title: [The binding characteristics of insulin-MTX to insulin receptor].
abstract: OBJECTIVE
  It has been reported that several kinds of tumors express increased insulin receptor and the molecules of insulin can be internalized in cells and may thence enter into the nuclei mediated by insulin receptor. In this study, we investigated the receptor binding characteristics of insulin-MTX for the possibility of using insulin as a carrier for carcinoma targeted therapy by receptor mediation.
  
  
  METHODS
  MTX(methotrexate) was covalently linked to insulin directly. The insulin-MTX conjugate was purified by polyacrylamine agarose gel electrophoresis and analysed by high performance liquid chromatography and SDS- polyacrylamine agarose gel electrophoresis. Histologically confirmed human hepatocellular carcinoma specimens were obtained from patients at surgery and immediately frozen under -80 degrees C. Cell membrane fractions were isolated by sucrose density gradient centrifugation. Competitive displacement of 125I-insulin with insulin and insulin-MTX binding to insulin receptor were carried out and the values of IC50 and Ki were calculated so as to observe the characteristics of insulin-MTX binding to insulin receptor.
  
  
  RESULTS
  Insulin-MTX competed as effectively as insulin with 125I-insulin for insulin receptor. The values of IC50 and Ki for insulin-MTX were 93.82 +/- 19.32 nmol/L and 91.88 +/- 16.86 nmol/L respectively, while the values of IC50 and Ki for insulin were 5.01 +/- 1.24 nmol/L and 4.85 +/- 1.12 nmol/L respectively.
  
  
  CONCLUSIONS
  Insulin-MTX could bind with insulin receptor with high affinity. The result demonstrates us that there is a possibility of using insulin as a carrier for carcinoma targeted therapy by receptor mediation.
authors.affiliation: Department of Nuclear Medicine, First Affiliated, Hospital WCUMS, Chengdu 610041, China.
authors.forename: X
authors.initials: X
authors.lastname: Ou
authors.forename: A
authors.initials: A
authors.lastname: Kuang
authors.forename: Z
authors.initials: Z
authors.lastname: Liang
authors.forename: X
authors.initials: X
authors.lastname: Peng
authors.forename: Y
authors.initials: Y
authors.lastname: Zhong
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000378:metabolism / Q000493:pharmacokinetics*; D001665:Binding Sites; D006528:Carcinoma, Hepatocellular / Q000473:pathology*; D002462:Cell Membrane / Q000378:metabolism; D002469:Cell Separation; D004337:Drug Carriers; D006801:Humans; D007328:Insulin / Q000378:metabolism; D008113:Liver Neoplasms / Q000473:pathology*; D008727:Methotrexate / Q000378:metabolism / Q000493:pharmacokinetics*; D011972:Receptor, Insulin / Q000378:metabolism*
chemical_list: D000964:Antimetabolites, Antineoplastic; D004337:Drug Carriers; D007328:Insulin; D011972:Receptor, Insulin; D008727:Methotrexate