Nanoparticle Retinoic Acid-Inducible Gene I Agonist for Cancer Immunotherapy

Pharmacological activation of the retinoic acid-inducible gene I (RIG-I) pathway holds promise for increasing tumor immunogenicity and improving the response to immune checkpoint inhibitors (ICIs). However, the potency and clinical efficacy of 5'-triphosphate RNA (3pRNA) agonists of RIG-I are hindered by multiple pharmacological barriers, including poor pharmacokinetics, nuclease degradation, and inefficient delivery to the cytosol where RIG-I is localized. Here, we address these challenges through the design and evaluation of ionizable lipid nanoparticles (LNPs) for the delivery of 3p-modified stem-loop RNAs (SLRs). Packaging of SLRs into LNPs (SLR-LNPs) yielded surface charge-neutral nanoparticles with a size of ∼100 nm that activated RIG-I signaling in vitro and in vivo. SLR-LNPs were safely administered to mice via both intratumoral and intravenous routes, resulting in RIG-I activation in the tumor microenvironment (TME) and the inhibition of tumor growth in mouse models of poorly immunogenic melanoma and breast cancer. Significantly, we found that systemic administration of SLR-LNPs reprogrammed the breast TME to enhance the infiltration of CD8+ and CD4+ T cells with antitumor function, resulting in enhanced response to αPD-1 ICI in an orthotopic EO771 model of triple-negative breast cancer. Therapeutic efficacy was further demonstrated in a metastatic B16.F10 melanoma model, with systemically administered SLR-LNPs significantly reducing lung metastatic burden compared to combined αPD-1 + αCTLA-4 ICI. Collectively, these studies have established SLR-LNPs as a translationally promising immunotherapeutic nanomedicine for potent and selective activation of RIG-I with the potential to enhance response to ICIs and other immunotherapeutic modalities.

STING-activating nanoparticles normalize the vascular-immune interface to potentiate cancer immunotherapy

The tumor-associated vasculature imposes major structural and biochemical barriers to the infiltration of effector T cells and effective tumor control. Correlations between stimulator of interferon genes (STING) pathway activation and spontaneous T cell infiltration in human cancers led us to evaluate the effect of STING-activating nanoparticles (STANs), which are a polymersome-based platform for the delivery of a cyclic dinucleotide STING agonist, on the tumor vasculature and attendant effects on T cell infiltration and antitumor function. In multiple mouse tumor models, intravenous administration of STANs promoted vascular normalization, evidenced by improved vascular integrity, reduced tumor hypoxia, and increased endothelial cell expression of T cell adhesion molecules. STAN-mediated vascular reprogramming enhanced the infiltration, proliferation, and function of antitumor T cells and potentiated the response to immune checkpoint inhibitors and adoptive T cell therapy. We present STANs as a multimodal platform that activates and normalizes the tumor microenvironment to enhance T cell infiltration and function and augments responses to immunotherapy.

A nanovaccine for enhancing cellular immunity via cytosolic co-delivery of antigen and polyIC RNA

Traditional approaches to cancer vaccines elicit weak CD8+ T cell responses and have largely failed to meet clinical expectations. This is in part due to inefficient antigen cross-presentation, inappropriate selection of adjuvant and its formulation, poor vaccine pharmacokinetics, and/or suboptimal coordination of antigen and adjuvant delivery. Here, we describe a nanoparticle vaccine platform for facile co-loading and dual-delivery of antigens and nucleic acid adjuvants that elicits robust antigen-specific cellular immune responses. The nanovaccine design is based on diblock copolymers comprising a poly(ethylene glycol)-rich first block that is functionalized with reactive moieties for covalent conjugation of antigen via disulfide linkages, and a pH-responsive second block for electrostatic packaging of nucleic acids that also facilitates endosomal escape of associated vaccine cargo to the cytosol. Using polyIC, a clinically-advanced nucleic acid adjuvant, we demonstrated that endosomolytic nanoparticles promoted the cytosolic co-delivery of polyIC and protein antigen, which acted synergistically to enhance antigen cross-presentation, co-stimulatory molecule expression, and cytokine production by dendritic cells. We also found that the vaccine platform increased the accumulation of antigen and polyIC in the local draining lymph nodes. Consequently, dual-delivery of antigen and polyIC with endsomolytic nanoparticles significantly enhanced the magnitude and functionality of CD8+ T cell responses relative to a mixture of antigen and polyIC, resulting in inhibition of tumor growth in a mouse tumor model. Collectively, this work provides a proof-of-principle for a new cancer vaccine platform that strongly augments anti-tumor cellular immunity via cytosolic co-delivery of antigen and nucleic acid adjuvant.

