DHFR Selection System for High-Producing Eukaryotic Cells
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Solution Overview
Problem
Current methods for selecting high-yield host cells for recombinant protein production in mammalian cells are challenging due to the need for high concentrations of toxic agents like methotrexate, which can alter cell genotypes and reduce the expression of the target gene of interest.
Innovation Solution
A selection system using a DHFR selectable marker with a limiting concentration of folate and DHFR inhibitor in the culture medium, allowing for stringent selection of high-producing host cells with reduced toxic agent usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high concentrations of DHFR inhibitor (methotrexate) are used for selection, then the stringency of selection is improved and high-producing cells are enriched, but the toxic effects on cells increase and cell genotype may be altered
Solution Approach 1:
The patent changes the concentration parameter of folate in the culture medium to a limiting level (low concentration), which fundamentally alters the selection mechanism. Instead of relying on high concentrations of toxic DHFR inhibitors, the system uses folate limitation to create selective pressure, allowing cells to be selected based on their DHFR expression levels without exposing them to high levels of methotrexate toxicity
Solution Approach 2:
The patent introduces folate as an intermediary substance that mediates the selection process. By controlling folate availability in the culture medium, the system indirectly selects for cells with high DHFR expression (and consequently high product expression) without requiring direct application of high concentrations of toxic inhibitors. The folate acts as a bridge between the selection pressure and the desired cellular response
2Productivity
If high concentrations of methotrexate are used to achieve stringent selection, then high-producing clones are enriched, but the expression of the target gene of interest is reduced
Solution Approach 1:
The patent changes the selection parameter from high methotrexate concentration to low folate concentration. This parameter change allows the selection process to favor cells with high DHFR and high product expression simultaneously, rather than creating a trade-off where high inhibitor concentration suppresses target gene expression
Solution Approach 2:
Instead of using high concentrations of DHFR inhibitor to select for high producers (the conventional approach), the patent inverts the strategy by using limiting concentrations of folate (the substrate/cofactor) to achieve the same selection goal. This inversion allows cells to thrive and express high levels of both DHFR and the target gene under folate-limited conditions
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach increases the stringency of selection at lower DHFR inhibitor concentrations, enriching high-producing cells and reducing the number of low producers, thereby increasing the chances of finding ultra-high producing clones with higher productivity.
Implementation Method 1
Dihydrofolate reductase (DHFR) catalyzes the NADP-dependent reduction of dihydrofolic acid to tetrahydrofolic acid
Implementation Method 2
culturing said plurality of eukaryotic host cells in a selective culture medium comprising at least an inhibitor of DHFR and folate in a limiting concentration
Data Source
AI summary
The present invention pertains to a method for selecting at least one eukaryotic host cell expressing a product of interest. The method entails providing a plurality of host cells which are dependent upon folate uptake and contain polynucleotides encoding for the product of interest and a DHFR enzyme. The cells are cultured in a selective culture medium containing at least an inhibitor of DHFR and folate. The expressed cells are then selected.