Carcinogenicity of "Alderlin" (pronethalol) in mice

Genes associated with the development of the male germ line

The development of the mammalian germ line has been well studied, from the designation of primordial germ cells and their migration in the embryo to their progression through gametogenesis. The pattern of germ cell development, as established through classical studies, is now being overlaid with molecular, genetic and epigenetic data. Eventually, proteonomics will lead to a deeper understanding of the function of these genes. Through knowledge of germ cell gene expression patterns, it is now possible to develop transgenic molecular tools for the isolation of germ cells at different stages of development. By linking stage-specific germ cell promoter regions to the green fluorescent protein (GFP) reporter gene it is possible to tag these cells genetically for histological identification and cell sorting. Our long-term goal is to develop male germ cells as stem cells for therapeutic purposes. It is hoped that this goal will be achieved by purifying germ cells at different stages in development and gaining a deeper understanding of them by studying their gene expression patterns, potency and plasticity, both in vivo and in vitro.

Mutagenic activity of a fluorinated analog of the beta-adrenoceptor ligand carazolol in the Ames test

S-1'[(18)F]-Fluorocarazolol (FCAR) is a fluorinated analog of the nonmutagenic beta-blocker carazolol (CAR). In former studies FCAR proved to be suitable for quantification of beta-adrenoceptors in vivo with positron emission tomography (PET). We report here that FCAR displays no acute toxicity in either rats or mice. However, FCAR induces a strong dose-related increase in the number of revertants in the Ames test. We conclude that FCAR yields mutagenic activity as measured by the Ames test.

Bioactivation of benzylic and allylic alcohols via sulfo-conjugation

Although sulfo-conjugation, in general, has been regarded as a detoxification process in the xenobiotic metabolism, there is a substantial body of data supporting that the same reaction can also lead to activation of certain types of chemical carcinogens and mutagens. Examples include some aromatic amines and amides, alkenylbenzenes, methyl-substituted polyaromatic hydrocarbons, nitrotoluenes and nitrosamines. The N- or O-hydroxy derivatives of these compounds undergo sulfonation to form extremely reactive sulfuric acid esters that can play a role as ultimate carcinogenic/mutagenic metabolites. Previous studies from several laboratories have shown that hydroxymethyl polyarenes, such as hydroxymethylbenz[a]anthracenes, 6-hydroxymethylbenzo[a]pyrene, and 1-hydroxymethylpyrene, are activated to reactive benzylic sulfuric acid esters, preferentially by rat hepatic hydroxysteroid sulfotransferase. Some aromatic hydrocarbons bearing the secondary benzylic hydroxy functionality can also yield electrophilic sulfate esters in the presence of hepatic sulfotransferase activity. Thus, benzylic mono- and dihydroxy derivatives of cyclopenta[cd]pyrene form mutagenic and DNA binding species when incubated with rat liver cytosol and the sulfo-group donor, 3'-phosphoadenosine-5'-phosphosulfate. 1-Hydroxy-3-methylcholanthrene that also possesses the cyclopenta-fused ring system appears to be metabolically activated through sulfo-conjugation. Likewise, benzo[a]pyrene tetraol might be activated through sulfuric acid esterification at one of two benzylic hydroxyl groups. Methylene-bridged polyarenols represent another potential group of cyclic secondary benzylic alcohols that can be activated by sulfotransferases. Certain non-polycyclic aromatic type benzylic alcohols have also been proposed to undergo sulfotransferase-mediated activation. Besides benzylic sulfonation, sulfuric acid esterification of certain allylic alcohols can produce reactive species.

Carcinogen activation by sulfate conjugate formation

The foregoing pages presented a substantial body of data that established that sulfotransferase conjugation can transform many xenobiotics into agents that can modify cellular macromolecules. However, activation by sulfation is rarely the only metabolic pathway that is open to these compounds; other pathways can become more important in response to a variety of factors. This metabolic switching can be produced by substrate concentration, cofactor availability, kinetic factors that dictate the velocity of the various possible conjugation reactions, and, in some cases, competition between Phase-I and Phase-II metabolism. Also, it is important to realize that demonstration of activation by sulfate ester formation in vitro does not necessarily mean that a similar activation process will occur in vivo. Experience also teaches that argument by analogy can be very misleading in the case of sulfate activation. Small structural differences can upset the delicate balance between sulfate activation and the various other competing pathways. Nevertheless, sulfation is an important mechanism by which a number of chemicals are transformed to their activated forms.

