AMILORIDE INHIBITION OF ANGIOGENESIS IN-VITRO

Angiogenesis is important to such processes as normal embryonic develo pment and tissue growth, and is also a central feature of diseases suc h as diabetic retinopathy and the growth of solid tumors. Understandin g the basic events governing angiogenesis has therefore attracted grea t interest. The ion channel blocking agent, amiloride, has been shown to inhibit angiogenesis in an in vivo model (Lansing et al.,'91). This suggested a vital role for Na+-coupled transport processes in angioge nesis. A large number of structural analogues of amiloride have been s ynthesized (Kleyman and Cragoe, '88), and many of these are well chara cterized with respect to biological activity. These analogues present an opportunity to dissect the process of angiogenesis and identify pot entially important physiological events. In this report we describe th e effects of amiloride on an in vitro model for angiogenesis employing vascularized tissue explants. Amiloride inhibits capillary morphogene sis completely and reversibly at concentrations as low as 134 mu M. It appears to act by blocking endothelial cell proliferation, but not mi gration. Inhibition is heightened by the introduction of hydrophobic g roups on the terminal guanidino nitrogen atom, or on the 5-amino posit ion. An analogue substituted at both of these positions is 30-fold mor e potent than the parent compound. Of amiloride's known biological act ivities, these results most closely correlate with the inhibition of C a2+ transport processes, and thereby suggest an important role for Ca2 + transport in capillary morphogenesis. (C) 1993 Wiley-Liss, Inc.