Primary effusion lymphoma cell death induced by bortezomib and AG 490 activates dendritic cells through CD91

Immunogenic cell death inducers for cancer therapy: An emerging focus on natural products

BACKGROUND

Immunogenic cell death (ICD) is a specific form of regulated cell death induced by a variety of stressors. During ICD, the dying cancer cells release damage-associated molecular patterns (DAMPs), which promote dendritic cell maturation and tumor antigen presentation, subsequently triggering a T-cell-mediated anti-tumor immune response. In recent years, a growing number of studies have demonstrated the potential of natural products to induce ICD and enhance tumor cell immunogenicity. Moreover, there is an increasing interest in identifying new ICD inducers from natural products.

PURPOSE

This study aimed to emphasize the potential of natural products and their derivatives as ICD inducers to promote research on using natural products in cancer therapy and provide ideas for future novel immunotherapies based on ICD induction.

METHOD

This review included a thorough search of the PubMed, Web of Science, Scopus, and Google Scholar databases to identify natural products with ICD-inducing capabilities. A comprehensive search for clinical trials on natural ICD inducers was also conducted using ClinicalTrials.gov, as well as the approved patents using the Espacenet and CNKI Patent Database.

RESULTS

Natural compounds that induce ICD can be categorized into several groups, such as polyphenols, flavonoids, terpenoids, and alkaloids. Natural products can induce the release of DAMPs by triggering endoplasmic reticulum stress, activation of autophagy-related pathways, and reactive oxygen species generation, etc. Ultimately, they activate anti-tumor immune response and improve the efficacy of cancer treatments.

CONCLUSION

A growing number of ICD inducers from natural products with promising anti-cancer potential have been identified. The detailed information presented in this review will contribute to the further development of natural ICD inducers and cancer treatment strategies based on ICD-induced responses.

Microbes mediated immunogenic cell death in cancer immunotherapy

Immunogenic cell death (ICD) is one of the 12 distinct cell death forms, which can trigger immune system to fight against cancer cells. During ICD, a number of cellular changes occur that can stimulate an immune response, including the release of molecules called damage-associated molecular patterns (DAMPs), signaling to immune cells to recognize and attack cancer cells. By virtue of their pivotal role in immune surveillance, ICD-based drug development has been a new approach to explore novel therapeutic combinations and personalized strategies in cancer therapy. Several small molecules and microbes can induce ICD-relevant signals and cause cancer cell death. In this review, we highlighted the role of microbe-mediate ICD in cancer immunotherapy and described the mechanisms through which microbes might serve as ICD inducers in cancer treatment. We also discussed current attempts to combine microbes with chemotherapy regimens or immune checkpoint inhibitors (ICIs) in the treatment of cancer patients. We surmise that manipulation of microbes may guide personalized therapeutic interventions to facilitate anticancer immune response.

Immunogenic cell death-inducing metal complexes: From the benchtop to the clinic

The immune system presents a complex array of processes designed to maintain homeostasis in malignant cellular growth. Malignancy is the result of a breakdown in immune surveillance by cancer cells evading immune recognition. Significant efforts have been made in modulating immune checkpoint signaling cascades to bypass the resulting immune evasion and establish an anticancer effect. More recently, it was discovered that a form of regulated cell death can involve the stimulation of immune response as its downstream effect and subsequently re-establish immune surveillance. This mechanism, known as immunogenic cell death (ICD), is being exploited as a target to prevent tumor relapse and prevent cancer metastasis. It is now appreciated that metal-based compounds play a key role in ICD activation due to their unique biochemical properties and interactions within cancer cells. With fewer than 1% of known anticancer agents documented as ICD inducers, recent efforts have been made to identify novel entities capable of stimulating a more potent anticancer immune response. While the recent reviews by us or others focus primarily on either discussing the chemical library of ICD inducers or intricate detailing of biological pathways associated with ICD, this review aims to bridge these two topics as a concise summary. Furthermore, early clinical evidence and future directions of ICD are briefly summarized.

NRF2 and STAT3: friends or foes in carcinogenesis?

NRF2 is a transcription factor that plays a pivotal role in carcinogenesis, also through the interaction with several pro-survival pathways. NRF2 controls the transcription of detoxification enzymes and a variety of other molecules impinging in several key biological processes. This perspective will focus on the complex interplay of NRF2 with STAT3, another transcription factor often aberrantly activated in cancer and driving tumorigenesis as well as immune suppression. Both NRF2 and STAT3 can be regulated by ER stress/UPR activation and their cross-talk influences and is influenced by autophagy and cytokines, contributing to shape the microenvironment, and both control the execution of DDR, also by regulating the expression of HSPs. Given the importance of these transcription factors, more investigations aimed at better elucidating the outcome of their networking could help to discover new and more efficacious strategies to fight cancer.

JQ-1/bortezomib combination strongly impairs MM and PEL survival by inhibiting c-Myc and mTOR despite the activation of prosurvival mechanisms

Multiple myeloma (MM) and primary effusion lymphoma (PEL) are two aggressive hematologic cancers against which bortezomib and JQ-1, proteasome and bromodomain and extraterminal domain (BET) inhibitors, respectively, have been shown to have a certain success. However, the combination of both seems to be more promising than the single treatments against several cancers, including MM. Indeed, in the latter, proteasome inhibition upregulated nuclear respiratory factor 1 (NRF1), and such a prosurvival effect was counteracted by BET inhibitors. In the present study, we found that JQ-1/bortezomib induced a strong cytotoxic effect against PEL and discovered new insights into the cytotoxic mechanisms induced by such a drug combination in PEL and MM cells. In particular, a stronger c-Myc downregulation, leading to increased DNA damage, was observed in these cells after treatment with JQ-1/bortezomib than after treatment with the single drugs. Such an effect contributed to mechanistic target of rapamycin (mTOR)-phosphorylated eukaryotic translation initiation factor 4E-binding protein 1 (p-4EBP1) axis inhibition, also occurring through c-Myc downregulation. However, besides the prodeath effects, JQ-1/bortezomib activated unfolded protein response (UPR) and autophagy as prosurvival mechanisms. In conclusion, this study demonstrated that JQ-1/bortezomib combination could be a promising treatment for MM and PEL, unveiling new molecular mechanisms underlying its cytotoxic effect, and suggested that UPR and autophagy inhibition could be exploited to further potentiate the cytotoxicity of JQ-1/bortezomib.

