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C J Michejda

Publications and source records attributed to C J Michejda.

At least 37 records · Page 2Linked to original sources
PubMed1995

Bisimidazoacridones and related compounds: new antineoplastic agents with high selectivity against colon tumors.

A new class of potent and highly selective antitumor agents has been synthesized. Bisimidazoacridones, where the tetracyclic ring systems are held together by either a N2-methyldiethylenetriamine or 3,3'-diamino-N-methyldipropylamine linker, and related asymmetrical compounds, where one of the imidazoacridone ring system was replaced by a triazoloacridone ring system, were found to be cytostatic and cytotoxic in vitro. Some of these compounds, such as 5,5'-[(methylimino)bis(3,1-propanediylimino)]bis[6H-imidazo[ 4,5,1-de]acridin-6-one] (4b) showed remarkably high activity and selectivity for colon cancer in the National Cancer Institute screen. This antitumor effect was also apparent in colony survival assays utilizing the colon cancer line, HCT-116, and in in vivo assays involving xenografts of tumor derived from HCT-116 in nude mice. The tested compounds exhibited relatively low acute toxicity and were well-tolerated by the treated animals. The bisimidazoacridones interact with nucleic acids in vitro but preliminary experimental and modeling data indicate that in spite of their structure, they may not be bis-intercalators. While the precise mode of action of these compounds is not yet understood, they appear to be excellent candidates for clinical development.

Aminoacridines↗
PubMed1995

Mechanism of action of bisimidazoacridones, new drugs with potent, selective activity against colon cancer.

Antitumor bisimidazoacridones are bifunctional DNA binders which have recently been shown to selectively target human colon carcinoma cells in vitro and in vivo and appear to be excellent candidates for clinical development. We have studied the mechanism of action of one bisimidazoacridone, WMC26, which is 1,000-10,000 times more toxic to human colon carcinoma cells (HCT116) than to melanoma cells (SKMEL2) in vitro. Plasmid DNA exposed to WMC26 showed enhanced digestion by DNase I at A-T-rich sites, suggesting alterations in DNA conformation upon drug binding. These results led us to investigate whether WMC26 was selectively toxic due to a specific recognition of DNA bends by repair excinucleases, as has been demonstrated with the DNA bisintercalator, ditercalinium. Both prokaryotic and eukaryotic cells with intact repair capacity were shown to be selectively sensitive to WMC26, strongly indicating that excision repair plays a role in its toxicity. Confocal microscopy studies utilizing fluorescence of the WMC26 chromophore showed compound localization in the perinuclear cytoplasmic area, as had been previously noted for ditercalinium, indicating that cytoplasmic DNA could be the target. This irreversible accumulation of compound was gradually followed by vacuolization of the cytoplasm and cell death. Cell cycle analysis of both lines treated with WMC26 or with ditercalinium showed that, while the latter induced HCT116 growth arrest at G1-G0, WMC26 also blocked the cell cycle at G2-M; SKMEL2 cells did not undergo any changes in cell cycle as a result of either treatment. Our data show that WMC26 is 10-100 times more cytotoxic than ditercalinium in vitro. Like ditercalinium, WMC26 appears to exert its toxicity via cytoplasmic elements, through a mechanism involving excision repair processes. However, its highly selective cytotoxicity may stem from additional undefined targets in sensitive colon cancer cells.

Aminoacridines↗
PubMed1994

Peptide-linked 1,3-dialkyl-3-acyltriazenes: gastrin receptor directed antineoplastic alkylating agents.

The gastrin receptor is expressed in various human cancers, such as the adenocarcinoma of the colon. The peptide hormone gastrin and the C-terminal peptides derived from it act as growth factors for these cancers. The hypothesis for the present work was to use the gastrin receptor as a target for appropriately constructed cytotoxic agents. We developed methods to link tetragastrin and pentagastrin by their N-termini to cytotoxic 1-(2-chloroethyl)-3-benzyl-3-succinoyltriazene. These compounds, CBS-4 and CBS-5, respectively, whose complete structures were determined by multinuclear NMR and mass spectrometry, competed effectively with gastrin in an assay using either guinea pig stomach fundus or the rat acinar tumor cell line AR42J as the source of the receptor. CBS-5 was cytotoxic to AR42J cells but was not toxic to A549 human lung cancer cells, which do not express the receptor.

