Mitochondria-targeted liposomes improve the apoptotic and cytotoxic action of sclareol

Near-Infrared Emissive Super Penetrating Conjugated Polymer Dots for Intratumoral Imaging in 3D Tumor Spheroid Models

This study describes the formation of single-chain polymer dots (Pdots) via ultrasonic emulsification of nonionic donor-acceptor-donor type (D-A-D) alkoxy thiophene-benzobisthiadiazole-based conjugated polymers (Poly BT) with amphiphilic cetyltrimethylammonium bromide (CTAB). The methodology yields Pdots with a high cationic surface charge (+56.5 mV ± 9.5) and average hydrodynamic radius of 12 nm. Optical characterization reveals that these Pdots emit near-infrared (NIR) light at a maximum wavelength of 860 nm owing to their conjugated polymer backbone consisting of D-A-D monomers. Both colloidal and optical properties of these Pdots make them promising fluorescence emissive probes for bioimaging applications. The significant advantage of positively charged Pdots is demonstrated in diffusion-limited mediums such as tissues, utilizing human epithelial breast adenocarcinoma, ATCC HTB-22 (MCF-7), human bone marrow neuroblastoma, ATCC CRL-2266 (SH-SY5Y), and rat adrenal gland pheochromocytoma, CRL-1721 (PC-12) tumor spheroid models. Fluorescence microscopy analysis of tumor spheroids from MCF-7, SH-SY5Y, and PC-12 cell lines reveals the intensity profile of Pdots, confirming extensive penetration into the central regions of the models. Moreover, a comparison with mitochondria staining dye reveals an overlap between the regions stained by Pdots and the dye in all three tumor spheroid models. These results suggest that single-chain D-A-D type Pdots, cationized via CTAB, exhibit long-range mean free path of penetration (≈1 µm) in dense mediums and tumors.

Unravelling the potential of mitochondria-targeted liposomes for enhanced cancer treatment

Mitochondria are the primary organelles of cells involved in various physiochemical and biochemical processes. Owing to their crucial role in cellular metabolism, mitochondria are favored therapeutic targets for the treatment and prevention of cancers. Recently, there has been growing interest in the use of mitochondria-specific functional nanoparticles for targeted delivery of therapeutic agents to these organelles. Among several nanosystems, liposomes have garnered considerable attention owing to their exceptional drug delivery capabilities, biocompatibility, biodegradability, ease of manufacturing and established regulatory guidelines for market approval. In this context, the present review provides a brief insight into the association between mitochondria and tumor formation and advantages of mitochondrial targeting in cancer therapy. Furthermore, it discusses mitochondria-targeting functional liposomes for the treatment of various cancers, such as breast, lung, colon, among others.

The bioactivities of sclareol: A mini review

Sclareol, a diterpene alcohol isolated from the herbal and flavor plant clary sage (Salvia sclarea L.), is far-famed as the predominant ingredient in the refined oil of Salvia sclarea (L.). The empirical medicine of Salvia sclarea L. focused on various diseases, such as arthritis, oral inflammation, digestive system diseases, whereas the sclareol possessed more extensive and characteristic bioactivities, including anti-tumor, anti-inflammation and anti-pathogenic microbes, even anti-diabetes and hypertension. However, there is a deficiency of literature to integrate and illuminate the pharmacological attributes of sclareol based on well-documented investigations. Interestingly, sclareol has been recently considered as the potential candidate against COVID-19 and Parkinson’s disease. Accordingly, the bioactive attributes of sclareol in cancer, inflammation, even pharmacochemistry and delivery systems are reviewed for comprehensively dissecting its potential application in medicine.

Mitochondrial targeting of potent nanoparticulated drugs in combating diseases

Mitochondrial dysfunction, characterized by the electron transport chain (ETC) leakage and reduced adenosine tri-phosphate synthesis, occurs primarily due to free radicals -induced mutations in either the mitochondrial deoxyribonucleic acid (mtDNA) or nuclear (n) DNA caused by pathogenic infections, toxicant exposures, adverse drug-effects, or other environmental exposures, leading to secondary dysfunction affecting ischemic, diabetic, cancerous, and degenerative diseases. In these concerns, mitochondria-targeted remedies may include a significant role in the protection and treatment of mitochondrial function to enhance its activity. Coenzyme Q10 pyridinol and pyrimidinol antioxidant analogues and other potent drug-compounds for their multifunctional radical quencher and other anti-toxic activities may take a significant therapeutic effectivity for ameliorating mitochondrial dysfunction. Moreover, the encapsulation of these bioactive ligands-attached potent compounds in vesicular system may enable them a superb biological effective for the treatment of mitochondria-targeted dysfunction-related diseases with least side effects. This review depicts mainly on mitochondrial enzymatic dysfunction and their amelioration by potent drugs with the usages of nanoparticulated delivery system against mitochondria-affected diseases.

