Inhibition of angiogenesis in vitro and in ovo with an inhibitor of cellular protein kinases, MDL 27032

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Abstract
Protein kinase C (PKC) was implicated as an important positive regulator of angiogenesis by studies showing that tumor promoting phorbol esters, which activate PKC, stimulate angiogenesis both in vitro and in vivo. Therefore, inhibitors of PKC might be expected to block angiogenesis. MDL 27032 [4‐propyl‐5‐(4‐pyridinyl)‐2(3H)‐oxazolone], an inhibitor of cellular protein kinases, prevented capillary‐like tube formation by human umbilical vein endothelial cells (HUVEC) on basement membrane preparations, an in vitro model for angiogenic activity. MDL 27032 had an IC50 = 50 μM, whereas MDL 27044, the 4‐methyl analog of MDL 27032, was less effective (IC50 > 100 μM). This selectivity was reflected in the relative abilities of the two compounds to inhibit PKC and protein kinase A (PKA) activity prepared from HUVEC, and also to inhibit the basic fibroblast growth factor stimulated proliferation of HUVEC. MDL 27032 (0.3 μg/egg) also significantly inhibited neovascularization in yolk sac membranes of developing chick embryos, whereas MDL 27044 added at concentrations up to 3 μg/egg was not inhibitory when compared with vehicle treated controls. Adhesion of HUVEC to individual extracellular matrix proteins, including laminin, fibronectin, and fibrinogen, but not to the mixture of matrix components or collagen type I and IV, was inhibited after treatment with MDL 27032. These studies suggest that MDL 27032, may have potential as an anti‐angiogenic agent because it disrupts both formation of tube‐like structures by HUVEC on Matrigel and normal neovascularization in ovo. This inhibition may in part be due to altered cellular interactions with the extracellular matrix.