Bone and Joint Tissue Penetration of the Staphylococcus-Selective Antibiotic Afabicin in Patients Undergoing Elective Hip Replacement Surgery.

Afabicin (formerly Debio 1450, AFN-1720) is a prodrug of afabicin desphosphono (Debio 1452, AFN-1252), a novel antibiotic in development which targets the staphylococcal enoyl-acyl carrier protein reductase (FabI) and exhibits selective potent antibacterial activity against staphylococcal species, including methicillin-resistant Staphylococcus aureus As part of clinical development in bone and joint infections, a distribution study in bone was performed in 17 patients who underwent elective hip replacement surgery. Patients received 3 doses of 240 mg afabicin orally (every 12 h) at various time points before surgery. Afabicin desphosphono concentrations were measured by liquid chromatography-tandem mass spectrometry in plasma, cortical bone, cancellous bone, bone marrow, soft tissue, and synovial fluid collected during surgery at 2, 4, 6, or 12 h after the third afabicin dose. The study showed good penetration of afabicin desphosphono into bone tissues, with mean area under the curve ratios for cortical bone-, cancellous bone-, bone marrow-, soft tissue-, and synovial fluid-to-total plasma concentrations of 0.21, 0.40, 0.32, 0.35, and 0.61, respectively. When accounting for the free fraction in plasma (2%) and synovial fluid (9.4%), the mean ratio was 2.88, which is indicative of excellent penetration and which showed that the afabicin desphosphono concentration was beyond the MIC90 of S. aureus over the complete dosing interval. These findings, along with preclinical efficacy data, clinical efficacy data for skin and soft tissue staphylococcal infection, the availability of both intravenous and oral formulations, and potential advantages over broad-spectrum antibiotics for the treatment of staphylococcal bone or joint infections, support the clinical development of afabicin for bone and joint infections. (This study has been registered at ClinicalTrials.gov under identifier NCT02726438.).

NK cells, but not NKT cells, are involved in Pseudomonas aeruginosa exotoxin A-induced hepatotoxicity in mice.

Pseudomonas aeruginosa exotoxin A (PEA) causes T cell- and Kupffer cell (KC)-dependent liver injury in mice. TNF-alpha as well as IL-18 and perforin are important mediators of liver damage following PEA injection. In this study, we focus on the role of NK and NKT cells in PEA-induced liver toxicity. Depletion of both NK and NKT cells by injection of anti-NK1.1 Ab as well as depletion of NK cells alone by anti-asialo GM1 Ab protected mice from PEA-induced hepatotoxicity, whereas mice lacking only NKT cells were susceptible. Additionally, we observed infiltration of NK cells, T cells, and neutrophils into liver parenchyma after injection of PEA. The number of NKT cells, however, remained unchanged. The increase in intrahepatic NK cells depended on KCs and the TNF-alpha-dependent up-regulation of the adhesion molecule VCAM-1 in the liver, but not on NKT cells. PEA also augmented the cytotoxicity of hepatic NK cells against typical NK target cells (YAC-1 cells). This effect depended on KCs, but not on TNF-alpha or NKT cells. Furthermore, only weak expression of MHC class I was detected on hepatocytes, which was further down-regulated in PEA-treated mice. This could explain the susceptibility of hepatocytes to NK cell cytolytic activity in this model. Our results demonstrate that NK cells, activated and recruited independently of NKT cells, contribute to PEA-induced T cell-dependent liver injury in mice.