Experimental studies with liarozole (R 75,251): an antitumoral agent which inhibits retinoic acid breakdown.

Liarozole reduced tumor growth in the androgen-dependent Dunning-G and the androgen-independent Dunning MatLu rat prostate carcinoma models as well as in patients with metastatic prostate cancer who had relapsed after orchiectomy. In vitro, liarozole did not have cytostatic properties, as measured by cell proliferation in breast MCF-7 and prostate DU145 and LNCaP carcinoma cell lines. It did not alter the metabolism of labeled testosterone i.e. the 5 alpha-reductase in cultured rat prostatic cells. In mouse F9 teratocarcinoma cells liarozole did not show any retinoid-like properties but enhanced the plasminogen activator production induced by retinoic acid. Furthermore, liarozole and retinoic acid similarly reduced the growth of the androgen-dependent Dunning-G tumor in nude mice and inhibited tumor promotion elicited by phorbol ester in mouse skin. These data have raised the hypothesis that the antitumoral properties of liarozole may be related to inhibition of retinoic acid degradation, catalyzed by a P-450-dependent enzyme that is blocked by the drug.     

Inflammatory cytokines inhibit myogenic differentiation through activation of nuclear factor-kappaB.

Muscle wasting is often associated with chronic inflammation. Because tumor necrosis factor alpha (TNF-alpha) has been implicated as a major mediator of cachexia, its effects on C2C12 myocytes were examined. TNF-alpha activated nuclear factor-kappaB (NF-kappaB) and interfered with the expression of muscle proteins in differentiating myoblasts. Introduction of a mutant form of inhibitory protein kappaBalpha (IkappaBalpha) restored myogenic differentiation in myoblasts treated with TNF-alpha or interleukin 1beta. Conversely, activation of NF-kappaB by overexpression of IkappaB kinase was sufficient to block myogenesis, illustrating the causal link between NF-kappaB activation and inhibition of myogenic differentiation. The inhibitory effects of TNF-alpha on myogenic differentiation were reversible, indicating that the effects of the cytokine were not due to nonspecific toxicity. Treatment of differentiated myotubes with TNF-alpha did not result in a striking loss of muscle-specific proteins, which shows that myogenesis was selectively affected in the myoblast stage by TNF-alpha. An important finding was that NF-kappaB was activated to the same extent in differentiating and differentiated cells, illustrating that once myocytes have differentiated they become refractory to the effects of NF-kappaB activation. These results demonstrate that inflammatory cytokines may contribute to muscle wasting through the inhibition of myogenic differentiation via a NF-kappaB-dependent pathway.     

An analysis of side chain interactions and pair correlations within antiparallel β-sheets: The differences between backbone hydrogen-bonded and non-hydrogen-bonded residue pairs

Cross-strand pair correlations are calculated for residue pairs in antiparallel β-sheet for two cases: pairs whose backbone atoms are hydrogen bonded together (H-bonded site) and pairs which are not (non-H-bonded site). The statistics show that this distinction is important. When glycine is located on the edge of a sheet, it shows a 3:1 preference for the H-bonded site. Thestrongest observed correlations are for pairs of disulfide-bonded cystines, many of which adopt a close-packed conformation with each cystine in a spiral conformation of opposite chirality to its partner. It is likely that these pairs are a signature for the family of small, cystine-rich proteins. Most other strong positive and negative correlations involve charged and polar residues. It appears that electrostatic compatibility is the strongest factor affecting pair correlation. Significant correlations are observed for β- and γ-branched residues inthe non-H-bonded site. An examination of the structures showsa directionality in side chain packing. There is a correlation between (1) the directionality in the packing interactions of non-H-bonded β- and γ-branched residue pairs, (2) the handedness of the observed enantiomers of chiral β-branched side chains, and (3) the handedness of the twist of β-sheet. These findings have implications for the formation of β-sheets during protein folding and the mechanism by which the sheet becomes twisted. © 1995 Wiley-Liss, Inc.