Modification of nuclear restriction in vitro by plasma from tumor-bearing animals.

Putative regulatory macromolecules, which may be useful in diagnosis or tumor detection, were identified in the peripheral blood plasma of tumor-bearing animals. We monitored the components by measuring their ability to stimulate messenger RNA (mRNA) release from isolated nuclei in a cell-free system of rat liver nuclei in fortified homologous cytosol. This in vitro test system exhibited near-normal in vivo nuclear RNA restriction. When added to the assay at a protein concentration of 3.0 mg/ml, dialyzed plasma from rats or mice with chemically induced transplantable or primary tumors stimulated mRNA release from 87% to more than 300% over control plasma from normal rats. Plasma from partially hepatectomized rats stimulated only 26% over control plasma. The test system derived from rat liver seemed to permit the monitoring of plasma from other species. Available evidence, particularly relating to tumor-host-interaction, suggests, but does not prove, that regulatory components are released from the tumor cells to the circulation.