Cell proliferative modulation of MCG 101 sarcoma from mice exposed to hyperbaric oxygenation.

Tumor cell kinetics were studied in C57 Bl/J mice with a transplantable sarcoma, MCG 101, exposed to hyperbaric oxygen (HBO2), 2.8 atm abs, 2 hours daily for 9 days or until spontaneous death. The isoenzymatic pattern of lactate dehydrogenase (LDH) confirmed that there was a significant shift toward aerobic metabolism in tumor tissue as well as in the liver and skeletal muscle. Recruitment of cells from the G0G1 state into DNA synthesis was associated with an increased mobilization of substrates for polyamine synthesis in terms of an elevated ornithine decarboxylase (ODC) activity. However, cell cycle turnover in terms of bivariate flow cytometric analysis after bromodeoxyuridine (BrdUrd) injection, final tumor weight, and survival time were not changed compared with the controls. Tumor cell metabolism demonstrated evidence of an unchanged net energy utilization, in that activities (V(max) of phosphofructokinase (PFK) and LDH were not significantly changed. When the tumor-bearing animals were exposed to advanced HBO2 pressure (3.7 atm abs) for 3 h as a single dose, the DNA distribution and growth rate were not changed immediately. However, 3.5 h later we observed a DNA pattern similar to that after repeated HBO2 treatments, 2.8 atm abs, concomitant with a preponderance of cells in the late S-phase, which is consistent with a block at the entry of G2M. We conclude that MCG 101 sarcoma recovers from HBO2 exposure by an accumulation of cells in the S-phase without significant changes of net tumor growth. This may have relevance to clinical radiocurability.