UV-INDUCED MELANOMA - A KARYOTYPE WITH A SINGLE TRANSLOCATION IS STABLE AFTER ALLOGRAFTING AND METASTASIS

Metastatic melanoma cell lines were derived from a lymph node of a lab oratory opossum, Monodelphis domestica, which had been exposed to mid- wavelength ultraviolet radiation (UVB) initially as a suckling young, and subsequently as a shaved juvenile and adult. The melanoma cell lin es were dendritic and pigmented in vitro and contained a t(6;8)(p13;q1 3) as the only cytogenetic abnormality. The translocation was detected in 15% of primary cultures (passage 2) from the affected lymph node a nd in 100% of two ring-clone-derived lines, L1 and L2. The breakpoint or resulting partial trisomy of chromosomes 8 may have played a functi onal role in the tumorigenesis or metastasis of the tumor. The t(6;8) served as a convenient cytogenetic marker for allogeneic grafting stud ies in Monodelphis, The L2 cells were allografted subcutaneously (s.c. ) into genetically diverse suckling young at 3 weeks of age and result ed in the growth of invasive, pigmented, primary and metastatic lesion s affecting lymph nodes, lung, and other tissues. Metastatic variant c ell lines, M1 and M3, were derived from the affected lungs of two anim als and both lines demonstrated the same t(6;8), without additional nu merical or structural chromosomal abnormalities. The maintenance of ka ryotypic stability with a single translocation during in vivo tumor gr owth and dissemination in this new allografting model is quite remarka ble, as most human metastatic melanomas exhibit multiple structural an d numerical cytogenetic abnormalities.