Polyinosinic/Polycytidylic Lipid Nanoparticles Enhance Immune Cell Infiltration and Improve Survival in the Glioblastoma Mouse Model

Glioblastoma (GBM) immunotherapy is particularly challenging due to the pro-tumorigenic microenvironment, marked by low levels and inactive immune cells. Toll-like receptor (TLR) agonists have emerged as potent immune adjuvants but failed to show improved outcomes in clinical trials when administered as a monotherapy. We hypothesize that a combined nanoparticulate formulation of TLR agonist and immunogenic cell death-inducing drug (doxorubicin) will synergize to induce improved GBM immunotherapy. Lipid nanoparticle (LNP) formulations of the TLR agonists CpG and polyinosinic/polycytidylic (pIpC), with and without Dox, were first prepared, achieving an encapsulation efficiency >75% and a size <140 nm. In vitro studies identified that LNP pIpC was superior to CpG at activating bone marrow-derived immune cell populations (dendritic cells and macrophages) with minimal toxicity. It was also observed that the pIpC formulation can skew macrophage polarization toward the antitumorigenic M1 phenotype and increase macrophage phagocytosis of cancer cells. Upon intratumoral administration, pIpC Dox LNPs led to significant immune cell infiltration and activation. In survival models, the inclusion of Dox into pIpC LNP improved mice survival compared to control. However, addition of Dox did not show significant improvement in mice's survival compared to singly formulated pIpC LNP. This study has illustrated the potential of pIpC LNP formulations in prospective GBM immunotherapeutic regimes. Future studies will focus on optimizing dosage regimen and/or combination with other modalities, including the standard of care (temozolomide), immune checkpoint blockade, or cancer vaccines.