INHIBITORY DNA LIGANDS TO PLATELET-DERIVED GROWTH-FACTOR B-CHAIN

We have identified a group of DNA molecules that bind to platelet-deri ved growth factor (PDGF)-AB with subnanomolar affinity from a randomiz ed DNA library using in vitro selection. Individual ligands cloned fro m the affinity-enriched pool bind to PDGF-AB and PDGF-BB with comparab ly high affinity (K-d approximate to 10(-10) M) and to PDGF-AA with lo wer affinity (> 10(-8) M), indicating specific recognition of the PDGF B-chain in the context of the hetero- or homodimer. The consensus sec ondary structure motif for most of the high-affinity ligands is a thre e-way helix junction with a three-nucleotide loop at the branch point. Photo-cross-linking experiments with 5-iodo-2'deoxyuridine-substitute d ligands establish a point contact between a thymidine nucleotide in the helix junction loop region and phenylalanine 84 of the PDGF-B chai n. Representative minimal DNA ligands inhibit the binding of I-125-PDG F-BB but not of I-125-PDGF-AA to PDGF alpha- or beta-receptors express ed in porcine aortic endothelial (PAE) cells in a concentration-depend ent manner with half-maximal effects of approximate to 1 nM. The same ligands also exhibit a similar inhibitory effect on PDGF-BB-dependent [H-3]thymidine incorporation in PAE cells expressing the PDGF beta-rec eptors. These DNA ligands represent a novel class of specific and pote nt antagonists of PDGF-BB and, by inference, PDGF-AB.