A phase I clinical trial of imiquimod, an oral interferon inducer, administered daily

A novel oral TLR7 agonist orchestrates immune response and synergizes with PD-L1 blockade via type I IFN pathway in lung cancer

Despite the groundbreaking impact of immune checkpoint blockade (ICB), response rates in non-small cell lung cancer remain modest, particularly in immune-excluded or immune-desert microenvironments. Toll-like receptor 7 (TLR7) emerges as a latent target bridging innate and adaptive immunity, offering a promising avenue for combination therapies to augment ICB efficacy. Here, we explored the anti-tumor activity of the novel oral TLR7 agonist TQ-A3334 and its potential to enhance anti-programmed death ligand 1 (PD-L1) therapy through a combination strategy in a syngeneic murine lung cancer model. Oral administration of TQ-A3334 significantly alleviated tumor burden in C57BL/6J mice, modulated by type I interferon (IFN), and exhibited low toxicity. This therapy elicited activation of both innate and adaptive immune cells in tumor tissue, particularly increasing the abundance of CD8+ TILs through type I IFN pathway and subsequent CXCL10 expression. In vitro examinations validated that IFN-α-stimulated tumor cells exhibited increased secretion of CXCL10, conducive to the promoted trafficking of CD8+ T cells. Furthermore, combining TQ-A3334 with anti-PD-L1 treatment exceeded tumor control, with a further increase in CD8+ TIL frequency compared to monotherapy. These findings suggest that TQ-A3334 can mobilize innate immunity and promote T cell recruitment into the tumor microenvironment; a combination of TQ-A3334 and anti-PD-L1 antibodies can intensify the sensitivity of tumors to anti-PD-L1 therapy, which demonstrates significant potential for treating poorly immune-infiltrated lung cancer.

A Defect-Engineered Nanozyme for Targeted NIR-II Photothermal Immunotherapy of Cancer

Multienzyme-mimicking redox nanozymes, curated by defect engineering, in synergy with immunotherapy offer promising prospects for safe and efficient cancer therapy. However, the spatiotemporally precise immune response often gets challenged by off-target adverse effects and insufficient therapeutic response. Herein, a tumor cell membrane coated redox nanozyme (CMO-R@4T1) is reported for combinational second near-infrared window (NIR-II) photothermal immunotherapy. CMO-R@4T1 consists of a Cu-doped MoOx (CMO) nanozyme as the core, which is cloaked with tumor-cell-derived fused membranes with immunostimulants immobilized in the membrane shell. In addition to the enhanced tumor accumulation, the nanozyme can cause oxidative damage to tumor cells by the production of reactive oxygen species and attenuation of the antioxidant mechanism. CMO-R@4T1 also mediates a photothermal effect under NIR-II photoirradiation to trigger tumor eradication and immunogenic cell death, where the liberated agonist elicits the immune activation. Such a controlled therapeutic paradigm potentiates systemic primary tumor ablation, inhibits cancer metastasis to distant tumor, and procures long-term immunological memory. Thereby, this study takes advantage of defect engineering to illustrate a generic strategy to prepare cell-membrane-camouflaged nanozymes for targeted photo-immunotherapy of cancer.

Tumor-specific activation of folate receptor beta enables reprogramming of immune cells in the tumor microenvironment

Folate receptors can perform folate transport, cell adhesion, and/or transcription factor functions. The beta isoform of the folate receptor (FRβ) has attracted considerable attention as a biomarker for immunosuppressive macrophages and myeloid-derived suppressor cells, however, its role in immunosuppression remains uncharacterized. We demonstrate here that FRβ cannot bind folate on healthy tissue macrophages, but does bind folate after macrophage incubation in anti-inflammatory cytokines or cancer cell-conditioned media. We further show that FRβ becomes functionally active following macrophage infiltration into solid tumors, and we exploit this tumor-induced activation to target a toll-like receptor 7 agonist specifically to immunosuppressive myeloid cells in solid tumors without altering myeloid cells in healthy tissues. We then use single-cell RNA-seq to characterize the changes in gene expression induced by the targeted repolarization of tumor-associated macrophages and finally show that their repolarization not only changes their own phenotype, but also induces a proinflammatory shift in all other immune cells of the same tumor mass, leading to potent suppression of tumor growth. Because this selective reprogramming of tumor myeloid cells is accompanied by no systemic toxicity, we propose that it should constitute a safe method to reprogram the tumor microenvironment.

Highly Active Myeloid Therapy for Cancer

Tumor-associated macrophages (TAM) interact with cancer and stromal cells and are integral to sustaining many cancer-promoting features. Therapeutic manipulation of TAM could therefore improve clinical outcomes and synergize with immunotherapy and other cancer therapies. While different nanocarriers have been used to target TAM, a knowledge gap exists on which TAM pathways to target and what payloads to deliver for optimal antitumor effects. We hypothesized that a multipart combination involving the Janus tyrosine kinase (JAK), noncanonical nuclear factor kappa light chain enhancer of activated B cells (NF-κB), and toll-like receptor (TLR) pathways could lead to a highly active myeloid therapy (HAMT). Thus, we devised a screen to determine drug combinations that yield maximum IL-12 production from myeloid cells to treat the otherwise highly immunosuppressive myeloid environments in tumors. Here we show the extraordinary efficacy of a triple small-molecule combination in a TAM-targeted nanoparticle for eradicating murine tumors, jumpstarting a highly efficient antitumor response by adopting a distinctive antitumor TAM phenotype and synergizing with other immunotherapies. The HAMT therapy represents a recently developed approach in immunotherapy and leads to durable responses in murine cancer models.

Identification of a Self-Assembling Small-Molecule Cancer Vaccine Adjuvant with an Improved Toxicity Profile

Protein or peptide cancer vaccines usually include immune potentiators, so-called adjuvants. However, it remains challenging to identify structurally simple, chemically accessible synthetic molecules that are effective and safe as vaccine adjuvant. Here, we present cholicamideβ (6), a self-assembling small-molecule vaccine adjuvant with an improved toxicity profile and proven efficacy in vivo. We demonstrate that cholicamideβ (6), which is less cytotoxic than its parent compound, forms virus-like particles to potently activate dendritic cells with the concomitant secretion of cytokines. When combined with a peptide antigen, cholicamideβ (6) potentiated the antigen presentation on dendritic cells to induce antigen-specific T cells. As a therapeutic cancer vaccine adjuvant in mice, a mixture of cholicamideβ (6) and a peptide antigen protected mice from the challenges of malignant cancer cells without overt toxicity. Cholicamideβ (6) may offer a translational opportunity as an unprecedented class of small-molecule cancer vaccine adjuvants.

Imidazoquinolines with improved pharmacokinetic properties induce a high IFNα to TNFα ratio in vitro and in vivo

TLR Agonists have promising activity in preclinical models of viral infection and cancer. However, clinical use is only in topical application. Systemic uses of TLR-ligands such as Resiquimod, have failed due to adverse effects that limited dose and thus, efficacy. This issue could be related to pharmacokinetic properties that include fast elimination leading to low AUC with simultaneously high c_max at relevant doses. The high c_max is associated with a sharp, poorly tolerated cytokine pulse, suggesting that a compound with a higher AUC/c_max-ratio could provide a more sustained and tolerable immune activation. Our approach was to design TLR7/8-agonist Imidazoquinolines intended to partition to endosomes via acid trapping using a macrolide-carrier. This can potentially extend pharmacokinetics and simultaneously direct the compounds to the target compartment. The compounds have hTLR7/8-agonist activity (EC50 of the most active compound in cellular assays: 75-120 nM hTLR7, 2.8-3.1 µM hTLR8) and maximal hTLR7 activation between 40 and 80% of Resiquimod. The lead candidates induce secretion of IFNα from human Leukocytes in the same range as Resiquimod but induce at least 10-fold less TNFα in this system, consistent with a higher specificity for human TLR7. This pattern was reproduced in vivo in a murine system, where small molecules are thought not to activate TLR8. We found that Imidazoquinolines conjugated to a macrolide or, substances carrying an unlinked terminal secondary amine, had longer exposure compared with Resiquimod. The kinetics of pro-inflammatory cytokine release for these substances in vivo were slower and more extended (for comparable AUCs, approximately half-maximal plasma concentrations). Maximal IFNα plasma levels were reached 4 h post application. Resiquimod-treated groups had by then returned to baseline from a peak at 1 h. We propose that the characteristic cytokine profile is likely a consequence of altered pharmacokinetics and, potentially, enhanced endosomal tropism of the novel substances. In particular, our substances are designed to partition to cellular compartments where the target receptor and a distinct combination of signaling molecules relevant to IFNα-release are located. These properties could address the tolerability issues of TLR7/8 ligands and provide insight into approaches to fine-tune the outcomes of TLR7/8 activation by small molecules.

