Autophagy-dependent danger signaling and adaptive immunity to poorly immunogenic tumors

Tetralol derivative NNC-55-0396 induces glioblastoma cell death by activating IRE1α, JNK1 and calcium signaling

Mibefradil and NNC-55-0396, tetralol derivatives with a proven -ability to block T-type calcium channels in excitable cells, reduce cancer cell viability in vitro, causing cell death. Furthermore, they reduce tumor growth in preclinical models of Glioblastoma multiforme (GBM), a brain tumor of poor prognosis. Here we found that GBM cells treated with cytotoxic concentrations of NNC-55-0396 paradoxically increased cytosolic calcium levels through the activation of inositol triphosphate receptors (IP₃R) and ER stress. We used pharmacological inhibitors and gene silencing to dissect the cell death pathway stimulated by NNC-55-0396 in GBM cell lines and biopsy-derived cultures. Calcium chelation or IP₃R inhibition prevented NNC-55-0396-mediated cytotoxicity, indicating that ER calcium efflux is the cause of cell death. Upstream of calcium mobilization, NNC-55-0396 activated the IRE1α arm of the Unfolded Protein Response (UPR) resulting in the nuclear translocation of pro-apoptotic CHOP. Consistent with these findings, silencing IRE1α or JNK1 rescued the cell death elicited by NNC-55-0396. Therefore, we demonstrate that activation of IRE1α and calcium signaling accounts for the cytotoxicity of NNC-55-0396 in GBM cells. The delineation of the signaling pathway that mediates the abrupt cell death triggered by this compound can help the development of new therapies for GBM.

Purinergic Signaling Within the Tumor Microenvironment

Accumulating studies have clearly demonstrated high concentrations of extracellular ATP (eATP) within the tumor microenvironment (TME). Implications of these findings are multifold as ATP-mediated purinergic signaling has been shown to mediate a variety of cancer-related processes, including cell migration, resistance to cytotoxic therapy, and immune regulation. Broad roles of ATP within the tumor microenvironment are linked to the abundance of ATP-regulated purinergic receptors on cancer and stromal and various immune cell types, as well as on the importance of ATP release and signaling in the regulation of multiple cellular processes. ATP release and downstream purinergic signaling are emerging as a central regulator of tumor growth and an important target for therapeutic intervention. In this chapter, we summarize the major roles of purinergic signaling in the tumor microenvironment with a specific focus on its critical roles in the induction of immunogenic cancer cell death and immune modulation.

Decoding cancer's camouflage: epithelial-mesenchymal plasticity in resistance to immune checkpoint blockade

Epithelial-mesenchymal plasticity (EMP) of cancer cells contributes to cancer cell heterogeneity, and it is well established that EMP is a critical determinant of acquired resistance to cancer treatment modalities including radiation therapy, chemotherapy, and targeted therapies. Here, we aimed to explore how EMP contributes to cancer cell camouflage, allowing an ever-changing population of cancer cells to pass under the radar of our immune system and consequently compromise the effect of immune checkpoint blockade therapies. The ultimate clinical benefit of any combination regimen is evidenced by the sum of the drug-induced alterations observed in the variety of cellular populations composing the tumor immune microenvironment. The finely-tuned molecular crosstalk between cancer and immune cells remains to be fully elucidated, particularly for the spectrum of malignant cells along the epithelial to mesenchymal axis. High-dimensional single cell analyses of specimens collected in ongoing clinical studies is becoming a key contributor to our understanding of these interactions. This review will explore to what extent targeting EMP in combination with immune checkpoint inhibition represents a promising therapeutic avenue within the overarching strategy to reactivate a halting cancer-immunity cycle and establish a robust host immune response against cancer cells. Therapeutic strategies currently in clinical development will be discussed.

The impact of autophagy during the development and survival of glioblastoma

Glioblastoma is the most common and aggressive adult brain tumour, with poor median survival and limited treatment options. Following surgical resection and chemotherapy, recurrence of the disease is inevitable. Genomic studies have identified key drivers of glioblastoma development, including amplifications of receptor tyrosine kinases, which drive tumour growth. To improve treatment, it is crucial to understand survival response processes in glioblastoma that fuel cell proliferation and promote resistance to treatment. One such process is autophagy, a catabolic pathway that delivers cellular components sequestered into vesicles for lysosomal degradation. Autophagy plays an important role in maintaining cellular homeostasis and is upregulated during stress conditions, such as limited nutrient and oxygen availability, and in response to anti-cancer therapy. Autophagy can also regulate pro-growth signalling and metabolic rewiring of cancer cells in order to support tumour growth. In this review, we will discuss our current understanding of how autophagy is implicated in glioblastoma development and survival. When appropriate, we will refer to findings derived from the role of autophagy in other cancer models and predict the outcome of manipulating autophagy during glioblastoma treatment.

