1. The effects of
A02011-1, a
pyrazole derivative, on the proliferation of rat vascular smooth muscle cells (VSMCs) were examined. 2.
A02011-1 (1-100 microM) concentration-dependently inhibited [3H]-
thymidine incorporation into
DNA in rat VSMCs that were synchronized by 48 h serum depletion and then re-stimulated by addition of foetal calf serum (FCS, 10%),
platelet-derived growth factor (PDGF, 10 ng ml-1),
5-hydroxytryptamine (10 microM) or
ADP (10 microM). The inhibitory effect of
A02011-1 was fully reversible. However, FCS-induced [3H]-
thymidine incorporation into rat endothelial cells was unaffected by
A02011-1. 3. The concentration of
A02011-1 necessary for inhibition of the FCS-induced proliferation was similar to that necessary for
adenosine 3':5'-cyclic monophosphate (
cyclic AMP) formation.
Adenylyl cyclase activity was increased in A02011-1-treated VSMCs, whereas
cyclic AMP-specific
phosphodiesterase activity was unchanged. 4.
A02011-1 was equipotent with
forskolin but was more potent than 8-bromo-cyclic
AMP against FCS (10%)-induced proliferation. 5. The antiproliferative action of
A02011-1 was mimicked by 8-bromo-cyclic
AMP, a membrane-permeable
cyclic AMP analogue and was antagonized by
2',5'-dideoxyadenosine, an
adenylyl cyclase inhibitor and by Rp-cyclic AMPS, a competitive inhibitor of
cyclic AMP-dependent protein kinase (PKA) type I and II.
3-Isobutyl-1-methylxanthine (
IBMX) caused significant potentiation of the antiproliferative activity of
A02011-1. However, Rp-8-bromo-cyclic
GMPS and
staurosporine did not affect the antiproliferative activity of
A02011-1. 6.
A02011-1 still inhibited the FCS-induced
DNA synthesis even when added 10-18h after restimulation of the serum-starved VSMCs with 10% FCS. Flow cytometry in synchronized cells revealed an acute blockade of FCS-inducible cell cycle progression at a point in the G,/S phase in A02011-1-treated cells. The inhibition of proliferation by A0201 1-1 was shown to be independent of cell damage,as documented by several criteria of cell viability.7. These results indicate that A0201 1-1 inhibition of VSMC proliferation was mediated by
cyclic AMP and was due to a delay in the progression from the G1 into S phase of the cell cycle.
A02011-1 did not cause cell toxicity and may thus hold promising potential for the prevention of
atherosclerosis or
vascular diseases.