Tumor Pigmentation Does Not Affect Light-Activated Belzupacap Sarotalocan Treatment but Influences Macrophage Polarization in a Murine Melanoma Model.

Purpose: Pigmentation in uveal melanoma is associated with increased malignancy and is known as a barrier for photodynamic therapy. We investigated the role of pigmentation in tumor behavior and the response to light-activated Belzupacap sarotalocan (Bel-sar) treatment in a pigmented (wild type) and nonpigmented (tyrosinase knock-out [TYR knock-out]) cell line in vitro and in a murine model. Methods: The B16F10 (TYR knock-out) was developed using CRISPR/Cas9. After the treatment with light-activated Bel-sar, cytotoxicity and exposure of damage-associated molecular patterns (DAMPs) were measured by flow cytometry. Treated tumor cells were co-cultured with bone marrow-derived macrophages (BMDMs) and dendritic cells (DCs) to assess phagocytosis and activation. Both cell lines were injected subcutaneously in syngeneic C57BL/6 mice. Results: Knock-out of the tyrosinase gene in B16F10 led to loss of pigmentation and immature melanosomes. Pigmented tumors contained more M1 and fewer M2 macrophages compared with amelanotic tumors. Bel-sar treatment induced near complete cell death, accompanied with enhanced exposure of DAMPs in both cell lines, resulting in enhanced phagocytosis of BMDMs and maturation of DCs. Bel-sar treatment induced a shift to M1 macrophages and delayed tumor growth in both in vivo tumor models. Following treatment, especially the pigmented tumors and their draining lymph nodes contained IFN-gamma positive CD8+T cells. Conclusions: Pigmentation influenced the type of infiltrating macrophages in the tumor, with more M1 macrophages in pigmented tumors. Belzupacap sarotalocan treatment induced immunogenic cell death and tumor growth delay in pigmented as well as in nonpigmented models and stimulated M1 macrophage influx in both models.

In Vitro Testing of the Virus-Like Drug Conjugate Belzupacap Sarotalocan (AU-011) on Uveal Melanoma Suggests BAP1-Related Immunostimulatory Capacity.

Purpose: The virus-like drug conjugate belzupacap sarotalocan (AU-011), currently under clinical investigation for first-line treatment of primary uveal melanoma (UM), shows enhanced tumor specificity by targeting heparan sulfate proteoglycans (HSPG). Such a treatment may potentially lead to systemic immune responses. We studied the potential of AU-011 treatment to induce immunogenic cell death as the first step to induce systemic immunity. Methods: We determined binding and uptake of AU-011 in ten primary and metastatic UM cell lines. The subcellular location of AU-011 was assessed by fluorescence microscopy. Following light activation (wavelength 690 nm) of AU-011, the half-maximal effective concentration (EC50) of AU-011 treatment and exposure of damage-associated molecular patterns (DAMPs) were assessed using flow cytometry. DAMPs were measured by RNAseq. Results: Fluorescence microscopy revealed most of the AU-011 was present in the cytoplasm. AU-011 binding and uptake by UM cells increased over time, with a lower uptake in BAP1-negative than in BAP1-positive cell lines. AU-011 activation induced cell death across all UM cell lines with EC50 values at picomolar concentrations. The AU-011 concentration and total light dose (J/cm2) were the most important parameters for the observed cytotoxicity. Finally, light-activated AU-011 induced exposure of DAMPs calreticulin (CRT) and HSP90. CRT exposure by light-activated AU-011 as well as CRT RNA exposure were lower in BAP1-negative compared to BAP1-positive UM cell lines. Conclusions: AU-011 treatment at low picomolar range induces immunogenic cell death in all 10 UM cell lines. The in vitro cytotoxicity was accompanied by exposure of DAMPs (HSP90 and CRT), suggesting AU-011 may contribute to the development of systemic immunity and be a suitable candidate for combination with immunotherapy in vivo. AU-011 treatment was more effective against BAP1-positive cell lines, with a lower EC50 and higher CRT exposure.

Current Challenges and Opportunities of Photodynamic Therapy against Cancer.

BACKGROUND: Photodynamic therapy (PDT) is an established, minimally invasive treatment for specific types of cancer. During PDT, reactive oxygen species (ROS) are generated that ultimately induce cell death and disruption of the tumor area. Moreover, PDT can result in damage to the tumor vasculature and induce the release and/or exposure of damage-associated molecular patterns (DAMPs) that may initiate an antitumor immune response. However, there are currently several challenges of PDT that limit its widespread application for certain indications in the clinic. METHODS: A literature study was conducted to comprehensively discuss these challenges and to identify opportunities for improvement. RESULTS: The most notable challenges of PDT and opportunities to improve them have been identified and discussed. CONCLUSIONS: The recent efforts to improve the current challenges of PDT are promising, most notably those that focus on enhancing immune responses initiated by the treatment. The application of these improvements has the potential to enhance the antitumor efficacy of PDT, thereby broadening its potential application in the clinic.

Upconversion nanoparticle platform for efficient dendritic cell antigen delivery and simultaneous tracking.

