Anticancer Effect of α-Tocopheryl Succinate Delivered by Mitochondria-Targeted Mesoporous Silica Nanoparticles

A non-residue surface modification strategy for active-targeting fluorescent silica nanoparticles to cellular organelles

Silica nanoparticles (SiNPs) with a chemically modified surface typically have a complicated chemical composition, which can significantly differ from their intended design. In this study, we systematically studied the effects of two surface modification methods on active-targeting of intracellular organelles of SiNPs: (1) the widely used step-by-step approach, which involves modifying SiNPs in two steps, i.e., the outer surface of SiNPs was firstly modified with amino groups and then these amino groups were linked with targeting groups, and (2) a newly developed one-step approach in which the ligand-silane complex is initially synthesized, followed by chemically immobilizing the complex on the surface of SiNPs. In the one-step approach, the molar ratio of reactants was precisely tuned so that there are no reactive groups left on the outer surface of SiNPs. Two essential organelles, mitochondria and the nucleus, were selected to compare the targeting performances of SiNPs synthesized via these two approaches. By characterizing physicochemical properties, including structural properties, the number of amino groups, surface charge, polydispersity, and cell colocalization, we demonstrated that SiNPs synthesized via the one-step approach with no residual linkage groups on their surface showed significantly improved mitochondria- and nucleus-targeting performances. This precise control of surface properties allows for optimized biological behavior and active-targeting efficiency of SiNPs. We anticipate that such simple and efficient synthetic strategies will enable the synthesis of effective SiNPs for active-targeting organelles in various biological applications.

Engineering metabolism to modulate immunity

Metabolic programming and reprogramming have emerged as pivotal mechanisms for altering immune cell function. Thus, immunometabolism has become an attractive target area for treatment of immune-mediated disorders. Nonetheless, many hurdles to delivering metabolic cues persist. In this review, we consider how biomaterials are poised to transform manipulation of immune cell metabolism through integrated control of metabolic configurations to affect outcomes in autoimmunity, regeneration, transplant, and cancer. We emphasize the features of nanoparticles and other biomaterials that permit delivery of metabolic cues to the intracellular compartment of immune cells, or strategies for altering signals in the extracellular space. We then provide perspectives on the potential for reciprocal regulation of immunometabolism by the physical properties of materials themselves. Lastly, opportunities for clinical translation are highlighted. This discussion contributes to our understanding of immunometabolism, biomaterials-based strategies for altering metabolic configurations in immune cells, and emerging concepts in this evolving field.

Mitochondrial Dysfunction: Pathophysiology and Mitochondria-Targeted Drug Delivery Approaches

Mitochondria are implicated in a wide range of functions apart from ATP generation, and, therefore, constitute one of the most important organelles of cell. Since healthy mitochondria are essential for proper cellular functioning and survival, mitochondrial dysfunction may lead to various pathologies. Mitochondria are considered a novel and promising therapeutic target for the diagnosis, treatment, and prevention of various human diseases including metabolic disorders, cancer, and neurodegenerative diseases. For mitochondria-targeted therapy, there is a need to develop an effective drug delivery approach, owing to the mitochondrial special bilayer structure through which therapeutic molecules undergo multiple difficulties in reaching the core. In recent years, various nanoformulations have been designed such as polymeric nanoparticles, liposomes, inorganic nanoparticles conjugate with mitochondriotropic moieties such as mitochondria-penetrating peptides (MPPs), triphenylphosphonium (TPP), dequalinium (DQA), and mitochondrial protein import machinery for overcoming barriers involved in targeting mitochondria. The current approaches used for mitochondria-targeted drug delivery have provided promising ways to overcome the challenges associated with targeted-drug delivery. Herein, we review the research from past years to the current scenario that has identified mitochondrial dysfunction as a major contributor to the pathophysiology of various diseases. Furthermore, we discuss the recent advancements in mitochondria-targeted drug delivery strategies for the pathologies associated with mitochondrial dysfunction.

