A dual-nuke backbone is no longer a viable option in the foreseeable future after the failure of PSI-938.
That's a bold statement to make. Just because one guanosine shows tox doesn't mean all the others in current pipelines will - or that adenosine's will succumb to the same fate. It could be a class issue, or maybe not. If it is, is it a purine class issue or a guanosine class issue? There are other companies actively looking into dual-nuke with data in the foreseeable future. VRUS isn't the only game in town.