Immunomodulation by imiquimod in patients with high-risk primary melanoma

Tumor eradication by triplet therapy with BRAF inhibitor, TLR 7 agonist, and PD-1 antibody for BRAF-mutated melanoma

Programmed death 1 (PD-1)/programmed death-ligand 1 inhibitors are commonly used to treat various cancers, including melanoma. However, their efficacy as monotherapy is limited, and combination immunotherapies are being explored to improve outcomes. In this study, we investigated a combination immunotherapy involving an anti-PD-1 antibody that blocks the major adaptive immune-resistant mechanisms, a BRAF inhibitor that inhibits melanoma cell proliferation, and multiple primary immune-resistant mechanisms, such as cancer cell-derived immunosuppressive cytokines, and a Toll-like receptor 7 agonist that enhances innate immune responses that promote antitumor T-cell induction and functions. Using a xenogeneic nude mouse model implanted with human BRAF-mutated melanoma, a BRAF inhibitor vemurafenib was found to restore T-cell-stimulatory activity in conventional dendritic cells by reducing immunosuppressive cytokines, including interleukin 6, produced by human melanoma. Additionally, intravenous administration of the Toll-like receptor 7 agonist DSR6434 enhanced tumor growth inhibition by vemurafenib through stimulating the plasmacytoid dendritic cells/interferon-α/natural killer cell pathways and augmenting the T-cell-stimulatory activity of conventional dendritic cells. In a syngeneic mouse model implanted with murine BRAF-mutated melanoma, the vemurafenib and DSR6434 combination synergistically augmented the induction of melanoma antigen gp100-specific T cells and inhibited tumor growth. Notably, only triplet therapy with vemurafenib, DSR6434, and the anti-PD-1 antibody resulted in complete regression of SIY antigen-transduced BRAF-mutated melanoma in a CD8 T-cell-dependent manner. These findings indicate that a triple-combination strategy targeting adaptive and primary resistant mechanisms while enhancing innate immune responses that promote tumor-specific T cells may be crucial for effective tumor eradication.

Toll-like receptor-guided therapeutic intervention of human cancers: molecular and immunological perspectives

Toll-like receptors (TLRs) serve as the body's first line of defense, recognizing both pathogen-expressed molecules and host-derived molecules released from damaged or dying cells. The wide distribution of different cell types, ranging from epithelial to immune cells, highlights the crucial roles of TLRs in linking innate and adaptive immunity. Upon stimulation, TLRs binding mediates the expression of several adapter proteins and downstream kinases, that lead to the induction of several other signaling molecules such as key pro-inflammatory mediators. Indeed, extraordinary progress in immunobiological research has suggested that TLRs could represent promising targets for the therapeutic intervention of inflammation-associated diseases, autoimmune diseases, microbial infections as well as human cancers. So far, for the prevention and possible treatment of inflammatory diseases, various TLR antagonists/inhibitors have shown to be efficacious at several stages from pre-clinical evaluation to clinical trials. Therefore, the fascinating role of TLRs in modulating the human immune responses at innate as well as adaptive levels directed the scientists to opt for these immune sensor proteins as suitable targets for developing chemotherapeutics and immunotherapeutics against cancer. Hitherto, several TLR-targeting small molecules (e.g., Pam3CSK4, Poly (I:C), Poly (A:U)), chemical compounds, phytocompounds (e.g., Curcumin), peptides, and antibodies have been found to confer protection against several types of cancers. However, administration of inappropriate doses of such TLR-modulating therapeutics or a wrong infusion administration is reported to induce detrimental outcomes. This review summarizes the current findings on the molecular and structural biology of TLRs and gives an overview of the potency and promises of TLR-directed therapeutic strategies against cancers by discussing the findings from established and pipeline discoveries.

Advanced Acral Melanoma Therapies: Current Status and Future Directions

Melanoma is one of the deadliest malignancies. Its incidence has been significantly increasing in most countries in recent decades. Acral melanoma (AM), a peculiar subgroup of melanoma occurring on the palms, soles, and nails, is the main subtype of melanoma in people of color and is extremely rare in Caucasians. Although great progress has been made in melanoma treatment in recent years, patients with AM have shown limited benefit from current therapies and thus consequently have worse overall survival rates. Achieving durable therapeutic responses in this high-risk melanoma subtype represents one of the greatest challenges in the field. The frequency of BRAF mutations in AM is much lower than that in cutaneous melanoma, which prevents most AM patients from receiving treatment with BRAF inhibitors. However, AM has more frequent mutations such as KIT and CDK4/6, so targeted therapy may still improve the survival of some AM patients in the future. AM may be less susceptible to immune checkpoint inhibitors because of the poor immunogenicity. Therefore, how to enhance the immune response to the tumor cells may be the key to the application of immune checkpoint inhibitors in advanced AM. Anti-angiogenic drugs, albumin paclitaxel, or interferons are thought to enhance the effectiveness of immune checkpoint inhibitors. Combination therapies based on the backbone of PD-1 are more likely to provide greater clinical benefits. Understanding the molecular landscapes and immune microenvironment of AM will help optimize our combinatory strategies.

