Validation of a CFD model for cell culture bioreactors at large scale and its application in scale-up

Among all the operating parameters that control the cell culture environment inside bioreactors, appropriate mixing and aeration are crucial to ensure sufficient oxygen supply, homogeneous mixing, and CO2 stripping. A model-based manufacturing facility fit approach was applied to define agitation and bottom air flow rates during the process scale-up from laboratory to manufacturing, of which computational fluid dynamics (CFD) was the core modeling tool. The realizable k-ε turbulent dispersed Eulerian gas-liquid flow model was established and validated using experimental values for the volumetric oxygen transfer coefficient (kLa). Model validation defined the process operating parameter ranges for application of the model, identified mixing issues (e.g., impeller flooding, dissolved oxygen gradients, etc.) and the impact of antifoam on kLa. Using the CFD simulation results as inputs to the models for oxygen demand, gas entrance velocity, and CO2 stripping aided in the design of the agitation and bottom air flow rates needed to meet cellular oxygen demand, control CO2 levels, mitigate risks for cell damage due to shear, foaming, as well as fire hazards due to high O2 levels in the bioreactor gas outlet. The recommended operating conditions led to the completion of five manufacturing runs with a 100% success rate. This model-based approach achieved a seamless scale-up and reduced the required number of at-scale development batches, resulting in cost and time savings of a cell culture commercialization process.

Use of spectroscopic process analytical technology for rapid quality evaluation during preparation of CHO cell culture media

Media preparation parameters contribute significantly to media quality, cell culture performance, productivity, and product quality. Establishing proper media preparation procedures is critical for ensuring a robust CHO cell culture process. Process analytical technology (PAT) enables unique ways to quantify assessments and improve media quality. Here, cell culture media were prepared under a wide range of temperatures (40-80°C) and pH (7.6-10.0). Media quality profiles were compared using three real-time PATs: Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, and excitation-emission matrix (EEM) spectroscopy. FTIR and Raman spectroscopies identified shifts in media quality under high preparation temperature (80°C) and at differing preparation pH which negatively impacted monoclonal antibody (mAb) production. In fed-batch processes for production of three different mAbs, viable cell density (VCD) and cell viability were mostly unaffected under all media preparation temperatures, while titer and cell specific productivity of mAb decreased when cultured in basal and feed media prepared at 80°C. High feed preparation pH alone was tolerated but cell growth and productivity profiles deviated from the control condition. Further, charge variants (main, acidic, basic species) and glycosylation (G0F, afucosylation, and high mannose) were examined. Statistically significant differences were observed for one or more of these quality attributes with any shifts in media preparation. In this study, we demonstrated strong associations between media preparation conditions and cell growth, productivity, and product quality. The rapid evaluation of media by PAT implementation enabled more comprehensive understanding of different parameters on media quality and consequential effects on CHO cell culture.

An innovative hybrid modeling approach for simultaneous prediction of cell culture process dynamics and product quality

The use of hybrid models is extensively described in the literature to predict the process evolution in cell cultures. These models combine mechanistic and machine learning methods, allowing the prediction of complex process behavior, in the presence of many process variables, without the need to collect a large amount of data. Hybrid models cannot be directly used to predict final product critical quality attributes, or CQAs, because they are usually measured only at the end of the process, and more mechanistic knowledge is needed for many classes of CQAs. The historical models can instead predict the CQAs better; however, they cannot directly relate manipulated process parameters to final CQAs, as they require knowledge of the process evolution. In this work, we propose an innovative modeling approach based on combining a hybrid propagation model with a historical data-driven model, that is, the combined hybrid model, for simultaneous prediction of full process dynamics and CQAs. The performance of the combined hybrid model was evaluated on an industrial dataset and compared to classical black-box models, which directly relate manipulated process parameters to CQAs. The proposed combined hybrid model outperforms the black-box model by 33% on average in predicting the CQAs while requiring only around half of the data for model training to match performance. Thus, in terms of model accuracy and experimental costs, the combined hybrid model in this study provides a promising platform for process optimization applications.

