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Here, we report the clinical pharmacology data from LUMINA‐1 (NCT03188666), a Phase 2 trial that evaluated garetosmab (a monoclonal antibody against activin A) in patients with fibrodysplasia ossificans progressiva. Forty‐four patients were randomly assigned to intravenous 10 mg/kg of garetosmab or placebo every 4 weeks in a double‐blind 28‐week treatment period, followed by a 28‐week open‐label treatment period with garetosmab, and subsequent open‐label extension. Serum samples were obtained to assess pharmacokinetics (PK), immunogenicity, and bone morphogenetic protein 9 (BMP9). Comparative exposure–response analyses for efficacy and safety were performed with trough concentrations (Ctrough) of garetosmab prior to dosing. Steady‐state PK was reached 12‐16 weeks after the first dose of garetosmab, with mean (standard deviation) Ctrough of 105 ± 30.8 mg/L. Immunogenicity assessments showed anti‐garetosmab antibody formation in 1 patient (1/43; 2.3%); titers were low, and did not affect PK or clinical efficacy. Median concentrations of BMP9 in serum were approximately 40 pg/mL at baseline. There were no meaningful differences in PK or BMP9 concentration–time profiles between patients who did and did not experience epistaxis or death. The comparative exposure–response analyses demonstrated no association between Ctrough and efficacy or safety. PK findings were consistent with prior data in healthy volunteers and were typical for a monoclonal antibody administered at doses sufficient to saturate target‐mediated clearance. There were no trends that suggested patients with higher serum exposures to garetosmab were more likely to experience a reduction in heterotopic ossification or adverse events. Garetosmab is being further evaluated in the Phase 3 OPTIMA trial. [ABSTRACT FROM AUTHOR]

Introduction: Osteogenesis Imperfecta is a rare genetic connective tissue disorder, characterized by skeletal dysplasia and fragile bones. Currently only two mouse models have been reported for haploinsufficient (HI) mild Osteogenesis Imperfecta (OI); the Col1a1+/Mov13 (Mov13) and the Col1a1+/-365 mouse model. The Mov13 mice were created by random insertion of the Mouse Moloney leukemia virus in the first intron of the Col1a1 gene, preventing the initiation of transcription. Since the development of the Mov13 mice almost four decades ago and its basic phenotypic characterization in the 90s, there have not been many further studies. We aimed to extensively characterize the Mov13 mouse model in order to critically evaluate its possible use for preclinical studies of HI OI. Methods: Bone tissue from ten heterozygous Mov13 and ten wild-type littermates (WT) C57BL/6J mice (50% males per group) was analyzed at eight weeks of age with bone histomorphometry, micro computed tomography (microCT), 3-point bending, gene expression of different collagens, as well as serum markers of bone turnover Results: The Mov13 mouse presented a lower bone strength and impaired material properties based on our results of 3-point bending and microCT analysis respectively. In contrast, no significant differences were found for all histomorphometric parameters. In addition, no significant differences in Col1a1 bone expression were present, but there was a significant lower P1NP concentration, a bone formation marker, measured in serum. Furthermore, bone tissue of Mov13 mice presented significantly higher expression of collagens (Col1a2, Col5a1 and Col5a2), and bone metabolism markers (Bglap, Fgf23, Smad7, Edn1 and Eln) compared to WT. Finally, we measured a significantly lower Collai expression in heart and skin tissue and also determined a higher expression of other collagens in the heart tissue. Conclusion: Although we did not detect a significant reduction in Collai expression in the bone tissue, a change in bone structure and reduction in bone strength was noted. Regrettably, the variability of the bone phenotype and the appearance of severe lymphoma in adult Mov13 mice, does not favor their use for the testing of new long-term drug studies. As such, a new HI OI type 1 mouse model is urgently needed. [ABSTRACT FROM AUTHOR]

