SYNERGISTIC INTERACTIONS BETWEEN SELECTIVE PHARMACOLOGICAL INHIBITORSOF PHOSPHODIESTERASE ISOZYME FAMILIES PDE-III AND PDE-IV TO ATTENUATEPROLIFERATION OF RAT VASCULAR SMOOTH-MUSCLE CELLS
Xl. Pan et al., SYNERGISTIC INTERACTIONS BETWEEN SELECTIVE PHARMACOLOGICAL INHIBITORSOF PHOSPHODIESTERASE ISOZYME FAMILIES PDE-III AND PDE-IV TO ATTENUATEPROLIFERATION OF RAT VASCULAR SMOOTH-MUSCLE CELLS, Biochemical pharmacology, 48(4), 1994, pp. 827-835
The interaction between selective inhibitors of 3',5'-cyclic-nucleotid
e phosphodiesterase (PDE) III (cyclic GMP inhibited phosphodiesterase)
and selective inhibitors of PDE IV (Ro 20-1724 inhibited phosphodiest
erase) to attenuate fetal bovine serum-stimulated incorporation of [H-
3]thymidine into DNA and cell proliferation was studied in a line (A10
) of vascular smooth muscle cells (VSMC). The nonselective PDE inhibit
ors 3-isobutyl-1-methylxanthine (IBMX) and papaverine attenuated DNA s
ynthesis with EC(50) values (16 and 18 mu M, respectively) in the same
range as their published IC50 values (2-50 and 2-25 mu M, respectivel
y) as PDE inhibitors. The selective PDE III inhibitors CI-930 and cilo
stamide used alone attenuated DNA synthesis with EC(50) values (>300 a
nd 5.3 mu M, respectively) that were much higher than published IC50 v
alues (0.15-0.46 and 0.005-0.064 mu M, respectively) for inhibition of
PDE III. In the presence of the PDE IV inhibitor rolipram (10 mu M),
their EC(50) values were shifted (0.66 and 0.16 mu M, respectively) mu
ch closer to their respective IC50 values. When the selective PDE IV i
nhibitors rolipram and Ro 20-1724 were used alone, they attenuated DNA
synthesis with EC(50) values (111 and >100 mu M, respectively) much h
igher than their IC50 values (0.6-2.6 and 2-13 mu M, respectively) as
inhibitors of PDE IV, but 10 mu M CI-930 (PDE III inhibitor) shifted t
heir EC(50) values (0.56 and 1.5 mu M, respectively) much closer to th
eir IC50 values. In experiments that assessed VSMC proliferation using
the MTT (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] m
ethod, IBMX and papaverine attenuated proliferation with EC(50) values
(27 and 58 mu M, respectively) close to their IC50 values. CI-930 and
cilostamide used alone did not cause 50% attenuation of proliferation
at the highest concentrations tested (100 and 10 mu M, respectively).
In the presence of 5 mu M rolipram, however, their effects were enhan
ced greatly with EC(50) values (0.86 and 0.23 mu M, respectively) that
were close to their IC50 values as PDE III inhibitors. Similarly, rol
ipram and Ro 20-1724 attenuated VSMC proliferation with EC(50) values
close to their IC50 values in the presence (2.1 and 4.6 mu M, respecti
vely) but not in the absence (>100 and >10 mu M, respectively) of 2 mu
M CI-930. The interactions between PDE III inhibitors and PDE IV inhi
bitors to attenuate DNA synthesis and VSMC proliferation were synergis
tic as determined by the combination index. The data demonstrate that
the synergistic interactions that attenuate incorporation of [H-3]thym
idine into DNA are accompanied by synergistic attenuations of VSMC div
ision. The closeness of the EC(50) values of PDE III inhibitors when P
DE IV is blocked, and of the PDE IV inhibitors when PDE III is blocked
, to their respective IC50 values as selective PDE inhibitors supports
the view that the effects on DNA synthesis and cell division are caus
ed by inhibition of the respective PDE isozymes. A hypothesis is propo
sed to explain the synergistic interactions.