Toll-like receptor agonists as cancer vaccine adjuvants

Cancer immunotherapy has emerged as a promising strategy to treat cancer patients. Among the wide range of immunological approaches, cancer vaccines have been investigated to activate and expand tumor-reactive T cells. However, most cancer vaccines have not shown significant clinical benefit as monotherapies. This is likely due to the antigen targets of vaccines, "self" proteins to which there is tolerance, as well as to the immunosuppressive tumor microenvironment. To help circumvent immune tolerance and generate effective immune responses, adjuvants for cancer vaccines are necessary. One representative adjuvant family is Toll-Like receptor (TLR) agonists, synthetic molecules that stimulate TLRs. TLRs are the largest family of pattern recognition receptors (PRRs) that serve as the sensors of pathogens or cellular damage. They recognize conserved foreign molecules from pathogens or internal molecules from cellular damage and propel innate immune responses. When used with vaccines, activation of TLRs signals an innate damage response that can facilitate the development of a strong adaptive immune response against the target antigen. The ability of TLR agonists to modulate innate immune responses has positioned them to serve as adjuvants for vaccines targeting infectious diseases and cancers. This review provides a summary of various TLRs, including their expression patterns, their functions in the immune system, as well as their ligands and synthetic molecules developed as TLR agonists. In addition, it presents a comprehensive overview of recent strategies employing different TLR agonists as adjuvants in cancer vaccine development, both in pre-clinical models and ongoing clinical trials.

PLGA-PEI nanoparticle covered with poly(I:C) for personalised cancer immunotherapy

Melanoma is the main cause of death among skin cancers and its incidence worldwide has been experiencing an appalling increase. However, traditional treatments lack effectiveness in advanced or metastatic patients. Immunotherapy, meanwhile, has been shown to be an effective treatment option, but the rate of cancers responding remains far from ideal. Here we have developed a personalized neoantigen peptide-based cancer vaccine by encapsulating patient derived melanoma neoantigens in polyethylenimine (PEI)-functionalised poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) and coating them with polyinosinic:polycytidylic acid (poly(I:C)). We found that PLGA NPs can be effectively modified to be coated with the immunoadjuvant poly(I:C), as well as to encapsulate neoantigens. In addition, we found that both dendritic cells (DCs) and lymphocytes were effectively stimulated. Moreover, the developed NP was found to have a better immune activation profile than NP without poly(I:C) or without antigen. Our results demonstrate that the developed vaccine has a high capacity to activate the immune system, efficiently maturing DCs to present the antigen of choice and promoting the activity of lymphocytes to exert their cytotoxic function. Therefore, the immune response generated is optimal and specific for the elimination of melanoma tumour cells.

Anti-melanoma Effects of Resiquimod (RSQ) In Vitro and in Combination with Immune Checkpoint Blockade In Vivo

Melanoma is the deadliest form of skin cancer and surgery is currently the most effective treatment. However, there are situations where surgery fails or is not an option to treat melanoma patients. Immunotherapy such as immune checkpoint blockade (e.g., anti-PD-1) can be effective as an alternative treatment for melanoma patients; however, the percentage of melanoma patients that exhibit complete responses from anti-PD-1 monotherapy is low, and a hostile immunosuppressive tumor microenvironment may be at least partly responsible. Resiquimod (RSQ) is an imidazoquinolinamine derivative and TLR-7/8 agonist that could enhance the antitumor activity of immune checkpoint blockade when these agents are combined as a treatment for melanoma. Here, the effect of combining systemic anti-PD-1 and locally administered RSQ on the survival of melanoma-challenged mice was tested. Our results demonstrated that anti-PD-1 in combination with RSQ can significantly prolong the survival of melanoma-challenged mice, compared to untreated mice and mice treated with anti-PD-1 alone. In addition, the in vitro studies showed that RSQ can mediate a direct anti-proliferative effect on melanoma cells. In conclusion, the combination of RSQ and anti-PD-1 may be a promising treatment for melanoma patients, especially as both treatments have already been used independently to safely treat melanoma patients.

