Changes in DNA content of rat tracheal epithelial cells during neoplastic progression in vitro

Flow cytometric DNA analysis was used to compare nuclear DNA content of carcinogen-induced F-344 rat tracheal epithelial cell lines as they progressed from non-tumorigenic (preneoplastic) to tumorigenic (neoplastic) populations in vitro. Normal tracheal cell populations were used as diploid reference cells. All of the tracheal epithelial cell lines established from carcinogen-treated tracheas showed increases in nuclear DNA content as compared to normal cell populations. For five cell lines, measurements were made during the preneoplastic state as well as after conversion to the neoplastic state. Four of the five cell lines showed a major shift in DNA content as the culture progressed from preneoplastic to neoplastic populations. However, there was no consistent change in DNA content as cultures progressed to neoplastic populations in vitro. Two cell lines showed shifts to higher levels as the cultures became tumorigenic, while two showed shifts to lower levels. Additionally two cell lines (3F3 and 165D) had DNA distribution profiles indicative of mixed cell populations during the neoplastic phase. Cloning experiments of cell line 3F3 confirmed that those cells having a model DNA value the same as that of their preneoplastic progenitor populations were non-tumorigenic. Evidence that such shifts in DNA content correlate with comparable changes in chromosome number was presented for the 3F3 cell line. These studies demonstrate that the transition from preneoplastic tracheal epithelial cells to neoplastic population is often associated with a change in DNA content, and would suggest that the malignant cell type emerges as a new cell type from preneoplastic progenitor populations.