A new 1-nitro-9-aminoacridine derivative targeting yeast topoisomerase II able to overcome fluconazole-resistance.

Fungal resistance remains a significant threat and a leading cause of death worldwide. Thus, overcoming microbial infections have again become a serious clinical problem. Although acridine derivatives are widely analyzed as anticancer agents, only a few reports have demonstrated their antifungal activity. In an effort to develop biologically active antifungals, twelve novel C-857 (9-(2'-hydroxyethylamino)-1-nitroacridine) and C-1748 (9-(2'-hydroxyethylamino)-4-methyl-1-nitroacridine) derivatives were synthesized. The evaluation of biological properties suggests that starting compounds: C-1748, C-857 and IE3 (2-[(4-methyl-1-nitroacridin-9-yl)amino]ethyl lysinate), IE4 (2-[(1-nitroacridin-9-yl)amino]ethyl lysinate) antifungal mode of action differ from that determined for IE5 (N'-{3-[(4-methyl-1-nitroacridin-9-yl)amino]propyl}lysinamide), IE6 (N'-{3-[(1-nitroacridin-9-yl)amino]propyl}lysinamide) and IE10 (3,3'-Bis-(1-nitroacridin-9-ylamino)-aminoethylaminoethylaminoethylamine). Although MIC values determined for the latter were higher, in contrast to C-857 and C-1748, newly synthesized IE5, IE6 and IE10 reduced C. albicans hyphal growth in different inducing media. Those compounds also exhibited antibiofilm activity, whereas IE10 was the most effective. Moreover, only IE6 exhibited antifungal activity against fluconazole resistant C. albicans strains with MICs values in the range of 16-64 µg mL-1. Our results also indicate that, in contrast to other analyzed derivatives, novel synthetized compounds IE6 and IE10 with antifungal activity target yeast topoisomerase II activity.

Efficient and Short Method for Conjugation of 1-Nitro-9-Aminoacridine to Important Peptidyl Fragments by a Solid Support Synthesis.

The efficient and short techniques for conjugation of 9-aminoacridine with different peptidyl fragments are necessary for the development of active pharmaceutical ingredients (API). They need to be adopted to generate a new branch of acridine conjugates, enhancing their bioavailability for the examination in biological systems. The branch of developing acridine conjugates, built via different linkers and synthesized in this study, are expected as potential effective chemotherapeutics with dual mechanism of action. Recently, the methodology based on a solid-phase technique has been successfully demonstrated in preparing a number of promising compounds. However, the reaction conditions for amide bond formation between 1-nitro-9-aminoacridine and peptidyl fragments need to be optimized. In this study, the optimization of amide bond formation was demonstrated with the use of the solid-phase synthesis to build a new promising group of 1-nitro-9-aminoacridines conjugated to lactoferrin fragments via especially carboxy linker length.

1,3-dimethyl-6-nitroacridine derivatives induce apoptosis in human breast cancer cells by targeting DNA.

The acridine derivatives can interact with the double-stranded DNA, which is regarded as the biological target of the anticancer drugs in cancer treatment. We designed and synthesized a new series of 1,3-dimethyl-6-nitroacridine derivatives as potential DNA-targeted anticancer agents. These compounds could partially intercalate into the calf thymus DNA, differing from the parent acridine. The results showed that the substitutions of the acridine ring had great effect on DNA binding affinity. The binding constants determined by UV-vis spectroscopy were found to be 105 M-1 grade. Anticancer activity of these compounds was screened using MTT assay. Most compounds inhibited 50% cancer cell growth at concentration below 30 µM, the results were consistent with the DNA binding ability. Compounds 1 and 6 were found to have more effective cytotoxicity, especially in human breast cancer cell lines. To investigate the action mechanism, we studied cell apoptosis, morphological changes, and cell cycle distribution in MCF-7 and MDA-MB-231 cells. Compounds 1 and 6 caused MCF-7 and MDA-MB-231 cells death due to apoptosis, and induced cell apoptosis in a dose-dependent manner. They also had significant effect on cell cycle progression and arrested cell cycle at G2/M phase. The results demonstrated that compounds 1 and 6 are promising candidates for cancer treatment.

Does C60 fullerene act as a transporter of small aromatic molecules?

