Destination 'lysosome': a target organelle for tumour cell killing?

A Carrier-Free Nanomedicine Enables Apoptosis-Ferroptosis Synergistic Breast Cancer Therapy by Targeting Subcellular Organelles

The heterogeneity of cancer cells disables the single-cell death patterns in subtypes of cells with different genotypes and phenotypes, such as refractory triple-negative breast cancer (TNBC). Therefore, the combination of multiple death modes, such as the proven cooperative apoptosis and ferroptosis, is expected to sensitize in treating TNBC. Herein, carrier-free theranostic ASP nanoparticles (NPs) were designed for wiping out TNBC by synergistic apoptosis and ferroptosis, which was self-assembled by aurantiamide acetate (Aa), scutebarbatine A (SA), and palmitin (P). Structurally, the rigid parent nucleus of SA and hydrophobic chain of P combined with the Aa to form an ordered nanostructure by noncovalent bonding forces. This self-assembly example applies to the design of nanomedicines based on more than two natural products. Notably, enhanced permeability and retention (EPR) effects and mitochondrial-lysosomal targeting empower ASP NPs to pinpoint tumor sites. Especially, Aa and P induced mitochondrial apoptosis of cancer cells, while SA and P inhibited TNBC by ferroptosis and upregulating p53. More interestingly, the combination of Aa, SA, and P enhanced the uptake of ASP NPs by cancer cell membranes. Overall, the three compounds synergize with each other to exert excellent anticancer effects.

A novel antimicrobial peptide M1-8 targets the lysosomal pathway to inhibit autolysosome formation and promote apoptosis in liver cancer cells

Lysosomes, a central regulator of autophagy, play a critical role in tumour growth. Lysosomal protease cathepsin D can initiate apoptosis when released from lysosomes into the cytosol. In this study, we observed that Musca domestica cecropin (Mdc) 1-8 (M1-8), a small anti-tumour peptide derived from Mdc, inhibits hepatoma cell growth by blocking autophagy-lysosome fusion. This effect is likely achieved by targeting lysosomes to activate lysosomal protease D. Additionally, we examined whether lysosomal content and cathepsin D release were involved in M1-8-induced apoptosis. After exposure to M1-8, human hepatoma HepG2 cells rapidly co-localized with lysosomes, disrupted lysosomal integrity, caused leakage of lysosomal protease cathepsin D, caspase activation and mitochondrial membrane potential changes; and promoted cell apoptosis. Interestingly, in M1-8-treated HepG2 cells, autophagic protein content increased and the lysosome-autophagosome fusion was inhibited, suggesting that M1-8 can cause apoptosis through autophagy and lysosomes. This result indicates that a small accumulation of autophagy and autolysosome inhibition in cells can cause cell death. Taken together, these data suggest a novel insight into the regulatory mechanisms of M1-8 in autophagy and lysosomes, which may facilitate the development of M1-8 as a potential cancer therapeutic agent.

flgC gene is involved in the virulence regulation of Pseudomonas plecoglossicida and affects the immune response of Epinephelus coioides

As a pathogen of cultured teleosts, Pseudomonas plecoglossicida has caused significant economic losses. flgC plays an important role in encoding flagellar basal-body rod proteins. Our previous studies revealed the high expression of P. plecoglossicida flgC in infected Epinephelus coioides. To explore the role of flgC in the virulence of P. plecoglossicida and the immune response of E. coioides to the infection of P. plecoglossicida, flgC gene of P. plecoglossicida was knocked down by RNA interference (RNAi). The results showed that the flgC gene in all four mutants of P. plecoglossicida was significantly knocked down, and the mutant with the best knockdown efficiency of 94.3% was selected for subsequent studies. Compared with the NZBD9 strain of P. plecoglossicida, the flgC-RNAi strain showed a significantly decrease in chemotaxis, motility, adhesion, and biofilm formation. Furthermore, compared with the E. coioides infected with the NZBD9 strain, the infection of flgC-RNAi strain resulted in the infected E. coioides a 1.5-day delay in the time of first death and an 80% increase in survival rate, far fewer white nodules upon the spleen surfaces, and lower pathogen load in the spleens. RNAi of flgC significantly influenced the metabolome and transcriptome of the spleen in infected E. coioides. KEGG enrichment analysis exhibited that the Toll-like receptor signaling pathway was the most enriched immune pathway; the most significantly enriched metabolic pathways were associated with Linoleic acid metabolism, Choline metabolism in cancer, and Glycerophospholipid metabolism. Further combined analysis of transcriptome and metabolome indicated significant correlations among pantothenate and CoA biosynthesis, beta-alanine metabolism, lysosome metabolites, and related genes. These results suggested that flgC was a pathogenic gene of P. plecoglossicida; flgC was associated with the regulation of chemotaxis, motility, biofilm formation, and adhesion; flgC influenced the immune response of E. coioides to the infection of P. plecoglossicida.

High Expression of the Lysosomal Protease Cathepsin D Confers Better Prognosis in Neuroblastoma Patients by Contrasting EGF-Induced Neuroblastoma Cell Growth

Neuroblastoma is a malignant extracranial solid tumor arising from the sympathoadrenal lineage of the neural crest and is often associated with N-MYC amplification. Cathepsin D has been associated with chemoresistance in N-MYC-overexpressing neuroblastomas. Increased EGFR expression also has been associated with the aggressive behavior of neuroblastomas. This work aimed to understand the mechanisms linking EGFR stimulation and cathepsin D expression with neuroblastoma progression and prognosis. Gene correlation analysis in pediatric neuroblastoma patients revealed that individuals bearing a high EGFR transcript level have a good prognosis only when CTSD (the gene coding for the lysosomal protease Cathepsin D, CD) is highly expressed. Low CTSD expression was associated with poor clinical outcome. CTSD expression was negatively correlated with CCNB2, CCNA2, CDK1 and CDK6 genes involved in cell cycle division. We investigated the biochemical pathways downstream to EGFR stimulation in human SH-SY5Y neuroblastoma cells engineered for overexpressing or silencing of CD expression. Cathepsin D overexpression decreased the proliferative potential of neuroblastoma cells through downregulation of the pro-oncogenic MAPK signaling pathway. EGFR stimulation downregulated cathepsin D expression, thus favoring cell cycle division. Our data suggest that chemotherapeutics that inhibit the EGFR pathway, along with stimulators of cathepsin D synthesis and activity, could benefit neuroblastoma prognosis.

LRRK2 along the Golgi and lysosome connection: a jamming situation

Parkinson's disease (PD) is an age-related neurodegenerative disorder, clinically characterized by bradykinesia, rigidity, and resting tremor. Leucine-Rich Repeat Kinase 2 (LRRK2) is a large, multidomain protein containing two enzymatic domains. Missense mutations in its coding sequence are amongst the most common causes of familial PD. The physiological and pathological impact of LRRK2 is still obscure, but accumulating evidence supports a role for LRRK2 in membrane and vesicle trafficking, mainly functioning in the endosome-recycling system, (synaptic) vesicle trafficking, autophagy, and lysosome biology. LRRK2 binds and phosphorylates key regulators of the endomembrane systems and is dynamically localized at the Golgi. The impact of LRRK2 on the Golgi may reverberate throughout the entire endomembrane system and occur in multiple intersecting pathways, including endocytosis, autophagy, and lysosomal function. This would lead to overall dysregulation of cellular homeostasis and protein catabolism, leading to neuronal dysfunction and accumulation of toxic protein species, thus underlying the possible neurotoxic effect of LRRK2 mutations causing PD.

