Francesca Velotti

Consensus guidelines for the detection of immunogenic cell death

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.

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.

Dietary ω-3 Polyunsaturated Fatty Acid DHA: A Potential Adjuvant in the Treatment of Cancer

ω-3 Polyunsaturated fatty acids (PUFAs), mainly present in fish oil, are part of the human diet. Among PUFAs, docosahexaenoic acid (DHA) has received particular attention for its anti-inflammatory, antiproliferative, proapoptotic, antiangiogenetic, anti-invasion, and antimetastatic properties. These data suggest that DHA can exert antitumor activity potentially representing an effective adjuvant in cancer chemotherapy. This review is focused on current knowledge supporting the potential use of DHA for the enhancement of the efficacy of anticancer treatments in relation to its ability to enhance the uptake of anticancer drugs, regulate the oxidative status of tumor cells, and inhibit tumor cell invasion and metastasis.

Omega-3 Fatty Acids and Cancer Cell Cytotoxicity: Implications for Multi-Targeted Cancer Therapy

Cancer is a major disease worldwide. Despite progress in cancer therapy, conventional cytotoxic therapies lead to unsatisfactory long-term survival, mainly related to development of drug resistance by tumor cells and toxicity towards normal cells. n-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), can exert anti-neoplastic activity by inducing apoptotic cell death in human cancer cells either alone or in combination with conventional therapies. Indeed, n-3 PUFAs potentially increase the sensitivity of tumor cells to conventional therapies, possibly improving their efficacy especially against cancers resistant to treatment. Moreover, in contrast to traditional therapies, n-3 PUFAs appear to cause selective cytotoxicity towards cancer cells with little or no toxicity on normal cells. This review focuses on studies investigating the cytotoxic activity of n-3 PUFAs against cancer cells via apoptosis, analyzing the molecular mechanisms underlying this effective and selective activity. Here, we highlight the multiple molecules potentially targeted by n-3 PUFAs to trigger cancer cell apoptosis. This analysis can allow a better comprehension of the potential cytotoxic therapeutic role of n-3 PUFAs against cancer, providing specific information and support to design future pre-clinical and clinical studies for a better use of n-3 PUFAs in cancer therapy, mainly combinational therapy.

Docosahexaenoic acid induces apoptosis in the human PaCa-44 pancreatic cancer cell line by active reduced glutathione extrusion and lipid peroxidation.

Abstract: We investigated the ability of fatty acids to induce growth inhibition and apoptosis in the human PaCa-44 pancreatic cancer cell line and the mechanism(s) underlying apoptosis. Butyric acid, α-linoleic acid, and docosahexaenoic acid (DHA) were supplemented at 200 μM concentration in the medium of cell cultures. Our results showed that all fatty acids inhibited cell growth, whereas only DHA induced cell apoptosis. An oxidative process was implicated in apoptosis induced by DHA because butylated hydroxytoluene and vitamin E prevented lipid peroxidation and reversed apoptosis. Intracellular and extracellular glutathione [reduced glutathione (GSH) and oxidized glutathione (GSSG)] concentrations were measured following DHA treatment in the presence or in the absence of GSH extrusion inhibitors such as cystathionine or methionine. DHA induced intracellular GSH depletion without affecting intracellular GSSG concentration and increased extracellular GSH and GSSG levels. Intracellular GSH depletion and extracellular GSH increase were both reversed by cystathionine. Inhibition of active GSH extrusion from the cell by cystathionine or methionine completely reversed lipid peroxidation and apoptosis. These data document the antiproliferative and apoptotic activities of DHA. The date provide evidence that intracellular GSH depletion represents an active extrusion process rather than a consequence of an oxidative stress, suggesting a causative role of GSH depletion in DHA-induced apoptosis.

Synthesis of a novel ester of hydroxytyrosol and α-lipoic acid exhibiting an antiproliferative effect on human colon cancer HT-29 cells

A novel ester of hydroxytyrosol and α-lipoic acid was synthesized in satisfactory yield by original and simple procedures and evaluated about its antiproliferative activity on the human colorectal adenocarcinoma HT-29 cell line. The compound exhibited a cell growth inhibitory activity significantly more potent than the corresponding parent natural compounds, very likely due to the induction of cell cycle arrest in the G2/M phase. These data suggest that the novel ester might exert a more effective antitumour activity than hydroxytyrosol and α-lipoic acid.

Naturally occurring hydroxytyrosol: synthesis and anticancer potential.