Local Administration of Caloric Restriction Mimetics to Promote the Immune Control of Lung Metastases

Caloric restriction mimetics (CRMs), compounds that mimic the biochemical effects of nutrient deprivation, administered via systemic route promote antitumor effects through the induction of autophagy and the modulation of the immune microenvironment; however, collateral effects due to metabolic changes and the possible weight loss might potentially limit their administration at long term. Here, we investigated in mice local administration of CRMs via aerosol to reduce metastasis implantation in the lung, whose physiologic immunosuppressive status favors tumor growth. Hydroxycitrate, spermidine, and alpha-lipoic acid, CRMs that target different metabolic enzymes, administered by aerosol, strongly reduced implantation of intravenously injected B16 melanoma cells without overt signs of toxicity, such as weight loss and changes in lung structure. Cytofluorimetric analysis of lung immune infiltrates revealed a significant increase of alveolar macrophages and CD103+ dendritic cells in mice treated with CRMs that paralleled an increased recruitment and activation of both CD3 T lymphocytes and NK cells. These effects were associated with the upregulation of genes related to M1 phenotype, as IL-12 and STAT-1, and to the decrease of M2 genes, as IL-10 and STAT-6, in adherent fraction of lung immune infiltrate, as revealed by real-time PCR analysis. Thus, in this proof-of-principle study, we highlight the antitumor effect of CRM aerosol delivery as a new and noninvasive therapeutic approach to locally modulate immunosurveillance at the tumor site in the lung.

Combination of anthracyclines and anti-CD47 therapy inhibit invasive breast cancer growth while preventing cardiac toxicity by regulation of autophagy

BACKGROUND

A perennial challenge in systemic cytotoxic cancer therapy is to eradicate primary tumors and metastatic disease while sparing normal tissue from off-target effects of chemotherapy. Anthracyclines such as doxorubicin are effective chemotherapeutic agents for which dosing is limited by development of cardiotoxicity. Our published evidence shows that targeting CD47 enhances radiation-induced growth delay of tumors while remarkably protecting soft tissues. The protection of cell viability observed with CD47 is mediated autonomously by activation of protective autophagy. However, whether CD47 protects cancer cells from cytotoxic chemotherapy is unknown.

METHODS

We tested the effect of CD47 blockade on cancer cell survival using a 2-dimensional high-throughput cell proliferation assay in 4T1 breast cancer cell lines. To evaluate blockade of CD47 in combination with chemotherapy in vivo, we employed the 4T1 breast cancer model and examined tumor and cardiac tissue viability as well as autophagic flux.

RESULTS

Our high-throughput screen revealed that blockade of CD47 does not interfere with the cytotoxic activity of anthracyclines against 4T1 breast cancer cells. Targeting CD47 enhanced the effect of doxorubicin chemotherapy in vivo by reducing tumor growth and metastatic spread by activation of an anti-tumor innate immune response. Moreover, systemic suppression of CD47 protected cardiac tissue viability and function in mice treated with doxorubicin.

CONCLUSIONS

Our experiments indicate that the protective effects observed with CD47 blockade are mediated through upregulation of autophagic flux. However, the absence of CD47 in did not elicit a protective effect in cancer cells, but it enhanced macrophage-mediated cancer cell cytolysis. Therefore, the differential responses observed with CD47 blockade are due to autonomous activation of protective autophagy in normal tissue and enhancement immune cytotoxicity against cancer cells.

Stress-induced cellular responses in immunogenic cell death: Implications for cancer immunotherapy

Cancer is evading the host's defense mechanisms leading to avoidance of immune destruction. During tumor progression, immune-evading cancer cells arise due to selective pressure from the hypoxic and nutrient-deprived microenvironment. Thus, therapies aiming at re-establishing immune destruction of pathological cells constitute innovating anti-cancer strategies. Accumulating evidence suggests that selected conventional chemotherapeutic drugs increase the immunogenicity of stressed and dying cancer cells by triggering a form of cell death called immunogenic cell death (ICD), which is characterized by the release of danger-associated molecular patterns (DAMPs). In this review, we summarize the effects of ICD inducers on DAMP signaling leading to adjuvanticity and antigenicity. We will discuss the associated stress response pathways that cause the release of DAMPs leading to improved immune recognition and their relevance in cancer immunotherapy. Our aim is to highlight the contribution of adaptive immunity to the long-term clinical benefits of anticancer treatments and the properties of immune memory that can protect cancer patients against relapse.