Immunogenic cell death (ICD)-inducers in non-small-cell lung carcinoma (NSCLC): current knowledge and future perspective

The prevalence of non-small-cell lung cancer (NSCLC) is rising every year all around the world. The interaction between cancer cells and the tumor microenvironment (TME) is a crucial factor in determining the development of human neoplasms. Organellar and cellular stress are induced during immunogenic cell death (ICD), a particularly functional response pattern. ICD is a separate but poorly characterized entity caused by various cancer treatments. The induction of ICD has the potential to change TME and the recruitment of tumor-infiltrating lymphocytes (TILs), and the coupling of ICD-inducers and other therapeutic approaches can have a synergistic role in boosting anticancer impacts. The purpose of this study is to review the studies in the field of NSCLC using ICD-inducers as a treatment strategy or as a combination therapy. This review provide for researches a better view of what has been done so far and the challenges they face in the future.

Mechanisms of Sensitivity and Resistance of Primary Effusion Lymphoma to Dimethyl Fumarate (DMF)

PEL is a rare B cell lymphoma associated with KSHV that mainly arises in immune-deficient individuals. The search for new drugs to treat this cancer is still ongoing given its aggressiveness and the poor response to chemotherapies. In this study, we found that DMF, a drug known for its anti-inflammatory properties which is registered for the treatment of psoriasis and relapsing–remitting MS, could be a promising therapeutic strategy against PEL. Indeed, although some mechanisms of resistance were induced, DMF activated NRF2, reduced ROS and inhibited the phosphorylation of STAT3 and the release of the pro-inflammatory and immune suppressive cytokines IL-6 and IL-10, which are known to sustain PEL survival. Interestingly, we observed that DMF displayed a stronger cytotoxic effect against fresh PEL cells in comparison to PEL cell lines, due to the activation of ERK1/2 and autophagy in the latter cells. This finding further encourages the possibility of using DMF for the treatment of PEL.

Immunogenic Cell Death-Relevant Damage-Associated Molecular Patterns and Sensing Receptors in Triple-Negative Breast Cancer Molecular Subtypes and Implications for Immunotherapy

Objectives

Triple-negative breast cancer (TNBC) is defined as a highly aggressive type of breast cancer which lacks specific biomarkers and drug targets. Damage-associated molecular pattern (DAMP)-induced immunogenic cell death (ICD) may influence the outcome of immunotherapy for TNBC patients. This study aims to develop a DAMPs gene signature to classify TNBC patients and to further predict their prognosis and immunotherapy outcome.

Methods

We identified the DAMPs-associated subtypes of 330 TNBCs using K-means analysis. Differences in immune status, genomic alterations, and predicted immunotherapy outcome were compared among each subtype.

Results

A total of 330 TNBCs were divided into three subtypes according to DAMPs gene expression: the nuclear DAMPs subtype, featuring the upregulation of nuclear DAMPs; the inflammatory DAMPs subtype, characterized by the gene set enrichment of the adaptive immune system and cytokine signaling in the immune system; and the DAMPs-suppressed subtype, having the lowest level of ICD-associated DAMPs. Among them, the inflammatory subtype patients had the most favorable survival, while the DAMPs-suppressed subtype was associated with the worst prognosis. The DAMPs subtyping system was successfully validated in the TCGA cohort. Furthermore, we systemically revealed the genomic alterations among the three DAMPs subtypes. The inflammatory DAMPs subtype was predicted to have the highest response rate to immunotherapy, suggesting that the constructed DAMPs clustering had potential for immunotherapy efficacy prediction.

Conclusion

We established a novel ICD-associated DAMPs subtyping system in TNBC, and DAMPs expression might be a valuable biomarker for immunotherapy strategies. Our work could be helpful to the development of new immunomodulators and may contribute to the development of precision immunotherapy for TNBC.

The bovine dialysable leukocyte extract IMMUNEPOTENT CRP induces immunogenic cell death in breast cancer cells leading to long-term antitumour memory

Background

Cancer recurrence is a serious problem in breast cancer (BC) patients, and immunogenic cell death (ICD) has been proposed as a strategy to overcome this recurrence. IMMUNEPOTENT CRP (ICRP) acts as an immunomodulator and can be cytotoxic to cancer cells. Thus, we evaluated if ICRP induces ICD in BC cells.

Methods

Immunogenicity of ICRP-induced cell death was evaluated in vitro, analysing the principal biochemical characteristics of ICD in MCF-7, MDA-MB-231 and 4T1 cells. Ex vivo, we assessed the ability of killed cancer cells (KCC) obtained from ICRP-treated 4T1 cells (ICRP-KCC) to induce DC maturation, T-cell priming and T-cell-mediated cancer cytotoxicity. In vivo, we evaluated tumour establishment and antitumour immune memory after prophylactic ICRP-KCC vaccination in BALB/c mice.

Results

ICRP induced caspase-independent, ROS-dependent cell death, autophagosome formation, P-eIF2α, chaperone protein exposure, CD47 loss, ATP and HMBG1 release in BC cells. Additionally, ICRP-KCC promoted DC maturation, which triggered T-cell priming and cancer cytotoxicity. Prophylactic vaccination with ICRP-KCC prevented tumour establishment and induced long-term antitumour memory in BALB/c mice, involving DC maturation in lymph nodes, CD8+ T-cell augmentation in lymph nodes, peripheral blood and tumour site and ex vivo tumour-specific cytotoxicity by splenocytes.

Conclusions

ICRP induces ICD in BC cells, leading to long-term antitumour memory.

Gas plasma irradiation of breast cancers promotes immunogenicity, tumor reduction, and an abscopal effect in vivo

While many new and emerging therapeutic concepts have appeared throughout the last decades, cancer still is fatal in many patients. At the same time, the importance of immunology in oncotherapy is increasingly recognized, not only since the advent of checkpoint therapy. Among the many types of tumors, also breast cancer has an immunological dimension that might be exploited best by increasing the immunogenicity of the tumors in the microenvironment. To this end, we tested a novel therapeutic concept, gas plasma irradiation, for its ability to promote the immunogenicity and increase the toxicity of breast cancer cells in vitro and in vivo. Mechanistically, this emerging medical technology is employing a plethora of reactive oxygen species being deposited on the target cells and tissues. Using 2D cultures and 3D tumor spheroids, we found gas plasma-irradiation to drive apoptosis and immunogenic cancer cell death (ICD) in vitro, as evidenced by an increased expression of calreticulin, heat-shock proteins 70 and 90, and MHC-I. In 4T1 breast cancer-bearing mice, the gas plasma irradiation markedly decreased tumor burden and increased survival. Interestingly, non-treated tumors injected in the opposite flank of mice exposed to our novel treatment also exhibited reduced growth, arguing for an abscopal effect. This was concomitant with an increase of apoptosis and tumor-infiltrating CD4⁺ and CD8⁺ T-cells as well as dendritic cells in the tissues. In summary, we found gas plasma-irradiated murine breast cancers to induce toxicity and augmented immunogenicity, leading to reduced tumor growth at a site remote to the treatment area.

