title: PDEPT: polymer-directed enzyme prodrug therapy. I. HPMA copolymer-cathepsin B and PK1 as a model combination.
abstract: Polymer-directed enzyme prodrug therapy (PDEPT) is a novel two-step antitumour approach using a combination of a polymeric prodrug and polymer-enzyme conjugate to generate cytotoxic drug selectively at the tumour site. In this study the polymeric prodrug N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer-Gly-Phe-Leu-Gly-doxorubicin conjugate PK1 (currently under Phase II clinical evaluation) was selected as the model prodrug, and HPMA copolymer-cathepsin B as a model for the activating enzyme conjugate. Following polymer conjugation (yield of 30-35%) HPMA copolymer-cathepsin B retained approximately 20-25% enzymatic activity in vitro. To investigate pharmacokinetics in vivo,(125)I-labelled HPMA copolymer-cathepsin B was administered intravenously (i.v.) to B16F10 tumour-bearing mice. HPMA copolymer-cathespin B exhibited a longer plasma half-life (free cathepsin B t(1/2alpha)= 2.8 h; bound cathepsin B t(1/2alpha)= 3.2 h) and a 4.2-fold increase in tumour accumulation compared to the free enzyme. When PK1 (10 mg kg(-1)dox-equiv.) was injected i.v. into C57 mice bearing subcutaneously (s.c.) palpable B16F10 tumours followed after 5 h by HPMA copolymer-cathepsin B there was a rapid increase in the rate of dox release within the tumour (3.6-fold increase in the AUC compared to that seen for PK1 alone). When PK1 and the PDEPT combination were used to treat established B16F10 melanoma tumour (single dose; 10 mg kg(-1)dox-equiv.), the antitumour activity (T/C%) seen for the combination PDEPT was 168% compared to 152% seen for PK1 alone, and 144% for free dox. Also, the PDEPT combination showed activity against a COR-L23 xenograft whereas PK1 did not. PDEPT has certain advantages compared to ADEPT and GDEPT. The relatively short plasma residence time of the polymeric prodrug allows subsequent administration of polymer-enzyme without fear of prodrug activation in the circulation and polymer-enzyme conjugates have reduced immunogenicity. This study proves the concept of PDEPT and further optimisation is warranted.
authors.affiliation: Centre for Polymer Therapeutics, The School of Pharmacy, University of London, 29-39 Brunswick Square, London WCIN IAX, UK.
authors.forename: R
authors.initials: R
authors.lastname: Satchi
authors.forename: T A
authors.initials: TA
authors.lastname: Connors
authors.forename: R
authors.initials: R
authors.lastname: Duncan
mesh_terms: D000818:Animals; D019540:Area Under Curve; D002401:Cathepsin B / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology*; D003131:Combined Modality Therapy; D004789:Enzyme Activation; D006207:Half-Life; D007262:Infusions, Intravenous; D008297:Male; D008545:Melanoma / Q000188:drug therapy / Q000662:veterinary; D051379:Mice; D008810:Mice, Inbred C57BL; D009374:Neoplasms, Experimental; D011109:Polymethacrylic Acids / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology*; D011355:Prodrugs; D012878:Skin Neoplasms / Q000188:drug therapy / Q000662:veterinary
chemical_list: D011109:Polymethacrylic Acids; D011355:Prodrugs; C011533:Duxon; D002401:Cathepsin B