Tumour growth and melanogenesis in hamster tumours in vivo and in vitro: growth, cytochemistry and ultrastructure of tissue cultural cell lines.

Cell lines were established from three hamster melanomas. One was a spontaneous melanotic tumour which lost its ability to produce pigment. Two were induced with DMBA (9.10 dimethyl 1,2-benz/a/anthracene). One of these was pigmented. The two amelanotic lines (CHT-1 and 2) produced highly malignant amelanotic tumours after reimplantation of tissue culture cells. Electron microscopy showed that melanin forming organelles were absent. Tyrosinase activity was also absent. The line established from the pigmented tumour (CHT-8) retained its pigment production for the first seven transfers. Cells from these cultures produced slow growing pigmented tumours. Cells from the 7th to the 35th transfer, a period of 28 weeks, failed to produce tumours but cells from the 36th and subsequent transfers produced slow growing amelanotic tumours. The change in tumorigenicity was not related to changes in the growth rate of the cells in vitro: this remained constant after the 11th transfer generation. Tyrosinase activity and a whole range of melanin forming organelles were present in cells of transfers 1 to 7 but absent from subsequent transfers. Type A and H virus particles were present in the two amelanotic cell lines, CHT-1 and 2. Although the two amelanotic lines produced highly malignant tumours the loss of a differentiated character--melanin production--was not invariably associated with increased malignancy. Three cell lines should provide a good system for studying the relationship between tumour differentiation and growth.