Effects of advanced leukemia on hepatic drug-metabolizing activity in the mouse

Mice that had received 10(6) P388 leukemia cells IV 8 days previously exhibited a decrease in the components of the hepatic microsomal mixed function oxidase, with a 58% decrease in cytochrome P-450, and up to a 60% decrease in hepatic microsomal metabolism of biphenyl. Liver weight was increased by 49% due to infiltration of the liver with leukemic cells. Changes in liver drug-metabolizing activity and liver weight were not seen 6 days after administration of P388 leukemia. There was a small increase in serum liver enzyme but no increase in total serum bilirubin in tumor-bearing mice. In vivo total-body plasma clearance of cyclophosphamide, a drug metabolized by hepatic cytochrome P-450, was decreased to 53 ml/min/kg in mice that had received P388 cells 8 days earlier, as against 97.2 ml/min/kg in control mice. Cytochrome P-450-independent metabolism of [14C]5-fluorouracil, measured by means of [14C]CO2 in the breath over 3 h, was decreased to 21% of the dose administered by 8 days after tumor cell administration, compared with 31% of the dose in control mice. P388 leukemia cells growing in the ascitic form in the intraperitoneal cavity of mice did not release an inhibitor of 5-fluorouracil metabolism into the ascitic fluid. Total-body plasma clearance of indocyanine green was decreased to 11 ml/min/kg by 8 days after P388 cell administration, compared with 36 ml/min/kg in control mice. The decrease in indocyanine green clearance might reflect a decrease in hepatic blood flow in the tumor-bearing mice. A possible explanation for the decrease in hepatic drug metabolism caused by P388 leukemia is that the hepatocytes are deprived of oxygen and nutrients by the tumor in the liver, coupled with or caused by a physical obstruction of hepatic blood flow.