C60 fullerene is reported to directly interact with biomolecules, such as aromatic mutagens or anticancer drugs. Therefore, it is extensively studied for its potential application in the fields of drug delivery and chemoprevention. Understanding the nature of fullerene-drugs interactions might contribute to optimization and modification of the existing chemotherapy systems. Possible interactions between ICR-191, a model acridine mutagen, with well-established biophysical properties and mutagenic activity, and C60 fullerene aqueous solution were investigated by broad range of biophysical methods, such as Dynamic Light Scattering, Isothermal Titration Calorimetry, and Atomic Force Microscopy. Additionally, to determine biological activity of ICR-191-C60 fullerene mixtures, Ames mutagenicity test was employed. It was demonstrated that C60 fullerene interacts non-covalently with ICR-191 and has strong affinity to bacterial membranes. The obtained results provide practical insight into C60 fullerene interactions with aromatic compounds.

DFT Simulation of Structural and Optical Properties of 9-Aminoacridine Half-Sandwich Ru(II), Rh(III), and Ir(III) Antitumoral Complexes and Their Interaction with DNA.

In this work, we use DFT-based methods to simulate the chemical structures, optical properties, and interaction with DNA of a recently synthesized chelated C^N 9-aminoacridine arene Ru(II) anticancer agent and two new closely related Rh(III) and Ir(III) complexes using DFT-based methods. Four chemical models and a number of theoretical approaches, which representatively include the PBE0, B97D, ωB97X, ωB97X-D, M06, and M06-L density functionals and the LANL2DZ, def2-SVP, and def2-TZVP basis sets, are tested. The best overall accuracy/cost performance for the optimization process is reached at the ωB97X-D/def2-SVP and M06/def2-SVP levels of theory. Inclusion of explicit solvent molecules (CHCl3) further refines the geometry, while taking into account the crystal network gives no significant improvements of the computed bond distances and angles. The analysis of the excited states reveals that the M06 level matches better the experimental absorption spectra, compared to ωB97X-D. The use of the M06/def2-SVP approach is therefore a well-balanced method to study theoretically the bioactivity of this type of antitumoral complexes, so we couple this TD-DFT approach to molecular dynamics simulations in order to assess their reactivity with DNA. The reported results demonstrate that these drugs could be used to inject electrons into DNA, which might broaden their applications in photoactivated chemotherapy and as new materials for DNA-based electrochemical nanodevices.

CpG methylation increases the DNA binding of 9-aminoacridine carboxamide Pt analogues.

This study investigated the effect of CpG methylation on the DNA binding of cisplatin analogues with an attached aminoacridine intercalator. DNA-targeted 9-aminoacridine carboxamide Pt complexes are known to bind at 5'-CpG sequences. Their binding to methylated and non-methylated 5'-CpG sequences was determined and compared with cisplatin. The damage profiles of each platinum compound were quantified via a polymerase stop assay with fluorescently labelled primers and capillary electrophoresis. Methylation at 5'-CpG was shown to significantly increase the binding intensity for the 9-aminoacridine carboxamide compounds, whereas no significant increase was found for cisplatin. 5'-CpG methylation had the largest effect on the 9-ethanolamine-acridine carboxamide Pt complex, followed by the 9-aminoacridine carboxamide Pt complex and the 7-fluoro complex. The methylation state of a cell's genome is important in maintaining normal gene expression, and is often aberrantly altered in cancer cells. An analogue of cisplatin which differentially targets methylated DNA may be able to improve its therapeutic activity, or alter its range of targets and evade the chemoresistance which hampers cisplatin efficacy in clinical use.

Targeting Topoisomerase II Activity in NSCLC with 9-Aminoacridine Derivatives.

