The synergistic anti-proliferative effect of the combination of diosmin and BEZ-235 (dactolisib) on the HCT-116 colorectal cancer cell line occurs through inhibition of the PI3K/Akt/mTOR/NF-κB axis

One of the most lethal malignancies worldwide is colorectal cancer (CRC). Alterations in various signalling pathways, including PI3K-mTOR and NF-κB, have been reported in CRC with subsequent dysregulation of proliferation, apoptosis, angiogenesis and, questionably, autophagy processes. BEZ-235 (dactolisib) is a dual PI3K-mTOR inhibitor with potent anti-tumour activity. However, the observed toxicity of BEZ-235 necessitated the termination of its clinical trials. Hence, we aimed to evaluate the potential long-lasting anti-carcinogenic effects of adding diosmin (DIO, a natural NF-κB inhibitor) to BEZ-235 in HCT-116 CRC cells. The median inhibitory concentrations (IC50s) of BEZ-235 and/or DIO were evaluated in the HCT-116 CRC cell line. Caspase-3 activity was assessed colorimetrically, and p-Akt, NF-κB, CD1, VEGF and LC3B levels were assessed by ELISA. Additionally, LC3-II and P62 gene expression were assessed using qRT-PCR. The observed CIs (combination indices) and DRIs (dose reduction indices) confirmed the synergistic effect of DIO and BEZ-235. Co-administration of both drugs either in combination-1 (1 μM for BEZ-235, 250 μM for DIO) or in combination-2 (0.51 μM for BEZ-235 + 101.99 μM for DIO) inhibited the PI3K/Akt/mTOR/NF-κB axis, leading to the induction of apoptosis (via active caspase-3), and the inhibition of proliferation marker (CD1), angiogenesis marker (VEGF), autophagy protein (LC3B) and altered effects on LC3-IIandP62 gene expression. Our results reveal the synergistic chemotherapeutic effects of DIO combined with BEZ-235 in the HCT-116 CRC cell line and encourage future preclinical and clinical studies of this combination with reduced BEZ-235 concentrations to avoid its reported toxicity.