Triphenylphosphonium Modified Mesoporous Silica Nanoparticle for Enhanced Algicidal Efficacy of Cyclohexyl-(3,4-dichlorobenzyl) Amine

Mesoporous silica nanoparticles (MSNPs) have been widely used for the delivery of different hydrophilic and hydrophobic drugs owing to their large surface area and ease of chemical alteration. On the other hand, triphenylphosphonium cation (TPP+) with high lipophilicity has a great mitochondrial homing property that stimulates the internalization of drugs into cells. Therefore, we designed a TPP-modified MSNP to enhance the algicidal activity of our new algicidal agent cyclohexyl-(3,4-dichlorobenzyl) amine (DP92). In this study, algicidal activity was evaluated by assessing the growth rate inhibition of two harmful algal blooms (HABs), Heterosigma akashiwo and Heterocapsa circularisquama, after treatment with DP92-loaded MSNP or TPP-MSNP and DP92 in DMSO (as control). For H. akashiwo, the IC50 values of TPP-MSNP and MSNP are 0.03 ± 0.01 and 0.16 ± 0.03 µM, respectively, whereas the value of the control is 0.27 ± 0.02 µM. For H. circularisquama, the IC50 values of TPP-MSNP and MSNP are 0.10 ± 0.02 and 0.29 ± 0.02 µM, respectively, whereas the value of the control is 1.90 ± 0.09 µM. Results have indicated that TPP-MSNP efficiently enhanced the algicidal activity of DP92, signifying the prospect of using DP92-loaded TPP-MSNP as an algicidal agent for the superior management of HABs.

Advances in Delivering Oxidative Modulators for Disease Therapy

Oxidation modulators regarding antioxidants and reactive oxygen species (ROS) inducers have been used for the treatment of many diseases. However, a systematic review that refers to delivery system for divergent modulation of oxidative level within the biomedical scope is lacking. To provide a comprehensive summarization and analysis, we review pilot designs for delivering the oxidative modulators and the main applications for inflammatory treatment and tumor therapy. On the one hand, the antioxidants based delivery system can be employed to downregulate ROS levels at inflammatory sites to treat inflammatory diseases (e.g., skin repair, bone-related diseases, organ dysfunction, and neurodegenerative diseases). On the other hand, the ROS inducers based delivery system can be employed to upregulate ROS levels at the tumor site to kill tumor cells (e.g., disrupt the endogenous oxidative balance and induce lethal levels of ROS). Besides the current designs of delivery systems for oxidative modulators and the main application cases, prospects for future research are also provided to identify intelligent strategies and inspire new concepts for delivering oxidative modulators.

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.

Drug delivery for metabolism targeted cancer immunotherapy

Drug delivery vehicles have made a great impact on cancer immunotherapies in clinics and pre-clinical research. Notably, the science of delivery of cancer vaccines and immunotherapeutics, modulating immune cell functions has inspired development of several successful companies and clinical products. Interestingly, these drug delivery modalities not only modulate the function of immune cells (often quantified at the mRNA and protein levels), but also modulate the metabolism of these cells. Specifically, cancer immunotherapy often leads to activation of different immune cells such as dendritic cells, macrophages and T cells, which is driven by energy metabolism of these cells. Recently, there has been a great excitement about interventions that can directly modulate the energy metabolism of these immune cells and thus affect their function and in turn lead to a robust cancer immune response. Here we review few strategies that have been tested in clinic and pre-clinical research for generating effective metabolism-associated cancer therapies and immunotherapies.

Mitochondria-Targeted Mesoporous Titanium Dioxide Nanoplatform for Synergistic Nitric Oxide Gas-Sonodynamic Therapy of Breast Cancer

Background

Sonodynamic therapy (SDT) has rapidly advanced as a promising alternative to conventional photodynamic therapy owing to its preferable therapeutic depth. However, single-modal SDT exhibits limited efficacy due to the long-term hypoxia in tumors.

Method and Results

To address these issues, we proposed a synergistic SDT strategy that integrates mitochondrial targeting with nitric oxide (NO) gas therapy by using multifunctional nanoplatforms. The nanoplatform, which was named as T-mTNPs@L-Arg, was composed of mesoporous titanium dioxide loaded with the NO donor precursor L-arginine (L-Arg) and modified with triphenyl phosphonium (TPP), a mitochondria-targeting ligand. Therefore, T-mTNPs@L-Arg could efficiently concentrate into mitochondria and release NO gas as well as generate reactive oxygen species (ROS) with ultrasound stimulus. Importantly, the released NO gas exerted multiple synergies with SDT, including inducing NO poisoning, generating more lethal reactive nitrogen species (RNS) by reaction with ROS, and alleviating hypoxia through NO-mediated mitochondrial respiration inhibition. On account of the synergistic effects, T-mTNPs@L-Arg showed an outstanding SDT efficacy and a reduced side effect.

Conclusion

This work designed a nanoplatform to integrate mitochondria targeting, SDT and NO gas therapy, providing a new strategy for highly efficient breast cancer therapy.

