RESUMEN
Insulin-like growth factor-binding protein 4 (IGFBP-4/IBP-4) has potent IGF-independent anti-angiogenic and antitumorigenic effects. In this study, we demonstrated that these activities are located in the IGFBP-4 C-terminal protein fragment (CIBP-4), a region containing a thyroglobulin type 1 (Tg1) domain. Proteins bearing Tg1 domains have been shown to inhibit cathepsins, lysosomal enzymes involved in basement membrane degradation and implicated in tumor invasion and angiogenesis. In our studies, CIBP-4 was shown to internalize and co-localize with lysosomal-like structures in both endothelial cells (ECs) and glioblastoma U87MG cells. CIBP-4 also inhibited both growth factor-induced EC tubulogenesis in Matrigel and the concomitant increases in intracellular cathepsin B (CatB) activity. In vitro assays confirmed CIBP-4 capacity to block recombinant CatB activity. Biodistribution analysis of intravenously injected CIBP-4-Cy5.5 in a glioblastoma tumor xenograft model indicated targeted accumulation of CIBP-4 in tumors. Most importantly, CIBP-4 reduced tumor growth in this animal model by 60%. Pleiotropic anti-angiogenic and anti-tumorigenic activities of CIBP-4 most likely underlie its observed therapeutic potential against glioblastoma.
Asunto(s)
Inhibidores de la Angiogénesis/farmacología , Catepsina B/antagonistas & inhibidores , Glioblastoma/tratamiento farmacológico , Proteína 4 de Unión a Factor de Crecimiento Similar a la Insulina/farmacología , Fragmentos de Péptidos/farmacología , Secuencia de Aminoácidos , Inhibidores de la Angiogénesis/metabolismo , Inhibidores de la Angiogénesis/farmacocinética , Animales , Catepsina B/metabolismo , Línea Celular Tumoral , Proliferación Celular/efectos de los fármacos , Embrión de Pollo , Células Endoteliales/efectos de los fármacos , Células Endoteliales/enzimología , Glioblastoma/enzimología , Glioblastoma/patología , Células HEK293 , Humanos , Proteína 4 de Unión a Factor de Crecimiento Similar a la Insulina/metabolismo , Proteína 4 de Unión a Factor de Crecimiento Similar a la Insulina/farmacocinética , Masculino , Ratones , Ratones Desnudos , Datos de Secuencia Molecular , Fragmentos de Péptidos/metabolismo , Fragmentos de Péptidos/farmacocinética , Distribución Tisular , Carga Tumoral/efectos de los fármacos , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
Insulin-like growth factor I (IGF-I) increases renal blood flow, glomerular filtration rate (GFR), and proximal tubule reabsorption of phosphate in humans and rodents. The biological effects of IGF-I are likely to be influenced by cellular localization of IGF-I within the kidney. We therefore tested whether the renal localization of infused IGF-I could be altered if given with selected IGF-binding proteins (IGFBPs). Rats were treated with intravenous injections of 125I-labeled IGF-I, 125I-IGFBP-3, or 125I-IGFBP-4 alone or with complexes of 125I-IGF-I and IGFBP-3 or IGFBP-4. The cellular localization of IGF and the IGFBP within the kidney was then determined. 125I-IGF-I, 125I-IGFBP-4, and 125I-IGF-I/IGFBP-4 complexes were found almost exclusively in vacuolar structures (endosomes) of proximal renal tubules. In contrast, about one-third of renal 125I-IGFBP-3 and 125I-IGF-I/IGFBP-3 was localized to glomeruli. When 125I-IGF-I was given alone, 3% was found in glomeruli and 89% in proximal tubules. When given as 125I-IGF-I/IGFBP-3, 29% was in glomeruli and 65% in proximal tubules. We conclude that the cellular localization of IGF-I within the kidney can be directed to glomerular elements if the IGF-I is given with IGFBP-3.
