Growth Inhibition by Interferon Beta and Gamma of MDA 886Ln Monolayer Cells and Multicellular Tumor Spheroids: A Differentiation Therapy Model for Squamous Cell Carcinoma

Abstract

OBJECTIVE: The ability of interferon beta (IFN-beta) and interferon gamma (IFN-gamma) to modulate growth and differentiation of squamous carcinoma was studied. DESIGN: Two squamous carcinoma models (MDA 886Ln monolayer cells and multicellular tumor spheroids [MTSs], an in vitro system with three-dimensional in vivo-like structure) were used. Effects of interferons were examined with growth and differentiation assays. RESULTS: In 5-day monolayer growth assays, both interferons (IFNs) exhibited dose-dependent growth inhibition between 0 and 10(4) U/mL; IFN-gamma was more inhibitory than IFN-beta (inhibitory concentration for 50% inhibition of 9 and 900 U/mL for IFN-gamma and IFN-beta, respectively). Multicellular tumor spheroid growth was examined by sizing MTSs over a 9-day growth period. Multicellular tumor spheroids were resistant to IFN-beta with exposures of up to 50,000 U/mL. Similarly, MTSs were resistant to IFN-gamma for the first several days, with growth inhibition becoming evident between days 7 to 9 of culture. As a marker of differentiation, transglutaminase activity was quantified after 5 days of treatment. Both IFNs induced increased transglutaminase activity in monolayer cells: IFN-beta was twice as effective as IFN-gamma. In contrast, 5-day treated MTSs showed no induction although their endogenous activity was higher. Flow cytometric analysis of monolayer cells for induction of class I and II major histocompatibility complex showed that both IFNs induced class I antigens but only IFN-gamma could induce class II. CONCLUSIONS: With their three-dimensional architecture, MTSs were more resistant to IFN-induced growth inhibition and differentiation induction than monolayer cells. Thus, mode of growth (monolayer vs MTS) is an important factor in responsiveness to IFN treatment; this suggests that MTSs may produce information that is more relevant to in vivo usage than monolayer cells.