MALIGNANT-MELANOMA IN ULTRAVIOLET-IRRADIATED LABORATORY OPOSSUMS - INITIATION IN SUCKLING YOUNG, METASTASIS IN ADULTS, AND XENOGRAFT BEHAVIOR IN NUDE-MICE

Litters of suckling young of the laboratory opossum (Monodelphis domes tica) were irradiated with UV light from sunlamps with a spectral emis sion peak at 302 nn (UVB) to induce melanocytic nevi. Total doses of 0 .87-5.0 kJ/m(2) were divided equally among up to 14 exposures during t he 19 days from birth. Of 358 sucklings exposed, 217 survived to weani ng, and 22 (10%) possessed a nevus when shaved and examined at or afte r weaning. Affected animals were then exposed 3 times/week to 125 J/m( 2) of UVB for up to 45 weeks to promote progression to malignancy. Nev i of 8 of the 20 chronically-exposed animals progressed to malignant m elanoma with metastases to lymph node(s). Cell cultures were prepared from affected nodes to confirm that pigmented nodal cells were metasta tic melanomas. One established cell line (TD15L) contained highly pigm ented, dendritic, malignant melanoma cells. These cells, injected s.c, as xenogeneic grafts into athymic nude mice, remained viable in the s ubcutis and were moderately tumorigenic in the dermis. UVR exposure of Monodelphis sucklings is a novel, effective, and proficient way of in itiating melanocytic lesions for studies on susceptibility and progres sion to melanoma, and the cell lines derived from these melanomas will provide promising new reagents for chemotherapy and immunotherapy inv estigations.