BACKGROUND: Etoposide and other type-II human topoisomerase (TOPOII) poisons are widely used for the treatment of many different cancer types, including non-small cell lung cancer (NSCLC). However, there is a risk for the development of therapy-related secondary leukemia following treatment with these TOPOII poisons. Five to seven years is the typical latency period for the development of secondary leukemia. One of the strategies to overcome this issue is to develop agents that do not act as poisons but still effectively inhibit topoisomerase activity. This has led to the development of acridine-based agents, which are catalytic TOPOII inhibitors, that do not generate DNA strand breaks that can lead to secondary malignancies in in vitro tests. MATERIALS AND METHODS: In this study, we showd antiproliferative activity of a series of acridine-based catalytic inhibitors of TOPOII using four NSCLC cell lines (H460, A549, H2009 and H2030). Cells were treated with four acridine-based compounds for 72 h. RESULTS: The results indicate that these compounds inhibit NSCLC cell proliferation with half-maximal effective concentration (EC50) ranging from 8.15 to 42.09 µM. Combination therapy with cisplatin resulted in increased potency. Poly (ADP-ribose) polymerase cleavage and Guava Nexin assays confirm that the primary mode of cell death was by apoptosis. CONCLUSION: This current work is part of a series of studies for this panel of acridine-based compounds bearing TOPOII-inhibitory activity against different solid tumor types. The acridine-based agents were found to substantially reduce NSCLC cell viability and induce apoptosis. In addition, the acridine-based compounds sensitized cells to cisplatin as measured by cell viability. The results are consistent with prior work on mesothelioma, small-cell lung cancer and pancreatic cancer with this same panel of 9-aminoacridine derivatives. These findings support further development of this type of catalytic TOPOII inhibitor as a novel agent for NSCLC therapy.

Modulation of acridine mutagen ICR191 intercalation to DNA by methylxanthines--analysis with mathematical models.

Caffeine (CAF) and other methylxanthines (MTX) may interact directly with several aromatic, intercalating ligands through mixed stacking aggregation. Formation of such stacking hetero-complexes may decrease their free form concentration and, in consequence, diminish their biological activity, which is often related to their direct interaction with DNA. In this paper interactions of acridine mutagen (ICR191) with DNA in the presence of three MTX: caffeine (CAF), pentoxifylline (PTX) and theophylline (TH) are investigated. Several mathematical models are used to calculate all association constant values and every component concentration in each analyzed mixture. Model McGhee-von Hippel is used to analyze ligand-DNA interaction, and model Zdunek et al.--to analyze ligand-MTX interactions. Finally, two distinct mathematical models are employed to analyze three-component mixture containing ligand, MTX and DNA molecules. The first model describes possible interactions of ligand with DNA and MTX, and rejects direct MTX interactions with DNA. The second model describes all interactions mentioned above and, additionally, allows MTX to interact directly with DNA. Results obtained using these models are similar. However, correspondence of theoretical results to experimental data is better for the first model than the second one. In this paper possible interactions of ICR191 with eukaryotic cell chromatin are also analyzed, showing that CAF reduces acridine mutagen potential to interact directly with cell chromatin. Additionally, it is demonstrated that MTX inhibit mutagenic activity of ICR191 in a dose-dependent manner. Furthermore, biological activity of ICR191-MTX mixtures corresponds with concentration of free mutagen form calculated using appropriate mathematical model.

Transformation of MCF-10A cells by random mutagenesis with frameshift mutagen ICR191: a model for identifying candidate breast-tumor suppressors.

BACKGROUND: Widely accepted somatic mutation theory of carcinogenesis states that mutations in oncogenes and tumor suppressor genes in genomes of somatic cells is the cause of neoplastic transformation. Identifying frequent mutations in cancer cells suggests the involvement of mutant genes in carcinogenesis. RESULTS: To develop an in vitro model for the analysis of genetic alterations associated with breast carcinogenesis, we used random mutagenesis and selection of human non-tumorigenic immortalized breast epithelial cells MCF-10A in tissue-culture conditions that mimic tumor environment. Random mutations were generated in MCF-10A cells by cultivating them in a tissue-culture medium containing the frameshift-inducing agent ICR191. The first selective condition we used to transform MCF1-10A cells was cultivation in a medium containing mutagen at a concentration that allowed cell replication despite p53 protein accumulation induced by mutagen treatment. The second step of selection was either cell cultivation in a medium with reduced growth-factor supply or in a medium that mimics a hypoxia condition or growing in soft agar. Using mutagenesis and selection, we have generated several independently derived cultures with various degrees of transformation. Gene Identification by Nonsense-mediated mRNA decay Inhibition (GINI) analysis has identified the ICR191-induced frameshift mutations in the TP53, smoothelin, Ras association (RalGDS/AF-6) domain family 6 (RASSF6) and other genes in the transformed MCF-10A cells. The TP53 gene mutations resulting in the loss of protein expression had been found in all independently transformed MCF-10A cultures, which form large progressively growing tumors with sustained angiogenesis in nude mice. CONCLUSION: Identifying genes containing bi-allelic ICR191-induced frameshift mutations in the transformed MCF-10A cells generated by random mutagenesis and selection indicates putative breast-tumor suppressors. This can provide a model for studying the role of mutant genes in breast carcinogenesis.