A Mitochondrial Oxidative Stress Amplifier to Overcome Hypoxia Resistance for Enhanced Photodynamic Therapy

Hypoxia-induced resistance to tumor treatment restricts further development of photodynamic therapy. Instead of simple reoxygenation to relieve hypoxia in traditional therapeutic approaches, a mitochondria-targeted reactive oxygen species (ROS) amplifier is constructed to reverse hypoxia resistance and enhance tumor sensitivity to hypoxia-resistant photodynamic therapy. Mesoporous silica nanoparticles are modified with triphenylphosphine to enhance its blood circulation and endow it with mitochondria-targeted specificity. α-Tocopherol succinate and indocyanine green are loaded in mitochondria-targeted mesoporous silica nanoparticles to reduce innate oxygen consumption by blocking mitochondrial respiration chain, leading to endogenous mitochondrial ROS burst and imaging-guided photodynamic therapy. This mitochondria-targeted oxidative stress amplifier not only disrupts mitochondrial redox homeostasis and triggers long-term high oxidative stress but also makes tumor more sensitive to hypoxia-resistant photodynamic therapy. The imaging-guided ROS amplifier confirms the feasibility and effectiveness of both in vitro and in vivo anticancer performance, suggesting a promising clinical strategy in hypoxia-related tumor treatment.

Nanoplatform based on GSH-responsive mesoporous silica nanoparticles for cancer therapy and mitochondrial targeted imaging

Mitochondria, as the energy factory of most cells, are not only responsible for the generation of adenosine triphosphoric acid (ATP) but also essential targets for therapy and diagnosis of various diseases, especially cancer. The safe and potential nanoplatform which can deliver various therapeutic agents to cancer cells and mitochondrial targeted imaging is urgently required. Herein, Au nanoparticles (AuNPs), mesoporous silica nanoparticles (MSN), cationic ligand (triphenylphosphine (TPP)), doxorubicin (DOX), and carbon nanodots (CDs) were utilized to fabricate mitochondrial targeting drug delivery system (denoted as CDs(DOX)@MSN-TPP@AuNPs). Since AuNPs, as the gatekeepers, can be etched by intracellular glutathione (GSH) via ligand exchange induced etching process, DOX can be released into cells in a GSH-dependent manner which results in the superior GSH-modulated tumor inhibition activity. Moreover, after etching by GSH, the CDs(DOX)@MSN-TPP@AuNPs can serve as promising fluorescent probe (λ_ex = 633 nm, λ_em = 650 nm) for targeted imaging of mitochondria in living cells with near-infrared fluorescence. The induction of apoptosis derived from the membrane depolarization of mitochondria is the primary anti-tumor route of CDs(DOX)@MSN-TPP@AuNPs. As a kind of GSH-responsive mitochondrial targeting nanoplatform, it holds great promising for effective cancer therapy and mitochondrial targeted imaging. The mitochondrial targeting drug delivery system was fabricated by AuNPs, MSN, TPP, and CDs. The nanoplatform can realize redox-responsive drug delivery and targeted imaging of mitochondria in living cells to improve the therapeutic efficiency and security.

Efficient drug delivery and anticancer effect of micelles based on vitamin E succinate and chitosan derivatives

Nanocarriers have emerged as a promising cancer drug delivery strategy. Multi-drug resistance caused by overexpression of multiple-drug excretion transporters in tumor cells is the major obstacle to successful chemotherapy. Vitamin E derivatives have many essential functions for drug delivery applications, such as biological components that are hydrophobic, stable, water-soluble enhancing compounds, and anticancer activity. In addition, vitamin E derivatives are also effective mitocan which can overcome multi-drug resistance by binding to P glycoproteins. Here, we developed a carboxymethyl chitosan/vitamin E succinate nano-micellar system (O-CMCTS-VES). The synthesized polymers were characterized by Fourier Transform IR, and ¹H NMR spectra. The mean sizes of O-CMCTS-VES and DOX-loaded nanoparticles were around 177 nm and 208 nm. The drug loading contents were 6.1%, 13.0% and 10.6% with the weight ratio of DOX to O-CMCTS-VES corresponding 1:10, 2:10 and 3:10, and the corresponding EEs were 64.3%, 74.5% and 39.7%. Cytotoxicity test, hemolysis test and histocompatibility test showed that it had good biocompatibility in vitro and in vivo. Drug release experiments implied good pH sensitivity and sustained-release effect. The DOX/O-CMCTS-VES nanoparticles can be efficiently taken up by HepG2 cancer cells and the tumor inhibition rate is up to 62.57%. In the in vivo study by using H22 cells implanted Balb/C mice, DOX/O-CMCTS-VES reduced the tumor volume and weight efficiently with a TIR of 35.58%. The newly developed polymeric micelles could successfully be utilized as a nanocarrier system for hydrophobic chemotherapeutic agents for the treatment of solid tumors.

