Changes in fluorescent intensity of the cyanine dye, 3,3'-dipropyl-2,2'-thiodicarbocyanine iodide [diS-C(3)-(5)], were monitored in Ehrlich ascites tumor cells (EATC) in correlation with glycolytic energy metabolism and endogenous respiration. After addition of glucose to EATC, membrane potentials monitored by diS-C(3)-(5) increased. The cyanine dyes were incorporated into EATC in proportion to the membrane potentials, and inhibited the endogenous respiration of EATC by more than 85% at a concentration of 100 μM. The inhibited respiration was partially released by addition of an uncoupler of oxidative phosphorylation (DNP). The respiratory activity of NAD-linked substrates in mitochondria (2.7 mg protein/ml) was also inhibited by diS-C(3)-(5), which inhibited the Rotenone-sensitive sites of the respiratory chains (Site 1) and increased Mg(++)ATPase activity. The inhibition by diS-C(3)-(5) of endogenous respiration in EATC in vivo was also effective even 24 hours after administration of the dye into the peritoneal cavity. The mean survival times of EATC-bearing mice were significantly prolonged by the administration of diS-C(3)-(5). The data suggest that the cell membrane potential is a useful factor when administering therapeutic drugs into target cells.
Ehrlich ascites tumor cell