autolysosome; autophagosome; chaperone-mediated autophagy; flux; LC3; lysosome; macroautophagy; phagophore; stress; vacuole
A paper recently published in Science Translational Medicine describes a next-generation antisense oligonucleotide that specifically downregulates the expression of human signal transducer and activator of transcription 3 (STAT3). Such an oligonucleotide, AZD9150, exerts antineoplastic effects on a selected panel of STAT3-dependent human cancer cells growing in vitro and in vivo (as xenografts in immunodeficient mice). Moreover, preliminary data from a Phase I clinical trial indicate that AZD9150 may cause partial tumor regression in patients with chemorefractory lymphoma and non-small cell lung carcinoma. STAT3 not only participates in cell-autonomous processes that are required for the survival and growth of malignant cells, but also limits their ability to elicit anticancer immune responses. Moreover, STAT3 contribute to the establishment of an immunosuppressive tumor microenvironment. Thus, the inhibition of STAT3 may promote immunosurveillance by a dual mechanism: (1) it may increase the immunogenicity of cancer cells via cell-autonomous pathways; and (2) it may favor the reprogramming of the tumor microenvironment toward an immunostimulatory state. It will therefore be important to explore whether immunological biomarkers predict the efficacy of AZD9150 in the clinic. This may ameliorate patient stratification and it may pave the way for rational combination therapies involving classical chemotherapeutics with immunostimulatory effects, AZD9150 and immunotherapeutic agents such as checkpoint blockers.
AZD9150; checkpoint blockers; IL-6; lymphoma; non-small cell lung carcinoma; PD-1
On 2015, October 27th, the US Food and Drug Administration (FDA) has officially approved talimogene laherparepvec (T-VEC, also known as OncoVEXGM-CSF) for use in melanoma patients with injectable but non-resectable lesions in the skin and lymph nodes. T-VEC (which is commercialized by Amgen, Inc. under the name of Imlygic®) becomes therefore the first oncolytic virus approved for cancer therapy in the US.
Granulocyte macrophage colony-stimulating factor; Imlygic®; OncoVEXGM-CSF; OPTiM; talimogene laherparepvec; T-vec
During the past decade, great efforts have been dedicated to the development of clinically relevant interventions that would trigger potent (and hence potentially curative) anticancer immune responses. Indeed, developing neoplasms normally establish local and systemic immunosuppressive networks that inhibit tumor-targeting immune effector cells, be them natural or elicited by (immuno)therapy. One possible approach to boost anticancer immunity consists in the (generally systemic) administration of recombinant immunostimulatory cytokines. In a limited number of oncological indications, immunostimulatory cytokines mediate clinical activity as standalone immunotherapeutic interventions. Most often, however, immunostimulatory cytokines are employed as immunological adjuvants, i.e., to unleash the immunogenic potential of other immunotherapeutic agents, like tumor-targeting vaccines and checkpoint blockers. Here, we discuss recent preclinical and clinical advances in the use of some cytokines as immunostimulatory agents in oncological indications.
Anticancer vaccines; checkpoint blockers; GM-CSF; IL-2; oncolytic virotherapy; Type I interferon
Oncolytic virotherapy relies on the administration of non-pathogenic viral strains that selectively infect and kill malignant cells while favoring the elicitation of a therapeutically relevant tumor-targeting immune response. During the past few years, great efforts have been dedicated to the development of oncolytic viruses with improved specificity and potency. Such an intense wave of investigation has culminated this year in the regulatory approval by the US Food and Drug Administration (FDA) of a genetically engineered oncolytic viral strain for use in melanoma patients. Here, we summarize recent preclinical and clinical advances in oncolytic virotherapy.
Cavatak™; GM-CSF; JX-594; ONCOS-102; Reolysin®; talimogene laherparepvec
CTLA4; ipilimumab; metastatic melanoma; nivolumab; PD-1; pembrolizumab
Accumulating preclinical evidence indicates that Toll-like receptor (TLR) agonists efficiently boost tumor-targeting immune responses (re)initiated by most, if not all, paradigms of anticancer immunotherapy. Moreover, TLR agonists have been successfully employed to ameliorate the efficacy of various chemotherapeutics and targeted anticancer agents, at least in rodent tumor models. So far, only three TLR agonists have been approved by regulatory agencies for use in cancer patients. Moreover, over the past decade, the interest of scientists and clinicians in these immunostimulatory agents has been fluctuating. Here, we summarize recent advances in the preclinical and clinical development of TLR agonists for cancer therapy.
