Retinoic acid and vitamin E modulate expression and release of CD178 in carcinoma cells: consequences for induction of apoptosis in CD95-sensitive cells.

CD178 (CD95-ligand) is expressed on several tumor cells and likely influences the interaction of the tumor with the host immune system. However, little is known about the mechanisms that regulate its expression on the cell surface. We have evaluated the ability of various compounds and cytokines to regulate cell surface expression and release of soluble CD178 in various carcinoma cell lines. Vitamin E succinate (VES) and retinoic acid (RA) were found to reduce CD178 surface expression, whereas interferon-gamma stimulated a slight upregulation. At 48 h, the regulation of surface CD178 by VES and RA arose from a small decrease in CD178 mRNA and to a greater extent due to an increase in the release of soluble CD178; the latter was blocked by addition of a metalloproteinase inhibitor. Accordingly, VES and RA treatment diminished the ability of tumor cells to kill CD95-sensitive cells and this effect was markedly reduced by the presence of a metalloproteinase inhibitor. Our results indicate that, in vitro, CD178 expression on the cell surface of tumor cells can be regulated by agents that alter both expression and release of the ligand. In vivo, such treatments may play an important role in the outcome of tumor sensitivity or resistance to host immune mechanisms.

Isoxazolines as potent antagonists of the integrin alpha(v)beta(3).

Starting with lead compound 2, we sought to increase the selectivity for alpha(v)beta(3)-mediated cell adhesion by examining the effects of structural changes in both the guanidine mimetic and the substituent alpha to the carboxylate. To prepare some of the desired aminoimidazoles, a novel reductive amination utilizing a trityl-protected aminoimidazole was developed. It was found that guanidine mimetics with a wide range of pK(a)'s were potent antagonists of alpha(v)beta(3). In general, it appeared that an acylated 2-aminoimidazole guanidine mimetic imparted excellent selectivity for alpha(v)beta(3)-mediated adhesion versus alpha(IIb)beta(3)-mediated platelet aggregation, with selectivity of approximately 3 orders of magnitude observed for compounds 3g and 3h. It was also found in this series that the alpha-substituent was required for potent activity and that 2,6-disubstituted arylsulfonamides were optimal. In addition, the selective alpha(v)beta(3) antagonist 3h was found to be a potent inhibitor of alpha(v)beta(3)-mediated cell migration.

Terphenyl cyclooxygenase-2 (COX-2) inhibitors: optimization of the central ring and o-biphenyl analogs.

The discovery of terphenyl derivatives as highly selective COX-2 inhibitors resulted from our efforts to overcome poor pharmacokinetics demonstrated by the COX-2 selective diarylthiophene DuP 697 [2-bromo-4-(4'-sulfonylmethyl)phenyl-5-(4'-fluoro)phenylthiophe ne]. Detailed SAR related to the ortho-biphenyls and variants of the central ring are described herein.

Rapid synthesis of RGD mimetics with isoxazoline scaffolds on solid phase: identification of alphavbeta3 antagonists lead compounds.

Isoxazoline containing RGD mimetics were rapidly synthesized on a solid phase to optimize linkers, regioisomers of isoxazoline scaffolds, and exosite binding groups to yield lead alphavbeta3 antagonists.

Identification of a novel inhibitor of mitogen-activated protein kinase kinase.

The compound U0126 (1,4-diamino-2,3-dicyano-1, 4-bis[2-aminophenylthio]butadiene) was identified as an inhibitor of AP-1 transactivation in a cell-based reporter assay. U0126 was also shown to inhibit endogenous promoters containing AP-1 response elements but did not affect genes lacking an AP-1 response element in their promoters. These effects of U0126 result from direct inhibition of the mitogen-activated protein kinase kinase family members, MEK-1 and MEK-2. Inhibition is selective for MEK-1 and -2, as U0126 shows little, if any, effect on the kinase activities of protein kinase C, Abl, Raf, MEKK, ERK, JNK, MKK-3, MKK-4/SEK, MKK-6, Cdk2, or Cdk4. Comparative kinetic analysis of U0126 and the MEK inhibitor PD098059 (Dudley, D. T., Pang, L., Decker, S. J., Bridges, A. J., and Saltiel, A. R. (1995) Proc. Natl. Acad. Sci U. S. A. 92, 7686-7689) demonstrates that U0126 and PD098059 are noncompetitive inhibitors with respect to both MEK substrates, ATP and ERK. We further demonstrate that the two compounds bind to deltaN3-S218E/S222D MEK in a mutually exclusive fashion, suggesting that they may share a common or overlapping binding site(s). Quantitative evaluation of the steady state kinetics of MEK inhibition by these compounds reveals that U0126 has approximately 100-fold higher affinity for deltaN3-S218E/S222D MEK than does PD098059. We further tested the effects of these compounds on the activity of wild type MEK isolated after activation from stimulated cells. Surprisingly, we observe a significant diminution in affinity of both compounds for wild type MEK as compared with the deltaN3-S218E/S222D mutant enzyme. These results suggest that the affinity of both compounds is mediated by subtle conformational differences between the two activated MEK forms. The MEK affinity of U0126, its selectivity for MEK over other kinases, and its cellular efficacy suggest that this compound will serve as a powerful tool for in vitro and cellular investigations of mitogen-activated protein kinase-mediated signal transduction.

