7-hydroxymethotrexate and Carcinoma--Ehrlich-Tumor

Studies were undertaken to characterize the cellular pharmacology of 7-hydroxymethotrexate (7-OH-MTX) in Ehrlich ascites tumor cells, compare it to that of methotrexate (MTX), and define the interactions between the parent compound and its catabolite. Transport of 7-OH-MTX is mediated by the MTX-tetrahydrofolate cofactor carrier, with a Km of 9 microM in comparison to the MTX Km of 5 microM. Both compounds mutually inhibit their influx and steady-state levels of free drug accumulated. While influx of 7-OH-MTX is slower than influx of MTX, 7-OH-MTX efflux is likewise slower, so that the steady-state level of 7-OH-MTX achieved is comparable to that of MTX. Influx of 7-OH-MTX is inhibited by extracellular 5-formyltetrahydrofolate and trans-stimulated in cells preloaded with this tetrahydrofolate cofactor. The energetics of 7-OH-MTX transport is similar to that of MTX in the influx and net transport are stimulated by sodium azide, while net transport is reduced by glucose. As observed for MTX, 7-OH-MTX transport is sensitive to the anionic composition of the extracellular compartment and was shown to be inhibited by organic and inorganic phosphates. 7-OH-MTX does not, alone, inhibit [3H]deoxyuridine incorporation into DNA at concentrations of up to 50 microM. However, the catabolite reduces MTX inhibition of deoxyuridine metabolism, presumably due to the reduction in the free level of intracellular MTX achieved. These findings support the possibility that when 7-OH-MTX accumulates to high levels relative to MTX in clinical regimens, it may modulate the pharmacological effects of MTX.

Topics: Animals; Azides; Binding, Competitive; Biological Transport; Carcinoma, Ehrlich Tumor; Folic Acid Antagonists; Glucose; Kinetics; Methotrexate; Mice; Sodium Azide; Tetrahydrofolate Dehydrogenase

The synthesis of poly-gamma-glutamyl derivatives of 7-hydroxymethotrexate (7-OH-4-NH2-10-CH3-pteroyl-glutamic acid (PteGlu1] was evaluated by direct hydroxylation of the tetraglutamyl derivative of methotrexate (4-NH2-10-CH3-PteGlu4) by a cell-free preparation of rabbit liver aldehyde oxidase and by polyglutamylation of 7-OH-methotrexate in Ehrlich ascites tumor cells in vitro. The polyglutamyl derivatives of 7-OH-methotrexate rapidly accumulate in cells to the 7-OH-4-NH2-10-CH3-PteGlu4. While 7-OH-methotrexate monoglutamate does not bind to dihydrofolate reductase, 7-OH-4-NH2-10-CH3-PteGlu4 does bind to the enzyme as established by gel filtration analysis of cell extracts and by use of purified dihydrofolate reductase from Ehrlich cells. Within cells, the rate of formation of 7-OH-methotrexate polyglutamyl derivatives exceeds that for methotrexate by a factor of 2.7 at comparable free monoglutamyl substrate levels, suggesting that 7-OH-methotrexate may be a better substrate than methotrexate for the folylpolyglutamate synthetase. 7-OH-methotrexate slows the rate of methotrexate polyglutamylation in cells, a consequence of the inhibition of methotrexate transport with reduced methotrexate substrate available for polyglutamylation. When 7-OH-methotrexate polyglutamyl derivatives were accumulated inside the cells following which extracellular 7-OH-methotrexate was removed, the monoglutamate, and to a lesser extent the diglutamate, exited the cells whereas the majority of the longer polyglutamyl derivatives were retained and continued to be metabolized to higher forms. These studies suggest that 7-OH-methotrexate and its polyglutamyl derivatives may play a role in modulating methotrexate action, either by their own inhibitory effects on folate-dependent enzymes or by their effects on methotrexate transport and metabolism within cells.

Topics: Aldehyde Oxidase; Aldehyde Oxidoreductases; Animals; Carcinoma, Ehrlich Tumor; Chromatography, High Pressure Liquid; Folic Acid; Kinetics; Liver; Methotrexate; Mice; Pteroylpolyglutamic Acids; Rabbits; Spectrophotometry, Ultraviolet; Structure-Activity Relationship; Tritium

Plasma concentrations of 7-hydroxymethotrexate were measured in 10 individuals receiving methotrexate, 8 of them per infusion. After the end of infusion, the plasma concentration of formed 7-hydroxymethotrexate fell less rapidly than that of methotrexate. At 24 h after infusion, plasma concentration ratios of 7-hydroxymethotrexate ranged from 30 to 1 (n = 8). The presence of 7-hydroxymethotrexate was shown to influence the transport of methotrexate into Ehrlich ascites tumor cells and human KB cells, cultured in vitro. These findings suggest that monitoring of 7-OHMTX is important in MTX treatment.

Topics: Animals; Biological Transport; Carcinoma, Ehrlich Tumor; Carcinoma, Squamous Cell; Cells, Cultured; Folic Acid Antagonists; Half-Life; Humans; Hydroxylation; Infusions, Parenteral; Injections, Intravenous; Methotrexate; Neoplasms