The role of tumor-associated macrophages and soluble mediators in pulmonary metastatic melanoma

Skin malignant melanoma is a highly aggressive skin tumor, which is also a major cause of skin cancer-related mortality. It can spread from a relatively small primary tumor and metastasize to multiple locations, including lymph nodes, lungs, liver, bone, and brain. What’s more metastatic melanoma is the main cause of its high mortality. Among all organs, the lung is one of the most common distant metastatic sites of melanoma, and the mortality rate of melanoma lung metastasis is also very high. Elucidating the mechanisms involved in the pulmonary metastasis of cutaneous melanoma will not only help to provide possible explanations for its etiology and progression but may also help to provide potential new therapeutic targets for its treatment. Increasing evidence suggests that tumor-associated macrophages (TAMs) play an important regulatory role in the migration and metastasis of various malignant tumors. Tumor-targeted therapy, targeting tumor-associated macrophages is thus attracting attention, particularly for advanced tumors and metastatic tumors. However, the relevant role of tumor-associated macrophages in cutaneous melanoma lung metastasis is still unclear. This review will present an overview of the origin, classification, polarization, recruitment, regulation and targeting treatment of tumor-associated macrophages, as well as the soluble mediators involved in these processes and a summary of their possible role in lung metastasis from cutaneous malignant melanoma. This review particularly aims to provide insight into mechanisms and potential therapeutic targets to readers, interested in pulmonary metastasis melanoma.

TLR agonist rMBP-NAP inhibits B16 melanoma tumor growth via induction of DCs maturation and T-cells cytotoxic response

Melanoma is the most aggressive skin cancer with increasing incidence and poor prognosis all over the world. Recent research has found that immunological abnormalities played a key role in the pathogenesis of melanoma. Increased understanding of tumor immune mechanisms has led to attract more attention for the potential of TLR agonists on treatment of melanoma. The present study aimed to determine the potential and efficacy of a novel TLR agonist rMBP-NAP for antitumor treatment in murine model of B16 melanoma. Subcutaneous administration of mice with rMBP-NAP remarkably inhibited tumor growth and tumor inhibitory rate was 77.72%. Additionally, rMBP‑NAP significantly upregulated the number of mature DCs (P < 0.05). Furthermore, the number and activation of CD4⁺ and CD8⁺ T cells were prominently enhanced following rMBP-NAP stimulation (P < 0.05). Overall, these results demonstrated that rMBP-NAP possessed the potential to be a novel immunomodulatory candidate drug for treating melanoma.

Roles of tumor-associated macrophages in tumor progression: implications on therapeutic strategies

Macrophages are heterogeneous cells that present as different functional phenotypes due to their plasticity. They can be classified into two categories, namely M1- and M2-like macrophages, which are involved in processes as diverse as anti-tumor activity and immunosuppressive tumor promotion. Tumor-associated macrophages (TAMs) are defined as being of an M2-type and are considered as the active component in tumor microenvironment. TAMs are involved in multiple processes of tumor progression through the expression of cytokines, chemokines, growth factors, protein hydrolases and more, which lead to enhance tumor cell proliferation, angiogenesis, and immunosuppression, which in turn supports invasion and metastasis. It is assumed that the abundance of TAMs in major solid tumors is correlated to a negative patient prognosis. Because of the currently available data of the TAMs’ role in tumor development, these cells have emerged as a promising target for novel cancer treatment strategies. In this paper, we will briefly describe the origins and types of TAMs and will try to comprehensively show how TAMs contribute to tumorigenesis and disease progression. Finally, we will present the main TAM-based therapeutic strategies currently available.

Evolution of Toll-like receptor 7/8 agonist therapeutics and their delivery approaches: From antiviral formulations to vaccine adjuvants

Imidazoquinoline derivatives (IMDs) and related compounds function as synthetic agonists of Toll-like receptors 7 and 8 (TLR7/8) and one is FDA approved for topical antiviral and skin cancer treatments. Nevertheless, these innate immune system-activating drugs have potentially much broader therapeutic utility; they have been pursued as antitumor immunomodulatory agents and more recently as candidate vaccine adjuvants for cancer and infectious disease. The broad expression profiles of TLR7/8, poor pharmacokinetic properties of IMDs, and toxicities associated with systemic administration, however, are formidable barriers to successful clinical translation. Herein, we review IMD formulations that have advanced to the clinic and discuss issues related to biodistribution and toxicity that have hampered the further development of these compounds. Recent strategies aimed at enhancing safety and efficacy, particularly through the use of bioconjugates and nanoparticle formulations that alter pharmacokinetics, biodistribution, and cellular targeting, are described. Finally, key aspects of the biology of TLR7 signaling, such as TLR7 tolerance, that may need to be considered in the development of new IMD therapeutics are discussed.

Immune mediated mechanisms of melanocyte destruction: Paving the way for efficient immunotherapeutic strategies against melanoma

Insights into immune reactions against benign and malignant melanocytes may help the development of more efficient immunotherapeutic treatments for melanoma. The interplay between an active systemic antitumor immunity and a responsive local tumor environment is crucial to achieve effective clinical responses. Increasing evidence confirms this strategy can lead to an adequate and durable immunosurveillance of melanocytes.