Isolation and characterization of novel phenotype CHO cell mutants defective in peroxisome assembly, using ICR191 as a potent mutagenic agent.

To elucidate molecular and cellular mechanisms of peroxisome biogenesis, we have isolated Chinese hamster ovary (CHO) cell mutants defective in peroxisome biogenesis by making use of enhanced green fluorescent protein (EGFP) and a frameshift-inducing mutagen ICR191. CHO-TKa cells stably expressing Pex2p were transformed with a cDNA encoding EGFP fused with peroxisomal targeting signal type 2 (PTS2-EGFP), termed Tka/EG2. TKa/EG2 cells were mutagenized with ICR191 and cultured in the presence of P9OH (9-(1'-pyrene) nonanol) followed by an exposure to UV. P9OH/UV-resistant and morphologically peroxisome-deficient mutant cells were isolated by directly observing cytosolic localization of EGFP, without cell staining. By a combination of cell-fusion and PEX transfection, we determined complementation groups (CGs) of 16 cell mutants isolated here. The mutants were classified into five CGs, including pex2, pex3, pex5, pex6, and pex7 cell mutants. In contrast to typical pex6 mutants with the impaired import of both PTS1- and PTS2-proteins, two clones, ZPEG236 and ZPEG244, showed a distinct, novel phenotype where PTS1-protein import was normal despite the abrogated PTS2 import. Dysfunction of Pex3p in pex3 ZPEG 238 was due to one base (G) insertion in the codon for Asn7 resulting in a frameshift, thereby inducing a distinct 31 amino-acid sequence and a termination. pex2 ZPEG239 showed a mutation in codon GAG for Glu(201) to a nonsense mutation, TAG. Thus, the method developed here using ICR191 could be useful for isolation of further novel cell mutants impaired in peroxisome biogenesis.

Attenuation of acridine mutagen ICR-191--DNA interactions and DNA damage by the mutagen interceptor chlorophyllin.

We have investigated the ability of chlorophyllin (CHL) to interact with acridine mutagen ICR-191 (2-methoxy-6-chloro-9-(3-(2-chloroethyl)aminopropylamino)acridine) and also its ability to decrease binding of ICR-191 to DNA in a simple three-component competition system: CHL-ICR-DNA. Our data indicate a strong association of ICR-191 with CHL, stronger even than the association of ICR-191 with DNA. Calculations based on the measured affinity data show that a two- to three-fold excess of CHL reduces by about two-fold the concentration of the mutagen-DNA complex. We also exposed human leukemic HL-60 cells to ICR-191 in the absence and presence of CHL and measured the mutagen-induced DNA damage. The extent of DNA damage was assessed by analysis of histone H2AX phosphorylation. While ICR-191 induced significant increase in expression of phosphorylated H2AX (gammaH2AX), particularly in DNA replicating cells, this increase was totally abolished in the cells treated with ICR-191 in the presence of CHL.

Identification of an aminoacridine derivative that binds to RNA tetraloops.

RNA folds into diverse structures that form unique targets for small molecules and thus provide significant potential for controlling biological processes involving RNA with small-molecule ligands. We are investigating molecular recognition of tetraloop RNA by small molecules. RNA tetraloops are four-nucleotide stem loops with unusual stability that are involved in biological processes involving RNA by forming binding sites for proteins and other RNAs. We have sequentially used the docking programs DOCK and AutoDock to screen 1990 small molecules in the NCI diversity set to identify molecules selective for RNA tetraloops over double-stranded RNA. The compounds predicted to bind to tetraloop RNA were evaluated for binding RNA tetraloops using 1H NMR spectroscopy and fluorescence techniques. An aminoacridine derivative (AD2) was identified that binds to a GAAA tetraloop in a 2:1 ratio with dissociation constants of 1.0 and 4.0 microM. AD2 binds with approximately 20-fold and 9-fold higher affinity to tetraloop RNA than to double- and single-stranded RNAs, respectively.

