2,3-Dimethoxybenzo[i]phenanthridines: topoisomerase I-targeting anticancer agents

Appropriately substituted benzo[i]phenanthridines structurally related to nitidine, a benzo[c]phenanthridine alkaloid with antitumor activity, are active as topoisomerase I-targeting agents. Studies on benzo[i]phenanthridines have indicated analogues that possess a 2,3-methylenedioxy moiety and at least one and preferably two methoxyl groups at the 8- and 9-positions, such as 8,9-dimethoxy-2,3-methylenedioxybenzo[i]phenanthridine, 2, are active as topoisomerase I-targeting agents. Tetramethoxylated benzo[i]phenanthridines, wherein the 2,3-methylenedioxy moiety is replaced with methoxyl groups at the 2- and 3-position, are inactive as a topoisomerase I-targeting agent. These results initially suggested that the 2,3-methylenedioxy moiety was critical to the retention of potent activity. Further studies revealed that 2,3-dimethoxy-8,9-methylenedioxybenzo[i]phenanthridine, 7a, is more potent than 2 as a topoisomerase I-targeting agent. The observation that 2,3-dimethoxylated benzo[i]phenanthridines can actually exhibit enhanced activity prompted the present study in which several 8-substituted 2,3-dimethoxybenzo[i]phenanthridines were prepared and their pharmacological activities evaluated. The influence of NH(2), CN, CH(2)OH, OBn, OCH(3), OH, and NHCOCH(3 )substituents at the 8-position on the relative activity of these 2,3-dimethoxybenzo[i]phenanthridines was examined. Relative to these derivatives, 7a was the most potent topoisomerase I-targeting agent, possessing similar cytotoxicity to that of nitidine in the human lymphoblast tumor cell line, RPMI8402.     

8,9-methylenedioxybenzo[i]phenanthridines: topoisomerase I-targeting activity and cytotoxicity

Substituted benzo[i]phenanthridines that have incorporated within their structure an 8,9-methylenedioxy group can exhibit topoisomerase I-targeting activity. Structure-activity studies were performed to examine the influence of saturation at the 11,12-positions of several substituted 8,9-methylenedioxybenzo[i]phenanthridines. The activities of these dihydro analogues were compared to those of their unsaturated analogues. In addition, the influence of varying substituents at the 2- and 3-positions within the A-ring of these 8,9-methylenedioxybenzo[i]phenanthridines on their relative potency as topoisomerase I-targeting agents and cell proliferation as determined using the MTT assay was investigated. 2,3-Dimethoxy-8,9-methylenedioxybenzo[i]phenanthridine and its 11,12-dihydro derivative were among the more potent analogues evaluated with regard to topoisomerase I-targeting activity and cytotoxicity.     

Substituted benzo[i]phenanthridines as mammalian topoisomerase-targeting agents

Several benzo[c]phenanthridine and protoberberine alkaloids, such as nitidine and berberrubine, are known to induce DNA cleavage in the presence of either topoisomerase I or II. Structure-activity studies performed on various analogues related to benzo[c]phenanthridine and protoberberine alkaloids have provided insights into structural features that influence this topoisomerase-targeting activity. Modifications within the A-ring of benzo[c]phenanthridine and protoberberine alkaloids can significantly alter their ability to enhance the cleavable complex formation that occurs between DNA and topoisomerases. Select benzo[i]phenanthridines were synthesized as potential bioisosteres of nitidine and its analogues. In the present study, 2,3-methylenedioxy-8,9-dimethoxybenzo[i]phenanthridine, 2,3-methylenedioxy-8,9-dimethoxy-5-methylbenzo[i]phenanthridine, 2,3,8,9-tetramethoxybenzo[i]phenanthridine and 5-methyl-2,3,8,9-tetramethoxybenzo[i]phenanthridine were synthesized. These benzo[i]phenanthridine derivatives were evaluated for their ability to enhance cleavable complex formation in the presence of topoisomerases and DNA as well as for their cytotoxicity against the human lymphoblastoma cell line, RPMI8402. 2,3-Methylenedioxy-8,9-dimethoxybenzo[i]phenanthridine (4a) and its 5-methyl derivative (4b) are active as topoisomerase I-targeting agents. In contrast to nitidine, the presence of the 5-methyl substituent in the case of 4b is not associated with enhanced activity. Consistent with previous structure-activity studies on nitidine and protoberberine alkaloids, 2,3,8,9-teramethoxybenzo[i]phenanthridine, 5a, and its 5-methyl derivative, 5b, are inactive as topoisomerase I-targeting agents. These studies were extended to an evaluation of the relative pharmacological activities of 2,8,9-trimethoxybenzo[i]phenanthridine, 3,8,9-trimethoxybenzo[i]phenanthridine, and 2,3-methylenedioxy-8,9-methylenedioxybenzo[i]phenanthridine.     

