Designing dedicated rapamycin nanoparticles for articular vectorization: A holistic pharmacological approach

International audienceIntroduction: Rapamycin, an immunosuppressant, is a mTOR inhibitor leading to autophagy restoration. It is a candidate (10 μM) for experimental intra-articular (IA) treatment of osteoarthritis (OA), autophagy being defective in OA. Material and methods: We performed in vitro cytotoxicity on human chondrocytes, synoviocytes, and mesenchymal stem cells (MSCs) after 24 h exposure in hypoxia and normoxia with various rapamycin concentrations (10 nM to 100 μM). We then evaluated autophagic (beclin1 and Atg7) and catabolic (MMP13) genes with 10 μM rapamycin exposure for 24 h. We also developed rapamycin-loaded nanoparticles (NPs) for IA injection to assess NPs' cytotoxicity vs free rapamycin. We finally studied in vivo pharmacokinetic parameters of free (IV & IA) or NPs-loaded rapamycin (IA) (10 μM) injections in blood and synovial tissue in rat knees: AUC, T1/2, and MRT. Results: In vitro, we observed the concentrationdependent toxicity of free rapamycin for chondrocytes, synoviocytes, and MSCs. The IC50 was: 68.7, 79.7, and 79.7 μM in normoxia and 79.1, 29.9 and 38.5 μM in hypoxia, respectively. No difference was observed for autophagic genes in the three cellular types, but the IL1β-induced MMP13 level decreased. Rapamycin NPs showed similar dose-dependent toxicity on articular cells. In vivo, we determined (10 μM) an AUC higher for IV free rapamycin than for IA injection (AUCIA free and AUCIA NP), with respectively 4248, 28, and 74 μg/ min/L in blood. We observed a difference between AUCIA free and AUCIA NP (3735 and 10513 μg/min/L) concerning synovium. T1/2 and MRT were higher after NPs than free rapamycin injections: 57.8-5.0 h, vs. 80.6-5.5 h, respectively. Histology revealed no knee injury. Discussion/Conclusion: In vitro, rapamycin (10 μM) did not induce articular cytotoxicity and reduced IL1β's phlogistic effects. Rapamycin NPs did not induce cytotoxicity on articular cells at 10 μM. In vivo, IA administration of 10 μM rapamycin NPs increased its local residency vs. free rapamycin with lower systemic diffusion