Approaches for targeting mitochondria in cancer therapy

Mitochondrial targeting derivatives of honokiol enhanced selective antitumor activity in NCI-H446 cells and decreased in vivo toxicity in Caenorhabditis elegans

Mitochondria, responsible for ATP production and apoptosis regulation, play a key role in cancer cells. Honokiol regulates apoptosis through the endogenous mitochondrial pathway but does not specifically target tumor cells. We designed 28 novel derivatives of honokiol using triple-function delocalized lipophilic cations such as berberine and F16 as mitochondrion-targeting carriers. While all derivatives exhibited enhanced cytotoxicity toward tumor cells compared to honokiol, the derivative 2E-3-F16 exhibited a substantial tumor cell selectivity between NCI-H446 cancer cells and HBE cells by one order of magnitude and enhanced the sensitivity of A549 cells to cisplatin. Mechanistically, it targeted mitochondria and induced apoptosis by preventing tumor cells from entering the G0/G1 phases as well as inducing an abnormal elevation of reactive oxygen species, thereby decreasing the mitochondrial membrane potential level. It also showed lower toxicity toward Caenorhabditis elegans than honokiol. This study provides a possible method for developing mitochondrion-targeting antitumor drugs with high efficiency and low toxicity based on natural products.

Tumor Abnormality-Oriented Nanomedicine Design

Anticancer nanomedicines have been proven effective in mitigating the side effects of chemotherapeutic drugs. However, challenges remain in augmenting their therapeutic efficacy. Nanomedicines responsive to the pathological abnormalities in the tumor microenvironment (TME) are expected to overcome the biological limitations of conventional nanomedicines, enhance the therapeutic efficacies, and further reduce the side effects. This Review aims to quantitate the various pathological abnormalities in the TME, which may serve as unique endogenous stimuli for the design of stimuli-responsive nanomedicines, and to provide a broad and objective perspective on the current understanding of stimuli-responsive nanomedicines for cancer treatment. We dissect the typical transport process and barriers of cancer drug delivery, highlight the key design principles of stimuli-responsive nanomedicines designed to tackle the series of barriers in the typical drug delivery process, and discuss the "all-into-one" and "one-for-all" strategies for integrating the needed properties for nanomedicines. Ultimately, we provide insight into the challenges and future perspectives toward the clinical translation of stimuli-responsive nanomedicines.

Photochemical Targeting of Mitochondria to Overcome Chemoresistance in Ovarian Cancer †

Ovarian cancer is the most lethal gynecologic malignancy with a stubborn mortality rate of ~65%. The persistent failure of multiline chemotherapy, and significant tumor heterogeneity, has made it challenging to improve outcomes. A target of increasing interest is the mitochondrion because of its essential role in critical cellular functions, and the significance of metabolic adaptation in chemoresistance. This review describes mitochondrial processes, including metabolic reprogramming, mitochondrial transfer and mitochondrial dynamics in ovarian cancer progression and chemoresistance. The effect of malignant ascites, or excess peritoneal fluid, on mitochondrial function is discussed. The role of photodynamic therapy (PDT) in overcoming mitochondria-mediated resistance is presented. PDT, a photochemistry-based modality, involves the light-based activation of a photosensitizer leading to the production of short-lived reactive molecular species and spatiotemporally confined photodamage to nearby organelles and biological targets. The consequential effects range from subcytotoxic priming of target cells for increased sensitivity to subsequent treatments, such as chemotherapy, to direct cell killing. This review discusses how PDT-based approaches can address key limitations of current treatments. Specifically, an overview of the mechanisms by which PDT alters mitochondrial function, and a summary of preclinical advancements and clinical PDT experience in ovarian cancer are provided.

Synthesis and discovery of mitochondria-targeting oleanolic acid derivatives for potential PI3K inhibition

Oleanolic acid and its derivatives have been widely reported for their antitumor activities. Recently, the introduction of a triphenylphosphonium cation moiety has been described to improve the selectivity and cytotoxicity of pentacyclic triterpenoids by targeting the mitochondria of human cancer cells. In this work, a series of novel mitochondria-targeting oleanolic acid derivatives were synthesized and their antitumor activities assessed. The majority of the compounds are more cytotoxicity to cancer cells than normal cells, especially for 6c with IC₅₀ of 0.81 μM in A549 cells, which showed a slight increase compared to doxorubicin (0.97 μM). Mechanism studies demonstrated that 6c induced apoptosis of A549 cells in a dose-dependent manner, and reactive oxygen species production, mitochondrial membrane potential depolarization, and particularly pro-apoptotic proteins upregulated by western blotting experiment may be responsible for the results. Moreover, 6c arrested the cell cycle at G2/M phase and cell migration in A549 cells. Compound 6c had a comparable or somewhat improved activity to the positive control LY294002 in molecular docking studies and in vitro testing, demonstrating that the apoptosis mechanism may involve inhibition of the PI3K-Akt pathway. These results augur well for the use of 6c as a novel triphenylphosphonium-conjugated anticancer agent.