Alkylating Agents↗
PubMed1994

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.

Animals↗
PubMed1993

An unexpected pathway for the metabolic degradation of 1,3-dialkyl-3-acyltriazenes.

In the presence of NADPH, rat liver microsomes catalyzed the degradation of a series of 1,3-dialkyl-3-acyltriazenes, and the extent of the reaction was correlated with compound lipophilicity. In the case of two methylcarbamoyltriazenes, 1-(2-chloroethyl)-3-benzyl-3- (methylcarbamoyl)triazene (CBzM) and 1-(2-chloroethyl)-3-methyl-3-(methylcarbamoyl)triazene (CMM), microsomal metabolites were isolated. Identification of the CBzM metabolites as 1-(2-chloroethyl)-3-benzyl-3-(hydroxymethylcarbamoyl)triazene and 1-(2-chloroethyl-3-benzyl-3-carbamoyltriazine, and the CMM metabolite as 1-(2-chloroethyl)-3-methyl-3-(hydroxymethylcarbamoyl)triazene indicated that the first metabolic step involves hydroxylation of the methylcarbamoyl substituent. Detailed studies of the metabolism of CBzM indicated that the Km for the reaction was 84 microM, and that metabolism was more efficient if microsomes were prepared from male than from female rats. During prolonged incubation, the metabolites of CBzM were also degraded. The degradation of CBzM and its metabolites was inhibited by SKF-525A and metyrapone, suggesting the involvement of a cytochrome P450 isozyme, and supporting the hypothesis that the process is oxidative rather than hydrolytic in both cases. Metabolic oxidation represents an alternative pathway to chemical or enzymatic hydrolysis for the in vivo decomposition of (methylcarbamoyl)triazenes. This mechanism may ultimately explain the antitumor efficacy and low acute toxicity of selected compounds.

Alkylating Agents↗
PubMed1992

Activation of a beta-hydroxyalkylnitrosamine to alkylating agents: evidence for the involvement of a sulfotransferase.

N-Nitrosomethyl(2-hydroxyethyl)amine (NMHEA), when administered by gavage, is a strong liver carcinogen in F344 female rats, but a weak liver carcinogen in male rats. After repeated exposure to NMHEA, either in drinking water or by gavage, female rats accumulated higher levels of DNA-guanine adducts than did their male counterparts, suggesting a correlation with the observed disparity in carcinogenicity. NMHEA has been shown to alkylate rat liver DNA in vivo in a dose-dependent manner. Chemical investigations of NMHEA suggest that it becomes a strong electrophile when a good leaving group is substituted on the hydroxyl. We have proposed that NMHEA is activated to its ultimate carcinogenic form by conjugation with sulfate. The sulfate ester was postulated to undergo rapid cyclization to 3-methyl-1,2,3-oxadizolinium ion, which has previously been found to be a potent methylating agent in vitro. The effect of sulfotransferase inhibitors on the DNA alkylation in rats by NMHEA was studied in vivo. Dichloronitrophenol, a powerful inhibitor of phenol sulfotransferase, had little effect on the methylation and O6-hydroxyethylation of DNA guanine in female rats, while depressing the hydroxyethylation of the N-7 position of guanine. Dichloronitrophenol, however, dramatically enhanced the methylation of DNA in male rats. It also slightly inhibited the N-nitrosodimethylamine-induced methylation of DNA. On the other hand, propylene glycol, an alcohol sulfotransferase inhibitor, had a profound inhibitory effect on DNA methylation induced by NMHEA, very little effect on the formation of N7-(2-hydroxyethyl)guanine, but a very strong effect on the O6-hydroxyethylguanine lesions. NMHEA-induced alkylation was also studied in male and female brachymorphic mice, which are deficient in the ability to synthesize the sulfate donor 3'-phosphoadenosine 5'-phosphosulfate required for sulfotransferase activity, and their heterozygous siblings. No significant differences were seen between the heterozygous and brachymorphic mice in overall levels of alkylation, except in the case of 7-hydroxyethylation. In contrast to rats, male mice showed higher levels of formation of all DNA guanine adducts than did the females. However, propylene glycol was found to depress all the levels of alkylation in the brachymorphic mice, except for N7-(2-hydroxyethyl)guanine, as was observed in rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Alkylation↗
PubMed1991