Insights into the Molecular Mechanisms Behind Intralesional Immunotherapies for Advanced Melanoma

The incidence of cutaneous melanoma, a highly malignant skin cancer, is increasing yearly. While surgical removal of the tumor is the mainstay of treatment for patients with locally confined disease, those with metastases face uncertainty when it comes to their treatment. As melanoma is a relatively immunogenic cancer, current guidelines suggest using immunotherapies that can rewire the host immune response to target melanoma tumor cells. Intralesional therapy, where immunomodulatory agents are injected directly into the tumor, are an emerging aspect of treatment for in-transit melanoma because of their ability to mitigate severe off-target immune-related adverse events. However, their immunomodulatory mechanisms are poorly understood. In this review, we will summarize and discuss the different intralesional therapies for metastatic melanoma with respect to their clinical outcomes and immune molecular mechanisms.

Control over Imidazoquinoline Immune Stimulation by pH-Degradable Poly(norbornene) Nanogels

The reactivation of the innate immune system by toll-like receptor (TLR) agonists holds promise for anticancer immunotherapy. Severe side effects caused by unspecific and systemic activation of the immune system upon intravenous injection prevent the use of small-molecule TLR agonists for such purposes. However, a covalent attachment of small-molecule imidazoquinoline (IMDQ) TLR7/8 agonists to pH-degradable polymeric nanogels could be shown to drastically reduce the systemic inflammation but retain the activity to tumoral tissues and their draining lymph nodes. Here, we introduce the synthesis of poly(norbornene)-based, acid-degradable nanogels for the covalent ligation of IMDQs. While the intact nanogels trigger sufficient TLR7/8 receptor stimulation, their degraded version of soluble, IMDQ-conjugated poly(norbornene) chains hardly activates TLR7/8. This renders their clinical safety profile, as degradation products are obtained, which would not only circumvent nanoparticle accumulation in the body but also provide nonactive, polymer-bound IMDQ species. Their immunologically silent behavior guarantees both spatial and temporal control over immune activity and, thus, holds promise for improved clinical applications.

A TLR7 agonist strengthens T and NK cell function during BRAF-targeted therapy in a preclinical melanoma model

Therapeutic success of targeted therapy with BRAF inhibitors (BRAFi) for melanoma is limited by resistance development. Observations from preclinical mouse models and recent insights into the immunological effects caused by BRAFi give promise for future development of combination therapy for human melanoma. In our study, we used the transplantable D4M melanoma mouse model with the BRAF^V600E mutation and concomitant PTEN loss in order to characterize alterations in tumor‐infiltrating effector immune cells when tumors become resistant to BRAFi. We found that BRAFi‐sensitive tumors displayed a pronounced inflammatory milieu characterized by high levels of cytokines and chemokines accompanied by an infiltration of T and NK cells. The tumor‐infiltrating effector cells were activated and produced high levels of IFN‐γ, TNF‐α and granzyme B. When tumors became resistant and progressively grew, they reverted to a low immunogenic state similar to untreated tumors as reflected by low mRNA levels of proinflammatory cytokines and chemokines and fewer tumor‐infiltrating T and NK cells. Moreover, these T and NK cells were functionally impaired in comparison to their counterparts in BRAFi‐sensitive tumors. Their effector cell function could be restored by additional peritumoral treatment with the TLR7 agonist imiquimod, a clinically approved agent for nonmelanoma skin cancer. Indeed, resistance to BRAFi therapy was delayed and accompanied by high numbers of activated T and NK cells in tumors. Thus, combining BRAFi with an immune stimulating agent such as a TLR ligand could be a promising alternative approach for the treatment of melanoma.

What's new?

While inhibitors targeting mutant BRAF proteins can induce melanoma regression, many tumors become resistant to these agents, possibly owing to immunological effects of BRAF inhibitor therapy. Here, using a preclinical mouse model, the authors show that during the early treatment phase with BRAF inhibitors, melanomas are highly immunogenic, with infiltrating T cells and natural killer cells. When resistance develops, however, tumors regress toward low immunogenicity, similar to untreated tumors. Experiments show that in the BRAF‐sensitive phase, peritumoral injection of the TLR7 ligand imiquimod preserves immunogenicity and delays resistance, thus representing a potentially effective novel therapeutic strategy for melanoma.

Dendritic Cells and Cancer: From Biology to Therapeutic Intervention

Inducing effective anti-tumor immunity has become a major therapeutic strategy against cancer. Dendritic cells (DC) are a heterogenous population of antigen presenting cells that infiltrate tumors. While DC play a critical role in the priming and maintenance of local immunity, their functions are often diminished, or suppressed, by factors encountered in the tumor microenvironment. Furthermore, DC populations with immunosuppressive activities are also recruited to tumors, limiting T cell infiltration and promoting tumor growth. Anti-cancer therapies can impact the function of tumor-associated DC and/or alter their phenotype. Therefore, the design of effective anti-cancer therapies for clinical translation should consider how best to boost tumor-associated DC function to drive anti-tumor immunity. In this review, we discuss the different subsets of tumor-infiltrating DC and their role in anti-tumor immunity. Moreover, we describe strategies to enhance DC function within tumors and harness these cells for effective tumor immunotherapy.