Ampligen™; bacillus Calmette-Guérin; G100; Hiltonol™; imiquimod; motolimod
Recently, we reported that saturated and unsaturated fatty acids trigger autophagy through distinct signal transduction pathways. Saturated fatty acids like palmitate (PA) induce autophagic responses that rely on phosphatidylinositol 3-kinase, catalytic subunit type 3 (PIK3C3, best known as VPS34) and beclin 1 (BECN1). Conversely, unsaturated fatty acids like oleate (OL) promote non-canonical, PIK3C3- and BECN1-independent autophagy. Here, we explored the metabolic effects of autophagy-inducing doses of PA and OL in mice. Mass spectrometry coupled to principal component analysis revealed that PA and OL induce well distinguishable changes in circulating metabolites as well as in the metabolic profile of the liver, heart, and skeletal muscle. Importantly, PA (but not OL) causes the depletion of multiple autophagy-inhibitory amino acids in the liver. Conversely, OL (but not PA) increased the hepatic levels of nicotinamide adenine dinucleotide (NAD), an obligate co-factor for autophagy-stimulatory enzymes of the sirtuin family. Moreover, PA (but not OL) raised the concentrations of acyl-carnitines in the heart, a phenomenon that perhaps is linked to its cardiotoxicity. PA also depleted the liver from spermine and spermidine, 2 polyamines have been ascribed with lifespan-extending activity. The metabolic changes imposed by unsaturated and saturated fatty acids may contribute to their health-promoting and health-deteriorating effects, respectively.
aging; amino acids; autophagy; NAD sirtuins; spermidine
The first study demonstrating that human colorectal carcinoma (CRC) is under robust immunosurveillance was published a decade ago. Today, it is clear that CRC patients with Stage III lesions abundantly infiltrated by effector memory T cells have a better prognosis than subjects with Stage I neoplasms exhibiting no or poor immune infiltration. Thus, immunological parameters have a superior prognostic value for CRC patients than TNM staging or the Dukes classification. In spite of the fact that CRC is the first neoplasia found to be under immunological control, most attempts made so far to cure this malignancy with immunotherapy have failed. With the exception of a minority of lesions characterized by microsatellite instability (MSI), CRC seems to be insensitive to the blockade of immunological checkpoints with monoclonal antibodies (mAbs) specific for cytotoxic T lymphocyte-associated protein 4 (CTLA4), programmed cell death 1 (PDCD1, best known as PD-1) and the PD-1 ligand CD274 (best known as PD-L1). Thus, CRC stands in contrast with an increasing number of malignancies that respond to checkpoint blockers. Efforts should therefore be dedicated to the development of strategies to (re)instate immunosurveillance in patients with MSI- CRC, perhaps based on the identification of novel, locally relevant immunological checkpoints.
CTLA4; ipilimumab; nivolumab; PD-1; PD-L1; pembrolizumab
Results from recent clinical trials demonstrate that a combinatorial immunotherapeutic regimen based on 2 distinct checkpoint blockers, namely, the CTLA4-targeting agent ipilimumab and the PD-1-specific molecule nivolumab, causes objective responses in a majority of subjects with advanced melanoma. These findings revolutionize the treatment of a neoplasm that was considered incurable until recently. Nonetheless, announcing the defeat of melanoma appears premature. Indeed, a sizeable fraction of patients does not respond to ipilimumab plus nivolumab, and the long-term efficacy of this immunotherapeutic regimen has not yet been investigated. Moreover, many patients experience severe side effects, calling for the development of strategies that uncouple the efficacy of ipilimumab plus nivolumab from their toxicity.