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A nano-micellar system (O-CMCTS-VES) constituted by carboxymethyl chitosan and vitamin E succinate was fabricated.

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The micelles hold high cytocompatibility, hemocompatibility, tissue compatibility, and drug load contents.

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Drug release experiments implied good pH sensitivity and sustained-release effect of O-CMCTS-VES.

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O-CMCTS-VES loading DOX showed efficient anti-tumor effect in vitro and in vivo.

Vitamin E succinate with multiple functions: A versatile agent in nanomedicine-based cancer therapy and its delivery strategies

Vitamin E succinate (VES), a succinic acid ester of vitamin E, is one of the most effective anticancer compounds of the vitamin E family. VES can inhibit tumor growth by multiple pathways mainly involve tumor proliferation inhibition, apoptosis induction, and metastasis prevention. More importantly, the mitochondrial targeting and damaging property of VES endows it with great potential in exhibiting synergetic effect with conventional chemotherapeutic drugs and overcoming multidrug resistance (MDR). Given the lipophilicity of VES that hinders its bioavailability and therapeutic activity, nanotechnology with multiple advantages has been widely explored to deliver VES and opened up new avenues for its in vivo application. This review aims to introduce the anticancer mechanisms of VES and summarize its delivery strategies using nano-drug delivery systems. Specifically, VES-based combination therapy for synergetic anticancer effect, MDR-reversal, and oral chemotherapy improvement are highlighted. Finally, the challenges and perspectives are discussed.

Poly(ester-thioether) microspheres co-loaded with erlotinib and α-tocopheryl succinate for combinational therapy of non-small cell lung cancer

Polymer microspheres are attracting wide attention in localized cancer therapy owing to the excellent biocompatibility and drug loading capacity, controllable biodegradation speeds, and minimized systemic toxicity. Herein, we presented poly(ester-thioether) microspheres, porous and nonporous, as drug depots for localized therapy of non-small cell lung cancer (NSCLC). Specifically, erlotinib and α-tocopheryl succinate (α-TOS), which are respectively an epidermal growth factor receptor (EGFR) inhibitor and mitochondria destabilizer, were efficiently loaded into porous and nonporous poly(ester-thioether) microspheres for the treatment of EGFR-overexpressing NSCLC (A549 cells). The poly(ester-thioether) microspheres significantly improved the bioavailability of both erlotinib and α-TOS in comparison to the free drug combination, realizing synergistic inhibition of A549 cells both in vitro and in vivo. The porous microspheres displayed faster degradation and drug release than the nonporous counterpart, thereby showing better anticancer efficacy. Overall, our study reported a new anticancer strategy of erlotinib and α-TOS combination for therapy of NSCLC, and established that poly(ester-thioether) microspheres could be a robust and biodegradable reservoir for drug delivery and localized cancer therapy.

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.

In vivo Targeting of Liver Cancer with Tissue- and Nuclei-Specific Mesoporous Silica Nanoparticle-Based Nanocarriers in mice

Purpose

Cancer tissue-specific and nuclei-targeted drug delivery is ideal for the delivery of chemotherapy. However, it has only been achieved in in vitro studies mainly due to low efficiency in vivo. In this study, we aimed to establish an efficient dual-targeted system that targets liver cancer tissue as well as the nuclei of cancer cells in vivo.

Methods

We first synthesized TAT peptide (TATp)-mesoporous silica nanoparticle (MSN) complex (TATp-MSN) and generated liposomes that carried liver cancer-specific aptamer TLS11a (TLS11a-LB). We then generated the drug TLS11a-LB@TATp-MSN/doxorubicin (DOX) by mixing TLS11a-LB and DOX-loaded TATp-MSN. After physical and chemical characterization of the nanoparticles, DOX release from these formulations was evaluated at pH 5.0 and 7.4. Furthermore, we also evaluated nuclear localization and cytotoxicity of the drug in H22 cells in vitro and investigated the liver cancer targeting and antitumor activities of the nano-drug in vivo using a H22 tumor-bearing mice model.

Results

TLS11a-LB@TATp-MSN/DOX and its controls were confirmed as nano-drugs (<100 nm) using transmission electron microscopy (TEM). The DOX release rate of TLS11a-LB@TATp-MSN/DOX was significantly faster at pH 5.0 than at pH 7.4. TLS11a-LB@TATp-MSN/DOX effectively targeted the nuclei of H22 cells and released DOX with a higher efficiency than that of the control groups. In addition, TLS11a-LB@TATp-MSN/DOX exhibited slight cytotoxicity, but not significantly more than controls. In vivo studies showed that TLS11a-LB@TATp-MSN accumulated in subcutaneous H22 tumors in the right axilla of BALB/c mice, reaching peak levels at 48 h after intravenous injection, respectively, and demonstrated that TLS11a-LB@TATp-MSN/DOX group enhanced tumor treatment efficacy while reducing systemic side effects.

