Abstract. Statins, anti-hypercholesterolemic agents, have previously been reported to induce apoptosis and exert antitumor activity when combined with other antitumor agents. The potential of lovastatin in combination with highly specific COX-2 inhibitor (MF-tricyclic) to induce anti- proliferative activity against tumour cells was evaluated using the combination index (CI) method. Murine colorectal cancer (colon-26, CMT-93), melanoma (B16F10) and human bladder carcinoma cells (T24) were tested. Exposure of colon-26 and CMT-93 cells resulted in synergistic interactions in both cell lines with CI<1 for 20-80% inhibition of cell growth in both cell lines. This synergy was not observed in the B16F10 melanoma and T24 bladder carcinoma cells. MF-tricyclic (40 μ g/ml), augmented lovastatin-induced apoptosis up to 2.5-fold in colon-26 cancer cells. Combination of a specific COX-2 inhibitor, MF-tricyclic, may increase antiproliferative effects of lovastatin in colon cancer cells and this effect was due to an augmented apoptosis. Introduction Epidemiological observations and laboratory research have suggested that non-steroidal anti-inflammatory drugs (NSAIDs) reduce the risk of colon cancer and that the inhibition of colon carcinogenesis by NSAIDs is mediated through the modulation of prostaglandin production by rate- limiting enzymes known as cyclooxygenases (COXs). Because traditional NSAIDs inhibit both COX-1 and COX-2, these drugs induce side effects, such as gastrointestinal ulceration and renal toxicity, through the inhibition of the constitutive COX-1 (1). Overexpression of COX-2 has been observed in colon tumours; therefore, specific inhibitors of COX-2 could serve as chemopreventive and/or therapeutic agents (for review see refs. 2 and 3). Selective COX-2 inhibitors have already been shown to reduce the formation of colorectal carcinomas in animal models (4,5). The precise mechanism of action of COX-2 inhibitors in inhibiting carcinogenesis has not been fully elucidated. However, it has been revealed that this growth inhibition results from antiproliferative, proapoptopic (6,7), and probably anti- angiogenic effects (8). On the other hand, HMG-CoA reductase inhibitors (the statins) have been shown to induce a potent apoptotic response (9,10) and to exert antitumor effects in mice (11-13). Statins have been used in medical practice, reducing cardiovascular- related morbidity and mortality (for review see ref. 14), and their application in clinical tumour therapy has also been studied (15-17). Since lovastatin was known to interfere with the function of Ras proteins (18) and selective inhibition of COX-2 activity inhibits growth and induces apoptosis of ras-transformed intestinal epithelial cells (19) one may expect, that lovastatin may enhance the antiproliferative and proapoptotic effects imposed by specific COX-2 inhibitors on tumour cells. In order to elucidate these questions we chose to combine lovastatin with MF-tricyclic, a novel, specific COX-2 inhibitor (Fig. 1). MF-tricyclic has already been shown to markedly attenuate the number and size of polyps in the Apc ¢716 knock- out mice (6) and possesses superior chemopreventive activity as compared with Rofecoxib, studied at equivalent doses in ONCOLOGY REPORTS 9: 879-885, 2002 879 Synergistic interaction between highly specific cyclooxygenase-2 inhibitor, MF-tricyclic and lovastatin in murine colorectal cancer cell lines WOJCIECH FELESZKO 1,2 , AHMAD JALILI 1 , DOMINIKA OLSZEWSKA 1 , IZABELA MLYNARCZUK 1,3 , TOMASZ GRZELA 3 , ADAM GIERMASZ 1 and MAREK JAKÓBISIAK 1 1 Department of Immunology, Centre of Biostructure Research, The Medical University of Warsaw; 2 Department of Paediatric Pneumonology, Allergic Diseases and Haematology, The Medical University Children's Hospital; 3 Department of Histology and Embryology, Centre of Biostructure Research, The Medical University of Warsaw, Warsaw, Poland Received January 22, 2002; Accepted March 1, 2002 _________________________________________ Correspondence to: Dr Wojciech Feleszko, Department of Paediatric Pneumonology, Allergic Diseases and Haematology, The Medical University Children's Hospital, ul. Dzialdowska 1/3, PL- 01-184 Warsaw, Poland E-mail: wfeleszk@ib.amwaw.edu.pl. Abbreviations: CI, combination index; NSAID, non-steroidal anti- inflammatory drugs; COX, cyclooxygenase; HMG-CoA, 3- hydroxy-3-methyl-glutaryl-coenzyme A; MF-tricyclic, 3-(3,4- difluoropentyl)-4-[ 4-(methylsulfonyl)phenyl]-2(5H)-furanone; MTT, l 3-(45-dimethylthiazol-2-yl)-diphenyltetrazolium bromide; SDS-PAGE, sodium-dodecyl-sulphate polyacrylamide gel electro- phoresis Key words: COX-2 inhibitors, lovastatin, colorectal cancer, apoptosis, synergism