2 '-O-acyl/alkyl-substituted arabinosyl nucleosides as inhibitors of humanmitochondrial thymidine kinase

Introduction of a bulky lipophilic acyl entity at the 2'-OH position of bot h 1-beta -D-arabinofuranosylthymine (araT) and (E)-5-(2-bromovinyl)- 1-beta -D-arabinofuranosyluracil (BVaraU), consistently resulted in a marked (sim ilar to 10-fold) increase in the inhibitory activity of these new arabinosy l nucleoside analogues for the mitochondrial thymidine kinase (TK-2)-cataly sed conversion of 2 muM [methyl-H-3]dThd to [methyl-H-3]dTMP. The most pote nt derivatives were inhibitory to [methyl-H-3]dThd phosphorylation by TK-2 within the lower micromolar concentration range, Substitution of the arabin osyl nucleoside derivative's with the acyl groups also dramatically increas ed the selectivity of these compounds. The inhibitory activity of araT and BVaraU to dThd phosphorylation by other related nucleoside kinases, includi ng herpes simplex virus type 1 TK, varicella-zoster virus TK. and cytosolic TK-1, was completely annihilated upon 2'-O-acyl substitution (IC50 greater than or equal to 1000 muM). Kinetic analysis revealed purely competitive i nhibition of 2'-O-acyl-BVaraU against TK-2-catalysed thymidine phosphorylat ion (K-i/K-m: 2.3). However, 2'-O-acyl-BVaraU was extremely poorly converte d to the corresponding arabinosyl nucleoside 5'-monophosphate by TK-2 as re vealed by [gamma-P-32]phosphate transfer studies from [gamma-P-32]ATP. Thus , the 2'-O-acyl derivatives of BVaraU did not behave as substrates, but rat her as potent and highly selective inhibitors of TK-2. This is the first re port on such a highly selective arabinosyl nucleoside inhibitor of mitochon drial TK-2, and opens perspectives for the rational design of selective mit ochondrial TK-2 inhibitors. (C) 2001 Elsevier Science Inc. All rights reser ved.