Spatiotemporal autophagic degradation of oxidatively damaged organelles after photodynamic stress is amplified by mitochondrial reactive oxygen species

Dual-/multi-organelle-targeted AIE probes associated with oxidative stress for biomedical applications

In situ monitoring of biological processes between different organelles upon oxidative stress is one of the most important research hotspots. Fluorescence imaging is especially suitable for biomedical applications due to its distinct advantages of high spatiotemporal resolution, high sensitivity, non-invasiveness, and in situ monitoring capabilities. However, most fluorescent probes can only achieve light-up imaging of single organelles, thus the combined use of two or more probes is usually required for monitoring biological processes between organelles, which can suffer from tedious staining and washing procedures, increased cytotoxicity and poor photostability. Exogenetic oxidants can affect broad-spectrum subcellular organelles, which are not conducive to in situ monitoring of biological processes between specific organelles. To tackle these challenges, a series of dual-/multi-organelle-targeted aggregation-induced emission (AIE) probes associated with oxidative stress have been designed and developed in the past few years. Herein, the recent progress of these AIE probes is summarized in biomedical applications, such as apoptosis monitoring, interplay between organelles, microenvironmental changes of organelles, organelle morphology tracking, precise cancer therapy, and so forth. Moreover, the further outlook for dual-/multi-organelle-targeted AIE probes is discussed, aiming to promote innovative research in biomedical applications.

Hypericin-mediated photodynamic therapy inhibits metastasis and EMT of colorectal cancer cells by regulating RhoA-ROCK1 signaling pathway

Colorectal cancer (CRC) is significantly contributed to global cancer mortality rates. Treating CRC is particularly challenging due to metastasis and drug resistance. There is a pressing need for new treatment strategies against metastatic CRC. Photodynamic therapy (PDT) offers a well-established, minimally invasive treatment option for cancer with limited side effects. Hypericin (HYP), a potent photosensitizer for PDT, has been documented to induce cytotoxicity and apoptosis in various types of cancers. However, there are few reports on the inhibitory effects of HYP-mediated PDT on the metastatic ability of CRC cells. Here, we evaluate the inhibitory effects of HYP-mediated PDT against metastatic CRC cells and define its underlying mechanisms. Wound-healing and Transwell assays show that HYP-mediated PDT suppresses migration and invasion of CRC cells. F-actin visualization assays indicate HYP-mediated PDT decreases F-actin formation in CRC cells. TEM assays reveal HYP-mediated PDT disrupts pseudopodia formation of CRC cells. Mechanistically, immunofluorescence and western blotting results show that HYP-mediated PDT upregulates E-cadherin and downregulates N-cadherin and Vimentin. HYP-mediated PDT also suppresses key EMT regulators, including Snail, MMP9, ZEB1 and α-SMA. Additionally, the expressions of RhoA and ROCK1 are downregulated by HYP-mediated PDT. Together, these findings suggest that HYP-mediated PDT inhibits the migration and invasion of HCT116 and SW620 cells by modulating EMT and RhoA-ROCK1 signaling pathway. Thus, HYP-mediated PDT presents a potential therapeutic option for CRC.

Fluorescence-Guided Laparoscopy after Oral Hypericin Administration for Staging of Locally Advanced Gastric Cancer-A Pilot Study

(1) Background: Laparoscopic staging is essential in gastric cancer (GC) to rule out peritoneal metastasis (PM). Hypericin, a plant-derived fluorescent compound, has been suggested to improve laparoscopic visualization of PM from GC. This prospective, single-arm, open-label clinical trial aimed to assess the feasibility and safety of oral hypericin administration as well as the suitability of fluorescence-guided laparoscopy (FGL) for improving the sensitivity and specificity of staging in GC patients (EudraCT-Number: 2015-005277-21; clinicaltrials.gov identifier: NCT-02840331). (2) Methods: GC patients received Laif® 900, an approved hypericin-containing phytopharmaceutical, once orally two to four hours before white light and ultraviolet light laparoscopy. The peritoneal cancer index was evaluated, biopsies taken and hypericin concentrations in serum and peritoneal tissue were determined by mass spectrometry. (3) Results: Between 2017 and 2021, out of 63 patients screened for eligibility, 50 patients were enrolled and treated per protocol. The study intervention was shown to be feasible and safe in all patients. Standard laparoscopy revealed suspicious lesions in 27 patients (54%), among whom 16 (59%) were diagnosed with PM. FGL identified suspicious areas in 25 patients (50%), among whom PM was confirmed in 13 cases (52%). Although hypericin concentrations in serum reached up to 5.64 ng/mL, no hypericin was detectable in peritoneal tissue biopsies. (4) Conclusions: FGL in patients with GC was shown to be feasible but futile in this study. Sufficient levels of hypericin should be ensured in target tissue prior to reassessing FGL with hypericin.

Antioxidant network-based signatures cluster glioblastoma into distinct redox-resistant phenotypes

Introduction

Aberrant reactive oxygen species (ROS) production is one of the hallmarks of cancer. During their growth and dissemination, cancer cells control redox signaling to support protumorigenic pathways. As a consequence, cancer cells become reliant on major antioxidant systems to maintain a balanced redox tone, while avoiding excessive oxidative stress and cell death. This concept appears especially relevant in the context of glioblastoma multiforme (GBM), the most aggressive form of brain tumor characterized by significant heterogeneity, which contributes to treatment resistance and tumor recurrence. From this viewpoint, this study aims to investigate whether gene regulatory networks can effectively capture the diverse redox states associated with the primary phenotypes of GBM.

Methods

In this study, we utilized publicly available GBM datasets along with proprietary bulk sequencing data. Employing computational analysis and bioinformatics tools, we stratified GBM based on their antioxidant capacities and evaluated the distinctive functionalities and prognostic values of distinct transcriptional networks in silico.

Results

We established three distinct transcriptional co-expression networks and signatures (termed clusters C1, C2, and C3) with distinct antioxidant potential in GBM cancer cells. Functional analysis of each cluster revealed that C1 exhibits strong antioxidant properties, C2 is marked with a discrepant inflammatory trait and C3 was identified as the cluster with the weakest antioxidant capacity. Intriguingly, C2 exhibited a strong correlation with the highly aggressive mesenchymal subtype of GBM. Furthermore, this cluster holds substantial prognostic importance: patients with higher gene set variation analysis (GSVA) scores of the C2 signature exhibited adverse outcomes in overall and progression-free survival.

