Toll-like receptors (TLR) 7 and 8 are pattern recognition receptors expressed in immune cells, such as dendritic cells (DC) and macrophages, that respond to viral and bacterial infections. TLR7/8 activation triggers a pro-inflammatory immune cascade that leads to T cell and NK cell activation. Hence, synthetic imidazoquinoline-structured TLR7/8 agonists were developed and demonstrated as potent immunotherapy candidates for cancer and as infectious disease vaccine adjuvants. However, whether antagonizing TLR7/8 can induce the opposite effect, which is to produce anti-inflammatory cytokines and induce immunosuppressive cellular phenotypes, is a gap in our knowledge. In this study, we investigated the immunosuppressive efficacy of a novel TLR7/8 antagonist (termed "621") using cellular and animal models of inflammation. The potent TLR7/8 agonist 558 was employed as a control group to contrast the underlying immune mechanisms induced by TLR7/8 antagonist 621. Using mouse DC assays, we found that 621 was a potent inducer of the anti-inflammatory cytokine IL-10 without triggering pro-inflammatory TNF production. When administered systemically, 621-treated mice showed an increased serum IL-10 and decreased serum TNF. 621-treated mice also showed increased frequencies of regulatory T cells (Treg) and M2 macrophages when challenged with immunostimulants such as TLR4 agonist lipopolysaccharide (LPS) or the canonical TLR7/8 agonist resiquimod (RESQ). Further, 621 therapy mitigated the DSS-colitis model by reducing colon pro-inflammatory cytokines and increasing splenic Tregs. Combined, our data suggest that 621 can facilitate robust anti-inflammatory and immunosuppressive immune responses and therefore can be applied as a novel therapy for inflammatory diseases.

Proteasomal degradation of intrinsically disordered proteins, such as tau, is a critical component of proteostasis in both aging and neurodegenerative diseases. In this study, we investigated proteasomal activation by MK886 (MK). We previously identified MK as a lead compound capable of modulating tau oligomerization in a cellular FRET assay and rescuing P301L tau-induced cytotoxicity. We first confirmed robust proteasomal activation by MK using 20S proteasomal assays and a cellular proteasomal tau-GFP cleavage assay. We then show that MK treatment can significantly rescue tau-induced neurite pathology in differentiated SHSY5Y neurospheres. Due to this compelling result, we designed a series of seven MK analogs to determine if proteasomal activity is sensitive to structural permutations. Using the proteasome as the primary MOA, we examined tau aggregation, neurite outgrowth, inflammation, and autophagy assays to identify two essential substituents of MK that are required for compound activity: (1) removal of the N-chlorobenzyl group from MK negated both proteasomal and autophagic activity and reduced neurite outgrowth; and (2) removal of the indole-5-isopropyl group significantly improved neurite outgrowth and autophagy activity but reduced its anti-inflammatory capacity. Overall, our results suggest that the combination of proteasomal/autophagic stimulation and anti-inflammatory properties of MK and its derivatives can decrease tau-tau interactions and help rebalance dysfunctional proteostasis. Further development of MK to optimize its proteasomal, autophagic, and anti-inflammatory targets may lead to a novel therapeutic that would be beneficial in aging and neurodegenerative diseases.

Tumor necrosis factor (TNF) plays an important role in the pathogenesis of inflammatory and autoimmune diseases such as rheumatoid arthritis and Crohn's disease. The biological effects of TNF are mediated by binding to TNF receptors, TNF receptor 1 (TNFR1), or TNF receptor 2 (TNFR2), and this coupling makes TNFR1-specific inhibition by small-molecule therapies essential to avoid deleterious side effects. Recently, we engineered a time-resolved fluorescence resonance energy transfer biosensor for high-throughput screening of small molecules that modulate TNFR1 conformational states and identified zafirlukast as a compound that inhibits receptor activation, albeit at low potency. Here, we synthesized 16 analogues of zafirlukast and tested their potency and specificity for TNFR1 signaling. Using cell-based functional assays, we identified three analogues with significantly improved efficacy and potency, each of which induces a conformational change in the receptor (as measured by fluorescence resonance energy transfer (FRET) in cells). The best analogue decreased NF-κB activation by 2.2-fold, IκBα efficiency by 3.3-fold, and relative potency by two orders of magnitude. Importantly, we showed that the analogues do not block TNF binding to TNFR1 and that binding to the receptor's extracellular domain is strongly cooperative. Despite these improvements, the best candidate's maximum inhibition of NF-κB is only 63%, leaving room for further improvements to the zafirlukast scaffold to achieve full inhibition and prove its potential as a therapeutic lead. Interestingly, while we find that the analogues also bind to TNFR2 in vitro, they do not inhibit TNFR2 function in cells or cause any conformational changes upon binding. Thus, these lead compounds should also be used as reagents to study conformational-dependent activation of TNF receptors.

