Potential effects of Cerbera odollam leaf extracts and neriifolin exposure in breast cancer treatment and progression

Despite improvements in treatment options for breast cancer, breast cancer remains the most prevalent cancer affecting women worldwide. The heterogeneous nature of breast cancer tumors and the prevalence of drug resistance towards antiestrogen therapy are two major impediments in the treatment of breast cancer. Initial experiments conducted on the leaf extract of Cerbera odollam revealed that the extract contains an extremely potent cytostatic agent which is more effective towards hormone-responsive cell lines compared to hormone-independent cell lines. The active compound within the extract was determined to be neriifolin, which causes prolonged cytostatic effects for up to 10 days at a dose of 18.7 nM. Gene expression analyses indicate that the cytostatic activity of neriifolin is mediated by the estrogen receptor-alpha (ERα) – estrogen signaling pathway as well as p53-dependent induction of the cell cycle inhibitor, p21WAF1. Increased oxidative DNA damage was observed as a result of neriifolin treatment, suggesting that neriifolin-induced cell death and cytostaticity occurs in response to DNA damage resulting from treatment. A high resolution melt-based method was developed to enable rapid detection of DNA methylation changes on the ERα gene (ESR1) promoter. While the active C. odollam plant fraction resulted in hypermethylation on the ESR1 promoter, treatment with neriifolin caused no detectable changes of DNA methylation patterns, suggesting that neriifolin treatment would not result in antiestrogen resistance. ESR1 promoter hypermethylation was also observed in cells deficient in p53. A possible relationship between ERα silencing and the formation of oxidative DNA damage was also investigated.