title: Patterns of cross-resistance to the antifolate drugs trimetrexate, metoprine, homofolate, and CB3717 in human lymphoma and osteosarcoma cells resistant to methotrexate.
abstract: Methotrexate (MTX)-resistant sublines of malignant human cells were selected in vitro by stepwise increase in drug concentration in the medium. By this procedure a subline of Burkitt's lymphoma cells (RAJI) was made 290-fold resistant (RAJI/MTX-R), T-cell leukemia cells (CCRF-CEM) were obtained 210-fold resistant (CEM/MTX-R), and 3 MTX-resistant human osteosarcoma lines were selected: TE-85/MTX-R (19-fold resistant; relative to wild-type); MG-63/MTX-R (8-fold resistant); and SAOS-2/MTX-R (200-fold resistant). We also studied a B-cell lymphoblastoid line, WI-L2/m4, that was 13,000-fold resistant. Assay of cellular dihydrofolate reductase (DHFR) showed the following pattern of activity in resistant cell lines, relative to parental cell activity: RAJI/MTX-R, 550-fold increased; CEM/MTX-R, unchanged; TE-85/MTX-R, 4-fold increased; MG-63/MTX-R, 6-fold increased; SAOS-2/MTX-R, unchanged; and WI-L2/m4, 110-fold increased. Measurement of MTX membrane transport showed decreased uptake in CEM/MTX-R and SAOS-2/MTX-R, relative to parental cell lines. The other DHFR-overproducing cells all gave normal initial MTX uptake rates but increased total uptake. The DHFR-overproducing lines all had significant cross-resistance to both metoprine and trimetrexate; the two lines with defective MTX transport were not cross-resistant, and the CEM/MTX-R cells showed collateral sensitivity to these agents. Only minor cross-resistance to homofolic acid was found in all MTX-resistant lines. The highly MTX-resistant RAJI/MTX-R and WI-L2/m4 cells showed minor cross-resistance to the dual inhibitor of thymidylate synthetase and DHFR, CB3717 (5- and 15-fold, respectively). These studies demonstrated that, depending upon the mechanism of resistance, MTX-resistant human tumor cells may be effectively killed by antifolates with different routes of uptake into cells, or with a different enzyme target. Thus, there are at least three functionally distinct classes of folate antagonist with antitumor activity.
mesh_terms: D000970:Antineoplastic Agents / Q000633:toxicity*; D001692:Biological Transport; D002051:Burkitt Lymphoma / Q000188:drug therapy / Q000378:metabolism; D002460:Cell Line; D004351:Drug Resistance; D005492:Folic Acid / Q000031:analogs & derivatives / Q000627:therapeutic use; D005493:Folic Acid Antagonists / Q000627:therapeutic use*; D006801:Humans; D007700:Kinetics; D007945:Leukemia, Lymphoid / Q000188:drug therapy / Q000378:metabolism; D008223:Lymphoma / Q000188:drug therapy* / Q000378:metabolism; D008727:Methotrexate / Q000378:metabolism / Q000627:therapeutic use*; D012516:Osteosarcoma / Q000188:drug therapy / Q000378:metabolism; D011739:Pyrimethamine / Q000031:analogs & derivatives* / Q000627:therapeutic use / Q000633:toxicity; D011799:Quinazolines / Q000627:therapeutic use / Q000633:toxicity; D013329:Structure-Activity Relationship; D013601:T-Lymphocytes / Q000187:drug effects; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism; D016597:Trimetrexate
chemical_list: D000970:Antineoplastic Agents; D005493:Folic Acid Antagonists; D011799:Quinazolines; C006308:metoprine; C100117:homofolic acid; C031662:CB 3717; D005492:Folic Acid; D013762:Tetrahydrofolate Dehydrogenase; D016597:Trimetrexate; D008727:Methotrexate; D011739:Pyrimethamine