Conclusion

In summary, we provide a set of transcriptional signatures that unveil the antioxidant potential of GBM, offering a promising prognostic application and a guide for therapeutic strategies in GBM therapy.

Photodynamic Modulation of Endoplasmic Reticulum and Mitochondria Network Boosted Cancer Immunotherapy

Immunogenic cell death (ICD) represents a promising approach for enhancing tumor therapy efficacy by inducing antitumor immune response. However, current ICD inducers often have insufficient endoplasmic reticulum (ER) enrichment and ineffectiveness in tumor immune escape caused by ER-mitochondria interaction. In this study, a kind of photoactivatable probe, THTTPy-PTSA, which enables sequential targeting of the ER and mitochondria is developed. THTTPy-PTSA incorporates p-Toluenesulfonamide (PTSA) for ER targeting, and upon light irradiation, the tetrahydropyridine group undergoes a photo oxidative dehydrogenation reaction, transforming into a pyridinium group that acts as a mitochondria-targeting moiety. The results demonstrate that THTTPy-PTSA exhibits exceptional subcellular translocation from the ER to mitochondria upon light irradiation treatment, subsequently triggers a stronger ER stress response through a cascade-amplification effect. Importantly, the augmented ER stress leads to substantial therapeutic efficacy in a 4T1 tumor model by eliciting the release of numerous damage-associated molecular patterns, thereby inducing evident and widespread ICD, consequently enhancing the antitumor immune efficacy. Collectively, the findings emphasize the pivotal role of photodynamic modulation of the ER-mitochondria network, facilitated by THTTPy-PTSA with precise spatial and temporal regulation, in effectively bolstering the antitumor immune response. This innovative approach presents a promising alternative for addressing the challenges associated with cancer immunotherapy.

Hypericin as a promising natural bioactive naphthodianthrone: A review of its pharmacology, pharmacokinetics, toxicity, and safety

Hypericin can be derived from St. John's wort, which is widely spread around the world. As a natural product, it has been put into clinical practice such as wound healing and depression for a long time. In this article, we review the pharmacology, pharmacokinetics, and safety of hypericin, aiming to introduce the research advances and provide a full evaluation of it. Turns out hypericin, as a natural photosensitizer, exhibits an excellent capacity for anticancer, neuroprotection, and elimination of microorganisms, especially when activated by light, potent anticancer and antimicrobial effects are obtained after photodynamic therapy. The mechanisms of its therapeutic effects involve the induction of cell death, inhibition of cell cycle progression, inhibition of the reuptake of amines, and inhibition of virus replication. The pharmacokinetics properties indicate that hypericin has poor water solubility and bioavailability. The distribution and excretion are fast, and it is metabolized in bile. The toxicity of hypericin is rarely reported and the conventional use of it rarely causes adverse effects except for photosensitization. Therefore, we may conclude that hypericin can be used safely and effectively against a variety of diseases. We hope to provide researchers with detailed guidance and enlighten the development of it.

Effects of Hypericin on Cultured Primary Normal Human Dermal Fibroblasts Under Increased Oxidative Stress

INTRODUCTION

Wound healing is a dynamic process that begins with inflammation, proliferation, and cell migration of a variety of fibroblast cells. As a result, identifying possible compounds that may improve fibroblast cell wound healing capacity is crucial. Hypericin is a natural quinine that has been reported to possess a wide range of pharmacological profiles, including antioxidant and anti-inflammatory, activities. Herein we examined for the first time the effect of hypericin on normal human dermal fibroblasts (NHDFs) under oxidative stress.

METHODS

NHDF were exposed to different concentrations of hypericin (0-20 μg/mL) for 24 h. For the oxidative stress evaluation, H2O2 was used as a stressor factor. Cell viability and proliferation levels were evaluated. Immunohistochemistry and flow cytometry were performed to assess cell apoptosis levels and with confocal microscopy we identified the mitochondrial superoxide production under oxidative stress and after the treatment with hypericin. Scratch assay was performed under oxidative stress to evaluate the efficacy of hypericin in wound closure. To gain an insight into the molecular mechanisms of hypericin bioactivity, we analyzed the relative expression levels of genes involved in oxidative response and in wound healing process.

RESULTS

We found that the exposure of NHDF to hypericin under oxidative stress resulted in an increase in cell viability and ATP levels. We found a decrease in apoptosis and mitochondrial superoxide levels after treatment with hypericin. Moreover, treatment with hypericin reduced wound area and promoted wound closure. The levels of selected genes showed that hypericin upregulated the levels of antioxidants genes. Moreover, treatment with hypericin in wound under oxidative stress downregulated the levels of proinflammatory cytokines, and metalloproteinases; and upregulated transcription factors and extracellular matrix genes.

CONCLUSION

These findings indicated that hypericin possesses significant in vitro antioxidant activity on NHDF and provide new insights into its potential beneficial role in the management of diabetic ulcers.

GPX4 in cell death, autophagy, and disease

Selenoprotein GPX4 (glutathione peroxidase 4), originally known as PHGPX (phospholipid hydroperoxide glutathione peroxidase), is the main oxidoreductase in the use of glutathione as a reducing agent in scavenging lipid peroxidation products. There are three GPX4 isoforms: cytosolic (cGPX4), mitochondrial (mGPX4), and nuclear (nGPX4), with distinct spatiotemporal expression patterns during embryonic development and adult life. In addition to inducing the main phenotype of ferroptosis, the loss of GPX4 can in some cells trigger apoptosis, necroptosis, pyroptosis, or parthanatos, which mediates or accelerates developmental defects, tissue damage, and sterile inflammation. The interaction of GPX4 with the autophagic degradation pathway further modulates cell fate in response to oxidative stress. Impaired GPX4 function is implicated in tumorigenesis, neurodegeneration, infertility, inflammation, immune disorders, and ischemia-reperfusion injury. Additionally, the R152H mutation in GPX4 can promote the development of Sedaghatian-type spinal metaphyseal dysplasia, a rare and fatal disease in newborns. Here, we discuss the roles of classical GPX4 functions as well as emerging GPX4-regulated processes in cell death, autophagy, and disease.Abbreviations: AA: arachidonic acid; cGPX4: cytosolic GPX4; CMA: chaperone-mediated autophagy; DAMPs: danger/damage-associated molecular patterns; mGPX4: mitochondrial GPX4; nGPX4: nuclear GPX4; GSDMD-N: N-terminal fragment of GSDMD; I/R: ischemia-reperfusion; PLOOH: phospholipid hydroperoxide; PUFAs: polyunsaturated fatty acids; RCD: regulated cell death; ROS: reactive oxygen species; Se: selenium; SSMD: Sedaghatian-type spondylometaphyseal dysplasia; UPS: ubiquitin-proteasome system.

