Novel cyclotides from Hedyotis biflora inhibit proliferation and migration of pancreatic cancer cell in vitro and in vivo

Hedyotis biflora is a well-known herb in traditional Chinese medicine which is used to treat various cancers, including pancreatic cancer. Recently, two cytotoxic cyclotides were found in H. biflora, suggesting that cyclotides may be bioactive ingredients in this herb. Cyclotides are heat-stable macrocyclic peptides from plants that display a wide range of biological activities. Currently, more than 200 cyclotides have been discovered. In this present study, another five novel cyclotides, hedyotide B5 (HB5) to HB9, from the leaves and root of H. biflora, were isolated, besides the known HB1 and HB2. By Edman degradation sequencing and gene cloning, we confirmed their amino acid sequence and obtained precursors of hedyotides. By in vitro MTT assay, all present hedyotides showed significant cytotoxicity on four kinds of pancreatic cancer cell lines, especially for HB7. By in vitro migration assay and wound-healing assay, HB7 inhibited the cell migration and invasion of capan2 cells; by in vivo xenograft model, HB7 could significantly inhibit the tumor weight and size compared with the placebo control. These results suggested that H. biflora may have more novel cyclotides, and these cyclotides may have a good anti-cancer bioactivity.