High FcγR Expression on Intratumoral Macrophages Enhances Tumor-Targeting Antibody Therapy

Therapy with tumor-specific Abs is common in the clinic but has limited success against solid malignancies. We aimed at improving the efficacy of this therapy by combining a tumor-specific Ab with immune-activating compounds. In this study, we demonstrate in the aggressive B16F10 mouse melanoma model that concomitant application of the anti-TRP1 Ab (clone TA99) with TLR3-7/8 or -9 ligands, and IL-2 strongly enhanced tumor control in a therapeutic setting. Depletion of NK cells, macrophages, or CD8⁺ T cells all mitigated the therapeutic response, showing a coordinated immune rejection by innate and adaptive immune cells. FcγRs were essential for the therapeutic effect, with a dominant role for FcγRI and a minor role for FcγRIII and FcγRIV. FcγR expression on NK cells and granulocytes was dispensable, indicating that other tumoricidal functions of NK cells were involved and implicating that FcγRI, -III, and -IV exerted their activity on macrophages. Indeed, F4/80⁺Ly-6C⁺ inflammatory macrophages in the tumor microenvironment displayed high levels of these receptors. Whereas administration of the anti-TRP1 Ab alone reduced the frequency of these macrophages, the combination with a TLR agonist retained these cells in the tumor microenvironment. Thus, the addition of innate stimulatory compounds, such as TLR ligands, to tumor-specific Ab therapy could greatly enhance its efficacy in solid cancers via optimal exploitation of FcγRs.

Intratumoral immunotherapy: using the tumor as the remedy

Immune checkpoint-targeted monoclonal antibodies directed at Programmed Death Receptor 1 (PD-1), Programmed Death Ligand 1 (PD-L1) and Cytotoxic T-Lymphocyte Associated Protein 4 (CTLA-4) are currently revolutionizing the prognosis of many cancers. By blocking co-inhibitory receptors expressed by antitumor T cells, these antibodies can break the immune tolerance against tumor cells and allow the generation of durable cancer immunity. Benefits in overall survival over conventional therapies have been demonstrated for patients treated with these immunotherapies, leading to multiple approvals of such therapies by regulatory authorities. However, only a minority of patients develop an objective tumor response with long-term survival benefits. Moreover, the systemic delivery of immunotherapies can be responsible for severe auto-immune toxicities. This risk increases dramatically with anti-PD(L)1 and anti-CTLA-4 combinations and currently hampers the development of triple combination immunotherapies. In addition, the price of these novel treatments is probably too high to be reimbursed by health insurances for all the potential indications where immunotherapy has shown activity (i.e. in more than 30 different cancer types). Intratumoral immunotherapy is a therapeutic strategy which aims to use the tumor as its own vaccine. Upon direct injections into the tumor, a high concentration of immunostimulatory products can be achieved in situ, while using small amounts of drugs. Local delivery of immunotherapies allows multiple combination therapies, while preventing significant systemic exposure and off-target toxicities. Despite being uncertain of the dominant epitopes of a given cancer, one can therefore trigger an immune response against the relevant neo-antigens or tumor-associated antigens without the need for their characterization. Such immune stimulation can induce a strong priming of the cancer immunity locally while generating systemic (abscopal) tumor responses, thanks to the circulation of properly activated antitumor immune cells. While addressing many of the current limitations of cancer immunotherapy development, intratumoral immunotherapy also offers a unique opportunity to better understand the dynamics of cancer immunity by allowing sequential and multifocal biopsies at every tumor injection.

Intravesical Immunomodulatory Imiquimod Enhances Bacillus Calmette-Guérin Downregulation of Nonmuscle-invasive Bladder Cancer

BACKGROUND

The Toll-like receptor (TLR)2/4 agonist bacillus Calmette-Guérin (BCG), although not failure proof, has been the most efficient immunomodulatory treatment of immunogenic nonmuscle-invasive bladder cancer (NMIBC) for > 40 years. We investigated the role of the immunomodulatory molecule TLR7 agonist imiquimod through the BCG key receptors TLR2/4 and the main downstream molecules of the mammalian target of rapamycin pathway in NMIBC treatment.

MATERIALS AND METHODS

A total of 40 Fischer-344 rats, 7 weeks old, received 4 doses of 1.5 mg/kg N-methyl-N-nitrosourea intravesically on weeks 0, 2, 4, and 6 for cancer induction. At week 8, the rats were randomized into 4 groups (10 per group) and treated intravesically once a week for 6 weeks: control (0.2 mL of vehicle); BCG (2 × 106 colony-forming units Connaught strain in 0.2 mL); imiquimod (20 mg/kg in 0.2 mL), and associated treatment BCG plus imiquimod in 0.2 mL. The bladders were extracted and analyzed for histopathology, immunohistochemistry, cell proliferation (Ki-67), apoptosis (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling [TUNEL]), and immunoblotting for TLR2, TLR4, p-P70S6K, and p-4E-BP1 proteins.

RESULTS

The histopathology results showed that BCG and imiquimod decreased bladder tumorigenesis compared with the control group, with a proliferation decrease (Ki-67) and an apoptosis increase (TUNEL). BCG upregulated TLR2/4, imiquimod upregulated TLR4, and both downregulated P70S6K1.

CONCLUSION

Imiquimod is able to efficiently decrease bladder carcinogenesis through upregulation of TLR7/4 and downregulation of P70S6K1 protein, generating new perspectives to boost BCG effects in the future.

Pharmacokinetics and pharmacodynamics of intravesical and intravenous TMX-101 and TMX-202 in a F344 rat model

OBJECTIVES

To evaluate and compare the pharmacokinetic and pharmacodynamic properties of 2 investigational Toll-like receptor 7 agonists, TMX-101, and TMX-202 after intravenous and intravesical administration in a rat model. TLR-7 agonists are successfully used as topical treatment for various (pre)malignant skin lesions and are now under investigation as intravesical therapy for non-muscle-invasive bladder cancer.

