Small-Molecule Modulators Targeting Toll-like Receptors for Potential Anticancer Therapeutics

Design and Synthesis of FR-β Targeting Chimeric Molecules for Reprogramming Tumor-Associated Macrophages Using 6-Substituted Pyrrolo[2,3-d]pyrimidines as Targeting Ligands

Tumor-associated macrophages (TAMs) are highly plastic tumor-infiltrating immune cells. Their reprogramming has emerged as a pivotal strategy in antitumor immunotherapy. The TLR7/8 agonist, IMDQ, has significant potential for reprogramming macrophages but lacks target specificity. To address this challenge, we developed novel folate receptor beta (FR-β) targeting chimeric molecules using 6-substituted pyrrolo[2,3-d]pyrimidines as high-affinity ligands, which demonstrate superior FR-β targeting capability compared with classical folic acid. These molecules integrate the FR-β targeting moiety with IMDQ, marking the first application of this immunomodulator in targeted chimeric constructs. In vitro and in vivo studies demonstrated that our chimeric molecules selectively reprogrammed TAMs toward an immunostimulatory phenotype, reshaped the tumor microenvironment, and inhibited tumor progression without systemic toxicity. Given that TAM accumulation is prevalent across all solid tumors, our strategy of precisely targeting and reprogramming of TAMs is universally applicable to treating various types of cancers, a potent and effective strategy for antitumor immunotherapy.

Unlocking the power of imidazoquinolines: recent advances in anticancer and immunotherapeutic strategies

The challenges in drug discovery aiming to mitigate cancer progression are the thrust area of scientific research for several decades. Since the advent of heterocyclic chemistry, drug discovery programs have made significant achievements that lead to the development of numerous drugs with broad spectrum of potencies, contributing to both diagnostic and therapeutic advancements. Till date, efforts to discover more potent and efficient drug candidates are underway to minimize adverse side effects of existing chemotherapeutics. In view of the above, small-molecule agonists that can interact with different immune modulators like toll like receptor-7 (TLR-7) and TLR-8 are being investigated and explored. These candidates are expected to display profound effect on anti-tumoral activity by enhancing the production of proinflammatory cytokines. Recently, numerous imidazoquinoline derivatives with proven TLR agonist activities have emerged as promising anticancer therapeutics. With advancements in technology and the evolution of new scopes in drug discovery, different strategies are being adopted, particularly with the help of nanotechnology, immune-technology, combination drug chemistry, etc., to curb the progression of various types of cancers. Herein, the novel strategies for cancer therapeutics with imidazoquinolines reported in the last 5 years, their structure-activity relationship along with important synthetic schemes for important TLR agonists, are discussed.

Tumor-Adhesive Chitosan-Derived Multi-Immune Agonist Unleashes Strong and Durable Anti-Cancer Immunity

The immunomodulation of the tumor microenvironment is critical for effective cancer immunotherapy, particularly for tumors that exhibit limited responses to conventional treatments. However, current immune agonists developed for tumor immunomodulation face several challenges, such as poor intratumoral retention, inadequate biocompatibility, and restricted cellular targets, which ultimately hamper their therapeutic efficacy and clinical application. In this study, a tumor-adhesive chitosan-tethered immune agonist construct (TACTIC) is introduced, which demonstrates good biocompatibility and robust immunostimulatory effects, enhancing the immunogenicity of tumor cells while simultaneously stimulating pro-inflammatory responses in various immune cell populations. Mechanistic investigations reveal that TACTIC targets multiple signaling pathways, conferring it to effectively remodel the irradiated tumor microenvironment, improve tumor control on murine cancer models post-radiotherapy, and elicit systemic immune responses with memory effects. The findings highlight the potential of TACTIC as a powerful macromolecular immune adjuvant, paving the way for its broader application in innovative cancer immunotherapies.

