Leukemia is the most common cancer in children, accounting for a prominent percentage of cancer-related death in that age-group. It is therefore very important to prevent and treat this cancer. In this study, the anticancer effects of 6 different parts of 4 selected species of medicinal plants in Nigerian, especially those grown in South-Western and South-Eastern regions, were investigated on Human leukemic-HL-60 cell line to identify potential natural alternatives for the development of antileukemic drugs and possible in vitro antioxidant activity. The plants / seeds were gathered from selected regions in Nigeria and their aerial parts extracted through repeated maceration in methanol 70%. The cytotoxic activity of extracts on human leukemic- HL-60 cell line was evaluated by Cell Counting Kit (CCK-8) assay 48 hours after treatment. The in vitro antioxidant activity was evaluated using DPPH radical scavenging method. Polyalthia longifolia seeds and leaves had marked anti-proliferative activity against HL-60 cells showing from the inhibitory concentration at 50% (IC50: 52.1 and 56.69µg/mL respectively). In a time-dependent fashion, Polyalthia longifolia Stem bark showed the lowest DPPH radical survival rate, demonstrating its promising antioxidant status. ? Our findings show that, Polyalthia longifolia seed possess both growth inhibitory potential against leukemic cell lines and in vitro antioxidant activity, therefore a good candidate for further investigation for active chemopreventive or/and therapeutic principles. Also, a further exploration via mechanistic studies for possible mechanism of cytotoxicity against leukemic and other cell lines is recommended.

Keywords: Leukemia; Phytomedicines; Radical scavenging activity; Antiproliferative; Drug discovery; Chemoprevention; Cytotoxicity.