title: Effect of different chemical bonds in pegylation of zinc protoporphyrin that affects drug release, intracellular uptake, and therapeutic effect in the tumor.
abstract: Pegylated zinc protoporphyrin (PEG-ZnPP) is a water-soluble inhibitor of heme oxygenase-1. In this study, we prepared two types of PEG-ZnPP conjugates with different chemical bonds between PEG and ZnPP, i.e., ester bonds and ether bonds, where both conjugates also contain amide bonds. Cleavability of these bonds in vitro and in vivo, especially cancer tissue, and upon intracellular uptake, was investigated in parallel with biological activities of the conjugates. Each conjugate showed different cleavability by plasma esterases and tumor proteases, as revealed by HPLC analyses. PEG-ZnPP with ester bond (esPEG-ZnPP) was more sensitive than PEG-ZnPP with ether bond (etPEG-ZnPP) for cleavage of PEG chains. etPEG-ZnPP showed no cleavage of PEG chains and had lower intracellular uptake and antitumor activity than did esPEG-ZnPP. The degradation of esPEG-ZnPP appeared to be facilitated by both serine and cysteine proteases in tumor tissues, whereas it was significantly slower in normal organs except the liver. Depegylated products such as free ZnPP had higher intracellular uptake than did intact PEG-ZnPP. We also studied hydrolytic cleavage by blood plasma of different animal species; mouse plasma showed the fastest cleavage whereas human plasma showed the slowest. These results suggest that ester-linked conjugates manifest more efficient cleavage of PEG, and greater yield of the active principle from the conjugates in tumor tissues than in normal tissues. More efficient intracellular uptake and thus an improved therapeutic effect with ester-linked conjugates are thus anticipated with fain stability, particularly in human blood.
authors.affiliation: Institute for Drug Delivery Science, Sojo University, Kumamoto, Japan; Laboratory of Pharmacokinetics, Faculty of Pharmaceutical Sciences, Sojo University, Kumamoto, Japan; Laboratory of Microbiology and Oncology, Faculty of Pharmaceutical Sciences, Sojo University, Kumamoto, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Tsukigawa
authors.affiliation: Institute for Drug Delivery Science, Sojo University, Kumamoto, Japan; Laboratory of Microbiology and Oncology, Faculty of Pharmaceutical Sciences, Sojo University, Kumamoto, Japan.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Nakamura
authors.affiliation: Institute for Drug Delivery Science, Sojo University, Kumamoto, Japan; Laboratory of Microbiology and Oncology, Faculty of Pharmaceutical Sciences, Sojo University, Kumamoto, Japan. Electronic address: fangjun@ph.sojo-u.ac.jp.
authors.forename: Jun
authors.initials: J
authors.lastname: Fang
authors.affiliation: Institute for Drug Delivery Science, Sojo University, Kumamoto, Japan; Laboratory of Pharmacokinetics, Faculty of Pharmaceutical Sciences, Sojo University, Kumamoto, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Otagiri
authors.affiliation: Institute for Drug Delivery Science, Sojo University, Kumamoto, Japan. Electronic address: hirmaeda@ph.sojo-u.ac.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Maeda
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry* / Q000494:pharmacology*; D045744:Cell Line, Tumor; D055598:Chemical Phenomena; D016503:Drug Delivery Systems / Q000379:methods; D065546:Drug Liberation / Q000502:physiology*; D019073:HT29 Cells; D006801:Humans; D020014:K562 Cells; D008297:Male; D008665:Metalloporphyrins / Q000737:chemistry* / Q000494:pharmacology*; D051379:Mice; D011092:Polyethylene Glycols / Q000737:chemistry* / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D008665:Metalloporphyrins; C476103:pegylated zinc protoporphyrin; D011092:Polyethylene Glycols
keywords: Antitumor effect; Intracellular uptake; PEG-cleavability; PEG-dilemma; PEG–ZnPP; Tumor proteases