11-Substituted 2,3-dimethoxy-8,9-methylenedioxybenzo[i]phenanthridine derivatives as novel topoisomerase I-targeting agents

Several 11-substituted benzo[i]phenanthridine derivatives were synthesized, and their TOP1-targeting activity and cytotoxicity were assessed. Comparative data indicate that TOP1-targeting was often the primary molecular target associated with their cytotoxicity. Several 11-aminoalkyl derivatives, 11-aminocarboxy derivatives as well as the 11-[(2-dimethylamino)ethyl]carboxamide of 2,3-dimethoxy-8,9-methylenedioxybenzo[i]phenanthridine were synthesized and did exhibit considerable cytotoxicity with IC(50) values ranging from 20 to 120 nM in the human lymphoblast tumor cell line RPMI8402.     

Esters and amides of 2,3-dimethoxy-8,9-methylenedioxy-benzo[i]phenanthridine-12-carboxylic acid: potent cytotoxic and topoisomerase I-targeting agents

The exceptional topoisomerase I-targeting activity and antitumor activity of 5-(2-N,N-dimethylamino)ethyl-8,9-dimethoxy-2,3-methylenedioxy-5H-dibenzo[c,h][1,6]naphthyridin-6-one (ARC-111, topovale) prompted studies on similarly substituted benzo[i]phenanthridine-12-carboxylic ester and amide derivatives. Among the benzo[i]phenanthridine-12-carboxylic esters evaluated, the 2-(N,N-dimethylamino)ethyl, 2-(N,N-dimethylamino)-1-methylethyl, and 2-(N,N-dimethylamino)-1,1-dimethylethyl esters possessed similar cytotoxicity, ranging from 30 to 55 nM in RPMI8402 and KB3-1 cells. Several of the carboxamide derivatives possess potent topoisomerase I-targeting activity and cytotoxicity. The 2-(N,N-dimethylamino)ethyl, 2-(N,N-diethylamino)ethyl, and 2-(pyrrolidin-1-yl)ethyl amides were among the more cytotoxic benzo[i]phenanthridine-12-carboxylic derivatives, with IC₅₀ values ranging from 0.4 to 5.0 nM in RPMI8402 and KB3-1 cells.     

Dimethoxybenzo[i]phenanthridine-12-carboxylic acid derivatives and 6H-dibenzo[c,h][2,6]naphthyridin-5-ones with potent topoisomerase I-targeting activity and cytotoxicity

The exceptional TOP1-targeting activity and antitumor activity of ARC-111, 1, prompted studies on similarly substituted benzo[i]phenanthridine-12-carboxylic ester and amide derivatives. These studies were extended to include 6-substituted 8,9-dimethoxy-2,3-methylenedioxy-dibenzo[c,h][2,6]naphthyridin-5-ones, which represent reversed lactam analogues of 1. Several of these analogues retained the potent TOP1-targeting activity and cytotoxicity observed for ARC-111.     

