Background: Lorecivivint (LOR) is a potential disease-modifying osteoarthritis (OA) drug in clinical development. It is a novel small-molecule inhibitor of Cdc2-Like Kinases (CLKs) and Dual-Specificity Tyrosine Phosphorylation-Regulated Kinases (DYRKs), intra-nuclear kinases involved in alternative splicing. Lorecivivint is thought to modulate Wnt/ inflammatory pathways and has demonstrated chondrogenic properties in vitro . It is not known whether LOR promotes cartilage regeneration in vivo .

Objectives: To investigate whether LOR promotes cartilage regeneration in vivo in a mouse model of joint surface injury that is permissive for endogenous healing.

Methods: Female mice carrying Gdf5-Cre and Cre-inducible tdTomato transgenes to label and trace endogenous joint reparative cells underwent unilateral surgical joint surface injury at 8-9 weeks of age. Mice were randomly divided into 3 groups. The first group (control) received 1 µl vehicle applied to the defect at time of surgery and 10 µl vehicle via intra-articular injection 1 week after surgery. The second group (1x LOR) received 1 µl vehicle at time of surgery and 10 µl of 9 µg/ml LOR via intra-articular injection 1 week after surgery. The third group (2x LOR) received 1 µl of 90 µg/ml LOR applied to the defect during surgery, and 10 µl of 9 µg/ml LOR via intra-articular injection 1 week after surgery. Cartilage repair was assessed histologically at 8 weeks after surgery by staining with Safranin O and Fast Green. Sections for staining were selected at set intervals and an average of 9 sections per knee (range: 5-13) were included in the analysis based on anatomical landmarks. Scoring of the repair tissue was performed independently by 3 researchers using an adaptation of the Wakitani scoring system with the following parameters: thickness of repair tissue (0-4), cell morphology (0-3), matrix staining (0-3), surface regularity (0-2), and integration (0-2), yielding a maximum summed score of 14 indicating poorest repair. Significant discrepancies between scorers were reviewed, and following discussion, amended as appropriate. Data from the 3 scorers were averaged, and expressed as the average of the 3 lowest (i.e. best repair) summed scores for each knee. All individuals involved in the study were blinded to treatment groups throughout all experimental procedures and analyses.

Results: Vehicle-treated joint surface defects (control group) typically showed a partial repair, with a predominantly fibrous-like tissue overlying bony tissue, as expected in this model. Analysis of summed repair scores identified a single statistical outlier in the 1x LOR group, based on Grubb’s outlier test at P<0.01, with a summed repair score of 13.8. After removal of the outlier, there was no statistically significant difference in summed repair scores between groups (P=0.20, Kruskal-Wallis test). However, mice receiving LOR showed a modest dose-dependent improvement in repair, with a summed repair score in the control group of 7.1 (95% CI 6.4 to 7.9, n=15), the 1x LOR group of 6.6 (95% CI 5.8 to 7.4, n=13), and the 2x LOR group of 5.9 (95% CI 4.9 to 7.0, n=16), which did not reach statistical significance (P=0.14 for 2x LOR versus control, Dunn’s post-test). Analysis of individual parameters showed that modest and statistically non-significant improvements in thickness, cell morphology, matrix staining and surface regularity contributed to the overall improved summed repair score in the 2x LOR compared to control group. The 2x LOR group included three mice with the best summed repair score (1.7, 3.1 and 3.2), showing cartilage-like repair tissue, while the best repair score in the 1x LOR group was 4.8 and in the control group was 5.0.

Conclusion: These findings indicate that LOR may promote cartilage repair, which could contribute to its OA-protective activity. Further studies with different dosing regimens are needed to confirm.

REFERENCES: NIL.

Acknowledgements: NIL.

Disclosure of Interests: Anke J Roelofs Biosplice Therapeutics Inc. (formerly Samumed LLC)., Susan M Clark: None declared, Jessica J McClure: None declared, Rebecca A Symons: None declared, Iain Cunningham: None declared, Megan Robertson: None declared, Alison Richmond: None declared, Fraser L Collins: None declared, Sarah Kennedy Biosplice Therapeutics Inc., Biosplice Therapeutics Inc., Jeyanesh R S Tambiah Biosplice Therapeutics Inc., Biosplice Therapeutics Inc., Cosimo De Bari UCB, Galapagos and Celltrion Healthcare, Biosplice Therapeutics Inc. (formerly Samumed LLC)