Folate-pool interconversions and inhibition of biosynthetic processes after exposure of L1210 leukemia cells to antifolates. Experimental and network thermodynamic analyses of the role of dihydrofolate polyglutamylates in antifolate action in cells

摘要: Folate analogs that inhibit dihydrofolate reductase result in only partial interconversion of tetrahydrofolate cofactors to with preservation the major portion reduced cellular folate L1210 leukemia cells. One possible explanation for this phenomenon is low levels polyglutamates accumulate presence antifolates block thymidylate synthase prevent depletion pools. This paper correlates biochemical analyses rapid interconversions radiolabeled folates and changes purine pyrimidine biosynthesis murine cells exposed network thermodynamic computer modeling assess hypothesis. When are 1 microM trimetrexate there an almost instantaneous inhibition [3H] deoxyuridine or [14C]formate incorporation into nucleotides which maximal within 5 min. associated a rise (t1/2 approximately 1.5 min), reaches steady state represents 27.9% total pool. Pretreatment fluorodeoxyuridine, by about 95% followed slows rate 25 min) but not final level achieved. consistent simulations predict direct 97, 98, 99% should increase half-time after 40, 60, 124 min, respectively, achieved always same as normal activity. The data reflect high degree catalytic activity relative cofactor pools enormous extent enzyme necessary slow addition antifolates. model predicts, demonstrate, virtually any residual will permit all available oxidation when abolished, be slowed. Additional indicate time course cessation tetrahydrofolate-dependent these can accounted solely on basis alone. These exclude possibility polyglutamates, other intracellular antifolates, account dihydrofolate.(ABSTRACT TRUNCATED AT 400 WORDS)