Canthin-6-one Isolated from Bruceajavanica Root Blocks Cancer Cells in the G2/M phase and Synergizes with Cisplatin

Poor prognosis of most cancer patients is in part, due to limited therapeutic options. Furthermore, as chemotherapy remains the standard-of-care for several cancers, partial or lack of response remains a concern and compounding this are the adverse side effects of the treatment that severely impacts the quality of life and survival. In pursuit of improving treatment options, we have opted to investigate the unique chemical skeleton of natural compounds as anticancer therapies. In this study, from an initial screen of 31 crude methanol extracts from -15 plant species using HL60 cells, the root extract of Bruceajavanica (L.) Merr indicated the presence of bioactive compounds. Subsequent bioassay-guided purification on the root extract yielded two alkaloids canthin-6-one (1) and bruceolline J (2), which were further investigated for their bioactivity in representative human cancer lines and normal phenotypic counterparts. MTT assay demonstrated ED50 values from 34.7-72.9 gM for 1 and 16.0-54.0 gM for 2 for the cancer cell lines panel. NP69 cells also demonstrated sensitivity to. both compounds (9.3 piM and 4.5 pM). As amount of 2 isolated were limiting, we focused on 1 to further identify novel anticancer properties in PC3 and HeLa cancer lines. We observed at 30 gM, I induced a G2/M phase arrest coinciding with decreased cell proliferation. Furthermore, I was able to synergize the cytotoxic effect of cisplatin when used in combination, suggesting the potential of combination therapy for those less responsive lesions to standard chemotherapy.