EFFECT OF PROTEIN-INTAKE ON TUMOR-GROWTH AND CELL-CYCLE KINETICS

Previous research has documented significant acceleration of tumor gro wth in animals receiving short-tern parenteral nutrition. This study w as performed to determine the effect of long-term enteral protein inta ke on tumor cell cycle kinetics in the tumor-bearing host. Fifty Lewis /Wistar rats with subcutaneous mammary tumor implants (AC-33) were ran domized to receive a standard protein diet (22.0% protein; 4.20 kcal/g ) or protein-depleted diet (0.03% protein; 4.27 kcal/g). Animals were sacrificed after 7 or 14 days on each diet and tumor cytokinetics dete rmined by flow cytometry. Tumor volume was significantly reduced in an imals receiving the protein-depleted versus standard protein diet afte r 14 days (P < 0.01). No difference was found in tumor cell cycle kine tics (% G(0)/G(1), S, or G(2)/M populations) or tumor growth fraction (S + G(2)/M) in animals receiving standard or protein-depeleted diet a fter 7 or 14 days. These results suggest that reduced tumor growth wit h prolonged protein depletion in this model occurs by either (a) movem ent of tumor cells from the active cell cycle to the dormant G(0) stat e or (b) uniform increase of cell cycle duration without changing the relative proportion of cells throughout the cell cycle. The potential therapeutic implications of nutrient-induced alterations in tumor grow th are discussed. (C) 1995 Academic Press, Inc.