Targeting immunogenic cell death in cancer

Immunogenic cell death (ICD) is a type of cancer cell death triggered by certain chemotherapeutic drugs, oncolytic viruses, physicochemical therapies, photodynamic therapy, and radiotherapy. It involves the activation of the immune system against cancer in immunocompetent hosts. ICD comprises the release of damage-associated molecular patterns (DAMPs) from dying tumor cells that result in the activation of tumor-specific immune responses, thus eliciting long-term efficacy of anticancer drugs by combining direct cancer cell killing and antitumor immunity. Remarkably, subcutaneous injection of dying tumor cells undergoing ICD has been shown to provoke anticancer vaccine effects in vivo. DAMPs include the cell surface exposure of calreticulin (CRT) and heat-shock proteins (HSP70 and HSP90), extracellular release of adenosine triphosphate (ATP), high-mobility group box-1 (HMGB1), type I IFNs and members of the IL-1 cytokine family. In this review, we discuss the cell death modalities connected to ICD, the DAMPs exposed during ICD, and the mechanism by which they activate the immune system. Finally, we discuss the therapeutic potential and challenges of harnessing ICD in cancer immunotherapy.

Immunostimulation with chemotherapy in the era of immune checkpoint inhibitors

Conventional chemotherapeutics have been developed into clinically useful agents based on their ability to preferentially kill malignant cells, generally owing to their elevated proliferation rate. Nonetheless, the clinical activity of various chemotherapies is now known to involve the stimulation of anticancer immunity either by initiating the release of immunostimulatory molecules from dying cancer cells or by mediating off-target effects on immune cell populations. Understanding the precise immunological mechanisms that underlie the efficacy of chemotherapy has the potential not only to enable the identification of superior biomarkers of response but also to accelerate the development of synergistic combination regimens that enhance the clinical effectiveness of immune checkpoint inhibitors (ICIs) relative to their effectiveness as monotherapies. Indeed, accumulating evidence supports the clinical value of combining appropriately dosed chemotherapies with ICIs. In this Review, we discuss preclinical and clinical data on the immunostimulatory effects of conventional chemotherapeutics in the context of ICI-based immunotherapy.

STAT3 and mutp53 Engage a Positive Feedback Loop Involving HSP90 and the Mevalonate Pathway

Oncosuppressor TP53 and oncogene STAT3 have been shown to engage an interplay in which they negatively influence each other. Conversely, mutant (mut) p53 may sustain STAT3 phosphorylation by displacing SH2 phosphatase while whether STAT3 could influence mutp53 has not been clarified yet. In this study we found that pharmacologic or genetic inhibition of STAT3 in both glioblastoma and pancreatic cancer cells, carrying mutp53 protein, reduced mutp53 expression level by down-regulating chaperone HSP90 as well as molecules belonging to the mevalonate pathway. On the other hand, HSP90 and the mevalonate pathway were involved in sustaining STAT3 phosphorylation mediated by mutp53. In conclusion, this study unveils for the first time that mutp53 can establish with STAT3, similarly to what observed with other oncogenic pathways, a criminal alliance with a crucial role in promoting cancerogenesis.

Trial watch: chemotherapy-induced immunogenic cell death in immuno-oncology

The term ‘immunogenic cell death’ (ICD) denotes an immunologically unique type of regulated cell death that enables, rather than suppresses, T cell-driven immune responses that are specific for antigens derived from the dying cells. The ability of ICD to elicit adaptive immunity heavily relies on the immunogenicity of dying cells, implying that such cells must encode and present antigens not covered by central tolerance (antigenicity), and deliver immunostimulatory molecules such as damage-associated molecular patterns and cytokines (adjuvanticity). Moreover, the host immune system must be equipped to detect the antigenicity and adjuvanticity of dying cells. As cancer (but not normal) cells express several antigens not covered by central tolerance, they can be driven into ICD by some therapeutic agents, including (but not limited to) chemotherapeutics of the anthracycline family, oxaliplatin and bortezomib, as well as radiation therapy. In this Trial Watch, we describe current trends in the preclinical and clinical development of ICD-eliciting chemotherapy as partner for immunotherapy, with a focus on trials assessing efficacy in the context of immunomonitoring.

Immunogenic Cell Death: An opportunity for Clinical Oncology?

Apoptosis was initially seen as a kind of silent cell death with non-induction of the immune response 1. However, in the recent past, it has been seen that death induced by either infections or actions of certain agents can elicit a specific immune response, namely immunogenic cell death (ICD)2. This ICD activates the immune system against antigens associated with deceased cells with the concomitant exposure and releasing of the so-called damage-associated molecular patterns (DAMPs) by dying cells3. Four principal DAMPs related to ICD have been identified (but not limited to): the endoplasmic reticulum (ER) chaperone calreticulin (CRT), heat shock proteins (HSPs), adenosine triphosphate (ATP) and high mobility group box-1 (HMGB-1)4.

Intrinsic cancer vaccination

Immunotherapy is revolutionizing the treatment of cancer, and the current immunotherapeutics have remarkably improved the outcomes for some cancer patients. However, we still need answers for patients with immunologically cold tumors that do not benefit from the current immunotherapy treatments. Here, we suggest a novel strategy that is based on using a very old and sophisticated system for cancer immunotherapy, namely "intrinsic cancer vaccination", which seeks to awaken our own immune system to activate tumor-specific T cells. To do this, we must take advantage of the genetic instability of cancer cells and the expression of cancer cell neoantigens to trigger immunity against cancer cells. It will be necessary to not only enhance the phagocytosis of cancer cells by antigen presenting cells but also induce immunogenic cancer cell death and the subsequent immunogenic clearance, cross-priming and generation of tumor-specific T cells. This strategy will allow us to avoid using known tumor-specific antigens, ex vivo manipulation or adoptive cell therapy; rather, we will efficiently present cancer cell neoantigens to our immune system and propagate the cancer-immunity cycle. This strategy simply follows the natural cycle of cancer-immunity from its very first step, and therefore could be combined with any other treatment modality to yield enhanced efficacy.

Autophagy manipulation as a strategy for efficient anticancer therapies: possible consequences

Autophagy is a catabolic process whose activation may help cancer cells to adapt to cellular stress although, in some instances, it can induce cell death. Autophagy stimulation or inhibition has been considered an opportunity to treat cancer, especially in combination with anticancer therapies, although autophagy manipulation may be viewed as controversial. Thus, whether to induce or to inhibit autophagy may be the best option in the different cancer patients is still matter of debate. Her we will recapitulate the possible advantages or disadvantages of manipulating autophagy in cancer, not only with the aim to obtain cancer cell death and disable oncogenes, but also to evaluate its interplay with the immune response which is fundamental for the success of anticancer therapies.