Upconversion nanoparticles (UCNPs) represent a group of NPs that can convert near-infrared (NIR) light into ultraviolet and visible light, thus possess deep tissue penetration power with less background fluorescence noise interference, and do not induce damage to biological tissues. Due to their unique optical properties and possibility for surface modification, UCNPs can be exploited for concomitant antigen delivery into dendritic cells (DCs) and monitoring by molecular imaging. In this study, we focus on the development of a nano-delivery platform targeting DCs for immunotherapy and simultaneous imaging. OVA 254-267 (OVA24) peptide antigen, harboring a CD8 T cell epitope, and Pam3CysSerLys4 (Pam3CSK4) adjuvant were chemically linked to the surface of UCNPs by amide condensation to stimulate DC maturation and antigen presentation. The OVA24-Pam3CSK4-UCNPs were thoroughly characterized and showed a homogeneous morphology and surface electronegativity, which promoted a good dispersion of the NPs. In vitro experiments demonstrated that OVA24-Pam3CSK4-UCNPs induced a strong immune response, including DC maturation, T cell activation, and proliferation, as well as interferon gamma (IFN-γ) production. In vivo, highly sensitive upconversion luminescence (UCL) imaging of OVA24-Pam3CSK4-UCNPs allowed tracking of UCNPs from the periphery to lymph nodes. In summary, OVA24-Pam3CSK4-UCNPs represent an effective tool for DC-based immunotherapy.

Combinatorial therapeutic approaches of photodynamic therapy and immune checkpoint blockade for colon cancer treatment.

Photodynamic therapy (PDT) has shown impressive therapeutic effects on various types of cancers by reactive oxygen species (ROS) generation and induction of immune responses. However, under certain conditions, the immune responses induced by PDT are not always sufficient to eradicate the remaining tumor cells. On the other hand, the photosensitizer indocyanine green (ICG) can mediate PDT under near-infrared (NIR) illumination, thereby enhancing the penetration depth of the excitation light into the tumor. We found that ICG is rapidly taken up in vitro by colorectal MC38 and CT26 tumor cells and it promotes PDT-mediated cell-killing effects. Our results furthermore revealed that ICG induces immunogenic cell death (ICD), as dendritic cells (DCs) were found to engulf ICG-PDT-treated tumor cells and undergo phenotypic maturation. ICG accumulated in tumors 2 h after administration, as measured by fluorescence and photoacoustic imaging. Considering the advantages of ICG as a photosensitizer, we sought to design a therapy that combines PDT and immune checkpoint blockade to maximize tumor control. To this end, a 25% thermosensitive polymer 407 hydrogel was included as a co-delivery platform for this treatment scheme. NIR-PDT under 808 nm irradiation in combination with cytotoxic T-lymphocyte-associated protein 4 (CTLA4)/programmed death-ligand 1 (PD-L1) checkpoint blockade prolonged survival rate of colorectal tumor-bearing mice by inducing a series of immune responses, like the phagocytosis of tumor debris by macrophages and DCs, and induction of acute inflammation, leukocyte infiltration, maturation and activation of DCs. Altogether, our work presents a NIR-triggered PDT strategy in combination with immune checkpoint blockade. Compared to a single treatment, the combination treatment increased efficiency to inhibit solid tumor growth and improved the survival rate of tumor-bearing mice.

Combinatorial Therapeutic Approaches with Nanomaterial-Based Photodynamic Cancer Therapy.

Photodynamic therapy (PDT), in which a light source is used in combination with a photosensitizer to induce local cell death, has shown great promise in therapeutically targeting primary tumors with negligible toxicity and minimal invasiveness. However, numerous studies have shown that noninvasive PDT alone is not sufficient to completely ablate tumors in deep tissues, due to its inherent shortcomings. Therefore, depending on the characteristics and type of tumor, PDT can be combined with surgery, radiotherapy, immunomodulators, chemotherapy, and/or targeted therapy, preferably in a patient-tailored manner. Nanoparticles are attractive delivery vehicles that can overcome the shortcomings of traditional photosensitizers, as well as enable the codelivery of multiple therapeutic drugs in a spatiotemporally controlled manner. Nanotechnology-based combination strategies have provided inspiration to improve the anticancer effects of PDT. Here, we briefly introduce the mechanism of PDT and summarize the photosensitizers that have been tested preclinically for various cancer types and clinically approved for cancer treatment. Moreover, we discuss the current challenges facing the combination of PDT and multiple cancer treatment options, and we highlight the opportunities of nanoparticle-based PDT in cancer therapies.

Bioorthogonal protein labelling enables the study of antigen processing of citrullinated and carbamylated auto-antigens.

