Kinetics of post-irradiation expression of cell surface protein associated with neoplastic transformation of human hybrid cells

Human hybrid cells (HeLa x skin fibroblast) can be neoplastically transformed by gamma radiation. The tumorigenic cells produced express a cell surface protein (M.WT.75KD) characteristics of spontaneous tumorigenic segregants for which we have a monoclonal antibody. Radiation-induced colonies and foci of neoplastic cells can be detected using an immunoperoxidase staining technique. Using this technique the authors previously reported a dose-response relationship for the induction of tumorigenic cells. The purpose of the present study is to establish the optimal experimental parameters for these experiments in terms of maximizing the yield of neoplastically transformed cells. Consequently they have measured this yield as a function of time post-irradiation for cells treated at high density and replated 6 hours post-irradiation at approximately 500 cells/T-25 flask or 1500 cells/T-75. The data indicate that colonies of neoplastically transformed cells can be detected as early as 17 days post-irradiation. The yield rises rapidly over the period 17-22 days following which it begins to stabilize. The mechanistic implications of this observation are discussed