IF a structure-based small-molecule orthosteric disruptor of the DKK1 CRD2–LRP6-E3 YWTD interface — designed as a cyclic peptidomimetic of the DKK1c loop (residues 222–231), incorporating pharmacophoric mimicry of Phe205/Trp206 (hydrophobic anchor) and Leu231/Ile233/Phe234 (hydrophobic finger) with a carboxylate bioisostere engaging Asp830 — delivered via intraperitoneal injection (10–30 mg/kg, 3×/week) or localized subcutaneous depot at target tissue sites,

is administered to aged (24-month-old) C57BL/6J male and female mice with documented bone mineral density loss, impaired muscle regeneration, and elevated circulating DKK1,

THEN competitive displacement of accumulated endogenous DKK1 protein from the LRP6-E3 YWTD propeller hydrophobic patch (Phe836, Trp875, Met877, Asp830) will be observed biochemically, accompanied by: (a) ≥30% restoration of LRP6 phosphorylation at Ser1490 in bone and skeletal muscle lysates; (b) ≥25% recovery of trabecular bone volume (BV/TV by μCT) within 12 weeks; (c) improved cardiotoxin-induced tibialis anterior regeneration index; and (d) reduced serum DKK1-LRP6 co-immunoprecipitation signal — all compared to vehicle-treated aged controls,

BECAUSE:

1. DKK1 is a secreted extracellular Wnt antagonist whose plasma and tissue levels rise significantly with aging, and chronically elevated DKK1 suppresses Wnt/β-catenin signaling in bone marrow stromal cells, satellite cells, and neural progenitors, constituting a form of accumulated extracellular functional damage that passively blocks tissue repair (DKK1 elevation in aged tissues suppresses Wnt)[described in structural and pharmacological context from the Evidence Set's druggability and HTS sections, PDB 3S8V structural framework].

2. The DKK1 CRD2 domain (residues ~180–266) engages LRP6-E3 through a defined, druggable hydrophobic pocket on the YWTD β-propeller top surface — residues Phe836, Trp875, Met877 provide the hydrophobic cradle and Asp830 provides a polar anchor — a site structurally validated by PDB 3S8V and computationally classified as druggable by SiteMap and FTMap probe-clustering analyses (LRP6-E3 pocket is druggable by FTMap/SiteMap consensus)[Evidence Set, Druggability Assessment section].

3. The DKK1 hotspot residues Phe205, Trp206 (hydrophobic anchor pair) and Leu231, Ile233, Phe234 (hydrophobic finger triad) from the DKK1c loop (222–231) constitute the energetic core of the interaction; a cyclic peptidomimetic or macrocyclic small molecule that reproduces these contacts while constraining the loop geometry into a receptor-competent conformation will competitively and orthosterically displace endogenous DKK1 from LRP6-E3 [DKK1 hotspot residues defined structurally][Evidence Set, Structural Characterization section; PDB 3S8V].

4. Prior validated hits (gallocyanine; IIIC3; NCI8642) from virtual screening and HTS campaigns targeting this interface confirm the pocket can accommodate drug-like small molecules and that DKK1-LRP6 displacement restores TOP...

SENS category: RepleniSENS