Ultrastructural study of the persistence of colchicine-induced cytological changes in Harding-Passey melanoma.

Electron microscopic observations were undertaken on Harding-Passey melanoma in control tumors, colchicine-treated tumors, and tumors that were passed through five transplantations in mice subsequent to colchicine treatment. The untreated Harding-Passey melanoma tumor was composed of pleomorphic cells the cytoplasm of which contained tubulovesicular mitochondria and numerous free and membrane-attached ribosomes. Type A virus particles were observed in both mitotic and interphase cells. Colchicine-treated tumors exhibited several typical colchicine mitotic cells arrested in metaphase. A most significant feature of the colchicine administration was the appearance of microfilaments in both interphase and mitotic cells, a feature not observed in cells of the untreated tumor. Electron microscopy of colchicine-treated tumors carried through five transplantations at biweekly intervals revealed the presence of microfilaments in tissues fixed at each of the transplantations. It therefore appears that the cytological effects of colchicine resulting in the appearance of filaments in melanocytes of the Harding-Passey melanoma are more enduring than they were initially presumed to be.