Autophagy inhibition strategy for advanced nanomedicine

Nano-enhanced immunotherapy: Targeting the immunosuppressive tumor microenvironment

The tumor microenvironment (TME), which is mostly composed of tumor cells, immune cells, signaling molecules, stromal tissue, and the vascular system, is an integrated system that is conducive to the formation of tumors. TME heterogeneity makes the response to immunotherapy different in different tumors, such as "immune-cold" and "immune-hot" tumors. Tumor-associated macrophages, myeloid-derived suppressor cells, and regulatory T cells are the major suppressive immune cells and their different phenotypes interact and influence cancer cells by secreting different signaling factors, thus playing a key role in the formation of the TME as well as in the initiation, growth, and metastasis of cancer cells. Nanotechnology development has facilitated overcoming the obstacles that limit the further development of conventional immunotherapy, such as toxic side effects and lack of targeting. In this review, we focus on the role of three major suppressive immune cells in the TME as well as in tumor development, clinical trials of different drugs targeting immune cells, and different attempts to combine drugs with nanomaterials. The aim is to reveal the relationship between immunotherapy, immunosuppressive TME and nanomedicine, thus laying the foundation for further development of immunotherapy.

Assessment of changes in autophagic vesicles in human immune cell lines exposed to nano particles

Background

Safe and rational development of nanomaterials for clinical translation requires the assessment of potential biocompatibility. Autophagy, a critical homeostatic pathway intrinsically linked to cellular health and inflammation, has been shown to be affected by nanomaterials. It is, therefore, important to be able to assess possible interactions of nanomaterials with autophagic processes.

Results

CEM (T cell), Raji (B lymphocyte), and THP-1 (human monocyte) cell lines were subject to treatment with rapamycin and chloroquine, known to affect the autophagic process, in order to evaluate cell line-specific responses. Flow cytometric quantification of a fluorescent autophagic vacuole stain showed that maximum observable effects (105%, 446%, and 149% of negative controls) were achieved at different exposure durations (8, 6, and 24 h for CEM, Raji, and THP-1, respectively). THP-1 was subsequently utilised as a model to assess the autophagic impact of a small library of nanomaterials. Association was observed between hydrodynamic size and autophagic impact (r² = 0.11, p = 0.004). An ELISA for p62 confirmed the greatest impact by 10 nm silver nanoparticles, abolishing p62, with 50 nm silica and 180 nm polystyrene also lowering p62 to a significant degree (50%, 74%, and 55%, respectively, p < 0.05).

Conclusions

This data further supports the potential for a variety of nanomaterials to interfere with autophagic processes which, in turn, may result in altered cellular function and viability. The association of particle size with impact on autophagy now warrants further investigation.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00648-8.

An Updated Review on Implications of Autophagy and Apoptosis in Tumorigenesis: Possible Alterations in Autophagy through Engineered Nanomaterials and Their Importance in Cancer Therapy

Most commonly recognized as a catabolic pathway, autophagy is a perplexing mechanism through which a living cell can free itself of excess cytoplasmic components, i.e., organelles, by means of certain membranous vesicles or lysosomes filled with degrading enzymes. Upon exposure to external insult or internal stimuli, the cell might opt to activate such a pathway, through which it can gain control over the maintenance of intracellular components and thus sustain homeostasis by intercepting the formation of unnecessary structures or eliminating the already present dysfunctional or inutile organelles. Despite such appropriateness, autophagy might also be considered a frailty for the cell, as it has been said to have a rather complicated role in tumorigenesis. A merit in the early stages of tumor formation, autophagy appears to be salutary because of its tumor-suppressing effects. In fact, several investigations on tumorigenesis have reported diminished levels of autophagic activity in tumor cells, which might result in transition to malignancy. On the contrary, autophagy has been suggested to be a seemingly favorable mechanism to progressed malignancies, as it contributes to survival of such cells. Based on the recent literature, this mechanism might also be activated upon the entry of engineered nanomaterials inside a cell, supposedly protecting the host from foreign materials. Accordingly, there is a good chance that therapeutic interventions for modulating autophagy in malignant cells using nanoparticles may sensitize cancerous cells to certain treatment modalities, e.g., radiotherapy. In this review, we will discuss the signaling pathways involved in autophagy and the significance of the mechanism itself in apoptosis and tumorigenesis while shedding light on possible alterations in autophagy through engineered nanomaterials and their potential therapeutic applications in cancer. SIGNIFICANCE STATEMENT: Autophagy has been said to have a complicated role in tumorigenesis. In the early stages of tumor formation, autophagy appears to be salutary because of its tumor-suppressing effects. On the contrary, autophagy has been suggested to be a favorable mechanism to progressed malignancies. This mechanism might be affected upon the entry of nanomaterials inside a cell. Accordingly, therapeutic interventions for modulating autophagy using nanoparticles may sensitize cancerous cells to certain therapies.

