In silico discovery of quinoxaline derivatives as novel LRP5/6-sclerostin interaction inhibitors.

The Wnt/ß-catenin signaling pathway is a key regulator of bone homeostasis. Sclerostin act as an extracellular inhibitor of canonical Wnt signaling through high-affinity binding to the Wnt co-receptor LRP5/6. Disruption of the interaction between LRP5/6 and sclerostin has been recognized as a therapeutic target for osteoporosis. We identified a quinoxaline moiety as a new small-molecule inhibitor of the LRP5/6-sclerostin interaction through pharmacophore-based virtual screening, docking simulations, and in vitro assays. Structure-activity relationship studies and binding mode hypotheses were used to optimize the scaffold and yield the compound BMD4503-2, which recovered the downregulated activity of the Wnt/ß-catenin signaling pathway by competitive binding to the LRP5/6-sclerostin complex. Overall, this study showed that the optimized structure-based drug design was a promising approach for the development of small-molecule inhibitors of the LRP5/6-sclerostin interaction. A novel scaffold offered considerable insights into the structural basis for binding to LRP5/6 and disruption of the sclerostin-mediated inhibition of Wnt signaling.

The bone anabolic effects of irisin are through preferential stimulation of aerobic glycolysis.

Irisin, a recently identified hormone secreted by skeletal muscle in response to exercise, exhibits anabolic effects on the skeleton primarily through the stimulation of bone formation. However, the mechanism underlying the irisin-stimulated anabolic response remains largely unknown. To uncover the underlying mechanism, we biosynthesized recombinant irisin (r-irisin) using an Escherichia coli expression system and used it to treat several osteoblast cell types. Our synthesized r-irisin could promote proliferation and differentiation of osteoblasts as evidenced by enhanced expression of osteoblast-specific transcriptional factors, including Runt-related transcription factor-2 (Runx2), Oster (Osx), as well as early osteoblastic differentiation markers such as alkaline phosphatase (Alp) and collagen type I alpha 1 (Col1a1). Furthermore, we showed that the promotion of r-irisin on the proliferation and differentiation of osteoblast lineage cells are preferentially through aerobic glycolysis, as indicated by the enhanced abundance of representative enzymes such as lactate dehydrogenase A (LDHA) and pyruvate dehydrogenase kinase 1 (PDK1), together with increased lactate levels. Suppression of r-irisin-mediated aerobic glycolysis with Dichloroacetate blunted its anabolic effects. The favorite of the aerobic glycolysis after r-irisin treatment was then confirmed in primary calvarial cells by metabolic analysis using gas chromatography-mass spectrometry. Thus, our results suggest that the anabolic actions of r-irisin on the regulation of osteoblast lineage cells are preferentially through aerobic glycolysis, which may help to develop new irisin-based bone anabolic agents.

Cyclized Oligopeptide Targeting LRP5/6-DKK1 Interaction Reduces the Growth of Tumor Burden in a Multiple Myeloma Mouse Model.

PURPOSE: Dickkopf 1 (DKK1) has been extensively investigated in mouse models of multiple myeloma, which results in osteolytic bone lesions. Elevated DKK1 levels in bone marrow plasma and serum inhibit the differentiation of osteoblast precursors. Present pharmaceutical approaches to target bone lesions are limited to antiresorptive agents. In this study, we developed a cyclized oligopeptide against DKK1-low density lipoprotein receptor-related protein (LRP) 5/6 interaction and tested the effects of the oligopeptide on tumor burden. MATERIALS AND METHODS: A cyclized oligopeptide based on DKK1-LRP5/6 interactions was synthesized chemically, and its nuclear magnetic resonance structure was assessed. Luciferase reporter assay and mRNA expressions of osteoblast markers were evaluated after oligopeptide treatment. MOPC315.BM.Luc cells were injected into the tail vein of mice, after which cyclized oligopeptide was delivered subcutaneously 6 days a week for 4 weeks. RESULTS: The cyclized oligopeptide containing NXI motif bound to the E1 domain of LRP5/6 effectively on surface plasmon resonance analysis. It abrogated the Wnt-ß-catenin signaling inhibited by DKK1, but not by sclerostin, dose dependently. RT-PCR and alkaline phosphatase staining showed increased expressions of osteoblast markers according to the treatment concentrations. Bioluminescence images showed that the treatment of cyclized oligopeptide reduced tumor burden more in oligopeptide treated group than in the vehicle group. CONCLUSION: The cyclized oligopeptide reported here may be another option for the treatment of tumor burden in multiple myeloma.

A Novel Human PTH Analog [Cys25]hPTH(1-34) Restores Bone Mass in Ovariectomized Mice.

CONTEXT: Recently, an arginine-to-cysteine homozygous mutation at position 25 in mature PTH was reported in a Korean patient with hypoparathyroidism. OBJECTIVE: To clarify whether the high bone mass phenotype observed in this patient was related to the hypoparathyroidism itself or to chronic elevation of mutant PTH. METHODS: A series of in vitro and in vivo experiments were performed in MC3T3E1, ROS 17/2.8, and SAOS2 cells treated with human (h)PTH(1-34), Cys25hPTH(1-34), Ala1Cys25hPTH(1-34), and Bpa1Cys25hPTH(1-34). The peptides were then sc delivered to ovariectomized mice as daily single injections. RESULTS: Compared with hPTH(1-34) and Ala1Cys25hPTH(1-34), treatment with Cys25hPTH(1-34) or Bpa1Cys25hPTH(1-34) resulted in decreases in the cAMP response and promoter-cAMP-response element luciferase reporter activity. Although the cAMP response was sustained with hPTH(1-34) in MC3T3E1 cells, such response was not observed with the other mutated peptides. Meanwhile, all PTH analogues exhibited ERK phosphorylation and cytoplasmic Ca++ signals comparable with hPTH(1-34). On microcomputed tomography analyses, trabecular and cortical bone parameters improved after 6 weeks of respective treatments as follows: hPTH(1-34) (80 µg/kg) = Ala1Cys25hPTH(1-34) (80 µg/kg) = Cys25hPTH(1-34) (80 µg/kg) > Bpa1Cys25hPTH(1-34) (80 µg/kg) > hPTH(1-34) (40 µg/kg). The increment of RANKL to OPG mRNA ratio in the MC3T3E1 cells after 6 hours of treatment of Cys25hPTH(1-34), AL1Cys25hPTH(1-34), and Bpa1Cys25hPTH(1-34) was less than that was obtained after hPTH(1-34) treatment. On bone histomorphometric analysis, AL1Cys25hPTH(1-34) increased the bone formation rate in both trabecular and periosteal bones compared with the control group. CONCLUSION: The high bone mass phenotype observed in this patient with hypoparathyrodism caused by a Cys mutation at the 25th residue of hPTH(1-84) may have arisen from both direct and indirect effects exerted by the mutant PTH itself on bone.