CSF1/CSF1R Signaling Inhibitor Pexidartinib (PLX3397) Reprograms Tumor-Associated Macrophages and Stimulates T-cell Infiltration in the Sarcoma Microenvironment.

Colony-stimulating factor 1 (CSF1) is a primary regulator of the survival, proliferation, and differentiation of monocyte/macrophage that sustains the protumorigenic functions of tumor-associated macrophages (TAMs). Considering current advances in understanding the role of the inflammatory tumor microenvironment, targeting the components of the sarcoma microenvironment, such as TAMs, is a viable strategy. Here, we investigated the effect of PLX3397 (pexidartinib) as a potent inhibitor of the CSF1 receptor (CSF1R). PLX3397 was recently approved by the Food and Drug Administration (FDA) to treat tenosynovial giant cell tumor and reprogram TAMs whose infiltration correlates with unfavorable prognosis of sarcomas. First, we confirmed by cytokine arrays of tumor-conditioned media (TCM) that cytokines including CSF1 are secreted from LM8 osteosarcoma cells and NFSa fibrosarcoma cells. The TCM, like CSF1, stimulated ERK1/2 phosphorylation in bone marrow-derived macrophages (BMDMs), polarized BMDMs toward an M2 (TAM-like) phenotype, and strikingly promoted BMDM chemotaxis. In vitro administration of PLX3397 suppressed pERK1/2 stimulation by CSF1 or TCM, and reduced M2 polarization, survival, and chemotaxis in BMDMs. Systemic administration of PLX3397 to the osteosarcoma orthotopic xenograft model significantly suppressed the primary tumor growth and lung metastasis, and thus improved metastasis-free survival. PLX3397 treatment concurrently depleted TAMs and FOXP3+ regulatory T cells and, surprisingly, enhanced infiltration of CD8+ T cells into the microenvironments of both primary and metastatic osteosarcoma sites. Our preclinical results show that PLX3397 has strong macrophage- and T-cell-modulating effects that may translate into cancer immunotherapy for bone and soft-tissue sarcomas.

An Alternative Macrophage Activation Pathway Regulator, CHIT1, May Provide a Serum and Synovial Fluid Biomarker of Periprosthetic Osteolysis.

BACKGROUND: Periprosthetic osteolysis (PPO) is a frequent indication for total hip replacement (THR) failure. Currently, PPO diagnosis occurs in advanced stages that often necessitate complex revisions due to bone loss. PPO biomarkers could facilitate earlier diagnosis. Alternative macrophage activation pathway regulators, chitotriosidase (CHIT1) and CC chemokine ligand 18 (CCL18), have increased periprosthetic expression in patients undergoing revision THR for osteolysis. We hypothesized that synovial fluid and serum levels of CHIT1 and CCL18 would be increased in patients undergoing revision THR for PPO versus controls without osteolysis. METHODS: In this prospective case-control study, 60 patients undergoing revision metal-on-polyethylene THR at Hospital for Special Surgery were screened preoperatively from January 2013 to December 2014. Twenty "osteolysis" patients who underwent revision for PPO (based on imaging and operative reports) and 10 "control" patients (with stable implants) who underwent revision for recurrent dislocation or a mechanical etiology were included. Among osteolysis and control patients, 11/20 and 4/10 were male; average age was 68 and 63 years, respectively; 9/20 and 3/10 had cemented femoral components; and average implant longevity was 15 and 5 years, respectively. Preoperative serum and intraoperative synovial fluid samples were collected. CHIT1 and CCL18 were quantified via enzyme-linked immunosorbent assay. Significance was assessed via nonparametric Mann-Whiney U test. RESULTS: CHIT1 was significantly increased in both synovial fluid (3727 versus 731 nanomoles [nM]) and serum (98 versus 39 nM) in the osteolysis versus control patients. CCL18 levels were also significantly increased in osteolysis versus control patients' synovial fluid (425 versus 180 nM) but not their serum. CONCLUSIONS: In this prospective case-control study, CHIT1 was identified as a novel synovial fluid and serum biomarker of PPO. CHIT1 expression is induced during macrophage activation in response to wear debris. CHIT1 monitoring may facilitate early diagnosis of THR PPO. Furthermore, CHIT1 may represent a novel therapeutic target for PPO.

Are there biological markers for wear or corrosion? A systematic review.

BACKGROUND: Identification of biomarkers associated with wear and tribocorrosion in joint arthroplasty would be helpful to enhance early detection of aseptic loosening and/or osteolysis and to improve understanding of disease progression. There have been several new reports since the last systematic review (which covered research through mid-2008) justifying a new assessment. QUESTIONS/PURPOSES: We sought to determine which biomarkers have the most promise for early diagnosis and monitoring of aseptic loosening and/or osteolysis related to wear or corrosion in total joint arthroplasty. METHODS: We performed a systematic review using MEDLINE and EMBASE databases, covering the period through December 2013, and identified 1050 articles. We restricted the definition of biomarker to biomolecules and imaging parameters useful for diagnosis and monitoring of disease progression, only including articles in English. We chose 65 articles for full review, including 44 from the original search and 21 from subsequent hand searches. We used the 22 articles in which patients with total joint arthroplasty who had aseptic loosening and/or periimplant osteolysis unrelated to sepsis had been compared with patients with total joint arthroplasty with stable implants. There were 90 comparisons of these two patient populations involving 35 different biomarkers. RESULTS: Diagnostic accuracy was assessed in nine of the 90 comparisons with the highest accuracy found for tartrate-resistant acid phosphatase 5b (0.96), although a separate comparison for this biomarker found a lower accuracy (0.76). Accuracy of > 0.80 was also found for crosslinked n-telopeptide of type I collagen, osteoprotegerin, and deoxypyridinoline. The most studied markers, tumor necrosis factor-α and interleukin-1ß, were found to differ in the affected and control groups in < 30% of the comparisons. Thirty of the 35 biomarkers were studied in four or fewer separate comparisons with nearly half of the biomarkers (17) studied in only one comparison. Many of the comparisons were not able to eliminate a number of confounding variables, and there was only one prospective study. CONCLUSIONS: Currently, there are no validated biomarkers for early diagnosis and monitoring of the biological sequelae of wear or tribocorrosion, although there are some promising leads, including markers of bone turnover.

Annexin A2 binds to endosomes following organelle destabilization by particulate wear debris.

Endosomal functions are contingent on the integrity of the organelle-limiting membrane, whose disruption induces inflammation and cell death. Here we show that phagocytosis of ultrahigh molecular weight polyethylene particles induces damage to the endosomal-limiting membrane and results in the leakage of cathepsins into the cytosol and NLRP3-inflammasome activation. Annexin A2 recruitment to damaged organelles is shown by two-dimensional DIGE protein profiling, endosomal fractionation, confocal analysis of endogenous and annexin A2-GFP transfected cells, and immunogold labelling. Binding experiments, using fluorescent liposomes, confirms annexin A2 recruitment to endosomes containing phagocytosed polyethylene particles. Finally, an increase in cytosolic cathepsins, NLRP3-inflammasome activation, and IL-1 production is seen in dendritic cells from annexin A2-null mice, following exposure to polyethylene particles. Together, the results indicate a functional role of annexin A2 binding to endosomal membranes following organelle destabilization.