Isolation and characterization of dominant and recessive IL-3-independent hematopoietic transformants.

Retroviral integration mutagenesis and treatment with the frameshift mutagen ICR191 were used to transform v-H-ras expressing PB-3c cells to interleukin-3 (IL-3) independence. Six clones displayed viral integrations into the 3' region of the IL-3 gene thus acting post-transcriptionally by disrupting the AU-rich instability element. Two clones contained reverse orientation integration into the raf-1 gene revealing an enhancer insertion mechanism. Growth by this mechanism was sensitive to the Raf-1 inhibitor BAY 43-9006 and the Mek inhibitor U0126. Following treatment with ICR191, IL-3-independent clones were recovered and studied by cell fusion. With 21/22 clones, IL-3 independence resulted from a recessive mechanism as cellular hybrids with parental cells reverted to IL-3 dependence. Recessive clone D2c displayed increased phospho-Erk1/2 levels and was growth sensitive to U0126, but not to BAY43-9006. The single dominant clone, D5a, showed no signs of mitogen-activated protein kinases pathway activation but displayed constitutive phosphorylation of Stat5. We conclude that PB-3c has several options to acquire IL-3 growth autonomy involving transcriptional or post-transcriptional mechanisms affecting the distal regulators Erk or Stat5. The reported panel of independent dominant and recessive transformants should provide a useful tool for inhibitor profiling.

Alleviation of mutagenic effects of polycyclic aromatic agents (quinacrine mustard, ICR-191 and ICR-170) by caffeine and pentoxifylline.

Previous studies performed by others indicated that apart from its other biological effects, caffeine (CAF) may have a role in protection of organisms against cancer. However, biological mechanism of this phenomenon remained unknown. Recent studies suggested that caffeine can form stacking (pi-pi) complexes with polycyclic aromatic chemicals. Therefore, one might speculate that effective concentrations of polycyclic aromatic mutagens could be reduced in the presence of caffeine. Here we demonstrate that caffeine and another xanthine, pentoxifylline (PTX), effectively alleviate mutagenic action of polycyclic aromatic agents (exemplified by quinacrine mustard (QM), 2-methoxy-6-chloro-9-(3-(2-chloroethyl)aminopropylamino)acridine.2HCl (ICR-191) and 1,3,7-propanediamine-N-(2-chloroethyl)-N'-(6-chloro-2-methoxy-9-acridinyl)-N-ethyl.2HCl (ICR-170)), but not of aliphatic mutagens (exemplified by mechlorethamine), in the recently developed mutagenicity test based on bacterium Vibrio harveyi. Biophysical studies indicated that caffeine and pentoxifylline can form stacking complexes with the aromatic agents mentioned above. Molecular modeling also confirmed a possibility of stacking interactions between examined molecules.

Acridinecarboxamide topoisomerase poisons: structural and kinetic studies of the DNA complexes of 5-substituted 9-amino-(N-(2-dimethylamino)ethyl)acridine-4-carboxamides.

For a series of antitumor-active 5-substituted 9-aminoacridine-4-carboxamide topoisomerase II poisons, we have used X-ray crystallography and stopped-flow spectrophotometry to explore relationships between DNA binding kinetics, biological activity, and the structures of their DNA complexes. The structure of 5-F-9-amino-[N-(2-dimethylamino)ethyl]-acridine-4-carboxamide bound to d(CGTACG)(2) has been solved to a resolution of 1.55 A in space group P6(4). A drug molecule intercalates between each of the CpG dinucleotide steps, its protonated dimethylamino group partially occupying positions close to the N7 and O6 atoms of guanine G2 in the major groove. A water molecule forms bridging hydrogen bonds between the 4-carboxamide NH and the phosphate group of the same guanine. Intercalation unwinds steps 1 and 2 by 12 degrees and 8 degrees, respectively compared with B-DNA, whereas the central TpA step is overwound by 10 degrees. Nonphenyl 5-substituents, on average, decrease mean DNA dissociation rates by a factor of three, regardless of their steric, hydrophobic, H-bonding, or electronic properties. Cytotoxicity is enhanced on average 4-fold and binding affinities rise by 3-fold, thus there is an apparent association between kinetics, affinity, and cytotoxicity. Taken together, the structural and kinetic studies imply that the main origin of this association is enhanced stacking interactions between the 5-substituent and cytosine in the CpG binding site. Ligand-dependent perturbations in base pair twist angles and their consequent effects on base pair-base pair stacking interactions may also contribute to the stability of the intercalated complex. 5-Phenyl substituents modify dissociation rates without affecting affinities, and variations in their biological activity are not correlated with DNA binding properties, which suggests that they interact directly with the topoisomerase protein.

