Improving the therapeutic potential of intravenous recombinant collagen VII as a protein replacement therapy for recessive dystrophic epidermolysis bullosa

Summary: We assessed the disease-modulating efficacy of intravenous infusion of PTR-01, a recombinant type VII collagen (C7) expressed in Chinese Hamster Ovary (CHO) cells, in a Phase 2 clinical trial involving 6 patients with recessive dystrophic epidermolysis bullosa (RDEB). While PTR-01 was well-tolerated and resulted in improvements in wound healing, no anchoring fibrils (AFs) were detected at the basement membrane zone of the skin, despite intact PTR-01 accumulation at the dermal-epidermal junction (DEJ). To understand why no AFs formed, we compared PTR-01 to C7 purified from dermal fibroblasts. On non-reducing western blots, additional bands of lower molecular weight were visible in PTR-01, suggesting reduced stability of CHO-derived PTR-01. Under reducing conditions, PTR-01 appeared as a doublet, and domain-specific antibodies revealed significant proteolytic maturation at the C-terminus. Proteomics of PTR-01 revealed altered glycosylation and a mixture of 40% wildtype C7 and 60% C7 with a D1033Y substitution in the FN type III domain of the NC1 domain. This variant acted dominantly negative, reducing the thermal stability of C7 and impairing binding to laminin-332 and collagen IV. Collectively, our data indicate that systemic delivery of C7 to the skin can be achieved and confer benefit in RDEB. However, the reduced affinity for DEJ ligands, lower thermal stability, and premature NC2 maturation likely impaired the ability of PTR-01 to assemble into AFs. We have since identified CHO clones that express only wild-type C7 and plan to develop this as an improved alternative to PTR-01. Edward Eid¹, Mark de Souza², Kelly Neelon², Jean Y. Tang¹, Mei Chen³, David Woodley³, Doug Keene⁴, Alexander Nyström⁵ 1. Dermatology, Stanford University School of Medicine, Stanford, CA, United States. 2. Bridgebio Pharma Inc, Palo Alto, CA, United States. 3. Dermatology, University of Southern California Keck School of Medicine, Los Angeles, CA, United States. 4. Shriners Hospitals for Children, Portland, OR, United States. 5. Dermatology, Albert-Ludwigs-Universitat Freiburg, Freiburg, BW, Germany. Translational Studies: Cell and Molecular Biology