Accumulation, intracellular metabolism, and antitumor activity of high- and low-dose methotrexate in human osteosarcoma xenografts.
High doses of methotrexate with leucovorin rescue are routinely used in the treatment of patients with osteosarcoma; the rationale for this application is controversial. Using human osteosarcoma xenografts growing in mice as a clinically relevant model, we compared the accumulation, intracellular metabolism, and tumor response of methotrexate administered as either high-dose (2400 mg/kg) or low-dose (150 mg/kg) infusions. The high-dose regimen, which included i.v. hydration and leucovorin rescue, resulted in plasma methotrexate levels that approximated those in patients receiving the drug at 12 g/m2. The low-dose infusion produced essentially the same toxicity as the higher dose level, without use of leucovorin. The HxOs33 tumor line was moderately sensitive to the high-dose infusion (55-day delay in tumor volume doubling time), whereas the second line, HxOs2, did not respond. Neither xenograft had a measurable response to low-dose methotrexate. Methotrexate was present in both tumors for up to 72 hr post-infusion, regardless of the dosage regimen. Only shorter-chain polyglutamates (MTXglu2 and MTXglu3) were detected over this period in the high-dose trial, and levels of these derivatives were uniformly higher in the resistant HxOs2 xenograft. Low-dose infusions were associated with formation of longer-chain polyglutamate species, with more abundant production in the HxOs2 line. Methotrexate polyglutamates exceeded baseline [3H]MTX binding of dihydrofolate reductase, as measured in tumor homogenates, at all testing intervals through 72 hr in both tumor lines. Nonetheless, high-dose methotrexate-induced suppression of [14C]formate incorporation into DNA was greater in the drug-sensitive HxOs33 tumor than in HxOs2. These results suggest a therapeutic advantage for high-dose methotrexate regimens in the treatment of human osteosarcoma but show that formation of tumor MTX polyglutamates is not the sole determinant of response to this agent.
Meyer
W H
WH
Department of Hematology-Oncology, St. Jude Children's Research Hospital, Memphis, TN 38105.
Loftin
S K
SK
Houghton
J A
JA
Houghton
P J
PJ
D000818:Animals; D001826:Body Fluids / Q000378:metabolism*; D002250:Carbon Radioisotopes; D004247:DNA / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005561:Formates / Q000378:metabolism; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008727:Methotrexate / Q000031:analogs & derivatives / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology; D051379:Mice; D009368:Neoplasm Transplantation; D012516:Osteosarcoma / Q000188:drug therapy*; D011099:Polyglutamic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D014183:Transplantation, Heterologous; D014316:Tritium
D002250:Carbon Radioisotopes; D005561:Formates; D014316:Tritium; D011099:Polyglutamic Acid; C014085:methotrexate polyglutamate; D004247:DNA; D008727:Methotrexate