Enhanced experimental metastatic capacity of a human tumor line following treatment with 5-azacytidine.

We have studied the effect of the nucleoside analogue 5-azacytidine (5-azaC) a known activator of gene expression, on the metastatic behavior of the human melanoma cell line DX3. After exposure to 3 microM 5-azaC for 24 h cells were carried through five subcultures before being tested for their metastatic capacity. Following i.v. injection in BALB/c nude mice, cells treated with 5-azaC showed a 40-fold increase in the number of lung tumor nodules as compared to that obtained with control cells. Tumors resulting from 5-azaC-treated cells exhibited a 5-fold increase in mitotic figures, considerable cellular pleomorphism, and variation in the histological character of the individual nodules. These in vivo differences were not reflected in vitro where treated and untreated cells showed no significant differences in morphology, karyotypes, growth rates, saturation densities, or plating efficiencies. Cells populating the lung tumor nodules retained their increased metastatic capacity through successive cycles of growth in vitro followed by reinjection into nude mice and indeed the ability of the cell lines to form lung tumors was increased with the succeeding cycles in vivo. These cell lines, each established from individual tumor nodules, maintained a human karyotype and reacted positively with human-specific antiserum. Characterization of these lines showed that while there were no alterations in in vitro growth behavior the selected lines exhibited a decreased latency period for s.c. tumor formation, increased retention in the lungs following i.v. injection, and enhanced lung nodule formation (60- to 80-fold compared to control cells). Examination of genomic DNA showed that treatment with 5-azaC brought about a significant decrease (50%) in the percentage of methylated cytosine residues but this extensive hypomethylation was not maintained in the lung tumor nodule-derived cell lines.