Toll-Like Receptors and Contact Dermatitis

Contact dermatitis (CD) is a common cutaneous inflammatory condition that affects millions of people worldwide. Xenobiotic agents are frequently encountered in substances used in everyday life, making it difficult to avoid personal and occupational exposure. Toll-like receptors (TLRs) are transmembrane receptors that modulate the innate immune system in response to tissue injury or infection. TLRs play a key role in the pathophysiology of contact dermatitis. TLR signaling is involved in three major forms of CD: protein CD, allergic contact dermatitis (ACD), and irritant CD. Of the 10 TLRs found in humans, three play an important role in ACD. This makes TLRs a useful potential therapeutic target to consider against CD. In this review, we discuss the role of TLRs in CD and summarize current and emerging treatments for CD that target TLRs.

Design, synthesis, in vitro and in vivo biological evaluation of pterostilbene derivatives for anti-inflammation therapy

Pterostilbene (PST) is a naturally derived stilbene compound in grapes, blueberries, and other fruits. It is also a natural dietary compound with a wide range of biological activities such as antioxidant, anti-inflammatory, antitumor, and so on. Structural modifications based on the chemical scaffold of the pterostilbene skeleton are of great importance for drug discovery. In this study, pterostilbene skeletons were used to design novel anti-inflammatory compounds with high activity and low toxicity. A total of 30 new were found and synthesised, and their anti-inflammatory activity and safety were screened. Among them, compound E2 was the most active (against NO: IC50 = 0.7 μM) than celecoxib. Further studies showed that compound E2 exerted anti-inflammatory activity by blocking LPS-induced NF-κB/MAPK signalling pathway activation. In vivo experiments revealed that compound E2 had a good alleviating effect on acute colitis in mice. In conclusion, compound E2 may be a promising anti-inflammatory lead compound.

Design and Optimization of Selectivity-Tunable Toll-like Receptor 7/8 Agonists as Novel Antibody-Drug Conjugate Payloads

Toll-like receptors 7 and 8 are involved in modulating the adaptive and innate immune responses, and their activation has shown promise as a therapeutic strategy in the field of immuno-oncology. While systemic exposure to TLR7/8 agonists can result in poor tolerance, combination therapies and targeted delivery through antibody-drug conjugates (ADCs) can help mitigate adverse effects. Described herein is the identification of a novel and potent series of pyrazolopyrimidine-based TLR7/8 agonists with tunable receptor selectivity. Representative agonists from this series were successfully able to induce the production of various proinflammatory cytokines and chemokines from human peripheral blood mononuclear cells. Anti-HER2-25 and anti-HER2-26 ADCs made from this class of payloads demonstrated mechanism-based activation of TLR7/8 in a THP1/N87 coculture system.

The Development of a Highly Potent and Selective Human Toll-like Receptor 2 Agonist: Synthesis and Biological Evaluation of CaLGL-1 and Its Derivatives

Toll-like receptor 2 (TLR2) plays a crucial role in detecting microbial pathogen-associated molecular patterns, offering potential applications as an adjuvant for vaccines and antitumor therapies. Here, we present the gram-scale synthesis of CaLGL-1 and its derivatives, natural products known for activating mouse TLR2 (EC50 = 3.2 μM). This synthesis involves a streamlined six-step reaction sequence utilizing oxidant-promoted acetalization, effectively preserving the acid-sensitive glycosidic bond for maintaining the compounds' functional integrity. Our structure-activity relationship studies identified R-7d as a potent human TLR2 activator. It demonstrated subnanomolar activity (EC50 = 116 pM) in human THP-1 cells, comparable to that of diprovocim (EC50 = 110 pM). Experiments revealed that R-7d enhances NF-kB promoter activation through TLR2/TLR1 heterodimers rather than TLR2/TLR6. The discovery of R-7d as a robust human TLR2 agonist opens up new possibilities for combination therapies.

Immune profiling of age and adjuvant-specific activation of human blood mononuclear cells in vitro