Origin and Consequences of Necroinflammation

When cells undergo necrotic cell death in either physiological or pathophysiological settings in vivo, they release highly immunogenic intracellular molecules and organelles into the interstitium and thereby represent the strongest known trigger of the immune system. With our increasing understanding of necrosis as a regulated and genetically determined process (RN, regulated necrosis), necrosis and necroinflammation can be pharmacologically prevented. This review discusses our current knowledge about signaling pathways of necrotic cell death as the origin of necroinflammation. Multiple pathways of RN such as necroptosis, ferroptosis, and pyroptosis have been evolutionary conserved most likely because of their differences in immunogenicity. As the consequence of necrosis, however, all necrotic cells release damage associated molecular patterns (DAMPs) that have been extensively investigated over the last two decades. Analysis of necroinflammation allows characterizing specific signatures for each particular pathway of cell death. While all RN-pathways share the release of DAMPs in general, most of them actively regulate the immune system by the additional expression and/or maturation of either pro- or anti-inflammatory cytokines/chemokines. In addition, DAMPs have been demonstrated to modulate the process of regeneration. For the purpose of better understanding of necroinflammation, we introduce a novel classification of DAMPs in this review to help detect the relative contribution of each RN-pathway to certain physiological and pathophysiological conditions.

Immunogenic cell death in anticancer chemotherapy and its impact on clinical studies

The traditional view holds that apoptosis is non-immunogenic and does not induce an inflammatory response. However, recent studies have suggested that certain chemotherapeutic drugs that induce tumor cell apoptosis can induce immunogenic cell death (ICD) in cancer cells. This process is characterized by not only up-regulation of a series of signaling molecules in cancer cells, including expose of calreticulin (CRT), secretion of adenosine triphosphate (ATP) and release of high mobility group box 1 (HMGB1). In this review, we summarize recent progress in identifying and classifying ICD inducers; concepts and molecular mechanisms of ICD; and the impact and potential applications of ICD in clinical studies. We also discuss the contributions of ICD inducers in combination with other anticancer drugs in clinical applications.

AG490 reverses phenotypic alteration of dendritic cells by bladder cancer cells

Past studies have confirmed that tumors can impair the function of dendritic cells (DCs) and promote tumor evasion. AG490, a Janus kinase 2/signal transducer and activator of transcription 3 inhibitor, has been shown to induce maturation of DCs and inhibit the growth of tumor cells. In the present study, DCs were generated from healthy human peripheral blood mononuclear cells. On day 5 of culture, the DCs were co-cultured with human bladder cancer pumc-91 cells for 24 h, and then purified using magnetic beads. The maturation of the DCs was induced by lipopolysaccharide. Subsequent to co-culture with pumc-91 cells, the expression of human leukocyte antigen-antigen D related (HLA-DR), cluster of differentiation (CD)86 and CD80 was found to be reduced in the DCs, accompanied by increased production of interleukin (IL)-10, but decreased production of IL-12p70. Furthermore, the DCs co-cultured with pumc-91 inhibited the proliferation of allogeneic T cells. Finally, AG490 restored the expression of HLA-DR, CD86 and CD80. These data identified that bladder cancer cells could inhibit the antigen-presenting function of the DCs and induce anergy in T cells. AG490 may partly reverse this inhibitory effect of bladder cancer cells on DCs, activate immunogenicity and induce the antitumor immunity response of DCs.

The inducers of immunogenic cell death for tumor immunotherapy

Immunotherapy is a promising treatment modality that acts by selectively harnessing the host immune defenses against cancer. An effective immune response is often needed to eliminate tumors following treatment which can trigger the immunogenicity of dying tumor cells. Some treatment modalities (such as photodynamic therapy, high hydrostatic pressure or radiotherapy) and agents (some chemotherapeutic agents, oncolytic viruses) have been used to endow tumor cells with immunogenicity and/or increase their immunogenicity. These treatments and agents can boost the antitumor capacity by inducing immune responses against tumor neoantigens. Immunogenic cell death is a manner of cell death that can induce the emission of immunogenic damage-associated molecular patterns (DAMPs). DAMPs are sufficient for immunocompetent hosts to trigger the immune system. This review focuses on the latest developments in the treatment modalities and agents that can induce and/or enhance the immunogenicity of cancer cells.

Immunosuppressive effect of bladder cancer on function of dendritic cells involving of Jak2/STAT3 pathway

Function of dendritic cells (DCs) is impaired by some cancer cells. However, the effect of bladder cancer cell (BCC) on phenotype and function of DCs remains unclear. In this study, healthy human peripheral blood mononuclear cells (PBMCs) derived DCs were co-cultured with BCC pumc-91 and adriamycin-resistant pumc-91/ADM. The expression of DC markers and costimulatory molecules decreased after co-culture. Co-cultured DCs rapidly underwent apoptosis, and had a declined capability to produce IL-8 and RANTES. Furthermore, co-cultured DCs showed impaired allogeneic T cell proliferation and T cell-derived cytokine secretion. Finally, AG490, a Jak2/STAT3 inhibitor, restored the expression of DC markers and costimulatory molecules. Of note, compared with control DCs, DCs co-cultured with pumc-91 produced more IP-10; DCs co-cultured with pumc-91/ADM secreted more MIG. Taken together, these results suggest BCC may inhibit maturation and function of DCs involving of Jak2/STAT3 pathway, and there may be different mechanisms by which adriamycin-resistant BCC restrains DC function in antitumor immune response.

Apigenin, by activating p53 and inhibiting STAT3, modulates the balance between pro-apoptotic and pro-survival pathways to induce PEL cell death

Background

Apigenin is a flavonoid widely distributed in plant kingdom that exerts cytotoxic effects against a variety of solid and haematological cancers. In this study, we investigated the effect of apigenin against primary effusion lymphoma (PEL), a KSHV-associated B cell lymphoma characterized by a very aggressive behavior, displaying constitutive activation of STAT3 as well as of other oncogenic pathways and harboring wtp53.

Methods

Cell death was assessed by trypan blue exclusion assay, FACS analysis as well as by biochemical studies. The latter were also utilized to detect the occurrence of autophagy and the molecular mechanisms leading to the activation of both processes by apigenin. FACS analysis was used to measure the intracellular ROS utilizing DCFDA.

Results

We show that apigenin induced PEL cell death and autophagy along with reduction of intracellular ROS. Mechanistically, apigenin activated p53 that induced catalase, a ROS scavenger enzyme, and inhibited STAT3, the most important pro-survival pathway in PEL, as assessed by p53 silencing. On the other hand, STAT3 inhibition by apigenin resulted in p53 activation, since STAT3 negatively influences p53 activity, highlighting a regulatory loop between these two pathways that modulates PEL cell death/survival.

