Insect cell physiology

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Viruses from the genus Baculovirus, are attractive as pesticides and as vectors for producing foreign proteins in insect cells. because insect cells are relatively easy to cultivate, faithfully perform some of the post-translational modifications, allow for complex formation to take place between the two proteins coexpressed in cultures infected with two hybrid viruses, and often can produce large quantities of proteins, baculovirus technology has found its way to a number of undustrial applications for expression of a variety of proteins (see review Murhammer, 1991; O’Reilly et al., 1992). In addition to proteins, production of baculovirus itself as insecticide represents a major potential for use of insect cell cultures (Wood, 1995). The final product yield whether a protein or the virus, is influenced by several factors such as the cell line (eg. Lynn & Hink, 1980; McIntosh & Grasela, 1984; Hink et al., 1991; Wickham et al., 1992) and virus type (Fraser, 1989), passage number of virus (Wickham et al., 1991), medium composition (eg. Cho et al., 1989; Hink et al., 1991), dissolved oxygen concentration (eg. Scott et al., 1992; Wang et al., 1993), time and the multiplicity of infection (MOI) (Licari & Bailey, 1991; Bedard et al., 1994) nature of protein (Hink et al., 1991), cell density (Wickham et al., 1992) and stage of growth and metabolism (eg. Caron et al., 1990; Lindsay et al., 1992; Reuveny et al., 1993). Despite significant advance in the genetics of Baculovirus/insect cell expression system, our understanding of cellular physiology during preand post infection is relatively limited. An expanded understanding of metabolic features of insect cells will prove extremely useful to the bioprocess and biochemical engineers who work towards improving insect cell culture productivity. Several recent articles have addressed consumption of carbohydrate and amino acid and formation of the metabolic by-products in insect cell cultures. Those studies, reviewed first in this article, have significantly enhanced the metabolic knowledge of insect cells. Substantially more insights, however, may be obtained by a regirous analysis of primary metabolic pathways. Our recent work (Ferrance et al., 1993), has demonstrated the feasibility of metabolic flow analysis for insect cell growth in a serum-free medium. This manusscript also provides a summary of metabolic pathway analysis and highlights the assumptions, describes the lessons learned, and ourlines the future work in a more critical fashion than is available in ferrance et al. (1993). Finally, future research directions critical for attaining detailed metabolic insights are outlined in the last section of this manuscript.