Chemotherapy Resistance: Role of Mitochondrial and Autophagic Components

Simple Summary

Chemotherapy resistance is a common occurrence during cancer treatment that cancer researchers are attempting to understand and overcome. Mitochondria are a crucial intracellular signaling core that are becoming important determinants of numerous aspects of cancer genesis and progression, such as metabolic reprogramming, metastatic capability, and chemotherapeutic resistance. Mitophagy, or selective autophagy of mitochondria, can influence both the efficacy of tumor chemotherapy and the degree of drug resistance. Regardless of the fact that mitochondria are well-known for coordinating ATP synthesis from cellular respiration in cellular bioenergetics, little is known its mitophagy regulation in chemoresistance. Recent advancements in mitochondrial research, mitophagy regulatory mechanisms, and their implications for our understanding of chemotherapy resistance are discussed in this review.

Abstract

Cancer chemotherapy resistance is one of the most critical obstacles in cancer therapy. One of the well-known mechanisms of chemotherapy resistance is the change in the mitochondrial death pathways which occur when cells are under stressful situations, such as chemotherapy. Mitophagy, or mitochondrial selective autophagy, is critical for cell quality control because it can efficiently break down, remove, and recycle defective or damaged mitochondria. As cancer cells use mitophagy to rapidly sweep away damaged mitochondria in order to mediate their own drug resistance, it influences the efficacy of tumor chemotherapy as well as the degree of drug resistance. Yet despite the importance of mitochondria and mitophagy in chemotherapy resistance, little is known about the precise mechanisms involved. As a consequence, identifying potential therapeutic targets by analyzing the signal pathways that govern mitophagy has become a vital research goal. In this paper, we review recent advances in mitochondrial research, mitophagy control mechanisms, and their implications for our understanding of chemotherapy resistance.

Metabolic tricks of cancer cells

One of the characteristics of cancer cells important for tumorigenesis is their metabolic plasticity. Indeed, in various stress conditions, cancer cells can reshape their metabolic pathways to support the increased energy request due to continuous growth and rapid proliferation. Moreover, selective pressures in the tumor microenvironment, such as hypoxia, acidosis, and competition for resources, force cancer cells to adapt by complete reorganization of their metabolism. In this review, we highlight the characteristics of cancer metabolism and discuss its clinical significance, since overcoming metabolic plasticity of cancer cells is a key objective of modern cancer therapeutics and a better understanding of metabolic reprogramming may lead to the identification of possible targets for cancer therapy.

Anticancer Activity of Urease Mimetic Cobalt (III) Complexes on A549-Lung Cancer Cells: Targeting the Acidic Microenvironment

Tumour cells maintain a local hypoxic and acidic microenvironment which plays a crucial role in cancer progression and drug resistance. Urease is a metallohydrolases that catalyses the hydrolysis of urea into ammonia and carbon dioxide, causing an abrupt increase of pH. This enzymatic activity can be employed to target the acidic tumour microenvironment. In this study, we present the anticancer activities of urease mimetic cobalt (III) complexes on A549 cells. The cells were treated with different doses of cobalt (III) complexes to observe the cytotoxicity. The change in cellular morphology was observed using an inverted microscope. The cell death induced by these complexes was analysed through ATP proliferation, LDH release and caspase 3/7 activity. The effect of extracellular alkalinization by the cobalt (III) complexes on the efficacy of the weakly basic drug, doxorubicin (dox) was also evaluated. This combination therapy of dox with cobalt (III) complexes resulted in enhanced apoptosis in A549 cells, as evidenced by elevated caspase 3/7 activity in treated groups. The study confirms the urease mimicking anticancer activity of cobalt (III) complexes by neutralizing the tumour microenvironment. This study will motivate the applications of transition metal-based enzyme mimics in targeting the tumour microenvironment for effective anticancer treatments.