Application of fucosylation inhibitors for production of afucosylated antibody

Fucosylation is an important quality attribute for therapeutic antibodies. Afucosylated antibodies exhibit higher therapeutic efficacies than their fucosylated counterparts through antibody-dependent cellular cytotoxicity (ADCC) mechanism. Since higher potency is beneficial in reducing dose or duration of the treatment, afucosylated antibodies have attracted a great deal of interest in biotherapeutics development. In this study, novel small molecules GDP-D-Rhamnose and its derivatives (Ac-GDP-D-Rhamnose and rhamnose sodium phosphate) were synthesized to inhibit the enzyme in the GDP-fucose synthesis pathway. Addition of these compounds into cell culture increased antibody afucosylation levels in a dose-dependent manner and had no significant impact on other protein quality attributes. A novel and effective mechanism to generate afucosylated antibody is demonstrated for biologics discovery, analytical method development, process development, and other applications.

Fed-batch performance profiles for mAb production using different intensified N - 1 seed strategies are CHO cell-line dependent

Recent optimizations of cell culture processes have focused on the final seed scale-up step (N - 1 stage) used to inoculate the production bioreactor (N-stage bioreactor) to enable higher inoculation cell densities (2-20 × 106 cells/mL), which could shorten the production culture duration and/or increase the volumetric productivity. N - 1 seed process intensification can be achieved by either non-perfusion (enriched-batch or fed-batch) or perfusion culture to reach those higher final N - 1 viable cell densities (VCD). In this study, we evaluated how different N - 1 intensification strategies, specifically enriched-batch (EB) N - 1 versus perfusion N - 1, affect cell growth profiles and monoclonal antibody (mAb) productivity in the final N-stage production bioreactor operated in fed-batch mode. Three representative Chinese Hamster Ovary (CHO) cell lines producing different mAbs were cultured using either EB or perfusion N - 1 seeds and found that the N-stage cell growth and mAb productivities were comparable between EB N - 1 and perfusion N - 1 conditions for two of the cell lines but were very different for the third. In addition, within the two similar cell growth cell lines, differences in cell-specific productivity were observed. This suggests that the impact of the N - 1 intensification process on production was cell-line dependent. This study revealed that the N - 1 intensification strategy and the state of seeds from the different N - 1 conditions may affect the outcome of the N production stage, and thus, the choice of N - 1 intensification strategy could be a new target for future upstream optimization of mAb production.

Recent advances in upstream process development for production of recombinant adeno-associated virus

Recombinant adeno-associated virus (rAAV) is rapidly emerging as the preferred delivery vehicle for gene therapies, with promising advantages in safety and efficacy. Key challenges in systemic in-vivo rAAV gene therapy applications are the gap in production capabilities versus potential market demand and complex production process. This review summarizes current available information on rAAV upstream manufacturing processes and proposed optimizations for production. The advancements in rAAV production media were reviewed with proposals to speed up the cell culture process development. Furthermore, major methods for genetic element delivery to host cells were summarized with their advantages, limitations, and future directions for optimization. In addition, culture vessel selection criteria were listed based on production cell system, scale, and development stage. Process control at the production step was also outlined with an in-depth understanding of production kinetics and quality control.

Experimental and computational characterization of mass transfer in high turndown bioreactors

Single-use bioreactors (SUBs, or disposable bioreactors) are extensively used for the clinical and commercial production of biologics. Despite widespread application, minimal results have been reported utilizing the turndown ratio; an operation mode where the working range of the bioreactor can be expanded to include low fluid volumes. In this work, a systematic investigation into free surface mass transfer and cell growth in high turndown single-use bioreactors is presented. This approach, which combines experimental mass transfer measurements with numerical simulation, deconvolutes the combined effects of headspace mixing and the free surface convective mass transfer on cell growth. Under optimized conditions, mass transfer across the interface alone may be sufficient to satisfy oxygen demands of the cell culture. Within the context of high turndown bioreactors, this finding provides a counterpoint to traditional sparge-based bioreactor operational philosophy. Multiple monoclonal antibody-producing cell lines grown using this high turndown approach showed similar viable cell densities to those cells expanded using a traditional cell bag rocker. Furthermore, cells taken directly from the turndown expansion and placed into production showed identical growth characteristics to traditionally expanded cultures. Taken together, these results suggest that the Xcellerex SUB can be run at a 5:1 working volume as a seed to itself, with no need for system modifications, potentially simplifying preculture operations.