Emerging trends in nano-bioactive-mediated mitochondria-targeted therapeutic stratagems using polysaccharides, proteins and lipidic carriers

The emergence of new lifestyle disorders and pharmaco-resistant variants of diseases has necessitated the search for effective therapeutic moieties and approaches that could overcome the limitations in the existing treatment modalities. In this context, bioactives such as flavonoids, polyphenols, tannins, terpenoids and alkaloids have demonstrated promise in therapy owing to their ability to scavenge free radicals and modulate the mitochondrial function as well as regulate metabolic pathways. However, their clinical applicability is low owing to their poor bioavailability and aqueous solubility. The encapsulation of bioactives in nanodimensional particles has overcome these limitations to a large extent while simultaneously conferring additional advantages of improved circulation time, enhanced cell uptake and target specific release. A wide range of nanocarriers derived from biopolymers such as polysaccharides, lipids and proteins, have been explored for encapsulation of different bioactives and have reported significant improvement of the bioavailability and therapeutic efficacy of the encapsulated cargo. However, incorporation of cell-specific and mitochondria-specific elements on the nanocarriers has been relatively less explored. This review summarizes some of the recent attempts to treat different disorders using bioactives encapsulated in biopolymer nanostructures and few instances of mitochondria-specific delivery.

A bright, red-emitting water-soluble BODIPY fluorophore as an alternative to the commercial Mito Tracker Red for high-resolution mitochondrial imaging

With the emergence and rapid development of super-resolution fluorescence microscopy, monitoring of mitochondrial morphological changes has aroused great interest for exploring the role of mitochondria in the process of cell metabolism. However, in the absence of water-soluble, photostable and low-toxicity fluorescent dyes, ultra-high-resolution mitochondrial imaging is still challenging. Herein, we designed two fluorescent BODIPY dyes, namely Mito-BDP 630 and Mito-BDP 760, for mitochondrial imaging. The results proved that Mito-BDP 760 underwent aggregation-caused quenching (ACQ) in the aqueous matrix owing to its hydrophobicity and was inaccessible to the cells, which restricted its applications in mitochondrial imaging. In stark contrast, water-soluble Mito-BDP 630 readily penetrated cellular and mitochondrial membranes for mitochondrial imaging with high dye densities under wash-free conditions as driven by membrane potential. As a comparison, Mito Tracker Red presented high photobleaching (the fluorescence intensity dropped by nearly 50%) and high phototoxicity after irradiation by a laser for 30 min. However, Mito-BDP 630 possessed excellent biocompatibility, photostability and chemical stability. Furthermore, clear and bright mitochondria distribution in living HeLa cells after incubation with Mito-BDP 630 could be observed by CLSM. Convincingly, the morphology and cristae of mitochondria could be visualized using an ultra-high-resolution microscope. In short, Mito-BDP 630 provided a powerful and convenient tool for monitoring mitochondrial morphologies in living cells. Given the facile synthesis, photobleaching resistance and low phototoxicity of Mito-BDP 630, it is an alternative to the commercial Mito Tracker Red.

Synthesis of Triphenylphosphonium Phospholipid Conjugates for the Preparation of Mitochondriotropic Liposomes

Surface modification of liposomes with a ligand is facilitated by the conjugation of the ligand to a hydrophobic molecule that serves to anchor the ligand to the liposomal bilayer. We describe here a simple protocol to conjugate a triphenylphosphonium group to several commercially available functionalized phospholipids. The resulting triphenylphosphonium-conjugated lipids can be used to prepare liposomes that preferentially associate with mitochondria when exposed to live mammalian cells in culture.

Mitochondrial nanomedicine: Subcellular organelle-specific delivery of molecular medicines

As mitochondria network together to act as the master sensors and effectors of apoptosis, ATP production, reactive oxygen species management, mitophagy/autophagy, and homeostasis; this organelle is an ideal target for pharmaceutical manipulation. Mitochondrial dysfunction contributes to many diseases, for example, β-amyloid has been shown to interfere with mitochondrial protein import and induce apoptosis in Alzheimer's Disease while some forms of Parkinson's Disease are associated with dysfunctional mitochondrial PINK1 and Parkin proteins. Mitochondrial medicine has applications in the treatment of an array of pathologies from cancer to cardiovascular disease. A challenge of mitochondrial medicine is directing therapies to a subcellular target. Nanotechnology based approaches combined with mitochondrial targeting strategies can greatly improve the clinical translation and effectiveness of mitochondrial medicine. This review discusses mitochondrial drug delivery approaches and applications of mitochondrial nanomedicines. Nanomedicine approaches have the potential to drive the success of mitochondrial therapies into the clinic.

