Monthly Administration of a Novel PTH-Collagen Binding Domain Fusion Protein is Anabolic in Mice

Abstract

We synthesized fusion proteins of parathyroid hormone (PTH) (1-33) and the collagen binding domain of ColH (CBD) and tested them for anabolic bone activity in mice. Two fusion proteins were synthesized, linking the carboxy terminus of PTH(1-33) either directly to the amino terminal of the CBD or to the CBD through an adjacent ColH domain (PTH-PKD-CBD). Both PTH-CBD and PTH-PKD-CBD increased cAMP accumulation in cells stably transfected with the PTH/PTHrP receptor, and both peptides bound to type 1 collagen in flow-through assays. Distribution studies indicated that the PTH-CBD was concentrated in the bone and skin, tissues with abundant collagen and blood flow. Administration of 320 μg/kg PTH-CBD either weekly (for 8 weeks) or monthly (for 6 months) to 7-week-old C57BL/6J mice resulted in a sustained increase in bone mineral density (BMD) (15% for weekly studies, 13% for monthly studies; P < 0.05). PTH-PKD-CBD showed only 5% increases in BMD after weekly administration, and, as expected, neither weekly nor monthly PTH(1-34) affected BMD. PTH-CBD increased serum alkaline phosphatase levels. Importantly, there were no significant increases in serum calcium observed. Collectively, the data suggest that PTH-CBD has a sustained anabolic effect in bone with either weekly or monthly administration. This approach of targeted delivery of PTH to bone may show promise for the treatment of disorders of low bone mass, such as postmenopausal osteoporosis.

New therapeutic targets for osteoporosis: Beyond denosumab

“…Once monthly and once yearly administration of PTH fused to a collagen-binding domain was recently shown to extend its anabolic activity in mice [16,17]. The pharmacokinetic profile of a single dose of a novel oral PTH formulation has been evaluated in healthy postmenopausal women [18].…”

Treating osteoporosis by targeting parathyroid hormone to bone

“…PTH-CBD binds collagen and activates the PTH-PTHrP receptor [26]. Distribution studies using radiolabeled PTH-CBD indicate the drug is distributed primarily to bone and skin within 12 hours [26,27].…”

“…Distribution studies using radiolabeled PTH-CBD indicate the drug is distributed primarily to bone and skin within 12 hours [26,27]. We also examined the pharmacokinetics of PTH-CBD in normal female rats receiving molar equivalent doses of PTH(1–34) (80 ug/kg) or PTH-CBD (320 ug/kg).…”

Structural Comparison of ColH and ColG Collagen-Binding Domains from Clostridium histolyticum

“…It was uncertain as to how Ser896 in s3 could construct the dual calciumbinding site in place of the bidentate Asp. To address its structureand-function relationship applicable for various drug delivery applications (14)(15)(16)(17)(18), structural work on s3 was initiated. The structures of dissimilar CBD molecules in the metallopeptidase family M9B enabled us to compare and contrast their Ca 2ϩ sites and collagen-binding mechanism.…”