Inhibitory effect of polynucleotides on solid tumor produced in mice by Ehrlich ascites cancer cells

Solid tumors produced in mice by Ehrlich ascites cancer cells were completely regressed by treatment with the copolymer of polyriboinosinic acid-polyribocytidylic acid (poly (I):(C)) when 200 microgram of this compound was intravenously injected 3 times a week for 3-4 weeks, starting 7-8 days after transplantation of the tumor. Although the first injection of poly (I):(C) caused hyporeactivity to re-induction of IFN, the subsequent 6 doses stimulated the formation of IFN at 3685 units/ml on average after each injection, strongly suggesting that IFN plays a role in the antitumoral effect of poly (I):(C).