CTLA4; Opdivo™; PD-1; PD-L1; pembrolizumab; Yervoy™
eIF2α; GCN2; inflammasome; mitophagy; reactive oxygen species
One particular paradigm of anticancer immunotherapy relies on the administration of (potentially) tumor-reactive immune effector cells. Generally, these cells are obtained from autologous peripheral blood lymphocytes (PBLs) ex vivo (in the context of appropriate expansion, activation and targeting protocols), and re-infused into lymphodepleted patients along with immunostimulatory agents. In spite of the consistent progress achieved throughout the past two decades in this field, no adoptive cell transfer (ACT)-based immunotherapeutic regimen is currently approved by regulatory agencies for use in cancer patients. Nonetheless, the interest of oncologists in ACT-based immunotherapy continues to increase. Accumulating clinical evidence indicates indeed that specific paradigms of ACT, such as the infusion of chimeric antigen receptor (CAR)-expressing autologous T cells, are associated with elevated rates of durable responses in patients affected by various neoplasms. In line with this notion, clinical trials investigating the safety and therapeutic activity of ACT in cancer patients are being initiated at an ever increasing pace. Here, we review recent preclinical and clinical advances in the development of ACT-based immunotherapy for oncological indications.
checkpoint blockers; chimeric antigen receptor; GM-CSF; TCR; TLR agonists; tumor-associated antigens
One type of anticancer vaccine relies on the administration of DNA constructs encoding one or multiple tumor-associated antigens (TAAs). The ultimate objective of these preparations, which can be naked or vectored by non-pathogenic viruses, bacteria or yeast cells, is to drive the synthesis of TAAs in the context of an immunostimulatory milieu, resulting in the (re-)elicitation of a tumor-targeting immune response. In spite of encouraging preclinical results, the clinical efficacy of DNA-based vaccines employed as standalone immunotherapeutic interventions in cancer patients appears to be limited. Thus, efforts are currently being devoted to the development of combinatorial regimens that allow DNA-based anticancer vaccines to elicit clinically relevant immune responses. Here, we discuss recent advances in the preclinical and clinical development of this therapeutic paradigm.
adjuvants; dendritic cell; electroporation; GX-188E; mucosal immunity; VGX-3100; AFP, α-fetoprotein; APC, antigen-presenting cell; CDR, complementarity-determining region; CEA, carcinoembryonic antigen; CIN, cervical intraepithelial neoplasia; CTLA4, cytotoxic T lymphocyte protein 4; DAMP, damage-associated molecular pattern; DC, dendritic cell; FDA, Food and Drug Administration; GM-CSF, granulocyte macrophage colony-stimulating factor; HCC, hepatocellular carcinoma; HNSCC, head and neck squamous cell carcinoma; HPV, human papillomavirus; IL, interleukin; OS, overall survival; OVA, ovalbumin; PAP, prostate acid phosphatase; SCGB2A2, secretoglobin, family 2A, member 2; SOX2, SRY (sex determining region Y)-box 2; T, brachyury homolog; TAA, tumor-associated antigen; TLR, Toll-like receptor; TRA, tumor rejection antigen; Treg, regulatory T cell; WT1, Wilms tumor 1
Immunomodulatory monoclonal antibodies (mAbs) differ from their tumor-targeting counterparts because they exert therapeutic effects by directly interacting with soluble or (most often) cellular components of the immune system. Besides holding promise for the treatment of autoimmune and inflammatory disorders, immunomodulatory mAbs have recently been shown to constitute a potent therapeutic weapon against neoplastic conditions. One class of immunomodulatory mAbs operates by inhibiting safeguard systems that are frequently harnessed by cancer cells to establish immunological tolerance, the so-called “immune checkpoints.” No less than 3 checkpoint-blocking mAbs have been approved worldwide for use in oncological indications, 2 of which during the past 12 months. These molecules not only mediate single-agent clinical activity in patients affected by specific neoplasms, but also significantly boost the efficacy of several anticancer chemo-, radio- or immunotherapies. Here, we summarize recent advances in the development of checkpoint-blocking mAbs, as well as of immunomodulatory mAbs with distinct mechanisms of action.
