Response of multicellular tumor spheroids to liposomes containing TNF-?

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Abstract
This publication describes a new model to investigate the influence of tumor necrosis factor-α (TNF-α) on a three-dimensional glial cell aggregate under defined, standardized, reproducible conditions using the glioma cell line A 172. The cells are initially grown as normal monolayer culture until they reach a cell density of up to 1×106. Subsequently they are grown as spheroids by the liquid overlay technique. Spheroids grown in this way were divided into ten groups of more than 50 cell aggregates. Three groups were coincubated with free TNF-α in increasing dosages (100 ng/ml, 200 ng/ml and 1000 ng/ml); three groups were incubated with empty liposomes (0.2 mg/ml, 0.4 mg/ml and 2 mg/ml); three groups received liposomes which had been loaded with TNF-α, and one group, which received no treatment, served as control. The diameter of the spheroids ranged from 80 μm to 350 μm. There was no significant difference in growth between the 3 groups treated with ‘free’ TNF-α. Comparing spheroids treated with TNF-α with those which had been coincubated with empty liposomes, there was a significant difference (p<0.001) in growth, which correlated with the amount of liposomes. Similarly, free TNF-α had a significantly (P<0.001) stronger growth-inhibiting effect as compared to liposomes loaded with TNF-α. Comparing the groups treated with liposomes only to those treated with liposomes loaded with TNF-α, the latter exhibited a more marked (although not significantly) growth-inhibiting effect. The preliminary conclusion is that the major growth-inhibiting effect seems to be mediated by the liposomes. This phenomenon is in agreement with results obtained in monolayer cultures.