Comprehensive Review on How Repurposed Drugs Modulate Antitumor Immunity: Harnessing Damage-Associated Molecular Patterns.

Immunogenic cell death, DAMPs and anticancer therapeutics: An emerging amalgamation

Pathobiology of Inflammation to Cell Death

Immunological cell death (ICD) is a form of cancer cell death induced by radiotherapy, photodynamic therapy and a few chemotherapeutic agents such as Doxorubicin, Mitoxantrone, and Oxaliplatin. Unlike apoptosis or necrosis, ICD can induce an effective immune response directed against the tumor whereby both dendritic cells and T lymphocytes are mediators of this response. Dying cancer cells recruit and activate immune cells by releasing damage-associated molecular patterns (DAMPS) that help and promote the immune response to antigenic tumor neo-epitopes. Three key DAMPS are associated with the ICD process: calreticulin exposition on the cell surface, ATP secretion and high-mobility group box 1 (HMGB1) release. Using our in-house developed screening strategy facilitated by an automated in vitro platform with four assays, we have identified and characterized six cell lines (human breast MDA-MB-436 and MDA-MB-231, human osteosarcoma U-2 OS, murine pancreas Pan02, murine colon CT26, murine liver Hepa 1-6) for the three key DAMPs and cell viability. Furthermore, the screening of Oncodesign’s Nanocyclix® library using the ICD bona fide cell lines described above resulted in the identification of ODS2006336, a potential in vitro ICD inducer. As dendritic cells (DCs) play a key role in the recognition of DAMPs associated with ICD and the subsequent uptake and presentation of tumor antigens, we examined the phagocytosis of ICD inducer-treated tumor cells by DCs. ICD inducer-treated CT26 cells when cultured with spleen-derived DCs were efficiently phagocytosed by DCs. An increase in IL-1β secretion in the co-culture supernatant was observed. IL-1β plays an important role in anti-tumor T cell priming. In addition, pro-inflammatory cytokines IL-6 and TNFα that promote T cell differentiation and NK cell activation were also detected. Increased secretion of IL-12 by activated DCs can also enhance NK cell functionality. Thus, ICD activates both innate and adaptive arms of the immune system. With respect to cancer immunotherapy, the ICD process elicits enhanced adjuvanticity and antigenicity from dying cancer cells and consequently, promotes the development of clinically desired antitumor immunity. In essence, we describe a novel strategy for the identification of ICD inducers within large chemical libraries followed by a streamlined ex-vivo co-culture assay to demonstrate enhanced DC function. Citation Format: Akanksha Gangar, Didier Grillot, Raphaelle Guillard-Huet, Jean-Francois Mirjolet, Fabrice Viviani. Induction of immunogenic cell death and enhancement of dendritic cell function: Development of an in vitro, ex vivo ICD platform for the identification of novel ICD inducers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 585.

Immunogenic cell death (ICD) is a form of regulated cell death (RCD) induced by various stresses and produces antitumor immunity via damage-associated molecular patterns (DAMPs) release or exposure, mainly including high mobility group box 1 (HMGB1), calreticulin (CRT), adenosine triphosphate (ATP), and heat shock proteins (HSPs). Emerging evidence has suggested that ionizing radiation (IR) can induce ICD, and the dose, type, and fractionation of irradiation influence the induction of ICD. At present, IR-induced ICD is mainly verified in vitro in mice and there is few clinical evidence about it. To boost the induction of ICD by IR, some strategies have shown synergy with IR to enhance antitumor immune response, such as hyperthermia, nanoparticles, and chemotherapy. In this review, we focus on the molecular mechanisms of ICD, ICD-promoting factors associated with irradiation, the clinical evidence of ICD, and immunogenic forms of cell death. Finally, we summarize various methods of improving ICD induced by IR.

Oncolytic Newcastle disease virus (NDV) induces immunogenic cell death (ICD), liberating danger‐associated molecular patterns (DAMPs) that provokes defiance in neoplastic malignancy. The present study aims to investigate whether and how oncolytic NDV triggers ICD in prostate cancer cells. We show that NDV/FMW, an oncolytic NDV strain FMW, elicited the expression and release of several ICD markers, that is calreticulin (CRT), heat shock proteins (HSP70/90) and high‐mobility group box 1 (HMGB1), in prostate cancer cells. Furthermore, pharmacological repression of apoptosis, necroptosis, autophagy or endoplasmic reticulum (ER) stress exerted diverse effects on the HMGB1 and HSP70/90 evacuation in NDV/FMW‐infected prostate cancer cells. Moreover, ICD markers induced in prostate cancer cells upon NDV/FMW infection, were enhanced by either treatment with a STAT3 (signal transducer and activator of transcription 3) inhibitor or shRNA‐mediated knockdown of STAT3. In nude mice bearing prostate cancer cell‐derived tumours, the tumours injected with the supernatants of NDV/FMW‐infected cells grew smaller than mock‐treated tumours. These results indicate that oncolytic NDV provokes the expression of ICD makers in prostate cancer cells. Our data also suggest that a combination of inhibition of STAT3 with oncolytic NDV could boost NDV‐based anti‐tumour effects against prostate cancer.

