Inhibition of human telomerase by 7-deaza-2 '-deoxyguanosine nucleoside triphosphate analogs: Potent inhibition by 6-thio-7-deaza-2 '-deoxyguanosine 5 '-triphosphate

We have examined analogs of the previously reported 7-deaza-2'-deoxypurine nucleoside triphosphate series of human telomerase inhibitors. Two new telo merase-inhibiting nucleotides are reported: 6-methoxy-7-deaza-2'-deoxyguano sine 5'-triphosphate (OMDG-TP) and 6-thio-7-deaza-2' -deoxyguanosine 5'-tri phosphate (TDG-TP). In particular, TDG-TP is a very potent inhibitor of hum an telomerase with an IC50 of 60 nM. TDG-TP can substitute for dGTP as a su bstrate for telomerase, but only at relatively high concentrations. Under c onditions in which TDG-TP is the only available guanosine substrate, telome rase becomes nonprocessive synthesizing short products that appear to conta in only one to three TDG residues. Similarly, the less potent telomerase in hibitor OMDG-TP gives rise to short telomerase products, but less efficient ly than TDG-TP. We show here that TDG-TP, and to a lesser extent OMDG-TP, c an serve as substrates for both templated (Klenow exo) and nontemplated (te rminal transferase) DNA polymerases. For either polymerase, the products ar ising from TDG-TP are relatively short, and give rise to bands of unusual m obility under PAGE conditions. These anomalous bands overt. under treatment with DTT, to normal mobility bands. indicating that these products may con tain thiol-labile disulfide linkages involving the incorporated TDG residue s. This observation of potential TDG-crosslinks may have bearing on the mec hanism of telomerase inhibition by this nucleotide analog. (C) 2001 Academi c Press.