Strategies for Controlling Afucosylation in Monoclonal Antibodies during Upstream Manufacturing

Core fucosylation is a highly prevalent and significant feature of N-glycosylation in therapeutic monoclonal antibodies produced by mammalian cells where its absence (afucosylation) plays a key role in treatment safety and efficacy. Notably, even slight changes in the level of afucosylation can have a considerable impact on the antibody-dependent cell-mediated cytotoxicity. Therefore, implementing control over afucosylation levels is important in upstream manufacturing to maintain consistent quality across batches of product, since standard downstream processing does not change afucosylation. In this review, the influences and strategies to control afucosylation are presented. In particular, there is emphasis on upstream manufacturing culture parameters and media supplementation, as these offer particular advantages as control strategies over alternative approaches such as cell line engineering and chemical inhibitors. The review discusses the relationship between the afucosylation influences and the underlying cellular metabolism to promote increased process understanding. Also, briefly highlighted is the value of empirical and mechanistic models in evaluating and designing control methods for core fucosylation. This article is protected by copyright. All rights reserved.

Upstream cell culture process characterization and in-process control strategy development at pandemic speed

As of early 2022, the coronavirus disease 2019 (COVID-19) pandemic remains a substantial global health concern. Different treatments for COVID-19, such as anti-COVID-19 neutralizing monoclonal antibodies (mAbs), have been developed under tight timelines. Not only mAb product and clinical development but also chemistry, manufacturing, and controls (CMC) process development at pandemic speed are required to address this highly unmet patient need. CMC development consists of early- and late-stage process development to ensure sufficient mAb manufacturing yield and consistent product quality for patient safety and efficacy. Here, we report a case study of late-stage cell culture process development at pandemic speed for mAb1 and mAb2 production as a combination therapy for a highly unmet patient treatment. We completed late-stage cell culture process characterization (PC) within approximately 4 months from the cell culture process definition to the initiation of the manufacturing process performance qualification (PPQ) campaign for mAb1 and mAb2, in comparison to a standard one-year PC timeline. Different strategies were presented in detail at different PC steps, i.e., pre-PC risk assessment, scale-down model development and qualification, formal PC experiments, and in-process control strategy development for a successful PPQ campaign that did not sacrifice quality. The strategies we present may be applied to accelerate late-stage process development for other biologics to reduce timelines.

Retrospective assessment of clonal origin of cell lines

Cell lines used for the manufacture of recombinant proteins are expected to arise from a single cell as a control strategy to limit variability and ensure consistent protein production. Health authorities require a minimum of two rounds of limiting dilution cloning or its equivalent to meet the requirement of single cell origin. However, many legacy cell lines may not have been generated with process meeting this criteria potentially impeding the path to commercialization. A general monoclonality assessment strategy was developed based on using the site of plasmid integration for a cell's identity. By comparing the identities of subclones from a master cell bank (MCB) to each other and that of the MCB, a probability of monoclonality was established. Two technologies were used for cell identity, Southern blot and a PCR assay based on plasmid-genome junction sequences identified by splinkerette PCR. Southern blot analysis revealed that subclones may have banding patterns that differ from each other and yet indicate monoclonal origin. Splinkerette PCR identifies cellular sequence flanking the point(s) of plasmid integration. The two assays together provide complimentary data for cell identity that enables proper monoclonality assessment and establishes that the three legacy cell lines investigated are all of clonal origin.

Metabolomic and quality data for early and late passages of an antibody-producing industrial CHO cell line

In this article, we provide four data sets for an industrial Chinese Hamster Ovary (CHO) cell line producing antibodies during a 14-day bioreactor run. This cell line was selected for further evaluation because of its significant titer loss as the cells were passaged over time. Four conditions that differed in cell bank ages were run for this dataset. Specifically, cells were passaged to passage 12, 21, 25, and 37 and then used in this experiment. Once the run commenced the following datasets were gathered: 1). Glycosylation data for each reactor 2). Size Exclusion Chromatography (SEC) data for the antibodies produced which allowed for the identification of high and low molecular weight species in the samples (N-Glycan and SEC data was taken on day 14 only). 3/4). Metabolites levels measured using Nuclear Magnetic Resonance (NMR) and liquid chromatography-mass spectroscopy (LC-MS) for all reactors over the time course of days 1, 4, 6, 8, 12, and 14. We also provide a graph of the glutamine levels for cells of different ages as an example of the utility of the data. These metabolomics data provide relative amounts for 36 metabolites (NMR) and 109 metabolites (LC-MS) over the 14-day time course. These data were collected in connection with a co-submitted paper [1].

