Studies involving indium-containing particles (ICPs) indium phosphide (InP) and indium tin-oxide (ITO) were completed. Studies are in progress to determine if prolonged chronic exposure to sub-lethal concentrations (0.5 and/or 1 M) of soluble InCl3 can transform human lung epithelial (HPL-1D) cells into malignant cancer cells in vitro. The purpose of this carcinogenicity study is based on previous chronic inhalation data in rats and mice showing that InP and ITO particles were highly carcinogenic to the lung combined with the fact that there is currently no cancer data linked to indium exposure in humans. As of week 38, increased expression of matrix metalloproteinases (MMPs) by indium-treated lung cells and morphologic changes suggest that transformation is occurring. Additional assays to examine the acquisition of cancer cell characteristics will include cell proliferation, serum-independent growth, colony formation in soft agar, invasion (using matrigel) and gene expression (using RT-PCR). The NTP is also running a micronucleus assay and Ames test to assess the genotoxicity of InCl3.
