Glycobiology Advance Access originally published online on September 26, 2003
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Glycobiology vol 14 no 1 pp. 27-37, 2004
© Oxford University Press 2004; all rights reserved.
Glycoforms obtained by expression in Pichia pastoris improve cancer targeting potential of a recombinant antibody-enzyme fusion protein
3 Mass Spectrometry Facility, Department of Pharmaceutical Chemistry, School of Pharmacy, University of California San Francisco, San Francisco, CA 94143-0446; and 4 Cancer Research U.K. Targeting and Imaging Group, Department of Oncology, Royal Free and University College Medical School, University of London, Royal Free Campus, Rowland Hill Street, London, NW3 2PF, U.K.
Received on June 18, 2003; revised on August 31, 2003; accepted on August 31, 2003
MFE-CP is a recombinant antibody-enzyme fusion protein used for antibody-mediated delivery of an enzyme to cancer deposits. After clearance from normal tissues, the tumor-targeted enzyme is used to activate a subsequently administered prodrug to give a potent cytotoxic in the tumor. MFE-CP localizes to cancer deposits in vivo, but we propose that its therapeutic potential could be improved by N-glycosylation, obtained by expression in Pichia pastoris. Glycosylation could enhance clearance from healthy tissue and result in better tumor:normal tissue ratios. To test this, glycosylated MFE-CP was expressed and purified from P. pastoris. The resultant MFE-CP fusion protein was enzymatically active and showed enhanced clearance from normal tissues in vivo. Furthermore, it showed effective tumor localization. This favorable glycosylation pattern was analyzed by tandem mass spectrometry. High-resolution, high-detection sensitivity collision-induced dissociation experiments proved essential for this task. Results showed that of the three potential N-glycosylation sites only two were consistently occupied with oligomannose structures. Asn-442 appeared the most heterogeneously populated with oligomannose carbohydrates extending from 5 to 13 units in length. Asn-484 was found only in its nonglycosylated form. There was less heterogeneity at Asn-492, which was glycosylated with oligosaccharide structures ranging from 8 to 10 mannose units. Nonglycosylated forms of Asn-442 and Asn-492 were not observed.
1 Present address: Ludger Ltd., Littlemore Park, Oxford, OX4 4SS, U.K.
2 To whom correspondence should be addressed; email: k.chester{at}ucl.ac.uk
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