Melanoma cells growing in aggregates on a non-adhesive poly(HEMA) substrate exhibit polykaryocytosis but do not develop an increased metastatic capability.

B16-F1 melanoma cells were plated onto plastic tissue-culture dishes rendered non-adhesive for cells by coating with 0.12 per cent poly(2-hydroxyethyl methylacrylate), poly(HEMA). These growth conditions caused the normally flat, adherent B16-F1 cells to grow as single cells in suspension. Within 24 hours, the rounded cells formed aggregates and grew at a slower rate than control cells grown at the same density on untreated plastic dishes. Microscopic observations provided evidence that polykaryocytosis was occurring among the aggregates. Following replating onto standard adhesive tissue-culture plastic, 20-30 per cent of the aggregates were observed to contain varying numbers of multinucleated giant cells (polykaryocytes). The study has revealed a previously undescribed propensity of certain B16-F1 cells cultivated as aggregates in suspension to develop into polykaryocytes, most probably as a result of spontaneous tumor cell-tumor cell fusion. The possible relevance of this behavior in vitro to events in tumor progression is discussed. This study, however, does not support the findings of others that the metastatic capability of B16-F1 cells is increased by such non-adherent culture conditions. No increase in metastatic potential was observed for B16-F1 cells, or for a low metastatic clone (F1-7) derived from it, grown for 72 or 96 hours in a spherical configuration compared to control cells grown in a flat, adherent monolayer.