Synthesis of N-substituted 5-[2-(N-alkylamino)ethyl]dibenzo[c,h][1,6]naphthyridines as novel topoisomerase I-targeting antitumor agents

Several N-alkyl and N,N-dialkyl 5H-8,9-dimethoxy-5-(2-aminoethyl)-2,3-methylenedioxydibenzo[c,h][1,6]naphthyridin-6-ones have been identified as topoisomerase I-targeting agents with potent antitumor activity. In the present study, the impact on biological activity of substitution of a trifluoromethyl, cyano, aminocarbonyl, or ethynyl group on a N-methyl substituent of N,N-dimethyl-, N-methyl-N-ethyl-, and N-methyl-N-isopropyl 5H-8,9-dimethoxy-5-(2-aminoethyl)-2,3-methylenedioxydibenzo[c,h][1,6]naphthyridin-6-ones was assessed.     

6-Substituted 6H-dibenzo[c,h][2,6]naphthyridin-5-ones: reversed lactam analogues of ARC-111 with potent topoisomerase I-targeting activity and cytotoxicity

6-Substituted 8,9-dimethoxy-2,3-methylenedioxy-6H-dibenzo[c,h][2,6]naphthyridin-5-ones were synthesized and evaluated for topoisomerase I-targeting activity and cytotoxicity. Several of these reversed lactam analogues of ARC-111 exhibited exceptional cytotoxicity with IC50 values ranging from 0.5 to 3.0 nM. In contrast to topotecan, no resistance was observed with several of these reversed lactam analogues in tumor cell lines that overexpressed the efflux transporters MDR1 or BCRP.     

11H-Isoquino[4,3-c]cinnolin-12-ones; novel anticancer agents with potent topoisomerase I-targeting activity and cytotoxicity

Recent studies have identified 2,3-dimethoxy-8,9-methylenedioxy-11-[(2-dimethylamino)ethyl]-11H-isoquino[4,3-c]cinnolin-12-one (1a) as a novel topoisomerase I-targeting agent with potent cytotoxic activity. The effect of varied substituents at the 11-position of 2,3-dimethoxy-8,9-methylenedioxy-11H-isoquino[4,3-c]cinnolin-12-ones on topoisomerase I-targeting activity and cytotoxicity was evaluated. Potent TOP1-targeting activity was observed when the 11-position was substituted with either a 2-(N,N-dimethylamino)ethyl, a 2-(N,N-diethylamino)ethyl, a n-butyl, or a 2-(pyrrolidin-1-yl)ethyl group. The addition of a beta-methyl group to 1a provided an analogue with dramatically reduced TOP1-targeting activity and cytotoxicity. Analogues of 1a wherein the 2-(N,N-dimethylamino)ethyl group was replaced with a (2-tetrahydrofuranyl)methyl, a 2-(piperidin-1-yl)ethyl, or a 2-(4-methylpiperazin-1-yl)ethyl substituent exhibited decreased activity as TOP1-targeting agents. Replacement of the dimethoxy groups of 1a with hydrogen atoms resulted in an analogue with significantly decreased TOP1-targeting activity and cytotoxicity. Removal of both the vicinal dimethoxyl groups and the methylenedioxy moiety resulted in a complete loss of TOP1-targeting activity. The presence of a 9-nitro substituent in place of the 8,9-methylenedioxy group of 1a resulted in a decrease in relative TOP1-targeting activity and cytotoxicity. Compounds 1a and the 11-n-butyl analogue 1d were evaluated for antitumor activity in the human tumor xenograft model using athymic nude mice. The non-estrogen responsive breast tumor cell line MDA-MB-435 was used in these assays. At dose levels that approached its maximum tolerated dose, 1a proved to be effective in inhibiting tumor growth in vivo when administered orally or by ip injection.     

