Tumor cytokinetic effects of acute starvation versus polyamine depletion in tumor-bearing mice.

Previous investigations in our laboratory have demonstrated that both acute host starvation and polyamine depletion by means of the irreversible ODC-inhibitor (ODC = ornithine-decarboxylase) fluoro-methylornithine (DFMO) lead to pronounced growth retardation of rapidly proliferating tumors. The aim of this investigation was to elucidate how these different interventions affect cell kinetics and cell cycle phases in vivo. Adult nongrowing mice (C57Bl/J) bearing a poorly differentiated rapidly growing methylcholanthrene induced sarcoma were used. Combined measurements of bromodeoxyuridine incorporation into DNA and flow cytometric techniques were used. Starvation and DFMO treatment resulted in a prolonged cell cycle transit compared to freely fed animals. Tumor cells from DFMO-treated mice demonstrated an increased time for DNA synthesis and a relatively larger accumulation of cells in the G2M phase, whereas tumor cells from starved animals were accumulated in the G0G1 phase. The fractional cell loss of tumor cell during proliferation was calculated to be around 18% higher in DFMO-treated animals compared to starved and freely fed tumor-bearing mice. This study demonstrates that different mechanisms are involved in tumor growth suppression from substrate deficiency (starvation) and from inhibition of polyamine synthesis.