An Esr Study of the Visible Light Photochemistry of Gilvocarcin V

Alegrı́a, Antonio E.; Krishna, C. Murali; Elespuru, Rosalie K.; Riesz, Peter

doi:10.1111/j.1751-1097.1989.tb04104.x

Cited by 22 publications

(11 citation statements)

References 57 publications

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“…The triplet quantum yield of gilvocarcin derivatives both in DMSO and in 25% DMSO/water (Table 1) can be compared with the sum of those reported for the formation of singlet oxygen and superoxide ion reported by Alegria et al (17,18). In DMSO, they reported quantum yields of 0.15 and 0.003 for singlet oxygen and superoxide fclrmation, respectively.…”

Section: Triplet Absorption Coefficient and Quantum Yields Of Tripletmentioning

confidence: 68%

“…In a previous paper, Alegria et al (17) suggested that light absorption by the gilvocarcin in DMSO/water mixtures could result in the photoreduction of DMSO leading to the formation of methyl radicals (Scheme 1) since spin adducts of the methyl radicals were detected (17,lS). They postulated as intermediates the GV triplet state and its radical cation.…”

Section: Characterization Of the Long-lived Transient Speciesmentioning

confidence: 99%

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The Photobiological Differences of Gilvocarcins V and M Are not Related to their Transient Intermediates and Triplet Yields

Arce

Oyola

Alegrı́a

1998

Photochem & Photobiology

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The transient absorption spectra of the intermediates produced by the 355 nm laser excitation of gilvocarcin derivatives have been investigated in various solvents. The spectra consist of a triplet-triplet absorption in the visible region and a residual absorption observed between 340 and 700 nm due to a long-lived species, assigned to the radical cation. A broad-fast decaying band with a maximum at around 700 nm attributed to the solvated electron is also seen in solutions containing a low DMSO/water volume ratio and at 266 nm irradiation of a 50% methanol/water solvent mixture. The molar absorption coefficient of the triplet state of gilvocarcin V (GV) and gilvocarcin M (GM), determined by the energy transfer method, is independent of the solvent properties and has a value of 3.0 x 10(4)/Mcm. The triplet decay rate constants for both drugs are between 1 and 5 x 10(4)/s. A similar initial yield and triplet decay rate constant of GV were observed in the presence of 3.4 mM thymine. Thus, a quenching rate constant of the GV's triplet state by thymine is estimated to be lower than 10(6)/Ms. The triplet quantum yields of both antibiotics determined by using the comparative method are higher in dimethylsulfoxide (DMSO) (0.18) than are those corresponding to 25% DMSO/water (0.06). The decrease in phi T in the presence of water could be attributed to an enhanced internal conversion rate constant from the S1 state or to an increase in the photoionization yield. The similarity of the transient intermediates and their yields for GV and GM suggest that their photobiological differences are due to other factors such as DNA binding constants, preferential localization of the drugs in the cell or the enhanced reactivity of the vinyl group toward cellular components.

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Section: Triplet Absorption Coefficient and Quantum Yields Of Tripletmentioning

confidence: 68%

Section: Characterization Of the Long-lived Transient Speciesmentioning

confidence: 99%

The Photobiological Differences of Gilvocarcins V and M Are not Related to their Transient Intermediates and Triplet Yields

Arce

Oyola

Alegrı́a

1998

Photochem & Photobiology

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“…Significantly, thymine modification, which is well documented for GV was also observed in our assay providing independent support for the interpretation that base residues completely resistant to DNAse I in the chimeric duplexes prepared correspond internucleotide cleavage positions directly adjacent to GV adduct positions. Gilvocarcin V photochemistry has also been shown to involve production of singlet oxygen and hydroxyl radicals in the presence of visible light (14). This property of GV has been invoked to explain the DNA nicking activity observed in studies of GV with superhelical DNA substrates (5,15).…”

Section: W-mentioning

confidence: 98%

Gilvocarcin V exhibits both equilibrium DNA binding and UV light induced DNA adduct formation which is sequence context dependent

Knobler¹,

Radlwimmer

Lane

1992

Nucl Acids Res

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The relative degree of both equilibrium binding and of ultraviolet light induced adduct formation for the antitumor antibiotic gilvocarin V with two hexaecamer DNA sequence isomers, d[ATATATAGCTATATAT]2 and d[AAAAAAAGCTTTTTTT]2, was assessed. The experiments reveal that gilvocarin V binds, under equilibrium conditions, and reacts, in the presence of exogenously applied UV light, more efficiently with the alternating purine:pyrimidine sequence hexadecamer than the homopurine:homopyrimidine duplex at identical gilvocarcin V to DNA duplex ratios. DNAse I digests of adduct containing duplexes derived from the d[AAAAAAAGCTTTTTTT]2 duplex, identified and isolated using gel shift assays employing denaturing polyacrylamide gels, confirm that gilvocarcin V adducts can be formed with thymine residues but suggest that adduct formation with either adenine or guanine residues is also possible.

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“…(24)] [44,51], since this radical species was trapped almost in all argon saturated dye solutions upon exposure (Tables 3 and 4). Alternatively, the methyl radicals could be formed by photoreduction of DMSO by photoexcited dye molecules [52].…”

Section: Dimethylsulphoxide Dye Solutions 3231 Oxygen In Order Tmentioning

confidence: 99%