Applications of small molecules in modulating productivity and product quality of recombinant proteins produced using cell cultures

Mammalian cell cultures have been used extensively for production of recombinant protein therapeutics such as monoclonal antibodies, fusion proteins and enzymes for decades. Small molecules have been investigated as media supplements to improve process productivity and reduce cost of goods. Those chemicals can lead to significant yield improvement through different mechanisms such as cell cycle modulation, cellular redox regulation, etc. In addition to productivity, small molecules have also been routinely used to regulate post-translational modifications of recombinant proteins. This review summarizes key applications of small molecules in protein productivity improvement and product quality control.

Osmolality as a lever to modulate the N-glycolylneuraminicacid (Neu5Gc) level of a recombinant glycoprotein produced in Chinese hamster ovary cells

Glycoproteins could be highly sialylated, and controlling the sialic acid levels for some therapeutic proteins is critical to ensure product consistency and efficacy. N-acetylneuraminic acid (Neu5Ac, or NANA) and N-glycolylneuraminic acid (Neu5Gc, or NGNA) are the two most common forms of sialic acids produced in mammalian cells. As Neu5Gc is not produced in humans and can elicit immune responses, minimizing Neu5Gc formation is important in controlling this quality attribute for complex glycoproteins. In this study, a sialylated glycoprotein was used as the model molecule to study the effect of culture osmolality on Neu5Gc. A 14-day fed-batch process with osmolality maintained at physiological levels produced high levels of Neu5Gc. Increase of culture osmolality reduced the Neu5Gc level up to 70-80%, and the effect was proportional to the osmolality level. Through evaluating different osmolality conditions (300-450 mOsm/kg) under low or high pCO₂ , we demonstrated that osmolality could be an effective process lever to modulate the Neu5Gc level. Potential mechanism of osmolality impact on Neu5Gc is discussed and is hypothesized to be cytosol NADH availability related. Compared with cell line engineering efforts, this simple process lever provides the opportunity to readily modulate the Neu5Gc level in a cell culture environment.

Understanding the effect of high gas entrance velocity on Chinese hamster ovary (CHO) cell culture performance and its implications on bioreactor scale-up and sparger design

There are three main potential sources for cell shear damage existing in stirred tank bioreactors. One is the potential high energy dissipation in the immediate impeller zones; another from small gas bubble burst; and third is from high gas entrance velocity (GEV) emitting from the sparger. While the first two have been thoroughly addressed for the scale-up of Chinese hamster ovary (CHO) cell culture knowing that a wide tolerable agitation range with non-damaging energy dissipation exists and the use of shear protectants like Pluronic F68 guard against cell damage caused by bubble burst, GEV remains a potential scale-up problem across scales for the drilled hole or open pipe sparger designs. GEV as high as 170 m/s due to high gas flow rates and relatively small sparger hole diameters was observed to be significantly detrimental to cell culture performance in a 12,000 L bioreactor when compared to a satellite 2 L bioreactor run with GEV of <1 m/s. Small scale study of GEV as high as 265 m/s confirmed this. Based on the results of this study, a critical GEV of >60 m/s for CHO cells is proposed, whereas previously 30 m/s has been reported for NS0 cells by Zhu, Cuenca, Zhou, and Varma (2008. Biotechnol. Bioeng., 101, 751-760). Implementation of new large scale spargers with larger diameter and more holes lowered GEV and helped improve the cell culture performance, closing the scale-up gap. Design of such new spargers was even more critical when hole plugging was discovered during large scale cultivation hence exacerbating the GEV impact. Furthermore, development of a scale down model based on mimicry of the large scale GEV profile as a function of time was proven to be beneficial for reproducing large scale results.

Enabling speed to clinic for monoclonal antibody programs using a pool of clones for IND-enabling toxicity studies

The importance of speed to clinic for medicines that may address unmet medical needs puts pressure on product development timelines. Historically, both toxicology and first-in-human clinical materials are generated using the same clonal-derived cells to ensure safety and minimize any development risks. However, cell line development with single cell cloning is time consuming, and aggravated by the time needed to screen for a lead clone based on cell line stability and manufacturability. In order to achieve faster timelines, we have used pools of up to six clones for earlier production of drug substance for regulatory filing-enabling toxicology studies, and then the final single clone was selected for production of clinical materials. This approach was enabled by using platform processes across all stages of early development, including expression vectors, host cell lines, media, and production processes. Through comprehensive cell culture and product quality analysis, we demonstrated that the toxicology material was representative of the clinical material for all six monoclonal antibody programs evaluated. Our extensive development experience further confirmed that using a pool of clones for toxicology material generation is a reliable approach to shorten the early development timeline.