Potential therapies and diagnosis based on Golgi-targeted nano drug delivery systems

With the rapid development of nanotechnology, organelle-targeted nano drug delivery systems (NDDSs) have emerged as a potential method which can transport drugs specifically to the subcellular compartments like nucleus, mitochondrion, lysosome, endoplasmic reticulum (ER) and Golgi apparatus (GA). GA not only plays a key role in receiving, modifying, packaging and transporting proteins and lipids, but also contributes to a set of cellular processes. Golgi-targeted NDDSs can alter the morphology of GA and will become a promising strategy with high specificity, low-dose administration and decreased occurrence of side effects. In this review, Golgi-targeted NDDSs and their applications in disease therapies and diagnosis such as cancer, metastasis, fibrosis and neurological diseases are introduced. Meanwhile, modifications of NDDSs to achieve targeting strategies, Golgi-disturbing agents to change the morphology of GA, special endocytosis to achieve endosomal/lysosomal escape strategies are also involved.

Dosage-controlled intracellular delivery mediated by acoustofluidics for lab on a chip applications

Biological research and many cell-based therapies rely on the successful delivery of cargo materials into cells. Intracellular delivery in an in vitro setting refers to a variety of physical and biochemical techniques developed for conducting rapid and efficient transport of materials across the plasma membrane. Generally, the techniques that are time-efficient (e.g., electroporation) suffer from heterogeneity and low cellular viability, and those that are precise (e.g., microinjection) suffer from low-throughput and are labor-intensive. Here, we present a novel in vitro microfluidic strategy for intracellular delivery, which is based on the acoustic excitation of adherent cells. Strong mechanical oscillations, mediated by Lamb waves, inside a microfluidic channel facilitate the cellular uptake of different size (e.g., 3-500 kDa, plasmid encoding EGFP) cargo materials through endocytic pathways. We demonstrate successful delivery of 500 kDa dextran to various adherent cell lines with unprecedented efficiency in the range of 65-85% above control. We also show that actuation voltage and treatment duration can be tuned to control the dosage of delivered substances. High viability (≥91%), versatility across different cargo materials and various adherent cell lines, scalability to hundreds of thousands of cells per treatment, portability, and ease-of-operation are among the unique features of this acoustofluidic strategy. Potential applications include targeting through endocytosis-dependant pathways in cellular disorders, such as lysosomal storage diseases, which other physical methods are unable to address. This novel acoustofluidic method achieves rapid, uniform, and scalable delivery of material into cells, and may find utility in lab-on-a-chip applications.

Recent progress of surface-enhanced Raman spectroscopy for subcellular compartment analysis

Organelles are involved in many cell life activities, and their metabolic or functional disorders are closely related to apoptosis, neurodegenerative diseases, cardiovascular diseases, and the development and metastasis of cancers. The explorations of subcellular structures, microenvironments, and their abnormal conditions are conducive to a deeper understanding of many pathological mechanisms, which are expected to achieve the early diagnosis and the effective therapy of diseases. Organelles are also the targeted locations of drugs, and they play significant roles in many targeting therapeutic strategies. Surface-enhanced Raman spectroscopy (SERS) is a powerful analytical tool that can provide the molecular fingerprint information of subcellular compartments and the real-time cellular dynamics in a non-invasive and non-destructive way. This review aims to summarize the recent advances of SERS studies on subcellular compartments, including five parts. The introductions of SERS and subcellular compartments are given. SERS is promising in subcellular compartment studies due to its molecular specificity and high sensitivity, and both of which highly match the high demands of cellular/subcellular investigations. Intracellular SERS is mainly cataloged as the labeling and label-free methods. For subcellular targeted detections and therapies, how to internalize plasmonic nanoparticles or nanostructure in the target locations is a key point. The subcellular compartment SERS detections, SERS measurements of isolated organelles, investigations of therapeutic mechanisms from subcellular compartments and microenvironments, and integration of SERS diagnosis and treatment are sequentially presented. A perspective view of the subcellular SERS studies is discussed from six aspects. This review provides a comprehensive overview of SERS applications in subcellular compartment researches, which will be a useful reference for designing the SERS-involved therapeutic systems.

Time-Resolved Luminescent High-Throughput Screening Platform for Lysosomotropic Compounds in Living Cells

Lysosomes are membrane-bound organelles that regulate protein degradation and cellular organelle recycling. Homeostatic alteration by lysosomotropic compounds has been suggested as a potential approach for the treatment of cancer. However, because of the high false-negative rate resulting from strong fluorescent background noise, few luminescent high-throughput screening methods for lysosomotropic compounds have been developed for cancer therapy. Imidazole is a five-membered heterocycle that can act within the acidic interior of lysosomes. To develop an efficient lysosomotropic compound screening system, we introduced an imidazole group to iridium-based complexes and designed a long-lifetime lysosomal probe to monitor lysosomal activity in living cells. By integrating time-resolved emission spectroscopy (TRES) with the novel iridium-based lysosomal probe, a high-throughput screening platform capable of overcoming background fluorescent interference in living cells was developed for discovering lysosomotropic drugs. As a proof-of-concept, 400 FDA/EMA-approved drugs were screened using the TRES system, revealing five compounds as potential lysosomotropic agents. Significantly, the most promising potent lysosomotropic compound (mitoxantrone) identified in this work would have showed less activity if screened using a commercial lysosomal probe because of interference from the intrinsic fluorescence of mitoxantrone. We anticipate that this TRES-based high-throughput screening system could facilitate the development of more lysosomotropic drugs by avoiding false results arising from the intrinsic fluorescence of both bioactive compounds and/or the cell background.

Fabry keratopathy: manifestations and changes over time

AIMS

The goal was to find if changes in Fabry keratopathy were clinically observable over time. Also observed were variations of Fabry keratopathy, supplemental features, unique presentations and differences between keratopathies of right and left corneas and the same family and genotype.

METHODS

Biomicroscopic images of Fabry keratopathy in 10 persons with classic Fabry disease, 5 men and 5 women, were captured over an 18-month period. The keratopathies were categorised and scrutinised for changes over time, and differences between corneas of the same individual, family and genotype.

RESULTS

Fabry keratopathy ranged from mild change to marked change over 18 months. There was a great variety of whorl patterns. A few keratopathies were amorphous without vortices and many vortices were supplemented with amorphous features. All keratopathies were accompanied by diffuse epithelial haze. There was a range from negligible difference to marked difference between right and left eyes of the same individuals with similarities appearing as imprecise mirror images of each other. In some corneas, prominent vertical streams from the superior limbus integrated into the primary keratopathy. Comparisons between persons with the same family and genotype were obscured by gender and differences between right and left eyes.