Enteric Toll-like receptor 7 stimulation causes acute exacerbation in lupus-susceptible mice

Autoimmune diseases are often accompanied by acute exacerbation. However, the mechanism underlying systemic lupus erythematosus (SLE) flares remains unclear. We investigated whether short-term enteric Toll-like receptor 7 (TLR7) stimulation can exacerbate SLE using B6SKG mice, which spontaneously develop SLE due to a mutation in the zeta‒chain‒associated protein kinase 70 (Zap70) gene. Imiquimod (IMQ) or phosphate-buffered saline (PBS) were orally administered on B6WT and B6SKG mice every other day for 2 weeks. SLE exacerbation was assessed via fluorescent immunohistochemical staining of glomeruli for IgG and C3, hematoxylin and eosin staining of kidneys, and enzyme-linked immunosorbent assay for antinuclear antibody (ANA). Flow cytometry was used to evaluate germinal center B cells (GCBs), plasma cells, follicular helper T cells (Tfhs), regulatory T cells (Tregs), effector T cells (Th1s and Th17s), plasmacytoid dendritic cells (pDCs), conventional dendritic cells (cDCs), and macrophages (Mφs) in spleens. Oral administration of IMQ every other day for 2 weeks resulted in exacerbation of splenomegaly, increased IgG and C3 deposition in glomeruli, and increased ANA production in the B6SKG IMQ (SKG-IMQ) group compared to the B6SKG PBS (SKG-PBS) group; the percentages of GCBs, plasma cells, Tfhs, Th1s, pDCs, and Mφs were also increased in the SKG-IMQ group. Splenomegaly, IgG, and C3 deposition in glomeruli, and the percentages of GCBs, plasma cells, Tfhs, and Th1s were enhanced in SKG-IMQ mice compared with B6SKG mice topically treated with IMQ (SKG-ear-IMQ). Oral TLR7 stimulation in a Zap70 genetic mutation background can cause acute exacerbations of SLE. Key Points • The mechanism of SLE flares is not well understood. • We have created a model that causes short-term SLE exacerbations in mice with a genetic background. • IMQ administered orally causes more SLE in mice than transdermally.

Theranostic Small-Molecule Prodrug Conjugates for Targeted Delivery and Controlled Release of Toll-like Receptor 7 Agonists

We previously reported the design and synthesis of a small-molecule drug conjugate (SMDC) platform that demonstrated several advantages over antibody–drug conjugates (ADCs) in terms of in vivo pharmacokinetics, solid tumor penetration, definitive chemical structure, and adaptability for modular synthesis. Constructed on a tri-modal SMDC platform derived from 1,3,5-triazine (TZ) that consists of a targeting moiety (Lys-Urea-Glu) for prostate-specific membrane antigen (PSMA), here we report a novel class of chemically identical theranostic small-molecule prodrug conjugates (T-SMPDCs), [^18/19F]F-TZ(PSMA)-LEGU-TLR7, for PSMA-targeted delivery and controlled release of toll-like receptor 7 (TLR7) agonists to elicit de novo immune response for cancer immunotherapy. In vitro competitive binding assay of [¹⁹F]F-TZ(PSMA)-LEGU-TLR7 showed that the chemical modification of Lys-Urea-Glu did not compromise its binding affinity to PSMA. Receptor-mediated cell internalization upon the PSMA binding of [¹⁸F]F-TZ(PSMA)-LEGU-TLR7 showed a time-dependent increase, indicative of targeted intracellular delivery of the theranostic prodrug conjugate. The designed controlled release of gardiquimod, a TLR7 agonist, was realized by a legumain cleavable linker. We further performed an in vivo PET/CT imaging study that showed significantly higher uptake of [¹⁸F]F-TZ(PSMA)-LEGU-TLR7 in PSMA⁺ PC3-PIP tumors (1.9 ± 0.4% ID/g) than in PSMA⁻ PC3-Flu tumors (0.8 ± 0.3% ID/g) at 1 h post-injection. In addition, the conjugate showed a one-compartment kinetic profile and in vivo stability. Taken together, our proof-of-concept biological evaluation demonstrated the potential of our T-SMPDCs for cancer immunomodulatory therapies.

Engaging Pattern Recognition Receptors in Solid Tumors to Generate Systemic Antitumor Immunity

Malignant tumors frequently exploit innate immunity to evade immune surveillance. The priming, function, and polarization of antitumor immunity fundamentally depends upon context provided by the innate immune system, particularly antigen presenting cells. Such context is determined in large part by sensing of pathogen specific and damage associated features by pathogen recognition receptors (PRRs). PRR activation induces the delivery of T cell priming cues (e.g. chemokines, co-stimulatory ligands, and cytokines) from antigen presenting cells, playing a decisive role in the cancer immunity cycle. Indeed, endogenous PRR activation within the tumor microenvironment (TME) has been shown to generate spontaneous antitumor T cell immunity, e.g., cGAS-STING mediated activation of antigen presenting cells after release of DNA from dying tumor cells. Thus, instigating intratumor PRR activation, particularly with the goal of generating Th1-promoting inflammation that stokes endogenous priming of antitumor CD8⁺ T cells, is a growing area of clinical investigation. This approach is analogous to in situ vaccination, ultimately providing a personalized antitumor response against relevant tumor associated antigens. Here I discuss clinical stage intratumor modalities that function via activation of PRRs. These approaches are being tested in various solid tumor contexts including melanoma, colorectal cancer, glioblastoma, head and neck squamous cell carcinoma, bladder cancer, and pancreatic cancer. Their mechanism (s) of action relative to other immunotherapy approaches (e.g., antigen-defined cancer vaccines, CAR T cells, dendritic cell vaccines, and immune checkpoint blockade), as well as their potential to complement these approaches are also discussed. Examples to be reviewed include TLR agonists, STING agonists, RIG-I agonists, and attenuated or engineered viruses and bacterium. I also review common key requirements for effective in situ immune activation, discuss differences between various strategies inclusive of mechanisms that may ultimately limit or preclude antitumor efficacy, and provide a summary of relevant clinical data.

Repolarization of Tumor-Infiltrating Myeloid Cells for Augmentation of CAR T Cell Therapies

Although CAR T cell therapies have proven to be effective in treating hematopoietic cancers, their abilities to regress solid tumors have been less encouraging. Mechanisms to explain these disparities have focused primarily on differences in cancer cell heterogeneity, barriers to CAR T cell penetration of solid tumors, and immunosuppressive microenvironments. To evaluate the contributions of immunosuppressive tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs) on CAR T cell efficacies, we have exploited the ability of a folate-targeted Toll-like receptor 7 agonist (FA-TLR7-1A) to specifically reactivate TAMs and MDSCs from an immunosuppressive to pro-inflammatory phenotype without altering the properties of other immune cells. We report here that FA-TLR7-1A significantly augments standard CAR T cell therapies of 4T1 solid tumors in immune competent mice. We further show that co-administration of the FA-TLR7-1A with the CAR T cell therapy not only repolarizes TAMs and MDSCs from an M2-like anti-inflammatory to M1-like pro-inflammatory phenotype, but also enhances both CAR T cell and endogenous T cell accumulation in solid tumors while concurrently increasing their states of activation. Because analogous myeloid cells in healthy tissues ar not altered by administration of FA-TLR7-1A, no systemic activation of the immune system nor accompanying weight loss is observed. These data argue that immunosuppressive myeloid cells contribute prominently to the failure of CAR T cells to eradicate solid tumors and suggest that methods to reprogram tumor associated myeloid cells to a more inflammatory phenotype could significantly augment the potencies of CAR T cell therapies.

