Studies on the antitumor activities of pyrimidinone-interferon inducers. I. Effect against artificial and spontaneous lung metastases of murine tumors.

Since pyrimidinone compounds induce interferon production in several animal species and have potent antivirus activities, it appeared important to determine whether these compounds could also induce antitumor activities in their recipients. Pyrimidinone compounds 2-amino-5-bromo-6-methyl-4-pyrimidinone (ABMP), 2-amino-5-brome-6-phenyl-4-pyrimidinone (ABPP), and 2-amino-5-iodo-6-phenyl-4-pyrimidinone (AIPP) were studied for their activities against artificial lung metastases of the weakly immunogenic spontaneous fibrosarcoma NFSa, the moderately immunogenic spontaneous mammary carcinoma MCa-K, and the strongly immunogenic 3-methylcholanthrene-induced fibrosarcoma FSa syngeneic to inbred C3Hf/Kam mice. In addition, the therapeutic efficacy of ABPP and AIPP was also determined against spontaneous lung metastases of NFSa. ABPP and AIPP given ip at 250 mg/kg for 2 or 3 consecutive days before or after iv inoculatin of NFSa, FSa, or MCa-K cells greatly reduced the number of tumor nodules developed in the lungs. ABMP, however, was considerably less effective. ABPP and AIPP were also effective in therapy of spontaneous lung metastases of NFSa, especially when these compounds were given before surgical removal of the primary tumor. Neither ABPP nor AIPP was effective against tumor nodules growing in whole-body irradiated (WBI) mice, but both protected mice against enhancement of lung metastasis formation induced by exposure to whole-body irradiation. ABPP was more effective than AIPP in inducing production of interferon in normal mice. When treated with ABPP, WBI mice, however, were unable to produce interferon. These results show that 6-phenyl-pyrimidinone compounds induce strong antitumor activities in mice, which correlated with neither tumor immunogenicity nor the ability of these agents to induce interferon, but which depended on the immune status of the tumor host.