Heat up, silence on: IDO1 gene silencing in THP-1-derived dendritic cells triggered by magnetic hyperthermia

Dendritic cells (DCs) are well-known antigen-presenting cells which have an important role in cancer immunomodulation due to the effective regulation of immune responses in the tumor microenvironment (TME). Indoleamine 2,3-dioxygenase 1 gene (IDO1) is upregulated in many types of cancers and associated with a poor prognosis, contributing to an immunosuppressive TME. IDO1 silencing in DCs is considered a promising new strategy in gene therapy owing to their capability to regulate T cells function and activation. This study focuses on the use of magnetic hyperthermia (MH) combined with bioorthogonal chemistry to promote siRNA transfection against IDO1 in THP-1-derived DCs. Magnetic nanoparticles (MNPs) functionalized with cyclooctyne moieties were attached by strain-promoted azide-alkyne cycloaddition to DCs membranes engineered to express artificial azide receptors. Upon the application of an alternating magnetic field, the MNPs generate heat and trigger the thermal disruption of the cell membrane. Results show that IDO1 gene expression decreases around 70% in THP-1-derived DCs, and that the MH-promoted transfection presents a silencing effect comparable to that attained with a gold standard Lipofectamine reagent, but with less cytotoxicity. Additionally, IDO1 silencing promotes the upregulation of mRNA levels of pro-inflammatory cytokines IL-6, TNF-α and IL-12A, and the downregulation of anti-inflammatory cytokine IL-10, providing a more immunogenic state which may lead to THP-1-derived DCs activation for future T cells antitumor response. Our findings reveal the potential of MH-mediated transfection to enhance the intracellular delivery of silencing moieties in cells difficult to transfect, such as DCs, as well as demonstrate the possibility of silencing IDO1 gene to overcome the immunosuppressive barrier imposed by the TME for cancer therapy.