title: PDEPT: polymer-directed enzyme prodrug therapy. 2. HPMA copolymer-beta-lactamase and HPMA copolymer-C-Dox as a model combination.
abstract: Polymer-directed enzyme prodrug therapy (PDEPT) is a novel two-step antitumor approach that uses a combination of a polymeric prodrug and polymer-enzyme conjugate to generate a cytotoxic drug rapidly and selectively at the tumor site. Previously we have shown that N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-bound cathepsin B can release doxorubicin intratumorally from an HPMA copolymer conjugate PK1. Here we describe for the first time the synthesis and biological characterization of a PDEPT model combination that uses an HPMA-copolymer-methacryloyl-glycine-glycine-cephalosporin-doxorubicin (HPMA-co-MA-GG-C-Dox) as the macromolecular prodrug and an HPMA copolymer conjugate containing the nonmammalian enzyme beta-lactamase (HPMA-co-MA-GG-beta-L) as the activating component. HPMA-co-MA-GG-C-Dox had a molecular weight of approximately 31 600 Da and a C-Dox content of 5.85 wt %. Whereas free beta-L has a molecular weight of 45 kDa, the HPMA-co-MA-GG-beta-L conjugate had a molecular weight in the range of 75-150 kDa, and following purification no free enzyme was detectable. Against the cephalosporin C or HPMA-co-MA-GG-C-Dox substrates, the HPMA-co-MA-GG-beta-L conjugate retained 70% and 80% of its activity, respectively. In vivo (125)I-labeled HPMA-co-MA-GG-beta-L showed prolonged plasma concentration and greater tumor targeting than (125)I-labeled beta-L due to the enhanced permeability and retention (EPR) effect. Moreover, administration of HPMA-co-MA-GG-C-Dox iv to mice bearing sc B16F10 melanoma followed after 5 h by HPMA-co-MA-GG-beta-L led to release of free Dox. The PDEPT combination caused a significant decrease in tumor growth (T/C = 132%) whereas neither free Dox nor HPMA-co-MA-GG-C-Dox alone displayed activity. The PDEPT combination displayed no toxicity at the doses used, so further evaluation of this approach to establish the maximum tolerated dose (MTD) is recommended.
authors.affiliation: Department of Cell Research and Immunology, Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
authors.forename: Ronit
authors.initials: R
authors.lastname: Satchi-Fainaro
authors.forename: Hanna
authors.initials: H
authors.lastname: Hailu
authors.forename: John W
authors.initials: JW
authors.lastname: Davies
authors.forename: Clive
authors.initials: C
authors.lastname: Summerford
authors.forename: Ruth
authors.initials: R
authors.lastname: Duncan
mesh_terms: D000818:Animals; D002401:Cathepsin B / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics; D045744:Cell Line, Tumor / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004317:Doxorubicin / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics*; D004789:Enzyme Activation; D008297:Male; D008546:Melanoma, Experimental / Q000188:drug therapy / Q000378:metabolism; D008689:Methacrylates / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D008956:Models, Chemical; D015394:Molecular Structure; D008970:Molecular Weight; D011108:Polymers / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics*; D011355:Prodrugs / Q000378:metabolism / Q000493:pharmacokinetics* / Q000627:therapeutic use; D013997:Time Factors; D001618:beta-Lactamases / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics*
chemical_list: D008689:Methacrylates; D011108:Polymers; D011355:Prodrugs; D004317:Doxorubicin; D002401:Cathepsin B; D001618:beta-Lactamases; C032802:hydroxypropyl methacrylate