METHODS

Rats received an intravesical instillation with TMX-101, TMX-202, or vehicle. Additionally 2 groups of rats received an intravenous injection with TMX-101 or TMX-202. Blood sampling was performed at different time points, including pre-exposure and postexposure to determine the plasma concentrations of study drugs for pharmacokinetic and pharmacodynamic analyses and to determine the plasma concentrations of cytokines (IL-2, IL-6, and TNF-α).

RESULTS

We observed no signs of toxicity after intravesical or intravenous administration. There was a limited dose dependent systemic uptake of TMX-101 and TMX-202 after intravesical administration. The systemic uptake of TMX-202 after intravesical instillation was 25 times lower compared to TMX-101.

CONCLUSIONS

This in vivo study confirms the safety of intravesical TMX-101 and TMX-202 administration, with TMX-202 showing lower systemic uptake. TMX-202 has a larger molecule-mass compared to TMX-101, and it may therefore have a favorable safety profile when treating patients with non-muscle-invasive bladder cancer intravesically.

Anti-Melanoma immunity and local regression of cutaneous metastases in melanoma patients treated with monobenzone and imiquimod; a phase 2 a trial

Vitiligo development in melanoma patients during immunotherapy is a favorable prognostic sign and indicates breakage of tolerance against melanocytic/melanoma antigens. We investigated a novel immunotherapeutic approach of the skin-depigmenting compound monobenzone synergizing with imiquimod in inducing antimelanoma immunity and melanoma regression. Stage III-IV melanoma patients with non-resectable cutaneous melanoma metastases were treated with monobenzone and imiquimod (MI) therapy applied locally to cutaneous metastases and adjacent skin during 12 weeks, or longer. Twenty-one of 25 enrolled patients were evaluable for clinical assessment at 12 weeks. MI therapy was well-tolerated. Partial regression of cutaneous metastases was observed in 8 patients and stable disease in 1 patient, reaching the statistical endpoint of treatment efficacy. Continued treatment induced clinical response in 11 patients, including complete responses in three patients. Seven patients developed vitiligo-like depigmentation on areas of skin that were not treated with MI therapy, indicating a systemic effect of MI therapy. Melanoma-specific antibody responses were induced in 7 of 17 patients tested and melanoma-specific CD8+T-cell responses in 11 of 15 patients tested. These systemic immune responses were significantly increased during therapy as compared to baseline in responding patients. This study shows that MI therapy induces local and systemic anti-melanoma immunity and local regression of cutaneous metastases in 38% of patients, or 52% during prolonged therapy. This study provides proof-of-concept of MI therapy, a low-cost, broadly applicable and well-tolerated treatment for cutaneous melanoma metastases, attractive for further clinical investigation.

Preventive Inhibition of Liver Tumorigenesis by Systemic Activation of Innate Immune Functions

Liver cancer has become the second most deadly malignant disease, with no efficient targeted or immune therapeutic agents available yet. While dissecting the roles of cytoplasmic signaling molecules in hepatocarcinogenesis using an inducible mouse gene targeting system, Mx1-cre, we identified a potent liver tumor-inhibitory effect of synthetic double-stranded RNA (dsRNA), polyinosinic-polycytidylic acid (pIC), an inducer of the Mx1-cre system. Injection of pIC at the pre-cancer stage robustly suppressed liver tumorigenesis either induced by chemical carcinogens or by Pten loss and associated hepatosteatosis. The immunostimulatory dsRNA inhibited liver cancer initiation, apparently by boosting multiple anti-tumor activities of innate immunity, including induction of immunoregulatory cytokines, activation of NK cells and dendritic cells, and reprogramming of macrophage polarization. This study paves the way for the development of preventive and early interfering strategies for liver cancer to reduce the rapidly increasing incidences of liver cancer in an ever-growing population with chronic liver disorders.

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.

Anti-tumor Activity of Toll-Like Receptor 7 Agonists

Toll-like receptors (TLRs) are a class of pattern recognition receptors that play a bridging role in innate immunity and adaptive immunity. The activated TLRs not only induce inflammatory responses, but also elicit the development of antigen specific immunity. TLR7, a member of TLR family, is an intracellular receptor expressed on the membrane of endosomes. TLR7 can be triggered not only by ssRNA during viral infections, but also by immune modifiers that share a similar structure to nucleosides. Its powerful immune stimulatory action can be potentially used in the anti-tumor therapy. This article reviewed the anti-tumor activity and mechanism of TLR7 agonists that are frequently applied in preclinical and clinical investigations, and mainly focused on small synthetic molecules, including imiquimod, resiquimod, gardiquimod, and 852A, etc.

Core/shell protein-reactive nanogels via a combination of RAFT polymerization and vinyl sulfone postmodification

AIM

A promising nanogel vaccine platform was expanded toward antigen conjugation.

MATERIALS & METHODS

Block copolymers containing a reactive ester solvophobic block and a PEG-like solvophilic block were synthesized via reversible addition-fragmentation chain-transfer polymerization. Following self-assembly in DMSO, the esters allow for core-crosslinking and hydrophilization by amide bond formation with primary amines. Free thiols were accessed at the polymer chain ends through aminolysis of the reversible addition-fragmentation chain-transfer groups, and into the nanogel core by reactive ester conversion with cysteamine. Subsequently, free thiols were converted into vinyl sulfone moieties.