CONCLUSIONS

Practitioners should be better able to detect Fabry disease having a fuller understanding of the variety of presentations of the dynamic, pathognomonic Fabry keratopathy. Routes of continuous centripetal renewal of corneal epithelium are spatially unique to each eye, in some cases subsidised by direct contribution of basal cells streamed from the superior limbus.

Recent Advances in Subcellular Targeted Cancer Therapy Based on Functional Materials

Recently, diverse functional materials that take subcellular structures as therapeutic targets are playing increasingly important roles in cancer therapy. Here, particular emphasis is placed on four kinds of therapies, including chemotherapy, gene therapy, photodynamic therapy (PDT), and hyperthermal therapy, which are the most widely used approaches for killing cancer cells by the specific destruction of subcellular organelles. Moreover, some non-drug-loaded nanoformulations (i.e., metal nanoparticles and molecular self-assemblies) with a fatal effect on cells by influencing the subcellular functions without the use of any drug molecules are also included. According to the basic principles and unique performances of each treatment, appropriate strategies are developed to meet task-specific applications by integrating specific materials, ligands, as well as methods. In addition, the combination of two or more therapies based on multifunctional nanostructures, which either directly target specific subcellular organelles or release organelle-targeted therapeutics, is also introduced with the intent of superadditive therapeutic effects. Finally, the related challenges of critical re-evaluation of this emerging field are presented.

Altered pH gradient at the plasma membrane of osteosarcoma cells is a key mechanism of drug resistance

Current therapy of osteosarcoma (OS), the most common primary bone malignancy, is based on a combination of surgery and chemotherapy. Multidrug resistance mediated by P-glycoprotein (P-gp) overexpression has been previously associated with treatment failure and progression of OS, although other mechanisms may also play a role. We considered the typical acidic extracellular pH (pHe) of sarcomas, and found that doxorubicin (DXR) cytotoxicity is reduced in P-gp negative OS cells cultured at pHe 6.5 compared to standard 7.4. Short-time (24-48 hours) exposure to low pHe significantly increased the number and acidity of lysosomes, and the combination of DXR with omeprazole, a proton pump inhibitor targeting lysosomal acidity, significantly enhanced DXR cytotoxicity. In OS xenografts, the combination treatment of DXR and omeprazole significantly reduced tumor volume and body weight loss. The impaired toxicity of DXR at low pHe was not associated with increased autophagy or lysosomal acidification, but rather, as shown by SNARF staining, with a reversal of the pH gradient at the plasma membrane (ΔpHcm), eventually leading to a reduced DXR intracellular accumulation. Finally, the reversal of ΔpHcm in OS cells promoted resistance not only to DXR, but also to cisplatin and methotrexate, and, to a lesser extent, to vincristine. Altogether, our findings show that, in OS cells, short-term acidosis induces resistance to different chemotherapeutic drugs by a reversal of ΔpHcm, suggesting that buffer therapies or regimens including proton pump inhibitors in combination to low concentrations of conventional anticancer agents may offer novel solutions to overcome drug resistance.

Selective induction of apoptosis in MCF7 cancer-cell by targeted liposomes functionalised with mannose-6-phosphate

Liposomes are versatile platforms to carry anticancer drugs in targeted drug delivery; they can be surface modified by different strategies and, when coupled with targeting ligands, are able to increase cellular internalisation and organelle-specific drug delivery. An interesting strategy of antitumoral therapy could involve the use of lysosomotropic ligand-targeted liposomes loaded with molecules, which can induce lysosomal membrane permeabilization (LMP), leakage of cathepsins into the cytoplasm and subsequent apoptosis. We have previously demonstrated the ability of liposomes functionalised with a mannose-6-phosphate to reach lysosomes; in this research we compare the behaviour of M6P-modified and non-functionalised liposomes in MCF7 tumour cell and in HDF normal cells. With this aim, we first demonstrated by Western blotting the overexpression of mannose-6-phosphate/insulin-like growth factor (M6P/IGF-II) receptor in MCF7. Then, we prepared calcein-loaded liposomes and we revealed the increased uptake of M6P-functionalised liposomes in MCF7 cells respect to HDF cells by flow cytometry analysis. Finally, we loaded functionalised and not functionalised liposomes with N-hexanoyl-d-erythro-sphingosine (C6Cer), able to initiate LMP-induced apoptosis; after having studied the stability of both vesicles in the presence of serum by Dynamic Light Scattering and Spectrophotometric turbidity measurements, we showed that ceramide-loaded M6P-liposomes significantly increased apoptosis in MCF7 with respect to HDF cells.

Autocrine mechanisms of cancer chemoresistance

An ever-increasing number of studies highlight the role of cancer secretome in the modification of tumour microenvironment and in the acquisition of cancer cell resistance to therapeutic drugs. The knowledge of the mechanisms underlying the relationship between cancer cell-secreted factors and chemoresistance is becoming fundamental for the identification of novel anticancer therapeutic strategies overcoming drug resistance and novel prognostic secreted biomarkers. In this review, we summarize the novel findings concerning the regulation of secreted molecules by cancer cells compromising drug sensitivity. In particular, we highlight data from available literature describing the involvement of cancer cell-secreted molecules determining chemoresistance in an autocrine manner, including: i) growth factors; ii) glycoproteins; iii) inflammatory cytokines; iv) enzymes and chaperones; and v) tumor-derived exosomes.

An Active 32-kDa Cathepsin L Is Secreted Directly from HT 1080 Fibrosarcoma Cells and Not via Lysosomal Exocytosis

Cathepsin L [EC 3.4.22.15] is secreted via lysosomal exocytosis by several types of cancer cells, including prostate and breast cancer cells. We previously reported that human cultured fibrosarcoma (HT 1080) cells secrete cathepsin L into the medium; this secreted cathepsin is 10-times more active than intracellular cathepsin. This increased activity was attributed to the presence of a 32-kDa cathepsin L in the medium. The aim of this study was to examine how this active 32-kDa cathepsin L is secreted into the medium. To this end, we compared the secreted active 32-kDa cathepsin L with lysosomal cathepsin L by using a novel gelatin zymography technique that employs leupeptin. We also examined the glycosylation and phosphorylation status of the proteins by using the enzymes endoglycosidase H [EC 3.2.1.96] and alkaline phosphatase [EC 3.1.3.1]. Strong active bands corresponding to the 32-kDa and 34-kDa cathepsin L forms were detected in the medium and lysosomes, respectively. The cell extract exhibited strong active bands for both forms. Moreover, both forms were adsorbed onto a concanavalin A-agarose column. The core protein domain of both forms had the same molecular mass of 30 kDa. The 32-kDa cathepsin L was phosphorylated, while the 34-kDa lysosomal form was dephosphorylated, perhaps because of the lysosomal marker enzyme, acid phosphatase. These results suggest that the active 32-kDa form does not enter the lysosomes. In conclusion, our results indicate that the active 32-kDa cathepsin L is secreted directly from the HT 1080 cells and not via lysosomal exocytosis.

