Inhibitory effect of phycocyanin from Spirulina platensis on the growth of human leukemia K562 cells

The effect of phycocyanin from Spirulina platensis on the growth of human chronic myelogenous leukemia-blast crisis K562 cells was studied by semi-solid agar assay and cell viability measurement. Phycocyanin significantly inhibited the growth of K562 cells in a dose-dependent manner. The IC50 value of the phycocyanin was 72.5 mg L-1. After the K562 cells were cultured with phycocyanin for 6 days, flow cytometric assays showed that more K562 cells were blocked to progress through S-phase and arrested at G1 phase. DNA fragmentation assay indicated that there was no ladder of DNA fragments of approximately 200-bp multiples, indicating that apoptosis had not occurred. Western blot analysis showed that Bcl-2 protein was expressed, but its level remained unchanged, whereas the expression level of c-myc increased. These findings suggest that phycocyanin may be able to inhibit the growth of K562 cells by pathways other than apoptosis, and that changed a expression pattern of the c-myc protein may be involved in such inhibition.