RESUMO
A fusion protein, FP 6/3, composed of IGF binding protein (IGFBP)-6 and IGFBP-3 was synthesized where the complete sequences of each binding protein were fused together into a single chimeric protein. The orientation of this fusion protein's structure has the N terminus of IGFBP-3 fused to the C terminus of IGFBP-6, leaving the key binding areas of each open. FP 6/3 bound to cells via its IGFBP-3 component and retained the increased affinity for IGF-II via its IGFBP-6 component. The effect of FP 6/3 on growth was determined in cell lines from both neuroblastoma and rhabdomyosarcoma, where IGF-II is an autocrine growth factor. In studies using FP 6/3, IGFBP-3, or IGFBP-6, a growth inhibition effect was shown for all when present under coincubation conditions with IGF-II. However, with transient exposure, FP 6/3 was the only IGFBP that retained this growth-inhibition property. Under transient exposure conditions, FP 6/3 was found to be effective when exposure was limited to as few as 10 min and concentrations were as low as 1 nm. These findings with FP 6/3 suggest that it potentially could lead be used as therapy against cancers in which IGF-II is an autocrine growth factor because it brings an inhibition action directly to tumor cells.
Assuntos
Proteína 3 de Ligação a Fator de Crescimento Semelhante à Insulina/farmacologia , Proteína 6 de Ligação a Fator de Crescimento Semelhante à Insulina/farmacologia , Neuroblastoma , Rabdomiossarcoma , Animais , Bovinos , Divisão Celular/efeitos dos fármacos , Linhagem Celular Tumoral/citologia , Linhagem Celular Tumoral/efeitos dos fármacos , Linhagem Celular Tumoral/metabolismo , Endotélio Vascular/citologia , Endotélio Vascular/metabolismo , Proteína 3 de Ligação a Fator de Crescimento Semelhante à Insulina/metabolismo , Proteína 6 de Ligação a Fator de Crescimento Semelhante à Insulina/metabolismo , Proteínas Recombinantes de Fusão/metabolismo , Proteínas Recombinantes de Fusão/farmacologia , Timidina/farmacocinéticaRESUMO
Specific binding of IGF-binding protein (IGFBP)-3 was shown to be present in the isolated, beating rat heart. The uptake of perfused (125)I-labeled IGF-I in the beating heart was decreased to 9% by blocking IGF-I binding sites with the IGF-I analog Long R(3) (LR(3)) IGF-I. When LR(3) was perfused with complexes of (125)I-IGF-I. IGFBP-3, uptake of (125)I-IGF-I was decreased to 41%, which was significantly greater than LR(3) and (125)I-IGF-I (41 vs. 9%). These data suggest that both microvessel IGF-I and IGFBP-3 binding sites contribute to the transport of IGF-I in the perfused rat heart. This also suggests a novel and plausible mechanism whereby circulating IGFs reach sites of IGF bioactivity.