RESULTS

Despite sterical constraints, nanogel-associated vinyl sulfone moieties remained well accessible for cysteins to enforce protein conjugation successfully.

CONCLUSION

Our present findings provide a next step toward well-defined vaccine nanoparticles that can co-deliver antigen and a molecular adjuvant.

pH-degradable imidazoquinoline-ligated nanogels for lymph node-focused immune activation

Agonists of Toll-like receptors (TLRs) are potent activators of the innate immune system and hold promise as vaccine adjuvant and for anticancer immunotherapy. Unfortunately, in soluble form they readily enter systemic circulation and cause systemic inflammatory toxicity. Here we demonstrate that by covalent ligation of a small-molecule imidazoquinoline-based TLR7/8 agonist to 50-nm-sized degradable polymeric nanogels the potency of the agonist to activate TLR7/8 in in vitro cultured dendritic cells is largely retained. Importantly, imidazoquinoline-ligated nanogels focused the in vivo immune activation on the draining lymph nodes while dramatically reducing systemic inflammation. Mechanistic studies revealed a prevalent passive diffusion of the nanogels to the draining lymph node. Moreover, immunization studies in mice have shown that relative to soluble TLR7/8 agonist, imidazoquinoline-ligated nanogels induce superior antibody and T-cell responses against a tuberculosis antigen. This approach opens possibilities to enhance the therapeutic benefit of small-molecule TLR agonist for a variety of applications.

Treatment of in-transit melanoma with intralesional bacillus Calmette-Guérin (BCG) and topical imiquimod 5% cream: a report of 3 cases

Local therapy for in-transit melanoma (ITM) is a treatment alternative for patients who are not good candidates for systemic therapy, regional therapy, or surgical management. In this case report, we describe 3 patients with ITM who were treated with intralesional Bacillus Calmette-Guérin (ILBCG) and/or topical imiquimod. Treatment course was dictated by the clinical response. Patient 1’s response to ILBCG monotherapy was not sufficient to cause disease regression; however, transition to topical imiquimod therapy resulted in complete and sustained response. Although patient 2 responded to ILBCG and imiquimod, she developed a hypersensitivity reaction to ILBCG; when topical imiquimod was continued as monotherapy, her clinical response was complete. Patient 3 responded completely to ILBCG monotherapy in injected lesions, but expired shortly thereafter from unrelated disease. Reports like this one are needed to define the success measures of local therapy in the treatment of ITM.

Severe cutaneous and neurologic toxicity in melanoma patients during vemurafenib administration following anti-PD-1 therapy

Immune checkpoint inhibitors such as ipilimumab and targeted BRAF inhibitors have dramatically altered the landscape of melanoma therapeutics over the past few years. Agents targeting the programmed cell death-1/ligand (PD-1/PD-L1) axis are now being developed and appear to be highly active clinically with favorable toxicity profiles. We report two patients with BRAF V600E mutant melanoma who were treated with anti-PD-1 agents as first-line therapy without significant toxicity, followed by vemurafenib at disease progression. Both patients developed severe hypersensitivity drug eruptions with multi-organ injury early in their BRAF inhibitor treatment course. One patient subsequently developed acute inflammatory demyelinating polyneuropathy (AIDP) and the other developed anaphylaxis upon low-dose vemurafenib rechallenge. Further investigation of the immune response during combination or sequences of melanoma therapeutics is warranted. Furthermore, clinicians should maintain a high index of suspicion for these toxicities when vemurafenib is administered following an anti-PD-1 agent.

Modes of action of TLR7 agonists in cancer therapy

From the numerous Toll-like receptor agonists, only TLR7 agonists have been approved for cancer treatment, although they are current restricted to topical application. The main target cells of TLR7 agonists are plasmacytoid dendritic cells, producing IFN-α and thus acting on other immune cells. Thereby dendritic cells acquire enhanced costimulatory and antigen-presenting capacity, priming an adaptive immune response. Besides NK cells, antigen-specific T cells are the main terminal effectors of TLR7 agonists in tumor therapy. This qualifies TLR7 agonists as vaccine adjuvants, which is currently being tested in clinical trials. However, the systemic application of TLR7 agonists shows insufficient efficacy, most likely owing to toxicity-limited dosing. The use of TLR7 agonists in combinational therapy holds the promise of synergistic activity and lower required doses.

Dual roles of TLR7 in the lung cancer microenvironment

Toll-like receptor 7 (TLR7) agonists are under investigation for their ability to enhance antitumor immune responses. However, these agonists can also stimulate TLR7-expressing tumor cells. High TLR7 expression in the primary tumor confers poor clinical outcome and resistance to chemotherapy in lung cancer patients. This protumorigenic effect of TLR7 has been validated in murine models of lung carcinoma.

Classification of current anticancer immunotherapies

During the past decades, anticancer immunotherapy has evolved from a promising therapeutic option to a robust clinical reality. Many immunotherapeutic regimens are now approved by the US Food and Drug Administration and the European Medicines Agency for use in cancer patients, and many others are being investigated as standalone therapeutic interventions or combined with conventional treatments in clinical studies. Immunotherapies may be subdivided into "passive" and "active" based on their ability to engage the host immune system against cancer. Since the anticancer activity of most passive immunotherapeutics (including tumor-targeting monoclonal antibodies) also relies on the host immune system, this classification does not properly reflect the complexity of the drug-host-tumor interaction. Alternatively, anticancer immunotherapeutics can be classified according to their antigen specificity. While some immunotherapies specifically target one (or a few) defined tumor-associated antigen(s), others operate in a relatively non-specific manner and boost natural or therapy-elicited anticancer immune responses of unknown and often broad specificity. Here, we propose a critical, integrated classification of anticancer immunotherapies and discuss the clinical relevance of these approaches.

