valinomycin and Leukemia-P388

Intraperitoneal administration of liposomal valinomycin (MLV-VM) with cis-diamminedichloroplatinum(II) (cDDP) had significant antitumor activity against murine P388 leukemia and inhibited the growth of OVCAR-3 tumors in a nude mouse model of human ovarian cancer. This tumor is a teratoma originating in the ovary with pathogenesis and metastatic properties similar to those of human ovarian cancer. Drug was given to the mice once every 5 days for 4 doses beginning 1 day after i.p. implantation of 10(7) or 5 x 10(7) OVCAR-3 tumor cells. For P388 leukemia, drug was given i.p. once or on days 1 and 5 after tumor inoculation. Despite the use of low doses of MLV-VM, the antitumor activity of the combination [increase in life span (%T/C), 289%-294%] represents a 4-log cell kill over the additive effect of the two drugs, indicating a synergistic interaction between MLV-VM and cDDP. Likewise, low doses of the drug combination produced a synergistic interaction on human ovarian OVCAR-3 tumors, and tumor-free, long-term survivors were obtained. Combined therapy of liposome-incorporated valinomycin and cisplatin was well tolerated and produced no overlapping nephrotoxicity, although a decrease in liver enzyme markers (alkaline phosphatase and/or alkaline aminotransferase) with MLV-VM was observed. These results appear to suggest that MLV-VM with cDDP may have considerable potential for the treatment of ovarian cancer disseminated within the peritoneal cavity, although the frequency and sequence of drug administration may need to be improved.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Cisplatin; Drug Carriers; Female; Humans; Infusions, Parenteral; Leukemia P388; Liposomes; Mice; Mice, Inbred Strains; Neoplasm Transplantation; Ovarian Neoplasms; Treatment Outcome; Valinomycin

In fura-2 stained drug-sensitive and multidrug-resistant P388 cells, 50 mM KCl failed to provoke an increase in the fluorescent signal, indicating that potential-dependent Ca2+ channels are not present in either cell line. Therefore the circumvention of drug-resistance by verapamil must be related to some other mechanism. In the present study, verapamil and two other circumventors of drug-resistance, tamoxifen and dipyridamole were found to induce an increase in the synthesis of phosphatidylcholine in multidrug-resistant but not in drug-sensitive cells. The relative resistance of multidrug resistance cells to permeabilization by digitonin indicates that the organization of the plasma membrane lipids in these cells must be different from the one occurring in drug-sensitive cells. Extended exposure of multidrug-resistant cells to verapamil negates the resistance to digitonin. This effect of verapamil reflects its ability to modify the lipid organization of the plasma membrane of multidrug-resistant cells. It is suggested that if the lipid composition of the cell membrane is altered by these drugs as was found for whole cells, the change could explain the increase in drug permeability.

Topics: Animals; Cell Membrane; Cell Membrane Permeability; Choline; Digitonin; Dipyridamole; Drug Resistance; Fura-2; Ionomycin; Leukemia P388; Lipids; Phosphatidylcholines; Potassium Chloride; Tamoxifen; Tumor Cells, Cultured; Valinomycin; Verapamil

Transport pathways for spermidine (Spd) were characterized in mammalian cells in culture of different origin, i.e. L 1210, P 388, C 6, U 251, Balb/c 3T3 normal and transformed by virus SV40 (SV40/3T3). The kinetic constants (Km and Vmax) for 14C-Spd uptake were found to be different in these cells. Spd uptake was inhibited by spermine and putrescine in all cells. Preloading of these cells with system A and other amino acids, including ornithine, usually did not affect Spd uptake, except in L 1210 and C 6 cells, where Spd uptake was accelerated by 2-aminoisobutyric acid, demonstrating that in these two cell lines the polyamines share the system A pathway. Iso-osmotic replacement of Na+ by choline chloride in the assay medium resulted in a decrease in Spd uptake which suggests that Spd uptake is Na+ activated. In all cells, Spd uptake was inhibited by gramicidin and the Ca2+ ionophore A 23187. The degree of inhibition varied among the cells. Valinomycin (K+ ionophore) inhibited Spd uptake by C 6, P 388, Balb/c 3T3 and SV40/3T3 but not by L 1210 and U 251 cells. Treatment with N-ethylmaleimide or p-L 1210, C 6, Balb/c 3T3 and SV40/3T3 cells did not affect appreciably the uptake process. Some newly synthesized polyamine analogues inhibited the Spd uptake of all cells.

