Enhanced antibody production at slowed growth rates: experimental demonstration and a simple structured model

A simple structured model for monoclonal antibody (MAb) production kinetics was formulated by combining the cell cycle theory with the estimated number of MAb-coded messenger RNA (mRNA) molecules per cell: it is assumed that the rate-controlling step is first order in this mRNA and that the growth rate variation does not alter the MAb synthesis rate within any cycle phase but only changes the relative time length of the individual phases. The model predicted "negatively growth associated" MAb production kinetics and thus an enhanced MAb production rate to be achieved by slowing the cell growth. Experiments consistent with these assumptions provided support for the model. Hybridoma cultures where growth was slowed by either a DNA synthesis inhibitor (thymidine or hydroxyurea) or by a selective inhibitor of initiation of nonantibody protein (potassium acetate) exhibited 50-130% MAb production rate enhancement for growth slowed up to 50%; however, further decreases in the growth rate also decreased the MAb production rate. Experiments inconsistent with these assumptions showed other behavior: general inhibition of protein chain elongation (by cycloheximide) or inhibition of ribosomal RNA (rRNA) synthesis (by actinomycin D) each slowed both growth and the specific MAb production rate, leading to net "positive" growth associated MAb production rates. Thus, a need for models with greater structure is also demonstrated.