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The influence of drug‐exposure conditions on the development of resistance to methotrexate or ZD1694 in cultured human leukaemia cells
Author(s) -
Takemura Yuzuru,
Kobayashi Hiroyuki,
Gibson William,
Kimbell Rosemary,
Miyachi Hayato,
Jackman Ann L.
Publication year - 1996
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/(sici)1097-0215(19960328)66:1<29::aid-ijc6>3.0.co;2-0
Subject(s) - antifolate , methotrexate , thymidylate synthase , pharmacology , antimetabolite , biology , medicine , chemotherapy , fluorouracil
Abstract The influence of drug‐exposure conditions on the development of resistance to methotrexate (MTX) or ZD1694 was studied by treating MOLT‐3 human lymphoblastic‐leukaemia cells in a continuous or a pulsatile (high‐dose, short‐term) drug‐exposure schedule. Continuous exposure of the cells to MTX with stepwise escalation of the drug concentrations resulted in a MTX‐resistant sub‐line (MOLT‐3/MTX 10,000 ) with impaired reduced‐folate carrier (RFC) and increased dihydrofolate‐reductase (DHFR) activity. Conversely, a MTX‐resistant clone (MOLT‐3/MTX·P‐9) with unaltered RFC and DHFR activity, but with decreased cellular accumulation of antifolates, was selected by high‐dose short‐term treatment of the cells with MTX. MTX resistance in the latter cells was pronounced after short‐term rather than continuous‐exposure incubation with MTX, suggesting defective polyglutamation of the drug. On the other hand, 2 ZD1694‐resistant sub‐lines which were established by continuous (MOLT‐3/ZD1694·C) or by pulsatile drug‐exposure schedule (MOLT‐3/ZD1694·P‐9) demonstrated extremely low accumulation and poor retention of [ 3 H]ZD1694, with no change of initial drug uptake and little or no increase of thymidylate‐synthase (TS) activity, irrespective of drug‐exposure conditions for their establishment. HPLC analysis displayed a virtual absence of ZD1694 polyglutamates in both ZD1694‐resistant sub‐lines and low accumulation in MOLT‐3/MTX·P‐9 as compared with the parent line. However, folylpolyglutamate‐synthetase (FPGS) mRNA was only moderately decreased in the 2 ZD1694‐resistant sub‐lines and to an even lesser extent in MOLT‐3/MTX·P‐9. In addition, γ‐glutamyl‐hydrolase (GGH) activity was not increased, but was slightly down‐regulated in the polyglutamation‐defective sublines. These results indicate that the mechanism(s) of the resistance developed may depend not only on drug‐exposure conditions while raising resistance but also on the biochemical properties of the drug. © 1996 Wiley‐Liss, Inc.