Conclusion

TLS11a-LB@TATp-MSN/DOX can efficiently deliver DOX to the nuclei of liver cancer cells by dual targeting liver cancer tissue and the nuclei of the cancer cells in mice. Thus, it is a promising nano-drug for the treatment of liver cancer.

Combination Delivery of Alpha-Tocopheryl Succinate and Curcumin Using a GSH-Sensitive Micelle (PAH-SS-PLGA) to Treat Pancreatic Cancer

Pancreatic cancer is one of the highest causes of mortality throughout the world; thus, it requires an effective treatment strategy. Some chemotherapeutic agents used in the clinics or under clinical trials are hydrophobic and have poor aqueous solubility; consequently, they also have minimal systemic bioavailability. Nanoparticle-based drug delivery tactics have the potential for overcoming these limitations and enhancing their therapeutic efficacy. Herein, a glutathione (GSH)-sensitive micelle (PAH-SS-PLGA) was synthesized for the combined delivery of alpha-tocopheryl succinate (TOS) and curcumin to improve its therapeutic efficacy. The chemical structures of PAH-SS-PLGA were analyzed using Proton Nuclear Magnetic Resonance (¹H-NMR) and Fourier Transform Infrared (FTIR) spectroscopy, whereas the particle size, zeta potential, and surface morphology were observed using dynamic light scattering (DLS) and transmission electron microscopy (TEM). In vitro drug release results revealed that more TOS and curcumin were released in the presence of GSH (5 mM) than the physiological pH value. Fluorescence microscopy images revealed that nanoformulated curcumin/rhodamine was uptaken by PAN02 pancreatic cancer cells. In vitro cytotoxicity assays showed higher cytotoxicity for nanoformulated TOS and/or curcumin than free TOS and/or curcumin. In addition, higher cytotoxicity was observed for combination drugs than free drugs alone. Most interestingly, at all tested concentrations of nanoformulated drugs (PAH-SS-PLGA, TOS, and curcumin), the calculated combination index (CI) value was less than one, which shows that TOS and curcumin have a synergistic effect on cellular proliferation inhibition. Overall, synthesized co-polymers are the best carriers for combination drugs, TOS, and curcumin, because they enhance the therapeutic efficacy and improve pancreatic cancer treatments.

Membrane Trafficking and Subcellular Drug Targeting Pathways

The movement of micro and macro molecules into and within a cell significantly governs several of their pharmacokinetic and pharmacodynamic parameters, thus regulating the cellular response to exogenous and endogenous stimuli. Trafficking of various pharmacological agents and other bioactive molecules throughout and within the cell is necessary for the fidelity of the cells but has been poorly investigated. Novel strategies against cancer and microbial infections need a deeper understanding of membrane as well as subcellular trafficking pathways and essentially regulate several aspects of the initiation and spread of anti-microbial and anti-cancer drug resistance. Furthermore, in order to avail the maximum possible bioavailability and therapeutic efficacy and to restrict the unwanted toxicity of pharmacological bioactives, these sometimes need to be functionalized with targeting ligands to regulate the subcellular trafficking and to enhance the localization. In the recent past the scenario drug targeting has primarily focused on targeting tissue components and cell vicinities, however, it is the membranous and subcellular trafficking system that directs the molecules to plausible locations. The effectiveness of the delivery platforms largely depends on their physicochemical nature, intracellular barriers, and biodistribution of the drugs, pharmacokinetics and pharmacodynamic paradigms. Most subcellular organelles possess some peculiar characteristics by which membranous and subcellular targeting can be manipulated, such as negative transmembrane potential in mitochondria, intraluminal delta pH in a lysosome, and many others. Many specialized methods, which positively promote the subcellular targeting and restrict the off-targeting of the bioactive molecules, exist. Recent advancements in designing the carrier molecules enable the handling of membrane trafficking to facilitate the delivery of active compounds to subcellular localizations. This review aims to cover membrane trafficking pathways which promote the delivery of the active molecule in to the subcellular locations, the associated pathways of the subcellular drug delivery system, and the role of the carrier system in drug delivery techniques.