Clinical and molecular overview of immunotherapeutic approaches for malignant skin melanoma: Past, present and future

Traditional therapeutic approaches for malignant melanoma, have proved to be limited and/or ineffective, especially with respect to their role in improving patient survival and tumor recurrence. In this regard, immunotherapy has been demonstrated to be a promising therapeutic alternative, boosting antitumor responses through the modulation of cell signaling pathways involved in the effector mechanisms of the immune system, particularly, the so-called "immunological checkpoints". Clinical studies on the efficacy and safety of immunotherapeutic regimens, alone or in combination with other antitumor approaches, have increased dramatically in recent decades, with very encouraging results. Hence, this review will discuss the current immunotherapeutic regimens used to treat malignant melanoma, as well as the molecular and cellular mechanisms involved. In addition, current clinical studies that have investigated the use, efficacy, and adverse events of immunotherapy in melanoma will also be discussed.

Topically Applied Resiquimod versus Imiquimod as a Potential Adjuvant in Melanoma Treatment

Melanoma is the most lethal form of skin cancer and surgery remains the preferred and most effective treatment. Nevertheless, there are cases where surgery is not a viable method and alternative treatments are therefore adopted. One such treatment that has been tested is topical 5% imiquimod (IMQ) cream, which, although showing promise as a treatment for melanoma, has been found to have undesirable off-target effects. Resiquimod (RSQ) is an immunomodulatory molecule that can activate immune responses by binding to Toll-like receptors (TLR) 7 and 8 and may be more effective than IMQ in the context of melanoma treatment. RSQ can cross the stratum corneum (SC) easily without requiring pretreatment of the skin. In a gel formulation, RSQ has been studied as a monotherapy and adjuvant for melanoma treatment in pre-clinical studies and as an adjuvant in clinical settings. Although side effects of RSQ in gel formulation were also reported, they were never severe enough for the treatment to be suspended. In this review, we discuss the potential use of RSQ as an adjuvant for melanoma treatment.

Melanoma therapeutics: a literature review

Melanoma is a relentless type of skin cancer which involves myriad signaling pathways which regulate many cellular processes. This makes melanoma difficult to treat, especially when identified late. At present, therapeutics include chemotherapy, surgical resection, biochemotherapy, immunotherapy, photodynamic and targeted approaches. These interventions are usually administered as either a single-drug or in combination, based on tumor location, stage, and patients' overall health condition. However, treatment efficacy generally decreases as patients develop treatment resistance. Genetic profiling of melanocytes and the discovery of novel molecular factors involved in the pathogenesis of melanoma have helped to identify new therapeutic targets. In this literature review, we examine several newly approved therapies, and briefly describe several therapies being assessed for melanoma. The goal is to provide a comprehensive overview of recent developments and to consider future directions in the field of melanoma.

Skin Penetration Enhancement Strategies Used in the Development of Melanoma Topical Treatments

Malignant melanoma is an aggressive form of skin cancer for which there is currently no reliable therapy and is considered one of the leading health issues in the USA. At present, surgery is the most effective and acceptable treatment; however, surgical excision can be impractical in certain circumstances. Topical skin delivery of drugs using topical formulations is a potential alternative approach which can have many advantages aside from being a non-invasive delivery route. Nevertheless, the presence of the stratum corneum (SC) limits the penetration of drugs through the skin, lowering their treatment efficacy and raising concerns among physicians and patients as to their effectiveness. Currently, research groups are trying to circumvent the SC barrier by using skin penetration enhancement (SPE) strategies. The SPE strategies investigated include chemical skin penetration enhancers (CPEs), physical skin penetration enhancers (PPEs), nanocarrier systems, and a combination of SPE strategies (cream). Of these, PPEs and cream are the most advanced approaches in terms of preclinical and clinical studies, respectively.

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.