Topics: Amino Acids; Animals; Biological Transport; Calcimycin; Fibroblasts; Glioma; Gramicidin; Humans; Leukemia L1210; Leukemia P388; Mice; Mice, Inbred BALB C; Polyamines; Sodium; Spermidine; Sulfhydryl Reagents; Tumor Cells, Cultured; Valinomycin

Use of liposomal drug delivery systems can enhance the therapeutic potential of membrane active anti-cancer and anti-infectious drugs. Thus, the therapeutic index of the important antifungal agent amphotericin B is markedly improved via incorporation of the drug into liposomes. The mechanistic basis of this effect seems to be an increase in the selectivity of the drug at the cellular level. Thus, free amphotericin B can readily partition into both fungal and mammalian membranes and can cause toxicity to both types of cells, giving rise to the notorious in vivo toxicity of this drug. By contrast, when amphotericin B is formulated in certain types of liposomes, the drug still readily partitions into fungal membranes but can no longer partition into animal cell membranes, thus markedly reducing its toxicity. Liposomes can also be used to reduce the toxicity of membrane-active antitumor drugs. Thus, the peptide ionophore valinomycin is far less toxic to animals when presented in liposomal form. Nonetheless, the drug retains useful antitumor activity in this form. The underlying basis of the enhanced therapeutic index of liposomal valinomycin is unknown at this time but is being explored. The development of membrane-active anti-tumor drugs, in conjunction with liposomal delivery systems, could be an important new approach in cancer chemotherapy. While no anticancer drug is likely to be free of toxic side effects, the toxicities engendered by membrane-active antitumor drugs are likely to affect a different spectrum of tissues and organs than those caused by "conventional" antitumor drugs. Thus membrane-active drugs could complement existing drugs and provide a valuable adjunct to therapy.

Topics: Amphotericin B; Animals; Candida; Cell Membrane; Chemistry, Pharmaceutical; Hemolysis; Infections; Kidney; Leukemia P388; Leukemia, Experimental; Liposomes; Microscopy, Electron, Scanning; Rubidium; Solubility; Valinomycin

Valinomycin (NSC 122023) is a cyclic depsipeptide antibiotic with potassium selective ionophoric activity. This drug has been reported to display antitumor effects but its utilization has been limited by its extreme toxicity. Here we report that the incorporation of valinomycin into multilamellar liposomes composed of dimyristoyl phosphatidyl choline:cholesterol:phosphatidyl serine (10:4:1 M ratio) results in a profound reduction in toxicity with maintainence of antitumor efficacy. Thus the median lethal dose (LD50) for i.p. administered valinomycin (VM) in C57BL/6 X DBA/2 mice is 1.7 mg/kg whereas the LD50 for liposome incorporated valinomycin (MVL-VM) is in excess of 50 mg/kg. In like manner, the LD50 for i.v. administered VM is 0.18 mg/kg where the LD50 for MLV-VM preparations passed through a 0.6-micron filter is greater than 10 mg/kg. The antitumor efficacies of i.p. administered VM or MLV-VM against i.p. P388 mouse leukemia were similar in multiple dose formats using doses below the maximal tolerated dose for VM. However, since MLV-VM was substantially less toxic than VM, the liposomal drug also produced significant (170% median survival time of treated mice/median survival time of untreated control) antitumor effects when administered as a single dose at levels above the maximal tolerated dose for free VM; single doses of free VM at the maximal tolerated dose were ineffective in this context. In experiments with i.v. inoculated P388 leukemia, MLV-VM but not free VM, displayed antitumor activity (144% median survival time of treated mice/median survival time of untreated control) when administered i.v. at equitoxic doses. Thus the use of a lipid vesicle drug carrier system permits a reduction in the toxicity of valinomycin with maintainence or enhancement of antitumor activity against i.p. or i.v. P388 leukemia.

Topics: Animals; Drug Administration Schedule; Leukemia P388; Leukemia, Experimental; Liposomes; Mice; Phospholipids; Valinomycin