Intracellular ribonucleotide pools as a tool for monitoring the physiological state of in vitro cultivated mammalian cells during production processes.

Intracellular analysis has been shown to be useful as a tool for control production processes based on in vitro cultivated hybridoma and recombinant animal cells. Nucleotides were found to present the best target as they reflect the exact physiological state of a culture. Following the progress of batch, perfused, and chemostat cultures cell specific regularities were found in various biochemical correlations which allowed the generation of three characteristic parameters based on the interaction of particular nucleotides: the nucleotide triphosphate (NTP) ratio ([ATP + GTP]/[UTP + CTP]), the uridine (U) ratio (UTP/UDP-GNAc), and the combined ratio NTP/U ([UDP-GNAc (ATP + GTP)/ UTP (UTP + CTP)]). These allowed a direct description of the growth cycle by means of specific values or behavior for every phase of the culture. In particular, the critical phase of entrance into the phase of reduced growth was predicted up to 24 h earlier than was possible with the classical method of microscopic cell control. A specific function for the application of in vitro cultivated processes is proposed with an NTP-to-U plot which combines the results obtained by the cell analysis and which offers a tool for the control and regulation of cell growth-derived procedures.