Carcinogenicity studies with medroxalol hydrochloride in rats and mice

The carcinogenic potential of medroxalol hydrochloride, an antihypertensive agent with beta 1 adrenergic cardiac blocking properties, and beta 2 and some alpha 1 vasodilating activity, was studied by dietary administration. Long Evans rats were treated for 2 years and CD-1 mice for 18 months at dosages of 0, 50, 250 or 500 mg/kg/day. Medroxalol did not produce any evidence of a tumorigenic effect in the Long Evans rat, but graying of pigmented hair was noted at 250 and 500 mg/kg/day and is probably related to melanin binding of the drug. In the CD-1 mouse, there was a dose related increase in uterine leiomyomas that was statistically significant (p less than 0.05) at doses of 250 and 500 mg/kg/day. The incidence at 50 mg/kg/day was not different from control. Endometrial stromal sarcomas were observed only in treated mice, and pairwise comparison with controls indicated a statistically significant difference (p less than 0.05) only at the lowest dosage (50 mg/kg/day). The latter finding may not be related to treatment since there was no dose response and the incidence in the two higher dose groups was neither statistically significant nor higher than occasionally seen in other control groups.

Effect of some beta-adrenergic blocking agents on tissue guanylate cyclase and cyclic nucleotides in the rat

Pretreatment of rats with the beta-adrenergic blocking agents, atenolol, practolol, pronethalol and propranolol, at a dosage of 150 mg/kg/day for 5 days, produced marked increases in guanylate cyclase activity in the liver, gastric and intestinal mucosae, but with concomitant decreases in cyclic GMP levels. The ratios of cAMP/cGMP in each of the tissues were not changed significantly from control values after pretreatment with these drugs. These observations indicate that any oncogenicity seen with beta-blocking agents is not due to the common pharmacological action of beta-adrenoreceptor blockade.

Studies on the possible mutagenicity of beta-adrenergic blocker drugs

The mutagenic potential of nine beta-adrenergic blocking agents was investigated in the Ames and micronucleus tests. None of the drugs studied showed any mutagenic response in the Ames test, either in the presence or in the absence of an activation system. At the highest concentration oxprenolol and propranolol exhibited a bactericidal effect. In the micronucleus test the same drugs showed a weak, but statistically non-significant response, but only at the highest doses. It is concluded that there is no overt mutagenic or carcinogenic potential associated with beta-adrenergic blocking drug activity.

A carcinogenicity study in mice of a beta-adrenergic antagonist, primidolol; increased total tumour incidence without tissue specificity

The beta-adrenergic blocking agent, primidolol hydrochloride, was administered, mixed in the diet, to mice (CD-1, Charles River, France) for 18 months. Experimental groups comprised untreated controls (100/sex) and those receiving 12.5, 25 and 50 mg drug/kg body weight (50/sex). There were no non-neoplastic lesions which could be attributed to the treatment. The pattern of tumour incidence was sex-related; in females the proportion of tumour-carrying animals was significantly higher in the top dose group (48%) than in the controls (24%), whereas in males the converse was found (30% in the top dose group vs. 48% in the controls). In the top dose female group there was no one tissue in which the tumour incidence was significantly higher than in the controls. We debate whether the analysis of total tumours in the absence of a target organ is an appropriate assay for carcinogenicity. Against a background of regulatory action towards beta-blocking agents, we discuss the possibility that the results of the present study could represent either a co-carcinogenic effect of beta-blocking agents or, alternatively, a statistical contingency.

Genetic activity spectra of some antischistosomal compounds, with particular emphasis on thioxanthenones and benzothiopyranoindazoles

In this review we note that hycanthone (Etrenol) is mutagenic for bacteriophage, bacteria, yeast, Neurospora, Drosophila, and for mammalian tissue culture cells, and we point out other genetic activities of this thioxanthenone and of related compounds. One alarming genetic activity is the ability of hycanthone to cause transformation of tissue culture cells in vitro in a test designed to detect carcinogens, results that parallel the direct demonstration of carcinogenic activity of hycanthone in the mouse in vivo. These and other results are compatible with the somatic mutation theory of cancer induction. Factors likely to affect the quantitative genetic activity of hycanthone and its congeners are summarized. Attempts are made to weave the more critical experimental evidence into a molecular model that accounts for the genetic activities of this series of compounds. We conclude that hycanthone is a directly acting mutagen that intercalates into DNA and preferentially alkylates deoxyguanosine residues via formation of a strongly electrophilic molecular species, the carbonium ion. Finally, we show that genetic activity can be dissociated from schistosomicidal activity by appropriate modifications in the thioxanthenone molecule. Preliminary experiments on a newly synthesized piperazinyl N-oxide derivative demonstrate no detectable mutagenic activity; yet considerable schistosomicidal activity is retained.