| Production of therapeutics from mammalian cell cultures has become an important component of the biopharmaceutical industry whose sales in the United States alone are expected to approach {dollar}16 billion by the year 2004. Unfortunately, the in vitro cultivation of mammalian cells often has associated with it a variety of insults potently capable of inducing apoptosis, or programmed cell death (PCD). Such apoptotic death is likely responsible for tremendous losses in revenue to biotechnology firms. Consequently, this work was dedicated to establishing methods capable of limiting PCD in order to determine strategies that could make bioprocesses more cost-effective. Initial efforts focused on the use of a number of chemical agents with anti-apoptotic activity including, N-acetylcysteine, pyrrolidine dithiocarbamate, bongkrekic acid, and N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone. Each of these reagents protected rat carcinomal cells from PCD induced upon infection with a virus vector, albeit to varying degrees. Furthermore, three of these chemicals allowed for gains in recombinant protein production relative to the untreated controls. Though promising, such reagents may be precluded from regular use during large scale cultures due to their cost. Therefore, further work examined the potential of generating cell lines capable of constitutively producing anti-apoptotic proteins. Several cell lines, most notably baby hamster kidney and Chinese hamster ovary, were engineered to overexpress either bcl-2 or bcl-xL and subsequently subjected to a variety of culture insults including virus vector infections, glucose deprivation, serum withdrawal, and exposure to ammonium chloride. During the virus infections, both genes demonstrated the ability to limit apoptosis in each cell line while, in many cases, enhancing production of a virally-encoded recombinant protein. Furthermore, upon exposure to the other culture insults, at least one gene product was able to prolong the viable lifetimes of each cell line, which enabled cultures to recover from the insult during rescue attempts. In its entirety, this work demonstrates the utility of inhibiting the apoptotic process as a means of extending culture periods while, in some cases, increasing product yields. |
