Chemically modified forms of tetraiodothyroacetic acid (tetrac), an L-thyroxine derivative, have been shown to exert their anticancer activity at plasma membrane integrin αvβ3 of tumor cells. Via a specific hormone receptor on the integrin, tetrac-based therapeutic agents modulate expression of genes relevant to cancer cell proliferation, survival and energy metabolism. P-bi-TAT, a novel bivalent tetrac-containing synthetic compound has anticancer activity in vitro and in vivo against Glioblastoma Multiforme (GBM) and other types of human cancers. In the current study, microarray analysis was carried out on a primary culture of human GBM cells exposed to P-bi-TAT (10-6 tetrac equivalent) for 24 h. P-bi-TAT significantly affected expression of a large panel of genes implicated in cancer cell stemness, growth, survival, and angiogenesis. Recent interest elsewhere in ATP synthase as a target in GBM cells caused us to focus attention on expression of genes involved in energy metabolism. Significantly downregulated transcripts included multiple energy metabolism-related genes: electron transport chain genes ATP5A1 (ATP synthase 1), ATP51, ATP5G2, COX6B1 (cytochrome c oxidase subunit 6B1), NDUFA8 (NADH dehydrogenase [ubiquinone] FA8), NDUFV2I and other NDUF genes. The NDUF and ATP genes are also relevant to control of oxidative phosphorylation and transcription. Qualitatively similar actions of P-bi-TAT on expression of energy metabolism-linked genes were also detected in established human GBM and pancreatic cancer cell lines. In conclusion, acting at αvβ3 integrin, P-bi-TAT caused downregulation in human cancer cells of expression of a large number of genes involved in electron transport and oxidative phosphorylation. These observations suggest that cell surface thyroid hormone receptors on αvβ3 regulate expression of genes relevant to tumor cell stemness and energy metabolism.

Much evidence now indicates a direct crosstalk between thyroid hormones (THs) and the immune system. We previously showed that THs behave as anti-inflammatory agents in human leukemic THP-1 monocytes, but a potential neuroprotective effect of THs in microglia have been under-investigated. Microglia, the primary innate immune cells of the brain, play a pivotal role in the regulation of neuroinflammation and nongenomic integrin αvβ3-mediated action of THs appear to be involved. Integrin αvβ3 was highly expressed in activated BV-2 cells, while it was decreased by THs. In addition, THs facilitated wound healing in BV-2 murine microglia cells activated by lipopolysaccharide (LPS), through integrin αvβ3 and reactive oxygen species (ROS), with tetrac (a metabolite of TH) potentiated the inhibition of migration. Nitric oxide (NO) played a role with different mechanisms in the presence of either T3 or T4. Our data showed the capability of TH and analogues to modulate the M1-to-M2 microglial transition and suggest a new spectrum of actions in the central nervous system (CNS).