Detection of a cell proliferation-inhibiting factor in the cell-free ascitic fluid of intraperitoneal mouse tumors.

Three cell-free ascitic fluids: MCG3AF, P815AF and SL2AF were obtained from mice injected with MCG3, P815 and SL2 tumor cells, respectively. These ascitic fluids were tested in culture with different normal and tumor mouse cells showing an inhibitory effect on 3H-thymidine and 3H-uridine uptake. The MCG3AF, selected for further study, was tested with a larger number of mouse tumor cell lines and also with normal mouse and human cells. This ascitic fluid inhibited 3H-thymidine and 3H-uridine uptake in all cases. The cell proliferation-inhibiting factor(s) (CPIF) detected in MCG3AF was found to be thermostable and nondialyzable. Further biochemical analysis showed that CPIF is a lipid but with no relationship with very low-density lipoproteins.