Our experiments were designed to determine whether recombinant
ribonuclease inhibitor (RNasin) could inhibit angiogenesis and reduce
tumor growth in adult mice. We used the Fajardo disc angiogenesis assay as the primary means of measuring new blood vessel growth. This assay measures the penetration of cells into a
polyvinyl alcohol sponge with a central core of
ELVAX-coated sponge containing test substances. Cell penetration was reduced to 29.3% of control (
phosphate-buffered saline; heat-inactivated RNasin) values. Endothelial cell influx was measured by
lectin staining and confirmed by culturing cells isolated from sponges by
collagenase treatment. RNasin also reduced the augmented reaction evoked by either
basic fibroblast growth factor (bFGF) or
sodium orthovanadate. To confirm the anti-angiogenic activity of RNasin, Hydron-coated
polyvinyl sponges containing bFGF or bFGF plus RNasin were implanted into adult mouse corneas. bFGF induced a strong angiogenic response that was almost completely inhibited by RNasin. RNasin-containing
ELVAX-coated sponges implanted subcutaneously underneath an intradermal inoculum of C755 mammary
tumor cells caused significant reduction in
tumor growth (P < 0.005). The antitumor effect of RNasin correlated with its effect on
tumor-induced neovascularization, suggesting that the ability of RNasin to affect
tumor growth was due to its ability to inhibit angiogenesis.