Anti-proliferative effects of diterpenoids from Sagittaria trifolia L. tubers on colon cancer cells by targeting the NF-κB pathway

A new labdane-type diterpenoid, ent-19-ol-13-epi-manoyl oxide,19-undecane ester, together with ten known diterpenes, were isolated from the ethanolic crude extract of the fresh tubers of Sagittaria trifolia L. The chemical structures of these compounds were determined by extensive 2-D NMR experiments and by comparison with the data reported in the literature. These compounds showed different inhibitory effects on various human cancer cells. Among these, compound 11 exhibited potential inhibition effects against human colon cancer cells. Moreover, flow cytometry demonstrated that compound 11 arrested the cell cycle at the G1 phase and induced cellular apoptosis, accompanied by mitochondrial membrane potential reduction. Mechanistic studies revealed that treatment with compound 11 inhibited IKKα/β phosphorylation and IκBα phosphorylation, which subsequently caused the blockage of NF-κB p65 phosphorylation and nuclear translocation. Compound 11 also inhibited the expression of c-Myc, Cyclin D1, and Bcl-2, the downstream targets of NF-κB. Therefore, our findings provided insight into the anticancer components of Sagittaria trifolia L. tubers, which could facilitate their utilization as functional food ingredients.

Nanomedicines for Subcellular Targeting: The Mitochondrial Perspective

BACKGROUND

Over the past decade, there has been a surge in the number of mitochondrialactive therapeutics for conditions ranging from cancer to aging. Subcellular targeting interventions can modulate adverse intracellular processes unique to the compartments within the cell. However, there is a dearth of reviews focusing on mitochondrial nano-delivery, and this review seeks to fill this gap with regards to nanotherapeutics of the mitochondria.

METHODS

Besides its potential for a higher therapeutic index than targeting at the tissue and cell levels, subcellular targeting takes into account the limitations of systemic drug administration and significantly improves pharmacokinetics. Hence, an extensive literature review was undertaken and salient information was compiled in this review.

RESULTS

From literature, it was evident that nanoparticles with their tunable physicochemical properties have shown potential for efficient therapeutic delivery, with several nanomedicines already approved by the FDA and others in clinical trials. However, strategies for the development of nanomedicines for subcellular targeting are still emerging, with an increased understanding of dysfunctional molecular processes advancing the development of treatment modules. For optimal delivery, the design of an ideal carrier for subcellular delivery must consider the features of the diseased microenvironment. The functional and structural features of the mitochondria in the diseased state are highlighted and potential nano-delivery interventions for treatment and diagnosis are discussed.

CONCLUSION

This review provides an insight into recent advances in subcellular targeting, with a focus on en route barriers to subcellular targeting. The impact of mitochondrial dysfunction in the aetiology of certain diseases is highlighted, and potential therapeutic sites are identified.

Smart Design of Nanomaterials for Mitochondria-Targeted Nanotherapeutics

Mitochondria are the powerhouse of cells. They are vital organelles that maintain cellular function and metabolism. Dysfunction of mitochondria results in various diseases with a great diversity of clinical appearances. In the past, strategies have been developed for fabricating subcellular-targeting drug-delivery nanocarriers, enabling cellular internalization and subsequent organelle localization. Of late, innovative strategies have emerged for the smart design of multifunctional nanocarriers. Hierarchical targeting enables nanocarriers to evade and overcome various barriers encountered upon in vivo administration to reach the organelle with good bioavailability. Stimuli-responsive nanocarriers allow controlled release of therapeutics to occur at the desired target site. Synergistic therapy can be achieved using a combination of approaches such as chemotherapy, gene and phototherapy. In this Review, we survey the field for recent developments and strategies used in the smart design of nanocarriers for mitochondria-targeted therapeutics. Existing challenges and unexplored therapeutic opportunities are also highlighted and discussed to inspire the next generation of mitochondrial-targeting nanotherapeutics.

Natural products and phytochemical nanoformulations targeting mitochondria in oncotherapy: an updated review on resveratrol

Mitochondria are intracellular organelles with two distinct membranes, known as an outer mitochondrial membrane and inner cell membrane. Originally, mitochondria have been derived from bacteria. The main function of mitochondria is the production of ATP. However, this important organelle indirectly protects cells by consuming oxygen in the route of energy generation. It has been found that mitochondria are actively involved in the induction of the intrinsic pathways of apoptosis. So, there have been efforts to sustain mitochondrial homeostasis and inhibit its dysfunction. Notably, due to the potential role of mitochondria in the stimulation of apoptosis, this organelle is a promising target in cancer therapy. Resveratrol is a non-flavonoid polyphenol that exhibits significant pharmacological effects such as antioxidant, anti-diabetic, anti-inflammatory and anti-tumor. The anti-tumor activity of resveratrol may be a consequence of its effect on mitochondria. Multiple studies have investigated the relationship between resveratrol and mitochondria, and it has been demonstrated that resveratrol is able to significantly enhance the concentration of reactive oxygen species, leading to the mitochondrial dysfunction and consequently, apoptosis induction. A number of signaling pathways such as sirtuin and NF-κB may contribute to the mitochondrial-mediated apoptosis by resveratrol. Besides, resveratrol shifts cellular metabolism from glycolysis into mitochondrial respiration to induce cellular death in cancer cells. In the present review, we discuss the possible interactions between resveratrol and mitochondria, and its potential application in cancer therapy.