La(iii)–curcumin-functionalized gold nanocomposite as a red light-activatable mitochondria-targeting PDT agent

Functionalization of La(iii)–curcumin to gold nanoparticles resulted in remarkable red-shifted UV-visible absorption and exhibited remarkable differential photodynamic ability towards cancer cells upon red-light activation.

Mitochondria-Targeted Nanocarriers Promote Highly Efficient Cancer Therapy: A Review

Mitochondria are the primary organelles which can produce adenosine triphosphate (ATP). They play vital roles in maintaining normal functions. They also regulated apoptotic pathways of cancer cells. Given that, designing therapeutic agents that precisely target mitochondria is of great importance for cancer treatment. Nanocarriers can combine the mitochondria with other therapeutic modalities in cancer treatment, thus showing great potential to cancer therapy in the past few years. Herein, we summarized lipophilic cation- and peptide-based nanosystems for mitochondria targeting. This review described how mitochondria-targeted nanocarriers promoted highly efficient cancer treatment in photodynamic therapy (PDT), chemotherapy, combined immunotherapy, and sonodynamic therapy (SDT). We further discussed mitochondria-targeted nanocarriers’ major challenges and future prospects in clinical cancer treatment.

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.

Novel Mitochondria-targeted Drugs for Cancer Therapy

The search for mitochondria-targeted drugs has dramatically risen over the last decade. Mitochondria are essential organelles serving not only as a powerhouse of the cell but also as a key player in cell proliferation and cell death. Their central role in the energetic metabolism, calcium homeostasis and apoptosis makes them an intriguing field of interest for cancer pharmacology. In cancer cells, many mitochondrial signaling and metabolic pathways are altered. These changes contribute to cancer development and progression. Due to changes in mitochondrial metabolism and changes in membrane potential, cancer cells are more susceptible to mitochondria-targeted therapy. The loss of functional mitochondria leads to the arrest of cancer progression and/or a cancer cell death. Identification of mitochondrial changes specific for tumor growth and progression, rational development of new mitochondria-targeted drugs and research on delivery agents led to the advance of this promising area. This review will highlight the current findings in mitochondrial biology, which are important for cancer initiation, progression and resistance, and discuss approaches of cancer pharmacology with a special focus on the anti-cancer drugs referred to as 'mitocans'.

Mitotropic triphenylphosphonium doxorubicin-loaded core-shell nanoparticles for cellular and mitochondrial sequential targeting of breast cancer

HYPOTHESES

Targeted therapy exploits cancerous niches' properties including acidic extracellular environment, hypoxic tumor core, and over expression of tumor-specific surface antigens. The present study aims to develop and evaluate a sequential targeted core-shell nanoparticulate (NPs) system for treatment of breast cancer. Sequential (double-stage) targeting was achieved at the cellular-level through employing the selective CD44- receptor binding hyaluronic acid (HA), followed by subcellular mitochondrial drug-delivery using the mitotropic triphenylphosphonium-conjugated doxorubicin (DOX-TPP⁺).

EXPERIMENTS

NPs were prepared through incorporation of the electrostatic-complexes of DOX.HCl/DOX-TPP⁺ with tripolyphosphate (STPP^-) into chitosan (CS) forming the core that was further coated with HA shell. Physicochemical characterization techniques namely; FTIR, DSC, DLS, morphological evaluation and spectroscopic assessments were implemented. Moreover, the drug entrapment efficiency (EE%), loading capacity (LC%), drug release profile and kinetics were investigated. Lastly, to validate the biological efficiency of the developed NPs, cytotoxic activity was evaluated as well as flow cytometric analyses to assess apoptosis induction and cell-cycle arrest were studied.

FINDINGS

Results showed that, the obtained core-shell NPs possessed a spherical shape with a mean size of 220-280 nm and attained high EE% and LC%. In-vitro cytotoxicity evaluations demonstrated successful apoptosis induction and cell-cycle abrogation. Moreover, in-vivo studies on Solid Ehrlich carcinoma (SEC)-bearing mice confirmed the efficient anticancer activity of the mitotropic DOX-TPP⁺-loaded NPs. Conclusively, the developed core-shell NPs proved efficient in sequential targeting of DOX to breast cancer.