ipilimumab; MEDI4736; MPDL3280A; nivolumab; pembrolizumab; urelumab; CRC, colorectal carcinoma; CTLA4, cytotoxic T lymphocyte-associated protein 4; FDA, Food and Drug Administration; IL, interleukin; KIR, killer cell immunoglobulin-like receptor; mAb, monoclonal antibody; NK, natural killer; NSCLC, non-small cell lung carcinoma; PD-1, programmed cell death 1; RCC, renal cell carcinoma; TGFβ1, transforming growth factor β1; TLR, Toll-like receptor; TNFRSF, tumor necrosis factor receptor superfamily; Treg, regulatory T cell
The blockade of immunological checkpoints has been successfully employed for the treatment of various solid neoplasms including melanoma, mesothelioma, non-small cell lung carcinoma, and renal cell carcinoma. A recent study indicates that the vast majority of patients with advanced, heavily pretreated Hodgkin's lymphoma (HL) also respond to a monoclonal antibody targeting programmed cell death 1 (PDCD1, best known as PD-1). Thus, checkpoint blockers may soon become part of our therapeutic armamentarium against hematological tumors. This would be particularly important as it would spare (at least some) patients the deleterious toxic effects of combinatorial chemotherapies and bone marrow transplantation. We anticipate that the realm of immunotherapy will eventually conquer vast portions of the territory that now belongs to hematological malignancies.
CTLA4; immunostimulatory monoclonal antibodies; ipilimumab; PD-L1; pembrolizumab; pidilizumab
The term “immunogenic cell death” (ICD) is now employed to indicate a functionally peculiar form of apoptosis that is sufficient for immunocompetent hosts to mount an adaptive immune response against dead cell-associated antigens. Several drugs have been ascribed with the ability to provoke ICD when employed as standalone therapeutic interventions. These include various chemotherapeutics routinely employed in the clinic (e.g., doxorubicin, epirubicin, idarubicin, mitoxantrone, bleomycin, bortezomib, cyclophosphamide and oxaliplatin) as well as some anticancer agents that are still under preclinical or clinical development (e.g., some microtubular inhibitors of the epothilone family). In addition, a few drugs are able to convert otherwise non-immunogenic instances of cell death into bona fide ICD, and may therefore be employed as chemotherapeutic adjuvants within combinatorial regimens. This is the case of cardiac glycosides, like digoxin and digitoxin, and zoledronic acid. Here, we discuss recent developments on anticancer chemotherapy based on ICD inducers.
antigen-presenting cell; autophagy; damage-associated molecular pattern; dendritic cell; endoplasmic reticulum stress; type I interferon; AML, acute myeloid leukemia; ALL, acute lymphoblastic leukemia; CML, chronic myeloid leukemia; DAMP, damage-associated molecular pattern; EGFR, epidermal growth factor receptor; EOX, epirubicin plus oxaliplatin plus capecitabine; ER, endoplasmic reticulum; FDA, Food and Drug Administration; FOLFIRINOX, folinic acid plus 5-fluorouracil plus irinotecan plus oxaliplatin; FOLFOX, folinic acid plus 5-fluorouracil plus oxaliplatin; GEMOX, gemcitabine plus oxaliplatin; GM-CSF, granulocyte-macrophage colony-stimulating factor; HCC, hepatocellular carcinoma; ICD, immunogenic cell death; mAb, monoclonal antibody; MM, multiple myeloma; NHL, non-Hodgkin's lymphoma; NSCLC, non-small cell lung carcinoma; TACE, transcatheter arterial chemoembolization; XELOX, capecitabine plus oxaliplatin
The induction of autophagy usually requires the activation of PIK3C3/VPS34 (phosphatidylinositol 3-kinase, catalytic subunit type 3) within a multiprotein complex that contains BECN1 (Beclin 1, autophagy related). PIK3C3 catalyzes the conversion of phosphatidylinositol into phosphatidylinositol 3-phosphate (PtdIns3P). PtdIns3P associates with growing phagophores, which recruit components of the autophagic machinery, including the lipidated form of MAP1LC3B/LC3 (microtubule-associated protein 1 light chain 3 β). Depletion of BECN1, PIK3C3 or some of their interactors suppresses the formation of MAP1LC3B+ phagophores or autophagosomes elicited by most physiological stimuli, including saturated fatty acids. We observed that cis-unsaturated fatty acids stimulate the generation of cytosolic puncta containing lipidated MAP1LC3B as well as the autophagic turnover of long-lived proteins in the absence of PtdIns3P accumulation. In line with this notion, cis-unsaturated fatty acids require neither BECN1 nor PIK3C3 to stimulate the autophagic flux. Such a BECN1-independent autophagic response is phylogenetically conserved, manifesting in yeast, nematodes, mice and human cells. Importantly, MAP1LC3B+ puncta elicited by cis-unsaturated fatty acids colocalize with Golgi apparatus markers. Moreover, the structural and functional collapse of the Golgi apparatus induced by brefeldin A inhibits cis-unsaturated fatty acid-triggered autophagy. It is tempting to speculate that the well-established health-promoting effects of cis-unsaturated fatty acids are linked to their unusual capacity to stimulate noncanonical, BECN1-independent autophagic responses.
