Human deoxycytidine kinase (dCK) phosphorylates the natural deoxyribonucleosides deoxycytidine (dC), deoxyguanosine (dG) and deoxyadenosine (dA) and is an essential enzyme for the phosphorylation of numerous nucleoside analog prodrugs routinely used in cancer and antiviral chemotherapy. For many of these compounds, the phosphorylation step catalyzed by dCK is the rate-limiting step in their overall activation pathway. To determine the factors that limit the phosphorylation efficiency of the prodrug, we solved the crystal structure of dCK to a resolution of 1.6 A in complex with its physiological substrate deoxycytidine and with the prodrugs AraC and gemcitabine. The structures reveal the determinants of dCK substrate specificity. Especially relevant to new prodrug development is the interaction between Arg128 and the hydrogen-bond acceptor at the sugar 2'-arabinosyl position of AraC and gemcitabine. On the basis of the structures, we designed a catalytically superior dCK variant that could be used in suicide gene-therapy applications.
Choline is a precursor of cellular phospholipid metabolism that provides Magnetic Resonance (MR) and Positron Emission Tomography (PET) biomarkers for cancer detection and response assessment. Employing Dynamic Nuclear Polarization we show that the MR signal of 15N in choline can be enhanced by at least 4 orders of magnitude with a relaxation time of ca. 4 min, providing a method to observe the action of choline kinase, an important target for novel cancer therapeutics.
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