The utility of a genetic progression risk test for Barrett esophagus.

This study sought to characterize the utility of a gene methylation-based biomarker test that has been validated to predict progression towards esophageal adenocarcinoma. Barrett esophagus (BE) is a precursor condition for esophageal adenocarcinoma (EAC) with somewhat variable approaches among gastroenterologists toward managing neoplastic progression risk. Capsulomics has developed a validated multigene DNA methylation-based biomarker assay performed on BE biopsies designed to address this variability by classifying BE patients into progression risk groups. In the current study, a survey was administered to practicing gastroenterologists in order to assess the potential impact of this assay on clinical practice. In this context, 89% (95% Cl: 85.4-92.6%) of surveyed physicians felt strongly that the multigene Barrett Esophagus test helped resolve uncertainties and optimize care of patients with BE by impacting their decisions on surveillance intervals and use of active treatments, such as ablation. The assay significantly impacted surveillance intervals for both high-risk (22.0 no assay vs 12.3 months with assay; P = 1.7E-8) and low-risk (7.9 no assay vs 11.4 months with assay, P = 8.8E-4) stratified case results. Finally, the assay also significantly impacted decisions to pursue active ablation treatments in both high-risk (5% recommending ablation without assay vs 42% with assay; P = 3.7E-11) and low-risk (42% recommending ablation without assay vs 29% with assay; P = .049) stratified case results. Results demonstrated a strong effect of the assay on clinical decision making, even in conjunction with established clinical guidelines.

The C8-2'-deoxyguanosine adduct of 2-amino-3-methylimidazo[1,2-d]naphthalene, a carbocyclic analogue of the potent mutagen 2-amino-3-methylimidazo[4,5-f]quinoline, is a block to replication in vitro.

2-Amino-3-methylimidazo[1,2-d]naphthalene (cIQ) is a carbocyclic analogue of the dietary carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in which a naphthalene ring system replaces the quinoline unit of IQ. The activity of cIQ in Ames Salmonella typhimurium tester strain TA98 is known to be 4-5 orders of magnitude lower than IQ. cIQ undergoes efficient bioactivation with rat liver microsomes. The C8-dGuo adduct was formed when calf thymus DNA was treated with the N-hydroxy-cIQ metabolite and either acetic anhydride or extracts from cells that overexpress N-acetyl transferase (NAT). These studies indicate that bioactivation, the stability of the N-hydroxylamine ester, and the reactivity of the nitrenium ion with DNA of cIQ are similar to IQ and that none of these factors account for the differences in mutagenic potency of these analogues in Ames assays. Oligonucleotides were synthesized that contain the C8-dGuo adduct of cIQ in the frameshift-prone CG-dinucleotide repeat unit of the NarI recognition sequence. We have examined the in vitro translesion synthesis of this adduct and have found it to be a strong replication block to Escherichia coli DNA polymerase I, Klenow fragment exo(-) (Kf(-)), E. coli DNA polymerase II exo(-) (pol II(-)), and Sulfolobus solfataricus P2 DNA polymerase IV (Dpo4). Previous studies by Fuchs and co-workers identified E. coli pol II as the polymerase responsible for two-base deletions of the C8-dGuo adduct of N-acetyl-2-aminofluorene in the NarI sequence. Our observation that pol II is strongly inhibited by the C8-dGuo adduct of cIQ suggests that one of the other SOS inducible polymerases (E. coli pol IV or pol V) is required for its bypass, and this accounts for the greatly attenuated mutagenicity in the Ames assays as compared with IQ.

Small molecule inhibitors of Myc/Max dimerization and Myc-induced cell transformation.

The preparation and evaluation of a series of inhibitors of Myc/Max dimerization and Myc-induced cell transformation are described providing mycmycin-1 (3) and mycmycin-2 (4).

CSI-FID: high throughput label-free detection of DNA binding molecules.