Caenorhabditis elegans; noncanonical autophagy; oleate; palmitate; Saccharomyces cerevisiae; stearate
An expanding panel of monoclonal antibodies (mAbs) that specifically target malignant cells or intercept trophic factors delivered by the tumor stroma is now available for cancer therapy. These mAbs can exert direct antiproliferative/cytotoxic effects as they inhibit pro-survival signal transduction cascades or activate lethal receptors at the plasma membrane of cancer cells, they can opsonize neoplastic cells to initiate a tumor-targeting immune response, or they can be harnessed to specifically deliver toxins or radionuclides to transformed cells. As an indication of the success of this immunotherapeutic paradigm, international regulatory agencies approve new tumor-targeting mAbs for use in cancer patients every year. Moreover, the list of indications for previously licensed molecules is frequently expanded to other neoplastic disorders as the results of large, randomized clinical trials become available. Here, we discuss recent advances in the preclinical and clinical development of tumor-targeting mAbs for oncological indications.
bevacizumab; cetuximab; obinutuzumab; ramucirumab; rituximab; trastuzumab; ADCC; antibody-dependent cell-mediated cytotoxicity; ALCL; anaplastic large-cell lymphoma; ALL; acute lymphocytic leukemia; AML; acute myeloid leukemia; BiTE; bispecific T-cell engager; CDC; complement-dependent cytotoxicity; CLL; chronic lymphocytic leukemia; CRC; colorectal carcinoma; DLBCL; diffuse large B-cell lymphoma; EGFR; epidermal growth factor receptor; F3; coagulation factor III; FDA; Food and Drug Administration; FOLFIRI; folinic acid; 5-fluorouracil; irinotecan; FOLFOX; folinic acid; 5-fluorouracil; oxaliplatin; HCC; hepatocellular carcinoma; HHV-8; human herpesvirus-8; IL; interleukin; mAb; monoclonal antibody; MMAE; monomethyl auristatin E; MCL; mantle cell lymphoma; MDS; myelodysplastic syndrome; NHL; non-Hodgkin's lymphoma; NSCLC; non-small cell lung carcinoma; ORR; overall response rate; OS; overall survival; PFS; progression-free survival; PI3K; phosphoinositide-3-kinase; RCC; renal cell carcinoma; SLL; small lymphocytic leukemia; TAA; tumor-associated antigen
Malignant cells express antigens that can be harnessed to elicit anticancer immune responses. One approach to achieve such goal consists in the administration of tumor-associated antigens (TAAs) or peptides thereof as recombinant proteins in the presence of adequate adjuvants. Throughout the past decade, peptide vaccines have been shown to mediate antineoplastic effects in various murine tumor models, especially when administered in the context of potent immunostimulatory regimens. In spite of multiple limitations, first of all the fact that anticancer vaccines are often employed as therapeutic (rather than prophylactic) agents, this immunotherapeutic paradigm has been intensively investigated in clinical scenarios, with promising results. Currently, both experimentalists and clinicians are focusing their efforts on the identification of so-called tumor rejection antigens, i.e., TAAs that can elicit an immune response leading to disease eradication, as well as to combinatorial immunostimulatory interventions with superior adjuvant activity in patients. Here, we summarize the latest advances in the development of peptide vaccines for cancer therapy.
