Control of endosomal Toll-like receptor (TLR) signaling by nanoparticles and applications in cancer therapy

Abstract

Toll-like receptors (TLRs) play critical roles in the activation of innate and adaptive immune responses. TLRs 3 and 9 are expressed in endosomal and lysosomal compartments and recognize nucleic acids. The activation of TLRs 3 and 9 leads to two distinct signaling pathways resulting in the nuclear translocation of nuclear factor kappa B (NF-κB) and interferon regulatory factor 7 (IRF-7). The NF-κB and IRF-7 pathways induce pro-inflammatory cytokines (such as IL-6) and type I interferons (IFNs such as IFN-α), respectively. Pro-inflammatory cytokines are associated with tumorigenesis, whereas type I IFNs can induce anticancer effects. In this work, the effects of biomaterial size and composition on the cytokine secretion profile of cells were studied. The effect of biomaterial size was evaluated by adsorbing TLR9 ligands onto micro- and sub-micro polystyrene particles. The cytokine profile was correlated with the pH of endosomes and lysosomes that internalized particles of different sizes were exposed to. The effect of biomaterial composition was evaluated by incorporating TLR3 and TLR9 ligands into polymer blend nanoparticles of precise polymer compositions. The polymer composition could be tuned to induce distinct cytokine profiles. Interestingly, the terpolymer blend was able to present TLR ligands in a manner that resulted in IFN-α induction only. Such control of TLR signaling provided the motivation for applications in breast cancer therapy. The efficacy of terpolymer blend particles containing TLR ligands was assessed for triple negative breast cancer cell lines. The treatment efficacy was determined by effects on cell proliferation, cell death, cell migration, and cell expression of CD44, a marker for a metastastic phenotype. TLR9 ligands encapsulated in terpolymer particles were not an effective treatment for both MDA-MB-231 and BT-20 cell lines. TLR3 ligands encapsulated in terpolymer particles were the most effective treatment for BT-20 cells, but were ineffective for MDA-MB-231 cells. The treatment efficacy was correlated with the level of type I IFNs.