Novel bisphosphonate-based cathepsin K-triggered compound targets the enthesis without impairing soft tissue-to-bone healing

Brendan Y Shi; Varun Sriram; Shannon Y Wu; Dave Huang; Alexis Cheney; Melodie F Metzger; Oskar Sundberg; Karen M Lyons; Charles E McKenna; Ichiro Nishimura; Thomas J Kremen Jr

doi:10.3389/fbioe.2024.1308161

Novel bisphosphonate-based cathepsin K-triggered compound targets the enthesis without impairing soft tissue-to-bone healing

Front Bioeng Biotechnol. 2024 Feb 16:12:1308161. doi: 10.3389/fbioe.2024.1308161. eCollection 2024.

Authors

Affiliations

¹ Department of Orthopaedic Surgery, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, United States.
² Department of Orthopaedic Surgery, Cedars-Sinai Medical Center, Los Angeles, CA, United States.
³ Department of Chemistry, University of Southern California, Los Angeles, CA, United States.
⁴ Department of Molecular, Cellular, and Developmental Biology, University of California at Los Angeles, Los Angeles, CA, United States.
⁵ Weintraub Center for Reconstructive Biotechnology, School of Dentistry, University of California at Los Angeles, Los Angeles, CA, United States.

Abstract

Background: Osteoadsorptive fluorogenic sentinel 3 (OFS-3) is a recently described compound that contains a bone-targeting bisphosphonate (BP) and cathepsin K (Ctsk)-triggered fluorescence signal. A prior study in a murine Achilles repair model demonstrated its effectiveness at targeting the site of tendon-to-bone repair, but the intrinsic effect of this novel bisphosphonate chaperone on tendon-to-bone healing has not been previously explored. We hypothesized that application of this bisphosphonate-fluorophore cargo conjugate would not affect the biomechanical properties or histologic appearance of tendon-bone repairs. Materials and Methods: Right hindlimb Achilles tendon-to-bone repair was performed on 12-week old male mice. Animals were divided into 2 groups of 18 each: 1) Achilles repair with OFS-3 applied directly to the repair site prior to closure, and 2) Achilles repair with saline applied prior to closure. Repaired hindlimbs from 12 animals per group were harvested at 6 weeks for biomechanical analysis with a custom 3D-printed jig. At 4 and 6 weeks, repaired hindlimbs from the remaining animals were assessed histologically using H&E, immunohistochemistry (IHC) staining for the presence of Ctsk, and second harmonic generation (SHG) imaging to evaluate collagen fibers. Results: At 6 weeks, there was no significant difference in failure load, stiffness, toughness, or displacement to failure between repaired hindlimbs that received OFS-3 versus saline. There was no difference in tissue healing on H&E or Ctsk staining on immunohistochemistry between animals that received OFS-3 versus saline. Finally, second harmonic generation imaging demonstrated no difference in collagen fiber parameters between the two groups. Conclusion: OFS-3 did not significantly affect the biomechanical properties or histologic appearance of murine Achilles tendon-to-bone repairs. This study demonstrates that OFS-3 can target the site of tendon-to-bone repair without causing intrinsic negative effects on healing. Further development of this drug delivery platform to target growth factors to the site of tendon-bone repair is warranted.

Keywords: biomechanics; enthesis; growth factor delivery; rotator cuff repair; targeted delivery.

Abstract

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