Mechanism of DNA binding by the oesophageal carcinogen N-nitroso-N-methylaniline.

N-Nitroso-N-methylaniline (NMA) is a strong oesophageal carcinogen in rats but exhibits few overt genotoxic effects. Previous work from our laboratory established that NMA is readily metabolized by cytochrome P450-catalysed N-demethylation to produce the benzenediazonium ion (BDI), a relatively stable but reactive electrophilic agent. We have also shown that BDI reacts with DNA to form an acid-labile adduct. We have now shown that BDI, generated chemically or by the metabolism of NMA in vitro, reacts with DNA to form a triazene coupling product at the N6-position of adenine residues. This adduct has also been shown to be produced in the liver DNA of rats treated with NMA. Procedures for the isolation of DNA and for analysis of the adduct are presented.

Animals↗
PubMed1990

1,3-Dialkyl-3-acyltriazenes, a novel class of antineoplastic alkylating agents.

Aliphatic triazenes, such as 1,3-dimethyltriazene, are potent biological alkylating agents because they form alkyldiazonium ions. They are also subject to very rapid proteolytic decomposition, even at physiological pH. The acylated analogues 1,3-dialkyl-3-acyltrizenes are much more stable in aqueous solution, but they also give rise to alkyldiazonium ions. Four acylated 1,3-dimethyltriazenes, where the acyl groups were diethylphosphoryl (DMP), carbethoxy (DMC), acetyl (DMA), and N-methylcarbamoyl (DMM), were studied kinetically. Rate-pH profiles indicated that the acyl group had a profound effect on the mechanism of decomposition. The cytotoxic potential of all four compounds was studied in vitro by using the MTT-tetrazolium assay. The compounds had fair-to-good activity against some cell lines, particularly those deficient in methylation repair. In vivo assays of DMC and DMM against several tumor xenografts in nude mice showed promising activity for some cancers, particularly in the case of DMM. In vitro assays were also carried out on three 1-(2-chloroethyl)-3-methyl-3-acyltriazenes. The acyl groups were carbethoxy (CMC), acetyl (CMA), and N-methylcarbamoyl (CMM). The activity of these compounds largely paralleled that of bis(2-chloroethyl)-N-nitrosourea (BCNU), except for those cell lines which exhibited the Rem phenotype; triazenes were more active in those lines than BCNU. The in vivo activity of CMC, CMA, and CMM was tested in the P388 leukemia assay. All three were active but CMC and CMA proved to be rather toxic. CMM was well tolerated and was examined in several tumor xenografts in nude mice. Significant activity was found against MX-1 mammary carcinoma, against LX-1 small cell lung carcinoma, and particularly against LOX amelanotic melanoma, where complete cures were effected. The antineoplastic activity of the acyltriazenes is well-correlated with their chemical behavior.

Alkylating Agents↗
PubMed1989

Synthetic non-peptide inhibitors of HIV protease.

We have studied the inhibition of HIV protease by the antifungal antibiotic cerulenin, as well as by several related synthetic, structurally simpler analogs. The effect of these compounds on HIV protease was conveniently studied by monitoring the cleavage of an authentic single peptide bond in a synthetic nonapeptide corresponding to a natural cleavage site in HIV-1 gag precursor polyprotein. The relative inhibitory effects of these compounds have afforded an insight into the structural characteristics which impart antiprotease activity.

Antifungal Agents↗
PubMed1988

Carcinogenicity of hydroxyalkylnitrosamines in F344 rats: contrasting behavior of beta- and gamma-hydroxylated nitrosamines.