Delivery of cisplatin and resiquimod in nanomicelles for the chemoimmunotherapy of ovarian cancer

Background

To explore the effect and mechanism of delivery of cisplatin (CDDP) and resiquimod in nanomicelles for the chemoimmunotherapy of ovarian cancer in vivo and in vitro.

Methods

Poly(l-glutamic acid)-graft-methoxypolyethylene glycols (PLG-g-mPEG) was used to carry cisplatin and resiquimod for the preparation of CDDP/resiquimod/PLG-g-mPEG. We determined the loading content (LC) and encapsulation efficiency (EE), and then observed the particle shape, particle size distribution and zeta potential. In this study, we recruited 30 healthy adult participants and isolated mononuclear cells, and they were randomly classified into a control group, a CDDP group, a resiquimod group, a CDDP/resiquimod/PLG-g-mPEG group and a IFN-γ + LPS group to identify macrophages markers in different polarization states. We conducted microprobe synchrotron radiation X-ray fluorescence (SRXRF) imaging to observe the cell uptake. Furthermore, we observed the effects of CDDP/resiquimod/PLG-g-mPEG on the growth and colony formation of SW626 cells and the expressions of apoptosis-associated genes and proteins. Tumor-bearing mouse models of ovarian cancer were prepared and randomized into a negative control group, a PLG-g-mPEG group, a CDDP group, a resiquimod group and a CDDP/resiquimod/PLG-g-mPEG group, so as to analyze the anti-cancer effect of CDDP/resiquimod/PLG-g-mPEG in vivo.

Results

The LC and EE of CDDP/resiquimod/PLG-g-mPEG were 19.42% and 90.12%, respectively. Nanoparticles were uniform spherical in shape and closely arranged together, with a typical core–shell structure, and their average particle size and zeta potential were 82.36 nm and − 23.69 mV, respectively. When CDDP/resiquimod/PLG-g-mPEG group was compared with the control group, the positive expression rate of CD16 in the CDDP/resiquimod/PLG-g-mPEG group highly increased, whereas the positive expression rate of CD163 dramatically decreased. In the meantime, Arg1 and Mrc1 mRNA expressions significantly decreased whereas IL-12 and NOS2 mRNA expressions dramatically increased (P < 0.05). Elemental mapping of cells exhibited notable internalization of cisplatin delivered by CDDP/resiquimod/PLG-g-mPEG to cytoplasm. We compared the cell survival rate between the CDDP/resiquimod/PLG-g-mPEG group and the control group, the CDDP/resiquimod/PLG-g-mPEG group sharply reduced (P < 0.05). What’s more, the inhibitory effect got strengthened as the reaction time was prolonged, with the synergy coefficient of 0.31.

Conclusion

PLG-g-mPEG-loaded CDDP and resiquimod effectively achieves the targeted delivery of chemotherapy and immunotherapy, with a strong synergistic anti-cancer effect.

Recent Advances in the Development of Toll-like Receptor Agonist-Based Vaccine Adjuvants for Infectious Diseases

Vaccines are powerful tools for controlling microbial infections and preventing epidemic diseases. Efficient inactive, subunit, or viral-like particle vaccines usually rely on a safe and potent adjuvant to boost the immune response to the antigen. After a slow start, over the last decade there has been increased developments on adjuvants for human vaccines. The development of adjuvants has paralleled our increased understanding of the molecular mechanisms for the pattern recognition receptor (PRR)-mediated activation of immune responses. Toll-like receptors (TLRs) are a group of PRRs that recognize microbial pathogens to initiate a host’s response to infection. Activation of TLRs triggers potent and immediate innate immune responses, which leads to subsequent adaptive immune responses. Therefore, these TLRs are ideal targets for the development of effective adjuvants. To date, TLR agonists such as monophosphoryl lipid A (MPL) and CpG-1018 have been formulated in licensed vaccines for their adjuvant activity, and other TLR agonists are being developed for this purpose. The COVID-19 pandemic has also accelerated clinical research of vaccines containing TLR agonist-based adjuvants. In this paper, we reviewed the agonists for TLR activation and the molecular mechanisms associated with the adjuvants’ effects on TLR activation, emphasizing recent advances in the development of TLR agonist-based vaccine adjuvants for infectious diseases.

Safety and clinical activity of intratumoral MEDI9197 alone and in combination with durvalumab and/or palliative radiation therapy in patients with advanced solid tumors

Background

MEDI9197 is an intratumorally administered toll-like receptor 7 and 8 agonist. In mice, MEDI9197 modulated antitumor immune responses, inhibited tumor growth and increased survival. This first-time-in-human, phase 1 study evaluated MEDI9197 with or without the programmed cell death ligand-1 (PD-L1) inhibitor durvalumab and/or palliative radiation therapy (RT) for advanced solid tumors.

Patients and methods

Eligible patients had at least one cutaneous, subcutaneous, or deep-seated lesion suitable for intratumoral (IT) injection. Dose escalation used a standard 3+3 design. Patients received IT MEDI9197 0.005–0.055 mg with or without RT (part 1), or IT MEDI9197 0.005 or 0.012 mg plus durvalumab 1500 mg intravenous with or without RT (part 3), in 4-week cycles. Primary endpoints were safety and tolerability. Secondary endpoints included pharmacokinetics, pharmacodynamics, and objective response based on Response Evaluation Criteria for Solid Tumors version 1.1. Exploratory endpoints included tumor and peripheral biomarkers that correlate with biological activity or predict response.

Results

From November 2015 to March 2018, part 1 enrolled 35 patients and part 3 enrolled 17 patients; five in part 1 and 2 in part 3 received RT. The maximum tolerated dose of MEDI9197 monotherapy was 0.037 mg, with dose-limiting toxicity (DLT) of cytokine release syndrome in two patients (one grade 3, one grade 4) and 0.012 mg in combination with durvalumab 1500 mg with DLT of MEDI9197-related hemorrhagic shock in one patient (grade 5) following liver metastasis rupture after two cycles of MEDI9197. Across parts 1 and 3, the most frequent MEDI9197-related adverse events (AEs) of any grade were fever (56%), fatigue (31%), and nausea (21%). The most frequent MEDI9197-related grade ≥3 events were decreased lymphocytes (15%), neutrophils (10%), and white cell counts (10%). MEDI9197 increased tumoral CD8+ and PD-L1+ cells, inducing type 1 and 2 interferons and Th1 response. There were no objective clinical responses; 10 patients in part 1 and 3 patients in part 3 had stable disease ≥8 weeks.

Conclusion

IT MEDI9197 was feasible for subcutaneous/cutaneous lesions but AEs precluded its use in deep-seated lesions. Although no patients responded, MEDI9197 induced systemic and intratumoral immune activation, indicating potential value in combination regimens in other patient populations.

Trial registration number

NCT02556463.

Employing Drug Delivery Strategies to Overcome Challenges Using TLR7/8 Agonists for Cancer Immunotherapy

Toll-like receptors (TLRs) are a potential target for cancer immunotherapy due to their role in the activation of the innate immune system. More specifically, TLR7 and TLR8, two structurally similar pattern recognition receptors that trigger interferon and cytokine responses, have proven to be therapeutically relevant targets for cancer in numerous preclinical and clinical studies. When triggered by an agonist, such as imiquimod or resiquimod, the TLR7/8 activation pathway induces cellular and humoral immune responses that can kill cancer cells with high specificity. Unfortunately, TLR7/8 agonists also present a number of issues that must be overcome prior to broad clinical implementation, such as poor drug solubility and systemic toxic effects. To overcome the key limitations of TLR7/8 agonists as a cancer therapy, biomaterial-based drug delivery systems have been developed. These delivery devices are highly diverse in their design and include systems that can be directly administered to the tumor, passively accumulated in relevant cancerous and lymph tissues, triggered by environmental stimuli, or actively targeted to specific physiological areas and cellular populations. In addition to improved delivery systems, recent studies have also demonstrated the potential benefits of TLR7/8 agonist co-delivery with other types of therapies, particularly checkpoint inhibitors, cancer vaccines, and chemotherapeutics, which can yield impressive anti-cancer effects. In this review, we discuss recent advances in the development of TLR7/8 agonist delivery systems and provide perspective on promising future directions.

