Binucleated cell formation and oncogene expression after particulate matter exposure is preceded by microtubule disruption, dysregulated cell cycle, prolonged mitosis, and septin binding

Abstract

Several biopersistent high aspect ratio nanomaterials show pronounced pathogenic effects, from chronic lung inflammation and fibrosis to cancer. For example, asbestos fibers are classified as carcinogens, whereas the carcinogenicity of highly inflammatory multi-wall carbon nanotubes (MWCNTs), and TiO2 nanomaterials is still being evaluated. The exact early mechanisms of their pathogenicity towards inflammation and cancer remains uncertain, but it is likely not due to genotoxic or mutagenic activity. A proposed early mode of action that might lead to the formation of cancerous cells for asbestos fibers is the formation of binucleated and multinucleated cells, resulting in genetic instability. Here, we show that two high aspect ratio nanomaterials, MWCNTs and TiO2 nanotubes, which both induce chronic lung inflammation, induce very different cancer-related changes in vitro. TiO2 nanotubes - but not low aspect-ratio nanocubes of the same crystalline structure - disrupt microtubule organization and prolong mitosis, as well as deform nuclear shape, induce the formation of binucleated cells, and downregulate the tumour suppressor protein p53, whereas only the MWCNTs activate the stimulator of the interferon genes (STING) pathway, a hallmark of lung cancer. The observed differences in cellular responses to different high aspect ratio materials imply the need for assessing each nanomaterial individually with a broad range of tests rather than relying solely on a single marker or pathway, or even morphological or bulk chemical properties to infer possible carcinogenic properties.