Conclusion

The findings of this study demonstrate that apigenin may modulate pro-apoptotic and pro-survival pathways representing a valid therapeutic strategy against PEL.

Relevance of the chaperone-like protein calreticulin for the biological behavior and clinical outcome of cancer

The death of cancer cells can be categorized as either immunogenic (ICD) or nonimmunogenic, depending on the initiating stimulus. The immunogenic processes of immunogenic cell death are mainly mediated by damage-associated molecular patterns (DAMPs), which include surface exposure of calreticulin (CRT), secretion of adenosine triphosphate (ATP), release of non-histone chromatin protein high-mobility group box 1 (HMGB1) and the production of type I interferons (IFNs). DAMPs are recognized by various receptors that are expressed by antigen-presenting cells (APCs) and potentiate the presentation of tumor antigens to T lymphocytes. Accumulating evidence indicates that CRT exposure constitutes one of the major checkpoints, that determines the immunogenicity of cell death both in vitro and in vivo in mouse models. Moreover, recent studies have identified CRT expression on tumor cells not only as a marker of ICD and active anti-tumor immune reactions but also as a major predictor of a better prognosis in various cancers. Here, we discuss the recent information on the CRT capacity to activate anticancer immune response as well as its prognostic and predictive role for the clinical outcome in cancer patients.

Trial watch: Immunogenic cell death induction by anticancer chemotherapeutics

The expression "immunogenic cell death" (ICD) refers to a functionally unique form of cell death that facilitates (instead of suppressing) a T cell-dependent immune response specific for dead cell-derived antigens. ICD critically relies on the activation of adaptive responses in dying cells, culminating with the exposure or secretion of immunostimulatory molecules commonly referred to as "damage-associated molecular patterns". Only a few agents can elicit bona fide ICD, including some clinically established chemotherapeutics such as doxorubicin, epirubicin, idarubicin, mitoxantrone, bleomycin, bortezomib, cyclophosphamide and oxaliplatin. In this Trial Watch, we discuss recent progress on the development of ICD-inducing chemotherapeutic regimens, focusing on studies that evaluate clinical efficacy in conjunction with immunological biomarkers.

Metformin triggers apoptosis in PEL cells and alters bortezomib-induced Unfolded Protein Response increasing its cytotoxicity and inhibiting KSHV lytic cycle activation

Metformin, the most used drug for the treatment of diabetes type 2 patients, has been shown to have anti-cancer properties. In this study, we found that metformin induced apoptosis in Primary Effusion Lymphoma (PEL) cells, an aggressive B cell lymphoma associated with KSHV against which the conventional therapies usually fail. The cytotoxic effect of metformin correlated with intracellular reactive oxygen species reduction, activation of AMPK, the inhibition of pro-survival pathways such as mTOR and STAT3 and the down-regulation of v-FLIP, a latent viral antigen that also plays a pivotal role in PEL cell survival. Interestingly, we found that metformin could be used to potentiate the bortezomib-mediated cytotoxicity against PEL cells and to inhibit the activation of KSHV lytic cycle, a side effect of this treatment that resulted in a block of autophagy in these cells. Mechanistically, metformin altered UPR activated by bortezomib, leading to a reduced expression of BiP, up-regulation of CHOP and down-regulation of Bcl-2. In summary, this study suggests that metformin could represent a promising strategy for the treatment of PEL alone or in combination with bortezomib. In the latter case, besides exerting a stronger cytotoxic effect, it might be used to restrain bortezomib-induced viral replication that is involved in the maintenance and progression of KSHV-associated malignancies.

Autophagy, autophagy-associated adaptive immune responses and its role in hematologic malignancies

Autophagy is a tightly regulated catabolic process that leads to the degradation of cytoplasmatic components such as aggregated/misfolded proteins and organelles through the lysosomal machinery. Recent studies suggest that autophagy plays such a role in the context of the anti-tumor immune response, make it an attractive target for cancer immunotherapy. Defective autophagy in hematopoietic stem cells may contribute to the development of hematologic malignancies, including leukemia, myelodysplastic syndrome, and lymphoproliferative disorder. In blood cancer cells, autophagy can either result in chemoresistance or induce autophagic cell death that may act as immunogenic. Based on the successful experimental findings in vitro and in vivo, clinical trials of autophagy inhibitor such as hydroxychloroquine in combination with chemotherapy in patients with blood cancers are currently underway. However, autophagy inactivation might impair autophagy-triggered anticancer immunity, whereas induction of autophagy might become an effective immunotherapy. These aspects are discussed in this review together with a brief introduction to the autophagic molecular machinery and its roles in hematologic malignancies.

Chloroquine supplementation increases the cytotoxic effect of curcumin against Her2/neu overexpressing breast cancer cells in vitro and in vivo in nude mice while counteracts it in immune competent mice

Autophagy is usually a pro-survival mechanism in cancer cells, especially in the course of chemotherapy, thus autophagy inhibition may enhance the chemotherapy-mediated anti-cancer effect. However, since autophagy is strongly involved in the immunogenicity of cell death by promoting ATP release, its inhibition may reduce the immune response against tumors, negatively influencing the overall outcome of chemotherapy. In this study, we evaluated the in vitro and in vivo anti-cancer effect of curcumin (CUR) against Her2/neu overexpressing breast cancer cells (TUBO) in the presence or in the absence of the autophagy inhibitor chloroquine (CQ). We found that TUBO cell death induced by CUR was increased in vitro by CQ and slightly in vivo in nude mice. Conversely, CQ counteracted the Cur cytotoxic effect in immune competent mice, as demonstrated by the lack of in vivo tumor regression and the reduction of overall mice survival as compared with CUR-treated mice. Immunohistochemistry analysis revealed the presence of a remarkable FoxP3 T cell infiltrate within the tumors in CUR/CQ treated mice and a reduction of T cytotoxic cells, as compared with single CUR treatment. These findings suggest that autophagy is important to elicit anti-tumor immune response and that autophagy inhibition by CQ reduces such response also by recruiting T regulatory (Treg) cells in the tumor microenvironment that may be pro-tumorigenic and might counteract CUR-mediated anti-cancer effects.

