The inhibitory effects of the diphosphates of 9-(2-phosphonylmethoxyethyl)adenine (PMEA) and its analogues on HIV reverse transcriptase and human DNA polymerases α, β, and γ have been studied. The analogues investigated are the diphosphates of 9-(2-phosphonylmethoxypropyl)adenine (PMPApp), 9-(2-phosphonylmethoxypropyl)-2,6-diaminopurine (PMPDAPpp), and (2R,5R)-9-[2,5-dihydro-5-(phosphonyl methoxy)-2-furanyl]adenine (D4APpp). These four compounds are much more inhibitory to HIV reverse transcriptase when an RNA template rather than a DNA template is used. The Ki, values for the four compounds range from 11 to 22 nM with an RNA template. The Ki, values for ddCTP and AZTTP are 54 nM and 8 nM, respectively. PMEApp and its analogues show varying degrees of inhibition of the human DNA polymerases. The Ki, values for PMEApp, PMPApp and PMPDAPpp against DNA polymerase α are in the micromolar range, while D4APpp is a poor inhibitor of this enzyme with a Ki, value of 65.9 μM. The inhibition of DNA polymerase β by PMEApp, PMPApp and D4APpp is minimal, while PMPDAPpp shows higher inhibition of DNA polymerase β with a Ki, value of 9.71 μM. The Ki, values for PMEApp and D4APpp against DNA polymerase γ are submicromolar, while PMPApp and PMPDAPpp are much less inhibitory to this enzyme. For comparison, ddCTP was found to be a more potent inhibitor of DNA polymerases β and γ than the diphosphates of PMEA and its analogues.
Stereospecificity of human DNA polymerases α,β,γ,§ and ɛ, HIV-reverse transcriptase, HSV- DNA polymerase, calf thymus terminal transferase andEscherichia coliDNA polymerase I in recognizing D- and L-thymidine 5′-triphosphate as substrate
