STRUCTURAL PREFERENCES AMONG FOLATE COMPOUNDS AND THEIR ANALOGS FOR ATPASE-MEDIATED EFFLUX BY INSIDE-OUT PLASMA-MEMBRANE VESICLES DERIVED FROM L1210 CELLS

Our prior studies with inside-out plasma membrane vesicles from L1210 cells (Schlemmer SR and Sirotnak FM, J Biol Chem 267: 14746-14752, 199 2) identified an outwardly directed, translocating ATPase as mediating the majority of methotrexate (MTX) efflux in these cells. In the curr ent studies, we examined by competitive inhibition with [H-3]MTX as pe rmeant some of the structural features that determine preferences amon g folate compounds and their analogues as permeants for this ATPase. T he results show that folate compounds are preferred over simple quinaz olines (5,8-dideaza-pteridines), and IL5-CH3-folateH(4), and probably other 5-substituted folates are preferred over folic acid. In the latt er regard, the observed equivalence in preference to IL5-CH3-folateH(4 ) of the 4-oxa-pyridopyrimidine, lometrexol (DDATHF), probably relates to its close similarity to folateH(4). The results also suggest that the 4-position in the case of folate analogues, but not in the case of the quinazoline analogues, is an important determinant with 4-amino p referred over 4-oxa. They also suggest that the N10 position on the br idge region in both series of compounds, and probably for the pyridopy rimidine lometrexol, is not an important determinant. In contrast to r esults seen with the simple quinazolines, the 2-CH3 desamino quinazoli ne ZEN D1694, modified as well by a 2-benzyl to thienyl replacement on the side chain, was highly preferred. The same relative differences s een among some of these analogues as inhibitors of [H-3]MTX efflux in inside-out vesicles were documented for their effectiveness as permean ts for ATP-dependent efflux in intact L1210 cells.