Immunogenic Apoptotic Cell Death and Anticancer Immunity

For many years it has been thought that apoptotic cells rapidly cleared by phagocytic cells do not trigger an immune response but rather have anti-inflammatory properties. However, accumulating experimental data indicate that certain anticancer therapies can induce an immunogenic form of apoptosis associated with the emission of damage-associated molecular patterns (DAMPs), which function as adjuvants to activate host antitumor immune responses. In this review, we will first discuss recent advances and the significance of danger signaling pathways involved in the emission of DAMPs, including calreticulin, ATP, and HMGB1. We will also emphasize that switching on a particular signaling pathway depends on the immunogenic cell death stimulus. Further, we address the role of ER stress in danger signaling and the classification of immunogenic cell death inducers in relation to how ER stress is triggered. In the final part, we discuss the role of radiotherapy-induced immunogenic apoptosis and the relationship of its immunogenicity to the fraction dose and concomitant chemotherapy.

Histone deacetylase inhibitors VPA and TSA induce apoptosis and autophagy in pancreatic cancer cells

PURPOSE

Histone deacetylase inhibitors (HDACi) are anti-neoplastic agents that are known to affect the growth of different cancer types, but their underlying mechanisms are still incompletely understood. Here, we compared the effects of two HDACi, i.e., Trichostatin A (TSA) and Valproic Acid (VPA), on the induction of cell death and autophagy in pancreatic cancer-derived cells that exhibit a high metastatic capacity and carry KRAS/p53 double mutations.

METHODS

Cell viability and proliferation tests were carried out using Trypan blue dye exclusion, MTT and BrdU assays. FACS analyses were carried out to assess cell cycle progression, apoptosis, reactive oxygen species (ROS) production and mitochondrial depolarization, while Western blot and immunoprecipitation analyses were employed to detect proteins involved in apoptosis and autophagy.

RESULTS

We found that both VPA and TSA can induce apoptosis in Panc1 and PaCa44 pancreatic cancer-derived cells by triggering mitochondrial membrane depolarization, Cytochrome c release and Caspase 3 activation, although VPA was more effective than TSA, especially in Panc1 cells. As underlying molecular events, we found that ERK1/2 was de-phosphorylated and that the c-Myc and mutant p53 protein levels were reduced after VPA and, to a lesser extent, after TSA treatment. Up-regulation of p21 and Puma was also observed, concomitantly with mutant p53 degradation. In addition, we found that in both cell lines VPA increased the pro-apoptotic Bim level, reduced the anti-apoptotic Mcl-1 level and increased ROS production and autophagy, while TSA was able to induce these effects only in PaCA44 cells.

CONCLUSIONS

From our results we conclude that both VPA and TSA can induce pancreatic cancer cell apoptosis and autophagy. VPA appears have a stronger and broader cytotoxic effect than TSA and, thus, may represent a better choice for anti-pancreatic cancer therapy.

Quercetin induces apoptosis and autophagy in primary effusion lymphoma cells by inhibiting PI3K/AKT/mTOR and STAT3 signaling pathways

Quercetin, a bioflavonoid contained in several vegetables daily consumed, has been studied for long time for its antiinflammatory and anticancer properties. Quercetin interacts with multiple cancer-related pathways such as PI3K/AKT, Wnt/β-catenin and STAT3. These pathways are hyperactivated in primary effusion lymphoma (PEL), an aggressive B cell lymphoma whose pathogenesis is strictly linked to the oncogenic virus Kaposis' Sarcoma-associated Herpesvirus (KSHV). In this study, we found that quercetin inhibited PI3K/AKT/mTOR and STAT3 pathways in PEL cells, and as a consequence, it down-regulated the expression of the prosurvival cellular proteins such as c-FLIP, cyclin D1 and cMyc. It also reduced the release of IL-6 and IL-10 cytokines, leading to PEL cell death. Moreover, quercetin induced a prosurvival autophagy in these cells and increased the cytotoxic effect of bortezomib, a proteasomal inhibitor, against them. Interestingly, quercetin decreased also the expression of latent and lytic KSHV proteins involved in PEL tumorigenesis and up-regulated the surface expression of HLA-DR and calreticulin, rendering the dying cells more likely detectable by the immune system. The results obtained in this study indicate that quercetin, which does not exert any cytotoxicity against normal B cells, may represent a good candidate for the treatment of this aggressive B cell lymphoma, especially in combination with autophagy inhibitors or with bortezomib.

Immunogenic and Non-immunogenic Cell Death in the Tumor Microenvironment

The host immune system is continuously exposed to dying cells and has evolved to distinguish between cell death events signaling potential threats and physiological apoptosis that should be tolerated. Tumors can use this distinction to their advantage, promoting apoptotic death of cancer cells to induce tolerance and evasion of immunosurveillance. On the other hand, stimuli that cause immunogenic death of cancer cells can induce an effective anti-tumor immune response. In this chapter we discuss different forms of cell death in the tumor microenvironment, and how these interact with host immune cells to impact tumor progression and cancer therapy. We focus on how cancer cells hijack aspects of cell death to promote tumor survival, and how anti-cancer treatments that activate immunogenic death modalities give strong and durable clinical efficacy.

Transplantation and Damage-Associated Molecular Patterns (DAMPs)

Upon solid organ transplantation and during cancer immunotherapy, cellular stress responses result in the release of damage-associated molecular patterns (DAMPs). The various cellular stresses have been characterized in detail over the last decades, but a unifying classification based on clinically important aspects is lacking. Here, we provide an in-depth review of the most recent literature along with a unifying concept of the danger/injury model, suggest a classification of DAMPs, and review the recently elaborated mechanisms that result in the emission of such factors. We further point out the differences in DAMP responses including the release following a heat shock pattern, endoplasmic reticulum stress, DNA damage-mediated DAMP release, and discuss the diverse pathways of regulated necrosis in this respect. The understanding of various forms of DAMPs and the consequences of their different release patterns are prerequisite to associate serum markers of cellular stresses with clinical outcomes.

DAMP-Induced Allograft and Tumor Rejection: The Circle Is Closing

The pathophysiological importance of the immunogenicity of damage-associated molecular patterns (DAMPs) has been pinpointed by their identification as triggers of allograft rejection following release from dying cells, such as after ischemia-reperfusion injury. In cancers, however, this strong trigger of a specific immune response gives rise to the success of cancer immunotherapy. Here, we review the recently literature on the pathophysiological importance of DAMP release and discuss the implications of these processes for allograft rejection and cancer immunotherapy, revealing a striking mechanistic overlap. We conclude that these two fields share a common mechanistic basis of regulated necrosis and inflammation, the molecular characterization of which may be helpful for both oncologists and the transplant community.