PEG-Ceramide Nanomicelles Induce Autophagy and Degrade Tau Proteins in N2a Cells

Purpose

Alzheimer’s disease (AD) is a neurodegenerative disorder that manifests as abnormal behavior and a progressive decline in memory. Although the pathogenesis of AD is due to the excessive deposition of amyloid β protein (Aβ) outside the neurons in the brain, evidence suggests that tau proteins may be a better target for AD therapy. In neurodegenerative diseases, a decrease in autophagy results in the failure to eliminate abnormally deposited or misfolded proteins. Therefore, induction of autophagy may be an effective way to eliminate tau proteins in the treatment of AD. We investigated the effects of polyethylene glycol (PEG)-ceramide nanomicelles on autophagy and on tau proteins in N2a, a murine neuroblastoma metrocyte cell line.

Methods

Ceramide is a sphingolipid bioactive molecule that induces autophagy. PEG-ceramide is a polymer that is composed of the hydrophobic chain of ceramide and the hydrophilic chain of PEG-2000. In this study, we prepared PEG-ceramide nanomicelles that were 10–20 nm in size and had nearly neutral zeta potential.

Results

The results show that PEG-ceramide nanomicelles caused an increase in the LC3-II/LC3-I ratio, while p62 protein levels decreased. Confocal microscopy revealed a significant increase in the number of dots corresponding to autophagosomes and autolysosomes, which indicated autophagic activation. Moreover, PEG-ceramide nanomicelles induced tau degradation in N2a cells through autophagy.

Conclusion

In summary, we have confirmed that PEG-ceramide nanomicelles enhanced autophagic flux and degraded overexpressed human tau proteins in N2a cells by regulating the autophagy pathway. Thus, PEG-ceramide nanomicelles show great promise as agents to induce autophagy and degrade tau proteins in the treatment of AD.

Intracellular Trafficking Network and Autophagy of PHBHHx Nanoparticles and their Implications for Drug Delivery

3-hydroxybutyrate-co-3-hydroxyhexanoate (PHBHHx), which is naturally generated by biodegradable polyhydroxyalkanoates synthesized by bacteria, is an attractive material for drug delivery due to its controllable physical properties, non-toxicity, environmental friendliness, degradable properties and good biocompatibility. However, the intracellular trafficking network pathways, especially the autophagy mechanism of PHBHHx nanoparticles (NPs), have rarely been investigated. In this paper, we successfully prepared the NPs used solvent displacement method and investigated the autophagy pathways and other intracellular trafficking mechanisms based on NPs with the assistance of Rab proteins. We found that NPs were internalized in cells mainly via clathrin endocytosis and caveolin endocytosis. Beside the classical pathways, we discovered two new pathways: the micropinocytosis early endosome (EEs)-micropinocytosis-lysosome pathway and the EEs-liposome-lysosome pathway. NPs were delivered to cells through endocytosis recycling vesicles and GLUT4 exocytosis vesicles. Similar to other nanoparticles, NPs also induced intracellular autophagy and were then degraded via endolysosomal pathways. 3-MA and CQ were used as autophagy inhibitors to avoid the degradation of NPs through lysosomes by blocking endolysosomal pathways. Tumor volumes and weights were significantly decreased when autophagy inhibitors and chemical drugs packaged in NPs were cooperatively used.