Regulation of Mitochondrial Respiration by VDAC Is Enhanced by Membrane-Bound Inhibitors with Disordered Polyanionic C-Terminal Domains

The voltage-dependent anion channel (VDAC) is the primary regulating pathway of water-soluble metabolites and ions across the mitochondrial outer membrane. When reconstituted into lipid membranes, VDAC responds to sufficiently large transmembrane potentials by transitioning to gated states in which ATP/ADP flux is reduced and calcium flux is increased. Two otherwise unrelated cytosolic proteins, tubulin, and α-synuclein (αSyn), dock with VDAC by a novel mechanism in which the transmembrane potential draws their disordered, polyanionic C-terminal domains into and through the VDAC channel, thus physically blocking the pore. For both tubulin and αSyn, the blocked state is observed at much lower transmembrane potentials than VDAC gated states, such that in the presence of these cytosolic docking proteins, VDAC’s sensitivity to transmembrane potential is dramatically increased. Remarkably, the features of the VDAC gated states relevant for bioenergetics—reduced metabolite flux and increased calcium flux—are preserved in the blocked state induced by either docking protein. The ability of tubulin and αSyn to modulate mitochondrial potential and ATP production in vivo is now supported by many studies. The common physical origin of the interactions of both tubulin and αSyn with VDAC leads to a general model of a VDAC inhibitor, facilitates predictions of the effect of post-translational modifications of known inhibitors, and points the way toward the development of novel therapeutics targeting VDAC.

Chimeric Drug Design with a Noncharged Carrier for Mitochondrial Delivery

Recently, it was proposed that the thiophene ring is capable of promoting mitochondrial accumulation when linked to fluorescent markers. As a noncharged group, thiophene presents several advantages from a synthetic point of view, making it easier to incorporate such a side moiety into different molecules. Herein, we confirm the general applicability of the thiophene group as a mitochondrial carrier for drugs and fluorescent markers based on a new concept of nonprotonable, noncharged transporter. We implemented this concept in a medicinal chemistry application by developing an antitumor, metabolic chimeric drug based on the pyruvate dehydrogenase kinase (PDHK) inhibitor dichloroacetate (DCA). The promising features of the thiophene moiety as a noncharged carrier for targeting mitochondria may represent a starting point for the design of new metabolism-targeting drugs.

Urupocidin C: a new marine guanidine alkaloid which selectively kills prostate cancer cells via mitochondria targeting

New bicyclic guanidine alkaloid, urupocidin C (Ur-C) along with the previously known urupocidin A (Ur-A) were isolated from the rare deep-sea marine sponge Monanchora pulchra, harvested in Northwestern Pacific waters. The unique structure of Ur-C was elucidated using 1D and 2D NMR spectroscopy as well as mass spectra. We discovered a promising selectivity of both alkaloids for human prostate cancer (PCa) cells, including highly drug-resistant lines, compared to non-malignant cells. In cancer cells, marine derived compounds were able to induce G1- and S-cell cycle arrest as well as caspase-mediated cell death. For the first time we have identified mitochondrial targeting as a central mechanism of anticancer action for these and similar molecules. Thus, treatment with the isolated alkaloids resulted in mitochondrial membrane permeabilization consequently leading to the release of cytotoxic mitochondrial proteins to cellular cytoplasm, ROS upregulation, consequent activation of caspase-9 and -3, followed by PARP cleavage, DNA fragmentation, and apoptosis. Moreover, synergistic effects were observed when Ur-A and Ur-C were combined with clinically approved PARP inhibitor olaparib. Finally, these alkaloids exhibited additive effects in combination with docetaxel and androgen receptor inhibitor enzalutamide, both applied in PCa therapy. In conclusion, urupocidin-like compounds are promising lead molecules for the development of new drugs for the treatment of advanced PCa.

Targeting the Multiple Physiologic Roles of VDAC With Steroids and Hydrophobic Drugs

There is accumulating evidence that endogenous steroids and non-polar drugs are involved in the regulation of mitochondrial physiology. Many of these hydrophobic compounds interact with the Voltage Dependent Anion Channel (VDAC). This major metabolite channel in the mitochondrial outer membrane (MOM) regulates the exchange of ions and water-soluble metabolites, such as ATP and ADP, across the MOM, thus governing mitochondrial respiration. Proteomics and biochemical approaches together with molecular dynamics simulations have identified an impressively large number of non-polar compounds, including endogenous, able to bind to VDAC. These findings have sparked speculation that both natural steroids and synthetic hydrophobic drugs regulate mitochondrial physiology by directly affecting VDAC ion channel properties and modulating its metabolite permeability. Here we evaluate recent studies investigating the effect of identified VDAC-binding natural steroids and non-polar drugs on VDAC channel functioning. We argue that while many compounds are found to bind to the VDAC protein, they do not necessarily affect its channel functions in vitro. However, they may modify other aspects of VDAC physiology such as interaction with its cytosolic partner proteins or complex formation with other mitochondrial membrane proteins, thus altering mitochondrial function.

