Preneoplastic phenotype and chromosome changes of cultured human Bloom syndrome fibroblasts (strain GM 1492).

The Bloom syndrome fibroblast strain, GM 1492, was examined for phenotypic properties generally associated with neoplastic cells. A serial clonogenicity assay indicated that these cells can proliferate in culture, achieving approximately twice the number of population doublings as compared to normal human skin fibroblasts. Strain GM 1492 appeared to be partially transformed in that these cells showed a slight degree of anchorage independence when grown in methylcellulose, and also appeared to have relaxed growth requirements compared to normal fibroblasts. GM 1492 cells are heteroploid, with 20 to 80 chromosomes/cell and a modal chromosome number of 44. Cytogenetic analysis of G-banded metaphase chromosomes indicated that most cells contained at least one copy of each normal human chromosome, and many cells exhibited only aneuploidies with no detectable chromosomal rearrangements. Minute chromosomes were seen in a few of the metaphase cells examined. GM 1492 cells did not form tumors in athymic nude mice. Since many of the characteristics of GM 1492 cells are similar to those seen only in tumor cells, but the strain is nontumorigenic, we suggest that GM 1492 cells are preneoplastic and thus represent an ideal system for the in vitro study of human neoplastic progression.