloquine |
19
± 19
|
13
± 1
|
| Chloroquine |
86±14
|
0
(constrained)
|
| Quinine |
67
± 22
|
33
± 5
|
| Quinidine |
56
± 12
|
13
± 5
|
| Amodiaquine |
52
± 16
|
24
± 5
|
| Primaquine |
127
± 18
|
15
± 3
|
| Pyronaridine
|
65
± 18
|
0±5
|
B)
| Quinolines |
IC50
(µM) %
|
non-inhibitable
|
| MK-571 |
1.2 ± 0.3
|
-4±5
|
| Mefloquine |
165±29
|
-11±6
|
| Pyronaridine |
494±113
|
0
(constrained)
|
| G(alternate fit) |
1108±550
|
-37±29
|
Table: Effect of various quinoline-based drugs on the ATP-dependent uptake of A) 3.3µM [3H]cGMP and B) 3µM [3H]DNP-SG by human erythrocyte membrane vesicles. Each data point is the mean of at least 4 independent experiments.
Borst, P. and Elferink
R.O. (2002) Ann Rev Biochem; 71:537-92.
Jedlitschky, G. et al., (1996) Cancer Res., 56, 988-994.
Klokouzas, A. et al., (2003) Eur. J. Biochem. 270, 3696-3708.
Vezmar M. and Georges E. (1998) Biochem Pharmacol. 56: 733-42.