Autophagy Regulation Using Multimodal Chlorin e6-Loaded Polysilsesquioxane Nanoparticles to Improve Photodynamic Therapy

Photodynamic therapy (PDT) is a promising anticancer noninvasive technique that relies on the generation of reactive oxygen species (ROS). Unfortunately, PDT still has many limitations, including the resistance developed by cancer cells to the cytotoxic effect of ROS. Autophagy, which is a stress response mechanism, has been reported as a cellular pathway that reduces cell death following PDT. Recent studies have demonstrated that PDT in combination with other therapies can eliminate anticancer resistance. However, combination therapy is usually challenged by the differences in the pharmacokinetics of the drugs. Nanomaterials are excellent delivery systems for the efficient codelivery of two or more therapeutic agents. In this work, we report on the use of polysilsesquioxane (PSilQ) nanoparticles for the codelivery of chlorin-e6 (Ce6) and an autophagy inhibitor for early- or late-stage autophagy. Our results, obtained from a reactive oxygen species (ROS) generation assay and apoptosis and autophagy flux analyses, demonstrate that the reduced autophagy flux mediated by the combination approach afforded an increase in the phototherapeutic efficacy of Ce6-PSilQ nanoparticles. We envision that the promising results in the use of multimodal Ce6-PSilQ material as a codelivery system against cancer pave the way for its future application with other clinically relevant combinations.

Hypericin: A natural anthraquinone as promising therapeutic agent

BACKGROUND

Hypericin is a prominent secondary metabolite mainly existing in genus Hypericum. It has become a research focus for a quiet long time owing to its extensively pharmacological activities especially the anti-cancer, anti-bacterial, anti-viral and neuroprotective effects. This review concentrated on summarizing and analyzing the existing studies of hypericin in a comprehensive perspective.

METHODS

The literature with desired information about hypericin published after 2010 was gained from electronic databases including PubMed, SciFinder, Science Direct, Web of Science, China National Knowledge Infrastructure databases and Wan Fang DATA.

RESULTS

According to extensive preclinical and clinical studies conducted on the hypericin, an organized and comprehensive summary of the natural and artificial sources, strategies for improving the bioactivities, pharmacological activities, drug combination of hypericin was presented to explore the future therapeutic potential of this active compound.

CONCLUSIONS

Overall, this review offered a theoretical guidance for the follow-up research of hypericin. However, the pharmacological mechanisms, pharmacokinetics and structure activity relationship of hypericin should be further studied in future research.

Upconversion nanoparticle-based optogenetic nanosystem for photodynamic therapy and cascade gene therapy

Most photosensitizer molecules used for the photodynamic therapy (PDT) are chemically-synthesized organic photosensitizer dyes which show several limitations such as unsatisfactory cell uptake, weak selectivity and off-target phototoxicity. Recently, genetically-encoded photosensitizers have attracted increasing attentions which provide the targeted cell elimination with single-cell precision. However, their applications are mainly limited by the shallow tissue penetration depth of the excitation light and the low cell apoptosis ratio. Herein, we developed a feasible upconversion nanoparticle (UCNP)-based optogenetic nanosystem with three-in-one functional integration: bio-imaging, NIR-triggered PDT and cascade gene therapy. Firstly, the mitochondria-targeted genetically-encoded photosensitizer was constructed and transfected into cancer cells. Then, the functional upconversion nanoprobe was constructed with the mitochondria targetability and then the siRNA was loaded on the surface of UCNPs via the reactive oxygen species (ROSs) sensitive chemical bond. After the transfection and incubation, both of the upconversion nanoprobe and the genetically-encoded photosensitizer were accumulated in the mitochondria of cancer cells. Under the NIR irradiation, the emission of UCNPs could excite the expressed protein photosensitizer to generate ROSs which then stimulated the release of siRNAs in a controllable manner, achieving PDT and cascade gene therapy. Since the generation of ROSs and the release of siRNA occurred in the mitochondria in-situ, the mitochondria-mediated cell apoptosis signal pathway would be activated to induce cell apoptosis and subsequently inhibit tumor growth. To the best of our knowledge, this is the first report about NIR laser-activated, organelle-localized genetically-encoded photosensitizers developed for cascade therapy, which will widen the application of optogenetic tools in the tumor therapy. STATEMENT OF SIGNIFICANCE: The application of genetically-encoded photosensitizers in photodynamic therapy (PDT) is mainly limited by the shallow tissue penetration depth of the excitation light and unsatisfactory therapeutic performance. In this experiment, we developed an upconversion nanoparticles-based optogenetic nanosystem to enhance the PDT and cascade gene therapy for malignant tumors. The expressed genetically-encoded photosensitizers were accumulated in the mitochondria, which were activated in situ by the upconversion nanoprobe. Besides, the photogenerated reactive oxygen species (ROSs) stimulated the release of siRNAs in a controllable manner. To the best of our knowledge, this is the first report about NIR laser-activated, genetically-encoded photosensitizers developed for organelle-localized controllable cascade therapy. We hope this work can accelerate the application of genetically-encoded photosensitizers in the tumor therapy.

Endoplasmic Reticulum Stress and Cancer: Could Unfolded Protein Response Be a Druggable Target for Cancer Therapy?

Unfolded protein response (UPR) is an adaptive response which is used for re-establishing protein homeostasis, and it is triggered by endoplasmic reticulum (ER) stress. Specific ER proteins mediate UPR activation, after dissociation from chaperone Glucose-Regulated Protein 78 (GRP78). UPR can decrease ER stress, producing an ER adaptive response, block UPR if ER homeostasis is restored, or regulate apoptosis. Some tumour types are linked to ER protein folding machinery disturbance, highlighting how UPR plays a pivotal role in cancer cells to keep malignancy and drug resistance. In this review, we focus on some molecules that have been revealed to target ER stress demonstrating as UPR could be a new target in cancer treatment.

