The eVect on cytotoxicity of combining a range of clinically important non-steroidal anti-in¯amma-tory drugs (NSAIDs) with a variety of chemotherapeutic drugs was examined in the human lung cancer cell lines DLKP, A549, COR L23P and COR L23R and in a human leukaemia line HL60/ADR. A speci®c group of NSAIDs (indomethacin, sulindac, tolmetin, acemetacin, zomepirac and mefenamic acid) all at non-toxic levels, signi®cantly increased the cytotoxicity of the anthracyclines (doxorubicin, daunorubicin and epirubicin), as well as teniposide, VP-16 and vincristine, but not the other vinca alkaloids vinblastine and vinorelbine. A substantial number of other anticancer drugs, including methotrexate, 5-¯uorouracil, cytarabine, hydroxyurea, chlorambucil, cyclophosphamide, cisplatin, carboplatin, mitoxantrone, actinomycin D, bleomycin, paclitaxel and camptothecin, were also tested, but displayed no synergy in combination with the NSAIDs. The synergistic eVect was concentration dependent. The eVect appears to be independent of the cyclo-oxygenase inhibitory ability of the NSAIDs, as (i) the synergistic combination could not be reversed by the addition of prostaglandins D 2 or E 2 ; (ii) sulindac sulphone, a metabolite of sulindac that does not inhibit the cyclooxygenase enzyme, was positive in the combination assay: and (iii) many NSAIDs known to be cyclo-oxygenase inhibitors, e.g. meclofenamic acid, diclofenac, naproxen, fenoprofen, phenylbutazone,¯ufenamic acid,¯urbi-profen, ibuprofen and ketoprofen, were inactive in the combination assay. The enhancement of cytotoxicity was observed in a range of drug sensitive tumour cell lines, but did not occur in P-170-overexpressing multidrug resistant cell lines. However, in the HL60/ADR and COR L23R cell lines, in which multidrug resistance is due to overexpression of the multidrug resistance-associated protein MRP, a signi®cant increase in cytotoxicity was observed in the presence of the active NSAIDs. Subsequent Western blot analysis of the drug sensitive parental cell lines, DLKP and A549, revealed that they also expressed MRP and reverse-transcription±polymerase chain reaction studies demonstrated that mRNA for MRP was present in both cell lines. It was found that the positive NSAIDs were among the more potent inhibitors of [ 3 H]-LTC 4 transport into inside-out plasma membrane vesicles prepared from MRP-expressing cells, of doxorubicin eZux from preloaded cells and of glutathione-Stransferase activity. The NSAIDs did not enhance cellular sensitivity to radiation. The combination of speci®c NSAIDs with anticancer drugs reported here may have potential clinical applications, especially in the circumvention of MRP-mediated multidrug resistance. #
