Comparison of the uptake of untargeted and targeted immunostimulatory nanoparticles by immune cells in the microenvironment of metastatic breast cancer

To alter the immunosuppressive tumor microenvironment (TME), we developed an immunostimulatory nanoparticle (NP) to reprogram a tumor's dysfunctional and inhibitory antigen-presenting cells (APCs) into properly activated APCs that stimulate tumor-reactive cytotoxic T cells. Importantly, systemic delivery allowed NPs to efficiently utilize the entire microvasculature and gain access into the majority of the perivascular TME, which coincided with the APC-rich tumor areas leading to uptake of the NPs predominantly by APCs. In this work, a 60 nm NP was loaded with a STING agonist, which triggered robust production of interferon β, resulting in activation of APCs. In addition to untargeted NPs, we employed 'mainstream' ligands targeting fibronectin, αvβ3 integrin and P-selectin that are commonly used to direct nanoparticles to tumors. Using the 4T1 mouse model, we assessed the microdistribution of the four NP variants in the tumor immune microenvironment in three different breast cancer landscapes, including primary tumor, early metastasis, and late metastasis. The different NP variants resulted in variable uptake by immune cell subsets depending on the organ and tumor stage. Among the NP variants, therapeutic studies indicated that the untargeted NPs and the integrin-targeting NPs exhibited a remarkable short- and long-term immune response and long-lasting antitumor effect.

The effect of PEGylation on the efficacy and uptake of an immunostimulatory nanoparticle in the tumor immune microenvironment

The efficacy of immunotherapies is often limited by the immunosuppressive tumor microenvironment, which is populated with dysfunctional innate immune cells. To reprogram the tumor-resident innate immune cells, we developed immunostimulatory silica mesoporous nanoparticles (immuno-MSN). The cargo of immuno-MSN is a Stimulator of Interferon Gene (STING) agonist, which activates innate immune cells leading to production of interferon (IFN) β. By proficiently trafficking its cargo into immune cells, the immuno-MSN induced a 9-fold increase of IFN-β secretion compared to free agonist. While an external PEG shield has historically been used to protect nanoparticles from immune recognition, a PEGylated immunostimulatory nanoparticle needs to strike a balance between immune evasion to avoid off-site accumulation and uptake by target immune cells in tumors. Using the 4T1 mouse model of metastatic breast cancer and flow cytometry, it was determined that the degree of PEGylation significantly influenced the uptake of 'empty' MSNs by tumor-resident innate immune cells. This was not the case for the agonist-loaded immuno-MSN variants. It should be noted the surface charge of the 'empty' MSNs was positive rather than neutral for the agonist-loaded immuno-MSNs. However, even though the cellular uptake was similar at 24 h after injection for the three immuno-MSN variants, we observed a significant beneficial effect on the activation and expansion of APCs especially in lung metastasis using the lightly PEGylated immuno-MSN variant.

Immunostimulatory silica nanoparticle boosts innate immunity in brain tumors

The high mortality associated with glioblastoma multiforme (GBM) is attributed to its invasive nature, hypoxic core, resistant cell subpopulations and a highly immunosuppressive tumor microenvironment (TME). To support adaptive immune function and establish a more robust antitumor immune response, we boosted the local innate immune compartment of GBM using an immunostimulatory mesoporous silica nanoparticle, termed immuno-MSN. The immuno-MSN was specifically designed for systemic and proficient delivery of a potent innate immune agonist to dysfunctional antigen-presenting cells (APCs) in the brain TME. The cargo of the immuno-MSN was cyclic diguanylate monophosphate (cdGMP), a Stimulator of Interferon Gene (STING) agonist. Studies showed the immuno-MSN promoted the uptake of STING agonist by APCs in vitro and the subsequent release of the pro-inflammatory cytokine interferon β, 6-fold greater than free agonist. In an orthotopic GBM mouse model, systemically administered immuno-MSN particles were taken up by APCs in the near-perivascular regions of the brain tumor with striking efficiency. The immuno-MSNs facilitated the recruitment of dendritic cells and macrophages to the TME while sparing healthy brain tissue and peripheral organs, resulting in elevated circulating CD8+ T cell activity (2.5-fold) and delayed GBM tumor growth. We show that an engineered immunostimulatory nanoparticle can support pro-inflammatory innate immune function in GBM and subsequently augment current immunotherapeutic interventions and improve their therapeutic outcome.

Nanoparticle Encapsulation of Synergistic Immune Agonists Enables Systemic Codelivery to Tumor Sites and IFNβ-Driven Antitumor Immunity

Effective cancer immunotherapy depends on the robust activation of tumor-specific antigen-presenting cells (APC). Immune agonists encapsulated within nanoparticles (NP) can be delivered to tumor sites to generate powerful antitumor immune responses with minimal off-target dissemination. Systemic delivery enables widespread access to the microvasculature and draining to the APC-rich perivasculature. We developed an immuno-nanoparticle (immuno-NP) coloaded with cyclic diguanylate monophosphate, an agonist of the stimulator of interferon genes pathway, and monophosphoryl lipid A, and a Toll-like receptor 4 agonist, which synergize to produce high levels of type I IFNβ. Using a murine model of metastatic triple-negative breast cancer, systemic delivery of these immuno-NPs resulted in significant therapeutic outcomes due to extensive upregulation of APCs and natural killer cells in the blood and tumor compared with control treatments. These results indicate that NPs can facilitate systemic delivery of multiple immune-potentiating cargoes for effective APC-driven local and systemic antitumor immunity. SIGNIFICANCE: Systemic administration of an immuno-nanoparticle in a murine breast tumor model drives a robust tumor site-specific APC response by delivering two synergistic immune-potentiating molecules, highlighting the potential of nanoparticles for immunotherapy.

Porphyrin-Loaded Pluronic Nanobubbles: A New US-Activated Agent for Future Theranostic Applications

Sonodynamic therapy (SDT) has become a promising noninvasive approach for cancer therapy. The treatment exploits the ability of particular molecules (i.e., porphyrins) to be excited by ultrasound and produce reactive oxygen species (ROS) during their decay process. These reactive species, in turn, result in cell death. To capitalize on the real-time visualization and on-demand delivery of ultrasound contrast agents, this study aims to combine porphyrins with nanobubbles (NBs) to obtain an ultrasound-activated theranostic agent that exploits the SDT activity in vitro. Two porphyrin classes, exposing different hydrophobic side chains, were synthesized. NB size and encapsulation efficiency were markedly dependent on the porphyrin structure. The combination of these porphyrin and NBs resulted in a significant reduction in cell viability upon sonication in pilot studies performed on the LS 174T colorectal cancer cell line.