Long-lived optical probes to image G-quadruplex DNA in live cells

There has been increasing experimental evidence suggesting that tetra-stranded DNA structures (G-quadruplexes) play important biological roles in telomere function and maintenance, replication and transcription.

The most direct evidence for their existence has come from immuno-staining in fixed cells as well as from recent deep sequencing studies. However, to date, we are still lacking tools that allows us to visualizing G-quadruplexes directly in live cells.

While several small-molecule probes that fluoresce upon interaction with DNA have been reported, none of them have been successful at imaging G-quadruplexes in a cellular environment.

This is mainly due to the fact that they rely on changes in intensity which are not possible to track properly in a cellular environment. Recently, the host lab reported a novel strategy to image G-quadruplexes in live cells.

This approach makes use of the changes in emission lifetime (rather than intensity) of optical probes upon their interaction with different topologies of DNA.

Since life-time is concentration independent, this approach can be successfully used to image G-quadruplexes in live cells.

While this has proven to be a highly successful approach, it is still in its infancy since the probe developed so far has a number of limitations such as low brightness, relatively small lifetime range and low selectivity.

Thus, this project aims to develop a new set of probes that address all these issues and use them to image the dynamics of G-quadruplexes in live cells in real time.

I propose to develop platinum complexes (which 'switch-on' their phosphorescent upon interactions with DNA) with high affinity and selectivity for G-quadruplexes. To achieve this, novel approaches for automated synthesis and high-throughput analysis will be developed.

The new probes will be used to carry out Phosphorescence Lifetime Imaging Microscopy (PLIM) studies to give evidence for the first time of the dynamics of G-quadruplexes in live cells.