title: In vitro and in vivo study of an albumin-binding prodrug of doxorubicin that is cleaved by cathepsin B.
abstract: OBJECTIVE
  This study was designed to evaluate the in vitro and in vivo antitumor activity of an albumin-binding prodrug of doxorubicin 1 which incorporates a maleimide moiety and a para-aminobenzyloxycarbonyl (PABC) spacer coupled to the dipeptide Phe-Lys that is cleaved by cathepsin B.
  
  
  METHODS
  Cleavage of the albumin conjugate was studied with cathepsin B and in homogenates of MDA-MB 435 tumors. For in vivo studies, nude mice were injected with (a) glucose buffer, (b) doxorubicin (2 x 8 mg/kg, i.v, on days 10 and 17), or (c) compound 1 (3 x 24 mg/kg doxorubicin equivalent, on days 10, 17 and 24).
  
  
  RESULTS
  Prodrug 1 once bound to albumin was effectively cleaved by cathepsin B and in tumor homogenates releasing doxorubicin. A cytotoxicity assay of the albumin conjugate of 1 in two human tumor cell lines showed that doxorubicin was ~6 times more active than the conjugate. In contrast, in an in vivo study, the prodrug exhibited superior antitumor activity (T/C 15%) compared to doxorubicin (T/C 49%) in an equitoxic comparison.
  
  
  CONCLUSIONS
  The cathepsin B cleavable spacer Phe-Lys-PABC incorporated in an albumin-binding prodrug is an effective way to increase the therapeutic index of doxorubicin.
authors.affiliation: Tumor Biology Center, Breisacher Strasse 117, 79106, Freiburg, Germany.
authors.forename: Khalid
authors.initials: K
authors.lastname: Abu Ajaj
authors.forename: Ralph
authors.initials: R
authors.lastname: Graeser
authors.forename: Iduna
authors.initials: I
authors.lastname: Fichtner
authors.forename: Felix
authors.initials: F
authors.lastname: Kratz
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D002401:Cathepsin B / Q000378:metabolism*; D004151:Dipeptides / Q000378:metabolism; D004317:Doxorubicin / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008301:Maleimides / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D011355:Prodrugs / Q000138:chemical synthesis / Q000378:metabolism*; D012709:Serum Albumin / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
chemical_list: D000903:Antibiotics, Antineoplastic; D004151:Dipeptides; D008301:Maleimides; D011355:Prodrugs; D012709:Serum Albumin; C043592:maleimide; D004317:Doxorubicin; D002401:Cathepsin B