Dmd064519 1882..1890

Follistatin 315 heparan sulfate-binding deficient mutant human IgG4 Fc fusion (FST-DHBS-Fc) is a follistatin (FST) based Fc fusion protein currently being developed as a novel therapy for several potential indications, including muscle wasting. Previous assessments of the pharmacokinetics and therapeutic activity of FST-DHBS-Fc have shown a close association of the exposure–response relationship. The current work builds upon these initial studies by investigating the glycosylation characteristics of FST-DHBS-Fc after recombinant expression and its impact on the pharmacokinetics in mice and Cynomolgus monkeys. The data presented indicate that FST-DHBSFc is heterogeneously glycosylated at the three putative sites in FST when recombinantly expressed in stably transfectedChinesehamster ovary cells. Such carbohydrate heterogeneity, especially with regards to sialic acid incorporation, directly results in sugar-dependent clearance in both mice and Cynomolgus monkeys. Examination of the pharmacokinetics of FST-DHBS-Fcmolecules containing variable sialic acid content in asialoglycoprotein receptor 1 (ASPGR-1) knockout mice supports the receptor’s role as part of the clearance mechanism of the molecules. Based on the evaluation of several variably sialylated lots ofmaterial in pharmacokinetic assessments, we define specifications for average sialic acid incorporation into FST-DHBS-Fc that result in limited sugar-mediated clearance. Taken together, these studies highlight the importance of establishing an early understanding of theglycosylation/pharmacokinetic relationshipsof FST-DHBS-Fc, which will provide a basis for future application toward optimal systemic drug delivery and dosing strategies.