Suitability of a generic virus safety evaluation for monoclonal antibody investigational new drug applications

Biologics produced from CHO cell lines with endogenous virus DNA can produce retrovirus-like particles in cell culture at high titers, and other adventitious viruses can find their way through raw materials into the process to make a product. Therefore, it is the industry standard to have controls to avoid introduction of viruses into the production process, to test for the presence of viral particles in unclarified cell culture, and to develop purification procedures to ensure that manufacturing processes are robust for viral clearance. Data have been accumulated over the past four decades on unit operations that can inactivate and clear adventitious virus and provide a high degree of assurance for patient safety. During clinical development, biological products are traditionally tested at process set points for viral clearance. However, the widespread implementation of platform production processes to produce highly similar IgG antibodies for many indications makes it possible to leverage historical data and knowledge from representative molecules to allow for better understanding and control of virus safety. More recently, individualized viral clearance studies are becoming the rate-limiting step in getting new antibody molecules to clinic, particularly in Phase 0 and eIND situations. Here, we explore considerations for application of a generic platform virus clearance strategy that can be applied for relevant investigational antibodies within defined operational parameters in order to increase speed to the clinic and reduce validation costs while providing a better understanding and assurance of process virus safety.

Advancement in bioprocess technology: parallels between microbial natural products and cell culture biologics

The emergence of natural products and industrial microbiology nearly eight decades ago propelled an era of bioprocess innovation. Half a century later, recombinant protein technology spurred the tremendous growth of biologics and added mammalian cells to the forefront of industrial producing cells in terms of the value of products generated. This review highlights the process technology of natural products and protein biologics. Despite the separation in time, there is a remarkable similarity in their progression. As the new generation of therapeutics for gene and cell therapy emerges, its process technology development can take inspiration from that of natural products and biologics.

Dramatic regression of coronary artery stenosis three years after diagnosis

While strategies for the prevention of the progression of coronary artery lesions have been proposed, documentation of the regression of significant coronary artery lesions is rare. Lifestyle modifications and exercise have been reported to influence the regression of coronary disease, but a dramatic disappearance of coronary artery lesions demonstrated angiographically has been rarely reported. We describe a case where diet and lifestyle modifications, along with lipid-lowering therapy, led to the significant regression of coronary artery stenosis.

Control of misincorporation of serine for asparagine during antibody production using CHO cells

A recombinant monoclonal antibody produced by Chinese hamster ovary (CHO) cell fed-batch culture was found to have amino acid sequence misincorporation upon analysis by intact mass and peptide mapping mass spectrometry. A detailed analysis revealed multiple sites for asparagine were being randomly substituted by serine, pointing to mistranslation as the likely source. Results from time-course analysis of cell culture suggest that misincorporation was occurring midway through the fed-batch process and was correlated to asparagine reduction to below detectable levels in the culture. Separate shake flask experiments were carried out that confirmed starvation of asparagine and not excess of serine in the medium as the root cause of the phenomenon. Reduction in serine concentration under asparagine starvation conditions helped reduce extent of misincorporation. Supplementation with glutamine also helped reduce extent of misincorporation. Maintenance of asparagine at low levels in 2 L bench-scale culture via controlled supplementation of asparagine-containing feed eliminated the occurrence of misincorporation. This strategy was implemented in a clinical manufacturing process and scaled up successfully to the 200 and 2,000 L bioreactor scales.

Heterogeneous distribution of lysine 6-aminotransferase during cephamycin C biosynthesis in Streptomyces clavuligerus demonstrated using green fluorescent protein as a reporter

The cellular distribution of the cephamycin biosynthetic enzyme lysine 6-aminotransferase (LAT) has been studied in Streptomyces clavuligerus hyphae by confocal microscopy using the S65T mutant of green fluorescent protein (GFP) as a reporter. LAT mediates the first committed step in the biosynthesis of the secondary metabolite cephamycin C by S. clavuligerus. The enzymic activity of LAT varies with time during the growth of S. clavuligerus in liquid medium. To investigate if this temporal variation occurs uniformly amongst all hyphae, S. clavuligerus was transformed with a plasmid containing the LAT-encoding gene translationally fused to the GFP-encoding gene. The LAT-GFP fusion product displayed fluorescence spectral characteristics of GFP, and showed similar temporal characteristics of LAT activity compared to the wild-type strain of S. clavuligerus. The transformed strain exhibited a heterogeneous distribution of fluorescence in mycelia grown in liquid cultures. This distribution varied significantly as the batch progressed: only a fraction of the mycelia fluoresced in the early growth phase, whereas nearly all hyphae fluoresced by the late growth phase. Thereafter, a non-uniform distribution of fluorescence was again observed in the declining growth phase. A large fraction of the non-fluorescent cells in the declining growth phase were found to be non-viable. Observations of S. clavuligerus colonies grown on solid agar also showed variation of LAT-GFP expression at different stages of growth. These observations in the solid phase can be explained in terms of nutrient deprivation and signalling molecules. The results suggest that physiological differentiation of S. clavuligerus mycelia leading to cephamycin C biosynthesis is both temporally and spatially distributed. The findings also revealed that the observed heterogeneity was independent of the position of individual cell compartments within the hypha. The potential of GFP as a reporter for the quantitative study of cephamycin biosynthesis at the cellular level has also been demonstrated.

