Inhibition of Receptor Signaling and of Glioblastoma-derived Tumor Growth by a Novel PDGFR beta Aptamer

Platelet-derived growth factor receptor beta (PDGFR beta) is a cell-surface tyrosine kinase receptor implicated in several cellular processes including proliferation, migration, and angiogenesis. It represents a compelling therapeutic target in many human tumors, including glioma. A number of tyrosine kinase inhibitors under development as antitumor agents have been found to inhibit PDGFR beta. However, they are not selective as they present multiple tyrosine kinase targets. Here, we report a novel PDGFR beta-specific antagonist represented by a nuclease-resistant RNA-aptamer, named Gint4.T. This aptamer is able to specifically bind to the human PDGFR beta ectodomain (Kd: 9.6 nmol/l) causing a strong inhibition of ligand-dependent receptor activation and of downstream signaling in cell lines and primary cultures of human glioblastoma cells. Moreover, Gint4.T aptamer drastically inhibits cell migration and proliferation, induces differentiation, and blocks tumor growth in vivo. In addition, Gint4.T aptamer prevents PDGFR beta heterodimerization with and resultant transactivation of epidermal growth factor receptor. As a result, the combination of Gint4.T and an epidermal growth factor receptor-targeted aptamer is better at slowing tumor growth than either single aptamer alone. These findings reveal Gint4.T as a PDGFR beta-drug candidate with translational potential.