In vitro activity: Ibuprofen works by inhibiting the enzyme cyclooxygenase COX-1 and COX-2, which convert arachidonic acid to prostaglandin H2 (PGH2). Its action is similar to aspirin, indomethacin and all other NSAIDs in intact cells, broken cells, and purified enzyme preparations. Ibuprofen inhibits the constitutive activation of NF-κB and IKKα in the androgen-independent prostate tumor cells PC-3 and DU-145. It sensitizes prostate cells to ionizing radiation and blocks stimulated activation of NF-κB following exposure to TNFα or ionizing radiation in the androgen-sensitive prostate tumor cell line LNCaP. Both of these cannot be attributed directly to inhibition of IκB-α kinase but to inhibition of an upstream regulator of IKKα. Ibuprofen exerts an anticancer effect by reducing survival of cancer cells. Ibuprofen is more efficacious than aspirin and acetaminophen, and comparable with (R)-flurbiprofen and indomethacin in induction of p75NTR protein (a tumor and metastasis suppressor) expression in cell lines from bladder and other organs.

Kinase Assay: 10 μL of purified COX-1 (0.7-0.8 μg) or COX-2 (3.0 units, 0.3μg) is activated with 50 μL of cofactor solution [l-epinephrine (1.3 mg/mL), reduced glutathione (0.3 mg/mL), and hematin (1.3 mg/mL) in oxygen-free Tris-HCl buffer (pH 8.0)]. The enzyme solution (60 μL) is added to Ibuprofen solutions or DMSO (20 μL) after [14C]arachidonic acid is added in 0.2 mL eight-strip test tubes and preincubated 10 minutes on ice. Samples are incubated for 15 minutes at 37 °C, after which the reaction is terminated by addition of 10 μL of 2 M HCl and 5 μL of carrier solution (PGE2 and PGF2α, 0.2 μg/mL of each in EtOH). The unmetabolized arachidonic acid is separated from the prostaglandin products by column chromatography and eluted with n-hexane-dioxane-glacial acetic acid (70:30:1). The prostaglandin products are then eluted with EtOAc-MeOH (85:15), and the samples are counted in a Packard scintillation spectrometer. IC50 values are obtained by linear regression analysis.

Cell Assay: Each cell line (Bladder epithelial cell line T24, RT-4 transitional cell papilloma bladder cell line, 5637 primary carcinoma bladder cell line, HCT-116, MDAMB231, MCF7, HEK293, A549, SKOV3 and DU145) is incubated with Ibuprofen of various concentrations for 48 hours. Cell survival is estimated by the MTT assay, and cell death is determined by Hoechst staining used to distinguish between intact cell nuclei and fragmented nuclei undergoing cell death. Cells are lysed and analyzed by western blotting for detection of the p75NTR protein.

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