Selective elimination of CML stem/progenitor cells by picropodophyllin in vitro and in vivo is associated with p53 activation.

Chronic myeloid leukemia (CML) is a hematologic malignancy originating from BCR-ABL oncogene-transformed hematopoietic stem cells (HSCs) known as leukemia stem cells (LSCs). Therefore, targeting LSCs is of primary importance to eradicate CML. The present study demonstrates that picropodophyllin (PPP) effectively induces apoptosis and inhibits colony formation in CML stem/progenitor cells as well as quiescent CML progenitors resistant to imatinib therapy, while sparing normal hematopoietic cells in vitro. Administration of PPP in vivo markedly diminishes CML stem/progenitor cells in a transgenic mouse model of CML by inhibition of cell proliferation and enhancement of apoptosis in LSK cells, and significantly improves survival of CML mice. Furthermore, PPP treatment preferentially leads to transcriptional activation of p53 in CML but not normal CD34+ cells, upregulation of p53 protein in LSCs-enriched Sca-1+ cells from CML mice, and increased phosphorylation of p53 and upregulation of Bax protein in Ku812 cells. These results suggest that the inhibitory effects of PPP on CML stem/progenitor cells are associated with selective activation of p53 pathway and propose that PPP is a potent agent that selectively targets CML LSCs, and may be of value in the CML therapy.