DIFFERENTIATION OF A HUMAN RHABDOMYOSARCOMA CELL-LINE AFTER ANTINEOPLASTIC DRUG-TREATMENT

The feasibility of treating solid tumours with differentiation therapy using antineoplastic drugs is currently being investigated, but the e mergence of multidrug resistance remains the major limitation to this therapeutic approach. A rhabdomyosarcoma cell line resistant to actino mycin D (RD-DAC) has been used as an in vitro model to investigate, wi th light and electron microscopy, the degree of differentiation in mul tidrug-resistant cells. The parental cell line (RD), derived from a hu man embryonic-type rhabdomyosarcoma, is undifferentiated, with no evid ence of specific ultrastructural markers. Examination of resistant cel ls by transmission electron microscopy revealed myofilaments arranged parallel to the long axis of the cell, which was considered clear evid ence of myogenic differentiation. These observations suggest that acti nomycin D, the drug of choice in the treatment of rhabdomyosarcoma, in duces differentiation in the cell line RD. It is postulated that multi drug resistance can interfere with cellular differentiation.