Substantial increases in idarubicin plasma concentration by liposome encapsulation mediates improved antitumor activity

Liposomes as Multifunctional Nano-Carriers for Medicinal Natural Products

Although medicinal natural products and their derivatives have shown promising effects in disease therapies, they usually suffer the drawbacks in low solubility and stability in the physiological environment, low delivery efficiency, side effects due to multi-targeting, and low site-specific distribution in the lesion. In this review, targeted delivery was well-guided by liposomal formulation in the aspects of preparation of functional liposomes, liposomal medicinal natural products, combined therapies, and image-guided therapy. This review is believed to provide useful guidance to enhance the targeted therapy of medicinal natural products and their derivatives.

Recent Treatment Advances and the Role of Nanotechnology, Combination Products, and Immunotherapy in Changing the Therapeutic Landscape of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is the most common acute leukemia that is becoming more prevalent particularly in the older (65 years of age or older) population. For decades, "7 + 3" remission induction therapy with cytarabine and an anthracycline, followed by consolidation therapy, has been the standard of care treatment for AML. This stagnancy in AML treatment has resulted in less than ideal treatment outcomes for AML patients, especially for elderly patients and those with unfavourable profiles. Over the past two years, six new therapeutic agents have received regulatory approval, suggesting that a number of obstacles to treating AML have been addressed and the treatment landscape for AML is finally changing. This review outlines the challenges and obstacles in treating AML and highlights the advances in AML treatment made in recent years, including Vyxeos®, midostaurin, gemtuzumab ozogamicin, and venetoclax, with particular emphasis on combination treatment strategies. We also discuss the potential utility of new combination products such as one that we call "EnFlaM", which comprises an encapsulated nanoformulation of flavopiridol and mitoxantrone. Finally, we provide a review on the immunotherapeutic landscape of AML, discussing yet another angle through which novel treatments can be designed to further improve treatment outcomes for AML patients.

A new strategy to prepare giant vesicles from surface active ionic liquids (SAILs): a study of protein dynamics in a crowded environment using a fluorescence correlation spectroscopic technique

A simple procedure for the preparation of giant vesicles using surface active ionic liquids (SAILs) has been provided in this paper.

Formulation and optimization of idarubicin thermosensitive liposomes provides ultrafast triggered release at mild hyperthermia and improves tumor response

Drug delivery through thermosensitive liposomes (TSL) in combination with hyperthermia (HT) has shown great potential. HT can be applied locally forcing TSL to release their content in the heated tumor resulting in high peak concentrations. To perform optimally the drug is ideally released fast (seconds) and taken up rapidly by tumor cells. The aim of this study was to develop a novel thermosensitive liposome formulation of the anthracycline idarubicin (IDA-TSL). The hydrophobicity of idarubicin may improve its release from liposomes and subsequently rapid cellular uptake when combined mild hyperthermia. Here, we investigated a series of parameters to optimize IDA-TSL formulation. The results show that the optimal formulation for IDA-TSL is DPPC/DSPC/DSPE-PEG (6/3.5/0.5 mol%), with ammonium EDTA of 6.5 pH as loading buffer and a size of ~85 nm. In vitro studies demonstrated minimal leakage of ~20% in FCS at 37 °C for 1h, while an ultrafast and complete triggered release of IDA was observed at 42 °C. On tumor cells IDA-TSL showed comparable cytotoxicity to free IDA at 42 °C, but low cytotoxicity at 37 °C. Intravital microscopy imaging demonstrated an efficient in vivo intravascular triggered drug release of IDA-TSL under mild hyperthermia, and a subsequent massive IDA uptake by tumor cells. In animal efficacy studies, IDA-TSL plus mild HT demonstrated prominent tumor growth inhibition and superior survival rate over free IDA with HT or a clinically used Doxil treatment. These results suggest beneficial potential of IDA-TSL combined with local mild HT.

