Carbocyclic phosphonate analogs of 2′,3′-dideoxyadenosine-5′-monophosphate as substrates of 5-phosphoribosyl-1-pyrophosphate (PRPP) synthetate

Acyclic purine and pyrimidine nucleotide analogs as ecto-5'-nucleotidase (CD73) inhibitors

Ecto-5'-nucleotidase (CD73) is a novel target in cancer (immuno)therapy. Its blockade prevents the formation of immunosuppressive and cancer-promoting adenosine from AMP. Here, we report on the development of a series of small molecules that mimic adenine nucleotides, in which the ribose moiety was replaced by an alkyl chain. Its length was found to be crucial for potency. A crystal structure of the N6-disubstituted acyclic ADP analog 26 (N6-benzyl,N6-methyladenine-9-yl)pentyloxydiphosphonate) in complex with human CD73 revealed that the flexible pentyl linker adopts to interdomain rotation angles differing by up to 18.5°. The most potent CD73 inhibitor of the present series was analog 27 (N6-benzyl,N6-methyladenine-9-yl)hexyloxydiphosphonate, PSB-24000) which exhibited submicromolar potency at human CD73 (Ki 563 nM at soluble CD73; Ki 481 nM at membrane-bound CD73 of triple-negative breast cancer cells). Acyclic nucleotide analogs may be advantageous compared to the previously reported nucleotidic CD73 inhibitors due to their high chemical stability, and because less off-target effects are to be expected. The structure-activity relationships discovered in this study provide valuable insights which will be useful for the development of CD73 inhibitors as immunotherapeutic drugs.

Adenine: an important drug scaffold for the design of antiviral agents

Adenine derivatives, in particular the scaffold bearing the acyclic nucleoside phosphonates (ANPS), possess significant antiviral and cytostatic activity. Till now, several effective adenine derivatives have been marketed for the treatment of HIV, HBV, CMV and other virus-infected diseases. These compounds are represented by tenofovir (PMPA), a medicine for both HIV and HBV, and adefovir as an anti-HBV agent. More than this, other analogs, such as GS9148, GS9131, and GS7340, are also well-known anti-viral agents that have been progressed to the clinical studies for their excellent activity. In general, the structures of these compounds include an adenine nucleobase linked to a phosphonate side chain. Considerable structural modifications on the scaffold itself and the peripheral sections were made. The structure-activity relationships (SARs) of this skeleton will provide valuable clues to identify more effective adenine derivatives as antiviral drugs. Here, we systematically summarized the SARs of the adenine derivatives, and gave important information for further optimizing this template.

Enzymatic phosphorylation and pyrophosphorylation of 2',3'-dideoxyadenosine-5'-monophosphate, a key metabolite in the pathway for activation of the anti-HIV (human immunodeficiency virus) agent 2',3'-dideoxyinosine

2',3'-Dideoxyadenosine-5'-monophosphate (ddAMP) is a key intermediate in the metabolic pathway involved in the activation of the anti-retroviral agent 2',3'-dideoxyinosine (ddI) to 2',3'-dideoxyadenosine-5'-triphosphate (ddATP). The potential phosphorylation of ddAMP by adenylate kinase (myokinase) and pyrophosphorylation by the reverse reaction of 5-phosphoribosyl-1-pyrophosphate (PRPP) synthetase were investigated. Using ATP as phosphate donor, ddAMP was phosphorylated by adenylate kinase with an efficiency of 8.8% of that for AMP, as estimated from the Vmax/Km ratios. In the presence of PRPP, Escherichia coli and rat PRPP synthetases catalysed the pyrophosphorylation of ddAMP with efficiencies of 52 and 35% of that determined for AMP, respectively. Two carbocyclic phosphonate analogues of ddAMP were not substrates of adenylate kinase. Yet, they were pyrophosphorylated by both PRPP synthetases, albeit less efficiently than ddAMP. In vivo, the usual function of PRPP synthetase is to synthesize PRPP from ribose-5-phosphate and ATP. In the forward reaction ddATP proved to be a substrate as efficient as ATP for rat PRPP synthetase. ddATP was also studied as a potential phosphate donor in the reaction catalysed by adenylate kinase with AMP as phosphate acceptor and found to be as efficient as ATP. The relevance of these in vitro results to the in vivo situation is discussed.