Gallic Acid as the Main in vitro Antileukemia Compound from Kalanchoe thyrsiflora Leaf Extract

Kalanchoe thyrsiflora Harv. (Crassulaceae) is a medicinal plant traditionally used in South Africa. As previously shown, the methanolic extracts from leaves and roots of K. thyrsiflora have antitumor activity against some cell lines. This study aimed to investigate the phenolic constituents of K. thyrsiflora leaves with the goal of detecting potential new treatments for acute lymphocytic leukemia (ALL), the most frequent type of cancer in children. The phenolic compounds isorhamnetin 3-O-β- glucopyranoside (1), astragalin (2), isoquercitrin (3), gallic acid (4), isorhamnetin (5) and kaempferol (6) were identified in the ethyl acetate fraction, based on 1H and 13C NMR data. The phenolic profile of the leaf extract was analyzed by HPLC-DAD. Our findings indicated that the enriched polyphenolic fraction has important cytotoxicity against lymphocytic leukemia cells, with gallic acid mainly contributing to this effect. The ethyl acetate fraction also inhibited leukemia cell proliferation and induced them into apoptosis, but without toxicity to mononuclear cells of healthy humans. This is the first report on the phenolic profile of K. thyrsiflora species and its antileukemia potential.