Ligation of toll-like receptors 7 and 8 (TLR7/8) can potently activate innate immune cells, including tumor-associated macrophages, to prime downstream T cell activation and drive potent, lasting anti-tumor immunity. TLR7/8 agonists have long been pursued as an anti-cancer therapeutic because of their potential in re-programing the immune system but the clinical utility has been limited by systemic toxicity. Several means of decreasing this systemic toxicity have been investigated, including intra-tumoral administration, nanoparticle encapsulation and conjugation to a tumor-targeting antibody (antibody-drug conjugates, ADCs). ADCs are a clinically validated technology designed to target drugs to disease tissues to reduce the systemic toxicity of highly potent payloads and improve anti-tumor activity. We have developed an imidazoquinoline-based dual TLR7 and TLR8 small molecule agonist that has been specifically designed as an ADC payload. The initial compound was chosen from a set of imidazoquinoline-based small molecules using HEK293 reporter cells expressing either TLR7 or TLR8. This newly identified TLR7/8 agonist potently reactivated immunosuppressive macrophages to produce inflammatory cytokines, increased phagocytosis of tumor cells and enhanced T cell activation and proliferation. A lead payload candidate based on a modified version of the initial TLR7/8 agonist was designed to decrease drug permeability to minimize non-targeted systemic immune activation. The lead TLR7/8 agonist was shown to be significantly less potent than the first-generation compound as a small molecule but demonstrated enhanced immune-stimulating capability when conjugated to a direct immune-targeting antibody. The increased potency as an ADC is hypothesized to be driven by enhanced intracellular retention of the less cell permeable payload and/or a higher binding affinity to the TLR7 or 8 receptors, which was predicted via modeling. The greater in vitro potency of the lead payload was also observed in vivo in an MC38 syngeneic tumor model where 33% complete tumor cures were observed with the lead versus only tumor delay with the permeable version. Drug linkers employing the lead payload were evaluated by varying payload linkage chemistry, drug linker hydrophobicity, and drug release mechanisms using in vivo anti-tumor activity in different syngeneic mouse tumor models as a readout. The optimized drug linker design increased the in vitro and in vivo potency up to 4-fold when compared with the initial linker/payload. These data clearly demonstrate the potency of TLR7/8 agonists as immune stimulants in anti-cancer therapies and outline how their optimization through chemical modification can make them suitable payloads for ADCs. Citation Format: Kung-Pern Wang, Chris Neumann, Angela Epp, Weiping Zeng, Thomas Griffith, David Ferguson, Shyra Gardai, Alyson J. Smith. Generation of an antibody-drug conjugate-optimized TLR 7/8 agonist payload [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1542.

