Effects of Hyperoxia on Growth Characteristics of Metastatic Murine Tumors in the Lung1

Suspensions of an oxygen-sensitive (MT-7) and of an oxygen-insensi tive (M109) tumor cell line were injected i.v. into BALB/c mice. Exposure to 100% O2 after injection of the cells did not modify the initial arrest of either cell line in the lung. Exposure of animals given injections of M I7 cells for 60 h to 100% oxygen decreased the number of lung colonies formed even when onset of oxygen exposure was delayed up to 10 days after injection of the cell suspension. Cell cycle time and growth fraction in lung colonies growing in vivo were estimated from an analysis of the percentage of mitoses labeled. In lung colonies formed by MT-7 cells, hyperoxia produced a mitot ic delay and a 30 to 40% reduction in the growth fraction. In M 109-derived colonies, oxygen did not change cell cycle times or reduce growth fraction. In earlier experiments done in vitro and reported by others it had been found that, in tumor cell lines other than the ones used in the present study, a prolongation of the early prophase was the most oxygen-sensitive event. The present data show that in vivo oxygen inhibits lung colony formation in MT-7 cells by a