Are parental CHO‐K1 cells appropriate negative controls for engineered CHO cell lines ?: Evidence from label‐free functional assays

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In functional assays, parental cell lines are commonly used as a negative control for cell lines expressing recombinant proteins. Since the apparent primary difference between the two lines is the expression level of the transfected receptor, it is usually assumed that endogenously expressed “background” receptors show similar functionality in both cell lines. Label‐free technologies enable responsiveness testing to a broad variety of endogenous receptors. We have used the Corning® Epic system to empirically test the degree of similarity in the functionality of endogenous receptors in parental CHO‐K1 and a muscarinic receptor‐expressing cell line (CHO‐M).The responsiveness of each cell line to a panel of ~150 receptor agonists (1 μM) was measured on the Epic System. While the two data sets were positively correlated, Bland‐Altman analysis indicated large differences in endogenous receptor responsiveness. Differences were larger when evaluated at later time points. These data indicate that: 1) equivalency of parental to engineered cell lines should be experimentally tested 2) the Epic technology provides an efficient approach for quickly surveying responsiveness to variety of agonists 3) differences between CHO‐K1 and CHO‐M cells extend beyond the expression of the muscarinic receptor and 4) correlation alone is not sufficient to guarantee response equivalency.