Energy metabolism and sources of oxidative stress in wooden breast - a review

Modern broilers show dramatic growth over a short interval and contribute directly to the success of the poultry meat industry. The growth performance of commercial broilers is a result of genetic selection for "performance traits", such as body size, meat yield, and feed conversion rate. However, due to the rapid growth rate of modern commercial broilers, several growth-related conditions have arisen, increasing economic losses and consumer concerns. Among the most economically consequential is the muscle disorder called wooden breast. Together with associated myopathies such as white striping and spaghetti meat, wooden breast is causing losses of $200 million a year in the U.S. alone and occurs worldwide. No causative factors are known for wooden breast to date. Wooden breast can affect over 80% of broilers in a flock, yet no methods of amelioration are currently available. Overall, the evidence suggests that wooden breast is a genetic, age-dependent condition associated with fast growth rate. The primary features of wooden breast are muscle degeneration and fibrosis, high levels of oxidative stress, hypoxia, and altered energy metabolism. Recent work has also implicated reduced pectoral vessel density in the pathogenesis of wooden breast. This review examines the history of myopathies in commercial broilers and the relationship of myopathies to metabolism and oxidative performance. This review summarizes the foundational knowledge of wooden breast and provides a platform for further investigation of wooden breast.

Combinatory antitumor therapy by cascade targeting of a single drug

Combination therapy has shown its promise in the clinic for enhancing the efficacy of tumor treatment. However, the dose control of multiple drugs and their non-overlapping toxicity from different drugs are still great challenge. In this work, a single model drug, paclitaxel (PTX), is used to realize combination therapy and solve the problems mentioned above. Either PTX or its triphenylphosphine derivative (TPTX) is encapsulated in galactose-modified liposomes (GLips) to obtain GLips-P or GLips-TP, which are simply mixed in different ratios to finely control the proportion of PTX and TPTX. These mixed liposomes, GLips-P/TP, feature a cascade target delivery of PTX, from tissue to cell, and then to organelle. PTX plays a primary role to cause the cytotoxicity by microtubule bindings in cytoplasm, while TPTX is proved to increase the intracellular levels of caspase-3 and caspase-9 that cause apoptosis via a mitochondria-mediated pathway. Notably, GLips-P/TP 3:1 exhibited the significant drug synergy in both cytotoxicity assay of HepG2 cells and the treatment efficacy in Heps xenograft ICR mouse models. This work not only demonstrates the great promise of a cascade targeting delivery for precise tumor treatment, but also offers a novel platform to design combinatory therapy systems using a single drug.

Distinct effects of etoposide on glutamine-addicted neuroblastoma

The majority of anticancer drugs are DNA-damaging agents, and whether or not they may directly target mitochondria remains unclear. In addition, tumors such as neuroblastoma exhibit addiction to glutamine in spite of it being a nonessential amino acid. Our aim was to evaluate the direct effect of widely used anticancer drugs on mitochondrial activity in combination with glutamine withdrawal, and possible apoptotic effects of such interaction. Our results revealed that etoposide inhibits mitochondrial respiratory chain Complex I causing the leakage of electrons and the superoxide radical formation. However, it was not sufficient to induce apoptosis, and apoptotic manifestation was detectable only alongside the withdrawal of glutamine, a precursor for antioxidant glutathione. Thus, the simultaneous depletion of glutathione and destabilization of mitochondria by ROS can compromise the barrier properties of the mitochondrial membrane, leading to cytochrome c release and the activation of the mitochondrial apoptotic pathway. Thus, the depletion of antioxidants or the inhibition of the pathways responsible for cellular antioxidant response can enhance mitochondrial targeting and strengthen antitumor therapy.

