Evaluation of 3-deaza-adenosine analogues as ligands for adenosine kinase and inhibitors of Mycobacterium tuberculosis growth.

OBJECTIVES Analyse a series of halogenated 3-deaza-adenosine analogues for efficacy against Mycobacterium tuberculosis H37Ra and determine if adenosine (Ado) kinase plays a role in the mechanism of action of these compounds. METHODS The MIC as determined by microdilution broth assay provided a measure of antitubercular efficacy. MIC values were measured in M. tuberculosis strains H37Ra, SRICK1 (an Ado kinase-deficient strain of M. tuberculosis derived from H37Ra) and SRICK1 complemented with adoK, the gene which codes for Ado kinase in M. tuberculosis, in order to determine if Ado kinase played a role in the mechanism of action of these compounds. Furthermore, each compound was analysed as both a substrate and inhibitor for purified Ado kinases from M. tuberculosis and human sources. RESULTS 2-Fluoro-3-deaza-adenosine, 3-fluoro-3-deaza-adenosine and 2,3-difluoro-3-deaza-adenosine exhibited antitubercular activity that was Ado kinase-dependent. Furthermore, these compounds were at least 10-fold better substrates for M. tuberculosis Ado kinase than the human homologue. CONCLUSIONS The Ado kinase-dependent antitubercular activity exhibited by several of the halogenated 3-deaza-adenosine analogues investigated in this study warrants further investigation of these compounds as antitubercular agents. Furthermore, substrate and inhibition studies provided insight into the Ado-binding domain of Ado kinase, indicating that steric hindrance may limit the size of exocyclic modifications at the 3-position of Ado.