5H-Dibenzo[c,h]1,6-naphthyridin-6-ones: novel topoisomerase I-targeting anticancer agents with potent cytotoxic activity

5H-Dibenzo[c,h]1,6-naphthyridine-6-ones can exhibit potent antitumor activity. The effect of varied substituents at the 5-position of 5H-8,9-dimethoxy-2,3-methylenedioxydibenzo[c,h]1,6-naphthyridine on relative cytotoxicity and topoisomerase I-targeting activity was evaluated. Potent TOP-1-targeting activity is observed when the 5-position is substituted with either a 2-(N,N-dimethylamino)ethyl group, as in 3a, or a 2-(pyrrolidin-1-yl)ethyl substituent, 3c. In contrast, the addition of a beta-methyl group or a beta-hydroxymethyl group to compound 3a, as in 3b and 3j, results in a loss of significant TOP1-targeting activity. While the presence of a 3-(N,N-dimethylamino)propyl substituent at the 5-position or a methyl(2-tetrahydrofuranyl) group allows for retention of TOP1-targeting activity, the 2-(4-methyl-1-piperazinyl)ethyl analogue, 3d, did not exhibit significant activity. Replacement of the N,N-dimethylamino group of 3a with either C(2)H(5) or OH, as in 3f and 3h, respectively, also had a negative impact on both cytotoxicity and TOP1-targeting activity. Treatment of 3a with LAH gave the 5,6-dihydrodibenzo[c,h]naphthyridine, 4a. This dihydro derivative has approximately 2/3 the potency of 3a as a TOP1-targeting agent. Compounds 3a, 3b, 3h, 3i, and 4a were evaluated for antitumor activity in the human tumor xenograft model using athymic nude mice. The non-estrogen responsive breast tumor cell line, MDA-MB-435, was used in these assays. Compound 3a proved to be effective in regressing tumor growth in vivo when administered either by ip injection or orally 3x week at a dose of 2.0mg/kg. Compound 4a when administered orally 5x weekly at a dose of 40 mg/kg also suppressed tumor growth.     

Syntheses and biological evaluation of topoisomerase I-targeting agents related to 11-[2-(N,N-dimethylamino)ethyl]-2,3-dimethoxy-8,9-methylenedioxy-11H-isoquino[4,3-c]cinnolin-12-one (ARC-31)

Several 11-ethyl-2,3-dimethoxy-8,9-methylenedioxy-11H-isoquino[4,3-c]cinnolin-12-ones with varied functionality on the ethyl substituent have exhibited potent topoisomerase I (TOP1) targeting activity and antitumor activity. The influence of various polar substituents at the 2-position of the 11-ethyl substituent, including N-methylamine, N-isopropylamine, hydroxyl, and hydroxylamino groups, on TOP1-targeting activity and cytotoxicity was assessed. The N-methylamine and N-isopropylamine derivatives were also evaluated as antitumor agents in athymic nude mice with MDA-MB-435 human tumor xenografts. Both compounds were active as antitumor agents upon either parenteral or oral administration.     

Substituted benz[a]acridines and benz[c]acridines as mammalian topoisomerase poisons

Coralyne and several other synthetic benzo[a,g]quinolizium derivatives related to protoberberine alkaloids have exhibited activity as topoisomerase poisons. These compounds are characterized by the presence of a positively charged iminium group, which has been postulated to be associated with their pharmacological properties. The objective of the present study was to devise stable noncharged bioisosteres of these compounds. Several similarly substituted benz[a]acridine and benz[c]acridine derivatives were synthesized and their relative activity as topoisomerase poisons was determined. While the benz[c]acridine derivatives evaluated as part of this study were devoid of topoisomerase poisoning activity, several dihydrobenz[a]acridines were able to enhance DNA cleavage in the presence of topo I. In contrast to certain protoberberine derivatives that did exhibit activity as topo II poisons, none of the benz[a]acridines derivatives enhanced DNA cleavage in the presence of topo II. Among the benz[a]acridines studied, 5,6-dihydro-3,4-methylenedioxy-9,10-dimethoxybenz[a]acridine, 13e, was the most potent topo I poison, with comparable potency to coralyne. These data suggest that heterocyclic compounds structurally related to coralyne can exhibit potent topo I poisoning activity despite the absence of an iminium cation within their structure. In comparison to coralyne or other protoberberine derivatives, these benz[a]acridine derivatives possess distinctly different physicochemical properties and represent a novel series of topo I poisons.     