NEAT1 Confers Radioresistance to Hepatocellular Carcinoma Cells by Inducing PINK1/Parkin-Mediated Mitophagy

A long noncoding RNA, nuclear paraspeckle assembly transcript 1 (NEAT1) variant 1 (NEAT1v1), confers radioresistance to hepatocellular carcinoma (HCC) cells by inducing autophagy via γ-aminobutyric acid A receptor-associated protein (GABARAP). Radiation induces oxidative stress to damage cellular components and organelles, but it remains unclear how NEAT1v1 protects HCC cells from radiation-induced oxidative stress via autophagy. To address this, we precisely investigated NEAT1v1-induced autophagy in irradiated HCC cell lines. X-ray irradiation significantly increased cellular and mitochondrial oxidative stress and mitochondrial DNA content in HCC cells while NEAT1v1 suppressed them. NEAT1v1 concomitantly induced the phosphatase and tensin homolog-induced kinase 1 (PINK1)/parkin-mediated mitophagy. Interestingly, parkin expression was constitutively upregulated in NEAT1v1-overexpressing HCC cells, leading to increased mitochondrial parkin levels. Superoxide dismutase 2 (SOD2) was also upregulated by NEAT1v1, and GABARAP or SOD2 knockdown in NEAT1v1-overexpressing cells increased mitochondrial oxidative stress and mitochondrial DNA content after irradiation. Moreover, it was suggested that SOD2 was involved in NEAT1v1-induced parkin expression, and that GABARAP promoted parkin degradation via mitophagy. This study highlights the unprecedented roles of NEAT1v1 in connecting radioresistance and mitophagy in HCC.

CO/light dual-activatable Ru(ii)-conjugated oligomer agent for lysosome-targeted multimodal cancer therapeutics

Stimuli-activatable and subcellular organelle-targeted agents with multimodal therapeutics are urgently desired for highly precise and effective cancer treatment. Herein, a CO/light dual-activatable Ru(ii)-oligo-(thiophene ethynylene) (Ru-OTE) for lysosome-targeted cancer therapy is reported. Ru-OTE is prepared via the coordination-driven self-assembly of a cationic conjugated oligomer (OTE-BN) ligand and a Ru(ii) center. Upon the dual-triggering of internal gaseous signaling molecular CO and external light, Ru-OTE undergoes ligand substitution and releases OTE-BN followed by dramatic fluorescence recovery, which could be used for monitoring drug delivery and imaging guided anticancer treatments. The released OTE-BN selectively accumulates in lysosomes, physically breaking their integrity. Then, the generated cytotoxic singlet oxygen (¹O₂) causes severe lysosome damage, thus leading to cancer cell death via photodynamic therapy (PDT). Meanwhile, the release of the Ru(ii) core also suppresses cancer cell growth as an anticancer metal drug. Its significant anticancer effect is realized via the multimodal therapeutics of physical disruption/PDT/chemotherapy. Importantly, Ru-OTE can be directly photo-activated using a two-photon laser (800 nm) for efficient drug release and near-infrared PDT. Furthermore, Ru-OTE with light irradiation inhibits tumor growth in an MDA-MB-231 breast tumor model with negligible side effects. This study demonstrates that the development of an activatable Ru(ii)-conjugated oligomer potential drug provides a new strategy for effective subcellular organelle-targeted multimodal cancer therapeutics.

The anticancer therapeutics of lysosome disruption/PDT/chemotherapy based on Ru-OTE complex was achieved, which provides a new strategy for developing multimodal and effective stimuli-activatable subcellular organelle-targeted cancer therapeutics.

Cyclometalated Iridium(III) Complexes as Mitochondria-targeting Photosensitizers against Cisplatin-resistant Cells†

Four iridium (III) complexes Ir1-Ir4 were synthesized and characterized. Possessing high singlet oxygen production ability and specific mitochondria-localization, Ir1 was developed as a mitochondria-targeting photosensitizer. Ir1 exhibited strong phototoxicity against cancer cell line A549 and its corresponding cisplatin-resistant one A549R. In contrast, Ir1 showed low cytotoxicity toward normal cell HLF. This selectivity resulted from the different uptake amount. With 405 nm irradiation, Ir1 induced mitochondria-mediated cell death in A549R cells, achieving the overcome of drug-resistant.

Autophagy Regulation and Photodynamic Therapy: Insights to Improve Outcomes of Cancer Treatment

Cancer is considered an age-related disease that, over the next 10 years, will become the most prevalent health problem worldwide. Although cancer therapy has remarkably improved in the last few decades, novel treatment concepts are needed to defeat this disease. Photodynamic Therapy (PDT) signalize a pathway to treat and manage several types of cancer. Over the past three decades, new light sources and photosensitizers (PS) have been developed to be applied in PDT. Nevertheless, there is a lack of knowledge to explain the main biochemical routes needed to trigger regulated cell death mechanisms, affecting, considerably, the scope of the PDT. Although autophagy modulation is being raised as an interesting strategy to be used in cancer therapy, the main aspects referring to the autophagy role over cell succumbing PDT-photoinduced damage remain elusive. Several reports emphasize cytoprotective autophagy, as an ultimate attempt of cells to cope with the photo-induced stress and to survive. Moreover, other underlying molecular mechanisms that evoke PDT-resistance of tumor cells were considered. We reviewed the paradigm about the PDT-regulated cell death mechanisms that involve autophagic impairment or boosted activation. To comprise the autophagy-targeted PDT-protocols to treat cancer, it was underlined those that alleviate or intensify PDT-resistance of tumor cells. Thereby, this review provides insights into the mechanisms by which PDT can be used to modulate autophagy and emphasizes how this field represents a promising therapeutic strategy for cancer treatment.

Selective photodynamic effects on cervical cancer cells provided by P123 Pluronic®-based nanoparticles modulating hypericin delivery

At present, cervical cancer is the fourth leading cause of cancer among women worldwide with no effective treatment options. In this study we aimed to evaluate the efficacy of hypericin (HYP) encapsulated on Pluronic® P123 (HYP/P123) photodynamic therapy (PDT) in a comprehensive panel of human cervical cancer-derived cell lines, including HeLa (HPV 18-positive), SiHa (HPV 16-positive), CaSki (HPV 16 and 18-positive), and C33A (HPV-negative), compared to a nontumorigenic human epithelial cell line (HaCaT). Were investigated: (i) cell cytotoxicity and phototoxicity, cellular uptake and subcellular distribution; (ii) cell death pathway and cellular oxidative stress; (iii) migration and invasion. Our results showed that HYP/P123 micelles had effective and selective time- and dose-dependent phototoxic effects on cervical cancer cells but not in HaCaT. Moreover, HYP/P123 micelles accumulated in endoplasmic reticulum, mitochondria and lysosomes, resulting in photodynamic cell death mainly by necrosis. HYP/P123 induced cellular oxidative stress mainly via type II mechanism of PDT and inhibited cancer cell migration and invasion mainly via MMP-2 inhibition. Taken together, our results indicate a potentially useful role of HYP/P123 micelles as a platform for HYP delivery to more specifically and effectively treat cervical cancers through PDT, suggesting they are worthy for in vivo preclinical evaluations.

