Effects of nIFN beta and rIFN gamma on growth and morphology of two human melanoma cell lines: comparison between two- and three-dimensional culture.

We compared the anti-proliferative effects of natural interferon beta (nIFN beta) and recombinant interferon gamma (rIFN gamma) on 2 human melanoma cell lines, IGRI and SK-Mel28, grown in 2-dimensional monolayer and in 3-dimensional spheroid culture. In monolayer culture, growth of both lines was inhibited in a dose-dependent manner by 5-day treatments with IFN in concentrations ranging between 1 and 5,000 IU/ml. Incubations with 120 IU/ml nIFN beta or 25 IU/ml rIFN gamma led to a 50% growth inhibition of IGRI cells. A 50% growth inhibition of SK-Me128 cells was obtained with 60 IU/ml nIFN beta, whereas even 5,000 IU/ml rIFN gamma inhibited the growth of this line by only 30%. Growing these melanoma cell lines in 3-dimensional spheroid culture for 5 days reduced their sensitivity to interferon. Growth inhibition values of 50% were achieved with 3,000 IU/ml rIFN gamma or 9,000 IU/ml nIFN beta for IGRI spheroids and 10,000 IU/ml nIFN beta for SK-Me128 spheroids, while 10,000 IU/ml rIFN gamma reduced the growth of SK-Me128 spheroids by only 25%. Outgrowth tests showed that the proliferative capacity after 5-day incubations with IFN was only reduced in IGRI spheroids treated with high doses of nIFN beta. The macroscopically observed increased density of interferon-treated spheroids could be confirmed by light microscopy as corresponding to reduced intercellular space in these spheroids. Scanning electron microscopy furthermore showed variations on the surface of IFN-treated spheroids as well as in cellular organization and structures between cells, hinting at a possible involvement of extracellular matrix substances in the reaction to interferons.(ABSTRACT TRUNCATED AT 250 WORDS)