Nitro and amino substitution within the A-ring of 5H-8,9-dimethoxy-5-(2-N,N-dimethylaminoethyl)dibenzo[c,h][1,6]naphthyridin-6-ones: influence on topoisomerase I-targeting activity and cytotoxicity

Recently, 5H-8,9-dimethoxy-5-(2-N,N-dimethylaminoethyl)-2,3-methylenedioxydibenzo[c,h][1,6]naphthyridin-6-one, 1, was identified as a TOP1-targeting agent with pronounced antitumor activity. In the present study, the effect on activity of substituting a single nitro or amino group in the A-ring in lieu of the methylenedioxy moiety of 1 was evaluated. The presence of either a nitro or amino substituent at the 4-position had a pronounced adverse affect on both TOP1-targeting activity and cytotoxicity. To a lesser extent, derivatives with a nitro or amino substituent at the 1-position were also less active than 1. Replacement of the methylenedioxy moiety of 1 with either a nitro or amino substituent at either the 2- and 3-position did result in analogues with potent TOP1-targeting activity and cytotoxicity.     

Mutagenicity of C24H14 PAH in human cells expressing CYP1A1

Relatively little is known about the mutagenicity of C24H14 PAH, a diverse group of five- and six-ring PAH, some of which are present at trace levels in the environment. To better understand the mutagenicity of this class of compounds, 11 C24H14 PAH, including benzo[a]perylene, benzo[b]perylene, dibenzo[a,e]fluoranthene, dibenzo[a,f]fluoranthene, dibenzo[j,l]fluoranthene, dibenzo[a,h]pyrene, dibenzo[a,i]pyrene, dibenzo[e,l]pyrene, naphtho[1,2-b]fluoranthene, naphtho[2,3-a]pyrene, and naphtho[2,3-e]pyrene, were tested in a mutagenicity assay based on human h1A1v2 cells. h1A1v2 cells are a line of human B-lymphoblastoid cells that have been engineered to express cytochrome P4501A1 (CYP1A1), an enzyme capable of metabolizing promutagenic PAH. Mutagenicity was measured at the thymidine kinase (tk) locus following a 72-h exposure period. Our results show that nine of the compounds were mutagenic. Benzo[a]perylene, dibenzo[a,e]fluoranthene, dibenzo[a,i]pyrene, and naphtho[2,3-a]pyrene were the most potent mutagens, having minimum mutagenic concentrations (MMC) (i.e., the dose at which the induced response was twice that of the negative controls) in the 1-5 ng/ml range. Benzo[b]perylene, dibenzo[a,h]pyrene, dibenzo[a,f]fluoranthene, and naphtho[2,3-e]pyrene were somewhat less potent mutagens, having MMC in the 10-30 ng/ml range. Dibenzo[e,l]pyrene, which had an MMC of 280 ng/ml, was the least potent mutagen. Dibenzo[j,l]fluoranthene and naphtho[1,2-b]fluoranthene were not mutagenic at the doses tested (1-3000 ng/ml). The most mutagenic compounds were also quite toxic. At the highest doses tested, benzo[a]perylene, dibenzo[a,e]fluoranthene, dibenzo[a,i]pyrene, dibenzo[a,h]pyrene, and dibenzo[a,f]fluoranthene induced > 60% killing, and naphtho[2,3-a]pyrene and naphtho[2,3-e]pyrene induced > 50% killing. Benzo[b]perylene, dibenzo[e,l]pyrene, dibenzo[j,l]fluoranthene, and naphtho[1,2-b]fluoranthene induced < 50% killing at the highest doses tested. Comparing these results to a previous study in which nine other C24H14 PAH were tested for mutagenicity in this same assay, it was found that dibenzo[a]pyrene isomers were generally more mutagenic than the other groups of C24H14 PAH tested. These observations are discussed with emphasis given to identifying C24H14 PAH that may be important environmental mutagens.     

