Indomethacin induces apoptosis via a MRP1-dependent mechanism in doxorubicin-resistant small-cell lung cancer cells overexpressing MRP1.

Small-cell lung cancers (SCLCs) initially respond to chemotherapy, but are often resistant at recurrence. The non-steroidal anti-inflammatory drug indomethacin is an inhibitor of multidrug resistance protein 1 (MRP1) function. The doxorubicin-resistant MRP1-overexpressing human SCLC cell line GLC(4)-Adr was highly sensitive for indomethacin compared with the parental doxorubicin-sensitive line GLC(4). The purpose of this study was to analyse the relationship between hypersensitivity to indomethacin and MRP1 overexpression. The experimental design involved analysis of the effect of MRP1 downregulation on indomethacin-induced cell survival and apoptosis in GLC(4)-Adr and GLC(4), using siRNA. In addition the effect of indomethacin on glutathione levels and mitochondrial membrane potential was investigated. Small interfering RNAs directed against MRP1 reduced MRP1 mRNA levels twofold and reduced efflux pump function of MRP1, which was reflected by a 1.8-fold higher accumulation of MRP1 substrate carboxyfluorescein, in si-MRP1 versus si-Luciferase-transfected GLC(4)-Adr cells. Multidrug resistance protein 1 downregulation decreased initial high apoptosis levels 2-fold in GLC(4)-Adr after indomethacin treatment for 24 h, and increased cell survival (IC(50)) from 22.8+/-2.6 to 30.4+/-5.1 microM following continuous indomethacin exposure. Multidrug resistance protein 1 downregulation had no effect on apoptosis in GLC(4) or on glutathione levels in both lines. Although indomethacin (20 microM) for 2 h decreased glutathione levels by 31.5% in GLC(4)-Adr, complete depletion of cellular glutathione by L-buthionine (S,R)-sulphoximine only resulted in a small increase in indomethacin-induced apoptosis in GLC(4)-Adr, demonstrating that a reduced cellular glutathione level is not the primary cause of indomethacin-induced apoptosis. Indomethacin exposure decreased mitochondrial membrane potential in GLC(4)-Adr cells, suggesting activation of the mitochondrial apoptosis pathway. Indomethacin induces apoptosis in a doxorubicin-resistant SCLC cell line through an MRP1-dependent mechanism. This may have implications for the treatment of patients with MRP1-overexpressing tumours.

Indomethacin-induced activation of the death receptor-mediated apoptosis pathway circumvents acquired doxorubicin resistance in SCLC cells.

Small-cell lung cancers (SCLCs) initially respond to chemotherapy but are often resistant at recurrence. A potentially new method to overcome resistance is to combine classical chemotherapeutic drugs with apoptosis induction via tumour necrosis factor (TNF) death receptor family members such as Fas. The doxorubicin-resistant human SCLC cell line GLC4-Adr and its parental doxorubicin-sensitive line GLC4 were used to analyse the potential of the Fas-mediated apoptotic pathway and the mitochondrial apoptotic pathway to modulate doxorubicin resistance in SCLC. Western blotting showed that all proteins necessary for death-inducing signalling complex formation and several inhibitors of apoptosis were expressed in both lines. The proapototic proteins Bid and caspase-8, however, were higher expressed in GLC4-Adr. In addition, GLC4-Adr expressed more Fas (3.1x) at the cell membrane. Both lines were resistant to anti-Fas antibody, but plus the protein synthesis inhibitor cycloheximide anti-Fas antibody induced 40% apoptosis in GLC4-Adr. Indomethacin, which targets the mitochondrial apoptotic pathway, induced apoptosis in GLC4-Adr but not in GLC4 cells. Surprisingly, in GLC4-Adr indomethacin induced caspase-8 and caspase-9 activation as well as Bid cleavage, while both caspase-8 and caspase-9 specific inhibitors blocked indomethacin-induced apoptosis. In GLC4-Adr, doxorubicin plus indomethacin resulted in elevated caspase activity and a 2.7-fold enhanced sensitivity to doxorubicin. In contrast, no effect of indomethacin on doxorubicin sensitivity was observed in GLC4. Our findings show that indomethacin increases the cytotoxic activity of doxorubicin in a doxorubicin-resistant SCLC cell line partly via the death receptor apoptosis pathway, independent of Fas.

Differential modulation of the TRAIL receptors and the CD95 receptor in colon carcinoma cell lines.

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) and CD95 ligand (CD95L) are potent inducers of apoptosis in various tumour cell types. Death receptors DR4 and DR5 can induce and decoy receptors DcR1 and DcR2 can inhibit TRAIL-mediated apoptosis. The study aim was to investigate whether anticancer agents can modulate similarly TRAIL-receptor and CD95 membrane expression and TRAIL and CD95L sensitivity. Three colon carcinoma cell lines (Caco-2, Colo320 and SW948) were treated with 5-fluorouracil (5-FU), cisplatin or interferon-gamma. TRAIL-receptor and CD95 membrane expression was determined flow cytometrically. Sensitivity to TRAIL or CD95L agonistic anti-CD95 antibody was determined with cytotoxicity and apoptosis assays. SW948 showed highest TRAIL sensitivity. The protein synthesis inhibitor cycloheximide decreased FLICE-like inhibitory protein levels in all cell lines, and the TRAIL-resistant cell lines Caco-2 and Colo320 became sensitive for TRAIL. Exposure of the cell lines to 5-FU, cisplatin and interferon-gamma left TRAIL-receptor membrane expression and TRAIL sensitivity unaffected. CD95 membrane expression and anti-CD95 sensitivity was, however, modulated by the same drugs in all lines. Cisplatin and interferon-gamma raised CD95 membrane levels 6-8-fold, interferon-gamma also increased anti-CD95 sensitivity. These results indicate that the CD95 and TRAIL pathways use different mechanisms to respond to various anticancer agents. Induced CD95 membrane upregulation was associated with increased anti-CD95 sensitivity, whereas no upregulation of TRAIL-receptor membrane expression or TRAIL sensitisation could be established. For optimal use of TRAIL-mediated apoptosis for cancer therapy in certain tumours, downregulation of intracellular inhibiting factors may be required.