Pro-Tumorigenic Macrophage Infiltration in Oral Squamous Cell Carcinoma and Possible Macrophage-Aimed Therapeutic Interventions

In Oral Squamous Cell Carcinomas (OSCC), as in other solid tumors, stromal cells strongly support the spread and growth of the tumor. Macrophages in tumors (tumor-associated macrophages or “TAMs”), can swing between a pro-inflammatory and anti-tumorigenic (M1-like TAMs) state or an anti‐inflammatory and pro-tumorigenic (M2-like TAMs) profile depending on the tumor microenvironment cues. Numerous clinical and preclinical studies have demonstrated the importance of macrophages in the prognosis of patients with different types of cancer. Here, our aim was to review the role of M2-like TAMs in the prognosis of patients with OSCC and provide a state of the art on strategies for depleting or reprogramming M2-like TAMs as a possible therapeutic solution for OSCC. The Clinical studies reviewed showed that higher density of CD163+ M2-like TAMs associated with worse survival and that CD206+ M2-TAMs are involved in OSCC progression through epidermal growth factor (EGF) secretion, underlining the important role of CD206 as a marker of OSCC progression and as a therapeutic target. Here, we provide the reader with the current tools, in preclinical and clinical stage, for depleting M2-like TAMs, re-educating them towards M1-like TAMs, and exploiting TAMs as drug delivery vectors.

Intratumoral immunotherapy using platelet-cloaked nanoparticles enhances antitumor immunity in solid tumors

Intratumoral immunotherapy is an emerging modality for the treatment of solid tumors. Toll-like receptor (TLR) agonists have shown promise for eliciting immune responses, but systemic administration often results in the development of adverse side effects. Herein, we investigate whether localized delivery of the TLR agonist, resiquimod (R848), via platelet membrane-coated nanoparticles (PNP-R848) elicits antitumor responses. The membrane coating provides a means of enhancing interactions with the tumor microenvironment, thereby maximizing the activity of R848. Intratumoral administration of PNP-R848 strongly enhances local immune activation and leads to complete tumor regression in a colorectal tumor model, while providing protection against repeated tumor re-challenges. Moreover, treatment of an aggressive breast cancer model with intratumoral PNP-R848 delays tumor growth and inhibits lung metastasis. Our findings highlight the promise of locally delivering immunostimulatory payloads using biomimetic nanocarriers, which possess advantages such as enhanced biocompatibility and natural targeting affinities.

Trial watch: FDA-approved Toll-like receptor agonists for cancer therapy

Toll-like receptors (TLRs) have first been characterized for their capacity to detect conserved microbial components like lipopolysaccharide (LPS) and double-stranded RNA, resulting in the elicitation of potent (innate) immune responses against invading pathogens. More recently, TLRs have also been shown to promote the activation of the cognate immune system against cancer cells. Today, only three TLR agonists are approved by FDA for use in humans: the bacillus Calmette-Guérin (BCG), monophosphoryl lipid A (MPL) and imiquimod. BCG (an attenuated strain of Mycobacterium bovis) is mainly used as a vaccine against tuberculosis, but also for the immunotherapy of in situ bladder carcinoma. MPL (derived from the LPS of Salmonella minnesota) is included in the formulation of Cervarix®, a vaccine against human papillomavirus-16 and -18. Imiquimod (a synthetic imidazoquinoline) is routinely employed for actinic keratosis, superficial basal cell carcinoma, and external genital warts (condylomata acuminata). In this Trial Watch, we will summarize the results of recently completed clinical trials and discuss the progress of ongoing studies that have evaluated/are evaluating FDA-approved TLR agonists as off-label medications for cancer therapy.

Activatable polymer nanoagonist for second near-infrared photothermal immunotherapy of cancer

Nanomedicine in combination with immunotherapy offers opportunities to treat cancer in a safe and effective manner; however, remote control of immune response with spatiotemporal precision remains challenging. We herein report a photothermally activatable polymeric pro-nanoagonist (APNA) that is specifically regulated by deep-tissue-penetrating second near-infrared (NIR-II) light for combinational photothermal immunotherapy. APNA is constructed from covalent conjugation of an immunostimulant onto a NIR-II semiconducting transducer through a labile thermo-responsive linker. Upon NIR-II photoirradiation, APNA mediates photothermal effect, which not only triggers tumor ablation and immunogenic cell death but also initiates the cleavage of thermolabile linker to liberate caged agonist for in-situ immune activation in deep solid tumor (8 mm). Such controlled immune regulation potentiates systemic antitumor immunity, leading to promoted cytotoxic T lymphocytes and helper T cell infiltration in distal tumor, lung and liver to inhibit cancer metastasis. Thereby, the present work illustrates a generic strategy to prepare pro-immunostimulants for spatiotemporal regulation of cancer nano-immunotherapy.

Precise control of immune response remains challenging for cancer immunotherapy. Here, the authors report on photothermally activatable semiconducting polymeric pro-agonist in response to second near-infrared window light for regulated photothermal immunotherapy.

The Next Generation of Pattern Recognition Receptor Agonists: Improving Response Rates in Cancer Immunotherapy

The recent success of checkpoint blocking antibodies has sparked a revolution in cancer immunotherapy. Checkpoint inhibition activates the adaptive immune system leading to durable responses across a range of tumor types, although this response is limited to patient populations with pre-existing tumor-infiltrating T cells. Strategies to stimulate the immune system to prime an antitumor response are of intense interest and several groups are now working to develop agents to activate the Pattern Recognition Receptors (PRRs), proteins which detect pathogenic and damageassociated molecules and respond by activating the innate immune response. Although early efforts focused on the Toll-like Receptor (TLR) family of membrane-bound PRRs, TLR activation has been associated with both pro- and antitumor effects. Nonetheless, TLR agonists have been deployed as potential anticancer agents in a range of clinical trials. More recently, the cytosolic PRR Stimulator of IFN Genes (STING) has attracted attention as another promising target for anticancer drug development, with early clinical data beginning to emerge. Besides STING, several other cytosolic PRR targets have likewise captured the interest of the drug discovery community, including the RIG-Ilike Receptors (RLRs) and NOD-like Receptors (NLRs). In this review, we describe the outlook for activators of PRRs as anticancer therapeutic agents and contrast the earlier generation of TLR agonists with the emerging focus on cytosolic PRR activators, both as single agents and in combination with other cancer immunotherapies.

The immunorecognition, subcellular compartmentalization, and physicochemical properties of nucleic acid nanoparticles can be controlled by composition modification

Nucleic acid nanoparticles (NANPs) have become powerful new platforms as therapeutic and diagnostic tools due to the innate biological ability of nucleic acids to identify target molecules or silence genes involved in disease pathways. However, the clinical application of NANPs has been limited by factors such as chemical instability, inefficient intracellular delivery, and the triggering of detrimental inflammatory responses following innate immune recognition of nucleic acids. Here, we have studied the effects of altering the chemical composition of a circumscribed panel of NANPs that share the same connectivity, shape, size, charge and sequences. We show that replacing RNA strands with either DNA or chemical analogs increases the enzymatic and thermodynamic stability of NANPs. Furthermore, we have found that such composition changes affect delivery efficiency and determine subcellular localization, effects that could permit the targeted delivery of NANP-based therapeutics and diagnostics. Importantly, we have determined that altering NANP composition can dictate the degree and mechanisms by which cell immune responses are initiated. While RNA NANPs trigger both TLR7 and RIG-I mediated cytokine and interferon production, DNA NANPs stimulate minimal immune activation. Importantly, incorporation of 2'F modifications abrogates RNA NANP activation of TLR7 but permits RIG-I dependent immune responses. Furthermore, 2'F modifications of DNA NANPs significantly enhances RIG-I mediated production of both proinflammatory cytokines and interferons. Collectively this indicates that off-target effects may be reduced and/or desirable immune responses evoked based upon NANPs modifications. Together, our studies show that NANP composition provides a simple way of controlling the immunostimulatory potential, and physicochemical and delivery characteristics, of such platforms.

