Several mosquito (Aedes albopictus) cell lines resistant to methotrexate, an inhibitor of the enzyme dihydrofolate reductase, have been characterized. On the basis of growth in the presence of methotrexate, the initial variants, Mtx-101, Mtx-102, Mtx-111, and Mtx-501, were 6.5-fold more resistant to methotrexate than the parental cells. From these cell lines, clones with increased resistance to methotrexate were selected. The second-level variants Mtx-5013 and Mtx-5011, were, respectively, 70- and 200-fold more resistant to methotrexate than wild type cells, and they contained 14- to 20-fold more dihydrofolate reductase activity. In extracts from Mtx-5013 and Mtx-5011 cells, the apparent affinity of dihydrofolate reductase for methotrexate was reduced about 20-fold with respect to that of wild type cells. Resistant cell lines became more sensitive to methotrexate during long-term passage in non-selective medium. This is the first description of methotrexate-resistant variants derived from cultured insect cells.
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Acknowledgements--This work was supported by grant AI-11290 from the National Institute of Allergy and Infectious Diseases and by a grant from the Foundation of the University of Medicine and Dentistry of New Jersey. I thank Mr Adhip Mukerjee for technical assistance and P. A. Vendula and M. Toth for typing the manuscript.
- Aedes albopictus
- Cultured mosquito cells
- dihydrofolate reductase
- methotrexate resistance