Luminescent Ru(ii)-thiol modified silver nanoparticles for lysosome targeted theranostics

Silver nanoparticles (AgNPs) modified by luminescent Ru(ii) complexes not only possess bright red fluorescence but also can target lysosomes. Cell imaging and a cytotoxicity study suggest that Ru1-2·AgNPs may act as a potential theranostic agent.

Ready player one? Autophagy shapes resistance to photodynamic therapy in cancers

Photodynamic therapy (PDT) is a procedure used in cancer therapy that has been shown to be useful for certain indications. Considerable evidence suggests that PDT might be superior to conventional modalities for some indications. In this report, we examine the relationship between PDT responsiveness and autophagy, which can exert a cytoprotective effect. Autophagy is an essential physiological process that maintains cellular homeostasis by degrading dysfunctional or impaired cellular components and organelles via a lysosome-based pathway. Autophagy, which includes macroautophagy and microautophagy, can be a factor that decreases or abolishes responses to various therapeutic protocols. We systematically discuss the mechanisms underlying cell-fate decisions elicited by PDT; analyse the principles of PDT-induced autophagy, macroautophagy and microautophagy; and present evidence to support the notion that autophagy is a critical mechanism in resistance to PDT. A combined strategy involving autophagy inhibitors may be able to further enhance PDT efficacy. Finally, we provide suggestions for future studies, note where our understanding of the relevant molecular regulators is deficient, and discuss the correlations among PDT-induced resistance and autophagy, especially microautophagy.

Immunogenic Cell Death and Immunotherapy of Multiple Myeloma

Over the past decades, immunotherapy has demonstrated a prominent clinical efficacy in a wide variety of human tumors. For many years, apoptosis has been considered a non-immunogenic or tolerogenic process whereas necrosis or necroptosis has long been acknowledged to play a key role in inflammation and immune-related processes. However, the new concept of “immunogenic cell death” (ICD) has challenged this traditional view and has granted apoptosis with immunogenic abilities. This paradigm shift offers clear implications in designing novel anti-cancer therapeutic approaches. To date, several screening studies have been carried out to discover bona fide ICD inducers and reveal the inherent capacity of a wide variety of drugs to induce cell death-associated exposure of danger signals and to bring about in vivo anti-cancer immune responses. Recent shreds of evidence place ER stress at the core of all the scenarios where ICD occur. Furthermore, ER stress and the unfolded protein response (UPR) have emerged as important targets in different human cancers. Notably, in multiple myeloma (MM), a lethal plasma cell disorder, the elevated production of immunoglobulins leaves these cells heavily reliant on the survival arm of the UPR. For that reason, drugs that disrupt ER homeostasis and engage ER stress-associated cell death, such as proteasome inhibitors, which are currently used for the treatment of MM, as well as novel ER stressors are intended to be promising therapeutic agents in MM. This not only holds true for their capacity to induce cell death, but also to their potential ability to activate the immunogenic arm of the ER stress response, with the ensuing exposure of danger signals. We provide here an overview of the up-to-date knowledge regarding the cell death mechanisms involved in situations of ER stress with a special focus on the connections with the drug-induced ER stress pathways that evoke ICD. We will also discuss how this could assist in optimizing and developing better immunotherapeutic approaches, especially in MM treatment.

Autophagy in Human Health and Disease: Novel Therapeutic Opportunities

SIGNIFICANCE

In eukaryotes, autophagy represents a highly evolutionary conserved process, through which macromolecules and cytoplasmic material are degraded into lysosomes and recycled for biosynthetic or energetic purposes. Dysfunction of the autophagic process has been associated with the onset and development of many human chronic pathologies, such as cardiovascular, metabolic, and neurodegenerative diseases as well as cancer. Recent Advances: Currently, comprehensive research is being carried out to discover new therapeutic agents that are able to modulate the autophagic process in vivo. Recent evidence has shown that a large number of natural bioactive compounds are involved in the regulation of autophagy by modulating several transcriptional factors and signaling pathways.

CRITICAL ISSUES

Critical issues that deserve particular attention are the inadequate understanding of the complex role of autophagy in disease pathogenesis, the limited availability of therapeutic drugs, and the lack of clinical trials. In this context, the effects that natural bioactive compounds exert on autophagic modulation should be clearly highlighted, since they depend on the type and stage of the pathological conditions of diseases.

FUTURE DIRECTIONS

Research efforts should now focus on understanding the survival-supporting and death-promoting roles of autophagy, how natural compounds interact exactly with the autophagic targets so as to induce or inhibit autophagy and on the evaluation of their pharmacological effects in a more in-depth and mechanistic way. In addition, clinical studies on autophagy-inducing natural products are strongly encouraged, also to highlight some fundamental aspects, such as the dose, the duration, and the possible synergistic action of these compounds with conventional therapy.

Breast cancer resistance protein is the enemy of hypericin accumulation and toxicity of hypericin-mediated photodynamic therapy

Breast cancer resistance protein (BCRP) belongs to the family of ATP-binding cassette (ABC) transporters, overexpression of which can confer a multidrug-resistant phenotype in cancer cells and tumors. BCRP mediates efflux of numerous xenobiotics, including various chemotherapeutic agents and photosensitizers. Hypericin (HY) is a naturally-occurring photosensitizer synthesized by plants of the genus Hypericum. Our recently published results indicate that accumulation of HY in cancer cells of different tissue origin can be affected mostly by BCRP. Considering all known facts, the main goal of this study was to verify whether not only HY accumulation but also toxicity of HY-mediated photodynamic therapy (PDT) can be affected by the presence of some ABC transporters. To specifically prove our hypothesis, we used an experimental model of human leukemia cell lines differing in the expression level of the main drug efflux transporters P-glycoprotein (P-gp), multidrug resistance-associated protein 1 (MRP1) and BCRP. The lowest HY accumulation, and consequently the highest resistance to HY-PDT, was found in cells overexpressing BCRP. Moreover, pretreatment with BCRP inhibitor Ko143 significantly increased HY accumulation and sensitized cells to HY-PDT. Therefore, our findings represent direct evidence that BCRP is the nemesis of HY accumulation and toxicity of HY-PDT. Thus, we should emphasize that individualized screening for BCRP expression and activity may represent a useful tool for prediction of HY-mediated photodynamic diagnosis (PDD) or PDT effectiveness.

