PDEPT:  Polymer-Directed Enzyme Prodrug Therapy. 2. HPMA Copolymer-β-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.

Polymer–drug conjugates: towards a novel approach for the treatment of endrocine-related cancer

“…In this case, a polymer -enzyme conjugate is prepared (PEGylated enzymes are already in routine clinical use (Table 1)) that will hydrolyse selectively a polymer drug linker within the tumour interstitium. The concept of PDEPT was exemplified first by an HPMA copolymer cathepsin B-PK1 combination , and subsequently a non-mammalian enzyme linker combination HPMA copolymer-b-lactamase combined with HPMA-copolymer-glycine-glycine-cephalosporindoxorubicin (Satchi-Fainaro et al 2003). We have also shown that HPMA copolymer-bound phospholipases can also be used to modulate drug liberation from liposomes .…”

Targeted nanoparticles for detecting and treating cancer

“…Doxorubicin, linked through various bonds to HPMA, including amide and hydrazone [Rihova et al, 2001] bonds, has been widely investigated. Additionally, linkers containing enzymecleavable peptides have been employed in a polymerdirected enzyme pro-drug therapy (PDEPT) using peptides cleavable by cathepsin B [Satchi et al, 2001] and lactamase [Satchi-Fainaro et al, 2003]. Targeting of HPMA structures has been attempted with doxorubicin-functionalized particles using saccharides that promote liver uptake [Seymour et al, 1991] and mAb fragments [Ulbrich et al, 2004;Kovar et al, 2003].…”

Polymer Therapeutics Designed for a Combination Therapy of Hormone‐Dependent Cancer

“…Further developments in this field include chemotherapy with two-step polymer-drug combinations (e.g. polymer-directed enzyme prodrug therapy (PDEPT) [16] ).…”