UCLA

Deoxycytidine kinase (dCK), a rate-limiting enzyme in the deoxyribonucleotide salvage pathway, participates in the production of deoxyribonucleoside triphosphates (dNTPs). dCK is highly expressed in hematopoietic tissues and many cancers. In addition, dCK is responsible for the phosphorylation, and thus activation of several antiviral and anticancer nucleoside analog pro-drugs. Austin, Toy, and colleagues have demonstrated that dCK deficient mice (dCK-/-) have severe developmental defects of the lymphoid and hematopoietic progenitor cells, indicating that dCK is pivotal for their normal development. Further study of the T, B, and erythroid lineages revealed nucleotide pool imbalances resulting in replication stress and cell cycle arrest in the early stages of DNA replication. Dual inactivation of both dCK and thymidine kinase 1 (TK1) in vivo supported our hypothesis that salvage of thymidine by TK1 was responsible for the allosteric block of the de novo pathway enzyme, ribonucleotide reductase, consequentially perturbing the nucleotide pools. These findings and the role of dCK in cancer led to our interest in developing a small molecule inhibitor. Positron Emission Tomography and the dCK-specific substrate, 18F-L-1-(2'-deoxy-2'-F luoroarabinofuranosyl) Cytosine, proved useful in the quick identification of top performing dCK inhibitors in vivo. Following a high throughput screen and a structure-activity relationship study we successfully identified high potency small molecule inhibitors of dCK (dCKi). The combination of the dCKi with pharmacological perturbations of de novo dNTP synthesis, via thymidine, in acute lymphoblastic leukemia cells depletes deoxycytidine triphosphate pools leading to DNA replication stress, cell cycle arrest, and apoptosis in vivo, without detectable toxicity to normal tissues. The results from our studies further our understanding of nucleotide metabolism in normal hematopoiesis and hematological malignancies, and identify dCK as a new therapeutic target in hematological malignancies.