Cell cycle-dependent priming action of granulocyte colony-stimulating factor (G-CSF) enhances in vitro apoptosis induction by cytarabine and etoposide in leukemia cell lines.

We investigated the priming effect and mechanism of granulocyte colony-stimulating factor (G-CSF) in chemotherapy with low-dose Ara-C and VP-16 for acute myeloid leukemia. We analyzed cell proliferation, apoptosis, and cell cycle in vitro using leukemia cell lines 32Dcl3, U937, HL-60, and Ba/F3. Cell proliferation assays were performed using the Trypan Blue dye exclusion method. For detection of apoptosis, the Annexin V-binding capacity of treated cells was examined by flow cytometry. To evaluate the cell cycle, we used an FITC BrdU Flow kit and conducted analysis by flow cytometry. The combination of Ara-C and VP-16 significantly enhanced the observed effects compared with those of Ara-C or VP-16 alone. Concurrent administration of G-CSF further reduced the cell number and viability of 32Dcl3 and U937 cells, but not of HL-60 and Ba/F3 cells. Apoptotic cells were significantly increased in number by the addition of G-CSF to 32Dcl3 and U937 cells, while G-CSF had no significant effect on HL-60 and Ba/F3 cell lines. The addition of G-CSF significantly decreased the percentage of G0/G1-phase cells and significantly increased that of S-phase cells among 32Dcl3 and U937 cells. No significant effect was observed for HL-60 and Ba/F3 cells. An enhancement was confirmed for the combination of Ara-C, VP-16, and G-CSF for 32Dcl3 and U937 cells but not for HL-60 and Ba/F3 cells. It was thought that this difference was a result of different responses to G-CSF. G-CSF potentiates Ara-C- and VP-16-induced cytotoxicities through apoptosis induction by mobilizing resting G0-G1-phase cells into S phase.