Integrin Activation Suppresses Etoposide-induced DNA Strand Breakage in Cultured Murine Tumor-derived Endothelial Cells

Tumor endothelium is critical for solid tumor growth and is a potential site for anticancer drug action. Within 2 h, etoposide caused marked DNA strand breakage in xenograft tumor-derived endothelial cells (TDECs). Etoposide-induced DNA breakage was inhibited by culturing TDECs on gelatin, type IV collagen, laminin, fibronectin, and the integrin ligand hexapeptide, GRGDSP, but not the inactive peptide, GRADSP. It was also inhibited when TDECs were on surfaces coated with antibodies to alpha 5, beta 1, or beta 3 integrin subunits and by clustering integrins with soluble antibodies. After 8 h with etoposide, TDECs detached from the monolayer, and 50-kb DNA fragments were seen. Fibronectin inhibited both processes. Thus, integrins are survival factors for TDEC that inhibit the genotoxicity of etoposide and may influence the sensitivity of tumors to drugs.