Enhanced Subcellular Trafficking of Resveratrol Using Mitochondriotropic Liposomes in Cancer Cells

Mitochondria are membrane-enclosed organelles present in most eukaryotic cells, described as “power houses of the cell”. The mitochondria can be a target for inducing cancer cell death and for developing strategies to bypass multi drug resistance (MDR) mechanisms. 4-Carboxybutyl triphenylphosphonium bromide-polyethylene glycol-distearoylphosphatidylethanolamine (TPP-DSPE-PEG) and dequalinium-polyethylene glycol-distearoylphosphatidylethanolamine (DQA-DSPE-PEG) were synthesized as mitochondriotropic molecules. Mitochondria-targeting liposomes carrying resveratrol were constructed by modifying the liposome’s surface with TPP-PEG or DQA-PEG, resulting in TLS (Res) and DLS (Res), respectively, with the aim to obtain longer blood circulation and enhanced permeability and retention (EPR). Both TLS (Res) and DLS (Res) showed dimensions of approximately 120 nm and a slightly positive zeta potential. The enhanced cellular uptake and selective accumulation of TLS (Res) and DLS (Res) into the mitochondria were demonstrated by behavioral observation of rhodamine-labeled TLS or DLS, using confocal microscopy, and by resveratrol quantification in the intracellular organelle, using LC–MS/MS. Furthermore, TLS (Res) and DLS (Res) induced cytotoxicity of cancer cells by generating reactive oxygen species (ROS) and by dissipating the mitochondrial membrane potential. Our results demonstrated that TLS (Res) and DLS (Res) could provide a potential strategy to treat cancers by mitochondrial targeting delivery of therapeutics and stimulation of the mitochondrial signaling pathway.

Long-Circulating Amphiphilic Doxorubicin for Tumor Mitochondria-Specific Targeting

The mitochondria have emerged as a novel target for cancer chemotherapy primarily due to their central roles in energy metabolism and apoptosis regulation. Here, we report a new molecular approach to achieve high levels of tumor- and mitochondria-selective deliveries of the anticancer drug doxorubicin. This is achieved by molecular engineering, which functionalizes doxorubicin with a hydrophobic lipid tail conjugated by a solubility-promoting poly(ethylene glycol) polymer (amphiphilic doxorubicin or amph-DOX). In vivo, the amphiphile conjugated to doxorubicin exhibits a dual function: (i) it binds avidly to serum albumin and hijacks albumin's circulating and transporting pathways, resulting in prolonged circulation in blood, increased accumulation in tumor, and reduced exposure to the heart; (ii) it also redirects doxorubicin to mitochondria by altering the drug molecule's intracellular sorting and transportation routes. Efficient mitochondrial targeting with amph-DOX causes a significant increase of reactive oxygen species levels in tumor cells, resulting in markedly improved antitumor efficacy than the unmodified doxorubicin. Amphiphilic modification provides a simple strategy to simultaneously increase the efficacy and safety of doxorubicin in cancer chemotherapy.

Subcellular drug distribution: mechanisms and roles in drug efficacy, toxicity, resistance, and targeted delivery

After administration, drug molecules usually enter target cells to access their intracellular targets. In eukaryotic cells, these targets are often located in organelles, including the nucleus, endoplasmic reticulum, mitochondria, lysosomes, Golgi apparatus, and peroxisomes. Each organelle type possesses unique biological features. For example, mitochondria possess a negative transmembrane potential, while lysosomes have an intraluminal delta pH. Other properties are common to several organelle types, such as the presence of ATP-binding cassette (ABC) or solute carrier-type (SLC) transporters that sequester or pump out xenobiotic drugs. Studies on subcellular drug distribution are critical to understand the efficacy and toxicity of drugs along with the body's resistance to them and to potentially offer hints for targeted subcellular drug delivery. This review summarizes the results of studies from 1990 to 2017 that examined the subcellular distribution of small molecular drugs. We hope this review will aid in the understanding of drug distribution within cells.

Nanopreparations for mitochondria targeting drug delivery system: Current strategies and future prospective

Mitochondria are a novel and promising therapeutic target for diagnosis, treatment and prevention of a lot of human diseases such as cancer, metabolic diseases and neurodegenerative disease. Owing to the mitochondrial special bilayer structure and highly negative potential nature, therapeutic molecules have multiple difficulties in reaching mitochondria. To overcome multiple barriers for targeting mitochondria, the researchers developed various pharmaceutical preparations such as liposomes, polymeric nanoparticles and inorganic nanoparticles modified by mitochondriotropic moieties like dequalinium (DQA), triphenylphosphonium (TPP), mitochondrial penetrating peptides (MPPs) and mitochondrial protein import machinery that allow specific targeting. The targeted formulations exhibited enhanced pharmacological effect and better therapeutic effect than their untargeted counterpart both in vitro and in vivo. Nanocarriers may be used for bio-therapeutic delivery into specific mitochondria that possess a great potential treatment of mitochondria related diseases.

