title: Novel delivery of SN38 markedly inhibits tumor growth in xenografts, including a camptothecin-11-refractory model.
abstract: OBJECTIVE
  Clinical development of SN38, the active metabolite of camptothecin-11 (CPT-11), has been hampered due to its poor solubility. We have developed a novel polymer-drug conjugate, EZN-2208, made by linking SN38 with a multiarm polyethylene glycol via a glycine linker.
  
  
  METHODS
  The in vitro cytotoxicity of EZN-2208 was tested using the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay. The therapeutic efficacy of EZN-2208 was evaluated in various xenografts, including an in vivo-selected CPT-11-refractory model. Tumor and blood concentration of EZN-2208, CPT-11, and SN38 was determined by high-performance liquid chromatography.
  
  
  RESULTS
  In vitro, EZN-2208 was 10- to 245-fold more potent than CPT-11 in a panel of human tumor cell lines. In xenograft models of MX-1 breast, MiaPaCa-2 pancreatic, or HT-29 colon carcinoma, treatment with either a single dose or multiple injections of EZN-2208 was more efficacious (and in some cases produced tumor eradication for >16 weeks) compared with CPT-11 at their respective maximum tolerated doses or corresponding dose levels (P < 0.01). Most interestingly, EZN-2208 showed marked antitumor activity in animals that developed resistance to an 8-day course of CPT-11 treatment, as well as outperformed CPT-11 as second-round therapy in mice initially sensitive to CPT-11. EZN-2208 had prolonged circulation in the blood compared with CPT-11, resulting in high tumor exposure. This resulted in higher and longer-lasting tumor exposure of free SN38 in mice given EZN-2208 compared with those given CPT-11.
  
  
  CONCLUSIONS
  Preclinical data suggest that EZN-2208 may be a promising anticancer agent in a wide variety of clinical settings, including tumors refractory to CPT-11 treatment.
authors.affiliation: Enzon Pharmaceuticals, Inc., Piscataway, New Jersey 08854, USA. puja.sapra@enzon.com
authors.forename: Puja
authors.initials: P
authors.lastname: Sapra
authors.forename: Hong
authors.initials: H
authors.lastname: Zhao
authors.forename: Mary
authors.initials: M
authors.lastname: Mehlig
authors.forename: Jennifer
authors.initials: J
authors.lastname: Malaby
authors.forename: Patricia
authors.initials: P
authors.lastname: Kraft
authors.forename: Clifford
authors.initials: C
authors.lastname: Longley
authors.forename: Lee M
authors.initials: LM
authors.lastname: Greenberger
authors.forename: Ivan D
authors.initials: ID
authors.lastname: Horak
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage; D001943:Breast Neoplasms / Q000188:drug therapy; D002166:Camptothecin / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000627:therapeutic use; D002277:Carcinoma / Q000188:drug therapy; D049109:Cell Proliferation / Q000187:drug effects*; D015179:Colorectal Neoplasms / Q000188:drug therapy; D004195:Disease Models, Animal; D016503:Drug Delivery Systems; D004353:Drug Evaluation, Preclinical; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D005260:Female; D006801:Humans; D000077146:Irinotecan; D051379:Mice; D008819:Mice, Nude; D008954:Models, Biological; D009369:Neoplasms / Q000188:drug therapy*; D010190:Pancreatic Neoplasms / Q000188:drug therapy; D011092:Polyethylene Glycols / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use*; D016896:Treatment Outcome; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; C528970:EZN-2208; D011092:Polyethylene Glycols; D000077146:Irinotecan; D002166:Camptothecin