Cancer cell death can be immunogenic or nonimmunogenic depending on the initiating stimulus. The immunogenic characteristics of immunogenic cell death are mainly mediated by damage-associated molecular patterns represented by preapoptotic exposure of calreticulin and heat shock proteins (HSP70 and HSP90) from endoplasmic reticulum at the cell surface and active secretion of adenosintriphospate. Other damage-associated molecular patterns are produced in late stage apoptosis as high mobility group box 1 protein (HMGB1) into the extracellular milieu. Such signals operate on various receptors expressed by antigen presenting cells, mainly by population of dendritic cells, to stimulate the activation of antigen specific T-cell response. In this review, we describe the current known immunogenic cell death inducers and their potential to activate antitumor immune response.

Apoptotic cell death generally characterized by a morphologically homogenous entity has been considered to be essentially non-immunogenic. However, apoptotic cancer cell death, also known as type 1 programmed cell death (PCD), was recently found to be immunogenic after treatment with several chemotherapeutic agents and oncolytic viruses through the emission of various danger-associated molecular patterns (DAMPs). Extensive studies have revealed that two different types of immunogenic cell death (ICD) inducers, recently classified by their distinct actions in endoplasmic reticulum (ER) stress, can reinitiate immune responses suppressed by the tumor microenvironment. Indeed, recent clinical studies have shown that several immunotherapeutic modalities including therapeutic cancer vaccines and oncolytic viruses, but not conventional chemotherapies, culminate in beneficial outcomes, probably because of their different mechanisms of ICD induction. Furthermore, interests in PCD of cancer cells have shifted from its classical form to novel forms involving autophagic cell death (ACD), programmed necrotic cell death (necroptosis), and pyroptosis, some of which entail immunogenicity after anticancer treatments. In this review, we provide a brief outline of the well-characterized DAMPs such as calreticulin (CRT) exposure, high-mobility group protein B1 (HMGB1), and adenosine triphosphate (ATP) release, which are induced by the morphologically distinct types of cell death. In the latter part, our review focuses on how emerging oncolytic viruses induce different forms of cell death and the combinations of oncolytic virotherapies with further immunomodulation by cyclophosphamide and other immunotherapeutic modalities foster dendritic cell (DC)-mediated induction of antitumor immunity. Accordingly, it is increasingly important to fully understand how and which ICD inducers cause multimodal ICD, which should aid the design of reasonably multifaceted anticancer modalities to maximize ICD-triggered antitumor immunity and eliminate residual or metastasized tumors while sparing autoimmune diseases.

Pathogenesis of Liver Injury in Acute Liver Failure

Advances in Immunogenic Cell Death for Cancer Immunotherapy

Immunogenic cell death (ICD) is a form of apoptosis that kills susceptible populations of cancer cells while teaching the immune system to attack the remaining resistant cells. Chemotherapeutics which induce ICD elicit their immune response by inducing tumor cells to display or release damage-associated molecular patterns (DAMPs). There are two key biomarkers for ICD: 1) during the apoptotic process, tumor cells secrete ATP (extracellular ATP or eATP) and 2) during secondary necrosis, tumor cells release HMGB1 (high mobility group box 1). Because the dying tumor cells display these DAMP molecules, they stimulate the recruitment of dendritic cells (DCs) into the tumor bed and ultimately “teach” cytotoxic T-lymphocytes (CTLs) to respond to these tumor specific antigens. These primed CTLs will then kill additional tumor cells through a direct cytotoxic response. Therefore, therapeutics which provoke an ICD response offer a therapeutically desirable outcome for cancer therapy. Current assay methods such as ELISA assays and flow cytometry for measuring these ICD biomarkers are laborious and involve multiple transfer and wash steps. We have developed homogeneous (no wash), single addition assays for measuring the two principle ICD biomarkers. The eATP assay uses optimized luciferase detection chemistry that is applied directly to live cells to measure ATP release over 24 hours. The HMGB1 assay uses a complementary luciferase fragment-labeled antibody approach to measure protein concentration. We demonstrated the use of these two assays with model systems for inducing Immunogenic Cell Death with human and murine cell lines including U2OS, EL4, and U937 cells. The potency and response magnitude of ICD-inducing compounds including doxorubicin, idarubicin and mitoxantrone differs depending on the model cell line used. Further, the timing of extracellular ATP release and HMGB1 release differs between cell lines and inducers. Improved assays to measure two markers of Immunogenic Cell Death will expedite the discovery and development of inducers of Immunogenic Cell Death, including small molecule therapeutics, oncolytic viruses, radiation therapy and other novel therapeutics, by streamlining the workflow, increasing sample throughput and providing real time live cell data. Citation Format: Richard L. Somberg, Kevin Kupcho, Andrew Niles, James Cali. Detection ofHMGB1 and extracellular ATP for the assessment of immunogenic cell death [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1112.

