Agro-Industrial Plant Biomass as a Sustainable Source of Anticancer Polyphenols: Molecular Mechanisms and Future Perspectives

The increasing global burden of cancer, together with the need for more sustainable resource management, has stimulated growing interest in the valorization of agro-industrial plant residues as sources of bioactive compounds with therapeutic potential. This review highlights the potential of plant by-products—including citrus peels, olive leaves, date palm residues, and tea and coffee processing wastes—as sustainable reservoirs of polyphenols and other phytochemicals with significant anticancer activity. Key compounds such as hesperidin and naringenin from citrus peels, oleuropein and hydroxytyrosol from olive leaves, quercetin and syringic acid from date palm residues, and chlorogenic acid and epigallocatechin gallate from tea and coffee by-products have demonstrated promising antitumor effects in both in vitro and in vivo studies. These molecules exert their activity through multiple mechanisms, including the inhibition of cancer cell proliferation, induction of apoptosis, regulation of the cell cycle, and modulation of major oncogenic signaling pathways such as PI3K/AKT, MAPK, NF-κB, and EGFR. For instance, hydroxytyrosol induces apoptosis and cell cycle arrest while inhibiting the PI3K/AKT and MAPK pathways. Quercetin limits metastasis and glycolysis and suppresses VEGF, PKM2, and AKT signaling. Ferulic acid suppresses tumor growth by inhibiting the PI3K/AKT and JAK2/STAT6 pathways, thereby promoting apoptosis (in vitro and in vivo). In addition to their pharmacological potential, the recovery of these compounds from plant waste supports circular economy strategies by reducing environmental impact and promoting the development of value-added products. Future research should focus on optimizing extraction methods, improving bioavailability and stability, and validating safety and efficacy through well-designed preclinical and clinical studies.