Development of thermosensitive resiquimod-loaded liposomes for enhanced cancer immunotherapy

Resiquimod (R848) is a toll-like receptor 7 and 8 (TLR7/8) agonist with potent antitumor and immunostimulatory activity. However, systemic delivery of R848 is poorly tolerated because of its poor solubility in water and systemic immune activation. In order to address these limitations, we developed an intravenously-injectable formulation with R848 using thermosensitive liposomes (TSLs) as a delivery vehicle. R848 was remotely loaded into TSLs composed of DPPC: DSPC: DSPE-PEG2K (85:10:5, mol%) with 100 mM FeSO₄ as the trapping agent inside. The final R848 to lipid ratio of the optimized R848-loaded TSLs (R848-TSLs) was 0.09 (w/w), 10-fold higher than the previously-reported values. R848-TSLs released 80% of R848 within 5 min at 42 °C. These TSLs were then combined with αPD-1, an immune checkpoint inhibitor, and ultrasound-mediated hyperthermia in a neu deletion (NDL) mouse mammary carcinoma model (Her2⁺, ER/PR negative). Combined with αPD-1, local injection of R848-TSLs showed superior efficacy with complete NDL tumor regression in both treated and abscopal sites achieved in 8 of 11 tumor bearing mice over 100 days. Immunohistochemistry confirmed enhanced CD8⁺ T cell infiltration and accumulation by R848-TSLs. Systemic delivery of R848-TSLs, combined with local hyperthermia and αPD-1, inhibited tumor growth and extended median survival from 28 days (non-treatment control) to 94 days. Upon re-challenge with reinjection of tumor cells, none of the previously cured mice developed tumors, as compared with 100% of age-matched control mice. The dose of R848 (10 μg for intra-tumoral injection or 6 mg/kg for intravenous injection delivered up to 4 times) was well-tolerated without weight loss or organ hypertrophy. In summary, we developed R848-TSLs that can be administered locally or systematically, resulting in tumor regression and enhanced survival when combined with αPD-1 in mouse models of breast cancer.

Imiquimod - A toll like receptor 7 agonist - Is an ideal option for management of COVID 19

According to numerous recent publications, the COVID-19 patients have lymphopenia, higher infection-related biomarkers and several elevated inflammatory cytokines (i.e. tumor necrosis factor (TNF)-α, interleukin IL-2R and IL-6). The total number of B cells, T cells and NK cells are significantly decreased. RNA viruses, SARS-CoV-2 included, hit the innate immune system in order to cause infection, through TLRs 3, 7 and 8. Imiquimod is an immune-stimulator that activates TLR 7 and can be used to enhance the innate and adaptive immunity. Preclinical and clinical trials are proposed.

Reprogramming of profibrotic macrophages for treatment of bleomycin-induced pulmonary fibrosis

Fibrotic diseases cause organ failure that lead to ~45% of all deaths in the United States. Activated macrophages stimulate fibrosis by secreting cytokines that induce fibroblasts to synthesize collagen and extracellular matrix proteins. Although suppression of macrophage-derived cytokine production can halt progression of fibrosis, therapeutic agents that prevent release of these cytokines (e.g., TLR7 agonists) have proven too toxic to administer systemically. Based on the expression of folate receptor β solely on activated myeloid cells, we have created a folate-targeted TLR7 agonist (FA-TLR7-54) that selectively accumulates in profibrotic macrophages and suppresses fibrosis-inducing cytokine production. We demonstrate that FA-TLR7-54 reprograms M2-like fibrosis-inducing macrophages into fibrosis-suppressing macrophages, resulting in dramatic declines in profibrotic cytokine release, hydroxyproline biosynthesis, and collagen deposition, with concomitant increases in alveolar airspaces. Although nontargeted TLR7-54 is lethal at fibrosis-suppressing doses, FA-TLR7-54 halts fibrosis without evidence of toxicity. Taken together, FA-TLR7-54 is shown to constitute a novel and potent approach for treating fibrosis without causing dose-limiting systemic toxicities.

Developments in anticancer vaccination: budding new adjuvants

The immune system has a limited capacity to recognize and fight cells that become cancerous and in cancer patients, the immune system has to seek the right balance between cancer rejection and host-immunosupression. The tumor milieu builds a protective shell and tumor cells rapidly accumulate mutations that promote antigen variability and immune-escape. Therapeutic vaccination of cancer is a promising strategy the success of which depends on a powerful activation of the cells of the adaptive immune system specific for tumor-cell detection and killing (e.g. CD4+and CD8+T-cells). In the last decades, the search for novel adjuvants that enhance dendritic cell (DC) function and their ability to prime T-cells has flourished and some Toll-like receptor (TLR) agonists have long been known to be valid immune adjuvants. The implementation of TLR-synthetic agonists in clinical studies of cancer vaccination is replacing the initial use of microbial-derived products with some encouraging results. The purpose of this review is to summarize the latest discoveries of TLR-synthetic agonists with adjuvant potential in anti-cancer vaccination.

Optimization of 8-oxoadenines with toll-like-receptor 7 and 8 activity

Toll-like receptors 7 and 8 (TLR7/8) agonists are potent immunostimulants that are attracting considerable interest as vaccine adjuvants. We recently reported the synthesis of a new series of 2-O-butyl-8-oxoadenines substituted at the 9-position with various linkers and N-heterocycles, and showed that TLR7/8 selectivity, potency and cytokine induction could be modulated by varying the alkyl linker length and the N-heterocyclic ring. In the present study, we further optimized the oxoadenine scaffold by investigating the effect of different substituents at the 2-position of the oxoadenine on TLR7/8 potency/selectivity, cytokine induction and DC maturation in human PBMCs. The results show that introducing a 1-(S)-methylbutoxy group at the 2-position of the oxoadenine significantly increased potency for TLR7/8 activity, cytokine induction and DC maturation.

Amphiphilic poly(esteracetal)s as dual pH- and enzyme-responsive micellar immunodrug delivery systems

Amphiphilic poly(esteracetal) micelles encapsulate potent immune modulatory drugs, but fall apart and release them upon dual pH or enzymatic stimuli.

Synthesis and immunostimulatory activity of sugar-conjugated TLR7 ligands

Toll-like receptors (TLRs) are a type of pattern recognition receptors (PRRs), which are activated by recognizing pathogen-associated molecular patterns (PAMPs). The activation of TLRs initiates innate immune responses and subsequently leads to adaptive immune responses. TLR agonists are effective immuomodulators in vaccine adjuvants for infectious diseases and cancer immunotherapy. In exploring hydrophilic small molecules of TLR7 ligands using the cell-targeted property of a vaccine adjuvant, we conjugated 1V209, a small TLR7 ligand molecule, with various low or middle molecular weight sugar molecules that work as carriers. The sugar-conjugated 1V209 derivatives showed increased water solubility and higher immunostimulatory activity in both mouse and human cells compared to unmodified 1V209. The improved immunostimulatory potency of sugar-conjugates was attenuated by an inhibitor of endocytic process, cytochalasin D, suggesting that conjugation of sugar moieties may enhance the uptake of TLR7 ligand into the endosomal compartment. Collectively our results support that sugar-conjugated TLR7 ligands are applicable to novel drugs for cancer and vaccine therapy.

Combretastatin A4 Nanoparticles Combined with Hypoxia-Sensitive Imiquimod: A New Paradigm for the Modulation of Host Immunological Responses during Cancer Treatment

Vascular disrupting agents (VDAs) have great potential in cancer treatment. However, in addition to their direct tumoral vascular collapse effect, VDAs activate host immunological responses, which can remarkably impair their anticancer efficacy. Here, a VDA nanomedicine, poly(l-glutamic acid)-graft-methoxy poly(ethylene glycol)/combretastatin A4 (CA4-NPs), is found to induce the intratumor infiltration of immature plasmacytoid dendritic cells (pDCs), thereby curtailing anticancer immunity. To overcome this problem, hypoxia-sensitive imiquimod (hs-IMQ) is developed, which is selectively activated into imiquimod (IMQ) in treated tumors following the catalysis of CA4-NPs-induced nitroreductase (NTR). The combination of hs-IMQ and CA4-NPs causes a 6.3-fold enhancement of active IMQ concentration in tumors, as compared to hs-IMQ treatment alone. The in situ-generated IMQ alters the tumor microenvironment from a state of immunosuppression to immune activation. Hs-IMQ achieves this effect through the conversion of immature pDCs into their active form, leading to the robust infiltration and priming of natural killer cells and cytotoxic T-lymphocytes in treated tumors. Thus, the CA4-NPs and hs-IMQ combination treatment synergistically inhibits tumor growth and metastasis in 4T1 tumor-bearing mice. This work offers new approaches to harness intratumor pDCs to reverse the immune suppression resulting from VDA treatment. These findings additionally provide a mechanistic rationale for the use of VDAs in combination with TLR agonists to trigger in situ immune activation and enhance anticancer efficacy.