Mitochondria-Targeted Triphenylphosphonium-Based Compounds: Syntheses, Mechanisms of Action, and Therapeutic and Diagnostic Applications

Mitochondria are recognized as one of the most important targets for new drug design in cancer, cardiovascular, and neurological diseases. Currently, the most effective way to deliver drugs specifically to mitochondria is by covalent linking a lipophilic cation such as an alkyltriphenylphosphonium moiety to a pharmacophore of interest. Other delocalized lipophilic cations, such as rhodamine, natural and synthetic mitochondria-targeting peptides, and nanoparticle vehicles, have also been used for mitochondrial delivery of small molecules. Depending on the approach used, and the cell and mitochondrial membrane potentials, more than 1000-fold higher mitochondrial concentration can be achieved. Mitochondrial targeting has been developed to study mitochondrial physiology and dysfunction and the interaction between mitochondria and other subcellular organelles and for treatment of a variety of diseases such as neurodegeneration and cancer. In this Review, we discuss efforts to target small-molecule compounds to mitochondria for probing mitochondria function, as diagnostic tools and potential therapeutics. We describe the physicochemical basis for mitochondrial accumulation of lipophilic cations, synthetic chemistry strategies to target compounds to mitochondria, mitochondrial probes, and sensors, and examples of mitochondrial targeting of bioactive compounds. Finally, we review published attempts to apply mitochondria-targeted agents for the treatment of cancer and neurodegenerative diseases.

Nanotechnology inspired tools for mitochondrial dysfunction related diseases

Mitochondrial dysfunctions are recognized as major factors for various diseases including cancer, cardiovascular diseases, diabetes, neurological disorders, and a group of diseases so called "mitochondrial dysfunction related diseases". One of the major hurdles to gain therapeutic efficiency in diseases where the targets are located in the mitochondria is the accessibility of the targets in this compartmentalized organelle that imposes barriers toward internalization of ions and molecules. Over the time, different tools and techniques were developed to improve therapeutic index for mitochondria acting drugs. Nanotechnology has unfolded as one of the logical and encouraging tools for delivery of therapeutics in controlled and targeted manner simultaneously reducing side effects from drug overdose. Tailor-made nanomedicine based therapeutics can be an excellent tool in the toolbox for diseases associated with mitochondrial dysfunctions. In this review, we present an extensive coverage of possible therapeutic targets in different compartments of mitochondria for cancer, cardiovascular, and mitochondrial dysfunction related diseases.

Mitochondria-targeting particles

Mitochondria are a promising therapeutic target for the detection, prevention and treatment of various human diseases such as cancer, neurodegenerative diseases, ischemia-reperfusion injury, diabetes and obesity. To reach mitochondria, therapeutic molecules need to not only gain access to specific organs, but also to overcome multiple barriers such as the cell membrane and the outer and inner mitochondrial membranes. Cellular and mitochondrial barriers can be potentially overcome through the design of mitochondriotropic particulate carriers capable of transporting drug molecules selectively to mitochondria. These particulate carriers or vectors can be made from lipids (liposomes), biodegradable polymers, or metals, protecting the drug cargo from rapid elimination and degradation in vivo. Many formulations can be tailored to target mitochondria by the incorporation of mitochondriotropic agents onto the surface and can be manufactured to desired sizes and molecular charge. Here, we summarize recently reported strategies for delivering therapeutic molecules to mitochondria using various particle-based formulations.

Novel therapeutic approaches for pulmonary arterial hypertension: Unique molecular targets to site-specific drug delivery

Pulmonary arterial hypertension (PAH) is a cardiopulmonary disorder characterized by increased blood pressure in the small arterioles supplying blood to lungs for oxygenation. Advances in understanding of molecular and cellular biology techniques have led to the findings that PAH is indeed a cascade of diseases exploiting multi-faceted complex pathophysiology, with cellular proliferation and vascular remodeling being the key pathogenic events along with several cellular pathways involved. While current therapies for PAH do provide for amelioration of disease symptoms and acute survival benefits, their full therapeutic potential is hindered by patient incompliance and off-target side effects. To overcome the issues related with current therapy and to devise a more selective therapy, various novel pathways are being investigated for PAH treatment. In addition, inability to deliver anti-PAH drugs to the disease site i.e., distal pulmonary arterioles has been one of the major challenges in achieving improved patient outcomes and improved therapeutic efficacy. Several novel carriers have been explored to increase the selectivity of currently approved anti-PAH drugs and to act as suitable carriers for the delivery of investigational drugs. In the present review, we have discussed potential of various novel molecular pathways/targets including RhoA/Rho kinase, tyrosine kinase, endothelial progenitor cells, vasoactive intestinal peptide, and miRNA in PAH therapeutics. We have also discussed various techniques for site-specific drug delivery of anti-PAH therapeutics so as to improve the efficacy of approved and investigational drugs. This review will provide gainful insights into current advances in PAH therapeutics with an emphasis on site-specific drug payload delivery.

