Some methods of assaying inhibitors of cell proliferation.

Inhibition of cell proliferation by leucocyte extracts containing the granulocytic chalone has been monitored in various ways. Target cells were rat bone marrow cells and chloroleukaemia cells cultured on cover glasses, as well as mouse marrow cells cultured in vivo and in vitro in diffusion chambers. Provided that the technique is optimized, the in vitro rat cell assays yielded reliable results with different types of radioactive DNA precursors. With the diffusion chamber techniques cells synthesizing DNA were killed specifically by hydroxyurea, rather than labelling them with e.g. 3H-thymidine. Inhibition of proliferation then showed up as a decreased cell killing, as compared with the controls. Inhibition of proliferation of both progenitor and transit cells could be demonstrated in this way, without interference by added thymidine.