Synthetic Toll-like Receptors 7 and 8 Agonists: Structure-Activity Relationship in the Oxoadenine Series

Toll-like receptors 7 and 8 (TLR7/8) are broadly expressed on antigen-presenting cells, making TLR7/8 agonists likely candidates for the development of new vaccine adjuvants. We previously reported the synthesis of a new series of 8-oxoadenines substituted at the 9-position with a 4-piperidinylalkyl moiety and demonstrated that TLR7/8 selectivity and potency could be modulated by varying the length of the alkyl linker. In the present study, we broadened our initial structure-activity relationship study to further evaluate the effects of N-heterocycle ring size, chirality, and substitution on TLR7/8 potency, receptor selectivity, and cytokine (IFNα and TNFα) induction from human peripheral blood mononuclear cells (PBMCs). TLR7/8 activity correlated primarily to linker length and to a lesser extent to ring size, while ring chirality had little effect on TLR7/8 potency or selectivity. Substitution of the heterocyclic ring with an aminoalkyl or hydroxyalkyl group for subsequent conjugation to phospholipids or antigens was well tolerated with the retention of both TLR7/8 activity and cytokine induction from human PBMCs.

Syringeable immunotherapeutic nanogel reshapes tumor microenvironment and prevents tumor metastasis and recurrence

The low response rate of current cancer immunotherapy suggests the presence of few antigen-specific T cells and a high number of immunosuppressive factors in tumor microenvironment (TME). Here, we develop a syringeable immunomodulatory multidomain nanogel (iGel) that overcomes the limitation by reprogramming of the pro-tumoral TME to antitumoral immune niches. Local and extended release of immunomodulatory drugs from iGel deplete immunosuppressive cells, while inducing immunogenic cell death and increased immunogenicity. When iGel is applied as a local postsurgical treatment, both systemic antitumor immunity and a memory T cell response are generated, and the recurrence and metastasis of tumors to lungs and other organs are significantly inhibited. Reshaping of the TME using iGel also reverts non-responding groups to checkpoint blockade therapies into responding groups. The iGel is expected as an immunotherapeutic platform that can reshape immunosuppressive TMEs and synergize cancer immunotherapy with checkpoint therapies, with minimized systemic toxicity.

The limited efficacy of current immunotherapy suggests low antigen-specific T cells and immunosuppressive factors in tumor microenvironment (TME). Here, the authors develop a syringeable immunomodulatory multi-domain nanogel that can reprogram the TME and induce enhanced cancer immunotherapy.

Immunological basis for enhanced immunity of nanoparticle vaccines

INTRODUCTION

Immunization has been a remarkably successful public health intervention; however, new approaches to vaccine design are essential to counter existing and emerging infectious diseases which have defied traditional vaccination efforts to date. Nanoparticles (ordered structures with dimensions in the range of 1-1000 nm) have great potential to supplement traditional vaccines based upon pathogen subunits, or killed or attenuated microorganisms, as exemplified by the successful licensure of virus-like particle vaccines for human papillomavirus and hepatitis B. However, the immunological mechanisms that underpin the potent immunity of nanoparticle vaccines are poorly defined.

AREAS COVERED

Here, we review the immunity of nanoparticle immunization. The display of antigen in a repetitive, ordered array mimics the surface of a pathogen, as does their nanoscale size. These properties facilitate enhanced innate immune activation, improved drainage and retention in lymph nodes, stronger engagement with B cell receptors, and augmented T cell help in driving B cell activation.

EXPERT OPINION

In the near future, increasingly complex nanoparticle vaccines displaying multiple antigens and/or co-delivered adjuvants will reach clinical trials. An improved mechanistic understanding of nanoparticle vaccination will ultimately facilitate the rational design of improved vaccines for human health.

Molecular Repolarisation of Tumour-Associated Macrophages

The tumour microenvironment (TME) is composed of extracellular matrix and non-mutated cells supporting tumour growth and development. Tumour-associated macrophages (TAMs) are among the most abundant immune cells in the TME and are responsible for the onset of a smouldering inflammation. TAMs play a pivotal role in oncogenic processes as tumour proliferation, angiogenesis and metastasis, and they provide a barrier against the cytotoxic effector function of T lymphocytes and natural killer (NK) cells. However, TAMs are highly plastic cells that can adopt either pro- or anti-inflammatory roles in response to environmental cues. Consequently, TAMs represent an attractive target to recalibrate immune responses in the TME. Initial TAM-targeted strategies, such as macrophage depletion or disruption of TAM recruitment, have shown beneficial effects in preclinical models and clinical trials. Alternatively, reprogramming TAMs towards a proinflammatory and tumouricidal phenotype has become an attractive strategy in immunotherapy. This work summarises the molecular wheelwork of macrophage biology and presents an overview of molecular strategies to repolarise TAMs in immunotherapy.

[Cytopenia under topical imiquimod in two patients treated with oral hydroxyurea]

BACKGROUND

Aldara^® is a topical immunomodulatory treatment. The risks of systemic passage are minimal. There have been rare reports of systemic adverse effects.

PATIENTS AND METHODS

Case 1. Five sachets weekly of imiquimod were prescribed for Bowen's disease on the forearm in a patient known to have essential thrombocytosis under Hydrea^®. His CBC was normal (6000 leukocytes/mm³, 2200 PMN/mm, 230,000 platelets/mm³). Imiquimod was given in 15 sachets weekly. Fifteen day later, the patient presented bicytopenia (3000 leukocytes/mm³, 1400 PMN/mm³, 119,000 platelets/mm³). Hydroxyurea and imiquimod were suspended until normalization of CBC. Hydroxyurea was resumed without recurrence of the bicytopenia. The patient's history included an identical episode following application of imiquimod. Case 2. Five sachets weekly of imiquimod were prescribed for actinic keratosis on the scalp in a patient known to have primary polycythemia under hydroxyurea. Her CBC was normal except for anemia (Hb 11.5g/L, 160,000 platelets/mm³, 1100 lymphocytes/mm³). Imiquimod was given in 12 sachets weekly. Ten days later, anemia increased (Hb 10g/dL) with lymphopenia (800/mm³) and thrombocytopenia (115,000/mm³). Suspension of imiquimod resulted in normalization of the previous CBC values.

DISCUSSION

. The literature review identified reports of dose-dependent lymphopenia under oral imiquimod but not under Aldara^®. The National Pharmacovigilance Database listed 10 cases of hematological disorders most likely caused by Aldara^®. Hydroxyurea may induce cytopenia, and while it was not considered the sole causative agent in this case, it is likely to have had a triggering role in these patients with blood dyscrasias. Our findings show that misuse of imiquimod carries a potential risk of hematologic abnormality in patients receiving concomitant hydroxyurea, a commonly combined drug.

Induction of oligoclonal CD8 T cell responses against pulmonary metastatic cancer by a phospholipid-conjugated TLR7 agonist

Recent advances in cancer immunotherapy have improved patient survival. However, only a minority of patients with pulmonary metastatic disease respond to treatment with checkpoint inhibitors. As an alternate approach, we have tested the ability of systemically administered 1V270, a toll-like receptor 7 (TLR7) agonist conjugated to a phospholipid, to inhibit lung metastases in two variant murine 4T1 breast cancer models, as well as in B16 melanoma, and Lewis lung carcinoma models. In the 4T1 breast cancer models, 1V270 therapy inhibited lung metastases if given up to a week after primary tumor initiation. The treatment protocol was facilitated by the minimal toxic effects exerted by the phospholipid TLR7 agonist compared with the unconjugated agonist. 1V270 exhibited a wide therapeutic window and minimal off-target receptor binding. The 1V270 therapy inhibited colonization by tumor cells in the lungs in an NK cell dependent manner. Additional experiments revealed that single administration of 1V270 led to tumor-specific CD8⁺ cell-dependent adaptive immune responses that suppressed late-stage metastatic tumor growth in the lungs. T cell receptor (TCR) repertoire analyses showed that 1V270 therapy induced oligoclonal T cells in the lungs and mediastinal lymph nodes. Different animals displayed commonly shared TCR clones following 1V270 therapy. Intranasal administration of 1V270 also suppressed lung metastasis and induced tumor-specific adaptive immune responses. These results indicate that systemic 1V270 therapy can induce tumor-specific cytotoxic T cell responses to pulmonary metastatic cancers and that TCR repertoire analyses can be used to monitor, and to predict, the response to therapy.