Idarubicin-loaded folic acid conjugated magnetic nanoparticles as a targetable drug delivery system for breast cancer

Conventional cancer chemotherapies cannot differentiate between healthy and cancer cells, and lead to severe side effects and systemic toxicity. Another major problem is the drug resistance development before or during the treatment. In the last decades, different kinds of controlled drug delivery systems have been developed to overcome these shortcomings. The studies aim targeted drug delivery to tumor site. Magnetic nanoparticles (MNP) are potentially important in cancer treatment since they can be targeted to tumor site by an externally applied magnetic field. In this study, MNPs were synthesized, covered with biocompatible polyethylene glycol (PEG) and conjugated with folic acid. Then, anti-cancer drug idarubicin was loaded onto the nanoparticles. Shape, size, crystal and chemical structures, and magnetic properties of synthesized nanoparticles were characterized. The characterization of synthesized nanoparticles was performed by dynamic light scattering (DLS), Fourier transform-infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) analyses. Internalization and accumulation of MNPs in MCF-7 cells were illustrated by light and confocal microscopy. Empty MNPs did not have any toxicity in the concentration ranges of 0-500μg/mL on MCF-7 cells, while drug-loaded nanoparticles led to significant toxicity in a concentration-dependent manner. Besides, idarubicin-loaded MNPs exhibited higher toxicity compared to free idarubicin. The results are promising for improvement in cancer chemotherapy.

Lead ions encapsulated in liposomes and their effect on Staphylococcus aureus

The aim of the study was the preparation of a liposome complex with encapsulated lead ions, which were electrochemically detected. In particular, experiments were focused on the potential of using an electrochemical method for the determination of free and liposome-encapsulated lead and determination of the encapsulation efficiency preventing the lead toxicity. Primarily, encapsulation of lead ions in liposomes and confirmation of successful encapsulation by electrochemical methods was done. Further, the reduction effect of the liposome matrix on the detected electrochemical signal was monitored. Besides encapsulation itself, comparison of toxicity of free lead ions and lead ions encapsulated in liposome was tested. The calculated IC50 values for evaluating the lead cytotoxicity showed significant differences between the lead enclosed in liposomes (28 µM) and free lead ions (237 µM). From the cytotoxicity studies on the bacterial strain of S. aureus it was observed that the free lead ions are less toxic in comparison with lead encapsulated in liposomes. Liposomes appear to be a suitable carrier of various substances through the inner cavity. Due to the liposome structure the lead enclosed in the liposome is more easily accepted into the cell structure and the toxicity of the enclosed lead is higher in comparison to free lead ions.

Gold surface supported spherical liposome-gold nano-particle nano-composite for label free DNA sensing

Immobilization of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) liposome-gold nano-particle (DOPE-AuNP) nano-composite covalently on 3-mercaptopropionic acid (MPA) on gold surface is demonstrated for the first time for electrochemical label free DNA sensing. Spherical nature of the DOPE on the MPA monolayer is confirmed by the appearance of sigmoidal voltammetric profile, characteristic behavior of linear diffusion, for the MPA-DOPE in presence of [Fe(CN)(6)](3-/4-) and [Ru(NH(3))(6)](3+) redox probes. The DOPE liposome vesicle fusion is prevented by electroless deposition of AuNP on the hydrophilic amine head groups of the DOPE. Immobilization of single stranded DNA (ssDNA) is made via simple gold-thiol linkage for DNA hybridization sensing in the presence of [Fe(CN)(6)](3-/4-). The sensor discriminates the hybridized (complementary target hybridized), un-hybridized (non-complementary target hybridized) and single base mismatch target hybridized surfaces sensitively and selectively without signal amplification. The lowest target DNA concentration detected is 0.1×10(-12)M. Cyclic voltammetry (CV), electrochemical impedance (EIS), differential pulse voltammetry (DPV) and quartz crystal microbalance (QCM) techniques are used for DNA sensing on DOPE-AuNP nano-composite. Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Atomic Force Microscopy (AFM), Dynamic Light Scattering (DLS) and Ultraviolet-Visible (UV) spectroscopic techniques are used to understand the interactions between the DOPE, AuNP and ssDNA. The results indicate the presence of an intact and well defined spherical DOPE-AuNP nano-composite on the gold surface. The method could be applied for fabrication of the surface based liposome-AuNP-DNA composite for cell transfection studies at reduced reagents and costs.