Cytotoxicity and mutagenicity of frameshift-inducing agent ICR191 in mismatch repair-deficient colon cancer cells.

BACKGROUND: Deficiency of DNA mismatch repair is a common feature of cancers exhibiting instability of microsatellite DNA sequences. Cancers with microsatellite instability are recognizable by their high rate of spontaneous frameshift mutations within microsatellite sequences, their resistance to killing by cytotoxic agents, and their localization to specific tissues, e.g., the proximal colon and stomach. We hypothesized that the mismatch repair deficiency of these cancers would make them vulnerable to environmental or chemical frameshift-inducing agents. This study was undertaken to test whether exogenous frameshift-inducing agents selectively induce mutations in mismatch repair-deficient cells of mutagen-exposed tissues like the colon and whether cytotoxic doses of these agents would preferentially kill those cells. METHODS: Cytotoxicity of the acridine mutagen 6-chloro-9-[3-(2-chloroethylamino)propylamino]-2-methoxy-acridine (ICR191), a DNA frameshift inducer, was determined in the mismatch repair-deficient human colon carcinoma cell line HCT116 versus the repair-reconstituted derivative HCT116+C3. Vulnerability to the mutagenic effects of ICR191 was determined by transfection of HCT116 or HCT116+C3 cells with a frameshift reporter vector, followed by treatment of the cells with ICR191. Alternatively, the reporter vector was reacted ex vivo with ICR191, and the derivatized vector was then transfected into HCT116 or HCT116+C3 cells. RESULTS: ICR191 proved to be fivefold to 10-fold more potent in inducing mutations in mismatch repair-deficient HCT116 cells than in mismatch repair-proficient HCT116+C3 cells. Moreover, at cytotoxic doses of ICR191, repair-deficient HCT116 cells proved to be fivefold more vulnerable to killing than did HCT116+C3 cells. CONCLUSIONS: Frameshift-inducing mutagens can selectively induce mutations in mismatch repair-deficient cells versus mismatch repair-proficient cells. Environmental exposures may, therefore, favor development of cancers with microsatellite instability in tissues like the gut. Frameshift-inducing agents can, however, also preferentially kill mismatch repair-deficient cancer cells and, thus, may be promising as model therapeutic compounds.

Modulation of the potency of promutagens and direct acting mutagens in bacteria by inhibitors of the multidrug resistance mechanism.

Multiple drug resistance (MDR) mechanisms are known to limit the effectiveness of some cancer chemotherapies, probably through enhancing P-glycoprotein-mediated drug efflux from mammalian cells. Similar mechanisms appear to act in other organisms, including bacteria, and may affect not only the toxicity but also the mutagenicity of certain chemicals. At least in some experimental situations, MDR can be overcome through concomitant treatment of the cells with various types of inhibitors. Two MDR inhibitors, verapamil, a calcium channel blocker, and trifluoperazine, a calmodulin inhibitor, were assayed for their ability to modulate the potency of nine mutagens with varying mechanisms of action in various Salmonella typhimurium his- strains. Neither verapamil nor trifluoperazine affected the direct mutagenicity of sodium dichromate and 2-methoxy-6-chloro-9[3-(2-chloroethyl)amino-propyl-amino] dihydrochloride (ICR 191) or the S9-mediated mutagenicity of benzo[a]pyrene and 2-amino-3,4-dimethyl-amidazo[4,5-f]quinoline (MeIQ). Both modulators enhanced the direct mutagenicity of doxorubicin. Moreover, trifluoperazine sharply increased the S9-mediated mutagenicity of cyclophosphamide and 2-aminofluorene, while it consistently decreased the mutagenicity of 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2). The contrasting effect towards the aromatic amine 2-aminofluorene and the heterocyclic amine Trp-P-2, representative of important chemical families responsible for the bacterial mutagenicity of cigarette smoke, may explain the observed lack of influence of trifluoperazine on the mutagenicity of a cigarette smoke condensate. These observations extend the known range of chemical types whose mutagenicity can be modulated by inhibitors of MDR and suggest that there may be value in adding MDR inhibitors, especially trifluoperazine, to optimize the detection of mutagenicity by certain types of chemicals in the Salmonella/mammalian microsome mutagenicity test.

