Cultivation of recombinant, insulin-secreting AtT-20 cells as free and entrapped spheroids

Animal cells from endocrine glands have potential applications in bioprocessing, for the production of hormones, enzymes, possibly also recombinant proteins, and in tissue engineering, for the development of immunoisolated, implantable devices for long-term treatment of endocrine disorders. Immunoisolation can be achieved by surrounding cells with a biocompatible polymer which allows diffusion of nutrients and metabolites, including hormones, but excludes higher molecular weight antibodies and cytotoxic cells. Primary hormone-secreting cells cannot be effectively amplified in culture, so the large-scale application of implantable systems based on such cells is limited by cell availability. In this study, we conducted an initial assessment of the feasibility of using transformed, continuous cell lines in immunoisolated devices. The model system employed consisted of mouse pituitary tumor AtT-20 cells which secrete recombinant proinsulin and an insulin-like peptide and exhibit a high growth potential. Cells were cultivated as spheroids in spinner flasks and entrapped as such in alginate/polylysine/alginate beads. Free and entrapped spheroids were propagated in fed-batch, suspension cultures. Entrapment did not significantly affect spheroid metabolism or basal secretion. Entrapped spheroids did not increase in size or number and maintained roughly constant metabolic and basal secretory activities over a 15-day period. Free spheroids in suspension increased in size during the sami period, but also maintained constant metabolism and basal secretion, apparently because of a concomitant increase in hypoxic and/or necrotic cells. The potential of using continuous cell lines in the development of bioartificial endocrine organs is discussed.