Impairment of lysosomal activity as a therapeutic modality targeting cancer stem cells of embryonal rhabdomyosarcoma cell line RD

Rhabdomyosarcoma is the most frequent soft tissue sarcoma in children and adolescents, with a high rate of relapse that dramatically affects the clinical outcome. Multiagent chemotherapy, in combination with surgery and/or radiation therapy, is the treatment of choice. However, the relapse rate is disappointingly high and identification of new therapeutic tools is urgently needed. Under this respect, the selective block of key features of cancer stem cells (CSC) appears particularly promising. In this study, we isolated rhabdomyosarcoma CSC with stem-like features (high expression of NANOG and OCT3/4, self-renewal ability, multipotency). Rhabdomyosarcoma CSC showed higher invasive ability and a reduced cytotoxicity to doxorubicin in comparison to native cells, through a mechanism unrelated to the classical multidrug resistance process. This was dependent on a high level of lysosome acidity mediated by a high expression of vacuolar ATPase (V-ATPase). Since it was not associated with other paediatric cancers, like Ewing’s sarcoma and neuroblastoma, V-ATPase higher expression in CSC was rhabdomyosarcoma specific. Inhibition of lysosomal acidification by the V-ATPase inhibitor omeprazole, or by specific siRNA silencing, significantly enhanced doxorubicin cytoxicity. Unexpectedly, lysosomal targeting also blocked cell growth and reduced the invasive potential of rhabdomyosarcoma CSC, even at very low doses of omeprazole (10 and 50 µM, respectively). Based on these observations, we propose lysosome acidity as a valuable target to enhance chemosensitivity of rhabdomyosarcoma CSC, and suggest the use of anti-V-ATPase agents in combination with standard regimens as a promising tool for the eradication of minimal residual disease or the prevention of metastatic disease.

In vitro and in vivo anticancer activity of surface modified paclitaxel attached hydroxyapatite and titanium dioxide nanoparticles

Targeted drug delivery using nanocrystalline materials delivers the drug at the diseased site. This increases the efficacy of the drug in killing the cancer cells. Surface modifications were done to target the drug to a particular receptor on the cell surface. This paper reports synthesis of hydroxyapatite and titanium dioxide nanoparticles and modification of their surface with polyethylene glycol (PEG) followed by folic acid (FA). Paclitaxel, an anticancer drug, is attached to functionalized hydroxyapatite and titanium dioxide nanoparticles. The pure and functionalised nanoparticles are characterised with XRD, TEM and UV spectroscopy. Anticancer analysis was carried out in DEN induced hepatocarcinoma animals. Biochemical, hematological and histopathological analysis show that the surface modified paclitaxel attached nanoparticles have an higher anticancer activity than the pure paclitaxel and surface modified nanoparticles without paclitaxel. This is due to the targeting of the drug to the folate receptor in the cancer cells.

Harnessing the lysosome-dependent antitumor activity of phenothiazines in human small cell lung cancer

Phenothiazines are a family of heterocyclic compounds whose clinical utility includes treatment of psychiatric disorders as well as chemotherapy-induced emesis. Various studies have demonstrated that these compounds possess cytotoxic activities in tumor cell lines of different origin. However, there is considerable confusion regarding the molecular basis of phenothiazine-induced cell death. Lung cancer (LC) remains one of the most prevalent and deadly malignancies worldwide despite considerable efforts in the development of treatment strategies, especially new targeted therapies. In this work, we evaluated the potential utility of phenothiazines in human LC. We show that phenothiazines as single treatment decreased cell viability and induced cell death preferentially in small cell lung carcinoma (SCLC) over non small cell lung carcinoma (NSCLC) cell lines. Sensitivity to phenothiazines was not correlated with induction of apoptosis but due to phenothiazine-induced lysosomal dysfunction. Interestingly, the higher susceptibility of SCLC cells to phenothiazine-induced cell death correlated with an intrinsically lower buffer capacity in response to disruption of lysosomal homeostasis. Importantly, this effect in SCLC occurred despite mutation in p53 and was not influenced by intrinsic sensitivity/resistance toward conventional chemotherapeutic agents. Our data thus uncovered a novel context-dependent activity of phenothiazines in SCLC and suggest that phenothiazines could be considered as a treatment regimen of this disease, however, extended cell line analyses as well as in vivo studies are needed to make such conclusion.

Liposomes containing mannose-6-phosphate-cholesteryl conjugates for lysosome-specific delivery

We present a novel liposomal nanocarrier containing mannose 6-phosphate-cholesteryl conjugates and show its ability to reach the lysosomes by means of confocal and fluorescence microscopy measurements.

Knockdown of cathepsin D in zebrafish fertilized eggs determines congenital myopathy

CD (cathepsin D) is a ubiquitous lysosomal hydrolase involved in a variety of pathophysiological functions, including protein turnover, activation of pro-hormones, cell death and embryo development. CD-mediated proteolysis plays a pivotal role in tissue and organ homoeostasis. Altered expression and compartmentalization of CD have been observed in diseased muscle fibres. Whether CD is actively involved in muscle development, homoeostasis and dystrophy remains to be demonstrated. Zebrafish (Danio rerio) is emerging as a valuable ‘in vivo’ vertebrate model for muscular degeneration and congenital myopathies. In this work, we report on the perturbance of the somitic musculature development in zebrafish larvae caused by MPO (morpholino)-mediated silencing of CD in oocytes at the time of fertilization. Restoring CD expression, using an MPO-non-matching mutated mRNA, partially rescued the normal phenotype, confirming the indispensable role of CD in the correct development and integrity of the somitic musculature. This is the first report showing a congenital myopathy caused by CD deficiency in a vertebrate experimental animal model.

Involvement of lysosomal exocytosis in the excretion of mesoporous silica nanoparticles and enhancement of the drug delivery effect by exocytosis inhibition

The exocytosis of phosphonate modified mesoporous silica nanoparticles (P-MSNs) is demonstrated and lysosomal exocytosis is identified as the mechanism responsible for this event. Regulation of P-MSN exocytosis can be achieved by inhibiting or accelerating lysosomal exocytosis. Slowing down P-MSN exocytosis enhances the drug delivery effect of CPT-loaded P-MSNs by improving cell killing.

Similarities and differences in the biogenesis, processing and lysosomal targeting between zebrafish and human pro-Cathepsin D: functional implications

The lysosomal protease Cathepsin D (CD) plays a role in neurodegenerative diseases, cancer, and embryo-fetus abnormalities. It is therefore of interest to know how this protein is synthesized in animal species used for modeling human diseases. Zebrafish (Danio rerio) is emerging as a valuable 'in vivo' vertebrate model for several human diseases. We have characterized the biogenetic pathways of zebrafish and human CD transgenically expressed in both human SH-SY5Y cells and zebrafish PAC2 cells. Differently from human CD, zebrafish CD was synthesized as a mono-glycosylated precursor (pro-CD) that was eventually processed into a single-chain mature polypeptide. In PAC2 cells, ammonium chloride and chloroquine impaired the N-glycosylation, and greatly stimulated the secretion, of pro-CD; still, a portion of un-glycosylated pro-CD reached the lysosomes and was processed to mature CD. The treatment with tunicamycin, which abrogates N-glycosylation, resulted in a similar effect. Zebrafish pro-CD was correctly processed when expressed in human cells, and its glycosylation, transport and maturation were not impaired by ammonium chloride. On the contrary, the transport and processing of human pro-CD expressed in zebrafish cells were profoundly altered: while the intermediate single-chain was not detectable, a small amount of double-chain mature CD still formed. This fact indicates that the enzyme machinery for single- to double-chain processing of mammal CD is present in zebrafish. Our data highlight the respective impact of the information imparted by the primary sequence and of the cellular transport and processing machineries in the biogenesis of lysosomal CD.