Vaccination reduces morbidity and mortality due to infections, but efficacy may be limited due to distinct immunogenicity at the extremes of age. This raises the possibility of employing adjuvants to enhance immunogenicity and protection. Early IFNγ production is a hallmark of effective vaccine immunogenicity in adults serving as a biomarker that may predict effective adjuvanticity. We utilized mass cytometry (CyTOF) to dissect the source of adjuvant-induced cytokine production in human blood mononuclear cells (BMCs) from newborns (~39-week-gestation), adults (~18-63 years old) and elders (>65 years of age) after stimulation with pattern recognition receptors agonist (PRRa) adjuvants. Dimensionality reduction analysis of CyTOF data mapped the BMC compartment, elucidated age-specific immune responses and profiled PRR-mediated activation of monocytes and DCs upon adjuvant stimulation. Furthermore, we demonstrated PRRa adjuvants mediated innate IFNγ induction and mapped NK cells as the key source of TLR7/8 agonist (TLR7/8a) specific innate IFNγ responses. Hierarchical clustering analysis revealed age and TLR7/8a-specific accumulation of innate IFNγ producing γδ T cells. Our study demonstrates the application of mass cytometry and cutting-edge computational approaches to characterize immune responses across immunologically distinct age groups and may inform identification of the bespoke adjuvantation systems tailored to enhance immunity in distinct vulnerable populations.

A fungal polysaccharide from Fomitopsis officinalis as a multi-target molecule to combat cancer

Some macrofungi have a long history of being used as traditional or folk medicines, making significant contributions to human health. To discover bioactive molecules with potential anticancer properties, a homogeneous heteropolysaccharide (FOBP90-1) was purified from the medicinal macrofungus Fomitopsis officinalis. FOBP90-1 was found to have a molecular weight of 2.87 × 104 g/mol and mainly consist of →6)-α-d-Galp-(1→, →2,6)-α-d-Galp-(1→, →3)-α-l-Fucp-(1→, →6)-β-d-Glcp-(1→, α-d-Manp-(1→, and 3-O-Me-α-l-Fucp-(1→ according to UV, FT-IR, methylation analysis, and NMR data. In addition to its structural properties, FOBP90-1 displayed anticancer activity in zebrafish models. The following mechanistic analysis discovered that the in vivo antitumor effect was linked to immune activation and angiogenesis inhibition. These effects were mediated by the interactions of FOBP90-1 with TLR-2, TLR-4, PD-L1, and VEGFR-2, as determined through a series of experiments involving cells, transgenic zebrafish, molecular docking simulations, and surface plasmon resonance (SPR). All the experimental findings have demonstrated that FOBP90-1, a purified fungal polysaccharide, is expected to be utilized as a cancer treatment agent.

Molecule engineering strategy of toll-like receptor 7/8 agonists designed for potentiating immune stimuli activation

Toll-like receptor 7/8 (TLR-7/8) agonists serve as a promising class of pattern recognition receptors that effectively evoke the innate immune response, making them promising immunomodulatory agents for tumor immunotherapy. However, the uncontrollable administration of TLR-7/8 agonists frequently leads to the occurrence of severe immune-related adverse events (irAEs). Thus, it is imperative to strategically design tumor-microenvironment-associated biomarkers or exogenous stimuli responsive TLR-7/8 agonists in order to accurately evaluate and activate innate immune responses. No comprehensive elucidation has been documented thus far regarding TLR-7/8 immune agonists that are specifically engineered to enhance immune activation. In this feature article, we provide an overview of the advancements in TLR-7/8 agonists, aiming to enhance the comprehension of their mechanisms and promote the clinical progression through nanomedicine strategies. The current challenges and future directions of cancer immunotherapy are also discussed, with the hope that this work will inspire researchers to explore innovative applications for triggering immune responses through TLR-7/8 agonists.

M. Subbaiah M, Kumar BV, Subramani L, Wang B, Li YX, Sivaprakasam P, Critton D, Mulligan D, Sandhu B, Xie C, Ramakrishnan R, Nagar J, Dudhgaonkar S, Oderinde MS, Murtaza A, Schieven GL, Mathur A, Gavai AV, Vite G, Gangwar S. Discovery of Novel TLR7 Agonists as Systemic Agent for Combination With aPD1 for Use in Immuno-oncology

We have designed and developed novel and selective TLR7 agonists that exhibited potent receptor activity in a cell-based reporter assay. In vitro, these agonists significantly induced secretion of cytokines IL-6, IL-1β, IL-10, TNFa, IFNa, and IP-10 in human and mouse whole blood. Pharmacokinetic and pharmacodynamic studies in mice showed a significant secretion of IFNα and TNFα cytokines. When combined with aPD1 in a CT-26 tumor model, the lead compound showed strong synergistic antitumor activity with complete tumor regression in 8/10 mice dosed using the intravenous route. Structure-activity relationship studies enabled by structure-based designs of TLR7 agonists are disclosed.