Recruitment of LC3 to damaged Golgi apparatus

LC3 is a protein that can associate with autophagosomes, autolysosomes, and phagosomes. Here, we show that LC3 can also redistribute toward the damaged Golgi apparatus where it clusters with SQSTM1/p62 and lysosomes. This organelle-specific relocation, which did not involve the generation of double-membraned autophagosomes, could be observed after Golgi damage was induced by various strategies, namely (i) laser-induced localized cellular damage, (ii) local expression of peroxidase and exposure to peroxide and diaminobenzidine, (iii) treatment with the Golgi-tropic photosensitizer redaporfin and light, (iv) or exposure to the Golgi-tropic anticancer peptidomimetic LTX-401. Mechanistic exploration led to the conclusion that both reactive oxygen species-dependent and -independent Golgi damage induces a similar phenotype that depended on ATG5 yet did not depend on phosphatidylinositol-3-kinase catalytic subunit type 3 and Beclin-1. Interestingly, knockout of ATG5 sensitized cells to Golgi damage-induced cell death, suggesting that the pathway culminating in the relocation of LC3 to the damaged Golgi may have a cytoprotective function.

Mechanistic and structural insights into the in vitro inhibitory action of hypericin on glutathione reductase purified from baker's yeast

This work aims at studying the interaction between glutathione reductase (GR) and hypericin. The type of inhibition was determined by measuring changes in GR activity at increasing concentrations of hypericin as well as at varying concentrations of glutathione disulfide (GSSG) and nicotinamide adenine dinucleotide phosphate (NADPH), and the binding pose of hypericin was predicted by molecular docking. Accordingly, hypericin emerges as an effective inhibitor of GR. When the variable substrate is GSSG, the type of inhibition is competitive. When the variable substrate is NADPH, however, the type of inhibition appears to be linear mixed-type competitive. Our computational analyses suggest that hypericin binds in the large intermonomer cavity of GR, and that it may interfere with the normal positioning/functioning of the redox-active disulfide center at the enzyme's active site. Overall, besides its contributory role in promoting oxidative stress via the formation of reactive oxygen species in photodynamic therapy, hypericin can also weaken cancer cells through inhibiting GR.

Inhibition of autophagy sensitizes cancer cells to Photofrin-based photodynamic therapy

Background

Accumulating evidence suggest that autophagy plays a pivotal role in various anticancer therapies, including photodynamic therapy (PDT), acting as a pro-death or pro-survival mechanism in a context-dependent manner. Therefore, we aimed to determine the role of autophagy in Photofrin-based PDT.

Methods

In vitro cytotoxic/cytostatic effects of PDT were evaluated with crystal violet cell viability assay. Autophagy induction was analyzed by immunoblotting and immunofluorescence using anti-LC3 antibody. Autophagy was inhibited by shRNA-mediated ATG5 knockdown or CRISPR/Cas9-mediated ATG5 knockout. Apoptosis was assessed by flow cytometry analysis of propidium iodide and anexin V-positive cells as well as by detection of cleaved PARP and caspase 3 proteins using immunoblotting. Protein carbonylation was evaluated by the 2,4-dinitrophenylhydrazine (DNPH) method.

Results

Photofrin-PDT leads to robust autophagy induction in two cancer cell lines, Hela and MCF-7. shRNA-mediated knockdown of ATG5 only partially blocks autophagic response and only marginally affects the sensitivity of Hela and MCF-7 cells to PDT. ATG5 knockout in HeLa cell line utilizing CRISPR/Cas9 genome editing results in increased PDT-mediated cytotoxicity, which is accompanied by an enhanced apoptotic response and increased accumulation of carbonylated proteins.

Conclusions

Altogether, these observations imply that autophagy contributes to Photofrin-PDT resistance by enabling clearance of carbonylated and other damaged proteins. Therefore, autophagy inhibition may serve as a strategy to improve PDT efficacy.

Activation of autophagy by elevated reactive oxygen species rather than released silver ions promotes cytotoxicity of polyvinylpyrrolidone-coated silver nanoparticles in hematopoietic cells

Silver nanoparticles (AgNPs) are the most commonly used engineered nanomaterials in commercialized products because of their antimicrobial activity. Previously, we have shown that polyvinylpyrrolidone (PVP)-coated AgNPs have an anti-leukemia effect against human myeloid leukemia cells; however, whether AgNPs are able to trigger autophagy in normal hematopoietic cells and the role of autophagy in AgNP-induced cytotoxicity remain unclear. In the current study, we observed that AgNPs were taken up by murine pro-B cells (Ba/F3), and then promoted accumulation of autophagosomes, which resulted from the induction of autophagy rather than the blockade of autophagic flux. AgNPs induced cytotoxicity in a dose-dependent manner accompanied by apoptosis and DNA damage through the production of reactive oxygen species (ROS) and the release of silver ions. The ROS-mediated mTOR signaling pathway was responsible for the induction of autophagy. More importantly, the inhibition of autophagy with the addition of 3-methyladenine (3-MA) or silencing of Atg5 significantly attenuated the cytotoxicity of AgNPs in Ba/F3. These findings suggest that autophagy is involved in the cytotoxicity of PVP-coated AgNPs in normal hematopoietic cells, and the inhibition of autophagy is a novel and potent strategy to protect normal hematopoietic cells upon treatment with AgNPs.

Autophagy supports generation of cells with high CD44 expression via modulation of oxidative stress and Parkin-mediated mitochondrial clearance

High CD44 expression is associated with enhanced malignant potential in esophageal squamous cell carcinoma (ESCC), amongst the deadliest of all human carcinomas. Although alterations in autophagy and CD44 expression are associated with poor patient outcomes in various cancer types, the relationship between autophagy and cells with high CD44 expression remains incompletely understood. In transformed esophageal keratinocytes, CD44^Low-CD24^High (CD44L) cells give rise to CD44^High-CD24^−/Low (CD44H) cells via epithelial-mesenchymal transition (EMT) in response to transforming growth factor (TGF)-β. We couple patient samples and xenotransplantation studies with this tractable in vitro system of CD44L to CD44H cell conversion to investigate the functional role of autophagy in generation of cells with high CD44 expression. We report that high expression of the autophagy marker cleaved LC3 expression correlates with poor clinical outcome in ESCC. In ESCC xenograft tumors, pharmacological autophagy inhibition with chloroquine derivatives depletes cells with high CD44 expression while promoting oxidative stress. Autophagic flux impairment during EMT-mediated CD44L to CD44H cell conversion in vitro induces mitochondrial dysfunction, oxidative stress and cell death. During CD44H cell generation, transformed keratinocytes display evidence of mitophagy, including mitochondrial fragmentation, decreased mitochondrial content and mitochondrial translocation of Parkin, essential in mitophagy. RNA interference-mediated Parkin depletion attenuates CD44H cell generation. These data suggest that autophagy facilitates EMT-mediated CD44H generation via modulation of redox homeostasis and Parkin-dependent mitochondrial clearance. This is the first report to implicate mitophagy in regulation of tumor cells with high CD44 expression, representing a potential novel therapeutic avenue in cancers where EMT and CD44H cells have been implicated, including ESCC.