Proteolysis is fundamental to many biological processes. In the immune system, it underpins the activation of the adaptive immune response: degradation of antigenic material into short peptides and presentation thereof on major histocompatibility complexes, leads to activation of T-cells. This initiates the adaptive immune response against many pathogens. Studying proteolysis is difficult, as the oft-used polypeptide reporters are susceptible to proteolytic sequestration themselves. Here we present a new approach that allows the imaging of antigen proteolysis throughout the processing pathway in an unbiased manner. By incorporating bioorthogonal functionalities into the protein in place of methionines, antigens can be followed during degradation, whilst leaving reactive sidechains open to templated and non-templated post-translational modifications, such as citrullination and carbamylation. Using this approach, we followed and imaged the post-uptake fate of the commonly used antigen ovalbumin, as well as the post-translationally citrullinated and/or carbamylated auto-antigen vinculin in rheumatoid arthritis, revealing differences in antigen processing and presentation.

Glycan modification of antigen alters its intracellular routing in dendritic cells, promoting priming of T cells.

Antigen uptake by dendritic cells and intracellular routing of antigens to specific compartments is regulated by C-type lectin receptors that recognize glycan structures. We show that the modification of Ovalbumin (OVA) with the glycan-structure Lewis(X) (Le(X)) re-directs OVA to the C-type lectin receptor MGL1. Le(X)-modification of OVA favored Th1 skewing of CD4(+) T cells and enhanced cross-priming of CD8(+) T cells. While cross-presentation of native OVA requires high antigen dose and TLR stimuli, Le(X) modification reduces the required amount 100-fold and obviates its dependence on TLR signaling. The OVA-Le(X)-induced enhancement of T cell cross-priming is MGL1-dependent as shown by reduced CD8(+) effector T cell frequencies in MGL1-deficient mice. Moreover, MGL1-mediated cross-presentation of OVA-Le(X) neither required TAP-transporters nor Cathepsin-S and was still observed after prolonged intracellular storage of antigen in Rab11(+)LAMP1(+) compartments. We conclude that controlled neo-glycosylation of antigens can crucially influence intracellular routing of antigens, the nature and strength of immune responses and should be considered for optimizing current vaccination strategies.

Bioorthogonal deprotection on the dendritic cell surface for chemical control of antigen cross-presentation.

The activation of CD8(+) T-cells requires the uptake of exogenous polypeptide antigens and proteolytic processing of these antigens to octamer or nonamer peptides, which are loaded on MHC-I complexes and presented to the T-cell. By using an azide as a bioorthogonal protecting group rather than as a ligation handle, masked antigens were generated-antigens that are not recognized by their cognate T-cell unless they are deprotected on the cell using a Staudinger reduction.

Design, automated synthesis and immunological evaluation of NOD2-ligand-antigen conjugates.

The covalent attachment of an innate immune system stimulating agent to an antigen can provide active vaccine modalities capable of eliciting a potent immune response against the incorporated antigen. Here we describe the design, automated synthesis and immunological evaluation of a set of four muramyl dipeptide-peptide antigen conjugates. Muramyl dipeptide (MDP) represents a well-known ligand for the intracellular NOD2 receptor and our study shows that covalently linking an MDP-moiety to an antigenic peptide can lead to a construct that is capable of stimulating the NOD2 receptor if the ligand is attached at the anomeric center of the muramic acid. The constructs can be processed by dendritic cells (DCs) and the conjugation does not adversely affect the presentation of the incorporated SIINFEKL epitope on MHC-I molecules. However, stimulation of the NOD2 receptor in DCs was not sufficient to provide a strong immunostimulatory signal.

Activity-based profiling reveals reactivity of the murine thymoproteasome-specific subunit beta5t.

Epithelial cells of the thymus cortex express a unique proteasome particle involved in positive T cell selection. This thymoproteasome contains the recently discovered beta5t subunit that has an uncharted activity, if any. We synthesized fluorescent epoxomicin probes that were used in a chemical proteomics approach, entailing activity-based profiling, affinity purification, and LC-MS identification, to demonstrate that the beta5t subunit is catalytically active in the murine thymus. A panel of established proteasome inhibitors showed that the broad-spectrum inhibitor epoxomicin blocks the beta5t activity and that the subunit-specific antagonists bortezomib and NC005 do not inhibit beta5t. We show that beta5t has a substrate preference distinct from beta5/beta5i that might explain how the thymoproteasome generates the MHC class I peptide repertoire needed for positive T cell selection.

Dendritic cells regulate exposure of MHC class II at their plasma membrane by oligoubiquitination.

Dendritic cells (DCs) initiate adaptive immune responses by activating T cells via cognate interactions between MHC-peptide complexes and T cell receptors. In immature DCs, MHC class II is predominantly stored in late endocytic compartments, where it has a short half-life because of degradation. In contrast, mature DCs recruit MHC class II to the plasma membrane. We here demonstrate that in immature DCs, the beta-chain of MHC class II was oligoubiquitinated after proteolytic processing of the associated invariant chain in endosomes and that this modification was required for efficient endocytosis and sorting into luminal vesicles of multivesicular bodies. Ubiquitination of MHC class II was suppressed in lipopolysaccharide-activated DCs. Mutated MHC class II lacking its ubiquitination site was expressed at the plasma membrane, irrespective of DC maturation. Together, these data provide a molecular basis for the regulation of MHC class II-mediated antigen presentation by DCs.