Inhibition of the ecto-beta subunit of F1F0-ATPase inhibits proliferation and induces apoptosis in acute myeloid leukemia cell lines

BACKGROUND: Leukemia, a heterogeneous clonal disorder of hematopoietic progenitor cells, presents a world-wide health problem, especially in childhood. F1F0 ATPase, an inner mitochondrial enzyme, is expressed on the plasma membrane of tumor cells, and its inhibition induces both anti-angiogenic and anti-tumorigenic activity. METHODS: Monoclonal Antibody (McAb) against ATPase was produced by polyethylene glycol-mediated fusions and screened by ELISA. Proliferation, cell cycle and apoptosis of cells were analyzed when the surface ATPase of cells was blockaded with McAb. RESULTS: We detected cell-membrane expression of the F1F0 ATPase β subunit on 0.1% to 56% of the 11 cell lines derived from leukemia, including acute myeloid leukemia (AML). We produced a monoclonal antibody, McAb7E10, which recognizes both the native and recombinant ATPase β subunit, with a dissociation constant (KD) of 3.26E(–10). We demonstrate that McAb7E10 binds to ATPase at the cell surface, where it is able to inhibit ATP synthesis. McAb7E10 significantly inhibited proliferation of AML cell lines in vitro: the relative inhibitory rates of 50 μg/mL McAb7E10 treated MV4-11and HL-60 cells were 69.6% and 81.9% respectively. Cell cycle analysis indicated that McAb7E10 significantly induced apoptosis in MV4-11 and HL-60 cells: the relative rates of apoptosis in 5, 10 and 50ug/mL McAb7E10 treated MV4-11 cells was 3.6 ± 0.83%, 8.4 ± 1.69% and 17.3 ± 2.56% compared to 1.5% ± 0.85% in mouse IgG treated cells (p < 0.01). The relative rate of apoptosis in 5, 10 and 50ug/mL McAb7E10 treated HL-60 cells was 5.5 ± 2.37%, 11.3 ± 3.62% and 19.9 ± 3.31% compared to 1.56% ± 0.97% in mouse IgG treated cells (p < 0.01). Annexin V staining demonstrated that the relative apoptotic rates in 50 μg/mL McAb7E10 treated MV4-11 and HL-60 cells were 50.5% ± 7.04% and 32.9% ± 4.52%, respectively, significantly higher than IgG control antibody treated cells were 21.9% ± 3.11% and 15.3% ± 3.95%, p < 0.01. CONCLUSIONS: These findings indicate that ectopic expression of ATPase β subunit may be a tumor-associated antigen in hematological malignancies. The F1F0 ATPase β subunit provides a potential target for immunotherapy in AML and hematological malignancies.