The extracellular levels of damage-associated molecular patterns (DAMPs) released during immunogenic cell death (ICD) are positively correlated with the magnitude and efficacy of the resulting in vivo immune response. Therefore, extracellular ATP (eATP) and high mobility group box 1 (HMGB1) have been identified as key biomarkers for their predictive capacity during in vitro ICD screening activities. Current methods for identifying eATP and HMGB1 inducers are laborious, costly, and hampered by poor throughput. To overcome these challenges, we developed easy-to-use, homogeneous, bioluminescent assays that measure dose-dependent release of these immunostimulatory agents directly in cell culture. The eATP assay utilizes an optimized ATP detection chemistry that can be employed directly to assess live-cell kinetic responses for up to 24 h, with even longer exposures supported by a staggered reagent addition approach. The HMGB1 assay measures the protein's concentration at exposure endpoint in the same sample well using complementary luciferase fragment-labelled monoclonal antibodies. We tested the utility of the assays using U20S, Jurkat and U937 cells dosed with serial dilutions of known ICD inducers (doxorubicin, idarubicin, mitoxantrone, and bortezomib). The resulting data suggest the potency of eATP and HMGB1 release is dependent upon cell model and agent but can be reproducibly and robustly measured in 96 and 384 well environments. Further, the eATP assay produced remarkable early dose-dependent response resolution whereas the HMGB1 data provided a confirmatory post-mortem ICD parameter. This new ICD biomarker detection workflow may help to efficiently define and rank-order the capacity of new chemical entities to induce apoptosis and immunogenic cell death. Citation Format: Andrew L. Niles, Kevin R. Kupcho, Dan F. Lazar, James J. Cali. Improved DAMP assays for the in vitro assessment of immunogenic cell death [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1933.

Oncolytic viruses (OVs) are novel immunotherapeutic agents whose anticancer effects come from both oncolysis and elicited antitumor immunity. OVs induce mostly immunogenic cancer cell death (ICD), including immunogenic apoptosis, necrosis/necroptosis, pyroptosis, and autophagic cell death, leading to exposure of calreticulin and heat-shock proteins to the cell surface, and/or released ATP, high-mobility group box 1, uric acid, and other damage-associated molecular patterns as well as pathogen-associated molecular patterns as danger signals, along with tumor-associated antigens, to activate dendritic cells and elicit adaptive antitumor immunity. Dying the right way may greatly potentiate adaptive antitumor immunity. The mode of cancer cell death may be modulated by individual OVs and cancer cells as they often encode and express genes that inhibit/promote apoptosis, necroptosis, or autophagic cell death. We can genetically engineer OVs with death-pathway-modulating genes and thus skew the infected cancer cells toward certain death pathways for the enhanced immunogenicity. Strategies combining with some standard therapeutic regimens may also change the immunological consequence of cancer cell death. In this review, we discuss recent advances in our understanding of danger signals, modes of cancer cell death induced by OVs, the induced danger signals and functions in eliciting subsequent antitumor immunity. We also discuss potential combination strategies to target cells into specific modes of ICD and enhance cancer immunogenicity, including blockade of immune checkpoints, in order to break immune tolerance, improve antitumor immunity, and thus the overall therapeutic efficacy.

The Alarmin Properties of DNA and DNA-associated Nuclear Proteins

During necrosis and following some instances of apoptosis (in particular in the absence of a proficient phagocytic system), the nonhistone chromatin component high-mobility group box 1 (HMGB1) is released in the extracellular space. In vivo, extracellular HMGB1 can bind Toll-like receptor 4 on the surface of dendritic cells, de facto operating as a danger-associated molecular pattern and alarming the organism to the presence of stressful conditions. Recent results indicate that the release of HMGB1 is one of the key features for cell death to be perceived as immunogenic, i.e., to be capable of triggering a cognate immune response in vivo. Thus, only anticancer agents that-among other features-allow for the release of HMGB1 as they induce cell death are expected to stimulate anticancer immune responses. To investigate the immunogenic potential of conventional anticancer agents and novel cell death inducers on a high-throughput scale, we engineered human osteosarcoma U2OS cells to express HMGB1 fused at the N-terminus of the green fluorescent protein (GFP). Coupled to fluorescence microscopy workstations for automated image acquisition and analysis, this HMGB1-GFP-based biosensor is amenable for the identification of potential inducers of immunogenic cell death among large chemical libraries.

Characterization of RAGE, HMGB1, and S100β in Inflammation-Induced Preterm Birth and Fetal Tissue Injury