Background: Of various cancers, pancreatic cancer has been known as one of the most difficult-to-treat cancers, because of inhibition of the penetration of anticancer drugs into the cancer tissues resulting from the dense extracellular matrix (ECM).  On the other hand, ECM-degrading enzymes, such as hyaluronidase and bromelain, are known to degrade the ECM in the cancer tissue. However, poor blood half-lives of ECM-degrading enzymes result in its low accumulation in cancer.  Recently, we developed the novel reversible polyethylene glycol (PEG) modification technology which is able to improve blood retention of proteins without loss of the activity, and termed it “Self-assembly PEGylation Retaining Activity (SPRA)” technology.  Objective: In this study, we newly prepared PEGylated hyaluronidase and PEGylated bromelain through SPRA technology (SPRA-hyaluronidase and SPRA-bromelain), and evaluated their utility as drug delivery systems for pancreatic cancer.  Materials and Methods: Firstly, we prepared host molecules of SPRA-ECM-degrading enzymes, i.e. PEGylated b-cyclodextrin (PEG-b-CyD).  Next we prepared guest molecule of SPRA-ECM-degrading enzymes, i.e. adamantane-modified hyaluronidase (Ad-hyaluronidase) and bromelain (Ad-bromelain).  Both SPRA-ECM-degrading enzymes were prepared by mixing the PEG-b-CyD and Ad-hyaluronidase or Ad-bromelain in water.  The in vitro ECM-degrading activities of SPRA-ECM-degrading enzymes and in vivo antitumor activity of the combination of SPRA-ECM-degrading enzymes and antitomor agents were also evaluated.  RESULTS: Both SPRA-hyaluronidase and SPRA-bromelain showed high in vitro ECM-degrading activity.  In addition, SPRA-bromelain enhanced not only the accumulation of FITC-dextran (2 MDa) in the tumor, but also the in vivo antitumor activities of doxorubicin and DOXIL in a mouse model of pancreatic cancer.  CONCLUSION: These findings suggest that SPRA-ECM-degrading enzymes could be powerful tools for drug delivery in pancreatic cancer.

Key words: Pancreatic cancer, Cyclodextrin, Hyaluronidase, Bromelain, Polyethylene glycol