carbohydrate-mimetic peptides; immune checkpoint blockers; immunostimulatory cytokines; survivin; synthetic long peptides; WT1; APC, antigen-presenting cell; CMP, carbohydrate-mimetic peptide; FDA, Food and Drug Administration; EGFR, epidermal growth factor receptor; GM-CSF, granulocyte macrophage colony stimulating factor; HPV, human papillomavirus; IDH1, isocitrate dehydrogenase 1 (NADP+), soluble; IDO1, indoleamine 2, 3-dioxygenase 1; IFNα, interferon α; IL-2, interleukin-2; MUC1, mucin 1; NSCLC, non-small cell lung carcinoma; PADRE, pan-DR binding peptide epitope; PPV, personalized peptide vaccination; SLP, synthetic long peptide; TAA, tumor-associated antigen; TERT, telomerase reverse transcriptase; TLR, Toll-like receptor; TRA, tumor rejection antigen
Changes in the interactions among the gut microbiota, intestinal epithelium, and host immune system are associated with many diseases, including cancer. We discuss how environmental factors influence this cross-talk during oncogenesis and tumor progression and how manipulations of the gut microbiota might improve the clinical activity of anticancer agents.
The use of patient-derived dendritic cells (DCs) as a means to elicit therapeutically relevant immune responses in cancer patients has been extensively investigated throughout the past decade. In this context, DCs are generally expanded, exposed to autologous tumor cell lysates or loaded with specific tumor-associated antigens (TAAs), and then reintroduced into patients, often in combination with one or more immunostimulatory agents. As an alternative, TAAs are targeted to DCs in vivo by means of monoclonal antibodies, carbohydrate moieties or viral vectors specific for DC receptors. All these approaches have been shown to (re)activate tumor-specific immune responses in mice, often mediating robust therapeutic effects. In 2010, the first DC-based preparation (sipuleucel-T, also known as Provenge®) has been approved by the US Food and Drug Administration (FDA) for use in humans. Reflecting the central position occupied by DCs in the regulation of immunological tolerance and adaptive immunity, the interest in harnessing them for the development of novel immunotherapeutic anticancer regimens remains high. Here, we summarize recent advances in the preclinical and clinical development of DC-based anticancer therapeutics.
antigen cross-presentation; autophagy; DC-based vaccination; immunogenic cell death; regulatory T cells; Toll-like receptor agonists; DC, dendritic cell; FDA, Food and Drug Administration; iDC, immature DC; IFN, interferon; mDC, mature DC; MRC1, mannose receptor, C type 1; MUC1, mucin 1; pDC, plasmacytoid DC; TAA, tumor-associated antigen; TLR, Toll-like receptor; Treg, regulatory T cell; WT1, Wilms tumor 1
CTLA4; ipilimumab; Keytruda™; nivolumab; PD-1; Yervoy™; CTLA4, cytotoxic T lymphocyte-associate protein 4; FDA, Food and Drug Administration; PDCD1/PD-1, programmed cell death 1
Indoleamine 2,3-dioxigenase 1 (IDO1) is the main enzyme that catalyzes the first, rate-limiting step of the so-called “kynurenine pathway”, i.e., the metabolic cascade that converts the essential amino acid L-tryptophan (Trp) into L-kynurenine (Kyn). IDO1, which is expressed constitutively by some tissues and in an inducible manner by specific subsets of antigen-presenting cells, has been shown to play a role in the establishment and maintenance of peripheral tolerance. At least in part, this reflects the capacity of IDO1 to restrict the microenvironmental availability of Trp and to favor the accumulation of Kyn and some of its derivatives. Also, several neoplastic lesions express IDO1, providing them with a means to evade anticancer immunosurveillance. This consideration has driven the development of several IDO1 inhibitors, some of which (including 1-methyltryptophan) have nowadays entered clinical evaluation. In animal tumor models, the inhibition of IDO1 by chemical or genetic interventions is indeed associated with the (re)activation of therapeutically relevant anticancer immune responses. This said, several immunotherapeutic regimens exert robust clinical activity in spite of their ability to promote the expression of IDO1. Moreover, 1-methyltryptophan has recently been shown to exert IDO1-independent immunostimulatory effects. Here, we summarize the preclinical and clinical studies testing the antineoplastic activity of IDO1-targeting interventions.