Structural Optimization and Biological Evaluation of Isoxazolo[5,4-d]pyrimidines as Selective Toll-Like Receptor 7 Agonists

Toll-like receptors (TLRs) are components of innate immunity that play a crucial role in several diseases, including chronic inflammatory and infectious diseases, autoimmune diseases, and cancer. In particular, TLR7 has been identified as a key player in the innate immune response against viral infections and small-molecule TLR7 agonists have shown potential for vaccine therapy, for treatment of asthma and allergies, and as anticancer drugs. Inspired by our previous discovery of selective TLR7 agonists, our goal was to develop and introduce a new chemotype of TLR7 agonists by replacing the quinazoline ring with a new heterocycle isoxazolo[5,4-d]pyrimidine. Here, we report design, optimized synthesis, and structure-activity relationship studies of a novel class of TLR7 agonists based on the 6-(trifluoromethyl)isoxazolo[5,4-d]pyrimidine-4-amine scaffold that demonstrate high selectivity and low micromolar potencies. The best-in-class agonist 21a, with an EC50 value of 7.8 μM, also proved to be noncytotoxic and induced secretion of cytokines, including IL-1β, IL-12p70, IL-8, and TNF-α, indicating its potential to modulate the immune response.

The Role of the Toll-like Receptor 2 and the cGAS-STING Pathways in Breast Cancer: Friends or Foes?

Breast cancer stands as a primary malignancy among women, ranking second in global cancer-related deaths. Despite treatment advancements, many patients progress to metastatic stages, posing a significant therapeutic challenge. Current therapies primarily target cancer cells, overlooking their intricate interactions with the tumor microenvironment (TME) that fuel progression and treatment resistance. Dysregulated innate immunity in breast cancer triggers chronic inflammation, fostering cancer development and therapy resistance. Innate immune pattern recognition receptors (PRRs) have emerged as crucial regulators of the immune response as well as of several immune-mediated or cancer cell-intrinsic mechanisms that either inhibit or promote tumor progression. In particular, several studies showed that the Toll-like receptor 2 (TLR2) and the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathways play a central role in breast cancer progression. In this review, we present a comprehensive overview of the role of TLR2 and STING in breast cancer, and we explore the potential to target these PRRs for drug development. This information will significantly impact the scientific discussion on the use of PRR agonists or inhibitors in cancer therapy, opening up new and promising avenues for breast cancer treatment.

Co-delivering irinotecan and imiquimod by pH-responsive micelle amplifies anti-tumor immunity against colorectal cancer

Irinotecan (IRT), a classic clinical chemotherapeutic agent for treating colorectal cancer, has been found to induce immunogenic cell death (ICD) while exerting cytotoxicity in tumor cells. This effect is likely to be amplified in combination with immune modulators. Unfortunately, free drugs without targeting capacity would receive poor outcomes and strong side effects. To address these issues, in this work, an acid-sensitive micelle based on an amphiphilic poly(β-amino ester) derivative was constructed to co-deliver IRT and the immune adjuvant imiquimod (IMQ), termed PII. PII kept stable under normal physiological conditions. After internalization by tumor cells, PII dissociated in acidic lysosomes and released IRT and IMQ rapidly. In the CT26 tumor mouse model, PII increased the intra-tumoral SN38 (the active metabolite of IRT) and IMQ concentrations by up to 9.39 and 3.44 times compared with the free drug solution. The tumor inhibition rate of PII achieved 87.29%. This might profit from that IRT induced ICD, which promoted dendritic cells (DCs) maturation and intra-tumoral infiltration of CD8+ T cells. In addition, IMQ enhanced the antigen presenting ability of DCs and stimulated tumor associated macrophages to secrete tumor-killing cytokines. PII provided an effective strategy to combat colorectal cancer by synergy of chemotherapy and immunoregulation.