Stable Nanoemulsions for the Delivery of Small Molecule Immune Potentiators

Adjuvants are required to enhance immune responses to typically poorly immunogenic recombinant antigens. Toll-like receptor agonists (TLRa) have been widely evaluated as adjuvants because they activate the innate immune system. Currently, licensed vaccines adjuvanted with TLRa include the TLR4 agonist monophosphoryl lipid, while additional TLRa are in clinical development. Unfortunately, naturally derived TLRa are often complex and heterogeneous entities, which brings formulation challenges. Consequently, the use of synthetic small-molecule TLRa has significant advantages because they are well-defined discrete molecules, which can be chemically modified to modulate their physicochemical properties. We previously described the discovery of a family of TLR7 agonists based on a benzonaphthyridine scaffold. In addition, we described how Alum could be used to deliver these synthetic TLRa. An alternative adjuvant approach with enhanced potency over Alum are squalene containing oil-in-water emulsions, which have been included in licensed influenza vaccines, including Fluad (MF59 adjuvanted) and Pandemrix (AS03 adjuvanted). Here, we describe how to enable the co-delivery of a TLR7 agonist in a squalene-based oil-in-water emulsion, for adjuvant evaluation.

TLR7/8-agonist-loaded nanoparticles promote the polarization of tumour-associated macrophages to enhance cancer immunotherapy

Tumour-associated macrophages (TAMs) are abundant in many cancers, and often display an immune-suppressive M2-like phenotype that fosters tumour growth and promotes resistance to therapy. Yet macrophages are highly plastic and can also acquire an anti-tumourigenic M1-like phenotype. Here, we show that R848, an agonist of the toll-like receptors (TLRs) TLR7 and TLR8 identified in a morphometric-based screen, is a potent driver of the M1 phenotype in vitro and that R848-loaded β-cyclodextrin nanoparticles (CDNPs) lead to efficient drug delivery to TAMs in vivo. As a monotherapy, the administration of CDNP-R848 in multiple tumour models in mice altered the functional orientation of the tumour immune microenvironment towards an M1 phenotype, leading to controlled tumour growth and protecting the animals against tumour rechallenge. When used in combination with the immune checkpoint inhibitor anti-PD-1, we observed improved immunotherapy response rates, also in a tumour model resistant to anti-PD-1 therapy. Our findings demonstrate the ability of rationally engineered drug–nanoparticle combinations to efficiently modulate TAMs for cancer immunotherapy.

Toll-like Receptor Agonist Conjugation: A Chemical Perspective

Toll-like receptors (TLRs) are vital elements of the mammalian immune system that function by recognizing pathogen-associated molecular patterns (PAMPs), bridging innate and adaptive immunity. They have become a prominent therapeutic target for the treatment of infectious diseases, cancer, and allergies, with many TLR agonists currently in clinical trials or approved as immunostimulants. Numerous studies have shown that conjugation of TLR agonists to other molecules can beneficially influence their potency, toxicity, pharmacokinetics, or function. The functional properties of TLR agonist conjugates, however, are highly dependent on the ligation strategy employed. Here, we review the chemical structural requirements for effective functional TLR agonist conjugation. In addition, we provide similar analysis for those that have yet to be conjugated. Moreover, we discuss applications of covalent TLR agonist conjugation and their implications for clinical use.

Environmentally Triggerable Retinoic Acid-Inducible Gene I Agonists Using Synthetic Polymer Overhangs

Retinoic acid-inducible gene I (RIG-I) is a cytosolic pattern recognition receptor (PRR) that potently activates antiviral innate immunity upon recognition of 5' triphosphorylated double-stranded RNA (pppRNA). Accordingly, RNA ligands of the RIG-I pathway have recently emerged as promising antiviral agents, vaccine adjuvants, and cancer immunotherapeutics. However, RIG-I is expressed constitutively in virtually all cell types, and therefore administration of RIG-I agonists causes risk for systemic inflammation and possible dose-limiting toxicities. Here, we establish proof-of-concept and initial design criteria for pppRNA prodrugs capable of activating the RIG-I pathway in response to specific environmental stimuli. We show that covalent conjugation of poly(ethylene glycol) (PEG) to the 3' end of the complementary strand, i.e., on the same side but opposite strand as the 5' triphosphate group, can generate a synthetic overhang that prevents RIG-I activation. Additionally, conjugation of PEG through a cleavable linker-here, a reducible disulfide bond-allows for removal of the synthetic overhang and restoration of immunostimulatory activity. Furthermore, we demonstrate that blockade of RIG-I activation via synthetic overhangs is dependent on PEG molecular weight, with a critical molecular weight between 550 and 1000 Da required to inhibit activity. Additionally, we demonstrate that blockade of RIG-I activity is conjugation site-dependent, as ligation of PEG to the opposite end of the RNA did not influence ligand activity. Collectively, this work demonstrates that conjugation of synthetic polymer overhangs to pppRNA through cleavable linkers is a viable strategy for the development of environmentally triggerable RIG-I-targeting prodrugs.

An Antigen-Free, Plasmacytoid Dendritic Cell-Targeting Immunotherapy To Bolster Memory CD8+ T Cells in Nonhuman Primates

The priming, boosting, and restoration of memory cytotoxic CD8⁺ T lymphocytes by vaccination or immunotherapy in vivo is an area of active research. Particularly, nucleic acid-based compounds have attracted attention due to their ability to elicit strong Ag-specific CTL responses as a vaccine adjuvant. Nucleic acid-based compounds have been shown to act as anticancer monotherapeutic agents even without coadministration of cancer Ag(s); however, so far they have lacked efficacy in clinical trials. We recently developed a second-generation TLR9 agonist, a humanized CpG DNA (K3) complexed with schizophyllan (SPG), K3-SPG, a nonagonistic Dectin-1 ligand. K3-SPG was previously shown to act as a potent monoimmunotherapeutic agent against established tumors in mice in vivo. In this study we extend the monoimmunotherapeutic potential of K3-SPG to a nonhuman primate model. K3-SPG activated monkey plasmacytoid dendritic cells to produce both IFN-α and IL-12/23 p40 in vitro and in vivo. A single injection s.c. or i.v. with K3-SPG significantly increased the frequencies of activated memory CD8⁺ T cells in circulation, including Ag-specific memory CTLs, in cynomolgus macaques. This increase did not occur in macaques injected with free CpG K3 or polyinosinic-polycytidylic acid. Injection of 2 mg K3-SPG induced mild systemic inflammation, however, levels of proinflammatory serum cytokines and circulating neutrophil influx were lower than those induced by the same dose of polyinosinic-polycytidylic acid. Therefore, even in the absence of specific Ags, we show that K3-SPG has potent Ag-specific memory CTL response-boosting capabilities, highlighting its potential as a monoimmunotherapeutic agent for chronic infectious diseases and cancer.