Influence of the Surface Functionalization on the Fate and Performance of Mesoporous Silica Nanoparticles

Mesoporous silica nanoparticles have been broadly applied as drug delivery systems owing to their exquisite features, such as excellent textural properties or biocompatibility. However, there are various biological barriers that prevent their proper translation into the clinic, including: (1) lack of selectivity toward tumor tissues, (2) lack of selectivity for tumoral cells and (3) endosomal sequestration of the particles upon internalization. In addition, their open porous structure may lead to premature drug release, consequently affecting healthy tissues and decreasing the efficacy of the treatment. First, this review will provide a comprehensive and systematic overview of the different approximations that have been implemented into mesoporous silica nanoparticles to overcome each of such biological barriers. Afterward, the potential premature and non-specific drug release from these mesoporous nanocarriers will be addressed by introducing the concept of stimuli-responsive gatekeepers, which endow the particles with on-demand and localized drug delivery.

Sequential-targeting nanocarriers with pH-controlled charge reversal for enhanced mitochondria-located photodynamic-immunotherapy of cancer

Targeting delivery of photosensitizers to mitochondria as the most sensitive cellular organelles to reactive oxygen species (ROS) by positively charged polymeric nanocarriers (NCs) is one of the useful methods for efficient photodynamic therapy (PDT). However, the NCs with positively charged mitochondria-targeting moieties are easily cleaned during circulation, restricting their in vivo applications. Herein, to address this issue and enhance in vivo PDT efficacy, we developed a sequential-targeting delivery system consisting of mitochondria-targeting micelles as the core prepared from the cationic amphiphilic copolymer for loading chlorin e6 (Ce6) and a tumor-targeting pH-dependent charge transformational layer as the shell obtained from 2,3-dimethylmaleic anhydride modified Biotin-PEG₄₀₀₀-NH₂ (BioPEGDMA) via electrostatic interaction. Concealed by the anionic shell, the as-prepared NCs showed longer retention within the first stage of tumor-targeting. Then, the accumulated NCs conversed to positive charge in tumor extracellular microenvironment (pH ∼ 6.5), which could be more effectively internalized by tumor cells, and the re-exposed triphenylphosphonium (TPP) groups endowed their second-stage targetability to the mitochondria. In vivo experiments revealed that the Ce6-loaded NCs exhibited remarkable tumor inhibition rates of 84.1% and 93.2% on BALB/c nude mice and Kunming mice, respectively, under 660 nm NIR irradiation, and stimulated immune responses with upregulated expression of IFN-γ, TNF-α and CD3⁺ in tumor tissues, and enhanced activation of CD3⁺/CD4⁺, CD3⁺/CD8⁺ T lymphocytes and DCs in both tumor tissues and lymph glands. This work provided a new pathway for the development of smart drug delivery system with advanced PDT efficacy. STATEMENT OF SIGNIFICANCE: Although the existing targeting delivery of photosensitizers to mitochondria by positively charged nanocarriers (NCs) have efficiently enhanced photodynamic therapy (PDT), their positive charges caused rapid clearance during circulation, which has restricted their in vivo applications. Therefore, we fabricated a novel sequential-targeting NC to solve the problem. The tumor accumulated NCs conversed to positive charge in tumor extracellular microenvironment, and the re-exposed triphenylphosphonium groups initiated second-stage targetability to mitochondria. This system exhibited remarkable tumor inhibition efficiency both in vitro and in vivo. Moreover, as we hypothesized, mitochondria-located PDT could promote immune response, resulting in improvement of PDT. The strategy of sequential targeting-based PDT in combination with augmented immune response showed a novel pathway for the development of smart drug delivery system with advanced PDT.

Development of Novel Silyl Cyanocinnamic Acid Derivatives as Metabolic Plasticity Inhibitors for Cancer Treatment

Novel silyl cyanocinnamic acid derivatives have been synthesized and evaluated as potential anticancer agents. In vitro studies reveal that lead derivatives 2a and 2b have enhanced cancer cell proliferation inhibition properties when compared to the parent monocarboxylate transporter (MCT) inhibitor cyano-hydroxycinnamic acid (CHC). Further, candidate compounds exhibit several-fold more potent MCT1 inhibition properties as determined by lactate-uptake studies, and these studies are supported by MCT homology modeling and computational inhibitor-docking studies. In vitro effects on glycolysis and mitochondrial metabolism also illustrate that the lead derivatives 2a and 2b lead to significant effects on both metabolic pathways. In vivo systemic toxicity and efficacy studies in colorectal cancer cell WiDr tumor xenograft demonstrate that candidate compounds are well tolerated and exhibit good single agent anticancer efficacy properties.