Design and Synthesis of Antitumor Heck-Coupled Sclareol Analogues: Modulation of BH3 Family Members by SS-12 in Autophagy and Apoptotic Cell Death

Sclareol, a promising anticancer labdane diterpene, was isolated from Salvia sclarea. Keeping the basic stereochemistry-rich framework of the molecule intact, a method for the synthesis of novel sclareol analogues was designed using palladium(II)-catalyzed oxidative Heck coupling reaction in order to study their structure-activity relationship. Both sclareol and its derivatives showed an interesting cytotoxicity profile, with 15-(4-fluorophenyl)sclareol (SS-12) as the most potent analogue, having IC50 = 0.082 μM against PC-3 cells. It was found that SS-12 commonly interacts with Bcl-2 and Beclin 1 BH3 domain proteins and enhances autophagic flux by modulating autophagy-related proteins. Moreover, inhibition of autophagy by autophagy inhibitors protected against SS-12-induced apoptosis. Finally, SS-12 effectively suppressed tumor growth in vivo in Ehrlich's ascitic and solid Sarcoma-180 mouse models.

Synthesis of triphenylphosphonium phospholipid conjugates for the preparation of mitochondriotropic liposomes

Surface modification of liposomes with a ligand is facilitated by the conjugation of the ligand to a hydrophobic molecule that serves to anchor the ligand to the liposomal bilayer. We describe here a simple protocol to conjugate a triphenylphosphonium group to several commercially available functionalized phospholipids. The resulting triphenylphosphonium conjugated lipids can be used to prepare liposomes that preferentially associate with mitochondria when exposed to live mammalian cells in culture.

Dual peptide conjugation strategy for improved cellular uptake and mitochondria targeting

Mitochondria are critical regulators of cellular function and survival. Delivery of therapeutic and diagnostic agents into mitochondria is a challenging task in modern pharmacology because the molecule to be delivered needs to first overcome the cell membrane barrier and then be able to actively target the intracellular organelle. Current strategy of conjugating either a cell penetrating peptide (CPP) or a subcellular targeting sequence to the molecule of interest only has limited success. We report here a dual peptide conjugation strategy to achieve effective delivery of a non-membrane-penetrating dye 5-carboxyfluorescein (5-FAM) into mitochondria through the incorporation of both a mitochondrial targeting sequence (MTS) and a CPP into one conjugated molecule. Notably, circular dichroism studies reveal that the combined use of α-helix and PPII-like secondary structures has an unexpected, synergistic contribution to the internalization of the conjugate. Our results suggest that although the use of positively charged MTS peptide allows for improved targeting of mitochondria, with MTS alone it showed poor cellular uptake. With further covalent linkage of the MTS-5-FAM conjugate to a CPP sequence (R8), the dually conjugated molecule was found to show both improved cellular uptake and effective mitochondria targeting. We believe these results offer important insight into the rational design of peptide conjugates for intracellular delivery.

Insight into nanoparticle cellular uptake and intracellular targeting

Collaborative efforts from the fields of biology, materials science, and engineering are leading to exciting progress in the development of nanomedicines. Since the targets of many therapeutic agents are localized in subcellular compartments, modulation of nanoparticle-cell interactions for efficient cellular uptake through the plasma membrane and the development of nanomedicines for precise delivery to subcellular compartments remain formidable challenges. Cellular internalization routes determine the post-internalization fate and intracellular localization of nanoparticles. This review highlights the cellular uptake routes most relevant to the field of non-targeted nanomedicine and presents an account of ligand-targeted nanoparticles for receptor-mediated cellular internalization as a strategy for modulating the cellular uptake of nanoparticles. Ligand-targeted nanoparticles have been the main impetus behind the progress of nanomedicines towards the clinic. This strategy has already resulted in remarkable progress towards effective oral delivery of nanomedicines that can overcome the intestinal epithelial barrier. A detailed overview of the recent developments in subcellular targeting as a novel platform for next-generation organelle-specific nanomedicines is also provided. Each section of the review includes prospects, potential, and concrete expectations from the field of targeted nanomedicines and strategies to meet those expectations.

Nanoparticles and their applications in cell and molecular biology

Nanoparticles can be engineered with distinctive composition, size, shape, and surface chemistry to enable novel techniques in a wide range of biological applications. The unique properties of nanoparticles and their behavior in biological milieu also enable exciting and integrative approaches to studying fundamental biological questions. This review will provide an overview of various types of nanoparticles and concepts of targeting nanoparticles. We will also discuss the advantages and recent applications of using nanoparticles as tools for drug delivery, imaging, sensing, and for the understanding of basic biological processes.

Molecular vehicles for mitochondrial chemical biology and drug delivery

The mitochondria within human cells play a major role in a variety of critical processes involved in cell survival and death. An understanding of mitochondrial involvement in various human diseases has generated an appreciable amount of interest in exploring this organelle as a potential drug target. As a result, a number of strategies to probe and combat mitochondria-associated diseases have emerged. Access to mitochondria-specific delivery vectors has allowed the study of biological processes within this intracellular compartment with a heightened level of specificity. In this review, we summarize the features of existing delivery vectors developed for targeting probes and therapeutics to this highly impermeable organelle. We also discuss the major applications of mitochondrial targeting of bioactive molecules, which include the detection and treatment of oxidative damage, combating bacterial infections, and the development of new therapeutic approaches for cancer. Future directions include the assessment of the therapeutic benefit achieved by mitochondrial targeting for treatment of disease in vivo. In addition, the availability of mitochondria-specific chemical probes will allow the elucidation of the details of biological processes that occur within this cellular compartment.