Unfolded Protein Response Is Activated by Aurora Kinase A in Esophageal Adenocarcinoma

Unfolded protein response (UPR) protects malignant cells from endoplasmic reticulum stress-induced apoptosis. We report that Aurora kinase A (AURKA) promotes cancer cell survival by activating UPR in esophageal adenocarcinoma (EAC). A strong positive correlation between AURKA and binding immunoglobulin protein (BIP) mRNA expression levels was found in EACs. The in vitro assays indicated that AURKA promoted IRE1α protein phosphorylation, activating prosurvival UPR in FLO-1 and OE33 cells. The use of acidic bile salts to mimic reflux conditions in patients induced high AURKA and IRE1α levels. This induction was abrogated by AURKA knockdown in EAC cells. AURKA and p-IRE1α protein colocalization was observed in neoplastic gastroesophageal lesions of the L2-IL1b mouse model of Barrett's esophageal neoplasia. The combined treatment using AURKA inhibitor and tunicamycin synergistically induced cancer cell death. The use of alisertib for AURKA inhibition in the EAC xenograft model led to a decrease in IRE1α phosphorylation with a significant reduction in tumor growth. These results indicate that AURKA activates UPR, promoting cancer cell survival during ER stress in EAC. Targeting AURKA can significantly reverse prosurvival UPR signaling mechanisms and decrease cancer cell survival, providing a promising approach for the treatment of EAC patients.

Pharmacological Activation of cGAS for Cancer Immunotherapy

When compartmentally mislocalized within cells, nucleic acids can be exceptionally immunostimulatory and can even trigger the immune-mediated elimination of cancer. Specifically, the accumulation of double-stranded DNA in the cytosol can efficiently promote antitumor immunity by activating the cGAMP synthase (cGAS) / stimulator of interferon genes (STING) cellular signaling pathway. Targeting this cytosolic DNA sensing pathway with interferon stimulatory DNA (ISD) is therefore an attractive immunotherapeutic strategy for the treatment of cancer. However, the therapeutic activity of ISD is limited by several drug delivery barriers, including susceptibility to deoxyribonuclease degradation, poor cellular uptake, and inefficient cytosolic delivery. Here, we describe the development of a nucleic acid immunotherapeutic, NanoISD, which overcomes critical delivery barriers that limit the activity of ISD and thereby promotes antitumor immunity through the pharmacological activation of cGAS at the forefront of the STING pathway. NanoISD is a nanoparticle formulation that has been engineered to confer deoxyribonuclease resistance, enhance cellular uptake, and promote endosomal escape of ISD into the cytosol, resulting in potent activation of the STING pathway via cGAS. NanoISD mediates the local production of proinflammatory cytokines via STING signaling. Accordingly, the intratumoral administration of NanoISD induces the infiltration of natural killer cells and T lymphocytes into murine tumors. The therapeutic efficacy of NanoISD is demonstrated in preclinical tumor models by attenuated tumor growth, prolonged survival, and an improved response to immune checkpoint blockade therapy.