Menin liver-specific hemizygous mice challenged with high fat diet show increased weight gain and markers of metabolic impairment

OBJECTIVE:

The menin tumor suppressor protein is abundantly expressed in the liver, although no function has been identified because of lack of tumor development in multiple endocrine neoplasia type 1 (Men1) null livers. We examine the phenotype of mice lacking one functional allele of Men1 (consistent with the phenotype in humans with MEN1 syndrome) challenged with high fat diet (HFD) to elucidate a metabolic function for hepatic menin.

METHODS:

In this study, we challenged mice harboring a liver-specific hemizygous deletion of Men1 (HETs) alongside wild-type (WT) counterparts with HFD for 3 months and monitored the severity of metabolic changes. We demonstrate that the HET mice challenged with HFD for 3 months show an increased weight gain with decreased glucose tolerance compared with WT counterparts. Along with these changes, there was a more severe serum hormone profile involving increased serum insulin, glucose and glucagon, all hallmarks of the type 2 diabetic phenotype. In concert with increased serum hormones, we found that these mice have significantly increased liver triglycerides coupled with increased liver steatosis and inflammatory markers. Quantitative real-time PCR and western blotting studies show increases in enzymes involved with lipogenesis and hepatic glucose production.

CONCLUSION:

We conclude that hepatic menin is required for regulation of diet-induced metabolism, and our studies indicate a protective role for the Men1 gene in the liver when challenged with HFD.

Polypeptide conjugates of D-penicillamine and idarubicin for anticancer therapy

We investigated anticancer therapy with a novel combination of D-penicillamine (D-pen) and Idarubicin (Ida) in a synthetic dual drug conjugate (DDC). D-pen and Ida were covalently linked to poly(α)-L-glutamic acid (PGA) via reducible disulfide and acid-sensitive hydrazone bonds, respectively. The DDCs showed cell uptake and sustained release of the bound drugs in conditions mimicking the intracellular release media (10mM glutathione and pH 5.2). The in-vitro cytotoxicity of DDCs was comparable to unconjugated Ida in several sensitive and resistant cancer cell lines and correlated with the rate of cell uptake. In a single equivalent-dose pharmacokinetic study, DDCs enhanced the drug exposure by 7-fold and prolonged the plasma circulation half-life (t(1/2)) by 5-fold over unconjugated Ida. The therapeutic index of DDCs was 2-3-fold higher than unconjugated drugs. DDCs caused 89% tumor growth inhibition compared to 60% by unconjugated Ida alone and led to significant enhancement in the median survival (17%) of athymic nu/nu mice bearing NCI-H460 tumor xenografts.

In vitro antifungal activity of DNA topoisomerase inhibitors

In this paper we report the results of the study of the in vitro effect of eight anticancer DNA topoisomerase inhibitors on the growth of Aspergillus fumigatus, A. niger, Candida glabrata and Cryptococcus neoformans. Only one compound, idarubicin, displayed promising antifungal activity against A. niger, C. glabrata and C. neoformans with MIC(50) values varying between 3.6 and 14.2 μM (1.8-7.1 μg/ml). Three other compounds, aclarubicin, doxorubicin and mitoxantrone, showed some antifungal activity against C. glabrata and C. neoformans with MIC(50) values in the mid micromolar range. The data of this study indicate that selected DNA topoisomerase inhibitors are a promising class of compounds for the development of new antifungal agents.

Multi-core vesicle nanoparticles based on vesicle fusion for delivery of chemotherapic drugs

The Pluronic nanoparticles (NPs) composed of Pluronic (F-68) and liquid polyethylene glycol (PEG, molecular wt: 400) containing docetaxel (DTX) were stabilized with the vesicle fusion. When DTX-loaded Pluronic NPs were mixed with vesicles in the aqueous medium, DTX-loaded Pluronic NPs were incorporated into vesicles to form multi-core vesicle NPs. The morphology and size distribution of multi-core vesicle NPs were observed using FE-SEM, cryo-TEM and a particle size analyzer. To apply multi-core vesicle NPs as a delivery system for DTX, a model anti-cancer drug, the release pattern of DTX was observed and the tumor growth was monitored by injecting the DTX-loaded multi-core vesicle NPs into the tail veins of tumor-bearing mice. We also evaluated the time-dependent excretion profile, in vivo biodistribution, circulation time, and tumor targeting capability of multi-core vesicle NPs using a non-invasive live animal imaging technology.