Determining the sequence specifity of DNA binding molecules is a non-trivial task. Here we describe the development of a platform for assaying the sequence specificity of DNA ligands using label free detection on high density DNA microarrays. This is achieved by combining Cognate Site Identification (CSI) with Fluorescence Intercalation Displacement (FID) to create CSI-FID. We use the well-studied small molecule DNA ligand netropsin to develop this high throughput platform. Analysis of the DNA binding properties of protein- and small molecule-based libraries with CSI-FID will advance the development of genome-anchored molecules for therapeutic purposes.

Discovery of inhibitors of aberrant gene transcription from Libraries of DNA binding molecules: inhibition of LEF-1-mediated gene transcription and oncogenic transformation.

The screening of a >9000 compound library of synthetic DNA binding molecules for selective binding to the consensus sequence of the transcription factor LEF-1 followed by assessment of the candidate compounds in a series of assays that characterized functional activity (disruption of DNA-LEF-1 binding) at the intended target and site (inhibition of intracellular LEF-1-mediated gene transcription) resulting in a desired phenotypic cellular change (inhibit LEF-1-driven cell transformation) provided two lead compounds: lefmycin-1 and lefmycin-2. The sequence of screens defining the approach assures that activity in the final functional assay may be directly related to the inhibition of gene transcription and DNA binding properties of the identified molecules. Central to the implementation of this generalized approach to the discovery of DNA binding small molecule inhibitors of gene transcription was (1) the use of a technically nondemanding fluorescent intercalator displacement (FID) assay for initial assessment of the DNA binding affinity and selectivity of a library of compounds for any sequence of interest, and (2) the technology used to prepare a sufficiently large library of DNA binding compounds.

Rational design, synthesis, and evaluation of key analogues of CC-1065 and the duocarmycins.

The design, synthesis, and evaluation of a predictably more potent analogue of CC-1065 entailing the substitution replacement of a single skeleton atom in the alkylation subunit are disclosed and were conducted on the basis of design principles that emerged from a fundamental parabolic relationship between chemical reactivity and cytotoxic potency. Consistent with projections, the 7-methyl-1,2,8,8a-tetrahydrocyclopropa[c]thieno[3,2-e]indol-4-one (MeCTI) alkylation subunit and its isomer 6-methyl-1,2,8,8a-tetrahydrocyclopropa[c]thieno[2,3-e]indol-4-one (iso-MeCTI) were found to be 5-6 times more stable than the MeCPI alkylation subunit found in CC-1065 and slightly more stable than even the DSA alkylation subunit found in duocarmycin SA, placing it at the point of optimally balanced stability and reactivity for this class of antitumor agents. Their incorporation into the key analogues of the natural products provided derivatives that surpassed the potency of MeCPI derivatives (3-10-fold), matching or slightly exceeding the potency of the corresponding DSA derivatives, consistent with projections made on the basis of the parabolic relationship. Notable of these, MeCTI-TMI proved to be as potent as or slightly more potent than the natural product duocarmycin SA (DSA-TMI, IC50 = 5 vs 8 pM), and MeCTI-PDE2 proved to be 3-fold more potent than the natural product CC-1065 (MeCPI-PDE2, IC50 = 7 vs 20 pM). Both exhibited efficiencies of DNA alkylation that correlate with this enhanced potency without impacting the intrinsic selectivity characteristic of this class of antitumor agents.

Synthesis of oligonucleotides containing the N2-deoxyguanosine adduct of the dietary carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline.

2-amino-3-methylimidazo[4,5-f]quinoline (IQ) is a highly mutagenic heterocyclic amine formed in all cooked meats. IQ has been found to be a potent inducer of frameshift mutations in bacteria and carcinogenic in laboratory animals. Upon metabolic activation, IQ forms covalent adducts at the C8- and N2-positions of deoxyguanosine with a relative ratio of up to approximately 4:1. We have previously incorporated the major dGuo-C8-IQ adduct into oligonucleotides through the corresponding phosphoramidite reagent. We report here the sequence-specific synthesis of oligonucleotides containing the minor dGuo-N2-IQ adduct. Thermal melting analysis revealed that the dGuo-N2-IQ adduct significantly destabilizes duplex DNA.