Nanoparticle delivery improves the pharmacokinetic properties of cyclic dinucleotide STING agonists to open a therapeutic window for intravenous administration

The stimulator of interferon genes (STING) pathway plays an important role in the immune surveillance of cancer and, accordingly, agonists of STING signaling have recently emerged as promising therapeutics for remodeling of the immunosuppressive tumor microenvironment (TME) and enhancing response rates to immune checkpoint inhibitors. 2'3'-cyclic guanosine monophosphate-adenosine monophosphate (2'3'-cGAMP) is the endogenous ligand for STING, but is rapidly metabolized and poorly membrane permeable, restricting its use to intratumoral administration. Nanoencapsulation has been shown to allow for systemic administration of cGAMP and other cyclic dinucleotides (CDN), but little is known about how nanocarriers affect important pharmacological properties that impact the efficacy and safety of CDNs. Using STING-activating nanoparticles (STING-NPs) - a polymersome platform designed to enhance cGAMP delivery - we investigate the pharmacokinetic (PK)-pharmacodynamic (PD) relationships that underlie the ability of intravenously (i.v.) administered STING-NPs to induce STING activation and inhibit tumor growth. First, we demonstrate that nanoencapsulation improves the half-life of encapsulated cGAMP by 40-fold, allowing for sufficient accumulation of cGAMP in tumors and activation of the STING pathway in the TME as assessed by western blot analysis and gene expression profiling. Nanoparticle delivery also changes the biodistribution profile, resulting in increased cGAMP accumulation and STING activation in the liver and spleen, which we identify as dose limiting organs. As a consequence of STING activation in tumors, i.v. administered STING-NPs reprogram the TME towards a more immunogenic antitumor milieu, characterized by an influx of >20-fold more CD4+ and CD8+ T-cells. Consequently, STING-NPs increased response rates to αPD-L1 antibodies, resulting in significant improvements in median survival time in a B16-F10 melanoma model. Additionally, we confirmed STING-NP monotherapy in an additional melanoma (YUMM1.7) and breast adenocarcinoma (E0771) models leading to >50% and 80% reduction in tumor burden, respectively, and significant increases in median survival time. Collectively, this work provides an examination of the PK-PD relationship governing STING activation upon systemic delivery using STING-NPs, providing insight for future optimization for nanoparticle-based STING agonists and other immunomodulating nanomedicines.

Potent STING activation stimulates immunogenic cell death to enhance antitumor immunity in neuroblastoma

BACKGROUND

Neuroblastoma (NB) is a childhood cancer for which new treatment options are needed. The success of immune checkpoint blockade in the treatment of adult solid tumors has prompted the exploration of immunotherapy in NB; however, clinical evidence indicates that the vast majority of NB patients do not respond to single-agent checkpoint inhibitors. This motivates a need for therapeutic strategies to increase NB tumor immunogenicity. The goal of this study was to evaluate a new immunotherapeutic strategy for NB based on potent activation of the stimulator of interferon genes (STING) pathway.

METHODS

To promote STING activation in NB cells and tumors, we utilized STING-activating nanoparticles (STING-NPs) that are designed to mediate efficient cytosolic delivery of the endogenous STING ligand, 2'3'-cGAMP. We investigated tumor-intrinsic responses to STING activation in both MYCN-amplified and non-amplified NB cell lines, evaluating effects on STING signaling, apoptosis, and the induction of immunogenic cell death. The effects of intratumoral administration of STING-NPs on CD8+ T cell infiltration, tumor growth, and response to response to PD-L1 checkpoint blockade were evaluated in syngeneic models of MYCN-amplified and non-amplified NB.

RESULTS

The efficient cytosolic delivery of 2'3'-cGAMP enabled by STING-NPs triggered tumor-intrinsic STING signaling effects in both MYCN-amplified and non-amplified NB cell lines, resulting in increased expression of interferon-stimulated genes and pro-inflammatory cytokines as well as NB cell death at concentrations 2000-fold to 10000-fold lower than free 2'3'-cGAMP. STING-mediated cell death in NB was associated with release or expression of several danger associated molecular patterns that are hallmarks of immunogenic cell death, which was further validated via cell-based vaccination and tumor challenge studies. Intratumoral administration of STING-NPs enhanced STING activation relative to free 2'3'-cGAMP in NB tumor models, converting poorly immunogenic tumors into tumoricidal and T cell-inflamed microenvironments and resulting in inhibition of tumor growth, increased survival, and induction of immunological memory that protected against tumor re-challenge. In a model of MYCN-amplified NB, STING-NPs generated an abscopal response that inhibited distal tumor growth and improved response to PD-L1 immune checkpoint blockade.

