Structure, physiological role, and specific inhibitors of human thymidine kinase 2 (TK2): present and future.

Human mitochondrial thymidine kinase (TK2) is a pyrimidine deoxynucleoside kinase (dNK) that catalyzes the phosphorylation of pyrimidine deoxynucleosides to their corresponding deoxynucleoside 5'-monophosphates by gamma-phosphoryl transfer from ATP. In resting cells, TK2 is suggested to play a key role in the mitochondrial salvage pathway to provide pyrimidine nucleotides for mitochondrial DNA (mtDNA) synthesis and maintenance. However, recently the physiological role of TK2turned out to have direct clinical relevance as well. Point mutations in the gene encoding TK2 have been correlated to mtDNA disorders in a heterogeneous group of patients suffering from the so-called mtDNA depletion syndrome (MDS). TK2 activity could also be involved in mitochondrial toxicity associated to prolonged treatment with antiviral nucleoside analogues like AZT and FIAU. Therefore, TK2 inhibitors can be considered as valuable tools to unravel the role of TK2 in the maintenance and homeostasis of mitochondrial nucleotide pools and mtDNA, and to clarify the contribution of TK2 activity to mitochondrial toxicity of certain antivirals. Highly selective TK-2 inhibitors having an acyclic nucleoside structure and efficiently discriminating between TK-2 and the closely related TK-1 have already been reported. It is actually unclear whether these agents efficiently reach the inner mitochondrial compartment. In the present review article,structural features of TK2, MDS-related mutations observed in TK2 and their role in MDS will be discussed. Also, an update on novel and selective TK2 inhibitors will be provided.

N1-substituted thymine derivatives as mitochondrial thymidine kinase (TK-2) inhibitors.

Novel N1-substituted thymine derivatives related to 1-[(Z)-4-(triphenylmethoxy)-2-butenyl]thymine have been synthesized and evaluated against thymidine kinase-2 (TK-2) and related nucleoside kinases [i.e., Drosophila melanogaster deoxynucleoside kinase (Dm-dNK) and herpes simplex virus type 1 thymidine kinase (HSV-1 TK)]. The thymine base has been tethered to a distal triphenylmethoxy moiety through a polymethylene chain (n = 3-8) or through a (2-ethoxy)ethyl spacer. Moreover, substitutions at position 4 of one of the phenyl rings of the triphenylmethoxy moiety have been performed. Compounds with a hexamethylene spacer (18, 26b, 31) displayed the highest inhibitory values against TK-2 (IC50 = 0.3-0.5 microM). Compound 26b competitively inhibited TK-2 with respect to thymidine and uncompetitively with respect to ATP. A rationale for the biological data was provided by docking some representative inhibitors into a homology-based model of human TK-2. Moreover, two of the most potent TK-2 inhibitors (18 and 26b) that also inhibit HSV-1 TK were able to reverse the cytostatic activity of 1-(beta-D-arabinofuranosyl)thymine (Ara-T) and ganciclovir in HSV-1 TK-expressing OST-TK-/HSV-1 TK+ cell cultures.

From ß-amino-γ-sultone to unusual bicyclic pyridine and pyrazine heterocyclic systems: synthesis and cytostatic and antiviral activities.

Herein we describe the first successful application of the ß-amino-γ-sultone system as an intermediate for the synthesis of hitherto virtually unknown 3H-[1,2]-oxathiole [4,3-b]pyridine and pyrazine 1,1-dioxide bicyclic heterocyclic systems. All novel compounds were evaluated for their antiviral and cytostatic activities. Compounds 3 a, 15 a, and 21 a inhibited HIV-1-induced cytopathicity. Compound 7 showed remarkable cytostatic activity, and can be regarded as a potential antitumor candidate for further exploration.

Design, synthesis and inhibitory activity against Mycobacterium tuberculosis thymidine monophosphate kinase of acyclic nucleoside analogues with a distal imidazoquinolinone.

Thymidine monophosphate kinase from Mycobacterium tuberculosis (TMPKmt) has been proposed as an attractive target in the search of new agents to fight against tuberculosis. We recently reported that thymine derivatives carrying a naphtholactam or naphthosultam moiety at position 4 of a (Z)-butenyl chain inhibit TMPKmt in the subµM range. Here we describe the replacement of the planar naphtholactam and naphthosultam rings in our identified hits by 5,6-dihydro-1H-imidazo[4,5,1-ij]quinolinones and a 5,6-dihydro-1H,4H-1,2,5-thiadiazolo[4,3,2-ij]quinoline-2,2-dioxide where the planarity has been broken. Interestingly, these non-planar compounds were similarly potent against the target enzyme than their aromatic analogues, suggesting a bioisosteric behavior that may also be applied to other biologically active compounds. The synthesis of the different targeted imidazoquinolinones has been successfully performed via a hypervalent iodide mediated oxidative cyclization of N-methoxyureas catalized by bis(trifluoroacetoxy)iodobenzene (PIFA) expanding the reported use of this reagent for the synthesis of differently substituted imidazoquinolinones.

Exploring acyclic nucleoside analogues as inhibitors of Mycobacterium tuberculosis thymidylate kinase.

In the search for novel inhibitors of the enzyme thymidine monophosphate kinase of Mycobacterium tuberculosis (TMPKmt), an attractive target for novel antituberculosis agents, we report herein the discovery of the first acyclic nucleoside analogues that potently and selectively inhibit TMPKmt. The most potent compounds in this series are (Z)-butenylthymines carrying a naphtholactam or naphthosultam moiety at position 4, which display K(i) values of 0.42 and 0.27 microM, respectively. Docking studies followed by molecular dynamics simulations performed to rationalize the interaction of this new family of inhibitors with the target enzyme revealed a key interaction between the distal substituent and Arg 95 in the target enzyme. The fact that these inhibitors are more easily synthesizable than previously identified TMPKmt inhibitors, together with their potency against the target enzyme, makes them attractive lead compounds for further optimization.