Drug-eluting bead transcatheter arterial chemoembolization (DEB-TACE) is a treatment procedure for liver cancer that involves the selective catheterization and subsequent embolization of tumor-feeding arteries with drug-eluting beads (DEBs). DEB-TACE elicits ischemic cell death in the embolized tumor while simultaneously delivering a local, sustained release of chemotherapy. We hypothesize that the application of DEBs loaded with an immunostimulatory adjuvant in the DEB-TACE procedure will promote local antigen presenting cells to utilize the antigens released by dying tumor cells to generate a systemic, adaptive anti-tumor immune response. This approach represents a novel form of transarterial immunoembolization (TIE). 558 is a highly potent, small molecule Toll-like receptor 7/8 agonist that activates both innate and adaptive immune responses to eliminate tumor cells in various preclinical tumor models. Hydrogel microspheres composed of cross-linked sulfobutylether-β-cyclodextrin (SBE-βCD) were investigated as DEBs for 558 in the current study. SBE-βCD hydrogel microspheres (SBE-βCDMS) of 10 - 300 μm diameter were synthesized via suspension polymerization of SBE-βCD and ethylene glycol diglycidyl ether followed by wet sieving. 558 loading was achieved by incubating blank SBE-βCDMS in aqueous solutions of 558. Under non-saturating conditions, SBE-βCDMS absorbed almost the entirety of 558 from loading solutions in 4 h. The dose of 558 loaded in SBE-βCDMS was tuned by altering the initial amount of 558 in solution, up to a maximum loading of 0.28 mg 558/mg dry SBE-βCDMS determined under saturating conditions. The time to 50% release of 558 from loaded SBE-βCDMS was less than 30 min when phosphate buffered saline was used as release media. However, the release of 558 was negligible when deionized water was used as release media. The released drug was as effective as free 558 in stimulating cytokine response from human peripheral blood mononuclear cells in vitro. As a surrogate for TIE, we evaluated plasma and tumor pharmacokinetics upon intratumoral injection of 558-loaded SBE-βCDMS (50 - 100 μm diameter) or free 558 at a dose of 100 μg in C57BL/6 mice bearing B16F10-OVA flank tumors. The gradual release of 558 from loaded SBE-βCDMS prevented an initial spike in plasma concentration that was observed for mice administered with free 558, and maintained constant tumor concentrations for at least 4 h post-injection. High-resolution MALDI mass spectrometry imaging of 15 μm-thick tumor cryosections indicated that 558 was initially concentrated within SBE-βCDMS after intratumoral injection, and extensively released into the surrounding tumor tissue 24 h post-injection. Taken together, these results suggest that 558-loaded SBE-βCDMS are a promising platform for local drug delivery and immune cell stimulation via TIE. Citation Format: Joel Updyke, Shubhmita Bhatnagar, Nitu Bhaskar, Rachel Parise, Swati Nagar, John Schultz, David Ferguson, Tamara Kucaba, Thomas Griffith, Ronald Siegel, Jayanth Panyam. Sulfobutylether-β-cyclodextrin hydrogel microspheres delivering TLR 7/8 agonist for transarterial immunoembolization [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1993.

Various classes of molecules including toll-like receptor (TLR) agonists, exosomes, and metallo compounds have been evaluated as adjuvants for cancer vaccines. However, their wide-spread clinical use has been limited by transient immune responses and serious side-effects. Here, we propose the use of a multi-adjuvant approach that combines two different classes of adjuvants, STING and TLR 7/8 agonists, based on their distinct immune cell targets, signalling pathways, and significant roles in the activation and maintenance of immune responses. We evaluated the potential of combining 522, a novel TLR 7/8 agonist, and DMXAA, a STING agonist, for stronger DC activation and greater CD8 T cell responses. Mouse bearing B16F10-OVA (murine melanoma cell line which expresses ovalbumin) tumors were immunized with OVA mixed with 522 or DMXAA or a combination of 522 and DMXAA daily for 5 days. Immunization with OVA+DMXAA+522 resulted in significant tumor growth inhibition (p < 0.05) and improved survival (p<0.05) compared to other controls. Using flow cytometry, the costimulatory molecule expression and immune cell infiltration in mouse lymph node, spleen and tumor were evaluated. Immunization with OVA+DMXAA+522 resulted in the activation of antigen presenting cells (APCs) in lymph nodes, spleen and tumor (additive or equivalent to single treated groups). The combination also elicited stronger antigen specific CD8 T cell and natural killer (NK) cell responses than control or individual treatment groups. OVA + DMXAA+ 522 immunization increased the number of OVA-specific CD44high CD8 T cells by over 4-fold compared to other treatment groups and control mice in spleen and lymph nodes. A reduction in the frequency of M2 macrophages was observed with OVA+DMXAA+522 treatment. Cytokine analysis demonstrated higher levels of pro-inflammatory cytokines like IFNγ and lower levels of pro-tumorigenic cytokines in the serum of OVA+DMXAA+522 immunized mice compared to that in untreated or OVA-only treated mice. Taken together, these results suggest that combination of TLR7/8 and STING agonists is a promising multi-adjuvant approach for cancer vaccination Citation Format: Shubhmita Bhatnagar, Vishnu Revuri, Manan Shah, Peter Larson, David Ferguson, Jayanth Panyam. Combination of STING and TLR 7/8 agonists as vaccine adjuvants for cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4215.