CONCLUSIONS

We have demonstrated that activation of the STING pathway, here enabled by a nanomedicine approach, stimulates immunogenic cell death and remodels the tumor immune microenvironment to inhibit NB tumor growth and improve responses to immune checkpoint blockade, providing a multifaceted immunotherapeutic approach with potential to enhance immunotherapy outcomes in NB.

Mucosal Immunization with a pH-Responsive Nanoparticle Vaccine Induces Protective CD8+ Lung-Resident Memory T Cells

Tissue-resident memory T cells (T_RM) patrol nonlymphoid organs and provide superior protection against pathogens that commonly infect mucosal and barrier tissues, such as the lungs, intestine, liver, and skin. Thus, there is a need for vaccine technologies that can induce a robust, protective T_RM response in these tissues. Nanoparticle (NP) vaccines offer important advantages over conventional vaccines; however, there has been minimal investigation into the design of NP-based vaccines for eliciting T_RM responses. Here, we describe a pH-responsive polymeric nanoparticle vaccine for generating antigen-specific CD8⁺ T_RM cells in the lungs. With a single intranasal dose, the NP vaccine elicited airway- and lung-resident CD8⁺ T_RM cells and protected against respiratory virus challenge in both sublethal (vaccinia) and lethal (influenza) infection models for up to 9 weeks after immunization. In elucidating the contribution of material properties to the resulting T_RM response, we found that the pH-responsive activity of the carrier was important, as a structurally analogous non-pH-responsive control carrier elicited significantly fewer lung-resident CD8⁺ T cells. We also demonstrated that dual-delivery of protein antigen and nucleic acid adjuvant on the same NP substantially enhanced the magnitude, functionality, and longevity of the antigen-specific CD8⁺ T_RM response in the lungs. Compared to administration of soluble antigen and adjuvant, the NP also mediated retention of vaccine cargo in pulmonary antigen-presenting cells (APCs), enhanced APC activation, and increased production of T_RM-related cytokines. Overall, these data suggest a promising vaccine platform technology for rapid generation of protective CD8⁺ T_RM cells in the lungs.

Correction: The efficiency of cytosolic drug delivery using pH-responsive endosomolytic polymers does not correlate with activation of the NLRP3 inflammasome

Correction for 'The efficiency of cytosolic drug delivery using pH-responsive endosomolytic polymers does not correlate with activation of the NLRP3 inflammasome' by Jessalyn J. Baljon et al., Biomater. Sci., 2019, DOI: 10.1039/c8bm01643g.

The efficiency of cytosolic drug delivery using pH-responsive endosomolytic polymers does not correlate with activation of the NLRP3 inflammasome

Inefficient cytosolic delivery has limited the development of many promising biomacromolecular drugs, a long-standing challenge that has prompted extensive development of drug carriers that facilitate endosomal escape. Although many such carriers have shown considerable promise for cytosolic delivery of a diversity of therapeutics, the rupture or destabilization of endo/lysosomal membranes has also been associated with activation of the inflammasome with attendant risk of inflammation and toxicity. In this study, we investigated relationships between pH-dependent membrane destabilization, cytosolic drug delivery, and inflammasome activation using a series of well-defined poly[(ethylene glycol)-block-[(2-(dimethylamino)ethyl methacrylate)-co-(butyl methacrylate)] copolymers of variable second block composition and pH-responsive properties. We found that polymers that demonstrated the most potent membrane-destabilizing activity at early endosomal pH values in an erythrocyte hemolysis assay were most efficient at delivery of siRNA, yet tended to be associated with the least amount of NOD-like related protein 3 (NLRP3) inflammasome activation. By contrast, polymers that displayed minimal hemolysis activity and poor siRNA knockdown, and instead mediated lysosomal rupture likely due to a proton sponge mechanism, strongly induced NLPR3 inflammasome activation in a caspase- and cathepsin-dependent manner. Collectively, these findings reinforce the importance of early endosomal escape in minimizing inflammasome activation and also demonstrate the ability to tune the degree inflammasome activation via control of polymer structure with potential implications for design of vaccine adjuvants and immunotherapeutics.