DNA sequence modulates the conformation of the food mutagen 2-amino-3-methylimidazo[4,5-f]quinoline in the recognition sequence of the NarI restriction enzyme.

The conformations of C8-dG adducts of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) positioned in the C-X1-G, G-X2-C, and C-X3-C contexts in the C-G1-G2-C-G3-C-C recognition sequence of the NarI restriction enzyme were compared, using the oligodeoxynucleotides 5'-d(CTCXGCGCCATC)-3'.5'-d(GATGGCGCCGAG)-3', 5'-d(CTCGXCGCCATC)-3'.5'-d(GATGGCGCCGAG)-3', and 5'-d(CTCGGCXCCATC)-3'.5'-d(GATGGCGCCGAG)-3' (X is the C8-dG adduct of IQ). These were the NarIIQ1, NarIIQ2, and NarIIQ3 duplexes, respectively. In each instance, the glycosyl torsion angle chi for the IQ-modified dG was in the syn conformation. The orientations of the IQ moieties were dependent upon the conformations of torsion angles alpha' [N9-C8-N(IQ)-C2(IQ)] and beta' [C8-N(IQ)-C2(IQ)-N3(IQ)], which were monitored by the patterns of 1H NOEs between the IQ moieties and the DNA in the three sequence contexts. The conformational states of IQ torsion angles alpha' and beta' were predicted from the refined structures of the three adducts obtained from restrained molecular dynamics calculations, utilizing simulated annealing protocols. For the NarIIQ1 and NarIIQ2 duplexes, the alpha' torsion angles were predicted to be -176 +/- 8 degrees and -160 +/- 8 degrees , respectively, whereas for the NarIIQ3 duplex, torsion angle alpha' was predicted to be 159 +/- 7 degrees . Likewise, for the NarIIQ1 and NarIIQ2 duplexes, the beta' torsion angles were predicted to be -152 +/- 8 degrees and -164 +/- 7 degrees , respectively, whereas for the NarIIQ3 duplex, torsion angle beta' was predicted to be -23 +/- 8 degrees . Consequently, the conformations of the IQ adduct in the NarIIQ1 and NarIIQ2 duplexes were similar, with the IQ methyl protons and IQ H4 and H5 protons facing outward in the minor groove, whereas in the NarIIQ3 duplex, the IQ methyl protons and the IQ H4 and H5 protons faced into the DNA duplex, facilitating the base-displaced intercalated orientation of the IQ moiety [Wang, F., Elmquist, C. E., Stover, J. S., Rizzo, C. J., and Stone, M. P. (2006) J. Am. Chem. Soc. 128, 10085-10095]. In contrast, for the NarIIQ1 and NarIIQ2 duplexes, the IQ moiety remained in the minor groove. These sequence-dependent differences suggest that base-displaced intercalation of the IQ adduct is favored when both the 5'- and 3'-flanking nucleotides in the complementary strand are guanines. These conformational differences may correlate with sequence-dependent differences in translesion replication.

Conformational differences of the C8-deoxyguanosine adduct of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) within the NarI recognition sequence.