The carcinogenicity of N-nitrosomethyl-(2-hydroxyethyl)amine (NMHEA), N-nitrosomethyl-(3-hydroxypropyl)amine (NMHPA), and the p-toluenesulfonate (tosylate) ester of NMHEA (NMHEATs) was tested in male and female F344 rats. The chemicals (25.6 mumol per application) were administered by twice-weekly gavage in corn oil (0.2 ml) for the lifetime of the animals. NMHEA was found to be an effective carcinogen under those conditions. The median survival time for the females was 9 mo after treatment was initiated, while for the males it was 12 mo. The principal cause of death of the females was hepatocellular carcinoma (14 of 20), while only 6 of 20 male rats exhibited that tumor. A few of the male rats had squamous cell carcinomas of the nasal epithelium (4 of 20), tumors which were not observed in the females. NMHPA was a much weaker carcinogen. Many of these rats survived for 2 yr and most had many age-related cancers. Nevertheless, 10 of the NMHPA-treated males and 2 females had adenocarcinoma of the lung, which was absent in the controls and also induced a significant number of neoplastic nodules in the livers of rats of both sexes. NMHEATs was also a weak carcinogen. However, besides many age-related tumors, it induced some hepatocellular carcinomas as well as hemangiosarcomas of the liver. NMHEATs was at least partially hydrolyzed to NMHEA, which was detected in the blood plasma of treated rats. A hypothesis has been advanced that NMHEA is activated to a proximate carcinogen by sulfate conjugation of the hydroxyl group; the present data do not contradict this hypothesis. The relatively lower carcinogenic potency of NMHPA, the different tumor spectrum induced by this chemical, and particularly the differences in chemical behavior suggest that its mode of activation is not the same as that for NMHEA.

Animals↗
PubMed1988

Alkylation of DNA in rats by N-nitrosomethyl-(2-hydroxyethyl)amine: dose response and persistence of the alkylated lesions in vivo.

The in vivo alkylation of DNA by N-nitrosomethyl-(2-hydroxyethyl)amine (NMHEA) was examined in male and female F-344/N rats. NMHEA is a strong hepatocarcinogen in female rats when administered by gavage but a weaker hepatocarcinogen in male rats. Groups of 5 rats of each sex were treated by gavage with various doses of NMHEA dissolved in corn oil. After 4 h the animals were sacrificed and the livers, lungs, and kidneys were removed. The DNA from each liver was isolated and the neutral thermal and mild acid hydrolysates were separated by high-performance liquid chromatography. The alkylated guanines were quantified by fluorescence spectroscopy. NMHEA gives rise to four fluorescent alkylated guanines, 7- and O6-methylguanines, and 7- and O6-hydroxyethylguanines. The dose-response data revealed that all four lesions increased with dose. There was approximately 10x more methylation than hydroxyethylation at the 7 position of guanine. There was less O6 alkylation, but both methylation and hydroxyethylation were observed at all of the doses studied. The overall alkylation was the same in males and females at the 10- and 20-mg/kg doses, but at higher doses the females exhibited significantly higher levels of alkylation than males. The level of alkylation of DNA isolated from non-target tissues, lung, and kidney was low. The persistence of these lesions in vivo was studied at a dose of 25 mg/kg. Groups of five animals each were sacrificed at various times from 0 to 96 h. There was no significant difference between the sexes in persistence of any of the lesions in the liver. The 7-alkylguanines disappeared slowly over the observation period. 7-Methylguanine was present at 30% of the maximum level after 96 h, while 7-hydroxyethylguanine appeared to be more stable. The O6-alkylguanines were removed rapidly from the liver, being at base level by 48 h. The rapid removal of O6-hydroxyethylguanine suggests a repair process independent of O6-alkylguanine-DNA guanine alkyl transferase: an excision repair is postulated. In vitro alkylation of calf thymus DNA by N-nitrosomethyl-(2-tosyloxyethyl)amine, a surrogate for the putative O-sulfate conjugate of NMHEA, resulted in exclusive methylation of DNA-guanine at both the 7 and O6 positions; no hydroxyethylation was detected. In vitro alkylation of calf thymus DNA with 2-hydroxyethyl-ethylnitrosourea resulted in exclusive hydroxyethylation of DNA-guanine at the 7 and O6 positions.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Tumors in F344 rats by oral administration of 1,3-diethyltriazene.

