Disparate mechanisms of antifolate resistance provoked by methotrexate and its metabolite 7-hydroxymethotrexate in leukemia cells: implications for efficacy of methotrexate therapy.
Methotrexate (MTX) is one of the leading drugs in the treatment of leukemia, but extensive metabolism to 7-hydroxymethotrexate (7-OHMTX) can limit its therapeutic efficacy. In this study we investigated whether 7-OHMTX itself can provoke anti-folate resistance that may further disrupt MTX efficacy. For this purpose, we developed resistance to 7-OHMTX as well as MTX in 2 human leukemia cell lines (CCRF-CEM and MOLT-4) by stepwise exposure to increasing concentrations of 7-OHMTX and MTX. Consequently, both leukemia cell lines displayed marked levels of resistance to 7-OHMTX (> 10-fold) and MTX (> 75-fold). The underlying mechanism of resistance in the MTX-exposed cells was a marked decrease (> 10-fold) in reduced folate carrier (RFC)-mediated cellular uptake of MTX. This was associated with transcriptional silencing of the RFC gene in MTX-resistant CCRF-CEM cells. In contrast, the molecular basis for the resistance to 7-OHMTX was due solely to a marked decreased (> 95%) in folylpolyglutamate synthetase (FPGS) activity, which conferred more than 100-fold MTX resistance upon a short-term exposure to this drug. This is the first demonstration that 7-OHMTX can provoke distinct modalities of antifolate resistance compared with the parent drug MTX. The implications of this finding for MTX efficacy and strategies to circumvent MTX resistance are discussed.
Department of Oncology and Pathology, Cancer Center Karolinska (CCK), Karolinska University Hospital, 171 76 Stockholm, Sweden.
Kambiz
K
Fotoohi
Gerrit
G
Jansen
Yehuda G
YG
Assaraf
Lilah
L
Rothem
Michal
M
Stark
Ietje
I
Kathmann
Jacek
J
Gregorczyk
Godefridus J
GJ
Peters
Freidoun
F
Albertioni
D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D001692:Biological Transport; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D005973:Glutamine / Q000378:metabolism; D006801:Humans; D007938:Leukemia; D008727:Methotrexate / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology*
D000964:Antimetabolites, Antineoplastic; D005973:Glutamine; C011864:7-hydroxymethotrexate; D008727:Methotrexate