On-line heat flux measurements improve the culture medium for the growth and productivity of genetically engineered CHO cells

With the increasingly competitive commercial production of target proteins by hybridoma and genetically engineered cells, there is an urgent requireme nt for biosensors to monitor and control on-line and in real time the growt h of cultured cells. Since growth is accompanied by an enthalpy change, hea t dissipation measured by calorimetry could act as an index for metabolic f low rate. Recombinant CHO cell suspensions producing interferon-gamma were pumped to an on-line flow calorimeter. The results showed that an early ref lection of metabolic change is size-specific heat flux obtained from dividi ng heat flow rate by the capacitance change of the cell suspension, using t he on-line probe of a dielectric spectroscope. Comparison of heat flux with glucose and glutamine fluxes indicated that the former most accurately ref lected decreased metabolic activity. Possibly this was due to accumulation of lactate and ammonia resulting from catabolic substrates being used as bi osynthetic precursors. Thus, the heat flux probe is an ideal on-line biosen sor for fed-batch culture. A stoichiometric growth reaction was formulated and data for material and heat fluxes incorporated into it. This showed tha t cell demand for glucose and glutamine was in the stoichiometric ratio of similar to 3:1 rather than the similar to 5:1 in the medium. It was demonst rated that the set of stoichiometric coefficients in the reaction were rela ted through the extent of reaction (advancement) to overall metabolic activ ity (flux). The fact that this approach can be used for medium optimisation is the basis for an amino-acid-enriched medium which improved cell growth while decreasing catabolic fluxes.