Rationale for the Combination of Dendritic Cell-Based Vaccination Approaches With Chemotherapy Agents

Owing to their central role in the initiation and regulation of antitumor immunity, dendritic cells (DCs) have been widely tested for use in cancer immunotherapy. Despite several encouraging clinical applications, existing DC-based immunotherapy efforts have yielded inconsistent results. Recent work has identified strategies that may allow for more potent DC-based vaccines, such as the combination with antitumor agents that have the potential to synergistically enhance DC functions. Selected cytotoxic agents may stimulate DCs either by directly promoting their maturation or through the induction of immunogenic tumor cell death. Moreover, they may support DC-induced adaptive immune responses by disrupting tumor-induced immunosuppressive mechanisms via selective depletion or inhibition of regulatory subsets, such as myeloid-derived suppressor cells and/or regulatory T cells (Tregs). Here, we summarize our current knowledge on the capacity of anticancer chemotherapeutics to modulate DC phenotype and functions and the results of ongoing clinical trials evaluating the use of DC-based immunotherapy in combination with chemotherapy in cancer patients.

The Impact of Chemotherapy, Radiation and Epigenetic Modifiers in Cancer Cell Expression of Immune Inhibitory and Stimulatory Molecules and Anti-Tumor Efficacy

Genomic destabilizers, such as radiation and chemotherapy, and epigenetic modifiers are used for the treatment of cancer due to their apoptotic effects on the aberrant cells. However, these therapies may also induce widespread changes within the immune system and cancer cells, which may enable tumors to avoid immune surveillance and escape from host anti-tumor immunity. Genomic destabilizers can induce immunogenic death of tumor cells, but also induce upregulation of immune inhibitory ligands on drug-resistant cells, resulting in tumor progression. While administration of immunomodulatory antibodies that block the interactions between inhibitory receptors on immune cells and their ligands on tumor cells can mediate cancer regression in a subset of treated patients, it is crucial to understand how genomic destabilizers alter the immune system and malignant cells, including which inhibitory molecules, receptors and/or ligands are upregulated in response to genotoxic stress. Knowledge gained in this area will aid in the rational design of trials that combine genomic destabilizers, epigenetic modifiers and immunotherapeutic agents that may be synergized to improve clinical responses and prevent tumor escape from the immune system. Our review article describes the impact genomic destabilizers, such as radiation and chemotherapy, and epigenetic modifiers have on anti-tumor immunity and the tumor microenvironment. Although genomic destabilizers cause DNA damage on cancer cells, these therapies can also have diverse effects on the immune system, promote immunogenic cell death or survival and alter the cancer cell expression of immune inhibitor molecules.

Immunogenic cell death in cancer and infectious disease

Immunogenicity depends on two key factors: antigenicity and adjuvanticity. The presence of exogenous or mutated antigens explains why infected cells and malignant cells can initiate an adaptive immune response provided that the cells also emit adjuvant signals as a consequence of cellular stress and death. Several infectious pathogens have devised strategies to control cell death and limit the emission of danger signals from dying cells, thereby avoiding immune recognition. Similarly, cancer cells often escape immunosurveillance owing to defects in the molecular machinery that underlies the release of endogenous adjuvants. Here, we review current knowledge on the mechanisms that underlie the activation of immune responses against dying cells and their pathophysiological relevance.

Inhibition of autophagy with chloroquine potentiates carfilzomib-induced apoptosis in myeloma cells in vitro and in vivo

The proteasome inhibitor bortezomib is now the cornerstone of combination therapy of multiple myeloma (MM). Carfilzomib, a second-generation inhibitor, has shown a substantial benefit vs bortezomib in combination regimes. Here we have analyzed in detail the mechanism of cell death induced by carfilzomib and its crosstalk with autophagy and applied the results to the in vivo treatment of MM in a mouse model. Carfilzomib induced apoptosis essentially by the intrinsic pathway, through the up-regulation of Puma and Noxa proteins followed by the interaction of Puma, Noxa and Bim with Bax and of Noxa with Bak. Carfilzomib also produces an increase in the formation of autophagosomes but, as apoptosis progresses, autophagy is disrupted, probably owing to Beclin 1 and p62 inactivation. Cotreatment with chloroquine, which blocks autophagy, strongly potentiated apoptosis in vitro and in vivo. Accordingly, combination therapy with carfilzomib plus chloroquine was highly effective in the treatment of MM in a mouse xenograft model. Chloroquine also enhanced carfilzomib-induced calreticulin exposure in MM cells undergoing apoptosis, increasing the immunogenic ability of carfilzomib. These results support design of trials combining carfilzomib with chloroquine to improve MM therapy.

Capsaicin triggers immunogenic PEL cell death, stimulates DCs and reverts PEL-induced immune suppression

Capsaicin, the pungent alkaloid of red pepper has been extensively studied for its many properties, especially the anti-inflammatory and anti-oxidant ones. It binds to vanilloid receptor 1, although it has been reported to be able to mediate some effects independently of its receptor. Another important property of Capsaicin is the anticancer activity against highly malignant tumors, alone or in combination with other chemotherapeutic agents. In this study, we found that Capsaicin induced an apoptotic cell death in PEL cells correlated with the inhibition of STAT3. STAT3 pathway, constitutively activated in PEL cells, is essential for their survival. By STAT3 de-phosphorylation, Capsaicin reduced the Mcl-1 expression level and this could represent one of the underlying mechanisms leading to the Capsaicin-mediated cell death and autophagy induction. Next, by pharmacological or genetic inhibition, we found that autophagy played a pro-survival role, suggesting that its inhibition could be exploited to increase the Capsaicin cytotoxic effect against PEL cells. Finally, we show that Capsaicin induced DAMP exposure, as for an immunogenic cell death, directly promoted DC activation and, more importantly, that it counteracted the immune-suppression, in terms of DC differentiation, mediated by the PEL released factors.

A transplant “immunome” screening platform defines a targetable epitope fingerprint of multiple myeloma

The myeloma transplant B-cell immunome is predictive for response to treatment. It may be exploited by immunosequencing and library technology as a source for unique target structures and antibodies for immunotherapy.

High glucose and hyperglycemic sera from type 2 diabetic patients impair DC differentiation by inducing ROS and activating Wnt/β-catenin and p38 MAPK

Type 2 is the type of diabetes with higher prevalence in contemporary time, representing about 90% of the global cases of diabetes. In the course of diabetes, several complications can occur, mostly due to hyperglycemia and increased reactive oxygen species (ROS) production. One of them is represented by an increased susceptibility to microbial infections and by a reduced capacity to clear them. Therefore, knowing the impact of hyperglycemia on immune system functionality is of utmost importance for the management of the disease. In this study, we show that medium containing high glucose reduced the in-vitro differentiation of monocytes into functional DCs and their activation mediated by PAMPs or DAMPs. Most importantly, the same effects were mediated by the hyperglycemic sera derived by type 2 diabetic patients, mimicking a more physiologic condition. DC dysfunction caused by hyperglycemia may be involved in the inefficient control of infections observed in diabetic patients, given the pivotal role of these cells in both the innate and adaptive immune response. Searching for the molecular mechanisms underlying DC dysfunction, we found that canonical Wnt/β-catenin and p38 MAPK pathways were activated in the DCs differentiated either in the presence of high glucose or of hyper-glycemic sera. Interestingly, the activation of these pathways and the DC immune dysfunction were partially counteracted by the anti-oxidant quercetin, a flavonoid already known to exert several beneficial effects in diabetes.