Inhibition of AURKA Reduces Proliferation and Survival of Gastrointestinal Cancer Cells With Activated KRAS by Preventing Activation of RPS6KB1

BACKGROUND & AIMS

Activation of KRAS signaling and overexpression of the aurora kinase A (AURKA) are often detected in luminal gastrointestinal cancers. We investigated regulation of ribosomal protein S6 kinase B1 (RPS6KB1) by AURKA and the effects of alisertib, an AURKA inhibitor, in mice xenograft tumors grown from human gastrointestinal cancer cells with mutant, activated forms of KRAS.

METHODS

We tested the effects of alisertib or AURKA overexpression or knockdown in 10 upper gastrointestinal or colon cancer cell lines with KRAS mutations or amplifications using the CellTiter-Glo luminescence and clonogenic cell survival assays. We used the proximity ligation in situ assay to evaluate protein co-localization and immunoprecipitation to study protein interactions. Nude mice with xenograft tumors grown from HCT116, SNU-601, SW480, or SNU-1 cells were given oral alisertib (40 mg/kg, 5 times/wk) for 4 weeks. Tumor samples were collected and analyzed by immunoblots and immunohistochemistry. Tissue microarrays from 151 paraffin-embedded human colon tumors, with adjacent normal and adenoma tissues, were analyzed by immunohistochemistry for levels of AURKA.

RESULTS

Alisertib reduced proliferation and survival of the cell lines tested. AURKA knockdown or inhibition with alisertib reduced levels of phosphorylated RPS6KB1 (at T389) and increased levels of proteins that induce apoptosis, including BIM, cleaved PARP, and cleaved caspase 3. AURKA co-localized and interacted with RPS6KB1, mediating RPS6KB1 phosphorylation at T389. We detected AURKA-dependent phosphorylation of RPS6KB1 in cell lines with mutations in KRAS but not in cells with wild-type KRAS. Administration of alisertib to mice with xenograft tumors significantly reduced tumor volumes (P < .001). Alisertib reduced phosphorylation of RPS6KB1 and Ki-67 and increased levels of cleaved caspase 3 in tumor tissues. In analyses of tissue microarrays, we found significant overexpression of AURKA in gastrointestinal tumor tissues compared with non-tumor tissues (P = .0003).

CONCLUSION

In studies of gastrointestinal cancer cell lines with activated KRAS, we found AURKA to phosphorylate RPS6KB1, promoting cell proliferation and survival and growth of xenograft tumors in mice. Agents that inhibit AURKA might slow the growth of gastrointestinal tumors with activation of KRAS.

Delivery of 5'-triphosphate RNA with endosomolytic nanoparticles potently activates RIG-I to improve cancer immunotherapy

RNA agonists of the retinoic acid gene I (RIG-I) pathway have recently emerged as a promising class of cancer immunotherapeutics, but their efficacy is hindered by drug delivery barriers, including nuclease degradation, poor intracellular uptake, and minimal access to the cytosol where RIG-I is localized. Here, we explore the application of pH-responsive, endosomolytic polymer nanoparticles (NPs) to enhance the cytosolic delivery and immunostimulatory activity of synthetic 5' triphosphate, short, double-stranded RNA (3pRNA), a ligand for RIG-I. Delivery of 3pRNA with pH-responsive NPs with an active endosomal escape mechanism, but not control carriers lacking endosomolytic activity, significantly increased the activity of 3pRNA in dendritic cells, macrophages, and cancer cell lines. In a CT26 colon cancer model, activation of RIG-I via NP delivery of 3pRNA induced immunogenic cell death, triggered expression of type I interferon and pro-inflammatory cytokines, and increased CD8+ T cell infiltration into the tumor microenvironment. Consequently, intratumoral (IT) delivery of NPs loaded with 3pRNA inhibited CT26 tumor growth and enhanced the therapeutic efficacy of anti-PD-1 immune checkpoint blockade, resulting in a 30% complete response rate and generation of immunological memory that protected against tumor rechallenge. Collectively, these studies demonstrate that pH-responsive NPs can be harnessed to strongly enhance the immunostimulatory activity and therapeutic efficacy of 3pRNA and establish endosomal escape as a critical parameter in the design of carriers for immunotherapeutic targeting of the RIG-I pathway.