Mitochondria-specific nano-emulsified therapy for myocardial protection against doxorubicin-induced cardiotoxicity

The quinonoid anthracycline, doxorubicin (Adriamycin), is a widely used potent antineoplastic agent, showing the broadest spectrum of antineoplastic activity against various types of solid carcinomas, hematological malignancies, and soft tissue sarcomas. Unfortunately, the clinical use of doxorubicin is associated with cumulative dose-limiting cardiac toxicity, manifested as cardiomyopathy and congestive heart failure, in which mitochondrial damage is primarily implicated. Free radical formation at and inside mitochondria, in particular the rise of reactive oxygen species (ROS), has long been hypothesized as the common mechanism by which doxorubicin causes this severe cardiotoxicity. Concomitant with newly gained insights into the central role of mitochondria in programmed cell death (apoptosis), irreversible destabilization of mitochondrial membrane permeability transition (mMPT), and disruption of mitochondrial Ca(2+) homeostasis have been strongly implicated in triggering myocardial apoptosis, due to accumulated doxorubicin dosing. Hence, our current protocols show the development of mitochondria-targeted nanoemulsions (NEs), based on previous work using nano-vesicle surface modification with mitochondriotropic triphenylphosphonium (TPP) ligands, which have successfully been demonstrated to target drug and DNA-loaded liposomes to mitochondria in living mammalian cells. Our mitochondria-specific TPP-coated therapeutic NEs are prepared using tocopherol oxygen scavengers and are highly loaded with mitochondria-stabilizing therapeutics, namely, cyclosporine A (CsA). Our targeted nano-formulation, proposed as injectable adjuvant therapy, is capable of reaching target affected mitochondria in sufficient therapeutic concentration, in order to revert or at least limit oxidative and non-oxidative doxorubicin-induced mitochondrial damage, manifested in affected cardiac muscle tissues, Based on several encouraging studies using in vitro model rat cardiac muscle, H9C2 cardiomyocytes, and vascular media tunica media, A10, cell cultures, our proof-of principal mitochondriotropic nano-therapy demonstrates strong potential to improve not only the cardiac safety profile, through concurrent rescue administration of targeted nano-encapsulated FDA-approved cyclosporine A (CSA), but also dosing range of the currently available potent adriamycin/doxorubicin-based chemotherapy regimens.

Imaging C-Fos Gene Expression in Burns Using Lipid Coated Spion Nanoparticles

MR imaging of gene transcription is important as it should enable the non-invasive detection of mRNA alterations in disease. A range of MRI methods have been proposed for in vivo molecular imaging of cells based on the use of ultra-small super-paramagnetic iron oxide (USPIO) nanoparticles and related susceptibility weighted imaging methods. Although immunohistochemistry can robustly differentiate the expression of protein variants, there is currently no direct gene assay technique that is capable of differentiating established to differentiate the induction profiles of c-Fos mRNA in vivo. To visualize the differential FosB gene expression profile in vivo after burn trauma, we developed MR probes that link the T2* contrast agent [superparamagnetic iron oxide nanoparticles (SPION)] with an oligodeoxynucleotide (ODN) sequence complementary to FosB mRNA to visualize endogenous mRNA targets via in vivo hybridization. The presence of this SPION-ODN probe in cells results in localized signal reduction in T2*-weighted MR images, in which the rate of signal reduction (R2*) reflects the regional iron concentration at different stages of amphetamine (AMPH) exposure in living mouse tissue. Our aim was to produce a superior contrast agent that can be administered using systemic as opposed to local administration and which will target and accumulate at sites of burn injury. Specifically, we developed and evaluated a PEGylated lipid coated MR probe with ultra-small super-paramagnetic iron oxide nanoparticles (USPION, a T2 susceptibility agent) coated with cationic fusogenic lipids, used for cell transfection and gene delivery and covalently linked to a phosphorothioate modified oligodeoxynucleotide (sODN) complementary to c-Fos mRNA (SPION-cFos) and used the agent to image mice with leg burns. Our study demonstrated the feasibility of monitoring burn injury using MR imaging of c-Fos transcription in vivo, in a clinically relevant mouse model of burn injury for the first time.