Active methods of drug loading into liposomes: recent strategies for stable drug entrapment and increased in vivo activity

INTRODUCTION

The use of liposomes increases the therapeutic index of many drugs, and also offers drug targeting and controlled release. The commercial impact of liposomes is strengthened by the invention of several active drug encapsulation methods, allowing the encapsulation of several weak base or weak acid drugs with very high drug-to-lipid ratios.

AREAS COVERED

In recent years, there have been reports on several new approaches to retain more hydrophobic drugs inside liposomes, in the circulation. Most of these methods apply drug precipitation inside preformed liposomes, as low soluble complexes with ions or chemicals. In some cases, drug derivatization was applied to enable active encapsulation of hydrophobic drugs, previously not reported to encapsulate, by active or remote loading. This review presents and compares most of the existing methods of active drug encapsulation and outlines recent strategies to achieve stable drug encapsulation in vivo.

EXPERT OPINION

At present, there is no single universal encapsulation method that offers stable encapsulation of most drugs; each drug requires a different approach to manage all of its properties. Now is the time to combine all these strategies to achieve the goal of a complex, but successful, anticancer therapy.

The role of the transition metal copper and the ionophore A23187 in the development of Irinophore C™

PURPOSE

A liposomal irinotecan formulation referred to as Irinophore C relies on the ability of copper to complex irinotecan within the liposome. It is currently being evaluated for critical drug-loading parameters. Studies presented here were designed to determine the optimum copper concentration required for the effective encapsulation and retention of irinotecan into liposomes.

METHODS

Distearoylphosphatidylcholine/cholesterol liposomes were formulated using buffers containing various copper or manganese concentrations, and irinotecan loading was determined in the presence and absence of divalent metal ionophore A23187. The rate and extent of irinotecan encapsulation and the rate of irinotecan release from the liposomes were assessed. The amount of copper retained inside liposomes following irinotecan loading and the effect of copper on membrane permeability were determined.

RESULTS

Efficient (>98%) irinotecan loading was achieved using encapsulated copper concentrations of 50 mM. However, irinotecan release was copper concentration dependent, with a minimum 300 mM concentration required for optimal drug retention. The presence of copper increased liposomal membrane permeability.

CONCLUSION

Results explain why irinotecan loading rates are enhanced in the presence of formulations prepared with copper, and we speculate that the Irinophore C formulation exhibits improved drug retention, due to generation of a complex between copper and irinotecan.

Simultaneous liposomal delivery of quercetin and vincristine for enhanced estrogen-receptor-negative breast cancer treatment

Breast cancers are either estrogen receptor-positive (ER) or negative (ER). ER breast cancers are clinically more aggressive and have fewer effective treatment options. Quercetin and vincristine are both active against ER breast cancers and exhibit synergism in vitro. However, the clinical use of quercetin is hampered by its low water solubility. In addition, optimal synergism can only be achieved at a particular ratio of the drugs. Therefore, the objectives of this study are to develop a liposomal formulation to solubilize quercetin, and to co-encapsulate and coordinate the release of quercetin and vincristine in their synergistic ratios to maximize anticancer activity. The optimal synergistic molar ratio of quercetin/vincristine was found to be 1 : 2 by in-vitro MTT assay. Quercetin liposomes were prepared by the film hydration method followed by extrusion, and vincristine was subsequently loaded into the core of the liposomes by remote loading with manganese sulfate and the ionophore A23187. The optimal liposome formulation co-encapsulating quercetin and vincristine comprised egg sphingomyelin/cholesterol/PEG2000 ceramide/quercetin (72.5 : 17.5 : 5 : 5 mol ratio). This formulation was physically stable, enhanced quercetin solubility 8.6 times, co-encapsulated quercetin and vincristine with efficiencies of 78.3 and 78.5%, respectively, and displayed coordinated release of both drugs to maintain the synergistic molar ratio. In-vitro MTT assays of this liposomal formulation showed significant synergism, with a combination index of 0.113 and a dose-reduction index value of 115 at ED50 for vincristine. Therefore, liposomal delivery represents a strategy to solubilize poorly soluble drugs and coordinate the release of two drugs in their synergistic ratio for optimal anticancer effect.

