Antioxidant Effects and in vitro Cytotoxicity on Human Cancer Cell Lines of Flavonoid-Rich Flamboyant (Delonix regia (Bojer) Raf.) Flower Extract.

Background: Cancer is a non-communicable disease with increasing incidence and mortality rates worldwide, including Thailand. Its apparent lack of effective treatments is posing challenging public health issues.

Introduction: Encouraging research results indicating probable anti-cancer properties of the Delonix regia flower Extract (DRE) have prompted us to evaluate the feasibility of developing a type of product for future cancer prevention or treatment.

Methods And Results: In the present report, using High-Performance Liquid Chromatography (HPLC), we demonstrate in the DRE the presence of high concentrations of three identifiable flavonoids, namely rutin 4.15±0.30% w/w, isoquercitrin 3.04±0.02 %w/w, and myricetin 2.61±0.01% w/w, respectively, while the IC50 of DPPH and ABTS assay antioxidation activity was 66.88±6.30 μg/ml and 53.65±7.24 μg/ml, respectively.

Discussion: Our cancer cell line studies using the MTT assay demonstrated DREs potent and dosedependent inhibition of murine leukemia cell line (P-388: 35.28±4.07% of cell viability remaining), as well as of human breast adenocarcinoma (MCF-7), human cervical carcinoma (HeLa), human oral cavity carcinoma (KB), and human colon carcinoma (HT-29) cell lines in that order of magnitude.

Conclusion: Three identifiable flavonoids (rutin, isoquercitrin and myricetin) with high antioxidation activity and potent and dose-dependent inhibition of murine leukemia cell line and five other cancer cell lines were documented in the DRE. The extract's lack of cytotoxicity in 3 normal cell lines is a rare advantage not usually seen in current antineoplastic agents. Yet another challenge of the DRE was its low dissolution rate and long-term storage stability, issues to be resolved before a future product can be formulated.