Engineering of blended nanoparticle platform for delivery of mitochondria-acting therapeutics

Mitochondrial dysfunctions cause numerous human disorders. A platform technology based on biodegradable polymers for carrying bioactive molecules to the mitochondrial matrix could be of enormous potential benefit in treating mitochondrial diseases. Here we report a rationally designed mitochondria-targeted polymeric nanoparticle (NP) system and its optimization for efficient delivery of various mitochondria-acting therapeutics by blending a targeted poly(d,l-lactic-co-glycolic acid)-block (PLGA-b)-poly(ethylene glycol) (PEG)-triphenylphosphonium (TPP) polymer (PLGA-b-PEG-TPP) with either nontargeted PLGA-b-PEG-OH or PLGA-COOH. An optimized formulation was identified through in vitro screening of a library of charge- and size-varied NPs, and mitochondrial uptake was studied by qualitative and quantitative investigations of cytosolic and mitochondrial fractions of cells treated with blended NPs composed of PLGA-b-PEG-TPP and a triblock copolymer containing a fluorescent quantum dot, PLGA-b-PEG-QD. The versatility of this platform was demonstrated by studying various mitochondria-acting therapeutics for different applications, including the mitochondria-targeting chemotherapeutics lonidamine and α-tocopheryl succinate for cancer, the mitochondrial antioxidant curcumin for Alzheimer's disease, and the mitochondrial uncoupler 2,4-dinitrophenol for obesity. These biomolecules were loaded into blended NPs with high loading efficiencies. Considering efficacy, the targeted PLGA-b-PEG-TPP NP provides a remarkable improvement in the drug therapeutic index for cancer, Alzheimer's disease, and obesity compared with the nontargeted construct or the therapeutics in their free form. This work represents the potential of a single, programmable NP platform for the diagnosis and targeted delivery of therapeutics for mitochondrial dysfunction-related diseases.

Surface conjugation of triphenylphosphonium to target poly(amidoamine) dendrimers to mitochondria

Dendrimers have emerged as promising carriers for the delivery of a wide variety of pay-loads including therapeutic drugs, imaging agents and nucleic acid materials into biological systems. The current work aimed to develop a novel mitochondria-targeted generation 5 poly(amidoamine) (PAMAM) dendrimer (G(5)-D). To achieve this goal, a known mitochondriotropic ligand triphenylphosphonium (TPP) was conjugated on the surface of the dendrimer. A fraction of the cationic surface charge of G(5)-D was neutralized by partial acetylation of the primary amine groups. Next, the mitochondria-targeted dendrimer was synthesized via the acid-amine-coupling conjugation reaction between the acid group of (3-carboxypropyl)triphenyl-phosphonium bromide and the primary amines of the acetylated dendrimer (G(5)-D-Ac). These dendrimers were fluorescently labeled with fluorescein isothiocyanate (FITC) to quantify cell association by flow cytometry and for visualization under confocal laser scanning microscopy to assess the mitochondrial targeting in vitro. The newly developed TPP-anchored dendrimer (G(5)-D-Ac-TPP) was efficiently taken up by the cells and demonstrated good mitochondrial targeting. In vitro cytotoxicity experiments carried out on normal mouse fibroblast cells (NIH-3T3) had greater cell viability in the presence of the G(5)-D-Ac-TPP compared to the parent unmodified G(5)-D. This mitochondria-targeted dendrimer-based nanocarrier could be useful for imaging as well as for selective delivery of bio-actives to the mitochondria for the treatment of diseases associated with mitochondrial dysfunction.

Liposomes loaded with paclitaxel and modified with novel triphenylphosphonium-PEG-PE conjugate possess low toxicity, target mitochondria and demonstrate enhanced antitumor effects in vitro and in vivo

Previously, stearyl triphenylphosphonium (STPP)-modified liposomes (STPP-L) were reported to target mitochondria. To overcome a non-specific cytotoxicity of STPP-L, we synthesized a novel polyethylene glycol-phosphatidylethanolamine (PEG-PE) conjugate with the TPP group attached to the distal end of the PEG block (TPP-PEG-PE). This conjugate was incorporated into the liposomal lipid bilayer, and the modified liposomes were studied for their toxicity, mitochondrial targeting, and efficacy in delivering paclitaxel (PTX) to cancer cells in vitro and in vivo. These TPP-PEG-PE-modified liposomes (TPP-PEG-L), surface grafted with as high as 8 mol% of the conjugate, were less cytotoxic compared to STPP-L or PEGylated STPP-L. At the same time, TPP-PEG-L demonstrated efficient mitochondrial targeting in cancer cells as shown by confocal microscopy in co-localization experiments with stained mitochondria. PTX-loaded TPP-PEG-L demonstrated enhanced PTX-induced cytotoxicity and anti-tumor efficacy in cell culture and mouse experiments compared to PTX-loaded unmodified plain liposomes (PL). Thus, TPP-PEG-PE can serve as a targeting ligand to prepare non-toxic liposomes as mitochondria-targeted drug delivery systems (DDS).

Functionalized nanosystems for targeted mitochondrial delivery

Mitochondrial dysfunction including oxidative stress and DNA mutations underlies the pathology of various diseases including Alzheimer's disease and diabetes, necessitating the development of mitochondria targeted therapeutic agents. Nanotechnology offers unique tools and materials to target therapeutic agents to mitochondria. As discussed in this paper, a variety of functionalized nanosystems including polymeric and metallic nanoparticles as well as liposomes are more effective than plain drug and non-functionalized nanosystems in delivering therapeutic agents to mitochondria. Although the field is in its infancy, studies to date suggest the superior therapeutic activity of functionalized nanosystems for treating mitochondrial defects.