Lack of Enantiospecificity of Human 2′-Deoxycytidine Kinase: Relevance for the Activation of β-l-Deoxycytidine Analogs as Antineoplastic and Antiviral Agents
- Annalisa Verri1,
- Federico Focher1,
- Giuseppina Priori1,
- Gilles Gosselin2,
- Jean-Louis Imbach2,
- Massimo Capobianco3,
- Anna Garbesi3 and
- Silvio Spadari1
- 1Istituto di Genetica Biochimica ed Evoluzionistica, Consiglio Nazionale delle Ricerche, I-27100 Pavia, Italy (A.V., F.F., G.P., S.S.), 2Laboratoire de Chimie BioOrganique UMR CNRS-USTL 5625, Université Montpellier II, France (G.G., J.-L.I.). 3I.Co.C.E.A., CNR, 101 I-40129 Bologna, Italy (M.C., A.G.)
Abstract
We demonstrate that human 2′-deoxycytidine kinase (dCK) is a nonenantioselective enzyme because it phosphorylates β-d-2′-deoxycytidine (d-dCyd), the natural substrate, and β-l-2′-deoxycytidine (l-dCyd), its enantiomer, with the same efficiency. Kinetic studies showed thatl-dCyd is a competitive inhibitor of the phosphorylation ofd-dCyd with a Kivalue of 0.12 μm, which is lower than theKm value ford-dCyd (1.2 μm). Chemical modifications of either the base or the pentose ring strongly decrease the inhibitory potency of l-dCyd.l-dCyd is resistant to cytidine deaminase and competes in cell cultures with the natural d-dCyd as substrate for dCK, thus reducing the incorporation of exogenous [3H]dCyd into DNA. l-dCyd had no effect on the pool of dTTP deriving from the salvage or from the de novo synthesis, does not inhibit short term RNA and protein syntheses, and shows little or no cytotoxicity. Our results indicate a catalytic similarity between human dCK and herpetic thymidine kinases, enzymes that also lack stereospecificity. This functional analogy underlines the potential role of dCK as activator ofl-deoxycytidine analogs as antiviral and antineoplastic agents and lends support to the hypothesis that herpesvirus thymidine kinase might have evolved from a captured cellular dCK gene, developing the ability to phosphorylate thymidine and retaining that to phosphorylate deoxycytidine.
Footnotes
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Send reprint requests to: Dr. Silvio Spadari, Istituto Di Genetica, Biochimica ed Evoluzionistica, Via Abbiategrasso n. 207, 27100 Pavia, Italy. E-mail:spadari{at}ipvgbe.igbe.pv.cnr.it
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↵1 M. E. Marongiu, unpublished observations.
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↵2 A. A. Krayevsky, personal communication.
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This work was supported in part by grants from Associazione Italiana Ricerca sul Cancro (F.F.), Istituto Superiore di Sanitá-AIDS (S.S.), and Agence Nationale de Recherche sur le SIDA (France; G.G. and J.-L.I.). A.V. was supported by an Istituto Superiore di Sanitá-AIDS Fellowship.
- Abbreviations:
- dCK
- 2′-deoxycytidine kinase
- dCyd
- deoxycytidine
- d-dCyd
- β-d-2′-deoxycytidine
- l-dCyd
- β-l-2′-deoxycytidine
- l-Cyd
- β-l-cytidine
- TK
- thymidine kinase
- CD
- cytidine deaminase
- dAdo
- 2′-deoxyadenosine
- dGuo
- 2′-deoxyguanosine
- ddCyd
- 2′,3′-dideoxycytidine
- α-l-dCyd
- α-l-2′-deoxycytidine
- α-d-dCyd
- α-d-2′-deoxycytidine
- l-F-ddCyd
- 2′,3′-dideoxy-β-l-5-fluoro-cytidine
- d-F-ddCyd
- 2′,3′-dideoxy-β-d-5-fluoro-cytidine
- IdU
- 5-iodo-2′-deoxy-l-uridine
- DMEM
- Dulbecco’s modified Eagle’s medium
- FCS
- fetal calf serum
- HPLC
- high performance liquid chromatography
- HEPES
- 4-(2-hydroxyethyl)-1-piperazineethansulfonic acid
- dThy
- deoxythymidine
- DTT
- dithiothreitol
- PMSF
- phenylmethylsulfonyl fluoride
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- Received July 16, 1996.
- Accepted October 2, 1996.
- The American Society for Pharmacology and Experimental Therapeutics