Synthesis and cytotoxic activity of benzo[c][1,7] and [1,8]phenanthrolines analogues of nitidine and fagaronine

Fagaronine and nitidine are natural benzo[c] phenanthridinium alkaloids, which display antileukemic activity. Both act as topoisomerase I and topoisomerase II inhibitors. The objective of the present study was to prepare noncharged isosters of these compounds, with replacement of the aromatic A ring by a pyridine ring, present in other topoisomerase I inhibitors. Various 7,8- and 8,9-dimethoxy and metylenedioxy benzo[c][1,7] and [1,8]phenanthrolines were readily synthesized by benzyne-mediated cyclization of the corresponding substituted N-(2-halobenzyl)-5-quinolinamines or 5-isoquinolinamines. In both series, compounds bearing oxygenated substituents at positions 8 and 9 exhibited cytotoxic properties towards L1210 murine leukemia cells, which may result from their capacities to intercalate into DNA. Topoisomerase I inhibition was observed for all active compounds.     

Aryl hydrocarbon receptor-mediated activity of mutagenic polycyclic aromatic hydrocarbons determined using in vitro reporter gene assay

Activation of aryl hydrocarbon receptor (AhR) by 30 polycyclic aromatic hydrocarbons (PAHs) was determined in the chemical-activated luciferase expression (CALUX) assay, using two exposure times (6 and 24h), in order to reflect the metabolization of PAHs. AhR-inducing potencies of PAHs were expressed as induction equivalency factors (IEFs) relative to benzo[a]pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In 24h exposure assay, the highest IEFs were found for benzo[k]fluoranthene, dibenzo[a,h]anthracene and dibenzo[a,k]fluoranthene (approximately three orders of magnitude lower than TCDD) followed by dibenzo[a,j]anthracene, benzo[j]fluoranthene, indeno[1,2,3-cd]pyrene, and naphtho[2,3-a]pyrene. The 6h exposure to PAHs led to a significantly higher AhR-mediated activity than the 24h exposure (generally by two orders of magnitude), probably due to the high rate of PAH metabolism. The strongest AhR inducers showed IEFs approaching that of TCDD. Several PAHs, including some strong mutagens, such as dibenzo[a,l]pyrene, cyclopenta[cd]pyrene, and benzo[a]perylene, elicited only partial agonist activity. Calculation of IEFs based on EC25 values and/or 6h exposure data is suggested as an alternative approach to estimation of toxic potencies of PAHs with high metabolic rates and/or the weak AhR agonists. The IEFs, together with the recently reported relative mutagenic potencies of PAHs [Mutat. Res. 371 (1996) 123; Mutat. Res. 446 (1999) 1] were combined with data on concentrations of PAHs in extracts of model environmental samples (river sediments) to calculate AhR-mediated induction equivalents and mutagenic equivalents. The highest AhR-mediated induction equivalents were found for benzo[k]fluoranthene and benzo[j]fluoranthene, followed by indeno[1,2,3-cd]pyrene, dibenzo[a,h]anthracene, benzo[a]pyrene, dibenzo[a,j]anthracene, chrysene, and benzo[b]fluoranthene. High mutagenic equivalents in the river sediments were found for benzo[a]pyrene, dibenzo[a,e]pyrene, and naphtho[2,3-a]pyrene and to a lesser extent also for benzo[a]anthracene, benzo[b]fluoranthene, indeno[1,2,3-cd]pyrene, benzo[j]fluoranthene, dibenzo[a,e]fluoranthene and dibenzo[a,i]pyrene. These data illustrate that AhR-mediated activity of PAHs, including the highly mutagenic compounds, occurring in the environment but not routinely monitored, could significantly contribute to their adverse effects.     

Indolo[3,2-c]cinnolines with antiproliferative, antifungal, and antibacterial activity.

