Reversal of cisplatin resistance by neferine/isoliensinine and their combinatorial regimens with cisplatin‐induced apoptosis in cisplatin‐resistant colon cancer stem cells (CSCs)

Cisplatin chemotherapy to the colorectal cancer cells (CRCs) is accompanied by dose‐limiting adverse effects along with the acquisition of drug resistance implicating low therapeutic outcomes. The present study is aimed to evaluate the chemosensitizing efficacy of neferine/isoliensinine or combinatorial regimen of neferine/isoliensinine with cisplatin against CSCs (cisplatin resistant colon stem cells). CSCs were developed using pulse exposure of cisplatin to parental HCT‐15 cells. Neferine/isoliensinine or combinatorial regimens of Neferine/isoliensinine and cisplatin exhibited a stronger cytotoxic activity against CSCs compared to control. IC50 doses were found to be 6.5 μM for neferine, 12.5 μM for isoliensinine, and 120 μM for cisplatin respectively. Furthermore, the combinatorial regimen of a low dose of cisplatin (40 μM) with 4 μM neferine/8 μM isoliensinine induced cell death in a synergistic manner as described by isobologram. Neferine/isoliensinine could confer extensive intracellular reactive oxygen species generation in CSCs. Neferine/isoliensinine or combinatorial regimens dissipated mitochondrial membrane potential and enhanced intracellular [Ca2+]i, which were measured by spectroflurimetry. Furthermore, these combinatorial regimens induced a significant increase in the sub G0 phase of cell cycle arrest and PI uptake and alleviated the expression of ERCC1 in CSCs. Combinatorial regimens or neferine/isoliensinine treatments downregulated the cell survival protein expression (PI3K/pAkt/mTOR) and activated mitochondria‐mediated apoptosis by upregulating Bax, cytochrome c, caspase‐3, and PARP cleavage expression while downregulating the BCl‐2 expression in CSCs. Our study confirms the chemosensitizing efficacy of neferine/isoliensinine or combinatorial regimens of neferine/isoliensinine with a low dose of cisplatin against CSCs.