valinomycin and Ovarian-Neoplasms

The purpose of this study was to determine whether the observed synergistic interaction between cisplatin and valinomycin (VM) in human ovarian carcinoma is the result of mitochondrial DNA (mtDNA) damage. A polymerase chain reaction (PCR)-based method was used to quantitate the lesion frequencies produced by cisplatin, VM and/or drug combination in a 1.1 kbp segment of mtDNA and a 0.536 kbp segment of the nuclear-located beta-globin gene in human ovarian CaOV-3 carcinoma cells. Our data indicates that the nuclear DNA (nDNA) received more cisplatin-induced damage at doses of 25 microM or less than did mtDNA. At higher cisplatin doses (50 microM or more), however, the damage was relatively equal in both segments. VM alone produced little or no damage on mtDNA, yet a significant amount of damage was detected within nDNA. However, when 1 microM VM was used in combination with low doses of cisplatin (0-40 microM), extensive mtDNA damage was detected as compared with the absence of detectable damage on nDNA. In mtDNA, the lesion frequency was 5.45 lesions/10 kb/10 microM cisplatin in the presence of 1 microM VM, whereas no detectable lesions were induced by cisplatin alone. This drug combination produced no detectable damage on DNA, indicating that cisplatin-induced mtDNA damage could be the basis for the observed synergistic interaction with VM. These results also correlate well with our recent in vivo study with the nude mice model of human ovarian cancer treated with a cisplatin/liposomal VM drug combination. Furthermore, this report shows evidence for the role of mitochondria and mtDNA as alternative targets for drug action in cancer therapy.

Topics: Base Sequence; Cell Nucleus; Cisplatin; DNA Damage; DNA, Mitochondrial; DNA, Neoplasm; Drug Synergism; Female; Humans; Molecular Sequence Data; Oligonucleotide Probes; Ovarian Neoplasms; Poisson Distribution; Polymerase Chain Reaction; Tumor Cells, Cultured; Valinomycin

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

Cisplatin is the most active agent in the chemotherapy of ovarian cancer and this activity can be enhanced by liposomal valinomycin (MLV-VM) in vitro. To test whether MLV-VM is capable of augmenting the cytotoxic and cytokinetic effects of other platinum analogs, drug combinations of MLV-VM and platinum drugs were tested against two human ovarian cancer cell lines (OVCAR-3 and CaOV-3) and on Chinese hamster ovary (CHO) cells in vitro. MLV-VM enhanced the sensitivity to cisplatin, ormaplatin and carboplatin on human ovarian carcinoma cells that show various degrees of drug sensitivity. This interaction was shown to be truly synergistic by median-effect analysis up to 90% cell kill. The combination index at 50% cell kill (Cl50) was also used to quantitate the extent of drug synergy. In the OVCAR-3 cell line, for example, the Cl50s were 0.62, 0.85 and 0.8 for cisplatin, ormaplatin and carboplatin, respectively. DNA histograms obtained by flow cytometry showed that CHO cells treated with cisplatin alone accumulated in the S-G2 segment, with a partial G2 block. The addition of 2 microM VM with cisplatin, significantly enhanced the accumulation of cells at the G2/M phase. Our results further demonstrate that in vitro treatment with VM, cisplatin and/or combination is associated with an increase in protein kinase C (PKC) activity. These findings suggest that accumulation of cells at G2/M phases and modulation of PKC activity could be among the basis for the cytotoxic synergism observed between cisplatin and VM.

Topics: Animals; Cell Cycle; Cell Membrane; CHO Cells; Cricetinae; Drug Carriers; Drug Synergism; Enzyme Activation; Female; G2 Phase; Humans; Liposomes; Mitosis; Organoplatinum Compounds; Ovarian Neoplasms; Protein Kinase C; Valinomycin

We have previously shown that the toxicity of valinomycin (VM), a membrane-active agent with antineoplastic activity, can be dramatically reduced with no loss of the antitumor efficacy of the drug by incorporating it into liposomes. In the present study, we investigated the interaction between cis-diamminedichloroplatinum(II) (CDDP) and VM in terms of in vitro cytotoxicity to human ovarian tumor cells. Using the MTT assay and analyzing the data using the median-effect principle, we showed that synergistic cytotoxic interactions exist between CDDP and VM in their liposomal form. The degree of cytotoxic synergism was influenced by the duration of drug exposure and the dose ratio. The cellular accumulation of platinum by ovarian cells at 37 degrees C was slightly higher after exposure to VM as compared with controls; however, it is not clear that this accounts for the cytotoxic synergism. These results suggest that the combination of liposomal VM and CDDP may have merit as a form of localized drug delivery for the treatment of ovarian cancer disseminated within the peritoneal space.

Topics: Antineoplastic Combined Chemotherapy Protocols; Carcinoma; Cell Line; Cell Survival; Cisplatin; Drug Carriers; Drug Screening Assays, Antitumor; Drug Synergism; Female; Humans; Liposomes; Ovarian Neoplasms; Platinum; Tumor Cells, Cultured; Valinomycin