Imidazoquinoxaline anticancer derivatives and imiquimod interact with tubulin: Characterization of molecular microtubule inhibiting mechanisms in correlation with cytotoxicity

Displaying a strong antiproliferative activity on a wide variety of cancer cells, EAPB0203 and EAPB0503 belong to the imidazo[1,2-a]quinoxalines family of imiquimod structural analogues. EAPB0503 has been shown to inhibit tubulin polymerization. The aim of the present study is to characterize the interaction of EAPB0203 and EAPB0503 with tubulin. We combine experimental approaches at the cellular and the molecular level both in vitro and in silico in order to evaluate the interaction of EAPB0203 and EAPB0503 with tubulin. We examine the influence of EAPB0203 and EAPB0503 on the cell cycle and fate, explore the binding interaction with purified tubulin, and use a computational molecular docking model to determine the binding modes to the microtubule. We then use a drug combination study with other anti-microtubule agents to compare the binding site of EAPB0203 and EAPB0503 to known potent tubulin inhibitors. We demonstrate that EAPB0203 and EAPB0503 are capable of blocking human melanoma cells in G2 and M phases and inducing cell death and apoptosis. Second, we show that EAPB0203 and EAPB0503, but also unexpectedly imiquimod, bind directly to purified tubulin and inhibit tubulin polymerization. As suggested by molecular docking and binding competition studies, we identify the colchicine binding site on β-tubulin as the interaction pocket. Furthermore, we find that EAPB0203, EAPB0503 and imiquimod display antagonistic cytotoxic effect when combined with colchicine, and disrupt tubulin network in human melanoma cells. We conclude that EAPB0203, EAPB0503, as well as imiquimod, interact with tubulin through the colchicine binding site, and that the cytotoxic activity of EAPB0203, EAPB0503 and imiquimod is correlated to their tubulin inhibiting effect. These compounds appear as interesting anticancer drug candidates as suggested by their activity and mechanism of action, and deserve further investigation for their use in the clinic.

Fatty Acid-Mimetic Micelles for Dual Delivery of Antigens and Imidazoquinoline Adjuvants

Vaccine design has undergone a shift towards the use of purified protein subunit vaccines, which offer increased safety and greater control over antigen specificity, but at the expense of immunogenicity. Here we report the development of a new polymer-based vaccine delivery platform engineered to enhance immunity through the co-delivery of protein antigens and the Toll-like receptor 7 (TLR7) agonist imiquimod (IMQ). Owing to the preferential solubility of IMQ in fatty acids, a series of block copolymer micelles with a fatty acid-mimetic core comprising lauryl methacrylate (LMA) and methacrylic acid (MAA), and a poly(ethylene glycol) methyl ether methacrylate (PEGMA) corona decorated with pyridyl disulfide ethyl methacrylate (PDSM) moieties for antigen conjugation were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Carriers composed of 50 mole% LMA (LMA50) demonstrated the highest IMQ loading (2.2 w/w%) and significantly enhanced the immunostimulatory capacity of IMQ to induce dendritic cell maturation and proinflammatory cytokine production. Conjugation of a model antigen, ovalbumin (OVA), to the corona of IMQ-loaded LMA50 micelles enhanced in vitro antigen uptake and cross-presentation on MHC class I (MHC-I). A single intranasal (IN) immunization of mice with carriers co-loaded with IMQ and OVA elicited significantly higher pulmonary and systemic CD8+ T cell responses and increased serum IgG titer relative to a soluble formulation of antigen and adjuvant. Collectively, these data demonstrate that rationally designed fatty acid-mimetic micelles enhance intracellular antigen and IMQ delivery and have potential as synthetic vectors for enhancing the immunogenicity of subunit vaccines.

The Snowballing Literature on Imiquimod-Induced Skin Inflammation in Mice: A Critical Appraisal

Since 2009, the imiquimod- or Aldara-induced (3M Pharmaceuticals, St. Paul, MN) model of acute skin inflammation has become the most widely used mouse model in preclinical psoriasis studies. Although this model offers researchers numerous benefits, there are important limitations and possible confounding variables to consider. The imiquimod model requires careful consideration and warrants scrutiny of the data generated by its use. In this perspective, we provide an overview of the advantages and disadvantages of this mouse model and offer suggestions for its use in psoriasis research.

Influence of PapMV nanoparticles on the kinetics of the antibody response to flu vaccine

BACKGROUND

The addition of an adjuvant to a vaccine is a promising approach to increasing strength and immunogenicity towards antigens. Despite the fact that adjuvants have been used in vaccines for decades, their mechanisms of action and their influence on the kinetics of the immune response are still not very well understood. The use of papaya mosaic virus (PapMV) nanoparticles-a novel TLR7 agonist-was recently shown to improve and broaden the immune response directed to trivalent inactivated flu vaccine (TIV) in mice and ferrets.

RESULTS

We investigated the capacity of PapMV nanoparticles to increase the speed of the immune response toward TIV. PapMV nanoparticles induced a faster and stronger humoral response to TIV that was measured as early as 5 days post-immunization. The addition of PapMV nanoparticles was shown to speed up the differentiation of B-cells into early plasma cells, and increased the growth of germinal centers in a CD4+ dependent manner. TIV vaccination with PapMV nanoparticles as an adjuvant protected mice against a lethal infection as early as 10 days post-immunization.

CONCLUSION

In conclusion, PapMV nanoparticles are able to accelerate a broad humoral response to TIV. This property is of the utmost importance in the field of vaccination, especially in the case of pandemics, where populations need to be protected as soon as possible after vaccination.

Synergistic Stimulation with Different TLR7 Ligands Modulates Gene Expression Patterns in the Human Plasmacytoid Dendritic Cell Line CAL-1

Objective. TLR7 ligation in plasmacytoid dendritic cells is promising for the treatment of cancer, allergy, and infectious diseases; however, high doses of ligands are required. We hypothesized that the combination of structurally different TLR7 ligands exponentiates the resulting immune response. Methods. CAL-1 (human pDC line) cells were incubated with the TLR7-specific adenine analog CL264 and single-stranded 9.2s RNA. Protein secretion was measured by ELISA. Microarray technique was used to detect modified gene expression patterns upon synergistic stimulation, revealing underlying functional groups and networks. Cell surface binding properties were studied using FACS analysis. Results. CL264 in combination with 9.2s RNA significantly enhanced cytokine and interferon secretion to supra-additive levels. This effect was due to a stronger stimulation of already regulated genes (by monostimulation) as well as to recruitment of thus far unregulated genes. Top scoring canonical pathways referred to immune-related processes. Network analysis revealed IL-1β, IL-6, TNF, and IFN-β as major regulatory nodes, while several minor regulatory nodes were also identified. Binding of CL264 to the cell surface was enhanced by 9.2s RNA. Conclusion. Structurally different TLR7 ligands act synergistically on gene expression patterns and on the resulting inflammatory response. These data could impact future strategies optimizing TLR7-targeted drug design.

In vivo characterization of the physicochemical properties of polymer-linked TLR agonists that enhance vaccine immunogenicity

The efficacy of vaccine adjuvants such as Toll-like receptor agonists (TLRa) can be improved through formulation and delivery approaches. Here, we attached small molecule TLR-7/8a to polymer scaffolds (polymer-TLR-7/8a) and evaluated how different physicochemical properties of the TLR-7/8a and polymer carrier influenced the location, magnitude and duration of innate immune activation in vivo. Particle formation by polymer-TLR-7/8a was the most important factor for restricting adjuvant distribution and prolonging activity in draining lymph nodes. The improved pharmacokinetic profile by particulate polymer-TLR-7/8a was also associated with reduced morbidity and enhanced vaccine immunogenicity for inducing antibodies and T cell immunity. We extended these findings to the development of a modular approach in which protein antigens are site-specifically linked to temperature-responsive polymer-TLR-7/8a adjuvants that self-assemble into immunogenic particles at physiologic temperatures in vivo. Our findings provide a chemical and structural basis for optimizing adjuvant design to elicit broad-based antibody and T cell responses with protein antigens.

Toll-like receptor 7 inactive ligands enhanced cytokine induction by conjugation to weak antigens

Toll-like receptors (TLRs) 7/8 are key targets in the design and development of small-molecule drugs serving as anticancer/antiviral agents and vaccine adjuvants. Clinical trials of imiquimod were discontinued owing to its serious adverse side effects. Herein we report the synthesis and biological evaluation of a series of 8-hydroxy-2-(2-methoxyethoxy)adenine derivatives that cannot induce cytokine production and that lack activity toward TLR 7/8. Their ability to triggering remarkable levels of cytokine production were revealed upon their conjugation with antigens that have weak immunogenicity. This discovery demonstrated that TLR 7 can be activated by coupling an antigen to the terminal carboxyl group at N9 of the inactive ligand adenine analogues. These inactive analogues may be well suited as new adjuvants with superior activity after conjugation, effectively decreasing the side effects caused by conventional adjuvants.