Interactions of nanomaterials and biological systems: Implications to personalized nanomedicine

The application of nanotechnology to personalized medicine provides an unprecedented opportunity to improve the treatment of many diseases. Nanomaterials offer several advantages as therapeutic and diagnostic tools due to design flexibility, small sizes, large surface-to-volume ratio, and ease of surface modification with multivalent ligands to increase avidity for target molecules. Nanomaterials can be engineered to interact with specific biological components, allowing them to benefit from the insights provided by personalized medicine techniques. To tailor these interactions, a comprehensive knowledge of how nanomaterials interact with biological systems is critical. Herein, we discuss how the interactions of nanomaterials with biological systems can guide their design for diagnostic, imaging and drug delivery purposes. A general overview of nanomaterials under investigation is provided with an emphasis on systems that have reached clinical trials. Finally, considerations for the development of personalized nanomedicines are summarized such as the potential toxicity, scientific and technical challenges in fabricating them, and regulatory and ethical issues raised by the utilization of nanomaterials.

Increased apoptosis in cancer cells in vitro and in vivo by ceramides in transferrin-modified liposomes

Lysosomes are a promising therapeutic target for induction apoptosis in cancer cells due to lysosomal membrane permeabilization (LMP) leading to leakage of hydrolytic enzymes, especially the cathepsins, into the cytoplasm. We hypothesized that with the modification of the ceramide-loaded liposomes with transferrin (Tf), we would achieve both tumor targeting and increased delivery of lysosome-destabilizing agents, such as ceramides to lysosomes, to initiate LMP-induced apoptosis. We prepared Tf-modified (TL) and plain (PL) liposomes and loaded with short (C6)- or long (C16) N-acyl chain ceramides. Uptake, intracellular localization of liposomes, stability of the lysosomal membrane and release of cathepsin D were investigated on Hela cells by fluorescence microscopy and flow cytometry. Apoptosis was evaluated by binding of fluorescently-labeled Annexin V. Antitumor and pro-apoptotic effects of C6Cer-loaded Tf-liposomes were demonstrated in vivo in an A2780-ovarian carcinoma xenograft mouse model. TL were internalized specifically via the TfR-dependent endocytic pathway and localized within the endosome-lysosomal compartment. Ceramide-loaded Tf-liposomes significantly increased apoptosis compared with ceramide-free and ceramide-loaded non-modified liposomes. The treatment of cancer cells with TL led to increased LMP and cytoplasmic relocation of the intralysosomal cathepsin D. A strong antitumor and pro-apoptotic effect of C6Cer-loaded TL was also demonstrated in vivo in an A2780-ovarian carcinoma xenograft mouse model. The lysosomal accumulation of ceramides delivered by Tf-liposomes initiates the permeabilization of the lysosomal membranes required for the release of lysosomal cathepsins into the cytoplasm and initiation of the cancer cell apoptosis both in vitro and in vivo.

Biocompatibility, endocytosis, and intracellular trafficking of mesoporous silica and polystyrene nanoparticles in ovarian cancer cells: effects of size and surface charge groups

Background and methods

Nanoparticles engineered to carry both a chemotherapeutic drug and a sensitive imaging probe are valid tools for early detection of cancer cells and to monitor the cytotoxic effects of anticancer treatment simultaneously. Here we report on the effect of size (10–30 nm versus 50 nm), type of material (mesoporous silica versus polystyrene), and surface charge functionalization (none, amine groups, or carboxyl groups) on biocompatibility, uptake, compartmentalization, and intracellular retention of fluorescently labeled nanoparticles in cultured human ovarian cancer cells. We also investigated the involvement of caveolae in the mechanism of uptake of nanoparticles.

Results

We found that mesoporous silica nanoparticles entered via caveolae-mediated endocytosis and reached the lysosomes; however, while the 50 nm nanoparticles permanently resided within these organelles, the 10 nm nanoparticles soon relocated in the cytoplasm. Naked 10 nm mesoporous silica nanoparticles showed the highest and 50 nm carboxyl-modified mesoporous silica nanoparticles the lowest uptake rates, respectively. Polystyrene nanoparticle uptake also occurred via a caveolae-independent pathway, and was negatively affected by serum. The 30 nm carboxyl-modified polystyrene nanoparticles did not localize in lysosomes and were not toxic, while the 50 nm amine-modified polystyrene nanoparticles accumulated within lysosomes and eventually caused cell death. Ovarian cancer cells expressing caveolin-1 were more likely to endocytose these nanoparticles.

Conclusion

These data highlight the importance of considering both the physicochemical characteristics (ie, material, size and surface charge on chemical groups) of nanoparticles and the biochemical composition of the cell membrane when choosing the most suitable nanotheranostics for targeting cancer cells.

Biocompatibility, endocytosis, and intracellular trafficking of mesoporous silica and polystyrene nanoparticles in ovarian cancer cells: effects of size and surface charge groups

BACKGROUND AND METHODS

Nanoparticles engineered to carry both a chemotherapeutic drug and a sensitive imaging probe are valid tools for early detection of cancer cells and to monitor the cytotoxic effects of anticancer treatment simultaneously. Here we report on the effect of size (10-30 nm versus 50 nm), type of material (mesoporous silica versus polystyrene), and surface charge functionalization (none, amine groups, or carboxyl groups) on biocompatibility, uptake, compartmentalization, and intracellular retention of fluorescently labeled nanoparticles in cultured human ovarian cancer cells. We also investigated the involvement of caveolae in the mechanism of uptake of nanoparticles.

RESULTS

We found that mesoporous silica nanoparticles entered via caveolae-mediated endocytosis and reached the lysosomes; however, while the 50 nm nanoparticles permanently resided within these organelles, the 10 nm nanoparticles soon relocated in the cytoplasm. Naked 10 nm mesoporous silica nanoparticles showed the highest and 50 nm carboxyl-modified mesoporous silica nanoparticles the lowest uptake rates, respectively. Polystyrene nanoparticle uptake also occurred via a caveolae-independent pathway, and was negatively affected by serum. The 30 nm carboxyl-modified polystyrene nanoparticles did not localize in lysosomes and were not toxic, while the 50 nm amine-modified polystyrene nanoparticles accumulated within lysosomes and eventually caused cell death. Ovarian cancer cells expressing caveolin-1 were more likely to endocytose these nanoparticles.

