Relationship between cell size and specific thrombopoietin productivity in Chinese hamster ovary cells during dihydrofolate reductase-mediated gene amplification

Abstract

When parental Chinese hamster ovary (CHO) cell clones that are capable of producing thrombopoietin (TPO) were subjected to high methotrexate (MTX) concentrations, clonal variations in cell growth were apparent. In the clones that had no significant enhancement in specific TPO productivity (q Tpo) when a higher level of MTX was administered, their growth was not depressed significantly nor their cell size changed significantly. On the other hand, those clones that showed a significant enhancement in q Tpo at higher a MTX dosage, cell growth was depressed initially but recovered during successive sub-cultures. Furthermore, their cell size increased, which suggested that changes in cell size may be indicative of an enhanced qTpo. When the enhancement of the qTpo of 9 clones after a high MTX dosage was plotted against the extent of the increase of their size, there was a linear correlation (r=0.80, P<0.001, ANOVA), which suggested that an enhancement of q after high MTX administration can be measured by the increase in their cell size. Taken together, our data demonstrate that the selection of amplified CHO cell clones with enhanced qTpo can be done based upon their increased size and growth pattern. This facilitates the development of highly productive recombinant CHO cell lines.