Drug ratio-dependent antagonism: a new category of multidrug resistance and strategies for its circumvention

A newly identified form of multidrug resistance (MDR) in tumor cells is presented, pertaining to the commonly encountered resistance of cancer cells to anticancer drug combinations at discrete drug:drug ratios. In vitro studies have revealed that whether anticancer drug combinations interact synergistically or antagonistically can depend on the ratio of the combined agents. Failure to control drug ratios in vivo due to uncoordinated pharmacokinetics could therefore lead to drug resistance if tumor cells are exposed to antagonistic drug ratios. Consequently, the most efficacious drug combination may not occur at the typically employed maximum tolerated doses of the combined drugs if this leads to antagonistic ratios in vivo after administration and resistance to therapeutic effects of the drug combination. Our approach to systematically screen a wide range of drug ratios and concentrations and encapsulate the drug combination in a liposomal delivery vehicle at identified synergistic ratios represents a means to mitigate this drug ratio-dependent MDR mechanism. The in vivo efficacy of the improved agents (CombiPlex formulations) is demonstrated and contrasted with the decreased efficacy when drug combinations are exposed to tumor cells in vivo at antagonistic ratios.

Preparation, optimization, and characterization of topotecan loaded PEGylated liposomes using factorial design

This study reports the development of liposomal system for a potent antitumor drug, topotecan. To achieve this goal conventional and PEGylated liposomes were prepared according to a factorial design by hydration method followed by extrusion. Parameters such as type of lipid, percentage of cholesterol, percentage of phosphatidylglycerols, percentage of polyethylene glycol (PEG)-lipids, and drug to lipid molar ratio were considered as important factors for the optimizing the entrapment and retention of topotecan inside the liposomes. The size and zeta-potential of the PEGylated and conventional liposomes were measured by particle size analyzer and zeta-potentiometer, respectively. The stability and release characteristics of PEGylated liposome loaded topotecan were compared with conventional liposomes and free topotecan. The optimized PEGylated [distearoyl phosphatidylcholine (DSPC)/cholesterol/ distearoyl phosphatidylglycerol (DSPG)/ distearoyl phosphatidylethanolamine-PEG(2000) (DSPE-PEG(2000)); 7:7:3:1.28] and related conventional [DSPC/cholesterol/DSPG; 7:7:3] liposomes showed a narrow size distribution with a polydipersity index of 0.15 and 0.10, an average diameter of 103.0 +/- 13.1 and 95.2 +/- 11.10 nm, and with drug loading of 11.44 and 6.21%, respectively. Zeta-potential was -10 +/- 2.3 and -22 +/- 2.8 mV for PEGylated and conventional liposomes, respectively. The results of stability evaluation showed that the lactone ring of topotecan was notably preserved upon liposome encapsulation. PEGylated liposomes containing topotecan showed a significant decrease (P < 0.001) in release rate in comparison with conventional leptosomes. These results indicate the suitability of PEGylated liposomes in controlling topotecan release. The prepared liposomes (especially PEGylated liposomes) as those described here may be clinically useful to stabilize and deliver topotecan for the treatment of cancer.

Nanoparticle-assisted surface immobilization of phospholipid liposomes

Phospholipid liposomes (100-200 nm diameter) are deposited onto solid substrates after stabilizing them against fusion with the solid by allowing charged nanoparticles to adsorb at approximately 25% surface coverage. The immobilized vesicles remain stable over a period of days. Epifluorescence imaging shows that they diffuse freely over surfaces with the same charge but adsorb tightly onto surfaces with opposite charge. Nanoparticle adsorption to surface patterns of opposite charge provides a facile method to create large-scale surface-supported arrays of intact liposomes. This surface attachment method is simple chemically and applies generally for solid surfaces that can be hydrophobic or hydrophilic. Offering routes to localize proteins and other vesicle-contained objects at surfaces in tailored spatial patterns, these immobilized liposome arrays may find diverse applications in the emerging field of nanobiotechnology.

Direct comparison of two pegylated liposomal doxorubicin formulations: Is AUC predictive for toxicity and efficacy?