Molecular mechanics force field calculations have historically shown significant limitations in modeling the energetic and conformational interconversions of highly substituted furanose rings. This is primarily due to the gauche effect that is not easily captured using pairwise energy potentials. In this study, we present a refinement to the set of torsional parameters in the General Amber Force Field (gaff) used to calculate the potential energy of mono, di-, and gem-fluorinated nucleosides. The parameters were optimized to reproduce the pseudorotation phase angle and relative energies of a diverse set of mono- and difluoro substituted furanose ring systems using quantum mechanics umbrella sampling techniques available in the IpolQ engine in the Amber suite of programs. The parameters were developed to be internally consistent with the gaff force field and the TIP3P water model. The new set of angle and dihedral parameters and partial charges were validated by comparing the calculated phase angle probability to those obtained from experimental nuclear magnetic resonance experiments.

Immunostimulatory adjuvants that potently activate antigen-presenting cells and (in turn) prime cytotoxic T cells are a key component of anticancer vaccines. In this study, we investigated a multi-adjuvant approach combining a TLR 7/8 agonist (522) and a STING agonist (DMXAA) to promote enhanced antigen cross-presentation, stimulate specific antitumor T-cell responses, and provide improved anticancer efficacy. In vitro experiments using bone marrow-derived dendritic cells (BMDCs) confirmed enhanced activation with the 522-DMXAA combination based on both co-stimulatory molecule expression and pro-inflammatory cytokine secretion. The immunization of mice with vaccines comprising both 522 and DMXAA resulted in greater antitumor efficacy in B16F10 melanoma and MB49 bladder tumor models relative to mono-agonist vaccines. Flow cytometry-based analysis of immune cells from immunized mice revealed the significant activation of antigen-presenting cells, increased numbers of activated and Ag-specific CD8+ T cells in the spleen and lymph nodes, modest NK cell activation, and an overall reduction in CD206+ macrophages. These results were supported by an increase in the levels of IFN-γ and a reduction in IL-10 levels in the sera. Taken together, these findings demonstrate the potential of the TLR7/8 and STING agonist combination as vaccine adjuvants to activate both innate and adaptive immune responses.

Despite significant advancements in immune checkpoint blockade (ICB) therapy, only few patients respond to the treatment. Non-immunogenic cold tumors lack T-cell infiltration, which results in reduced ICB therapeutic efficiency. Immune adjuvants can reprogram the non-immunogenic cold tumor microenvironment (TME) to inflamed hot TME by activating antigen presenting cells and improving T-cell homing. Here, we investigate the potentials of 558 (a novel TLR 7/8 agonist) and ADU-S100 (stimulator of interferon gene (STING) agonist in clinical trials) combination on improving the activity of ICB. Human TLR-specific reporter cell assay using HEK-Blue™-hTLR7 and 8, confirmed the activation of both TLR 7 and TLR 8 with EC50 of 0.18 µM and 5.34 µM respectively, when treated with 558. In addition, treatment of human PBMCs with 558 increased the IFN-γ and TNF-α cytokine secretions. Moreover, the levels of IL-10, an anti-inflammatory cytokine were not increased upon treatment with 558. Although treatment of bone marrow derived dendritic cells (BMDC) with 558 resulted in CD40 expression, a reduced expression of CD80 and CD86, costimulatory molecules that are required for T-cell activation, was observed. Interestingly, 558 in combination with ADU-S100 not only increased the CD40 expression but also improved the expression of CD80 (4-fold) and CD86 on BMDCs. Furthermore, the levels of pro-inflammatory cytokines TNF-α and IL-6 was significantly increased when BMDCs were treated with 558 and ADU-S100 combination compared to the individual treatments. TME constitute M2 polarized macrophages that promote secretion of anti-inflammatory cytokines and favor tumor progression. Interestingly, 558 and ADU-S100 combination reduced the expression of CD206, a mannose receptor that is highly expressed on M2 macrophages and improved the expression of CD80 (25-fold) and CD86 (6-fold) compared to 558 treatments alone. These results confirmed the polarization of M2 macrophages to immunogenic M1 macrophages. Overall, these studies indicate promising potential of 558 and ADU-S100 combination in reprogramming the TME to aid in effective cancer treatments. Citation Format: Vishnu Revuri, Shubhmita Bhatnagar, John Schultz, Peter Larson, David M. Ferguson, Jayanth Panyam. STING and TLR 7/8 Agonist combination can improve immune checkpoint blockade therapy efficiency [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5587.

