Growth Inhibition and Apoptosis Induction by Vincetoxicum pumilum Decne. on HL-60 and K562 Leukemic Cell Lines

Phenanthroindolizidine alkaloids have been isolated from many species of Vincetoxicum. These alkaloids show promising anti-cancer activity and are a current topic of interest. The inhibition of cell viability by different extracts of V. pumilum was measured in vitro in HL-60 and K562 human leukemic cancer cell lines and in freshly-isolated peripheral blood lymphocytes as a normal cell line. Using resazurin staining, cell viability was measured. In addition, the presence of apoptotic cells was determined using propidium iodide (PI) staining of DNA fragments (sub-G1 peak). Employing western blot analysis, levels of Bax, Bcl-2, and PARP cleavage were measured. The CH2Cl2 fraction of V. pumilum showed a potent dose-related inhibitory effect on cell viability. The CH2Cl2 fraction showed IC50 values of 8.3 and 12.5 µg/mL in the K562 and HL-60 cell lines, respectively. A sub-G1 peak in the flow cytometry histograms of treated cells induced by the CH2Cl2 fraction suggested an induction of apoptosis. Further, both the parent methanol extract and its CH2Cl2 sub-fraction increased the expression of the pro-apoptotic protein Bax and of cleaved PARP in the cells. Collectively, the V. pumilum extracts showed remarkable cytotoxic activity and merit further investigation as anticancer agents.