Molecular and Translational Classifications of DAMPs in Immunogenic Cell Death

The immunogenicity of malignant cells has recently been acknowledged as a critical determinant of efficacy in cancer therapy. Thus, besides developing direct immunostimulatory regimens, including dendritic cell-based vaccines, checkpoint-blocking therapies, and adoptive T-cell transfer, researchers have started to focus on the overall immunobiology of neoplastic cells. It is now clear that cancer cells can succumb to some anticancer therapies by undergoing a peculiar form of cell death that is characterized by an increased immunogenic potential, owing to the emission of the so-called “damage-associated molecular patterns” (DAMPs). The emission of DAMPs and other immunostimulatory factors by cells succumbing to immunogenic cell death (ICD) favors the establishment of a productive interface with the immune system. This results in the elicitation of tumor-targeting immune responses associated with the elimination of residual, treatment-resistant cancer cells, as well as with the establishment of immunological memory. Although ICD has been characterized with increased precision since its discovery, several questions remain to be addressed. Here, we summarize and tabulate the main molecular, immunological, preclinical, and clinical aspects of ICD, in an attempt to capture the essence of this phenomenon, and identify future challenges for this rapidly expanding field of investigation.

Tyrosine kinase inhibitor tyrphostin AG490 triggers both apoptosis and autophagy by reducing HSF1 and Mcl-1 in PEL cells

PEL cells relay on the constitutive activation of STAT3 for their survival, thus its inhibition by AG490 leads to apoptotic cell death. In this study, we found that the cytotoxic activity of AG490 correlated with the reduction of HSP70 and its master regulator HSF1 that, based on knocking-down experiments, was found to play a pro-survival role in PEL cells. To counteract the pro-death effect mediated by HSF1/HSP70 down-regulation, AG490 induced a complete autophagy, whose inhibition potentiated its cytotoxic effect against PEL cells. AG490 as well as HSF1 siRNA reduced the expression of Mcl-1, a Bcl-2 family member that negatively regulates apoptosis and autophagy. These results suggest that STAT3 inhibition, by down-regulating the expression of HSF1/HSP70, reduces Mcl-1 and leads to both apoptosis and autophagy induction in PEL cells.

Bright expression of CD91 identifies highly activated human dendritic cells that can be expanded by defensins

CD91 is a scavenger receptor expressed by different immune cells and its ligands defensins have been demonstrated to contribute to immune responses against infections and tumours. We previously demonstrated that CD91 is expressed on human monocyte-derived dendritic cells (moDCs) and that human defensins stimulate in vitro the activation of these cells. In this study, we observed that CD91 is expressed at different levels on two distinct moDC subsets: CD91(dim) and CD91(bright) moDCs. Although CD91(bright) moDCs represented a small proportion of total moDCs, this subset showed higher levels of activation and maturation markers compared with CD91(dim) moDCs. The frequency of CD91(bright) moDCs increased by ~ 50% after in vitro stimulation with recombinant human neutrophil peptide-1 (rHNP-1) and recombinant human β defensin-1 (rHBD-1), while lipopolysaccharide (LPS) stimulation decreased it by ~ 35%. Both defensins up-regulated moDC expression of CD80, CD40, CD83 and HLA-DR, although to a lower extent compared with LPS. Notably, upon culture with rHNP-1 and rHBD-1, CD91(bright) moDCs maintained their higher activation/maturation status, whereas this was lost upon culture with LPS. Our findings suggest that defensins promote the differentiation into activated CD91(bright) DCs and may encourage the exploitation of the CD91/defensins axis as a novel therapeutic strategy to potentiate antimicrobial and anti-tumour immune response.

Combinatorial strategies for the induction of immunogenic cell death

The term "immunogenic cell death" (ICD) is commonly employed to indicate a peculiar instance of regulated cell death (RCD) that engages the adaptive arm of the immune system. The inoculation of cancer cells undergoing ICD into immunocompetent animals elicits a specific immune response associated with the establishment of immunological memory. Only a few agents are intrinsically endowed with the ability to trigger ICD. These include a few chemotherapeutics that are routinely employed in the clinic, like doxorubicin, mitoxantrone, oxaliplatin, and cyclophosphamide, as well as some agents that have not yet been approved for use in humans. Accumulating clinical data indicate that the activation of adaptive immune responses against dying cancer cells is associated with improved disease outcome in patients affected by various neoplasms. Thus, novel therapeutic regimens that trigger ICD are urgently awaited. Here, we discuss current combinatorial approaches to convert otherwise non-immunogenic instances of RCD into bona fide ICD.

Trial Watch: Proteasomal inhibitors for anticancer therapy

The so-called "ubiquitin-proteasome system" (UPS) is a multicomponent molecular apparatus that catalyzes the covalent attachment of several copies of the small protein ubiquitin to other proteins that are generally (but not always) destined to proteasomal degradation. This enzymatic cascade is crucial for the maintenance of intracellular protein homeostasis (both in physiological conditions and in the course of adaptive stress responses), and regulates a wide array of signaling pathways. In line with this notion, defects in the UPS have been associated with aging as well as with several pathological conditions including cardiac, neurodegenerative, and neoplastic disorders. As transformed cells often experience a constant state of stress (as a result of the hyperactivation of oncogenic signaling pathways and/or adverse microenvironmental conditions), their survival and proliferation are highly dependent on the integrity of the UPS. This rationale has driven an intense wave of preclinical and clinical investigation culminating in 2003 with the approval of the proteasomal inhibitor bortezomib by the US Food and Drug Administration for use in multiple myeloma patients. Another proteasomal inhibitor, carfilzomib, is now licensed by international regulatory agencies for use in multiple myeloma patients, and the approved indications for bortezomib have been extended to mantle cell lymphoma. This said, the clinical activity of bortezomib and carfilzomib is often limited by off-target effects, innate/acquired resistance, and the absence of validated predictive biomarkers. Moreover, the antineoplastic activity of proteasome inhibitors against solid tumors is poor. In this Trial Watch we discuss the contribution of the UPS to oncogenesis and tumor progression and summarize the design and/or results of recent clinical studies evaluating the therapeutic profile of proteasome inhibitors in cancer patients.