Toll-like receptors (TLRs) 7 and 8 are key targets in the development of immunomodulatory drugs for treating infectious disease, cancer, and autoimmune disorders. These receptors can adopt both agonist and antagonist binding conformations that switch the receptor signal on or off to the downstream production of cytokines. In this study, we examined the effect of simple isomeric substitutions to the C2-butyl group of two imidazoquinoline agonists and evaluated the activity of these analogs using both TLR7 and TLR8 reporter cells and cytokine induction assays. Results are presented showing the C2-isobutyl and C2-cyclopropylmethyl isomers are both mixed TLR7/8 competitive antagonists of the parent agonist [4-Amino-1-(4-(aminomethyl)benzyl)-2-butyl-7-methoxycarbonyl-1H-imidazo[4,5-c]quinoline], indicating the conformation of the dimeric receptor complex is highly sensitive to steric perturbations to the ligand binding pocket. This observation is consistent with prior work demonstrating TLR7 and TLR8 activity is directly correlated to C2-alkyl substitutions that project into a hydrophobic pocket at the dimer interface of the receptor. The close structural relationship of the agonist/antagonist pairs identified here highlights the importance of this pocket in tipping the balance between the agonist and antagonist binding states of the receptor which may have significant ramifications to the design of imidazoquinoline-based immunomodulatory agents.

A series of acridone and xanthone-based compounds bearing 1,2-epoxypropyl or 1,2-propanediol substituents were synthesized and evaluated for activity against MRSA and MSSA bacterial strains. The results indicate a correlation exists between the number of epoxide groups and activity, with peak MIC values observed for bis-epoxy derivatives. Both activity and heathy cell toxicity was shown to decrease with the addition of a third epoxy group. The corresponding ring-opened diol analogs were devoid of activity, demonstrating the critical function of the epoxide in mediating antimicrobial activity. The most active compounds were also screened using a regulated antisense RNA expression library. The results show no increase in activity against cells sensitized by down-regulation of the most common drug targets, including DNA gyrase, DNA topoisomerase, tRNA synthetase, and the fatty acid biosynthesis pathway. The compounds are postulated to function as membrane disrupting agents, similar to the xanthone natural product α-mangostin.

There is a significant interest in designing therapeutic agents that can enhance ADCC and thereby improve clinical responses with approved antibodies. We recently reported the combination of an imidazoquinoline-based TLR7/8 agonist (522) with a monoclonal antibody improved ADCC in vitro and in vivo. In the present study, we tested several new small molecule TLR7/8 agonists that induce significantly higher cytokines compared to both the FDA-approved TLR7 agonist, imiquimod, and 522. We evaluated these agonists in combination with monoclonal antibody therapy, with the main goal of enhancing ADCC. Our studies show these TLR7/8 agonists induce robust pro-inflammatory cytokine secretion and activate NK cells. Specifically, we found the agonists 574 and 558 significantly enhanced NK cell-mediated ADCC in vitro as well as enhanced the anti-cancer efficacy of monoclonal antibodies in two different in vivo mouse models. Additionally, we found the agonists were able to stimulate CD8 T cells, likely indicative of an early adaptive immune response.