CONCLUSION

These data highlight the importance of considering both the physicochemical characteristics (ie, material, size and surface charge on chemical groups) of nanoparticles and the biochemical composition of the cell membrane when choosing the most suitable nanotheranostics for targeting cancer cells.

Targeted polymeric therapeutic nanoparticles: design, development and clinical translation

Polymeric materials have been used in a range of pharmaceutical and biotechnology products for more than 40 years. These materials have evolved from their earlier use as biodegradable products such as resorbable sutures, orthopaedic implants, macroscale and microscale drug delivery systems such as microparticles and wafers used as controlled drug release depots, to multifunctional nanoparticles (NPs) capable of targeting, and controlled release of therapeutic and diagnostic agents. These newer generations of targeted and controlled release polymeric NPs are now engineered to navigate the complex in vivo environment, and incorporate functionalities for achieving target specificity, control of drug concentration and exposure kinetics at the tissue, cell, and subcellular levels. Indeed this optimization of drug pharmacology as aided by careful design of multifunctional NPs can lead to improved drug safety and efficacy, and may be complimentary to drug enhancements that are traditionally achieved by medicinal chemistry. In this regard, polymeric NPs have the potential to result in a highly differentiated new class of therapeutics, distinct from the original active drugs used in their composition, and distinct from first generation NPs that largely facilitated drug formulation. A greater flexibility in the design of drug molecules themselves may also be facilitated following their incorporation into NPs, as drug properties (solubility, metabolism, plasma binding, biodistribution, target tissue accumulation) will no longer be constrained to the same extent by drug chemical composition, but also become in-part the function of the physicochemical properties of the NP. The combination of optimally designed drugs with optimally engineered polymeric NPs opens up the possibility of improved clinical outcomes that may not be achievable with the administration of drugs in their conventional form. In this critical review, we aim to provide insights into the design and development of targeted polymeric NPs and to highlight the challenges associated with the engineering of this novel class of therapeutics, including considerations of NP design optimization, development and biophysicochemical properties. Additionally, we highlight some recent examples from the literature, which demonstrate current trends and novel concepts in both the design and utility of targeted polymeric NPs (444 references).

Labeling and exocytosis of secretory compartments in RBL mastocytes by polystyrene and mesoporous silica nanoparticles

Background

For a safe ‘in vivo’ biomedical utilization of nanoparticles, it is essential to assess not only biocompatibility, but also the potential to trigger unwanted side effects at both cellular and tissue levels. Mastocytes (cells having secretory granules containing cytokines, vasoactive amine, and proteases) play a pivotal role in the immune and inflammatory responses against exogenous toxins. Mastocytes are also recruited in the tumor stroma and are involved in tumor vascularization and growth.

Aim and methods

In this work, mastocyte-like rat basophilic leukemia (RBL) cells were used to investigate whether carboxyl-modified 30 nm polystyrene (PS) nanoparticles (NPs) and naked mesoporous silica (MPS) 10 nm NPs are able to label the secretory inflammatory granules, and possibly induce exocytosis of these granules. Uptake, cellular retention and localization of fluorescent NPs were analyzed by cytofluorometry and microscope imaging.

Results

Our findings were that: (1) secretory granules of mastocytes are accessible by NPs via endocytosis; (2) PS and MPS silica NPs label two distinct subpopulations of inflammatory granules in RBL mastocytes; and (3) PS NPs induce calcium-dependent exocytosis of inflammatory granules.

Conclusion

These findings highlight the value of NPs for live imaging of inflammatory processes, and also have important implications for the clinical use of PS-based NPs, due to their potential to trigger the unwanted activation of mastocytes.

Active targeting of cancer cells using folic acid-conjugated platinum nanoparticles

Interaction of nanoparticles with human cells is an interesting topic for understanding toxicity and developing potential drug candidates. Water soluble platinum nanoparticles were synthesized via reduction of hexachloroplatinic acid using sodium borohydride in the presence of capping agents. The bioactivity of folic acid and poly(vinyl pyrrolidone) capped platinum nanoparticles (Pt-nps) has been investigated using commercially available cell lines. In the cell viability experiments, PVP-capped nanoparticles were found to be less toxic (>80% viability), whereas, folic acid-capped platinum nanoparticles showed a reduced viability down to 24% after 72 h of exposure at a concentration of 100 μg ml(-1) for MCF7 breast cancer cells. Such toxicity, combined with the possibility to incorporate functional organic molecules as capping agents, can be used for developing new drug candidates.

A series of naphthalimide derivatives as intra and extracellular pH sensors

A series of new naphthalimide derivatives were synthesized and studied. Three of the materials (SM1, SM2, and SM3) possess methacrylate(s) moieties as pH sensor monomers, enabling these compounds to be polymerized with other monomers for thin film preparation for extracellular pH sensing. Herein, poly(2-hydroxyethyl methacrylate)-co-poly(acrylamide) (PHEMA-co-PAM) was chosen as the polymer matrix. Structure influences on pH responses and pK(a) values were studied. The film P3 composed of the sensing moiety SM3 has a pK(a) close to the usual biological environmental pH of approximately 7. It was used as an extracellular pH sensor to monitor pH change during the metabolism of prokaryotic Escherichia coli (E. coil). On the other hand, the three sensor monomers are new intracellular biomarkers to sense lysosomes of eukaryotic cells since (1) their pK(a) values are in a range of 5.9-6.8; (2) their emission intensities at acidic conditions (such as at pH 5) are much stronger than those at a neutral condition of pH 7; (3) lysosomes range in size from 0.1 to 1.2 mum in diameter with pH ranging from 4.5 to 5.0, which is much more acidic than the pH value of the cytoplasm (usually with a pH value of approximately 7.2); and (4) the acidity of lysosomes enables a protonation of the amino groups of the pH probes making the sensors emit brightly in acidic organelles by inhibiting the photo-induced electron transfer from the amino groups to the fluorophores. Lysosome sensing was demonstrated using live human brain glioblastoma U87MG cell line, human cervical cancer HeLa cell line, and human esophagus premalignant CP-A and CP-D cell lines by observations of small acidic spherical organelles (lysosomes) and significant colocalizations (82-95%) of the sensors with a commercially available lysosome-selective staining probe LysoTracker Red under confocal fluorescence microscopy.

