We showed previously that dietary eicosapentaenoic acid [EPA, 20:5(n-3)] is antitumorigenic in the APC:(Min/+) mouse, a genetic model of intestinal tumorigenesis. Only a few studies have evaluated the effects of dietary fatty acids, including EPA and docosahexaenoic acid [DHA, 22:6(n-3)], in this animal model and none have evaluated the previously touted antitumorigenicity of alpha-linolenic acid [ALA, 18:3(n-3)], conjugated linoleic acid [CLA, 77% 18:2(n-7)], or gamma-linolenic acid [GLA, 18:3(n-6)]. Stearidonic acid [SDA, 18:4(n-3)], the Delta6-desaturase product of ALA, which is readily metabolized to EPA, has not been evaluated previously for antitumorigenic efficacy. This study was undertaken to evaluate the antitumorigenicity of these dietary fatty acids (ALA, SDA, EPA, DHA, CLA and GLA) compared with oleic acid [OA, 18:1(n-9)] at a level of 3 g/100 g in the diets of APC:(Min/+) mice and to determine whether any alterations in tumorigenesis correspond to alterations in prostaglandin biosynthesis. Tumor multiplicity was significantly lower by approximately 50% in mice fed SDA or EPA compared with controls, whereas less pronounced effects were observed in mice fed DHA (P: = 0.15). ALA, CLA and GLA were ineffective at the dose tested. Although lower tumor numbers coincided with significantly lower prostaglandin levels in SDA- and EPA-fed mice, ALA and DHA supplementation resulted in equally low prostaglandin levels, despite proving less efficacious with regard to tumor number. Prostaglandin levels did not differ significantly in the CLA and GLA groups compared with controls. These results suggest that SDA and EPA attenuate tumorigenesis in this model and that this effect may be related in part to alterations in prostaglandin biosynthesis.

Prostaglandin (PG) E(1) has been shown to possess anti-inflammatory properties and to modulate vascular reactivity. These activities are sometimes distinct from those of PGE(2), suggesting that endogenously produced PGE(1) may have some beneficial therapeutic effects compared with PGE(2). Increasing the endogenous formation of PGE(1) requires optimization of two separate processes, namely, enrichment of cellular lipids with dihomo-gamma-linolenic acid (20:3 n-6; DGLA) and effective cyclo-oxygenase-dependent oxygenation of substrate DGLA relative to arachidonic acid (AA; 20:4 n-6). DGLA and AA had similar affinities (K(m) values) and maximal reaction rates (V(max)) for cyclo-oxygenase-2 (COX-2), whereas AA was metabolized preferentially by cyclo-oxygenase-1 (COX-1). To overcome the kinetic preference of COX-1 for AA, CP-24879, a mixed Delta(5)/Delta(6) desaturase inhibitor, was used to enhance preferential accumulation of DGLA over AA in cells cultured in the presence of precursor gamma-linolenic acid (18:3 n-6). This protocol was tested in two cell lines and both yielded a DGLA/AA ratio of approx. 2.8 in the total cellular lipids. From the enzyme kinetic data, it was calculated that this ratio should offset the preference of COX-1 for AA over DGLA. PGE(1) synthesis in the DGLA-enriched cells was increased concurrent with a decline in PGE(2) formation. Nevertheless, PGE(1) synthesis was still substantially lower than that of PGE(2). It appears that employing a dietary or a combined dietary/pharmacological paradigm to augment the cellular ratio of DGLA/AA is not an effective route to enhance endogenous synthesis of PGE(1) over PGE(2), at least in cells/tissues where COX-1 predominates over COX-2.

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A synthetic glucocorticoid receptor (GR) ligand with the efficacy of a glucocorticoid, but without the accompanying side effects, would meet an unmet medical need for the treatment of inflammatory diseases. It was hypothesized that a GR ligand that shifted helix 12 in a manner distinct from an agonist and an antagonist would confer a distinct GR conformation, resulting in differential gene expression and, ultimately, dissociation of antiinflammatory activity from side effects. A structural feature expected to interfere with helix 12 was incorporated into a nonsteroidal, tricyclic scaffold to create novel, high-affinity, and selective GR ligands that manifested a dual function in cellular assays, partial but robust agonist activity for inflammatory cytokine inhibition, and full antagonist activity for reporter gene activation. In contrast, analogs not likely to hinder helix 12 exhibited partial agonist activity for reporter gene activation. The requirement of full antagonist activity for substantial side effect dissociation was demonstrated in primary human preadipocytes, hepatocytes, and osteoblasts in which effects on adipogenesis, key genes involved in gluconeogenesis, and genes important for bone formation were examined, respectively. The dissociated GR ligands, despite lacking significant reporter gene activation, weakly recruit a limited number of coactivators such as peroxisomal proliferator-activated receptor-γ coactivator 1α. Transcriptional activation was sensitive to both peroxisomal proliferator-activated receptor-γ coactivator 1α and GR levels, providing a basis for cell-selective modulation of gene expression. The antiinflammatory activity of the dissociated ligands was further demonstrated in mouse models of inflammation. Together these results suggest that these ligands are promising candidates with robust antiinflammatory activity and likely dissociation against glucocorticoid-induced side effects.

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