ABSTRACT
Hydrophobic bile acids such as deoxycholate are known tumor promoters in the gastrointestinal tract. We have previously shown that deoxycholate induces apoptosis in colon epithelial cells and that these cells can be made resistant to deoxycholate-induced apoptosis. We now show that the nitric oxide synthase/nitric oxide/guanylate cyclase/cyclic guanosine monophosphate/cGMP-activated protein kinase (NOS/NO/GC/cGMP/PKG) signaling module contributes, in part, to the observed resistance of the cultured DOC-resistant colon epithelial cells (HCT-116R) using pharmacological inhibitors/antagonists (NS2028, Rp-8pCPT-cGMP, KT5823) of members of this signaling module. A novel finding from this study is the caspase-6 mediated cleavage of guanylate cyclase alpha 1 during deoxycholate-induced apoptosis of deoxycholate-sensitive HCT-116SA cells and the absence of guanylate cyclase alpha 1 cleavage in deoxycholate-treated HCT-116R resistant cells using Western blot analyses. This cleavage was specific to caspases as lysosomal, proteasomal, serine protease, cathepsin and calpain inhibitors failed to prevent the cleavage, whereas a general caspase inhibitor and a specific caspase-6 inhibitor did prevent guanylate cyclase alpha 1 cleavage.
Subject(s)
Caspases/metabolism , Colonic Neoplasms/enzymology , Deoxycholic Acid/pharmacology , Epithelial Cells/enzymology , Guanylate Cyclase/metabolism , Animals , Apoptosis/drug effects , Caspase 6 , Cyclic GMP/metabolism , Enzyme Inhibitors/pharmacology , Humans , Nitric Oxide Donors/pharmacology , Nitric Oxide Synthase/antagonists & inhibitors , Nitric Oxide Synthase/metabolism , Reactive Oxygen Species/metabolism , Tumor Cells, CulturedABSTRACT
Combination chemotherapy for non-small cell lung cancer (NSCLC) and ovarian cancer typically consists of a regimen of a taxane such as paclitaxel and a platinum-containing agent. Bleomycin, which halts cell cycle progression at G2 phase, is an agent which might thereby increase taxane cytotoxicity. The goal of this study was to evaluate the effect of different paclitaxel-platinum or paclitaxel-bleomycin schedules on cytotoxicity in human NSCLC and ovarian cancer cells. The simultaneous combination of paclitaxel and carboplatin exhibited simple additivity in vitro, while sequential exposure studies indicated that carboplatin followed by paclitaxel produced greater than additive cytotoxicity using the isobologram analysis of combinatorial effects. In contrast, the simultaneous combination of paclitaxel and bleomycin consistently exhibited greater than additive effects indicating a potentially synergistic combination. Sequential exposure studies of bleomycin followed by paclitaxel produced similar synergistic findings. Experiments in SCID mice evaluating the combinations of paclitaxel and bleomycin supported the in vitro results, as significantly enhanced A549 lung tumor growth inhibition was observed when paclitaxel was administered 1 h after bleomycin. The synergistic activity shown by the combination of bleomycin and paclitaxel indicates a potentially beneficial novel combination for treatment of NSCLC and ovarian cancer.
Subject(s)
Antineoplastic Combined Chemotherapy Protocols/therapeutic use , Carcinoma, Non-Small-Cell Lung/drug therapy , Cystadenocarcinoma/drug therapy , Lung Neoplasms/drug therapy , Ovarian Neoplasms/drug therapy , Animals , Antineoplastic Combined Chemotherapy Protocols/pharmacology , Bleomycin/administration & dosage , Body Weight/drug effects , Carboplatin/administration & dosage , Drug Synergism , Female , Flow Cytometry , Humans , Male , Mice , Mice, SCID , Paclitaxel/administration & dosage , Tumor Cells, Cultured/drug effectsABSTRACT
Imexon is a cyanoaziridine derivative that has antitumor activity in multiple myeloma. Previous studies have shown that imexon induces oxidative stress and apoptosis in the RPMI 8226 myeloma cell line. This study reports that imexon has cytotoxic activity in other malignant cell lines including NCI-H929 myeloma cells and NB-4 acute promyelocytic leukemia cells, whereas normal lymphocytes and U266 myeloma cells are substantially less sensitive. Flow cytometric experiments have shown that imexon treatment is associated with the formation of reactive oxygen species (ROS) and the loss of mitochondrial membrane potential (Deltapsi(m)) in imexon-sensitive myeloma cell lines and NB-4 cells. In contrast, reduction of Deltapsi(m) and increased levels of ROS were not observed in imexon-resistant U266 cells. Treatment of imexon-sensitive RPMI 8226 cells with the antioxidant N-acetyl-L-cysteine (NAC) protects cells against these effects of imexon. Mitochondrial swelling was observed by electron microscopy in RPMI 8226 myeloma cells treated with 180 microM imexon as early as 4 hours. Damage to mitochondrial DNA was detected by a semiquantitative polymerase chain reaction assay in imexon-treated RPMI 8226 cells; however, nuclear DNA was not affected. Finally, partial protection of RPMI 8226 cells against the imexon effects was achieved by treatment with theonyltrifluoroacetone, an inhibitor of superoxide production at mitochondrial complex II. These changes are consistent with mitochondrial oxidation and apoptotic signaling as mediators of the growth inhibitory effects of imexon. Interestingly, oxidative damage and decrease of Deltapsi(m) induced by imexon highly correlates with sensitivity to imexon in several myeloma cell lines and an acute promyelocytic leukemia cell line. (Blood. 2001;97:3544-3551)