Effects of hypoxia on expression of a panel of stem cell and chemoresistance markers in glioblastoma-derived spheroids

Tumor hypoxia has been attributed to play a crucial role in tumorigenesis and therapeutic resistance. Recently, it has been suggested that hypoxia leads to and maintains the undifferentiated state of tumor stem cells, thereby contributing to chemoresistance. The aim of the present study is to investigate the influence of hypoxia on the protein expression of a panel of stem cell and chemoresistance markers using in vivo-like multicellular tumor spheroids derived from a glioblastoma short-term culture with tumor stem cell properties (SJ-1) as well as a conventional glioblastoma cell line (U87). Spheroids were formed in 21% and 1% O(2) in serum-free medium. The immunohistochemical panel included hypoxia (HIF-1α, HIF-2α), proliferation (Ki-67), and stem cell markers (CD133, podoplanin, Bmi-1, nestin, Sox-2) as well as markers related to chemoresistance (MGMT, TIMP-1, Lamp-1, MRP1, MDR-1). As spheroids derived in hypoxia were smaller than in normoxia, a set of experiments was included in which the culturing time of hypoxic spheroids was extended to obtain equally sized spheroids. The results showed that expression of HIF-1α and HIF-2α was increased in hypoxia, whereas Ki-67 was reduced. Expression of stem cell markers CD133, podoplanin, Bmi-1, and nestin was increased in hypoxia, whereas Sox-2 was increased in SJ-1 only. TIMP-1 and Lamp-1 were increased in both SJ-1 and U87. In conclusion, the tumor cell phenotype related to stemness, and thereby potentially to chemoresistance, seems to depend on the oxygen tension, suggesting that development of therapeutic strategies targeting tumor stem cells should take oxygen tension into account.

Differential role of cathepsins B and L in autophagy-associated cell death induced by arsenic trioxide in U87 human glioblastoma cells

Arsenic trioxide (arsenite) was the first chemotherapeutic drug to be described and is now being rediscovered in cancer treatment, including glioblastoma multiforme. Arsenite toxicity triggers autophagy in cancer cells, although final stages of the process involve executive caspases, suggesting an interplay between autophagic and apoptotic pathways that awaits to be explained at a molecular level. We evaluated the contribution of the lysosomal cathepsins (Cat) L and B, which are upregulated in glioblastomas, in the mechanism of arsenite toxicity in human glioblastoma cells. Arsenite treatment induced autophagosome formation and permeabilization of mitochondria, followed by caspase 3/7-mediated apoptosis. The autophagy inhibitor 3-methyladenine protected from arsenite toxicity, whereas bafilomycin A1 did not. Furthermore, arsenite significantly decreased CatB levels and selectively inhibited its cellular and recombinant protein activity, while not affecting CatL. However, downregulation of CatL greatly enhanced apoptosis by arsenite. Our results show that arsenite toxicity involves a complex interplay between autophagy and apoptosis in human glioblastoma cells and is associated with inhibition of CatB, and that this toxicity is highly exacerbated by simultaneous CatL inhibition. The latter points to a synergy that could be used in clinical treatment to lower the therapeutic dose, thus avoiding the toxic side effects of arsenite in glioblastoma management.

Photoactive hybrid nanomaterials: indocyanine immobilized in mesoporous MCM-41 for "in-cell" bioimaging

Mesoporous silica nanoparticles are being explored as versatile tools for various biomedical and biotechnological applications including disease diagnosis, drug delivery, and intracellular imaging. In this paper, the synthesis and characterization of a fluorescent hybrid mesoporous silica nanomaterial, which is noncytotoxic and shows great potential for "in-cell" bioimaging applications, will be described. The hybrid mesoporous material has been obtained by confining highly fluorescent organic dyes, belonging to the indocyanine family, within the channels of mesoporous MCM-41. To explore the dispersion of the dye inside the mesoporous channels and the formation of dye aggregates, several hybrid samples with increasing dye/MCM-41 loading (up to 100 mg/g) were prepared. A uniform distribution of monomeric 1,1'-diethyl-3,3,3',3'-tetramethylindocarbocyanine iodide has been achieved at low dye loading (1 mg/g), as evidenced by photoluminescence spectra and lifetime, while a progressive formation of J-aggregates is induced by an increase in the dye loading. To elucidate the properties of the dye immobilized in mesoporous MCM-41, a detailed physical chemical characterization by structural (X-ray diffraction), volumetric and optical (Fourier transform infrared, diffuse-reflectance UV-vis and photoluminescence) techniques has been performed. By ultrasonication of the bulk material, nanoparticles of 2-20 nm diameter were obtained. Biocompatibility, endocytic uptake, and intracellular compartmentalization of such fluorescent nanoparticles were investigated in mammalian cultured cells.

Chemotherapy drug response in ovarian cancer cells strictly depends on a cathepsin D-Bax activation loop

The ovarian cancer cell lines A2780 (wild-type p53) and NIHOVCAR3 (mutated p53) showed, respectively, sensitivity and resistance towards several chemotherapy drugs. We hypothesized that the two cell lines differ in their ability to activate the intrinsic death pathway and have, therefore, dissected the lysosome-mitochondrion signalling pathway by pharmacological inhibition or genetic manipulation of key regulators and executioners. Biochemical and morphological confocal fluorescence studies showed that: (1) In A2780 cells bcl-2 is expressed at an undetectable level, whereas Bax is expressed at a rather high level; by contrast, bcl-2 is highly expressed and Bax is expressed at extremely low levels in NIHOVCAR3 cells; (2) Chemotherapy treatment reduced the expression of bcl-2 in NIHOVCAR3 cells, yet these cells resisted to drug toxicity; (3) Cathepsin D (CD), not cathepsin B or L, mediates the activation of the mitochondrial intrinsic death pathway in A2780 cells; (4) Lysosome leakage and cytosolic relocation of CD occurs in the chemosensitive A2780 cells, not in the chemoresistant NIHOVCAR3 cells; (5) Bax is essential for the permeabilization of both lysosomes and mitochondria in A2780 cells exposed to chemotherapy drugs; (6) CD activity is mandatory for the oligomerization of Bax on both mitochondrial and lysosomal membranes; (7) Bax activation did not occur in the resistant NIHOVCAR3 cells despite their high content in CD. The present data are consistent with a model in which on treatment with a cytotoxic drug the activation of a CD-Bax loop leads to the generalized permeabilization of lysosomes and eventually of mitochondria, thus reaching the point of no return, and culminates with the activation of the caspase cascade. Our data also imply that dysfunctional permeabilization of lysosomes contributes to the development of chemoresistance.

Mannose 6-phosphate receptor targeting and its applications in human diseases

The cation-independent mannose 6-phosphate receptor is a multifunctional protein which binds at the cell surface to two distinct classes of ligands, the mannose 6-phosphate (M6P) bearing proteins and IGF-II. Its major function is to bind and transport M6P-enzymes to lysosomes, but it can also modulate the activity of a variety of extracellular M6P-glycoproteins (i.e., latent TGFbeta precursor, urokinase-type plasminogen activator receptor, Granzyme B, growth factors, Herpes virus). The purpose of this review is to highlight the synthesis and potential use of high affinity M6P analogues able to target this receptor. Several M6P analogues with phosphonate, carboxylate or malonate groups display a higher affinity and a stronger stability in human serum than M6P itself. These derivatives could be used to favour the delivery of specific therapeutic compounds to lysosomes, notably in enzyme replacement therapies of lysosomal diseases or in neoplastic drug targeting. In addition, their potential applications in preventing clinical disorders, which are associated with the activities of other M6P-proteins involved in wound healing, cell growth or viral infection, will be discussed.

