Laurence Hurley

PMID: 6993205;Abstract:

Tobacco smoke condensates (TSC) were tested for DNA repair inhibition in both repair proficient and different classes of repair deficient strains of Saccharomyces cerevisiae. TSC was also tested for induction and potentiation of mutations and mitotic gene conversion in unirradiated and uv-irradiated yeast cells. TSC was found to sensitize all the strains of yeast to uv-inactivation indicating that it acts in a nonspecific manner and does not specifically inhibit a particular repair pathway. Genetic studies showed that TSC, without exogenous metabolic activation, failed to produce mutations while it induced mitotic gene conversion in the diploid strain. At specific concentrations, TSC potentiated both mutagenic and gene convertogenic effects uv-light while at higher concentrations of TSC a reduction of mutations was observed. The results are discussed as they relate to carcinogenesis and cocarcinogenesis/tumor promotion. © 1980.

PMID: 19581307;PMCID: PMC2749137;Abstract:

myc is a proto-oncogene that plays an important role in the promotion of cellular growth and proliferation. Understanding the regulation of c-myc is important in cancer biology, as it is overexpressed in a wide variety of human cancers, including most gynecological, breast, and colon cancers. We previously demonstrated that a guanine-rich region upstream of the P1 promoter of c-myc that controls 85-90% of the transcriptional activation of this gene can form an intramolecular G-quadruplex (G4) that functions as a transcriptional repressor element. In this study, we used an affinity column to purify proteins that selectively bind to the human c-myc G-quadruplex. We found that nucleolin, a multifunctional phosphoprotein, binds in vitro to the c-myc G-quadruplex structure with high affinity and selectivity when compared with other known quadruplex structures. In addition, we demonstrate that upon binding, nucleolin facilitates the formation and increases the stability of the c-myc G-quadruplex structure. Furthermore, we provide evidence that nucleolin overexpression reduces the activity of a c-myc promoter in plasmid presumably by inducing and stabilizing the formation of the c-myc G-quadruplex. Finally, we show that nucleolin binds to the c-myc promoter in HeLa cells, which indicates that this interaction occurs in vivo. In summary, nucleolin may induce c-myc G4 formation in vivo. © 2009 by The American Society for Biochemistry and Molecular Biology, Inc.

PMID: 2979741;Abstract:

The DNA alkylation and sequence specificity of a group of natural and synthetic pyrrolo-[1,4]benzodiazepines [P(1,4)Bs] were evaluated by using an exonuclease III stop assay, and the results were compared with in vitro and in vivo biological potency and antitumor activity. The P(1,4)B antibiotics are potent antitumor agents produced by various Actinomycetes, which are believed to mediate their cytotoxic effects by covalent bonding through N-2 of guanine in the minor groove of DNA. In this article we describe the results of a sensitive DNA alkylation assay using exonuclease III which permits both estimation of the extent of DNA modification as well as location of the precise guanines to which the drugs are covalently bound. Using this assay, we have evaluated a series of natural and synthetic compounds of the P(1,4)B class for their ability to bind to DNA and also determined their DNA sequence preference. The compounds included in this study are P(1,4)Bs carrying different substituents in the aromatic ring, having varying degrees of saturation in the five-membered ring, or differing in the stereochemistry at C-11a. These same compounds were evaluated for in vitro cytotoxic activity against B16 melanoma cells, for potency in vivo in B6D2F1 mice (LD50), and for antitumor activity (ILSmax) against P388 leukemia cells. A good correlation was found between extent of DNA alkylation and in vitro and in vivo potency. Furthermore, on the basis of electronic and steric considerations, it was possible to rationalize why those compounds that showed negligible biological activity were unable to bond covalently to DNA. Last, we have determined that the degree of saturation in the five-membered ring of the P(1,4)Bs has a significant effect on the DNA bonding reactivity and biological activity of this class of compounds. © 1988 American Chemical Society.

PMID: 7853333;Abstract:

The quinobenzoxazine compounds A-62176 and A-85226 belong to a novel class of antineoplastic agents that are catalytic inhibitors of topoisomerase II and also structural analogs of the antibacterial DNA gyrase inhibitor Norfloxacin. In vitro studies have shown that their antineoplastic activity is dependent upon the presence of divalent metal ions such as Mg²⁺ and Mn²⁺, although the precise role of these ions in the mechanism of action is unknown. In this study we have investigated the structures of the binary complex between the quinobenzoxazines and Mg²⁺ and the ternary complex between quinobenzoxazine-Mg²⁺ and DNA. The stoichiometry of the binary and ternary complexes and the biophysical studies suggest that a 2:2 drug:Mg²⁺ complex forms a "heterodimer complex" with respect to DNA in which one drug molecule is intercalated into DNA and the second drug molecule is externally bound, held to the first molecule by two Mg²⁺ bridges, which themselves are chelated to phosphates on DNA. There is a cooperativity in binding of the quinobenzoxazines to DNA, and a 4:4 drug:Mg²⁺ complex is proposed in which the two externally bound molecules from two different 2:2 dimers interact via π-π interactions. The externally bound quinobenzoxazine molecules can be replaced by the quinolone antibacterial compound Norfloxacin to form mixed-structure dimers on DNA. Based upon the proposed model for the 2:2 quinobenzoxazine:Mg²⁺ complex on DNA, a parallel model for the antibacterial quinolone-Mg²⁺-DNA gyrase complex is proposed that relies upon the ATP-fueled unwinding of DNA by gyrase downstream of the cleavable complex site. These models, which have analogies to leucine zippers, represent a new paradigm for the structure of drug-DNA complexes. In addition, these models have important implications for the design of new gyrase and topoisomerase II inhibitors, in that optimization for structure-activity relationships should be carried out on two different quinolone molecules rather than a single molecule. © 1995 American Chemical Society.

PMID: 15599;Abstract:

Anthramycin, tomaymycin and sibiromycin are pyrrolo(1,4)benzodiazepine antitumor antibiotics. These compounds react with DNA and other guanine-containing polydeoxynucleotides to form covalently bound antibiotic · polydeoxynucleotide complexes. Experiments utilizing radiolabelled antibiotics have led to the following conclusions: 1. 1. Sibiromycin reacts much faster than either anthramycin or tomaymycin with DNA. 2. 2. At saturation binding the final antibiotic to base ratios for sibiromycin, anthramycin and tomaymycin are 1 : 8.8, 1 : 12.9, and 1 : 18.2 respectively. 3. 3. No reaction with RNA or protein occurs with the pyrrolo(1,4)benzodiazepine antibiotics. 4. 4. Sibiromycin effectively competes for the same DNA binding sites as anthramycin and tomaymycin; however, there is only partial overlap for the same binding sites between anthramycin and tomaymycin. 5. 5. Whereas all three pyrrolo(1,4)benzodiazepine antibiotic · DNA complexes are relatively stable to alkaline conditions, their stability under acidic conditions increases in the order tomaymycin, anthramycin and sibiromycin. 6. 6. No loss of non-exchangeable hydrogens in either the pyrrol ring or the side chains of these antibiotics occurs upon formation of their complexes with DNA. 7. 7. Unchanged antibiotic has been demonstrated to be released upon acid treatment of the anthramycin · DNA and tomaymycin · DNA complexes. 8. 8. A Schiffbase linkage between the antibiotics and DNA has been eliminated. The comparative reactivity of the three antibiotics towards DNA and the stability of their DNA complexes is discussed in relation to their structures. A working hypothesis for the formation of the antibiotic · DNA covalent complexes is proposed based upon the available information. © 1977.