Nonsteroidal Dorsomorphin AMPK inhibitor anti-inflammatory drugs (NSAIDs) that can block the activity of COXs are reported to have chemopreventive effects in several experimental studies and clinical trials [10�C14]. Accordingly, the supression of COX-2 has been proposed to underlie the chemopreventive effects of NSAIDS. Recent reports suggest that the anticancer effects of NSAIDs and selective COX-2 inhibitors can occur through COX-independent pathways [15, 16]. However, evidence for the use of COX inhibitors in cancer prevention and the mechanism by which NSAIDs cause protective and anticarcinogenic effects are still to be determined.Piroxicam is an NSAID used for treatment of osteoarthritis and also found to be effective in the treatment of transitional cell carcinoma of the bladder [17], in the treatment of inflammatory mammary carcinoma [18] and oral squamous cell carcinoma in dogs [19].

Also, it was shown to have antitumor activity against naturally acquired tumors in dogs in phase I and phase II clinical trials. In addition, high concentrations of piroxicam have been shown to inhibit cellular proliferation of canine osteosarcoma [20] and canine mammary carcinoma in vitro [21]. However, no significant reduction in cell growth occurred at concentrations that could be achieved in vivo without a significant risk of severe toxic side effects [21]. Deracoxib is a selective COX-2 inhibitor licensed for the treatment of pain and inflammation associated with osteoarthritis and orthopedic surgery in canines [22]. Deracoxib was shown to have in vivo antitumor activity and in vitro cytotoxic properties.

Also, deracoxib was found to reduce the growth of canine mammary cancer xenografts in mice [14] and was found to be cytotoxic in osteosarcoma cell lines [20]. The present study, therefore, was designed to determine the antineoplastic mechanism of piroxicam and deracoxib especially to determine the efficiency of the combination of these drugs on canine mammary carcinoma cells. 2. Materials and Methods 2.1. Cell LineThe canine mammary carcinoma cell line CMT-U27 (a generous gift from Assoc Professor Eva Hellm��n) was obtained from the Uppsala University, Sweden. CMT-U27 cell line was derived from a primary Batimastat tumor (infiltrating ductal carcinoma) and when inoculated in the fat mammary pad of female nude mice, it metastasized to the lymph nodes, lungs, liver, and heart [23].2.2. Cell Culture and TreatmentMammary carcinoma cells, at passage 134, were cultured in Dulbecco’s modified Eagle’s medium-F12 (Sigma Chemicals, St.