Time-lapsed confocal microscopy reveals temporal and spatial expression of the lysine epsilon-aminotransferase gene in Streptomyces clavuligerus

To investigate the temporal and spatial expression patterns of the gene (lat ) encoding lysine epsilon-aminotransferase (LAT) for cephamycin C biosynthesis, a mutant form of green fluorescent protein (mut1GFP) was integrated into the Streptomyces clavuligerus chromosome (strain LH369), resulting in a translational fusion with lat. LAT activity and fluorescence profiles of the recombinant protein paralleled the native LAT enzyme activity profile in wild-type S. clavuligerus, which peaked during exponential growth phase and decreased slowly towards stationary phase. These results indicate that the LAT-Mut1GFP fusion protein retains both LAT and GFP functionality in S. clavuligerus LH369. LH369 produced wild-type levels of cephamycin C in minimal medium culture conditions supplemented with lysine. Time-lapsed confocal microscopy of the S. clavuligerus LH369 strain revealed the temporal and spatial characteristics of lat gene expression and demonstrated that physiological development of S. clavuligerus colonies leading to cephamycin C biosynthesis is limited to the substrate mycelia.

Precursor and cofactor as a check valve for cephamycin biosynthesis in Streptomyces clavuligerus

The biosynthesis of secondary metabolites is closely linked to primary metabolism via the supply of precursors, cofactors, and cellular energy. The availability of these precursors and cofactors can potentially be rate-limiting for secondary metabolism. A combined experimental and kinetic modeling approach was used to examine the regulation of flux in the cephamycin biosynthetic pathway in Streptomyces clavuligerus. The kinetic parameters of lysine 6-aminotransferase (LAT), the first enzyme leading to cephamycin biosynthesis and one which was previously identified as being a rate-limiting enzyme, were characterized. LAT converts lysine to alpha-aminoadipic acid using alpha-ketoglutarate as a cosubstrate. The K(m) values for lysine and alpha-ketoglutarate were substantially higher than those for their intracellular concentrations, suggesting that lysine and alpha-ketoglutarate may play a key role in regulating the flux of cephamycin biosynthesis. The important role of this precursor/cosubstrate was supported by simulated results using a kinetic model. When the intracellular concentrations and high K(m) values were taken into account, the predicted intermediate concentration was similar to the experimental measurements. The results demonstrate the controlling roles that precursors and cofactors may play in the biosynthesis of secondary metabolites.

Metabolic engineering of cephalosporin biosynthesis in Streptomyces clavuligerus

The biosynthesis of beta-lactams is one of the most thoroughly studied antibiotic pathways. The availability of the characteristics and the time profiles of activities of enzymes involved in the biosynthesis allows one to critically evaluate the potential rate-limiting steps in its production. Our approach to understanding the control of beta-lactam biosynthesis has been pursued using a two-stage strategy: (1) to predict the rate-limiting steps using a kinetic model and (2) to relax the rate-limiting steps by engineering the biosynthetic pathway or by altering the kinetic parameters of the predicted key rate-limiting enzyme. Kinetic analysis of the pathway dynamics of cephamycin C production in Streptomyces clavuligerus was performed using data obtained from wild type. Sensitivity analysis revealed that the availability of precursor alpha-aminoadipic acid and activity of ACV synthetase were the potential rate-limiting steps. Relaxation of the precursor limitation was accomplished by integration of an additional copy of the gene encoding lysine-epsilon-aminotransferase (lat) into the chromosome. The recombinant strain showed an increased level of cephamycin C production as expected. The intracellular levels of different intermediates in the pathway in batch cultures were analyzed.