Suppression of c-mos expression in teratocarcinoma cells with a new type of inducer of differentiation, 3,5-di-tert-butylchalcone 4'-carboxylic acid

In silico discovery of novel retinoic acid receptor agonist structures

BACKGROUND

Several Retinoic Acid Receptors (RAR) agonists have therapeutic activity against a variety of cancer types; however, unacceptable toxicity profiles have hindered the development of drugs. RAR agonists presenting novel structural and chemical features could therefore open new avenues for the discovery of leads against breast, lung and prostate cancer or leukemia.

RESULTS

We have analysed the induced fit of the active site residues upon binding of a known ligand. The derived binding site models were used to dock over 150,000 molecules in silico (or virtually) to the structure of the receptor with the Internal Coordinates Mechanics (ICM) program. Thirty ligand candidates were tested in vitro.

CONCLUSIONS

Two novel agonists resulting from the predicted receptor model were active at 50 nM. One of them displays novel structural features which may translate into the development of new ligands for cancer therapy.

Chalcones, myo-inositol and other novel inhibitors of pulmonary carcinogenesis

The objective of the studies reported here has been to find novel chemopreventive agents effective against carcinogenesis of the lung. In particular, identification of suppressing agents, i.e., compounds preventing the evolution of the neoplastic process, has been sought. For this purpose, inhibition of pulmonary neoplasia in female A/J mice given the test agent starting one week after the last administration of three doses of benzo[a]pyrene has been employed as the experimental model. Under these conditions, chalcone, 4'-methoxychalcone,myo-inositol, dexamethasone, and "terpeneless" orange oil added to the diet suppressed pulmonary adenoma formation. Chalcone and 4'-methoxychalcone are open chain flavonoids, neither of these compounds occurs naturally, and their mechanism of action is not known. myo-Inositol is a naturally occurring compound of particular interest because of its exceedingly low toxicity. Dexamethasone is a potent glucocorticoid. Amongst its biological properties is the capacity to induce maturation of Type 2 alveolar cells and to stimulate production of surfactant by these cells. "Terpeneless" orange oil is a fraction of orange oil consisting predominantly of compounds with carbonyl or hydroxyl groups. The constituent or constituents responsible for the inhibitory effects observed is not known. The above studies are in an early phase of development and their ramifications remain to be determined.

Inhibition of carcinogen-induced pulmonary and mammary carcinogenesis by chalcone administered subsequent to carcinogen exposure

A study of the capacity of chalcone to inhibit benzo[alpha]pyrene(BP)-induced carcinogenesis of the lungs and forestomach in female A/J mice and N-methyl-N-nitrosourea (MNU)-induced mammary carcinogenesis in female Sprague-Dawley rats has been carried out. Chalcone, 5 mg/g of diet, had a inhibitory effect on pulmonary adenoma formation (29%) and on mammary tumor formation (49%) when the compound was fed starting one week after final carcinogen administration. Chalcone did not inhibit forestomach tumor formation. In an additional study, chalcone started 4 weeks after MNU and fed for 3-week courses alternating with 3-week courses of control diet for the duration of the protocol also inhibited mammary tumor formation by 49%. The data showing that chalcone has inhibitory effects against both pulmonary and mammary carcinogenesis when given after carcinogen administration provides the basis for further investigations of this and possibly other chalcones as chemopreventive suppressing agents.

Intracellular actions of vitamin A

Because the effects of vitamin A vary with tissue type and often with the form of vitamin A itself, a complete understanding of the mechanism(s) of action still has not been attained. The action of vitamin A may be at the level of genomic expression, at the membrane level, or both. Intercellular and intracellular transport of vitamin A are facilitated by specific binding proteins but probably not in the cellular uptake of vitamin A. Subcellularly, vitamin A may exert a direct effect on transit through the Golgi apparatus, as observed from both biochemical and morphological studies. In my laboratory, recent work using cell-free systems has shown that retinol stimulates transition vesicle formation from endoplasmic reticulum in a GTP-requiring step.

Changes of c-mos expression in response to 2-O-tetradecanoylphorbol-13-acetate in undifferentiated teratocarcinoma cells

Treatment of the cells of the 311 cell line, a pluripotent mouse teratocarcinoma cell line, with 12-O-tetradecanoylphorbol-13-acetate (TPA) modulates c-mos expression. Transient suppression of 6.1 and 4.6 kilobases (kb) transcripts and activation of 1.8 transcript indicate that TPA mediates concurrently positive and negative regulation of c-mos transcription. The results show that the c-mos gene is a TPA-modulated gene. In addition, a TPA-responsive element (GTGACTCA), which exists in the 5'-flanking region of c-mos gene of Balb/c mice [1,2], is suggested to be involved in this response. However, these changes were not accompanied by early marker changes associated with endodermal cell differentiation, i.e., morphological change, induction of plasminogen activator and suppression of glucose transport activity.