Abstract
We examined the antitumor efficacy of rTNF-alpha administration on established tumor at two visceral sites, lungs and liver. Treatment of B6 mice harboring multiple (greater than 100 foci of less than or equal to 0.5 mm diameter) 10-day pulmonary macrometastases from the MCA-106 sarcoma, with dosages of rTNF-alpha (5-10 micrograms, single dose i.v.) that caused hemorrhagic necrosis and regression of a 6 mm MCA-106 s.c. tumor, had no impact on the number (or size) of lung nodules. Similarly, rTNF-alpha failed to show an antitumor effect in B6 mice with advanced day 8 or 10 multiple (greater than 100 foci of less than or equal to 0.5 mm diameter) hepatic metastases at single i.v. doses up to 20 micrograms, as measured by either enumeration of residual liver nodules or survival. B6 mice injected s.c. with MCA-106 sarcoma and treated with rTNF-alpha as a single i.v. dose on day 0, 3, 5, or 7 experienced marked tumor regression only after the day 7 rTNF-alpha injection, when the tumor had achieved a size of 5-6 mm in diameter. Since tumor size appeared important for rTNF-alpha susceptibility in vivo, we next induced a single hepatic tumor of the MCA-106 sarcoma by the direct injection of cells into the left lobe of the liver and treated these mice at day 10 when the nodule had achieved a size of 5-6 mm in diameter. Increasing doses of rTNF-alpha (up to 8 micrograms) given as a single i.v. injection resulted in increasingly greater reductions in hepatic tumor as well as significant survival benefit of the treated mice. Sites of regressing hepatic tumor exhibited central necrosis accompanied by polymorphonuclear leukocytes and lymphocytes. Collectively, these results show that rTNF-alpha administration can mediate a significant antitumor effect on visceral tumor and suggest that tumor size is an important factor in rTNF-alpha susceptibility not only for tumors growing at s.c. sites but also for those established at visceral sites.