Several epidemiological and animal studies have suggested that polyphenols, a group of secondary plant metabolites occurring mainly in the plant kingdom, may have a protective effect against some chronic degenerative diseases such as cancer. Polyphenols are part of the human diet, being present in vegetal food and beverages. Among them, an olive biophenol named hydroxytyrosol [2-(3,4- dihydroxyphenyl)ethanol, HTyr] has recently received particular attention because of its antioxidant, antiproliferative, pro-apoptotic, and anti-inflammatory activities, which have the potential to specifically counteract all cancer hallmarks, thus representing the expectant biological activities underlying the anti-tumor properties of this polyphenol. After a description of the synthetic procedures to prepare pure HTyr, this review takes into consideration the chemopreventive and chemotherapeutic potential of HTyr as the result of its antioxidant, antiproliferative and anti-inflammatory activities. In particular, the review is focused on the current knowledge of the main cellular and molecular mechanisms used by HTyr to affect carcinogenesis, highlighting the specific oncogenic and inflammatory signaling pathways potentially targeted by HTyr.

Induction of Apoptosis in Human Pancreatic Cancer Cells by Docosahexaenoic Acid

Abstract: Polyunsaturated fatty acids have been indicated to induce anti‐proliferative and/or apoptotic effects in various tumor cells. We showed that, at a 200‐μM concentration, both alpha‐linoleic (18:2 n‐6; LA) or docosahexaenoic (22:6 n‐3; DHA) acid inhibited cell growth, while only DHA induced apoptosis in the human Paca‐44 pancreatic cancer cell line. Investigating the mechanism underlying DHA‐induced apoptosis, we showed that DHA induced a rapid and dramatic (>60%) intracellular depletion of reduced glutathione (GSH), without affecting oxidized glutathione (GSSG). Moreover, using two specific inhibitors of carrier‐mediated GSH extrusion, cystathionine or methionine, we observed that GSH depletion occurred via an active GSH extrusion, and that inhibition of GSH efflux completely reversed apoptosis. These results provide the first evidence for a possible causative role of GSH depletion in DHA‐induced apoptosis.

Human Urinary Bladder Transitional Cell Carcinomas Acquire the Functional Fas Ligand during Tumor Progression

The interaction between FasL on tumor cells and Fas on lymphocytes may represent a tumor immune escape mechanism. We explored FasL expression and function in human urinary bladder transitional cell carcinomas (TCCs). FasL expression was observed in situ in 45% of TCCs (n = 45) and was absent in normal urothelium (n = 20). A correlation existed between FasL expression and high tumor grade (0% in G1, 14% in G2, and 75% in G3; P < 0.0001) and stage (13% in superficial Ta-T1 versus 81% in invasive T2-T4; P < 0.0001). FasL function was shown by the ability of two FasL-positive primary culture TCC cell lines (established from two FasL-positive invasive TCCs) to induce Fas-mediated killing not only of conventional Fas-sensitive targets (such as Jurkat cells or phytohemagglutinin-lymphoblasts), but also of autologous T lymphocytes generated in a mixed lymphocyte tumor-cell culture. In addition, an association between FasL expression by TCC cells and activated caspase-8, -9, and -3 expression by interferon-gamma-producing CD8-positive tumor-infiltrating lymphocytes was observed in situ. Our results show a functional expression of TCC-expressed FasL that correlates with tumor progression. These results suggest that TCC-expressed FasL may induce apoptosis of anti-tumor T lymphocytes in vivo, providing new insights on the mechanisms involved in bladder TCC progression.

Hydroxytyrosol-Derived Compounds: A Basis for the Creation of New Pharmacological Agents for Cancer Prevention and Therapy

Hydroxytyrosol [2-(3,4-dihydroxyphenyl)ethanol, HTyr] is a phenolic compound found in olive leaves and fruits and extra-virgin olive oil, which has well-known strong antioxidant and radical-scavenging properties. Recently, it has received particular attention for its antiproliferative and apoptotic activities and its anti-inflammatory properties. During the past few years, more efforts have been focused on synthesizing HTyr-derived compounds with enhanced biological activities for their potential use in different chronic degenerative diseases. In this paper, we report a dissertation on the current knowledge of selected synthetic HTyr derivatives and analogues and their potential use in cancer prevention and therapy, which are related to their antioxidant, antiproliferative/apoptotic, and anti-inflammatory properties. On the basis of the perspective of using HTyr-derived compounds as anticancer agents, we have taken into account only studies that were performed in experimental cell-based models.