Cisplatin and resveratrol induce apoptosis and autophagy following oxidative stress in malignant mesothelioma cells

Malignant mesothelioma (MM) is characterized by poor responsiveness to current chemotherapeutic drugs, usually owing to high resistance to apoptosis. Here, we investigated chemosensitizing effects of phytochemical resveratrol, in combination with cisplatin, on MM cells. The combination treatment of cisplatin and resveratrol (CDDP/RSV) synergistically induced apoptosis, as evidenced by typical cell morphological changes, the appearance of sub-G0/G1 peak, an increase in the Annexin V(+) cells and the cleavage of caspase-3 and PARP. CDDP/RSV increased ROS production and depolarization of mitochondrial membrane potential with an increase in the Bax/Bcl-2 ratio. These changes were attenuated by pretreatment with N-acetylcysteine, suggesting that CDDP/RSV induced apoptosis through oxidative mitochondrial damage. Compared with MSTO-211H cells, CDDP/RSV was less efficient in killing H-2452 cells. H-2452 cells exhibited an enhanced autophagy to CDDP/RSV, as observed by an increase in viable cells exhibiting intense LysoTracker Red staining and up-regulation of Beclin-1 and LC3A. Inhibition of autophagy by bafilomycin A1 rendered cells more sensitive to CDDP/RSV-induced cytotoxicity and this was associated with induction of apoptosis. These data indicate that the increased resistance of H-2452 cells to CDDP/RSV is closely related to the activation of self-defensive autophagy, and provide the rationale for targeting the autophagy regulation in the treatment of MM.

Hypericin in the Light and in the Dark: Two Sides of the Same Coin

Hypericin (4,5,7,4',5',7'-hexahydroxy-2,2'-dimethylnaphtodianthrone) is a naturally occurring chromophore found in some species of the genus Hypericum, especially Hypericum perforatum L. (St. John's wort), and in some basidiomycetes (Dermocybe spp.) or endophytic fungi (Thielavia subthermophila). In recent decades, hypericin has been intensively studied for its broad pharmacological spectrum. Among its antidepressant and light-dependent antiviral actions, hypericin is a powerful natural photosensitizer that is applicable in the photodynamic therapy (PDT) of various oncological diseases. As the accumulation of hypericin is significantly higher in neoplastic tissue than in normal tissue, it can be used in photodynamic diagnosis (PDD) as an effective fluorescence marker for tumor detection and visualization. In addition, light-activated hypericin acts as a strong pro-oxidant agent with antineoplastic and antiangiogenic properties, since it effectively induces the apoptosis, necrosis or autophagy of cancer cells. Moreover, a strong affinity of hypericin for necrotic tissue was discovered. Thus, hypericin and its radiolabeled derivatives have been recently investigated as potential biomarkers for the non-invasive targeting of tissue necrosis in numerous disorders, including solid tumors. On the other hand, several light-independent actions of hypericin have also been described, even though its effects in the dark have not been studied as intensively as those of photoactivated hypericin. Various experimental studies have revealed no cytotoxicity of hypericin in the dark; however, it can serve as a potential antimetastatic and antiangiogenic agent. On the contrary, hypericin can induce the expression of some ABC transporters, which are often associated with the multidrug resistance (MDR) of cancer cells. Moreover, the hypericin-mediated attenuation of the cytotoxicity of some chemotherapeutics was revealed. Therefore, hypericin might represent another St. John's wort metabolite that is potentially responsible for negative herb-drug interactions. The main aim of this review is to summarize the benefits of photoactivated and non-activated hypericin, mainly in preclinical and clinical applications, and to uncover the "dark side" of this secondary metabolite, focusing on MDR mechanisms.

SIRT3-SOD2-mROS-dependent autophagy in cadmium-induced hepatotoxicity and salvage by melatonin

Cadmium is one of the most toxic metal compounds found in the environment. It is well established that Cd induces hepatotoxicity in humans and multiple animal models. Melatonin, a major secretory product of the pineal gland, has been reported to protect against Cd-induced hepatotoxicity. However, the mechanism behind this protection remains to be elucidated. We exposed HepG2 cells to different concentrations of cadmium chloride (2.5, 5, and 10 μM) for 12 h. We found that Cd induced mitochondrial-derived superoxide anion-dependent autophagic cell death. Specifically, Cd decreased SIRT3 protein expression and activity and promoted the acetylation of SOD2, superoxide dismutase 2, mitochondrial, thus decreasing its activity, a key enzyme involved in mitochondrial ROS production, although Cd did not disrupt the interaction between SIRT3 and SOD2. These effects were ameliorated by overexpression of SIRT3. However, a catalytic mutant of SIRT3 (SIRT3^H248Y) lacking deacetylase activity lost the capacity to suppress Cd-induced autophagy. Notably, melatonin treatment enhanced the activity but not the expression of SIRT3, decreased the acetylation of SOD2, inhibited mitochondrial-derived O₂^•− production and suppressed the autophagy induced by 10 μM Cd. Moreover, 3-(1H-1,2,3-triazol-4-yl)pyridine, a confirmed selective SIRT3 inhibitor, blocked the melatonin-mediated suppression of autophagy by inhibiting SIRT3-SOD2 signaling. Importantly, melatonin suppressed Cd-induced autophagic cell death by enhancing SIRT3 activity in vivo. These results suggest that melatonin exerts a hepatoprotective effect on mitochondrial-derived O₂^•−-stimulated autophagic cell death that is dependent on the SIRT3/SOD2 pathway.

Autophagy, a major adaptation pathway shaping cancer cell death and anticancer immunity responses following photodynamic therapy

Autophagy is fundamentally a cytoprotective and pro-survival process yet studies have shown that it has an exceedingly contextual role in cancer biology; depending on the phase, location or type of oncogenic trigger and/or therapy, its role could fluctuate from pro- to anti-tumourigenic.

