Jianghai Wang

SYNTHESIS AND BIOLOGICAL EVALUATION OF BORONATED NUCLEOSIDES FOR BORON NEUTRON CAPTURE THERAPY (BNCT) OF CANCER

Several N-3 substituted carboranyl Thd analogs were synthesized. These agents as well as some non-boronated nucleosides were evaluated in phosphoryl transfer assays with recombinant human TK1 and TK2. For some carboranyl thymidine analogs, TK1 phosphorylation rates approached 38% that of thymidine. Their in vitro cytotoxicty appeared to correlate with the TK1 levels in the tested cells. In some cases increased uptake in tumor cell nuclei compared with the surrounding cytoplasm was detected in vitro.

Substrate Specificities of Mitochondrial Thymidine Kinase and Cytosolic Deoxycytidine Kinase Against 5-Aryl Substituted Pyrimidine-2′-deoxyribose Analogues

Abstract Some 5-aryl-2′-deoxyuridine and -deoxycytidine analogues, many with known antiviral activity, were evaluated as substrates for pure deoxycytidine kinase (dCK) and pure mitochondrial thymidine kinase (TK2). Some of the deoxyuridine compounds were also tested with pure cytosolic thymidine kinase (TK1). TK2 showed the highest activity with this type of analogues.

The Enantioselectivity of the Cellular Deoxynucleoside Kinases

Cytosolic thymidine kinase (TK1) and deoxycytidine kinase (dCK) and the mitochondrial thymidine kinase (TK2) and deoxyguanosine kinase (dGK) phosphorylate deoxynucleosides and their analogs. Recombinant human TK1 only phosphorylated beta-D Thd, but recombinant TK2, dCK and dGK all phosphorylated equally well beta-D and beta-L as well as to some extent alpha-D and alpha-L deoxynucleosides.

Evaluation of Carboranyl 2′-Deoxyuridine Derivatives as Substrates for Human Thymidine Kinases 1 and 2

Cellular nucleoside kinases play a pivotal role in the use of nucleosides for cancer and antiviral therapy.1 For BNCT, the cytosolic thymidine kinase (TK1) may be a particularly important target enzyme. TK1 activity is present in proliferating cells but is virtually absent from all quiescent cells.2 Boron-containing thymidine derivatives, that are good substrates for TK1, may be entrapped in proliferating neoplastic cells after conversion to the monophosphate. Therefore, such agents may be excellent vehicles for the selective delivery of boron-10 to those compartments of a tumor consisting of viable cells. A substantial number of nucleosides modified with various boron moieties at different positions have been synthesized and evaluated biologically for use in BNCT.3 Some thymidine derivatives were found to be phosphorylated in vitro 4 and in phos-phoryl transfer assays with purified human thymidine kinases.5 In these experiments, the observed rates of phosphorylation were generally low compared to natural nucleosides and did not distinguish between phosphorylation by TK1 and mitochondr-ial thymidine kinase (TK2) which appears to be equally active in proliferating and non-proliferating cells, thus providing no basis for selective uptake of boronated nucleosides in tumor cells.6

Expression of Human Cytosolic Thymidine Kinase in Escherichia Coli

In mammalian proliferating cells cytosolic thymidine kinase (TK1) phosphorylate thymidine and deoxyuridine to the corresponding monophosphate, thus providing precursors for DNA synthesis through a salvage route. In addition, TK1 is capable of phosphory-lating many nucleoside analogs. The expression of TK1 is highly cell cycle dependent, which leads to large variations among different cells in their capacity to phosphorylate deoxynucleosides (Arne r and Eriksson, 1995).