Endocytic mechanisms for targeted drug delivery

Advances in the delivery of targeted drug systems have evolved to enable highly regulated site specific localization to subcellular organelles. Targeting therapeutics to individual intracellular compartments has resulted in benefits to therapies associated with these unique organelles. Endocytosis, a mechanism common to all cells in the body, internalizes macromolecules and retains them in transport vesicles which traffic along the endolysosomal scaffold. An array of vesicular internalization mechanisms exist, therefore understanding the key players specific to each pathway has allowed researchers to bioengineer macromolecular complexes for highly specialized delivery. Membrane specific receptors most frequently enter the cell through endocytosis following the binding of a high affinity ligand. High affinity ligands interact with membrane receptors, internalize in membrane bound vesicles, and traffic through cells in different manners to allow for accumulation in early endosomal fractions or lysosomally associated fractions. Although most drug delivery complexes aim to avoid lysosomal degradation, more recent studies have shown the clinical utility in directed protein delivery to this environment for the enzymatic release of therapeutics. Targeting nanomedicine complexes to the endolysosomal pathway has serious potential for improving drug delivery for the treatment of lysosomal storage diseases, cancer, and Alzheimer's disease. Although several issues remain for receptor specific targeting, current work is investigating a synthetic receptor approach for high affinity binding of targeted macromolecules.

Hypoxia inhibits TRAIL-induced tumor cell apoptosis: involvement of lysosomal cathepsins

Tumor hypoxia interferes with the efficacy of chemotherapy, radiotherapy, and tumor necrosis factor-alpha. TRAIL (tumor necrosis factor-related apoptosis inducing ligand) is a potent apoptosis inducer that limits tumor growth without damaging normal cells and tissues in vivo. We present evidence for a central role of lysosomal cathepsins in hypoxia and/or TRAIL-induced cell death in oral squamous cell carcinoma (OSCC) cells. Hypoxia or TRAIL-induced activation of cathepsins (B, D and L), caspases (-3 and -9), Bid cleavage, release of Bax and cytochrome c, and DNA fragmentation were blocked independently by zVAD-fmk, CA074Me or pepstatin A, consistent with the involvement of lysosomal cathepsin B and D in cell death. Lysosome stability and mitochondrial membrane potential were reduced in hypoxia and TRAIL-induced apoptosis. However, TRAIL treatment under hypoxic condition resulted in diminished apoptosis rates compared to treatment under normoxia. This inhibitory effect of hypoxia on TRAIL-induced apoptosis may be based on preventing Bax activation and thus protecting mitochondria stability. Our data show that TRAIL or hypoxia independently triggered activation of cathepsin B and D leading to apoptosis through Bid and Bax, and suggest that hypoxic tissue regions provide a selective environment for highly apoptosis-resistant clonal cells. Molecular therapy approaches based on cathepsin inhibitors need to address this novel tumor-preventing function of cathepsins in OSCC.

Antiprotease therapy in cancer: hot or not?

The activity of a set of peptidases (proteases) involved in cancer progression is collectively known as the cancer 'degradome'. Invasion and metastasis were initially considered as late events in cancer development and the processes in which proteases were involved. However, recent studies indicate that invasion and metastasis are not late events, but can occur during early stages as well. Moreover, other processes occurring in various stages of cancer progression are also protease-dependent, such as (upregulation of) cell proliferation, (downregulation of) apoptosis, involvement of white blood cells, angiogenesis and induction of multi-drug resistance. Proteolytic activity in tumours is regulated in a complex manner, as both genetically unstable cancer cells and stable stromal cells, such as fibroblasts, endothelial cells and inflammatory cells, are involved. In vitro studies and studies using animal models have clearly shown protease dependency of many processes in carcinogenesis. However, clinical trials using protease inhibitors have thus far been unsuccessful except for a few applications of matrix metalloprotease (MMP) inhibitors when used in combination with cytostatic anticancer agents and/or in the early stages of cancer. Antithrombotics, such as low-molecular-weight heparin and warfarin, were also successful in clinical trials, probably by interfering with proteases of the coagulation cascade. The two-way association between cancer and thrombosis has long been recognised in the clinic. The poor outcome of other clinical trials of protease inhibitors is probably due to the late stages of cancer of the patient populations included, and the limited understanding of the complex regulation and effects of the activity of the various proteases in tumours depending on, among others, tumour type and stage, interactions between the cancer cells, other cells and the extracellular matrix in tumours. Therefore, a better fundamental understanding of the proteolytic complexity in tumours is essential before clinical trials can be rationally designed. At present, antithrombotics, the urokinase-type plasminogen activator system, the membrane-bound membrane-type 1-MMP, cathepsin L and the proteasome seem the most promising candidates as targets for anticancer strategies in early stages of cancer in combination with cytotoxic drugs. Moreover, metronomic therapy is an attractive approach using low doses of inhibitors for prolonged periods of time without interruption to specifically target endothelial cells that are involved in angiogenesis.

Lysosomes and lysosomal proteins in cancer cell death (new players of an old struggle)

Death of cancer cells influences tumor development and progression, as well as the response to anticancer therapies. This can occur through different cell death programmes which have recently been shown to implicate components of the acidic organelles, lysosomes. The role of lysosomes and lysosomal enzymes, including cathepsins and some lipid hydrolases, in programmed cell death associated with apoptotic or autophagic phenotypes is presented, as evidenced from observations on cultured cells and living animals. The possible molecular mechanisms that underlie the action of lysosomes during cell death are also described. Finally, the contribution of lysosomal proteins and lysosomes to tumor initiation and progression is discussed. Elucidation of this role and the underlying mechanisms will shed a new light on these 'old' organelles and hopefully pave the way for the development of novel anticancer strategies.

Cathepsin B mediates TRAIL-induced apoptosis in oral cancer cells

PURPOSE

The death ligand TRAIL (tumor necrosis factor-related apoptosis inducing ligand) triggers apoptosis in a variety of cancer cells, which implies the potential for therapeutic applications. The purpose of this study was to investigate the role of the lysosomal protease cathepsin B (CB) in mediating TRAIL-induced cell death in oral squamous cell carcinoma (OSCC) cells.

METHODS

OSCC cell lines from primary tumor and lymph node metastasis were examined for expression of apoptosis markers by Western blots, enzyme activity assays, nuclear fragmentation assays, and FACS analysis. Gene-specific ribozymes or chemical inhibitors were used to inhibit CB or caspases in target cells.

RESULTS

TRAIL-induced activation of caspase-3, cleavage of Bid and poly-ADP-ribose polymerase, release of cytochrome c, and DNA fragmentation were blocked either by a pan-caspase inhibitor (zVAD-fmk) or a CB inhibitor (CA074Me), consistent with the involvement of TRAIL as well as CB in cell death. The primary tumor cells were more susceptible to apoptosis than their corresponding lymph node metastatic cells. Stable transfection of a ribozyme which inhibited CB expression also decreased the apoptotic process.

CONCLUSIONS

We conclude that TRAIL-induced apoptotic cell death in OSCC cells is mediated through CB or through caspase activation. Our data point to a new tumor-suppressive role for CB in OSCC which is opposed to the invasion- and metastasis-promoting functions of lysosomal proteases.