2-amino-3-methylimidazo[4,5-f]quinoline (IQ) is a highly mutagenic heterocyclic amine found in cooked meats. The major DNA adduct of IQ is at the C8-position of dGuo. We have previously reported the incorporation of the C8-IQ adduct into oligonucleotides, namely, the G1-position of codon 12 of the N-ras oncogene sequence (G1G2T) and the G3-position of the NarI recognition sequence (G1G2CG3CC) (Elmquist et al. (2004) J. Am. Chem. Soc. 126, 11189-11201). Ultraviolet spectroscopy and circular dichroism studies indicated that the conformation of the adduct in the two oligonucleotides was different, and they were assigned as groove-bound and base-displaced intercalated, respectively. The conformation of the latter was subsequently confirmed through NMR and restrained molecular dynamics studies (Wang et al. (2006) J. Am. Chem. Soc. 128, 10085-10095). We report here the incorporation of the C8-IQ adduct into the G1- and G2-positions of the NarI sequence. A complete analysis of the UV, CD, and NMR chemical shift data for the IQ protons are consistent with the IQ adduct adopting a minor groove-bound conformation at the G1- and G2-positions of the NarI sequence. To further correlate the spectroscopic data with the adduct conformation, the C8-aminofluorene (AF) adduct of dGuo was also incorporated into the NarI sequence; previous NMR studies demonstrated that the AF-modified oligonucleotides were in a sequence-dependent conformational exchange between major groove-bound and base-displaced intercalated conformations. The spectroscopic data for the IQ- and AF-modified oligonucleotides are compared. The sequence-dependent conformational preferences are likely to play a key role in the repair and mutagenicity of C8-arylamine adducts.

Chemical and electrochemical oxidation of C8-arylamine adducts of 2'-deoxyguanosine.

The electrochemical and chemical oxidation of a series of C8-arylamine adducts of 2'-deoxyguanosine has been examined. The oxidations were found to be reversible by cyclic and square-wave voltammetry in both aqueous buffer and aprotic organic solvent. The mechanism of the oxidation in protic media was either one- or two-electron, depending on the aryl group. The chemical oxidation resulted in guanidinohydantoin and spiroiminodihydantoin rearrangement products similar to those observed for 8-oxo-7,8-dihydro-2'-deoxyguanosine.

Translesion synthesis past the C8- and N2-deoxyguanosine adducts of the dietary mutagen 2-Amino-3-methylimidazo[4,5-f]quinoline in the NarI recognition sequence by prokaryotic DNA polymerases.

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) is found in cooked meats and forms DNA adducts at the C8- and N2-positions of dGuo after appropriate activation. IQ is a potent inducer of frameshift mutations in bacteria and is carcinogenic in laboratory animals. We have incorporated both IQ-adducts into the G1- and G3-positions of the NarI recognition sequence (5'-G1G2CG3CC-3'), which is a hotspot for arylamine modification. The in vitro replication of the oligonucleotides was examined with Escherichia coli pol I Klenow fragment exo-, E. coli pol II exo-, and Sulfolobus solfataricus P2 DNA polymerase IV (Dpo4), and the extension products were sequenced by tandem mass spectrometry. Replication of the C8-adduct at the G3-position resulted in two-base deletions with all three polymerases, whereas error-free bypass and extension was observed at the G1-position. The N2-adduct was bypassed and extended by all three polymerases when positioned at the G1-position, and the error-free product was observed. The N2-adduct at the G3-position was more blocking and was bypassed and extended only by Dpo4 to produce an error-free product. These results indicate that the replication of the IQ-adducts of dGuo is strongly influenced by the local sequence and the regioisomer of the adduct. These results also suggest a possible role for pol II and IV in the error-prone bypass of the C8-IQ-adduct leading to frameshift mutations in reiterated sequences, whereas noniterated sequences result in error-free bypass.

Base-displaced intercalated structure of the food mutagen 2-amino-3-methylimidazo[4,5-f]quinoline in the recognition sequence of the NarI restriction enzyme, a hotspot for -2 bp deletions.