The mechanism of lauric acid-modified protein nanocapsules escape from intercellular trafficking vesicles and its implication for drug delivery

Protein nanocapsules have exhibited promising potential applications in the field of protein drug delivery. A major issue with various promising nano-sized biotherapeutics including protein nanocapsules is that owing to their particle size they are subject to cellular uptake via endocytosis, and become entrapped and then degraded within endolysosomes, which can significantly impair their therapeutic efficacy. In addition, many nano-sized biotherapeutics could be also sequestered by autophagosomes and degraded through the autolysosomal pathway. Thus, a limiting step in achieving an effective protein therapy is to facilitate the endosomal escape and auto-lysosomal escape to ensure cytosolic delivery of the protein drugs. Here, we prepared a protein nanocapsule based on BSA (nBSA) and the BSA nanocapsules modified with a bilayer of lauric acid (LA-nBSA) to investigate the escape effects from the endosome and autophagosome. The size distribution of nBSA and LA-nBSA analyzed using DLS presents a uniform diameter centered at 10 nm and 16 nm. The data also showed that FITC-labeled nBSA and LA-nBSA were taken up by the cells mainly through Arf-6-dependent endocytosis and Rab34-mediated macropinocytosis. In addition, LA-nBSA could efficiently escape from endosomal before the degradation in endo-lysosomes. Autophagy could also sequester the LA-nBSA through p62 autophagosome vesicles. These two types of nanocapsules underwent different intracellular destinies and lauric acid (LA) coating played a vital role in intracellular particle retention. In conclusion, the protein nanocapsules modified with LA could enhance the protein nanocapsules escape from intercellular trafficking vesicles, and protect the protein from degradation by the lysosomes.

Nanodiamond-based non-canonical autophagy inhibitor synergistically induces cell death in oxygen-deprived tumors

Blockage of autophagic flux by nanodiamonds induces apoptosis in hypoxic tumor cells with minimal toxicity to normal tissues and enhances the effects of anti-angiogenic therapy.

A functional nanocarrier that copenetrates extracellular matrix and multiple layers of tumor cells for sequential and deep tumor autophagy inhibitor and chemotherapeutic delivery

To further enhance the intensity of deep tumor drug delivery and integrate a combined therapy, we herein report on a core-shell nanocarrier that could simultaneously overcome the double barriers of the extracellular matrix (ECM) and multiple layers of tumor cells (MLTC). A pH-triggered reversible swelling-shrinking core and an MMP2 (matrix metallopeptidase 2) degradable shell were developed to encapsulate chemotherapeutics and macroautophagy/autophagy inhibitors, respectively. MMP2 degraded the shell, which was followed by the autophagy inhibitors' release. The exposed core could diffuse along the pore within the ECM to deliver chemotherapeutics into deep tumors, and it was able to swell in lysosomes and shrink back in the cytoplasm or ECM. The swelling of the core resulted in the rapid release of chemotherapeutics to kill autophagy-inhibited cells. After leaving the dead cells, the shrinking core could act on neighboring cells that were closer to the center of the tumor. The core thus could also cross MLTC layer by layer to deliver chemotherapeutics into the deep tumor.

Nanomedicine strategies for sustained, controlled and targeted treatment of cancer stem cells

Cancer stem cells (CSCs) are original cancer cells that are of characteristics associated with normal stem cells. CSCs are toughest against various treatments and thus responsible for cancer metastasis and recurrence. Therefore, development of specific and effective treatment of CSCs plays a key role in improving survival and life quality of cancer patients, especially those in the metastatic stage. Nanomedicine strategies, which include prodrugs, micelles, liposomes and nanoparticles of biodegradable polymers, could substantially improve the therapeutic index of conventional therapeutics due to its manner of sustained, controlled and targeted delivery of high transportation efficiency across the cell membrane and low elimination by intracellular autophagy, and thus provide a practical solution to solve the problem encountered in CSCs treatment. This review gives briefly the latest information to summarize the concept, strategies, mechanisms and current status as well as future promises of nanomedicine strategies for treatment of CSCs.

Cationic liposomes induce cell necrosis through lysosomal dysfunction and late-stage autophagic flux inhibition

AIM

The application of cationic liposomes (CLs) as nonviral vectors is hampered by their cellular toxicity. Thus we aim to investigate the mechanisms underlying the cellular toxicity of CLs.

