gms | German Medical Science

Objectives: Although fracture treatment has considerably improved in recent decades, delayed fracture healing is still a relevant problem. So far, systemic drug therapies to enhance bone formation during fracture healing are limited to few substances, including teriparatide or modulators of Wnt signaling. We found previously that cyclin-dependent kinase 5 (Cdk5) was a strong suppressor of osteoblast differentiation in vitro and that its pharmacological inhibition with roscovitine increases bone mass by enhancing osteoblastogenesis in vivo (unpublished data). Here we investigated, whether the inhibition of Cdk5 with roscovitine improves bone formation in vivo during fracture healing in mice.

Methods: The animal experiment was approved by the Regierungspräsidium Tübingen, Germany (Nr. 1402). 12-week old male BALB/cAnNCrl mice received a unilateral femur osteotomy stabilized by an external fixator. Starting on the day of surgery, mice received injections of either vehicle (PBS/DMS/Solutol 17:1:2) or roscovitine solution (150mg/kg, Selleckchem) intraperitoneally every second day until the day of sacrifice (days 14 and 23, n=5-8 per group). Bone healing was evaluated using biomechanical testing (3-point bending), µCT analysis and histomorphometry. Statistics: Student's t-test (GraphPad Prism 9).

Results and Conclusion: On day 14 post fracture, histomorphometry revealed a significantly increased bone formation in the fracture callus of roscovitine treated mice (+ 87%, p<0.05) while the amount of soft tissue and cartilage was not significantly affected. On day 23, µCT analysis showed a significantly increased bone volume fraction (BV/TV + 22%, p<0.05), bone mineral density (BMD + 16%, p<0.05) and increased bending stiffness (+ 32%, p=0.08). Histomorphometrical analysis confirmed these findings with an increased bone formation (+29%, p=0.26) while the amount of cartilage and soft tissue stayed unaffected.

Our results demonstrate that systemic administration of Cdk5 inhibitor, roscovitine, improved bone formation during fracture healing in mice, confirming a crucial function of Cdk5 as a negative regulator of osteoblast differentiation. This study implicates that Cdk5 may be a promising drug target for the development of systemic osteoanabolic therapies, considering that inhibiting compounds of cyclin dependent kinases, including roscovitine, are already in clinical trials for various diseases.