Imiquimod inhibits melanoma development by promoting pDC cytotoxic functions and impeding tumor vascularization

Imiquimod (IMQ) is a synthetic Toll-like receptor (TLR7/8) ligand that can trigger antiviral and antitumor activities. Despite evidence of potent therapeutic effects, the clinical use of IMQ in melanoma is impeded by incomplete understanding of its mechanisms of action. Mice and humans differ in many aspects of immunity, including TLR7 expression patterns, thus impeding the use of mouse models in translating discoveries into clinical applications. In this article, we investigated the mechanisms behind IMQ effects in vivo in a human context of melanoma and immunity using an innovative melanoma-bearing humanized mouse model. In this model, IMQ strongly inhibited melanoma tumor development through prompt mobilization of plasmacytoid dendritic cells and by triggering their cytotoxic functions, and through upregulation of expression of type 1 IFN response genes. IMQ also drastically impeded tumor vascularization by inducing the downregulation of angiogenic factors vascular endothelial growth factor, angiogenin, IL-8, and fibroblast growth factor. Our results revealed the short- and long-term multifactorial effects of IMQ converging toward inhibition of melanoma development. By providing a better understanding of the mechanisms of action of IMQ in melanoma, our study opens the way for its further clinical use in the treatment of metastatic melanoma.

Trial Watch: Toll-like receptor agonists for cancer therapy

Toll-like receptors (TLRs) have long been known for their ability to initiate innate immune responses upon exposure to conserved microbial components such as lipopolysaccharide (LPS) and double-stranded RNA. More recently, this family of pattern recognition receptors has been attributed a critical role in the elicitation of anticancer immune responses, raising interest in the development of immunochemotherapeutic regimens based on natural or synthetic TLR agonists. In spite of such an intense wave of preclinical and clinical investigation, only three TLR agonists are currently licensed by FDA for use in cancer patients: bacillus Calmette-Guérin (BCG), an attenuated strain of Mycobacterium bovis that operates as a mixed TLR2/TLR4 agonist; monophosphoryl lipid A (MPL), a derivative of Salmonella minnesota that functions as a potent agonist of TLR4; and imiquimod, a synthetic imidazoquinoline that activates TLR7. One year ago, in the August and September issues of OncoImmunology, we described the main biological features of TLRs and discussed the progress of clinical studies evaluating the safety and therapeutic potential of TLR agonists in cancer patients. Here, we summarize the latest developments in this exciting area of research, focusing on preclinical studies that have been published during the last 13 mo and clinical trials launched in the same period to investigate the antineoplastic activity of TLR agonists.

Combined intralesional Bacille Calmette-Guérin (BCG) and topical imiquimod for in-transit melanoma

The introduction of numerous immunotherapeutic agents into the clinical arena has allowed the long-time promise of immunotherapy to begin to become reality. Intralesional immunotherapy has demonstrated activity in multiple tumor types, and as the number of locally applicable agents has increased, so has the opportunity for therapeutic combinations. Both intralesional Bacille Calmette-Guérin (ILBCG) and topical 5% imiquimod cream have been used as single agents for the treatment of dermal/subcutaneous lymphatic metastases or in-transit melanoma, but the combination has not previously been reported. We used this combination regimen in 9 patients during the period from 2004 to 2011 and report their outcomes here. All patients were initially treated with ILBCG, followed by topical imiquimod after development of an inflammatory response to BCG. In this retrospective study, we examined their demographics, tumor characteristics, clinical and pathologic response to treatment, associated morbidities, local and distant recurrence, and overall survival. The 9 patients (8 male) had a mean age of 72 years (range, 56-95 y). Mild, primarily local toxicities were noted. Five patients (56%) had complete regression of their in-transit disease and 1 had a partial response. The 3 others had "surgical" complete responses with resection of solitary resistant lesions. The mean interval between the first treatment and complete resolution of in-transit disease was of 6.5 months (range, 2-12 mo). With a mean follow-up of 35 months (range 12-58 mo), 7 patients (78%) had not developed recurrent in-transit disease. Two patients (22%) have died of nonmelanoma causes, and none have died due to melanoma.

Future directions in cancer prevention

Prevention of cancer remains the most promising strategy for reducing both its incidence and the mortality due to this disease. For more than four decades, findings from epidemiology, basic research and clinical trials have informed the development of lifestyle and medical approaches to cancer prevention. These include selective oestrogen receptor modulators and aromatase inhibitors for breast cancer, the 5-α-reductase inhibitors finasteride and dutasteride for prostate cancer, and the development of vaccines for viruses that are associated with specific cancers. Future directions include genetic, proteomic and other molecular approaches for identifying pathways that are associated with cancer initiation and development, as well as refining the search for immunologically modifiable causes of cancer.