The type II transmembrane serine protease TMPRSS2 facilitates the entry of coronaviruses, such as SARS-CoV-2, into host cells by cleaving the S1/S2 interface of the viral spike protein. Based on structural data derived from X-ray crystallographic data of related trypsin-like proteases, a homology model of TMPRSS2 is described and validated using the broad spectrum COVID-19 drug candidate camostat as a probe. Both active site recognition and catalytic function are examined using quantum mechanics/molecular mechanics molecular dynamic (QM/MM MD) simulations of camostat and its active metabolite, 4-(4-guanidinobenzoyloxy) phenylacetate (GBPA). Substrate binding is shown to be primarily stabilized through salt bridge formation between the shared guanidino pharmacophore and D435 in pocket A (flanking the catalytic S441). Based on the binding mode of GBPA, residues K342 and W461 have been identified as potential contacts involved in TMPRSS2 selective binding and activity. Additional data is reported that indicates the transition state structure is stabilized through H-bonding interactions with the backbone N–H groups within an oxyanion hole following bottom-side attack of the carbonyl by S441. This is supported by prior work on related serine proteases suggesting further strategies to exploit in the design of more potent inhibitors. Taken overall, the proposed structure along with the key contact sites and mechanistic features identified should prove highly advantageous to the design and rational development of safe and effective therapeutics that target TMPRSS2 and avoid inhibition of other trypsin-dependent processes.

4-Amino-imidazo-, oxazolo-, and thiazoloquinolines are key structural scaffolds in the design of nucleoside base analogs for use as therapeutic agents. Current strategies for arriving at diverse substitutions at the C6–C9 positions of the thiazolo- and oxazoloquinolines, however, are limited due to difficulties in arriving at the thiazoloquinoline-5N-oxide intermediate using electron deficient aromatic systems. Here, we demonstrate a synthetic route to obtain substituted thiazoloquinolines with electron-withdrawing groups at the C7 position. The target compound, 4-amino-2-butyl-7-methoxycarbonylthiazolo[4,5-c]quinoline, is obtained in eight steps using a 7-bromo surrogate as a precursor to the successful generation of the N-oxide intermediate, and final transformation via Pd-mediated C7-acylation.

The transmembrane protease serine subfamily (TMPRSS) has at least eight members with known protein sequence: TMPRSS2, TMPRRS3, TMPRSS4, TMPRSS5, TMPRSS6, TMPRSS7, TMPRSS9, TMPRSS11, TMPRSS12 and TMPRSS13. A majority of these TMPRSS proteins have key roles in human hemostasis as well as promoting certain pathologies, including several types of cancer. In addition, TMPRSS proteins have been shown to facilitate the entrance of respiratory viruses into human cells, most notably TMPRSS2 and TMPRSS4 activate the spike protein of the SARS-CoV-2 virus. Despite the wide range of functions that these proteins have in the human body, none of them have been successfully crystallized. The lack of structural data has significantly hindered any efforts to identify potential drug candidates with high selectivity to these proteins. In this study, we present homology models for all members of the TMPRSS family including any known isoform (the homology model of TMPRSS2 is not included in this study as it has been previously published). The atomic coordinates for all homology models have been refined and equilibrated through molecular dynamic simulations. The structural data revealed potential binding sites for all TMPRSS as well as key amino acids that can be targeted for drug selectivity.

Activated natural killer (NK) cells can kill malignant tumor cells via granule exocytosis and secretion of IFN-γ, a key regulator of the TH1 response. Thus, mobilization of NK cells can augment cancer immunotherapy, particularly when mediated through antibody-dependent cellular cytotoxicity (ADCC). Stimulation of toll-like receptor (TLR)7/8 activity in dendritic cells promotes pro-inflammatory cytokine secretion and costimulatory molecule upregulation, both of which can potentiate NK cell activation. However, currently available TLR7/8 agonists exhibit unfavorable pharmacokinetics, limiting their in vivo efficacy. To enable efficient delivery to antigen-presenting cells, we encapsulated a novel imidazoquinoline-based TLR7/8 agonist in pH-responsive polymeric NPs. Enhanced costimulatory molecule expression on dendritic cells and a stronger pro-inflammatory cytokine response were observed with a NP-encapsulated agonist, compared to that with the soluble form. Treatment with NP-encapsulated agonists resulted in stronger in vivo cytotoxicity and prolonged activation of NK cells compared to that with a soluble agonist. In addition, TLR7/8 agonist-loaded NPs potentiated stronger NK cell degranulation, which resulted in enhanced in vitro and in vivo ADCC mediated by the epidermal growth factor receptor-targeting antibody cetuximab. TLR7/8 agonist-loaded NP treatment significantly enhanced the antitumor efficacy of cetuximab and an anti-HER2/neu antibody in mouse tumor models. Collectively, our data show that a pH-responsive NP-encapsulating TLR7/8 agonist could be used as a potent immunostimulatory adjuvant for antibody-based cancer immunotherapy by promoting NK cell activation.