A group of 20 male F344 rats was given by gavage a solution of 2.5 mg of 1,3-diethyltriazene in 0.2 ml corn oil twice a week for 20 weeks. Diethyltriazene is very unstable in hydroxylic solvents, but when administered in oil by gavage it induced tumors in almost all of the treated animals, 16 of which had neoplasms of the forestomach; 13 of which were carcinomas. In addition 9 rats had adenomas of the nasal mucosa, two had alveolar-bronchiolar adenomas of the lung, one had a carcinoma of the esophagus and one an adenocarcinoma of the ileum. Half of the rats had died by week 56 of the experiment, the first at week 40 and the last at week 73. The induction of tumors at sites distant from the stomach indicate that diethyltriazene is more stable in the body than would be predicted from its chemical behavior. Although diethyltriazene is a protected alkyldiazonium ion, its carcinogenic effects in rats differ from ethylnitrosoureas, which are also ethylating agents.

Administration, Oral↗
PubMed1987

Recent findings on the metabolism of beta-hydroxyalkylnitrosamines.

beta-Hydroxynitrosamines appear to be refractory to alpha-oxidation, the common pathway of metabolism of simple dialkylnitrosamines. Some years ago, we postulated that nitrosamines bearing a hydroxyl in the beta position may be activated to alkylating agents by metabolic transformation to sulfate conjugates. Recent evidence has provided support for this hypothesis. A sulfate ester of N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine (NHPOPA) has been found in the urine of hamsters treated with the nitrosamine. It has also been found that inhibition of sulfotransferases inhibited the development of DNA single-strand breaks in livers of rats treated with several beta-hydroxy-nitrosamines. Alkylation of rat liver DNA in vivo by N-nitroso(2-hydroxyethyl)methylamine (NHEMA) favoured methylation over 2-hydroxyethylation by a factor of 10. The methylation reaction was inhibited by sulfotransferase inhibitors. Thus, sulfation appears to be an important pathway for activation of beta-hydroxy-nitrosamines. There are, however, other pathways, such as the oxidation of the beta-hydroxyl group to a carbonyl, which may also result in the formation of electrophilic species capable of modifying cellular macromolecules.

Alkylation↗
PubMed1986

Carcinogenic effects of sequential administration of two nitrosamines in Fischer 344 rats.

The carcinogenic effects of sequential treatment of female F344 rats with two nitrosamines were studied. The animals received either methylethylnitrosamine (NMEA), a strong liver carcinogen, N-nitrosomethylaniline (NMA), a moderately strong esophageal carcinogen, or N-nitrosopyrrolidine, (NPyr), a weaker liver carcinogen. The sequentially treated groups were given NMEA followed by NMA and vice versa, NPyr followed by NMEA and vice versa. The dose and duration for each chemical in the sequentially treated groups were identical for the individual treatments. The animals were allowed to die or were killed when moribund. The animals surviving longer than 110 weeks were sacrificed. The NMEA-NPyr and NPyr-NMEA groups had a tumor spectrum characteristic for NMEA alone (a mixture of hepatic carcinomas and sarcomas with extensive metastases to the lungs). The survival was reduced in the NMEA-NPyr group compared to the NMEA alone group. The time to death of the NMA-NMEA group was not affected by the NMA treatment, but many of the animals had esophageal neoplasms. The NMEA-NMA group survival was reduced when compared to the NMEA alone group but the tumor spectrum was dominated by NMEA. The data indicate that when the target organ is the same, the effect of two nitrosamines is additive with the stronger carcinogen dominating the tumor spectrum. When the target organs are different, the initial exposure influences the tumor spectrum, although the treatment with the second nitrosamine enhances the tumorigenicity of the initial nitrosamine.

Animals↗