Results of a phase 1 dose escalation study of intravesical TMX-101 in patients with nonmuscle invasive bladder cancer

PURPOSE

Imiquimod, a toll like receptor 7 (TLR-7) agonist, is effective as a topical treatment for skin malignancies. TMX-101 is a liquid formulation of imiquimod. In this study we establish a safety profile of TMX-101 in patients with nonmuscle invasive bladder cancer.

MATERIALS AND METHODS

We conducted a multicenter phase 1 dose escalation study in patients with nonmuscle invasive bladder cancer. Patients were included in 1 of 4 dose groups (0.05%, 0.1%, 0.2% or 0.4%) and treated with 6 weekly instillations of TMX-101, starting 2 weeks after transurethral resection of bladder tumor. Patients were evaluated weekly, and pharmacokinetic and pharmacodynamic parameters were measured.

RESULTS

A total of 16 patients were included in the study with 4 per dose group. Two patients dropped out after instillation 2 in dose groups 1 and 2. Overall, 88 instillations were administered without serious adverse events. There were 118 adverse events, of which 84 were related to the study drug. All adverse events were mild or moderate and number or severity was not correlated with dose group. Of the related adverse events 70% were confined to the genitourinary tract and resolved without intervention. There was a dose dependent systemic uptake with low plasma levels up to dose group 3 (0.2%, 100 mg). Maximum plasma concentration in dose group 4 (0.4%, 200 mg) was 71.7 ng/ml. This is below plasma concentrations of 123 and 128 ng/ml without significant side effects measured in healthy volunteers after subcutaneous (30 mg) or oral intake (100 mg) of imiquimod, respectively.

CONCLUSIONS

Intravesical treatment with TMX-101 is safe. The side effects are common but mild and mostly limited to the genitourinary tract. There is a low systemic uptake.

Synergy of topical toll-like receptor 7 agonist with radiation and low-dose cyclophosphamide in a mouse model of cutaneous breast cancer

PURPOSE

This study tested the hypothesis that topical Toll-like receptor (TLR) 7 agonist imiquimod promotes antitumor immunity and synergizes with other treatments in a model of skin-involving breast cancer.

EXPERIMENTAL DESIGN

TSA mouse breast carcinoma cells were injected s.c. into syngeneic mice. Imiquimod 5% or placebo cream was applied topically on the shaved skin overlying tumors three times/wk. In some experiments, local ionizing radiation therapy (RT) was delivered to the tumor in three fractions of 8 Gy, given on consecutive days. Cyclophosphamide was given intraperitoneally (i.p.) in one dose of 2 mg/mouse. Mice were followed for tumor growth and survival.

RESULTS

Treatment with imiquimod significantly inhibited tumor growth, an effect that was associated with increased tumor infiltration by CD11c(+), CD4(+), and CD8(+) cells, and abolished by depletion of CD8(+) cells. Administration of imiquimod in combination with RT enhanced significantly tumor response compared with either treatment alone (P < 0.005), and 11% to 66% of irradiated tumors completely regressed. Importantly, the addition of topical imiquimod also resulted in growth inhibition of a secondary tumor outside of the radiation field. Low-dose cyclophosphamide given before start of treatment with imiquimod and RT further improved tumor inhibition and reduced tumor recurrence. Mice that remained tumor-free rejected a tumorigenic inoculum of TSA cells, showing long-term immunologic memory.

CONCLUSIONS

Topical imiquimod inhibits tumor growth and synergizes with RT. Addition of cyclophosphamide further increases the therapeutic effect and induces protective immunologic memory, suggesting that this combination is a promising strategy for cutaneous breast cancer metastases.

Topical TLR7 agonist imiquimod can induce immune-mediated rejection of skin metastases in patients with breast cancer

PURPOSE

Skin metastases of breast cancer remain a therapeutic challenge. Toll-like receptor 7 agonist imiquimod is an immune response modifier and can induce immune-mediated rejection of primary skin malignancies when topically applied. Here we tested the hypothesis that topical imiquimod stimulates local antitumor immunity and induces the regression of breast cancer skin metastases.

EXPERIMENTAL DESIGN

A prospective clinical trial was designed to evaluate the local tumor response rate of breast cancer skin metastases treated with topical imiquimod, applied 5 d/wk for 8 weeks. Safety and immunologic correlates were secondary objectives.

RESULTS

Ten patients were enrolled and completed the study. Imiquimod treatment was well tolerated, with only grade 1 to 2 transient local and systemic side effects consistent with imiquimod's immunomodulatory effects. Two patients achieved a partial response [20%; 95% confidence interval (CI), 3%-56%]. Responders showed histologic tumor regression with evidence of an immune-mediated response, showed by changes in the tumor lymphocytic infiltrate and locally produced cytokines.

CONCLUSION

Topical imiquimod is a beneficial treatment modality for breast cancer metastatic to skin/chest wall and is well tolerated. Importantly, imiquimod can promote a proimmunogenic tumor microenvironment in breast cancer. Preclinical data generated by our group suggest superior results with a combination of imiquimod and ionizing radiation and we are currently testing in patients whether the combination can further improve antitumor immune and clinical responses.

Topical treatment of recurrent vaginal melanoma in situ with imiquimod: A case report

► Vaginal melanoma in situ is a rare neoplasm with a paucity of data regarding the optimal management. ► More conservative approaches are needed to avoid the disfigurement, pain and postoperative complications associated with repeated surgical interventions. ► Imiquimod may prove to be a useful treatment modality for patients with vulvar or vaginal melanoma in situ.