Background: Insulin-like growth factor (IGF)-I receptor (IGF-IR) signaling is required for tumorigenicity and tumor progression of gastrointestinal cancers. The authors previously reported the success of therapy for gastrointestinal cancers using adenoviruses that expressed dominant-negative IGF-IR (IGF-IR/dn). In addition, it has been demonstrated that IGF-IR signaling affects vascular endothelial growth factor (VEGF) expression in some other types of tumors. The objective of the current study was to evaluate this interaction by studying the roles of IGF-IR in tumor angiogenesis and lymphangiogenesis and their implications for targeted therapy in gastric cancer.
Methods: The impact of IGF signals on the expression of VEGF-A and VEGF-C in a human gastric cancer cell, MKN45, and vascular formation were assessed. The effects of IGF-IR/dn with or without bevacizumab on angiogenesis, lymphangiogenesis, and tumor suppression in mouse xenografts were assessed.
Results: IGFs induced the expression of VEGF ligands and up-regulated in vitro vascular vessel formation. IGF-IR/dn reduced VEGF expression, reduced the activation of both protein kinase B (Akt) and mitogen-activated protein kinase (MAPK), and reduced vascular formation, indicating that IGF-IR/dn inhibited tumor growth in mice by inhibiting both angiogenesis and lymphangiogenesis. However, IGF-IR/dn did not affect either blood sugar or body weight in these mice. The combination of IGF-IR/dn and bevacizumab was highly effective against these xenograft tumors, and only this combination resulted in the complete regression of 43% of tumors, reduced the expression of VEGF, and induced apoptosis.
Conclusions: The current results indicated that IGF-IR is involved in angiogenesis and lymphangiogenesis through the modulation of VEGF ligand expression in the gastric cancer cell line MKN45. Targeting IGF-IR in combination with agents that block the VEGF pathway may have therapeutic utility for gastric cancer therapy.
Copyright © 2011 American Cancer Society.