A series of indolo[3,2-c]cinnoline derivatives was prepared and tested to evaluate their biological activity. Most of them inhibited the proliferation of leukemia, lymphoma and solid tumor-derived cell lines at micromolar concentrations, whereas none of the compounds were active against HIV-1. With the exception of 7g, all title compounds showed antibacterial activity against gram-positive bacteria, being up to 200 times more potent than the reference drug streptomycin. Some of the indolo[3,2-c]cinnolines were also endowed with good antifungal activity, particularly against Criptococcus neoformans.     

Identification of benzo[c]phenanthridine metabolites in human hepatocytes by liquid chromatography with electrospray ion-trap and quadrupole time-of-flight mass spectrometry

The metabolism of the benzo[c]phenanthridine alkaloids was studied using human hepatocytes which are an excellent model system for biotransformation studies. For analysis of the alkaloids and their metabolites, an electrospray quadrupole ion-trap mass spectrometry (ESI ion-trap MS) connected to a reversed phase chromatographic system based on cyanopropyl modified silica was used. The optimized experimental protocol allowed simultaneous analysis of the alkaloids and their metabolites and enabled study of their uptake into and interconversion in human hepatocytes. The results show that formation of the dihydro metabolite which may be followed by specific O-demethylenation/O-demethylation processes, is probably the main route of biotransformation (detoxification) of the benzo[c]phenanthridines in human hepatocytes. The structure of the main O-demethyl metabolite (2-methoxy-12-methyl-12,13-dihydro-[1,3]dioxolo[4',5':4,5]benzo[1,2-c]phenanthridin-1-ol; 336.1 m/z,) was proposed by the multi-stage MS and quadrupole time-of-flight MS methods using chemically synthesized standard.     

Investigation of the genotoxicity of dibenzo[c,p]chrysene in human carcinoma MCF-7 cells in culture

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants that have been linked to certain human cancers. The fjord region PAH dibenzo[a,l]pyrene exhibits the highest levels of carcinogenic activity of all PAH as yet tested in rodent tumor models. Another hexacyclic aromatic hydrocarbon, dibenzo[c,p]chrysene (DBC), is a unique PAH that possesses one bay region and two fjord regions within the same molecule. Due to its structure, which is a merger of the fjord region PAHs benzo[c]phenanthrene, benzo[c]chrysene, and benzo[g]chrysene, DBC is of considerable research interest. In order to investigate the pathway of regioselective metabolism we have studied the cytotoxicity, metabolic activation and DNA adduct formation of DBC in human mammary carcinoma MCF-7 cells in culture. The cytotoxicity assay indicated undisturbed cell proliferation even at concentrations as high as 4.5 microM (1.5 micro g/ml) DBC. Concurrently, DNA adducts were detected in MCF-7 cells treated with DBC only in low amounts (0.6 pmol adducts/mg DNA). On the contrary, exposure to anti-DBC-1,2-diol-3,4-epoxide and anti-DBC-11,12-diol-13,14-epoxide, two putatively genotoxic metabolites of DBC, resulted in high levels of DNA adducts (33 and 51 pmol adducts/mg DNA, respectively). Although DBC was not efficiently transformed into DNA-reactive metabolites in MCF-7 cells in culture, the results from our study indicate that the two fjord region diol-epoxide derivatives of DBC may serve as ultimate genotoxic metabolites once they are enzymatically generated under certain circumstances in vitro or in vivo.     

Synthesis and antiviral effect against herpes simplex type 1 of 12-substituted benzo[c]phenanthridinium salts

The synthesis of benzo[c]phenanthridine alkaloid derivatives is described. In vitro antiviral activity against herpes simplex type 1 (HSV1) has been investigated. Contrary to the natural product fagaronine, which did not have any activity in the HSV1 antiviral tests, four 12-alkoxy derivatives showed good activity demonstrating the importance of the 12-substitution in the structure-activity relationships.