A xenograft model to evaluate the bone forming effects of sclerostin antibody in human bone derived from pediatric osteogenesis imperfecta patients

Abstract

Osteogenesis imperfecta (OI) is a rare and severe skeletal dysplasia marked by low bone mass and poor bone quality which is especially burdensome during childhood. Since clinical trials for pediatric OI are difficult, there is a widespread reliance on genetically modified murine models to understand the skeletal effects of emerging therapeutics. However a common model does not yet exist to understand how patient-specific genotype may influence treatment efficacy. Recently, sclerostin antibody (SclAb) has been introduced as a novel putative anabolic therapy for diseases of low bone mass, but effects in pediatric patients remain unexplored. In this study, we aim to establish a direct xenograft approach using OI patient-derived bone isolates which retain patientspecific genetic defects and cells residing in their intrinsic extracellular environment to evaluate the bone-forming effects of SclAb as a bridge to clinical trials.OI and age matched non-OI patient bone typically discarded as surgical waste during corrective orthopaedic procedures were collected, trimmed and implanted subcutaneously (s.c.) on the dorsal surface of 4-6-week athymic mice. A subset of implanted mice were evaluated at short (1 week), intermediate (4 week), and long-term (12 week) durations to assess bone cell survival and presence of donor bone cells in order to determine an appropriate treatment duration. Remaining implanted mice were randomly assigned to a two or four-week SclAb-treated (25 mg/kg s.c. 2QW) or untreated control group. Immunohistochemistry determined osteocyte and osteoblast donor/host relationship, TRAP staining quantified osteoclast activity, and TUNEL assay was used to understand rates of bone cell apoptosis at each implantation timepoint. Longitudinal changes of in vivo μCT outcomes and dynamic histomorphometry were used to assess treatment response and ex

The Osteocyte as the New Discovery of Therapeutic Options in Rare Bone Diseases

“…Sclerostin antibody romosozumab clears a phase III trial with satisfactory outcomes and already got approval for osteoporosis treatment ( 185 ). This sclerostin antibody has shown promising potential to treat osteogenesis imperfecta ( 127 , 186 , 187 ). Therefore, romosozumab might be beneficial to treat rare bone disease patients with low bone mass phenotypes, such as osteogenesis imperfecta, Wnt1 mutation, and PLS3 mutation.…”

Gene Expression Profile and Acute Gene Expression Response to Sclerostin Inhibition in Osteogenesis Imperfecta Bone

“…Our first description using this xenograft showed that cortical-derived bone with minimal human marrow cells at the time of implantation requires longer implantation duration to elicit a bone-forming response and that trabecularderived implanted patient tissue demonstrates a greater magnitude of response. (43) When the parallel cortical-derived bone tissue from OI3 and OI6 were treated acutely in vitro, we did observe an upregulation in osteoblast markers (particularly SP7) and an upregulation (compensatory response) in inhibitory regulators SOST and DKK1 indicating a treatment response. Future analysis using the proposed xenograft model should evaluate gene expression response analogous to the panel reported in the present study to determine the effects of SclAb in the hostderived microenvironment in comparison with the in vitro response.…”

“…We extended treatment to human bone from three OI patients in vivo using a xenograft model to evaluate the bone forming response to SclAb in an environment that more closely recapitulates the patient environment. (43) We implanted both cortical-derived (OI3 and OI6) and trabecular-derived tissue (OI4) and observed a greater magnitude of response to SclAb in trabecular-derived implants following 2 weeks of treatment in both μCT and histomorphometry outcomes. For OI4, trabecular-derived implants, this response appeared to attenuate following 4 weeks of treatment where μCT changes measured from pre-to posttreatment decreased in magnitude compared with the 2-week-treated implants from the same patient.…”

“…1B) using the methods described in detail in Surowiec and colleagues. (43) In short, 14 bone samples in total were implanted and mice were randomly assigned to an untreated or SclAb-treated group. SclAb treatment (25 mg/kg) was administered to the host (mouse) s.c. 2 times a week for either 2 or 4 weeks; then the mice were euthanized by CO 2 inhalation followed by bilateral Fig.…”

“…Because of the amount of donor bone tissue procured, a subset of bone tissue from patients OI3, OI4, and OI6 were collected to media and immediately implanted s.c. on the dorsal surface of an athymic mouse (Foxn nu [002019]; The Jackson Laboratory, Bar Harbor, ME, USA) representing our xenograft model to evaluate the effects of SclAb in a host‐derived system more closely recapitulating the in vivo microenvironment (Fig. 1 B ) using the methods described in detail in Surowiec and colleagues . In short, 14 bone samples in total were implanted and mice were randomly assigned to an untreated or SclAb‐treated group.…”