New functions of mitochondria associated membranes in cellular signaling

In all eukaryotic cells, the endoplasmic reticulum (ER) and the mitochondria establish a tight interplay, which is structurally and functionally modulated through a proteinaceous tether formed at specific subdomains of the ER membrane, designated mitochondria-associated membranes or MAMs. The tethering function of the MAMs allows the regulation of lipid synthesis and rapid transmission of calcium (Ca(2+)) signals between the ER and mitochondria, which is crucial to shape intracellular Ca(2+) signaling and regulate mitochondrial bioenergetics. Research on the molecular characterization and function of MAMs has boomed in the last few years and the list of signaling and structural proteins dynamically associated with the ER-mitochondria contact sites in physiological and pathological conditions, is rapidly increasing along with the realization of an unprecedented complexity underlying the functional role of MAMs. Besides their established role as a signaling hub for Ca(2+) and lipid transfer between ER and mitochondria, MAMs have been recently shown to regulate mitochondrial shape and motility, energy metabolism and redox status and to be central to the modulation of various key processes like ER stress, autophagy and inflammasome signaling. In this review we will discuss some emerging cell-autonomous and cell non-autonomous roles of the MAMs in mammalian cells and their relevance for important human diseases. This article is part of a Special Issue entitled: Calcium signaling in health and disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.

ER stress, autophagy and immunogenic cell death in photodynamic therapy-induced anti-cancer immune responses

Tumours are a form of pseudo-organs with their own microenvironment where the cancer cells nurture a dysfunctional immune environment incapable of inciting anti-tumour immunity. It had been proposed that the only way to counteract such an immune system dysfunction in tumours is by eliciting, therapeutically, a cancer cell death pathway that is accompanied by high immunogenicity and possibly inhibits or reduces the influence of the pro-tumourigenic cytokine signalling. Subsequently, a small and a large-scale screening study as well as several targeted studies found that few, selected anticancer therapeutic regimens are able to induce a promising kind of cancer cell demise called immunogenic cell death (ICD), which can activate the immune system owing to the spatiotemporally defined emission of danger signals. Recently, photodynamic therapy (PDT) utilizing the photosensitiser, hypericin (Hyp), became the first PDT paradigm characterized to be capable of inducing bona fide ICD. In the present perspective, we discuss the various technical, conceptual, and molecular advancements and unprecedented results revealed by Hyp-PDT that have influenced the fields of ICD, ER stress biology, cancer cell death, anti-cancer immune responses, photoimmunology and PDT.

p38(MAPK)-regulated induction of p62 and NBR1 after photodynamic therapy promotes autophagic clearance of ubiquitin aggregates and reduces reactive oxygen species levels by supporting Nrf2-antioxidant signaling

Emerging evidence indicates that oxidative stress instigates the formation of ubiquitin (Ub) aggregates, substrates of autophagy, through a process requiring the ubiquitin binding adaptors p62/SQSTM1 and NBR1. Here, we have investigated the role of p62 and NBR1 in cell survival after hypericin-mediated photodynamic therapy (Hyp-PDT), a procedure known to incite robust reactive oxygen species (ROS)-based endoplasmic reticulum stress and autophagy pathways. We found that Hyp-PDT stimulated the formation of p62- and NBR1-associated Ub aggregates in normal and cancer cells, which were ultimately removed by autophagy, through a mechanism partially regulated by p38(MAPK). In line with this, genetic or pharmacological p38(MAPK) inhibition reduced p62 and NBR1 levels and aggregate formation and impaired Nrf2 activation, thus increasing photo-oxidative stress and cell death. p62-deficient cells, or cells lacking p62 and with reduced levels of NBR1 (through siRNA knockdown), also displayed reduced aggregate formation but exhibited attenuated ROS levels, reduced caspase activation, and improved survival after Hyp-PDT. The increased resistance to photo-oxidative stress exhibited by cells lacking p62 and/or NBR1 was overruled by the inhibition of p38(MAPK), which restored cytotoxic ROS levels, thus indicating the relevance of this signal in the control of cell viability. Taken together these findings provide evidence that in photodynamically treated cells a p38(MAPK)-regulated pathway coordinates the p62/NBR1-mediated clearance of cytosolic aggregates and mitigates PDT-induced proteotoxicity. They also reveal that a functional p38(MAPK)-Nrf2 signal is required to keep ROS levels in check and protect against PDT-induced proteotoxicity, independent of aggregate formation.

Autophagy-dependent suppression of cancer immunogenicity and effector mechanisms of innate and adaptive immunity

The inspection of the mechanisms through which autophagy modulates immunogenic cell death revealed that the autophagic response of cancer cells to reactive oxygen species-dependent endoplasmic reticulum stress suppresses the exposure of calreticulin on the cell surface, the phenotypic maturation of dendritic cells (DCs) as well as their ability to release interleukin-6 and to support the proliferative expansion of (interferon γ-producing) CD4⁺ and CD8⁺ T lymphocytes. These findings unveil an unprecedented role for therapy-induced autophagy in suppressing key mechanisms that underlie anticancer immune responses as elicited by immunogenic cell death.

The omega-3 polyunsaturated fatty acid DHA induces simultaneous apoptosis and autophagy via mitochondrial ROS-mediated Akt-mTOR signaling in prostate cancer cells expressing mutant p53

Docosahexaenoic acid (DHA) induces autophagy-associated apoptotic cell death in wild-type p53 cancer cells via regulation of p53. The present study investigated the effects of DHA on PC3 and DU145 prostate cancer cell lines harboring mutant p53. Results show that, in addition to apoptosis, DHA increased the expression levels of lipidated form LC3B and potently stimulated the autophagic flux, suggesting that DHA induces both autophagy and apoptosis in cancer cells expressing mutant p53. DHA led to the generation of mitochondrial reactive oxygen species (ROS), as shown by the mitochondrial ROS-specific probe mitoSOX. Similarly, pretreatment with the antioxidant N-acetyl-cysteine (NAC) markedly inhibited both the autophagy and the apoptosis triggered by DHA, indicating that mitochondrial ROS mediate the cytotoxicity of DHA in mutant p53 cells. Further, DHA reduced the levels of phospho-Akt and phospho-mTOR in a concentration-dependent manner, while NAC almost completely blocked that effect. Collectively, these findings present a novel mechanism of ROS-regulated apoptosis and autophagy that involves Akt-mTOR signaling in prostate cancer cells with mutant p53 exposed to DHA.