This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Casto, B. C. Articles by DiPaolo, J. A. Search for Related Content PubMed PubMed Citation Articles by Casto, B. C. Articles by DiPaolo, J. A.

Development of a Focus Assay Model for Transformation of Hamster Cells in Vitro by Chemical Carcinogens¹

BioLabs, Inc., Northbrook, Illinois 60062 [B. C. C., N. J.], and Biology Branch, Carcinogenesis Program, National Cancer Institute, Bethesda, Maryland 20014 [J. A. D.]

A reproducible, quantitative focus assay for transformation of freshly isolated diploid Syrian hamster embryo cells by chemical carcinogens has been developed by modifying the technique used for the colony assay. The transformed foci are observed against a normal cell background, and the transformed morphology is verified by examination with a stereomicroscope; consequently, the number of areas that need to be examined is greatly reduced relative to the colony assay.

Transformed cell foci were induced in hamster secondary cells after treatment for 6 days with acetoxyacetylaminofluorene, alfatoxin B₁, benzo(a)pyrene, ß-propiolactone, dibenz(a,h)anthracene, ethyl methanesulfonate, 3-methyl-cholanthrene, methyl methanesulfonate, or N-methyl-N'-nitro-N-nitrosoguanidine. Three types of foci were observed: a fibroblast-like, an epithelial-like, and a round-cell focus. Cells from isolated, transformed foci grew to higher cell densities than controls, lacked oriented growth, and formed tumors when inoculated into weanling hamsters.

The frequency of focus formation ranged from 4 to 7 foci/10⁵ surviving cells at chemical concentrations that killed less than 90% of the cells. The transformation frequency was independent of cell number from 5 x 10³ to 5 x 10⁴ cells/dish, but it was dependent upon chemical concentration, length of treatment, and time of chemical addition after cell transfer. The expression of transformed foci was inhibited by reduction of the fetal bovine serum from 10 to 1%, substitution of calf serum for fetal bovine serum, or addition of dextran sulfate, diethylaminoethyl dextran, or 0.5% agar to the medium within 3 days after chemical treatment.

¹ The work upon which this publication is based was performed at the National Cancer Institute and at BioLabs, Inc., pursuant to NIH-NCI Contract NO1-CP-45615 with the National Cancer Institute, Department of Health, Education and Welfare.

Received 9/15/76. Accepted 7/11/77.