Flavonoid-inspired vascular disrupting agents: Exploring flavone-8-acetic acid and derivatives in the new century

Naturally occurring flavonoids are found as secondary metabolites in a wide number of plants exploited for both medicine and food and have long been known to be endowed with multiple biological activities, making them useful tools for the treatment of different pathologies. Due to the versatility of the scaffolds and the vast possibilities of appropriate decoration, they have also been regarded as fruitful sources of lead compounds and excellent chemical platforms for the development of bioactive synthetic compounds. Flavone-8-acetic acid (FAA) and 5,6-dimethylxanthone acetic acid (DMXAA) emerged for their antitumour potential due to the induction of cytokines and consequent rapid haemorrhagic necrosis of murine tumour vasculature, and different series of derivatives have been designed thereafter. Although the promising DMXAA failed in phase III clinical trials because of strict species-specificity, a boost in research came from the recent identification of the stimulator of interferon genes (STING), responsible for supporting tumoural innate immune responses, as a possible biological target. Consequently, in the last decade a renewal of interest for these flavonoid-based structures was noticed, and novel derivatives have been synthesised and evaluated for a deeper understanding of the molecular features needed for affecting human cells. Un-doubtedly, these natural-derived molecules deserve further investigation and still appear attractive in an anticancer perspective.