Limitations to the amplification and stability of human tissue-type plasminogen activator expression by Chinese hamster ovary cells

Authors

  • C. H. Fann,

    1. Biotechnology Laboratory, University of British Columbia, 237-6174 University Boulevard, Vancouver, British Columbia V6T 1Z3, Canada; telephone: 604-822-5835; fax 604-822-2114
    2. Department of Chemical and Biological Engineering, University of British Columbia, 237-6174 University Boulevard, Vancouver, British Columbia V6T 1Z3, Canada; telephone: 604-822-5835; fax 604-822-2114
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  • F. Guirgis,

    1. Biotechnology Laboratory, University of British Columbia, 237-6174 University Boulevard, Vancouver, British Columbia V6T 1Z3, Canada; telephone: 604-822-5835; fax 604-822-2114
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  • G. Chen,

    1. Biotechnology Laboratory, University of British Columbia, 237-6174 University Boulevard, Vancouver, British Columbia V6T 1Z3, Canada; telephone: 604-822-5835; fax 604-822-2114
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  • M. S. Lao,

    1. MDS Panlabs Biosafety, Bothell, Washington, USA
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  • J. M. Piret

    Corresponding author
    1. Biotechnology Laboratory, University of British Columbia, 237-6174 University Boulevard, Vancouver, British Columbia V6T 1Z3, Canada; telephone: 604-822-5835; fax 604-822-2114
    2. Department of Chemical and Biological Engineering, University of British Columbia, 237-6174 University Boulevard, Vancouver, British Columbia V6T 1Z3, Canada; telephone: 604-822-5835; fax 604-822-2114
    • Biotechnology Laboratory, University of British Columbia, 237-6174 University Boulevard, Vancouver, British Columbia V6T 1Z3, Canada; telephone: 604-822-5835; fax 604-822-2114
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Abstract

Chinese hamster ovary cell production of recombinant tissue-type plasminogen activator (t-PA) was increased by amplification of cotransfected dihydrofolate reductase cDNA using stepwise adaptation to increasing methotrexate (MTX) concentrations. The highest producing clones were isolated at 5 μM MTX and yielded 26,000 U/106 cells/day t-PA (43 μg/106 cells/day). Above 25 μM MTX, cell specific t-PA production rates became increasingly variable and the cDNA copynumbers decreased. No apparent correlation between the cell specific t-PA production rate and the growth rate was observed upon subcloning of the amplified cells. When MTX selection was removed, the t-PA production rate decreased up to tenfold within 40 days; this was accompanied by an up to 60% drop in cDNA copynumber. Subclones isolated after 108 days of culture in the absence of MTX were, on average, sixfold more stable than their parental cells. In culture without MTX, the maximum stable t-PA production rate obtained (over 250 days) was 7000 ± 750 U/106 cells/day (∼12 μg/106 cells/day), approximately threefold lower than the maximum unstable levels of production reached under selective pressure. Taken together, these results define a wide range of the highest t-PA expression rates obtained under MTX selection, for which stable expression without selection has not been reported. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 69: 204–212, 2000.

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