The Mechanism of Transport of the Multitargeted Antifolate (MTA) and Its Cross-resistance Pattern in Cells with Markedly Impaired Transport of Methotrexate
MTA (LY231514) is an antifolate that targets multiple folate-dependent enzymes. In this report, MTA transport was characterized in wild-type L1210 cells and variants with impaired membrane transport or polyglutamation. MTA influx via the reduced folate carrier was somewhat faster (∼30%) than that fo...
Saved in:
Published in | Clinical cancer research Vol. 6; no. 9; pp. 3687 - 3695 |
---|---|
Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
Philadelphia, PA
American Association for Cancer Research
01.09.2000
|
Subjects | |
Online Access | Get full text |
Cover
Loading…
Summary: | MTA
(LY231514) is an antifolate that targets multiple folate-dependent
enzymes. In this report, MTA transport was characterized in wild-type
L1210 cells and variants with impaired membrane transport or
polyglutamation. MTA influx via the reduced folate carrier was somewhat
faster (∼30%) than that for methotrexate (MTX). Unlike MTX, MTA was
rapidly polyglutamated in L1210 cells; hence, a
folylpoly-γ-glutamate synthetase-deficient L1210 variant was
used to assess net transport and efflux properties. The MTA
transmembrane gradient for exchangeable drug was 2.5 times greater than
the MTX gradient, attributable primarily to an efflux rate constant
40% that of MTX. No MTA was bound to dihydrofolate reductase.
When grown with folic acid, MTX-resistant L1210 variants with mutations
in the reduced folate carrier demonstrated cross-resistance to MTA,
markedly reduced MTA accumulation, and only a slightly decreased
intracellular folate cofactor pool as compared to L1210 cells. However,
when 5-formyltetrahydrofolate was the growth substrate, these
MTX-resistant cells were less resistant or negligibly resistant to MTA,
accumulated more MTA, and had a lower folate pool as compared to L1210
cells. MTA activity and the intracellular folate pool in L1210 cells
were inversely related. These data indicate that MTA polyglutamation in
L1210 cells is favored by both the generation of high intracellular
drug levels and high MTA affinity for FPGS relative to MTX. Cells
resistant to MTX because of impaired transport may retain appreciable
sensitivity to MTA because of a concurrent reduction in
tetrahydrofolate cofactor transport resulting in cellular folate
depletion, which diminishes endogenous folate suppression of MTA
polyglutamation. |
---|---|
ISSN: | 1078-0432 1557-3265 |