Comparative analysis of radiometric and autoradiographic methods in the investigation of DNA synthetic activity of tumor cells in vitro.

DNA synthesis in cell cultures of Ehrlich ascites carcinoma (EAC) was studied by means of autoradiography and liquid scintillation radiometry. The following parameters were compared for estimation of DNA synthesis: a) total radioactivity of incorporated [H-3]thymidine registered by a liquid scintillation counter, b) labeling index (LI) reflecting the relative number of cells which synthesize DNA, and c) mean grain count (MGC) indicating average intensity of DNA synthesis in the S-phase of the cell cycle. Kinetics of total radioactivity of incorporated [H-3]thymidine was determined to correlate better with LI.

The Ehrlich ascites carcinoma (EAC) contains 300-500 Da inhibitor(s) suppressing DNA synthesis in cultured EAC cells and EAC cell division in tumor-bearing mice.

A protein preparation obtained from the Ehrlich ascites carcinoma (EAC) by acetone precipitation, water extraction and subsequent two-step alcohol fractionation reduced significantly EAC cell proliferation in vivo and in vitro. The preparation was found to contain a low molecular-weight growth-inhibitory activity, suppressing both DNA synthesis in cultured EAC cells and EAC cell division in tumor-bearing mice. The approximate molecular weight of this inhibitory component(s) is about 300-500 Da, corresponding to oligopeptide molecule(s).