In Situ Synthesis of Fluorescent Mesoporous Silica-Carbon Dot Nanohybrids Featuring Folate Receptor-Overexpressing Cancer Cell Targeting and Drug Delivery

Multifunctional nanocarrier-based theranostics is supposed to overcome some key problems in cancer treatment. In this work, a novel method for the preparation of a fluorescent mesoporous silica-carbon dot nanohybrid was developed. Carbon dots (CDs), from folic acid as the raw material, were prepared in situ and anchored on the surface of amino-modified mesoporous silica nanoparticles (MSNs-NH₂) via a microwave-assisted solvothermal reaction. The as-prepared nanohybrid (designated MSNs-CDs) not only exhibited strong and stable yellow emission but also preserved the unique features of MSNs (e.g., mesoporous structure, large specific surface area, and good biocompatibility), demonstrating a potential capability for fluorescence imaging-guided drug delivery. More interestingly, the MSNs-CDs nanohybrid was able to selectively target folate receptor-overexpressing cancer cells (e.g., HeLa), indicating that folic acid still retained its function even after undergoing the solvothermal reaction. Benefited by these excellent properties, the fluorescent MSNs-CDs nanohybrid can be employed as a fluorescence-guided nanocarrier for the targeted delivery of anticancer drugs (e.g., doxorubicin), thereby enhancing chemotherapeutic efficacy and reducing side effects. Our studies may provide a facile strategy for the fabrication of multifunctional MSN-based theranostic platforms, which is beneficial in the diagnosis and therapy of cancers in future.

Facile Strategy Enabling Both High Loading and High Release Amounts of the Water-Insoluble Drug Clofazimine Using Mesoporous Silica Nanoparticles

The use of nanocarriers to deliver poorly soluble drugs to the sites of diseases is an attractive and general method, and mesoporous silica nanoparticles (MSNs) are increasingly being used as carriers. However, both loading a large amount of drugs into the pores and still being able to release the drug is a challenge. In this paper, we demonstrate a general strategy based on a companion molecule that chaperones the drug into the pores and also aids it in escaping. A common related strategy is to use a miscible co-solvent dimethyl sulfoxide (DMSO), but although loading may be efficient in DMSO, this co-solvent frequently diffuses into an aqueous environment, leaving the drug behind. We demonstrate the method by using acetophenone (AP), an FDA-approved food additive as the chaperone for clofazimine (CFZ), a water-insoluble antibiotic used to treat leprosy and multidrug-resistant tuberculosis. AP enables a high amount of CFZ cargo into the MSNs and also carries CFZ cargo out from the MSNs effectively when they are in an aqueous biorelevant environment. The amount of loading and the CFZ release efficiency from MSNs were optimized; 4.5 times more CFZ was loaded in MSNs with AP than that with DMSO and 2300 times more CFZ was released than that without the assistance of the AP. In vitro treatment of macrophages infected by Mycobacterium tuberculosis with the optimized CFZ-loaded MSNs killed the bacteria in the cells in a dose-dependent manner. These studies demonstrate a highly efficient method for loading nanoparticles with water-insoluble drug molecules and the efficacy of the nanoparticles in delivering drugs into eukaryotic cells in aqueous media.

An α-tocopheryl succinate enzyme-based nanoassembly for cancer imaging and therapy

Nanoassembly (NA) based on a D-α-tocopherol succinate (αTS) conjugated lysozyme (Lys) (Lys-αTS) was fabricated for tumor-selective delivery of curcumin (CUR) for breast cancer therapy. Lys and αTS were used as a biocompatible enzyme and a hydrophobic residue, respectively, for the preparation of nanocarriers in this study. Compared with CUR-loaded cross-linked Lys (c-Lys/CUR) NA, Lys-αTS/CUR NA exhibited a smaller hydrodynamic size (213 nm mean diameter), a narrower size distribution, and a more spherical shape. Sustained drug release was observed from the Lys-αTS/CUR NA for five days at a normal physiological pH (pH 7.4). The developed Lys-αTS/CUR NA showed enhanced cellular accumulation, antiproliferative effects, and apoptotic efficacies in MDA-MB-231 human breast adenocarcinoma cells. According to the results of optical imaging test in the MDA-MB-231 tumor-bearing mouse models, the Lys-αTS/CUR NA-injected group exhibited a more tumor-selective accumulation pattern, rather than being distributed in the normal tissues and organs. The observed tumor targetability of Lys-αTS/CUR was further studied, which revealed improved in vivo anticancer activities (better inhibition of tumor growth and induction of apoptosis in the tumor tissue) after an intravenous administration in the MDA-MB-231 tumor-bearing mouse models. All these results indicate that the newly developed enzyme-based nanocarrier, the Lys-αTS NA, can be a promising candidate for the therapy of breast cancers.

