Slow cytotoxicity of the polysaccharide levan on tumor cells in vitro

Previous studies have shown that 1 h preincubation with levan caused a sharp decrease in tumorigenicity of tumor cells, although cell viability was not affected. In the present study, the possibility that levan might change the sensitivity of Lewis lung carcinoma cells to the host immune system and that levan might cause delayed damage were tested. Cell morphology, DNA synthesis, cell multiplication and viability as well as osmotic fragility were followed during several days in culture. Levan was found not to affect cell immunogenicity. The polysaccharide destroyed tumor cells by a rather peculiar mechanism: after a seemingly normal or even enhanced growth in culture during 3-5 days, cells suddenly burst. During the apparently normal growth, several morphological changes were observed: cell volume increased, cytoplasm swelled by apparent water uptake and some cells contained two or more nuclei. Levan-treated cells were found to be more susceptible to osmotic shock than non-treated cells. The reason for the sudden cell death could be a gradual increase in volume, up to a point which is no more compatible with membrane integrity, resulting in cell lysis.