Recent advances in treating female genital human papillomavirus related neoplasms with topical imiquimod

Human papillomavirus (HPV) encompasses a group of viruses that infect the skin and mucous membranes. In the presence of certain factors, persistent infection with high-risk HPVs can trigger a process of neoplastic transformation. Imiquimod is a topical agent that acts as a Toll-like receptor 7/8 agonist, stimulating the innate and adaptive immune system to exert antitumor and antiviral effects. It has been approved for the treatment of various skin conditions, however, its efficacy and safety in the management of HPV-related-neoplasms of the lower genital tract, such as vulvar, vaginal, and cervical neoplasia, are still under investigation. This review summarizes the current evidence on the use of imiquimod for the treatment of HPV-induced lesions of the female lower genital tract, focusing on its indications, mechanisms of action, outcomes, and predictors of response.

Therapeutic Potential of Methotrexate-Loaded Superparamagnetic Iron Oxide Nanoparticles Coated with Poly(lactic-co-glycolic acid) and Polyethylene Glycol against Breast Cancer: Development, Characterization, and Comprehensive In Vitro Investigation

Novel superparamagnetic iron oxide nanoparticles (SPIONs) of Methotrexate (MTX) were developed using supercritical liquid technology and optimized with a Box-Behnken design in order to assess its potential as a candidate for the treatment of breast cancer. MTX-SPIONs coated with poly(lactic-co-glycolic acid)-polyethylene glycol 400 had an aggregate size of 500 nm and an encapsulation efficiency of 46.8 ± 3.9%. The Fourier-transformed infrared spectroscopy analysis revealed a shift in the main bands due to intermolecular hydrogen bonds, whereas the differential scanning calorimetry analysis revealed the absence of the MTX melting endotherm, indicating complete encapsulation with oxide nanoparticles. The zeta potential results indicated a value of 4.98 mV, whereas the in vitro release study revealed an initial burst release followed by a considerable release of 35.1 ± 2.78% after 12 h. Using flow cytometry, control, MTX, and MTX-SPIONs were evaluated for apoptosis, with MTX-SPIONs exhibiting greater apoptosis than the control group and MTX. In addition, MTX-SPIONs inhibited cell division and content organization while substantially increasing the proportion of cells in the G1 and G2 phases relative to the control group. MTX-SPIONs exhibited prolonged anticancer effects against MCF-7 cell lines compared to MTX alone, indicating that SPION-delivered chemotherapeutics may increase cytotoxicity. The medication was stable with low encapsulated drug loss, suggesting that the supercritical liquid technology-based method is a promising way for generating drug-polymer magnetic composite nanoparticles for cancer treatment.

Synthetic transformation of 6-Fluoroimidazo[1,2-a]Pyridine-3-carbaldehyde into 6-Fluoroimidazo[1,2-a]Pyridine-Oxazole Derivatives: In vitro urease inhibition and in silico study

Purpose

Ulcer is a serious disease that is caused due to different bacteria and over usage of various NSAIDs which caused to reduce the defensive system of stomach. Therefore, some novel series are needed to overcome these issues.

Methods

Oxazole-based imidazopyridine scaffolds (4a-p) were designed and synthesized by two step reaction protocol and then subjected to urease inhibition profile (in vitro). All the newly afforded analogs (4a-p) were found potent and demonstrated moderate to significant inhibition profile.

Results

Particularly, the analogs 4i (IC₅₀ = 5.68 ± 1.66 μM), 4o (IC₅₀ = 7.11 ± 1.24 μM), 4 g (IC₅₀ = 9.41 ± 1.19 μM) and 4 h (IC₅₀ = 10.45 ± 2.57 μM) were identified to be more potent than standard thiourea drug (IC₅₀ = 21.37 ± 1.76 μM). Additionally, the variety of spectroscopic tools such as ¹H NMR, ¹³C NMR and HREI-MS analysis were employed to confirm the precise structures of all the newly afforded analogs.

Discussion

The structure-activity relationship (SAR) studies showed that analogs possess the substitution either capable of furnishing strong HB like -OH or had strong EW nature such as -CF₃ & -NO₂ groups displayed superior inhibitory potentials than the standard thiourea drug. A good PLI (protein-ligand interaction) profile was shown by most active analogs when subjected to molecular study against corresponding target with key significant interactions such as pi-pi stacking, pi-pi T shaped and hydrogen bonding.