Phosphorylation of levan by microwave-assisted synthesis enhanced anticancer ability

Levan is an exopolysaccharide produced by Bacillus licheniformis (strain FRI MY-55) that shows promising pharmacological activity. Phosphorylation is a chemical modification that can increase the biological and antioxidant properties of levan. In this study, levan was phosphorylated by microwave-assisted synthesis to achieve a degree of substitution of 0.29. The hydroxyl radical scavenging activity of microwave-assisted phosphorylated levan (microwave P) increased significantly (6-fold) over native levan; this activity was only slightly lower than vitamin C. Other free radical scavenging and reducing power tests revealed that Microwave P activity was increased by 30–40%. Microwave P inhibited the proliferation of HCT-116 and A549 cancer cell lines more readily than native levan with an IC50 of 1.03 mg/mL and 1.38 mg/mL for HCT-116 and A549 cells, respectively. Cells treated with native levan and its derivatives remained in the sub-G1 phase according to cell cycle analysis, whereas Microwave P treatment increased the proportion of cells undergoing apoptosis. Furthermore, Microwave P effectively upregulated pro-apoptosis marker Bax and downregulated anti-apoptosis marker Bcl-2, in addition to inducing the expression of caspase-9 and caspase-3. These findings show that levan phosphorylated via microwave-assisted synthesis showed increased antioxidant and antitumor activity over native levan or levan phosphorylated via traditional long-term heating. In particular, Microwave P possesses antiproliferative activity and can induce apoptosis through mitochondrial pathways in cancerous cells.