Rationally designed liposomes could improve the therapeutic indexes of chemotherapeutic drugs, which is due to alterations in the pharmacokinetics and biodistribution of encapsulated drugs. For traditional drug delivery systems, the accumulation of drugs in healthy and malignant tissues could be correlated with toxicity and efficacy. Some previous studies also indicate that the higher tumor AUC, the better therapeutic efficacy, suggestive of the possible existence of positive correlation. Are AUC values of liposomal drugs really predictive? For the purpose to address this question, we designed two pegylated liposomal doxorubicin formulations (PLD-75 and PLD-100), which had the same lipid/drug ratio and bilayer composition, but different size and internal ammonium sulfate concentration. In vitro drug retention experiments revealed that drug was released at a faster rate from PLD-75, a small size formulation. The plasma pharmacokinetics of PLD-75 was similar to that of PLD-100, regardless of whether the mice were tumor-free or not. It should be noted, though, that in tumor-bearing mice the plasma doxorubicin level in PLD-75 group was only about 59% of that in PLD-100 group at 48 h post injection. Furthermore, their biodistribution behavior in S-180 tumor-bearing KM mice was significantly different. Compared with animals receiving PLD-100, those receiving PLD-75 showed a 19.2%, 27.8%, and 23.5% decrease in liver (p<0.01), spleen (p<0.001) and lung (p<0.05) AUC, respectively. In other healthy tissues except kidney, the drug deposition also reduced by 10-15%, but the difference was not significant. The tumor AUC after administration of PLD-100 and PLD-75 were 1285.3 ugh/g and 762.0 ugh/g, respectively (p<0.001). Maximum drug levels achieved in the tumors were 33.80 microg/g (for PLD-100) and 20.85 microg/g (for PLD-75), and peak tumor concentration was achieved faster in PLD-75 group. However, enhanced drug accumulation does not mean increased antineoplastic effect, and at the same doxorubicin dose level, PLD-75 was more efficacious. As for toxicity studies, PLD-75 caused more rapid and severe body weight loss despite the fact that drug accumulation in healthy tissues was reduced. Our data indicate that liposomal systems are more complicated than conventional drug delivery systems, and it is hard to predict the toxicity and efficacy of liposomal drugs through the measure of liposomal drug accumulation.

Simultaneous delivery of doxorubicin and GG918 (Elacridar) by new polymer-lipid hybrid nanoparticles (PLN) for enhanced treatment of multidrug-resistant breast cancer

Multidrug-resistant (MDR) cancer may be treated using combinations of encapsulated cytotoxic drugs and chemosensitizers. To optimize for the effectiveness of this combinational approach, novel polymer-lipid hybrid nanoparticle (PLN) formulations capable of delivering a cytotoxic drug, doxorubicin (Dox), a chemosensitizer, GG918, or their combination were prepared. Both acute and long-term anticancer activities of various combinations of Dox and GG918 in solution or PLN form were evaluated in a human MDR breast cancer cell line (MDA435/LCC6/MDR1) using trypan blue exclusion and clonogenic assays. Cellular Dox uptake and drug distribution within the cells were determined by fluoremetry and fluorescence microscopy. The results showed that the encapsulation efficiencies of Dox and GG918 in PLN were up to 89% and were not compromised by co-encapsulation of the two agents. Of various combinational treatment approaches, the Dox and GG918 co-encapsulated PLN formulation ((DG)n) demonstrated the greatest Dox uptake and anticancer activity to the MDR cells, while co-administration of two single-agent loaded PLN was least effective. Fluorescence microscopy indicated cellular internalization of (DG)n. These findings suggest that in addition to the total drug concentrations, the simultaneous delivery of Dox and GG918 to the same cellular location is critical in determining the therapeutic effectiveness of this anticancer drug-chemosensitizer combination.

How to stabilize phospholipid liposomes (using nanoparticles)

The simple strategy of mixing phospholipid liposomes with charged nanoparticles and using sonication to mix them at low volume fraction produces particle-stabilized liposomes that repel one another and do not fuse. Subsequently, the volume fraction can be raised as high as approximately 50%, reversibly, still without fusion. In studies of liposome longevity, we verified the stability of particle-stabilized liposome suspensions with volume fraction up to 16% for up to 50 days, the longest period investigated. Fluorescent dyes were encapsulated within the particle-stabilized liposomes, without leakage. Although these particle-stabilized liposomes were stable against fusion, approximately 75% of the outer liposome surface remained unoccupied. This opens the door to using particle-stabilized liposomes in various applications.