The preparation of tritium and deuterium‐labelled camptothecin

Ronman, Peter; Wani, Mansukh C.; Wall, Monroe E.

doi:10.1002/jlcr.2580180306

Cited by 6 publications

(1 citation statement)

References 3 publications

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“…These compounds were dissolved in DMSO at 10 mM concentrations and stored at -20 °C. [3 ****H]Camptothecin (13 Ci/mmol; labeled at C-5 and C-7) was prepared according to published procedures (Ronman et al, 1981) and dissolved in ethanol. Nitrocellulose filters were purchased from Schleicher and Schuell.…”

Section: Methodsmentioning

confidence: 99%

On the mechanism of topoisomerase I inhibition by camptothecin: evidence for binding to an enzyme-DNA complex

Hertzberg¹,

Caranfa²,

Hecht³

1989

Biochemistry

512

294

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Camptothecin, a cytotoxic antitumor compound, has been shown to produce protein-linked DNA breaks mediated by mammalian topoisomerase I. We have investigated the mechanism by which camptothecin disrupts DNA processing by topoisomerase I and have examined the effect of certain structurally related compounds on the formation of a DNA-topoisomerase I covalent complex. Enzyme-mediated cleavage of supercoiled plasmid DNA in the presence of camptothecin was completely reversed upon the addition of exogenous linear DNA or upon dilution of the reaction mixture. Camptothecin and topoisomerase I produced the same amount of cleavage from supercoiled DNA or relaxed DNA. In addition, the alkaloid decreased the initial velocity of supercoiled DNA relaxation mediated by catalytic quantities of topoisomerase I. Inhibition occurred under conditions favoring processive catalysis as well as under conditions favoring distributive catalysis. By use of [3H]camptothecin and an equilibrium dialysis assay, the alkaloid was shown to bind reversibly to a DNA-topoisomerase I complex, but not to isolated enzyme or isolated DNA. These results are consistent with a model in which camptothecin reversibly traps an intermediate involved in DNA unwinding by topoisomerase I and thereby perturbs a set of equilibria, resulting in increased DNA cleavage. By examining certain compounds that are structurally related to camptothecin, it was found that the 20-hydroxy group, which has been shown to be essential for antitumor activity, was also necessary for stabilization of the covalent complex between DNA and topoisomerase I. In contrast, no such correlation existed for UV-light-induced cleavage of DNA by Cu(II)-camptothecin derivatives.

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Section: Methodsmentioning

confidence: 99%

On the mechanism of topoisomerase I inhibition by camptothecin: evidence for binding to an enzyme-DNA complex

Hertzberg¹,

Caranfa²,

Hecht³

1989

Biochemistry

512

294

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Stabilities of 3H- and 2H-labelled camptothecins

Hinz

Harris

Giovanella

et al. 1996

J Label Compd Radiopharm

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SUMMARYCommercially available [3Hl-camptothecin, labeled mainly at the C-5 position, had partially lost the tritium label after recovery from the plasma of a patient injected with this drug or after incubation in plasma at 38OC for 72 h. Carnptothecin dissolved in CH302H/2Hz0, incorporated deuterium at the C-5 position with a 50% uptake after one day at pH 11 .O or after 10-1 1 days at pH 7.4. At pH 2.0, the deuterium uptake was negligible. Camptothecin, dissolved in deuterated sulfuric acid, incorporated 37 or 80% deuterium at C-14 when heated to 65 or 80°C, respectively. Commercially available [3Hl-camptothecin, labeled mainly at the C-5 position, is thus not useful for in vivo metabolism or pharmacokinetic studies due to rapid loss of tritium in plasma. In contrast, [3Hl-camptothecin prepared as described in this paper for ['HI-camptothecin is expected to be useful.

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Synthesis of tritiated (S)‐10‐bromoacetamidomethylcamptothecin

Shu

Jakas²,

Heys

1990

Labelled Comp Radiopharmac

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Tritiated (S)-1 0-bromoacetamidomethylcamptothecin was prepared starting from (S)-1 0-hydroxycamptothecin. The key step consisted of palladium catalyzed direct tritium exchange on the intermediate (S)-10-aminomethylcamptothecin. 3H NMR spectroscopy indicated the tritium label was located exclusively at the C-5 position. Key Words:1 0-Bromoacetamidomethylcarnptothecin, Camptothecin, Tritium exchange, 3H NMR. IntroductionCamptothecin (1 ), a naturally occurring antineoplastic agent,' binds reversibly to DNA-topoisomerase I covalent complex and stablizes the enzyme-mediated DNA cleavage, inhibiting religation.2 In order to investigate whether the presence of a peripheral electrophilic substituent, for instance the bromoacetyl appendage in derivative 2 (SK&F S-lO6470), would render such binding irreversible, a radio-labeled analog of 2 was required.2 Investigation of the nature of any covalent binding of [3H]2 could provide information relative to the position of camptothecin binding on the DNA-topoisomerase I complex. Based upon the precedent that a deuterated analog of carnptothecin was prepared by deuterium exchange on the parent compound in the presence of Pd/C,3 our synthetic strategy employed a similar approach in introducing the tritium label into the intermediate (S)-l O-aminomethylcarnptothecin (6). In this paper we report the synthesis of [3H]SK&F S-106470 (8) and the use of 3H NMR to elucidate the position of the tritium label.

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The preparation of tritium and deuterium‐labelled camptothecin

Cited by 6 publications

References 3 publications

On the mechanism of topoisomerase I inhibition by camptothecin: evidence for binding to an enzyme-DNA complex

On the mechanism of topoisomerase I inhibition by camptothecin: evidence for binding to an enzyme-DNA complex

Stabilities of 3H- and 2H-labelled camptothecins

Synthesis of tritiated (S)‐10‐bromoacetamidomethylcamptothecin

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