The potentially conflicting cell autonomous and cell non-autonomous functions of autophagy in mediating tumor response to cancer therapy

Autophagy, a virtually uniform response to external stress such as that induced by chemotherapy and radiation, is generally considered to be cytoprotective in function, providing a foundation for multiple clinical trials designed to enhance therapeutic response via autophagy inhibition. However, this cell autonomous response can also be cytotoxic or nonprotective, with the consequence that autophagy inhibition would be counterproductive or ineffective, respectively. The non-cell autonomous function of autophagy remains quite controversial, with evidence both for and against autophagy-mediated activation of the immune system. If autophagy inhibition antagonizes the immune response, this would likely interfere with the potential sensitization resulting from suppression of the cell autonomous protective function. An additional complication, which has rarely been considered, is the nature of the contribution of therapy-induced autophagy in the tumor microenvironment, particularly the tumor stroma. Taken together, it is likely that the outcome of the current clinical trials, whether positive or negative, will be difficult to interpret given the complexity of the role of autophagy relating to the tumor cell (cell autonomous), the immune system (cell non-autonomous) and the tumor microenvironment.

Anti-tumour effects of polysaccharide extracted from Acanthopanax senticosus and cell-mediated immunity

Acanthopanax senticosus, also known as Siberian ginseng, is widely distributed throughout northern Asia and used in traditional Chinese medicine; it has been reported to prevent a number of diseases. However, the association between the antitumour and immunostimulatory activities of polysaccharide extracted from A. senticosus (ASPS) remains to be elucidated. The aim of the present study was to investigate the anti-tumour and immunomodulatory effects of polysaccharide extracted from ASPS on Crocker sarcoma S180, hepatic carcinoma H22 and uterine cervical carcinoma U14 tumour cell lines implanted in mice. High performance liquid chromatography, gas chromatography and infrared spectroscopy were used to analyse the monosaccharide composition of ASPS. The monosaccharide composition of ASPS (Arabic candy: Xylose: Glucose: Mannose) was 7.1:22.3:7.6:1.0. On day 0, female Kunming mice, were injected subcutaneously with 1×108 tumour cells in 0.2 ml. The inoculated mice were subsequently divided into five groups (10 mice/group) as follows: Model group, treated with normal saline; positive control group, treated with 30 mg/kg cyclophosphamide (CTX); and three treatment groups, treated with 200, 100 or 50 mg/kg ASPS. Non-inoculated mice were divided into the normal group, which was treated with normal saline, and the negative control group, which was treated with 200 mg/kg ASPS (n=10/group). CTX and ASPS were administered intragastrically once daily for 10 days. All mice were sacrificed on day 11. ASPS was observed to have an inhibitory effect on the growth of S180, H22 and U14 cells in solid and ascites tumour-bearing mice. Serum interleukin (IL)-2 and IL-12 levels were significantly increased in S180 solid tumour-bearing mice treated with 200 or 100 mg/kg ASPS compared with mice in the normal, control and model groups (P<0.05), whereas serum IL-2 and IL-12 levels were significantly decreased in the cyclophosphamide treatment group compared with the normal, control and model groups (P<0.05). No significant difference in serum levels of tumour necrosis factor-α level was observed between any groups. In S180 and U14 solid tumour-bearing mice, no significant differences in serum levels of interferon (INF)-γ level in were observed between groups; however, in H22 solid tumour-bearing mice, treatment with ASPS significantly increased serum INF-γ compared with the positive control group (P<0.05). The results may provide a basis for the potential application of ASPS in clinical treatment for cancer.

Trial Watch: Immunostimulatory monoclonal antibodies for oncological indications

The goal of cancer immunotherapy is to establish new or boost pre-existing anticancer immune responses that eradicate malignant cells while generating immunological memory to prevent disease relapse. Over the past few years, immunomodulatory monoclonal antibodies (mAbs) that block co-inhibitory receptors on immune effectors cells - such as cytotoxic T lymphocyte-associated protein 4 (CTLA4), programmed cell death 1 (PDCD1, best known as PD-1) - or their ligands - such as CD274 (best known as PD-L1) - have proven very successful in this sense. As a consequence, many of such immune checkpoint blockers (ICBs) have already entered the clinical practice for various oncological indications. Considerable attention is currently being attracted by a second group of immunomodulatory mAbs, which are conceived to activate co-stimulatory receptors on immune effector cells. Here, we discuss the mechanisms of action of these immunostimulatory mAbs and summarize recent progress in their preclinical and clinical development.