Deoxycytidine kinase (dCK), a rate-limiting enzyme in the cytosolic deoxyribonucleoside (dN) salvage pathway, is an important therapeutic and positron emission tomography (PET) imaging target in cancer. PET probes for dCK have been developed and are effective in mice but have suboptimal specificity and sensitivity in humans. To identify a more suitable probe for clinical dCK PET imaging, we compared the selectivity of two candidate compounds—[18F]Clofarabine; 2-chloro-2′-deoxy-2′-[18F]fluoro-9-β-d-arabinofuranosyl-adenine ([18F]CFA) and 2′-deoxy-2′-[18F]fluoro-9-β-d-arabinofuranosyl-guanine ([18F]F-AraG)—for dCK and deoxyguanosine kinase (dGK), a dCK-related mitochondrial enzyme. We demonstrate that, in the tracer concentration range used for PET imaging, [18F]CFA is primarily a substrate for dCK, with minimal cross-reactivity. In contrast, [18F]F-AraG is a better substrate for dGK than for dCK. [18F]CFA accumulation in leukemia cells correlated with dCK expression and was abrogated by treatment with a dCK inhibitor. Although [18F]CFA uptake was reduced by deoxycytidine (dC) competition, this inhibition required high dC concentrations present in murine, but not human, plasma. Expression of cytidine deaminase, a dC-catabolizing enzyme, in leukemia cells both in cell culture and in mice reduced the competition between dC and [18F]CFA, leading to increased dCK-dependent probe accumulation. First-in-human, to our knowledge, [18F]CFA PET/CT studies showed probe accumulation in tissues with high dCK expression: e.g., hematopoietic bone marrow and secondary lymphoid organs. The selectivity of [18F]CFA for dCK and its favorable biodistribution in humans justify further studies to validate [18F]CFA PET as a new cancer biomarker for treatment stratification and monitoring.

No abstract

Recently, we have shown that small molecule dCK inhibitors in combination with pharmacological perturbations of de novo dNTP biosynthetic pathways could eliminate acute lymphoblastic leukemia cells in animal models. However, our previous lead compound had a short half-life in vivo. Therefore, we set out to develop dCK inhibitors with favorable pharmacokinetic properties. We delineated the sites of the inhibitor for modification, guided by crystal structures of dCK in complex with the lead compound and with derivatives. Crystal structure of the complex between dCK and the racemic mixture of our new lead compound indicated that the R-isomer is responsible for kinase inhibition. This was corroborated by kinetic analysis of the purified enantiomers, which showed that the R-isomer has >60-fold higher affinity than the S-isomer for dCK. This new lead compound has significantly improved metabolic stability, making it a prime candidate for dCK-inhibitor based therapies against hematological malignancies and, potentially, other cancers.

Background-Deoxycytidine kinase (dCK) is an essential enzyme for production of nucleotides via the salvage pathway; DI-87 is a novel dCK inhibitor in preclinical development for use in anticancer therapy. The current study utilizes PET imaging to evaluate PK-PD relationships and to determine optimal dosing of the drug.Methods-NSG mice bearing CEM tumors had plasma and tumor PK assessed using mass spectrometry following oral administration of DI-87. dCK inhibition was assessed after a single dose of oral DI-87 followed by a [ 18 F]CFA PET probe and PET imaging. Tumor growth inhibition was assessed by orally administering DI-87 with concurrent intraperitoneal thymidine.

Seed (2009) The synthesis and mesogenic behaviour of the first series of low molar mass thieno[3,2-b]thiophene-2-carboxylate ester-based mesogens, Liquid Crystals, 37:1, 101-108,The synthesis of a family of alkyl 5-(4-hexyloxyphenyl)thieno[3,2-b]thiophene-2-carboxylate liquid crystals is described. The synthetic methodology utilised includes a Fiesselmann synthesis of the thieno[3,2-b]thiophene core, and the first report of a completely regioselective a-bromination of the resulting thieno[3,2-b]thiophene-2-carboxylate ester. The target materials display enantiotropic smectic A phases with melting points and transition temperatures that are significantly higher than their phenyl analogues. The synthesis and mesomorphic behaviour of these new materials is reported and discussed.