Valorization of Sardinian Grapevine Leaves as a Sustainable Source of Flavonols with Anticancer Potential

Grapevine (Vitis vinifera L.) leaves are an abundant agricultural by-product and an under- 20 exploited source of bioactive polyphenols. This study characterized hydroalcoholic leaf 21 extracts from autochthonous Sardinian cultivars and evaluated their effects in RKO hu- 22 man colorectal carcinoma cells. LC–HRMS revealed flavonol-rich profiles dominated by 23 glycosylated derivatives of quercetin, kaempferol, and isorhamnetin, with marked culti- 24 var-dependent differences and higher total flavonols abundance in Cannonau and 25 Nieddera. Cyclic voltammetry showed distinct redox reactivity among extracts, with Ver- 26 mentino and Martellada Bianca displaying the strongest electrochemical responses, con- 27 sistent with their modulation of intracellular reactive oxygen species. In RKO cells, the 28 extracts reduced metabolic activity in a dose-dependent manner, with IC50 values rang- 29 ing from 100.3 to 251.8 μg/mL. At the molecular level, treatments modulated c-myb ex- 30 pression and shifted the bax/bcl2 balance toward a pro-apoptotic profile. These effects 31 were supported by DAPI staining, showing chromatin condensation and nuclear frag- 32 mentation, and by moderate activation of caspase-3/7. Overall, Sardinian grapevine leaf 33 extracts showed cultivar-specific phenolic composition, redox activity, and pro-apoptotic 34 effects in an in vitro colorectal cancer model, supporting their potential valorization as 35 sustainable sources of bioactive compounds. Further studies addressing bioavailability, 36 metabolism, and in vivo effects are required to assess their physiological relevance and 37 translational potential.