Cell Surface ATP Synthase: A Potential Target for Anti-Angiogenic Therapy - Extracellular ATP and Adenosine as Regulators of Endothelial Cell Function - page 141

Fig. 9.4 Inhibition of HUVEC proliferation by polyclonal antibodies against ATP synthase.
HUVECproliferation was induced by basic fibroblast growth factor (bFGF, 10 ng/ml) and vas-
cular endothelial growth factor (VEGF, 3 ng/ml). Cells were treated with 1 μ M angiostatin ( 1 ),

100 μ g/ml polyclonal antibody against the β -subunit of ATP synthase ( 2 ), 100 μ g/ml pre-immune

serum ( 3 ), or 10 subunit

inhibited endothelial cell proliferation to a greater degree than angiostatin. (Adapted from [25],
reprinted by permission of Proceedings of the National Academy of Sciences , Copyright 2001
National Academy of Sciences, USA [25])

μ g/ml cycloheximide as a positive control ( 4 ). The antibody against the β

α β

antibodies against the and subunits also inhibit this reverse reaction, while an

antibody against the subunit does not affect ATP hydrolysis. In addition, treatment

with angiostatin or anti-

γ

-ATP synthase polyclonal antibody inhibits HUVEC pro-
liferation (Fig. 9.4) [25]. A later publication by the Higuti laboratory supported these
results, demonstrating decreased extracellular ATP synthesis and inhibited prolifer-
ation of endothelial cells in the presence of other ATP synthase inhibitors [2]. These
results indicated that molecules targeting ATP synthase could potentially mimic the
anti-angiogenic activity of angiostatin. Data from the Moser et al. study suggest that
an inhibitory antibody against the

β

catalytic subunit of ATP synthase could mimic
the in vivo anti-angiogenic activity of angiostatin without the potential risk posed by
other small molecule inhibitors of ATP synthase, e.g. piceatannol, that could enter
the cell and inhibit oxidative phosphorylation [25].

β

9.2.2 Target for Anti-Angiogenic Treatment

In 2007 Chi et al. further demonstrated that cell surface ATP synthase is a promis-
ing therapeutic target by demonstrating the anti-angiogenic activity of a monoclonal
antibody (MAb3D5AB1) against its β subunit. The antibody utilized in this study

binds to the subunit with 25-fold greater affinity than angiostatin and inhibits both

ATP synthesis and hydrolysis by the enzyme. As with angiostatin, the inhibition of
ATP synthase activity occurs specifically under conditions of low external pH (pH e ),
which will be discussed in greater detail in the following section. Furthermore,
MAb3D5AB1 disrupts endothelial cell tube formation under acidic conditions and
inhibits bFGF-stimulated angiogenesis in vivo in the CAM model (Fig. 9.5) [15].

β