Non-peptidic guanidinium-functionalized silica nanoparticles as selective mitochondria-targeting drug nanocarriers

We report on the design and fabrication of a Fe₃O₄ core-mesoporous silica nanoparticle shell (Fe₃O₄@MSNs)-based mitochondria-targeting drug nanocarrier. A guanidinium derivative (GA) was conjugated onto the Fe₃O₄@MSNs as the mitochondria-targeting ligand. The fabrication of the Fe₃O₄@MSNs and their functionalization with GA were carried out by the sol-gel polymerization of alkoxysilane groups. Doxorubicin (DOX), an anti-cancer drug, was loaded into the pores of a GA-attached Fe₃O₄@MSNs due to both its anti-cancer properties and to allow for the fluorescent visualization of the nanocarriers. The selective and efficient mitochondria-targeting ability of a DOX-loaded GA-Fe₃O₄@MSNs (DOX/GA-Fe₃O₄@MSNs) was demonstrated by a co-localization study, transmission electron microscopy, and a fluorometric analysis on isolated mitochondria. It was found that the DOX/GA-Fe₃O₄@MSNs selectively accumulated into mitochondria within only five minutes; to the best of our knowledge, this is the shortest accumulation time reported for mitochondria targeting systems. Moreover, 2.6 times higher amount of DOX was accumulated in mitochondria by DOX/GA-Fe₃O₄@MSNs than by DOX/TPP-Fe₃O₄@MSNs. A cell viability assay indicated that the DOX/GA-Fe₃O₄@MSNs have high cytotoxicity to cancer cells, whereas the GA-Fe₃O₄@MSNs without DOX are non-cytotoxic; this indicates that the DOX/GA-Fe₃O₄@MSNs have great potential for use as biocompatible and effective mitochondria-targeting nanocarriers for cancer therapy.

Multifunctional Magnetic Mesoporous Silica Nanoagents for in vivo Enzyme-Responsive Drug Delivery and MR Imaging

In this study, we report novel multifunctional nanoagents for in vivo enzyme-responsive anticancer drug delivery and magnetic resonance imaging (MRI), based on mesoporous silica coated iron oxide nanoparticles (Fe3O4@MSNs). The anticancer drug, DOX, was encapsulated in the porous cavities with a MMP-2 enzyme responsive peptide being covalently linked to the nanoparticles surface. The in vitro experiment results indicated that the enzyme responsive nanoagents own high specificity for controlled drug release in the cell line with high MMP-2 expression. Furthermore, the targeted delivery of the nanoagents to the tumor site purpose has been successfully achieved through magnet-guided nanocarrier accumulation by utilizing the magnetic properties of the Fe3O4 nanocores, which resulted in efficient inhibition of the tumor growth. Additionally, these novel nanoagents can also be used as MRI agent for the real-time diagnosis the tumor treatment process of living animals. Taking the advantages of high specificity, controllable drug release and real-time MRI imaging, we believe these multifunctional nanoagents could also be used as a general platform for the design of stimulus-responsive multifunctional nanomaterials for the aim of accurate diagnosis and efficient treatment of other diseases.

Bacteria-Targeting Nanoparticles with Microenvironment-Responsive Antibiotic Release To Eliminate Intracellular Staphylococcus aureus and Associated Infection

Staphylococcus aureus ( S. aureus) is a causative agent in life-threatening human diseases that afflict millions of people annually. Traditional antibiotic treatments are becoming less efficient because S. aureus can invade host cells including osteoblasts and macrophages, constituting a reservoir that is relatively protected from antibiotics that can lead to recrudescent infection. We herein report a unique intracellular antibiotic delivery nanoparticle, which is composed of (i) a mesoporous silica nanoparticle (MSN) core loaded with gentamicin, (ii) an infected microenvironment (bacterial toxin)-responsive lipid bilayer surface shell, and (iii) bacteria-targeting peptide ubiquicidin (UBI_29-41) that is immobilized on the lipid bilayer surface shell. The lipid material acts as a gate that prevents drug release before the MSNs reach the target cells or tissue, at which point they are degraded by bacterial toxins to rapidly release the drug, thus eliminating efficient bacteria. We confirm rapid drug release in the presence of bacteria in an extracellular model and observe that S. aureus growth is effectively inhibited both in vitro and in vivo of planktonic and intracellular infection. The inflammation-related gene expression in infected preosteoblast or macrophage is also downregulated significantly after treatment by the antibiotic delivery nanoparticles. The antibiotic delivery nanoparticles offer advantages in fighting intracellular pathogens and eliminating the inflammation caused by intracellular bacterial infections.

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.