Fibrodysplasia ossificans progressiva (FOP) is a genetic disease characterized by heterotopic ossification (HO). The disease is caused by a mutation in the activin receptor type 1 (ACVR1) gene that enhances this receptor's responsiveness to Activin‐A. Binding of Activin‐A to the mutated ACVR1 receptor induces osteogenic differentiation. Whether Activin‐A also affects osteoclast formation in FOP is not known. Therefore we investigated its effect on the osteoclastogenesis‐inducing potential of periodontal ligament fibroblasts (PLF) from teeth of healthy controls and patients with FOP. We used western blot analysis of phosphorylated SMAD3 (pSMAD3) and quantitative polymerase chain reaction to assess the effect of Activin‐A on the PLF. PLF‐induced osteoclast formation and gene expression were studied by coculturing control and FOP PLF with CD14‐positive osteoclast precursor cells from healthy donors. Osteoclast formation was also assessed in control CD14 cultures stimulated by macrophage colony‐stimulating factor (M‐CSF) and receptor activator of nuclear factor kappa‐B ligand (RANK‐L). Although Activin‐A increased activation of the pSMAD3 pathway in both control and FOP PLF, it increased ACVR1, FK binding protein 12 (FKBP12), an inhibitor of DNA binding 1 protein (ID‐1) expression only in FOP PLF. Activin‐A inhibited PLF mediated osteoclast formation albeit only significantly when induced by FOP PLF. In these cocultures, it reduced M‐CSF and dendritic cell‐specific transmembrane protein (DC‐STAMP) expression. Activin‐A also inhibited osteoclast formation in M‐CSF and RANK‐L mediated monocultures of CD14+ cells by inhibiting their proliferation. This study brings new insight on the role of Activin A in osteoclast formation, which may further add to understanding FOP pathophysiology; in addition to the known Activin‐A‐mediated HO, this study shows that Activin‐A may also inhibit osteoclast formation, thereby further promoting HO formation. Fibrodysplasia ossificans progressiva (FOP) is a genetic disease characterized by heterotopic bone formation induced by enhanced responsiveness to Activin‐A. Activin‐A inhibits periodontal ligament fibroblasts‐mediated osteoclast formation in healthy donors and in patients with FOP. This inhibitory effect is probably mediated via a direct effect on the osteoclast precursors. [ABSTRACT FROM AUTHOR]

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder leading to progressive heterotopic ossifications (HO) of muscles, tendons, and ligaments, which can be induced by trauma or by surgery. Despite strong medical advice to the contrary, an FOP patient insisted on surgery to alleviate her complete trismus, which caused an unbearable impact on her quality of life (QOL). The entire trismus history of this FOP patient is presented. [18F]‐NaF position emission tomography/computed tomography (PET/CT) scans were introduced as an imaging method for heterotopic bone formation activity. To place our findings into context, a systematic review on jaw surgery in FOP was performed. After falling down the stairs, a 9‐year‐old patient developed mobility impairment of her left‐sided jaw. During the following 13 years bone scintigraphy showed persistent activity of the disease leading to progressive left‐sided zygomatico‐mandibular fusion by HO, resulting in complete trismus. Within 1 month after HO removal on the left side and a matching right coronoidectomy, [18F]‐NaF PET/CT demonstrated a substantial flare‐up activity followed by new HO in both masseter and temporalis muscles. Despite recurrent HO and trismus her QOL increased due to a stable increased interincisal opening of 5.5 mm. Although systematic review reveals a 100% risk of HO recurrence after jaw surgery, information on improved QOL is scarce. In conclusion, surgery in FOP may be beneficial for QOL despite new HO formation. Assessment of disease activity using [18F]‐NaF PET/CT is possible before HO is evident on CT and may serve as a new and quantitative marker of the disease. © 2017 The Authors. JBMR Plus Published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research. [ABSTRACT FROM AUTHOR]

Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare disorder, characterized by progressive heterotopic ossification (HO) and painful soft-tissue inflammatory flare-ups. This was a post hoc analysis from a phase 2 (NCT03188666) trial in which adults with FOP received intravenous anti-activin A antibody garetosmab 10 mg/kg or placebo every 4 wk over 28 wk (Period 1), followed by a 28-wk open-label treatment and extension (Periods 2 and 3). Here we describe flare-ups, their relationship to new HO lesions, and the impact of garetosmab on flare-ups. Volume of new HO lesions was measured by CT. Patient-reported flare-ups were defined by any 2 of the following: new onset of pain, swelling, joint stiffness, decrease in movement, or perceived presence of HO. Flare-ups were experienced by 71% (17/24) of placebo-treated patients, 59% (10/17) of whom developed a new HO lesion irrespective of flare-up location; 24% of flare-ups location-matched new HO lesions. Twenty-nine new HO lesions occurred in the placebo cohort by week 28, of which 12 (41%) occurred in the same location as new or ongoing flare-ups. A higher volume of newly formed heterotopic bone (week 28) occurred in placebo-treated patients who had experienced a prior flare-up vs those without (median [Q1:Q3] of 16.6 [12.0:31.1] vs 3.2 cm3). Garetosmab was previously shown to decrease patient-reported flare-up frequency in Period 1; here, garetosmab reduced the median (Q1:Q3) duration of patient-reported flares (15.0 [6.0:82.0] vs 48.0 [15.0:1.00] d) and the severity of flare-ups vs placebo. Frequency of corticosteroid use was numerically reduced in those treated with garetosmab (40.0%) vs placebo (58.3%). In this analysis, 71% of placebo-treated adults with FOP experienced flare-ups over 28 wk, which were associated with an increased volume of newly formed heterotopic bone. Garetosmab reduced the severity and duration of flare-ups, with effects sustained during the entire trial., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society for Bone and Mineral Research.)