Abstract Antibody-dependent cell-mediated cytotoxicity (ADCC) is a key mechanism of action for some therapeutic antibodies. ADCC involves killing of an antibody-coated target cell by an effector cell through the release of cytotoxic or cell death-inducing molecules. ADCC is triggered through interaction of Fcγ receptors present on the effector cell surface with the Fc region of the target-bound antibody. Natural killer (NK) cells are one of the primary effector cells that mediate ADCC. There is significant interest in designing therapeutic agents that can enhance ADCC because this can result in improved clinical responses with approved antibodies. We have developed a suite of highly substituted imidazoquinolines, which activate TLR 7 and/or 8 and induce significantly higher levels of cytokines compared to the FDA-approved TLR7 agonist imiquimod. In the current study, we evaluated our series of TLR7-specific, 8-specific and 7/8 dual selective agonists for their ability to improve ADCC with Cetuximab. We investigated NK cell activation in the presence of these compounds, as well as NK cell mediated ADCC against an EGFR expressing lung cancer cell line, A549. In addition, we also measured cytokine induction in human peripheral blood mononuclear cells in response to these compounds. Our studies show dual TLR 7/8 and 8-specific agonists induce robust pro-inflammatory cytokine secretion and activate NK cells. however, mixed agonists also induce greater immunosuppressive cytokines compared to TLR8-specific agonists. Further, these agonists also significantly enhanced Cetuximab mediated ADCC in vitro. In vivo studies examining the anticancer efficacy of the combination of selected TLR7/8 agonists and Cetuximab are ongoing. Citation Format: Vidhi Khanna, Hyunjoon Kim, Wenqui Zhang, Peter Larson, David Ferguson, Jayanth Panyam. Novel small molecule TLR7/8 agonists for enhancing NK cell-mediated ADCC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4129.

Introduction: Toll-like receptors (TLRs) are important pattern recognition receptors through which innate immune cells recognize invasive microorganisms. The immunostimulatory property of TLR agonists allows for activation of dendritic cells (DCs) and enables their use as anticancer vaccine adjuvants. Because TLR 7 and 8 can be activated by synthetic small molecules, they are of particular interest as a target in vaccine adjuvant discovery. However, a key drawback of these synthetic small molecules is that they also induce immunosuppressive cytokines, resulting in immunosuppression. Methods: We have previously developed a suite of highly substituted imidazoquinolines, which potently activate TLR 7 and/or 8. In this study, we tested some selected TLR7, TLR8 and TLR7/8 dual agonists for their ability to activate DCs without inducing immune suppressive cytokines. Murine bone marrow-derived dendritic cells (BMDCs) were generated from C57BL/6 mice. BMDCs were treated with one of seven TLR agonists for 72 hrs. Cells were collected and stained for flow cytometry analysis, and the culture supernatants were examined for secretion of pro-inflammatory cytokines, IL-12p70 and IFN-γ, and an immunosuppressive cytokine, IL-10, by ELISA. We also investigated activation of T cells by these agonists. Human peripheral blood mononuclear cells (hPBMCs) from healthy donors were incubated with one of seven TLR agonists overnight and cells were analyzed by flow cytometry for the expression of T cell activation marker CD69 and production of IFN-γ. Results: All the TLR agonists investigated activated BMDCs, as evidenced by the upregulation of costimulatory markers CD40, CD80 and CD86 on DCs. In addition, all the agonists examined induced the secretion of IL-12p70 and IFN-γ. TLR 8 agonists showed the least induction of IL-10 secretion. All the TLR agonists activated both CD4 and CD8 T cells. TLR 8 agonists induced higher production of IFN-γ in both type of T cells than other candidates. Conclusion: Both TLR 8 and TLR 7/8 agonists activated BMDCs and stimulated strong pro-inflammatory cytokine production. However, TLR8 activation was associated with less immunosuppression. These results suggest that these new imidazoquinoline esters are promising candidates for use as anti-cancer vaccine adjuvants. Citation Format: Wenqiu Zhang, Hyunjoon Kim, Vidhi Khanna, David M. Ferguson, Thomas Griffith, Jayanth Panyam. TLR agonists for anticancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4985.