The solution structure of the oligodeoxynucleotide 5'-d(CTCGGCXCCATC)-3'.5'-d(GATGGCGCCGAG)-3' containing the heterocyclic amine 8-[(3-methyl-3H-imidazo[4,5-f]quinolin-2-yl)amino]-2'-deoxyguanosine adduct (IQ) at the third guanine in the NarI restriction sequence, a hot spot for -2 bp frameshifts, is reported. Molecular dynamics calculations restrained by distances derived from 24 (1)H NOEs between IQ and DNA, and torsion angles derived from (3)J couplings, yielded ensembles of structures in which the adducted guanine was displaced into the major groove with its glycosyl torsion angle in the syn conformation. One proton of its exocyclic amine was approximately 2.8 A from an oxygen of the 5' phosphodiester linkage, suggesting formation of a hydrogen bond. The carcinogen-guanine linkage was defined by torsion angles alpha' [N9-C8-N(IQ)-C2(IQ)] of 159 +/- 7 degrees and beta' [C8-N(IQ)-C2(IQ)-N3(IQ)] of -23 +/- 8 degrees . The complementary cytosine was also displaced into the major groove. This allowed IQ to intercalate between the flanking C.G base pairs. The disruption of Watson-Crick hydrogen bonding was corroborated by chemical-shift perturbations for base aromatic protons in the complementary strand opposite to the modified guanine. Chemical-shift perturbations were also observed for (31)P resonances corresponding to phosphodiester linkages flanking the adduct. The results confirmed that IQ adopted a base-displaced intercalated conformation in this sequence context but did not corroborate the formation of a hydrogen bond between the IQ quinoline nitrogen and the complementary dC [Elmquist, C. E.; Stover, J. S.; Wang, Z.; Rizzo, C. J. J. Am. Chem. Soc. 2004, 126, 11189-11201].

Biochemical basis of genotoxicity of heterocyclic arylamine food mutagens: Human DNA polymerase eta selectively produces a two-base deletion in copying the N2-guanyl adduct of 2-amino-3-methylimidazo[4,5-f]quinoline but not the C8 adduct at the NarI G3 site.

Heterocyclic arylamines are highly mutagenic and cause tumors in animal models. The mutagenicity is attributed to the C8- and N2-G adducts, the latter of which accumulates due to slower repair. The C8- and N 2-G adducts derived from 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) were placed at the G1 and G3 sites of the NarI sequence, in which the G3 site is an established hot spot for frameshift mutation with the model arylamine derivative 2-acetylaminofluorene but G1 is not. Human DNA polymerase (pol) eta extended primers beyond template G-IQ adducts better than did pol kappa and much better than pol iota or delta. In 1-base incorporation studies, pol eta inserted C and A, pol iota inserted T, and pol kappa inserted G. Steady-state kinetic parameters were measured for these dNTPs opposite the C8- and N 2-IQ adducts at both sites, being most favorable for pol eta. Mass spectrometry of pol eta extension products revealed a single major product in each of four cases; with the G1 and G3 C8-IQ adducts, incorporation was largely error-free. With the G3 N 2-IQ adduct, a -2 deletion occurred at the site of the adduct. With the G1 N 2-IQ adduct, the product was error-free at the site opposite the base and then stalled. Thus, the pol eta products yielded frame-shifts with the N 2 but not the C8 IQ adducts. We show a role for pol eta and the complexity of different chemical adducts of IQ, DNA position, and DNA polymerases.

Synthesis of the N2-deoxyguanosine adduct of the potent dietary mutagen IQ.

[structure: see text] After bioactivation, the potent dietary mutagen 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ) reacts with DNA to give two regioisomeric adducts of deoxyguanosine. The synthesis of the minor N2-adduct has been achieved utilizing the Buchwald-Hartwig palladium-catalyzed N-arylation reaction as the key step.

Site-specific synthesis and properties of oligonucleotides containing C8-deoxyguanosine adducts of the dietary mutagen IQ.

The site-specific synthesis of oligonucleotides containing the C8-deoxyguanosine adduct of the highly mutagenic heterocyclic amine 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) has been achieved, and the oligonucleotides were characterized by UV melting temperature analysis, circular dichroism, and UV absorption spectroscopy. Examination of these data indicated that the IQ-adduct is accommodated in dramatically different environments. This sequence-dependent conformational preference is likely to play a key role in the mutagenicity and repair of IQ-modified oligonucleotides.