Judicial structural modifications of 5: 7-fused ring-expanded nucleosides (RENs), based on molecular modeling studies with one of its known targets, human RNA helicase (hDDX3), led to the lead, novel, 5: 7-5-fused tricyclic heterocycle (1). The latter exhibited promising broad-spectrum in vitro anti-cancer activity against a number of cancer cell lines screened. This paper describes our systematic, albeit limited, structure–activity relationship (SAR) ...