Nanomaterials are commonly defined as particles or fibers of less than 1 micron in diameter. For these reasons, they may be respirable in humans and have the potential, based upon their geometry, composition, size and transport or durability in the body, to cause adverse effects on human health, especially if they are inhaled at high concentrations. Rodent inhalation models to predict the toxicity and pathogenicity of nanomaterials are prohibitive in terms of time and expense. For these reasons, a panel of in vitro assays is described below. These include cell culture assays for cytotoxicity (altered metabolism, decreased growth, lytic or apoptotic cell death), proliferation, genotoxicity, and altered gene expression. The choice of cell type for these assays may be dictated by the procedure or endpoint selected. Most of these assays have been standardized in our laboratory using pathogenic minerals (asbestos, silica) and nonpathogenic particles (fine titanium dioxide or glass beads) as negative controls. The results of these in vitro assays should predict whether testing of selected nanomaterials should be pursued in animal inhalation models that simulate physiologic exposure to inhaled nanomaterials. Conversely, intrathoracic or intrapleural injection of nanomaterials into rodents can be misleading as they bypass normal clearance mechanisms, and nonpathogenic fibers and particles can test positively in these assays.

BackgroundPleural fibrosis and malignant mesotheliomas (MM) occur after exposures to pathogenic fibers, yet the mechanisms initiating these diseases are unclear.ResultsWe document priming and activation of the NLRP3 inflammasome in human mesothelial cells by asbestos and erionite that is causally related to release of IL-1β, IL-6, IL-8, and Vascular Endothelial Growth Factor (VEGF). Transcription and release of these proteins are inhibited in vitro using Anakinra, an IL-1 receptor antagonist that reduces these cytokines in a human peritoneal MM mouse xenograft model.ConclusionsThese novel data show that asbestos-induced priming and activation of the NLRP3 inflammasome triggers an autocrine feedback loop modulated via the IL-1 receptor in mesothelial cell type targeted in pleural infection, fibrosis, and carcinogenesis.

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Asbestos fibers cause chronic inflammation that may be critical to the development of malignant mesothelioma (MM). Two human MM cell lines (Hmeso, PPM Mill) were used in a SCID mouse xenograft model to assess time-dependent patterns of inflammation and tumor formation. After intraperitoneal (IP) injection of MM cells, mice were euthanized at 7, 14, and 30 days, and peritoneal lavage fluid (PLF) was examined for immune cell profiles and human and mouse cytokines. Increases in human MM-derived IL-6, IL-8, bFGF, and VEGF were observed in mice at 7 days postinjection of either MM line, and a striking neutrophilia was observed at all time points. Free-floating tumor spheroids developed in mice at 14 days, and both spheroids and adherent MM tumor masses occurred in all mice at 30 days. Results suggest that inflammation and cytokine production precede and may be critical to the development of MMs.

Purpose Malignant mesothelioma (MM) is a devastating disease with a need for new treatment strategies. In the present study we demonstrated the importance of ERK5 in MM tumor growth and treatment. Experimental Design ERK5 as a target for MM therapy was verified using mesothelial and mesothelioma cell lines as well as by xenograft SCID mouse models. Results We first showed that crocidolite asbestos activated ERK5 in LP9 cells and mesothelioma cell lines exhibit constitutive activation of ERK5. Addition of doxorubicin resulted in further activation of ERK5 in MM cells. ERK5 silencing increased DOX-induced cell death and DOX retention in MM cells. In addition, shERK5 MM lines exhibited both attenuated colony formation on soft agar and invasion of MM cells in vitro that could be related to modulation of gene expression linked to cell proliferation, apoptosis, migration/invasion and drug resistance as shown by microarray analysis. Most importantly, injection of shERK5 MM cell lines into SCID mice showed significant reduction in tumor growth using both subcutaneous and intraperitoneal models. Assessment of selected human cytokine profiles in peritoneal lavage fluid from IP shERK5 and control tumor-bearing mice showed that ERK5 was critical in regulation of various proinflammatory (RANTES/CCL5, MCP-1) and angiogenesis related (IL-8, VEGF) cytokines. Finally, use of doxorubicin and cisplatin in combination with ERK5 inhibition showed further reduction in tumor weight and volume in the IP model of tumor growth. Conclusion ; ERK5 inhibition in combination with chemotherapeutic drugs is a beneficial strategy for combination therapy in MM patients.