PDEPT: Polymer-directed enzyme prodrug therapy. 2. HPMA copolymer-β-lactamase and HPMA copolymer-C-Dox as a model combination

Ronit Satchi-Fainaro, Hanna Hailu, John W. Davies, Clive Summerford, Ruth Duncan*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

89 Scopus citations


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 β-lactamase (HPMA-co-MA-GG - β-L) as the activating component. HPMA-co-MA-GG - C-Dox had a molecular weight of ∼31 600 Da and a C-Dox content of 5.85 wt %. Whereas free β-L has a molecular weight of 45 kDa, the HPMA-co-MA-GG - β-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 - β-L conjugate retained 70% and 80% of its activity, respectively. In vivo 125I-labeled HPMA-co-MA-GG - β-L showed prolonged plasma concentration and greater tumor targeting than 125I-labeled β-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 - β-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.

Original languageEnglish
Pages (from-to)797-804
Number of pages8
JournalBioconjugate Chemistry
Issue number4
StatePublished - 2003


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