Stereoselectivity, Sequence Specificity and Mechanism of Action of the Azinomycin Epoxide

Probing cytochrome P450-mediated activation with a truncated azinomycin analogue

Selective cytochrome P450 bioactivation of truncated azinomycin.

Essential role of an unknown gene aziU3 in the production of antitumor antibiotic azinomycin B verified by utilizing optimized genetic manipulation systems for Streptomyces sahachiroi

Streptomyces sahachiroi ATCC 33158 produces the potent antitumor antibiotic azinomycin B, which is featured with a set of unusual functionalized moieties. However, the genetic analyses of azinomycin B biosynthetic pathway are hampered by the low efficiency of S. sahachiroi genetic manipulation. In this study, we developed two efficient DNA transfer systems for S. sahachiroi ATCC 33158 by optimizing a variety of parameters known to affect intergeneric conjugation and protoplast transformation. High efficiencies of 4 × 10(2) transformants per μg DNA and 2.47 × 10(-4) conjugants per recipient were achieved when using the integrative vector pJTU2554. With the use of these improved genetic manipulation systems, aziU3 was discovered to play a key role in the biosynthesis of azinomycin B. In-frame deletion and complementation experiments demonstrated clearly that aziU3 is essential for azinomycin B biosynthesis. Changing the native promoter and insertion of an additional aziU3 gene copy resulted in two mutant strains over-producing azinomycin B. Real-time PCR verified that overexpression of aziU3 significantly improved the azinomycin B production in these mutant strains.

In vitro anticancer activity, toxicity and structure-activity relationships of phyllostictine A, a natural oxazatricycloalkenone produced by the fungus Phyllosticta cirsii

The in vitro anticancer activity and toxicity of phyllostictine A, a novel oxazatricycloalkenone recently isolated from a plant-pathogenic fungus (Phyllosticta cirsii) was characterized in six normal and five cancer cell lines. Phyllostictine A displays in vitro growth-inhibitory activity both in normal and cancer cells without actual bioselectivity, while proliferating cells appear significantly more sensitive to phyllostictine A than non-proliferating ones. The main mechanism of action by which phyllostictine displays cytotoxic effects in cancer cells does not seem to relate to a direct activation of apoptosis. In the same manner, phyllostictine A seems not to bind or bond with DNA as part of its mechanism of action. In contrast, phyllostictine A strongly reacts with GSH, which is a bionucleophile. The experimental data from the present study are in favor of a bonding process between GSH and phyllostictine A to form a complex though Michael attack at C=C bond at the acrylamide-like system. Considering the data obtained, two new hemisynthesized phyllostictine A derivatives together with three other natural phyllostictines (B, C and D) were also tested in vitro in five cancer cell lines. Compared to phyllostictine A, the two derivatives displayed a higher, phyllostictines B and D a lower, and phyllostictine C an almost equal, growth-inhibitory activity, respectively. These results led us to propose preliminary conclusions in terms of the structure-activity relationship (SAR) analyses for the anticancer activity of phyllostictine A and its related compounds, at least in vitro.

Biosynthesis of 3-methoxy-5-methyl naphthoic acid and its incorporation into the antitumor antibiotic azinomycin B

Azinomycin B is a potent antitumor antibiotic that features a set of unusual, densely assembled functionalities. Among them, the 3-methoxy-5-methylnaphthoic acid (NPA) moiety provides an important noncovalent association with DNA, and may, therefore, contribute to the specificity of DNA alkylation for biological activity exhibition. We have previously cloned and sequenced the azinomycin B biosynthetic gene cluster, and proposed that four enzymes: AziB, AziB1, AziB2, and AziA1, are involved in the naphthoate moiety formation and incorporation. In this study, we report in vivo and/or in vitro characterizations of the P450 hydroxylase AziB1, the O-methyltransferase AziB2, and the substrate specificity of the non-ribosomal peptide synthetase (NRPS) AziA1, providing insights into the timing of individual steps in the late-stage modification of 5-methyl-NPA synthesized by the iterative type I polyketide synthase AziB. AziB1 catalyzes a regiospecific hydroxylation at the C3 position of the free naphthoic acid 5-methyl-NPA to produce 3-hydroxy-5-methyl-NPA, and the resulting hydroxyl group is subsequently O-methylated by AziB2 to furnish the methoxy functionality. The di-domain NRPS AziA1 specifically incorporates 3-methoxy-5-methyl-NPA via an unusual A domain to initiate the backbone formation of azinomycin B. AziA1 activates several analogues of the natural starter unit, suggesting a potential for production by metabolic engineering of new azinomycin analogues differing in their NPA moieties.

