Novel cyclotides from Hedyotis diffusa induce apoptosis and inhibit proliferation and migration of prostate cancer cells

Background: Hedyotis diffusa is a well-known herb in traditional Chinese Medicine (TCM) which is used to treat various cancers including prostate cancer. Recently, lots of cyclotides possessing anti-cancer activities were found in Hedyotis family plants, suggesting that H.diffusa may also contain these bioactive ingredients. Cyclotides are heat-stable macrocyclic peptides from plants that display a wide range of biological activities. Currently, over 250 cyclotides have been discovered. Objective: This study tried to isolate novel cyclotides from H.diffusa and further investigate their anti-cancer activities for the prostate cancer cells in vitro and in vivo. Methods: The novel cyclotides from H.diffusa were isolated and purified by High-performance liquid chromatography (HPLC), amino acid sequences in their primary structure were confirmed using Edman degradation and gene cloning. Colorimetric cell viability assay (CCK8 assay), wound healing assay and human prostate cancer xenograft were used to analyze their anti-prostate cancer activity in vitro and in vivo. Results: Three novel cyclotides, termed as Diffusa cyclotide 1 to 3 (DC1-3) from the leaves and root of H.diffusa, were isolated firstly based on my knowledge. Using Edman degradation sequencing and gene cloning, we confirmed their amino acid sequence and obtained precursors of these peptides. By CCK8 assay, all present cyclotides showed potent cytotoxicity against all three prostate cancer cell lines, especially for DC3. In migration assay and wound healing assay, DC3 inhibited the cell migration and invasion Of LNCap cells. By model of prostate xenograft, DC3 could significantly inhibit development of the tumor in weight and size compared to the placebo. Conclusion: The novel cyclotides extracted from H.Diffusa have anti-cancer effects, and they are potential bioactive ingredients in H.diffusa.