Inhibition of anti-inflammatory drugs of prostaglandin production in cultured macrophages.

1. A sensitive, simple, reproducible, and economical assay for structure-activity investigations of non-steroidal anti-inflammatory drugs (NSAID) is lacking. This has prompted us to investigate the advantages and limitations of defining for that purpose the potency of NSAID's as inhibitors of tumour promoter-induced prostaglandin (PG) release from mouse peritoneal macrophages in culture. 2. These cells release mainly PGE2 and PGI2 (measured as its stable hydrolysis product 6-keto-PGF1 alpha) upon stimulation with the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). 3. The PG release was dose-dependently inhibited by a variety of NSAID's. Their inhibitory potency was dependent on the culture conditions employed. The widely used acidic NSAID's were more potent when assayed under serum free culture conditions at low pH. 4. Dose response curves for acidic NSAID tested under serum free conditions allowed for the definition of IC50 values being reproducible within their 95% confidence limits. 5. The IC50 values obtained for different standard acidic NSAID's varied within 4 orders of magnitude. They corresponded favourably to their clinical potency and their potency in a variety of standard tests for anti-inflammatory drugs. 6. IC50 values of five congeners of indomethacin differed up to 2 orders of magnitude in agreement with in vivo observations indicating the applicability of this assay for structure-activity investigations.