Structure-activity relationships and mechanism of action of antitumor bis 8-hydroxyquinoline substituted benzylamines

A series of twenty six 8-hydroxyquinoline substituted amines, structurally related to compounds 2 and 3, were synthesized to evaluate the effects of structural changes on antitumor activity and understand their mechanism of action. The studies were performed on a wide variety of cancer cell lines within glioma and carcinoma models. The results obtained from chemical models and biological techniques such as microarrays suggest the following hypothesis that a quinone methide intermediate which does not react with DNA but which gives covalent protein thiol adducts. Micro-array analysis showed that the drugs induce the expression of a variety of stress related genes responsible for the cytotoxic and cytostatic effects in carcinoma and glioblastoma cells respectively. The described analogues could represent new promising anti-cancer candidates with specific action mechanisms, targeting accessible thiols from specific proteins and inducing potent anti-cancer effects.

Investigating the biochemical impact of DNA damage with structure-based probes: abasic sites, photodimers, alkylation adducts, and oxidative lesions

DNA sustains a wide variety of damage, such as the formation of abasic sites, pyrimidine dimers, alkylation adducts, or oxidative lesions, upon exposure to UV radiation, alkylating agents, or oxidative conditions. Since these forms of damage may be acutely toxic or mutagenic and potentially carcinogenic, it is of interest to gain insight into how their structures impact biochemical processing of DNA, such as synthesis, transcription, and repair. Lesion-specific molecular probes have been used to study polymerase-mediated translesion DNA synthesis of abasic sites and TT dimers, while other probes have been developed for specifically investigating the alkylation adduct O(6)-Bn-G and the oxidative lesion 8-oxo-G. In this review, recent examples of lesion-specific molecular probes are surveyed; their specificities of incorporation opposite target lesions compared to unmodified nucleotides are discussed, and limitations of their applications under physiologically relevant conditions are assessed.

Regiospecific O-methylation of naphthoic acids catalyzed by NcsB1, an O-methyltransferase involved in the biosynthesis of the enediyne antitumor antibiotic neocarzinostatin

Neocarzinostatin, a clinical anticancer drug, is the archetypal member of the chromoprotein family of enediyne antitumor antibiotics that are composed of a nonprotein chromophore and an apoprotein. The neocarzinostatin chromophore consists of a nine-membered enediyne core, a deoxyaminosugar, and a naphthoic acid moiety. We have previously cloned and sequenced the neocarzinostatin biosynthetic gene cluster and proposed that the biosynthesis of the naphthoic acid moiety and its incorporation into the neocarzinostatin chromophore are catalyzed by five enzymes NcsB, NcsB1, NcsB2, NcsB3, and NcsB4. Here we report the biochemical characterization of NcsB1, unveiling that: (i) NcsB1 is an S-adenosyl-L-methionine-dependent O-methyltransferase; (ii) NcsB1 catalyzes regiospecific methylation at the 7-hydroxy group of its native substrate, 2,7-dihydroxy-5-methyl-1-naphthoic acid; (iii) NcsB1 also recognizes other dihydroxynaphthoic acids as substrates and catalyzes regiospecific O-methylation; and (iv) the carboxylate and its ortho-hydroxy groups of the substrate appear to be crucial for NcsB1 substrate recognition and binding, and O-methylation takes place only at the free hydroxy group of these dihydroxynaphthoic acids. These findings establish that NcsB1 catalyzes the third step in the biosynthesis of the naphthoic acid moiety of the neocarzinostatin chromophore and further support the early proposal for the biosynthesis of the naphthoic acid and its incorporation into the neocarzinostatin chromophore with free naphthoic acids serving as intermediates. NcsB1 represents another opportunity that can now be exploited to produce novel neocarzinostatin analogs by engineering neocarzinostatin biosynthesis or applying directed biosynthesis strategies.

Synthesis of Functional “Top-Half” Partial Structures of Azinomycin A and B

The design and synthesis of a detailed series of functional "top-half" substructures of azinomycin A and B is described.

Dependence of DNA Sequence Selectivity and Cell Cytotoxicity on Azinomycin A and B Epoxyamide Stereochemistry

Evaluation of the importance of C18/C19 stereochemistry of azinomycin A/B epoxyamide partial structures with respect to DNA alkylation sequence selectivity is reported using a unique assay with a DNA oligomer containing imbedded normal (5'-GGC-3'/3'-CCG-5') and inverted (5'-CGG-3'/3'-GCC-5') azinomycin consensus cross-linking sequences. Both species were found to have unique selectivity profiles and alkylate DNA in a manner distinct from azinomycin B. Computational docking experiments support altered binding modes for the enantiomers.