Tetra-end-linked G-rich oligonucleotides: design, synthesis and application in aptamers technology

The word aptamer, which stems from the Latin "aptus" (to fit) and the Greek "meros" (region or part), indicates DNA or RNA oligonucleotides (ONs) selected for their ability to bind with high affinity and specificity to a given target, and as such suitable for therapeutics or diagnostics applications. The ability of DNA and RNA aptamers to self-assemble into ordered structural motifs (e.g. hairpins, pseudoknots, G-quadruplexes) according to their ON sequence, accounts for their striking binding affinity and specificity. However, the development of aptamer technology is affected by two main drawbacks: i) the requirement of synthesizing 25 to 90 bases-long ONs (to allow the proper folding) and ii) the necessity of protecting the ON aptamers from the action of ubiquitous nucleases by post-selection chemical modifications. In 2004 we presented a new class of G-quadruplex forming ONs obtained by linking four short G-rich ON strands to the four arms of a tetra branched linker (TEL linker). This strategy allows the obtainment of parallel-stranded G-quadruplexes endowed with enhanced thermodynamic and kinetics parameters, as well as with improved resistance to nucleases starting from ON strands as short as 4 nucleobases. In this talk, I will comment on the optimization of the TEL strategy and on its exploitation for the development of new aptamers capable of protecting human CEM cells from HIV infection at submicromolar concentrations.