QSAR of acridines, III. Structure-activity relationship for antitumour imidazoacridinones and intercorrelations between in vivo and in vitro tests.

A study on quantitative relationships between the biological activity and physicochemical properties of antitumour 5-alkylaminoimidazoacridinone derivatives was carried out. The activity was based on the results of several in vitro tests as well as experimental antileukaemic therapy. The capacity factor, log k', determined by the reverse-phase HPLC method, was a measure of lipophilic properties. UV and NMR spectra of the compounds were employed to describe electronic parameters. Values of steric descriptors were calculated as topological indexes. Results obtained by means of principal component analysis (PCA) allow us to group biological tests into two subsets: the lipophilicity-dependent and lipophilicity-independent test groups. The highest intercorrelation, R = 0.92, was shown between the optimal dose, pOD, determined in leukaemia P388-bearing mice and cytotoxicity expressed as pEC50 in leukaemia cells. The equation describing this relationship could be applied to predict the therapeutic doses of imidazoacridinone derivatives which would be effective in experimental antileukaemic therapy. The quantitative structure-activity relationship (QSAR) study showed that lipophilic properties significantly influence cytotoxicity, pEC50, and antileukaemic potency, pOD, only in the case of 8-hydroxy analogues of imidazoacridinones, whereas the activity of the remaining derivatives is very low and does not depend on lipophilicity. Electronic resonance properties seem to influence this specific impact of lipophilicity on the biological activity of 8-hydroxy derivatives. Hence, it may be possible to improve the antitumour activity of 8-hydroxyimidazoacridinones by obtaining more hydrophilic derivatives, up to the optimal value of the lipophilic parameter.

Specificity of base substitutions induced by the acridine mutagen ICR-191: mispairing by guanine N7 adducts as a mutagenic mechanism.

As the most nucleophilic site in DNA, the guanine N7 atom is a major site of adduction by a large number of alkylating mutagens and carcinogens. Aflatoxin B1, a powerful mutagen, is believed to act through its reaction with this DNA site. On the basis of the specificity of base substitutions induced by various adduct forms of aflatoxin, we have proposed that bulky guanine N7 adducts elicit base substitutions by two mechanisms. The first mechanism is similar to that observed for a number of bulky noninstructive lesions, whereas the second mechanism invokes mispairing between N7-adducted guanine and thymine. A prediction of the mispairing hypothesis is that diverse bulky guanine N7 adducts (regardless of structural similarities with the aflatoxins) should induce predominantly G-to-A transitions. Accordingly, we have recently observed that base substitutions induced by the acridine half-mustard ICR-191 in the M13 double-stranded DNA transfection system are predominantly G:C-to-A:T transitions. Here, by transfecting ICR-191-treated M13 AB28 single-stranded DNA into Escherichia coli, we show that base substitutions are predominantly targeted to guanines. Since the N7-adducted-guanine:thymine mispairing is proposed to require N1 deprotonation promoted by the primary N7 lesion, guanine imidazole ring-opening should abolish this mispairing property, and thereby alter the specificity of mutagenesis. Here, we show that the incubation of ICR-191-treated RF DNA at pH 10.5 results in a significant reversal of the specificity of G:C-targeted substitutions such that G-to-T transversions predominated over G-to-A transitions.(ABSTRACT TRUNCATED AT 250 WORDS)