1-methyl-D-tryptophan; INCB024360; indoximod; interferon γ; NLG919; peptide-based anticancer vaccines; AHR, aryl hydrocarbon receptor; BIN1, bridging integrator 1; CTLA4, cytotoxic T lymphocyte associated protein 4; DC, dendritic cell; FDA, Food and Drug Administration; GCN2, general control non-derepressible 2; HCC, hepatocellular carcinoma; IDO, indoleamine 2,3-dioxigenase; IFNγ, interferon γ; Kyn, L-kynurenine; NK, natural killer; ODN, oligodeoxynucleotide; TDO2, tryptophan 2,3-dioxigenase; TLR, Toll-like receptor; Treg, regulatory T cell; Trp, L-tryptophan
Apoptotic cells have long been considered as intrinsically tolerogenic or unable to elicit immune responses specific for dead cell-associated antigens. However, multiple stimuli can trigger a functionally peculiar type of apoptotic demise that does not go unnoticed by the adaptive arm of the immune system, which we named “immunogenic cell death” (ICD). ICD is preceded or accompanied by the emission of a series of immunostimulatory damage-associated molecular patterns (DAMPs) in a precise spatiotemporal configuration. Several anticancer agents that have been successfully employed in the clinic for decades, including various chemotherapeutics and radiotherapy, can elicit ICD. Moreover, defects in the components that underlie the capacity of the immune system to perceive cell death as immunogenic negatively influence disease outcome among cancer patients treated with ICD inducers. Thus, ICD has profound clinical and therapeutic implications. Unfortunately, the gold-standard approach to detect ICD relies on vaccination experiments involving immunocompetent murine models and syngeneic cancer cells, an approach that is incompatible with large screening campaigns. Here, we outline strategies conceived to detect surrogate markers of ICD in vitro and to screen large chemical libraries for putative ICD inducers, based on a high-content, high-throughput platform that we recently developed. Such a platform allows for the detection of multiple DAMPs, like cell surface-exposed calreticulin, extracellular ATP and high mobility group box 1 (HMGB1), and/or the processes that underlie their emission, such as endoplasmic reticulum stress, autophagy and necrotic plasma membrane permeabilization. We surmise that this technology will facilitate the development of next-generation anticancer regimens, which kill malignant cells and simultaneously convert them into a cancer-specific therapeutic vaccine.
ATP release; autophagy; calreticulin; endoplasmic reticulum stress; HMGB1; immunotherapy; APC, antigen-presenting cell; ATF6, activating transcription factor 6; BAK1, BCL2-antagonist/killer 1; BAX, BCL2-associated X protein; BCL2, B-cell CLL/lymphoma 2 protein; CALR, calreticulin; CTL, cytotoxic T lymphocyte; Δψm, mitochondrial transmembrane potential; DAMP, damage-associated molecular pattern; DAPI, 4′,6-diamidino-2-phenylindole; DiOC6(3), 3,3′-dihexyloxacarbocyanine iodide; EIF2A, eukaryotic translation initiation factor 2A; ER, endoplasmic reticulum; FLT3LG, fms-related tyrosine kinase 3 ligand; G3BP1, GTPase activating protein (SH3 domain) binding protein 1; GFP, green fluorescent protein; H2B, histone 2B; HMGB1, high mobility group box 1; HSP, heat shock protein; HSV-1, herpes simplex virus type I; ICD, immunogenic cell death; IFN, interferon; IL, interleukin; MOMP, mitochondrial outer membrane permeabilization; PDIA3, protein disulfide isomerase family A; member 3; PI, propidium iodide; RFP, red fluorescent protein; TLR, Toll-like receptor; XBP1, X-box binding protein 1