Sequential application of small molecule therapy enhances chondrogenesis and angiogenesis in murine segmental defect
Charles H Rundle1,2, Gustavo A Gomez1, Sheila Pourteymoor1
1Musculoskeletal Disease Center, VA Loma Linda Healthcare System, Loma Linda, California, USA.
Abstract:
The increasing incidence of physiologic/pathologic conditions that impair the otherwise routine healing of endochondral bone fractures and the occurrence of severe bone injuries necessitate novel approaches to enhance clinically challenging bone fracture repair. To promote the healing of nonunion fractures, we tested an approach that used two small molecules to sequentially enhance cartilage development and conversion to the bone in the callus of a murine femoral segmental defect nonunion model of bone injury. Systemic injections of smoothened agonist 21k (SAG21k) were used to stimulate chondrogenesis through the activation of the sonic hedgehog (SHH) pathway early in bone repair, while injections of the prolyl hydroxylase domain (PHD)2 inhibitor, IOX2, were used to stimulate hypoxia signaling-mediated endochondral bone formation. The expression of SHH pathway genes and Phd2 target genes was increased in chondrocyte cell lines in response to SAG21k and IOX2 treatment, respectively. The segmental defect responded to sequential systemic administration of these small molecules with increased chondrocyte expression of PTCH1, GLI1, and SOX9 in response to SAG and increased expression of hypoxia-induced factor-1α and vascular endothelial growth factor-A in the defect tissues in response to IOX2. At 6 weeks postsurgery, the combined SAG-IOX2 therapy produced increased bone formation in the defect with the bony union over the injury. Clinical significance: This therapeutic approach was successful in promoting cartilage and bone formation within a critical-size segmental defect and established the utility of a sequential small molecule therapy for the enhancement of fracture callus development in clinically challenging bone injuries.
Insights
Sequential small molecule therapy using smoothened agonist 21k (SAG21k) and prolyl hydroxylase domain 2 inhibitor (IOX2) successfully promoted bone fracture healing. This approach enhanced cartilage and bone formation in a critical-size defect, aiding bony union.
Area of Science:
- Orthopedics
- Regenerative Medicine
- Pharmacology
Background:
- Bone fracture healing is often impaired by various conditions, necessitating advanced repair strategies.
- Nonunion fractures and severe bone injuries pose significant clinical challenges.
- Novel therapeutic approaches are crucial for enhancing bone repair in difficult cases.
Purpose of the Study:
- To evaluate a sequential small molecule therapy for promoting endochondral bone fracture repair.
- To enhance cartilage development and its conversion to bone in a nonunion fracture model.
Main Methods:
- Utilized a murine femoral segmental defect nonunion model.
- Administered smoothened agonist 21k (SAG21k) to stimulate chondrogenesis via the sonic hedgehog (SHH) pathway.
- Administered prolyl hydroxylase domain (PHD)2 inhibitor, IOX2, to stimulate hypoxia signaling and endochondral ossification.
Main Results:
- Sequential SAG21k and IOX2 treatment increased SHH pathway gene expression and hypoxia-induced factor-1α.
- The combined therapy led to increased chondrocyte expression of PTCH1, GLI1, and SOX9.
- Significant bone formation and bony union were observed in the defect at 6 weeks post-surgery.
Conclusions:
- Sequential small molecule therapy is effective in promoting cartilage and bone formation in critical-size bone defects.
- This approach shows utility in enhancing fracture callus development for challenging bone injuries.
- The study establishes a novel therapeutic strategy for bone fracture repair.