MEK inhibitors: the chemistry and biological activity of U0126, its analogs, and cyclization products.

In search of antiinflammatory drugs with a new mechanism of action, U0126 was found to functionally antagonize AP-1 transcriptional activity via noncompetitive inhibition of the dual specificity kinase MEK with an IC50 of 0.07 microM for MEK 1 and 0.06 microM for MEK 2. U0126 can undergo isomerization and cyclization reactions to form a variety of products, both chemically and in vivo, all of which exhibit less affinity for MEK and lower inhibition of AP-1 activity than parent, U0126.

Structure-activity relationships (SAR) of some tetracyclic heterocycles related to the immunosuppressive agent Brequinar Sodium.

The structure-activity relationships of some tetracyclic heterocycles related to Brequinar were explored. Activities as inhibitors of dihydroorotate dehydrogenase and the mixed lymphocyte reaction are related to ring system, heteroatom placement, and pendant ring substitution.

Sodium economy in white-tailed deer (Odocoileus virginianus).

Sodium is considered the mineral most limiting to growth and reproduction of mammalian herbivores worldwide. Notwithstanding the large database on physiological adaptations to low sodium intake, information on maintenance sodium requirements and sodium dynamics of mammals is depauperate. We measured sodium intake and output in adult, nonreproductive white-tailed deer (n = 15) over four seasons to estimate daily requirements for sodium on a seasonal and an annual basis. Dietary sodium content was based on best available predictions of sodium requirements. With regression techniques, we estimated metabolic fecal excretion and endogenous urinary losses of sodium. Average daily sodium requirement, defined as the minimum sodium intake at which intake equaled excretion, was estimated to be 3.27 mg kg-1 body mass d-1. Seasonal estimates did not vary. We propose that sodium requirements for maintenance in mammalian herbivores scale to body mass at an exponent that is similar to that for metabolic rate and forage intake (0.71-0.75). Development of an allometric relationship between sodium need and body mass would permit stronger inference regarding the role of sodium in population regulation, foraging decisions, or distribution and movements of mammalian herbivores.

The immunosuppressive metabolite of leflunomide is a potent inhibitor of human dihydroorotate dehydrogenase.

The active metabolite of leflunomide. A771726, is a novel immunosuppressive compound that has been shown to be a powerful antiproliferative agent for mononuclear and T-cells. The molecular mechanism of action for this compound has not been clearly established. In vitro cellular and enzymatic assays, however, demonstrate that leflunomide is an inhibitor of several protein tyrosine kinases, with IC50 values between 30 and 100 microM. The in vivo properties of A771726 are reminiscent of another immunosuppressive agent, brequinar sodium, which has been shown to be a nonomolar inhibitor (Ki = 10-30 nM) of the enzyme dihydroorotate dehydrogenase (DHODase). On the basis, we have investigated the effects of leflunomide and A771726 on the activity of purified recombinant human DHODase. We find that A771726 is a potent inhibitor of DHODase (Ki = 179 +/- 19 nM), while the parent compound, leflunomide, had no inhibitory effect at concentrations as high as 1 microM. Studies of the dependence of inhibition on the concentrations of the substrates ubiquinone and dihydroorotate demonstrate that A771726 is a competitive inhibitor of the ubiquinone binding site and is noncompetitive with respect to dihydroorotate. The potency of A771726 as a DHODase inhibitor is thus 100-100-fold greater than that reported for its inhibition of protein tyrosine kinases. These data suggest that an alternative explanation for the immunosuppressive efficacy of A771726 may be the potent inhibition of DHODase by this compound.