MATERIALS & METHODS

The effect of CLs on the autophagic flux, autophagosome-lysosome fusion, lysosome membrane permeabilization and cell necrosis of liver cells was investigated.

RESULTS & CONCLUSION

Our results reveal a novel mechanism of CL-induced cell necrosis involving the induction of lysosome membrane permeabilization and late-stage autophagic flux inhibition that resulted in cytoplasmic release of cathepsin B, mitochondrial dysfunction and reactive oxygen species production, which are the key mediators of cell necrosis. Our study is important for revealing the cellular toxicity of CLs and designing safer gene delivery systems.

Intracellular Trafficking Network of Protein Nanocapsules: Endocytosis, Exocytosis and Autophagy

The inner membrane vesicle system is a complex transport system that includes endocytosis, exocytosis and autophagy. However, the details of the intracellular trafficking pathway of nanoparticles in cells have been poorly investigated. Here, we investigate in detail the intracellular trafficking pathway of protein nanocapsules using more than 30 Rab proteins as markers of multiple trafficking vesicles in endocytosis, exocytosis and autophagy. We observed that FITC-labeled protein nanoparticles were internalized by the cells mainly through Arf6-dependent endocytosis and Rab34-mediated micropinocytosis. In addition to this classic pathway: early endosome (EEs)/late endosome (LEs) to lysosome, we identified two novel transport pathways: micropinocytosis (Rab34 positive)-LEs (Rab7 positive)-lysosome pathway and EEs-liposome (Rab18 positive)-lysosome pathway. Moreover, the cells use slow endocytosis recycling pathway (Rab11 and Rab35 positive vesicles) and GLUT4 exocytosis vesicles (Rab8 and Rab10 positive) transport the protein nanocapsules out of the cells. In addition, protein nanoparticles are observed in autophagosomes, which receive protein nanocapsules through multiple endocytosis vesicles. Using autophagy inhibitor to block these transport pathways could prevent the degradation of nanoparticles through lysosomes. Using Rab proteins as vesicle markers to investigation the detail intracellular trafficking of the protein nanocapsules, will provide new targets to interfere the cellular behaver of the nanoparticles, and improve the therapeutic effect of nanomedicine.

Nanomaterial-modulated autophagy: underlying mechanisms and functional consequences

Autophagy is an essential lysosome-dependent process that controls the quality of the cytoplasm and maintains cellular homeostasis, and dysfunction of this protein degradation system is correlated with various disorders. A growing body of evidence suggests that nanomaterials (NMs) have autophagy-modulating effects, thus predicting a valuable and promising application potential of NMs in the diagnosis and treatment of autophagy-related diseases. NMs exhibit unique physical, chemical and biofunctional properties, which may endow NMs with capabilities to modulate autophagy via various mechanisms. The present review highlights the impacts of various NMs on autophagy and their functional consequences. The possible underlying mechanisms for NM-modulated autophagy are also discussed.

Enhancing therapeutic effects of docetaxel-loaded dendritic copolymer nanoparticles by co-treatment with autophagy inhibitor on breast cancer

Dendrimers are synthetic nanocarriers that comprise a highly branched spherical polymer as new, efficient tools for drug delivery. However, the fate of nanocarriers after being internalized into cells has seldom been studied. Docetaxel loaded dendritic copolymer H40-poly(D,L-lactide) nanoparticles, referred to as “DTX-H40-PLA NPs”, were prepared and used as a model to evaluate whether the NPs were sequestered by autophagy and fused with lysosomes. Besides being degraded through the endolysosomal pathway, the DTX-loaded H40-PLA NPs were also sequestered by autophagosomes and degraded through the autolysosomal pathway. DTX-loaded H40-PLA NPs may stop exerting beneficial effects after inducing autophagy of human MCF-7 cancer cells. Co-delivery of autophagy inhibitor such as chloroquine and chemotherapeutic drug DTX by dendritic copolymer NPs greatly enhanced cancer cell killing in vitro, and decreased both the volume and weight of the tumors in severe combined immunodeficient mice. These findings provide valuable evidence for development of nanomedicine such as dendritic copolymer NPs for clinical application.