Mitochondria-targeted cationic liposomes modified with alkyltriphenylphosphonium bromides loaded with hydrophilic drugs: preparation, cytotoxicity and colocalization assay

The purpose of this work was to obtain cationic liposomes based on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine noncovalently modified using alkyltriphenylphosphonium bromides (TPPB-n) with different lengths of hydrocarbon tail for targeted delivery to mitochondria. The hydrodynamic diameter and electrokinetic potential of hybrid liposomes depending on the lipid/surfactant ratio were monitored in time with the aim to optimize the composition with sufficient stability and positive charge for mitochondria-targeted delivery. It was found that increasing the alkyl tail length of the surfactant (up to TPPB-14) leads to an increase in the positive charge of the liposomes. The most optimal results of stability were obtained for hybrid liposomes based on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and TPPB-12, TPPB-14. The obtained modified liposomes were loaded with hydrophilic substrates (a model probe Rhodamine B and medicines metronidazole and doxorubicin). This is one of the first examples of fabrication of liposomes noncovalently modified using an amphiphilic TPP cation, with the alkyl tail length of surfactant and TPP/lipid ratio optimized in terms of stability of the liposomes and the binding/release behavior of hydrophilic probes. Using the confocal microscopy method, it was shown that modification of liposomes with a triphenylphosphonium cation results in targeted delivery of encapsulated compounds to mitochondria.

The Development of Functional Non-Viral Vectors for Gene Delivery

Gene therapy is manipulation in/of gene expression in specific cells/tissue to treat diseases. This manipulation is carried out by introducing exogenous nucleic acids, such as DNA or RNA, into the cell. Because of their negative charge and considerable larger size, the delivery of these molecules, in general, should be mediated by gene vectors. Non-viral vectors, as promising delivery systems, have received considerable attention due to their low cytotoxicity and non-immunogenicity. As research continued, more and more functional non-viral vectors have emerged. They not only have the ability to deliver a gene into the cells but also have other functions, such as the performance of fluorescence imaging, which aids in monitoring their progress, targeted delivery, and biodegradation. Recently, many reviews related to non-viral vectors, such as polymers and cationic lipids, have been reported. However, there are few reviews regarding functional non-viral vectors. This review summarizes the common functional non-viral vectors developed in the last ten years and their potential applications in the future. The transfection efficiency and the transport mechanism of these materials were also discussed in detail. We hope that this review can help researchers design more new high-efficiency and low-toxicity multifunctional non-viral vectors, and further accelerate the progress of gene therapy.

A neutral water-soluble mitochondria-targeting polymer

We report the first neutral and water-soluble polymer capable of strong mitochondrial targeting in vitro and in vivo, zwitterionic poly[2-(N-oxide-N,N-diethylamino)ethyl methacrylate] (OPDEA). OPDEA is quickly internalized via macropinocytosis by various cancer cells and transferred into the mitochondria, which slightly lowers the mitochondrial membrane potential as determined by the JC-1 assay.

The clinical impact and biological mechanisms of skeletal muscle aging

Skeletal muscle is a highly plastic tissue that remarkably adapts to diverse stimuli including exercise, injury, disuse, and, as discussed here, aging. Humans achieve peak skeletal muscle mass and strength in mid-life and then experience a progressive decline of up to 50% by the ninth decade. The loss of muscle mass and function with aging is a phenomenon termed sarcopenia. It is evidenced by the loss and atrophy of muscle fibers and the concomitant accretion of fat and fibrous tissue. Sarcopenia has been recognized as a key driver of limitations in physical function and mobility, but is perhaps less appreciated for its role in age-related metabolic dysfunction and loss of organismal resilience. Similar to other tissues, muscle is prone to multiple forms of age-related molecular and cellular damage, including disrupted protein turnover, impaired regenerative capacity, cellular senescence, and mitochondrial dysfunction. The objective of this review is to highlight the clinical consequences of skeletal muscle aging, and provide insights into potential biological mechanisms. In light of population aging, strategies to improve muscle health in older adults promise to have a profound public health impact.

Activation of Pyroptotic Cell Death Pathways in Cancer: An Alternative Therapeutic Approach

Cancer can be considered the result of a series of genetic variations that lead to a normal cell being transformed into a malignant one while avoiding cell death-atypical characteristics of tumor development. Although a large number of genomics and epigenetic alterations have been identified in cells undergoing apoptotic, autophagic or necrotic cell death, the treatment of cancer remains thought-provoking. Pyroptosis is differentiated from other types of programmed cell death and is mainly activated by Caspase-1. To initiate pyroptosis, cells receive specific "death" messages, produce cytokines, swell, burst, and ultimately die. The deficiency of Caspase-1 expression may lead to inflammation-mediated tumor progression. Hence, the molecular mechanisms for the Caspase-1 activation in tumor tissues are yet to be exploited extensively. This review aims to summarise the latest discoveries about pyroptosis and its new exciting role in inducing cancer cell death.

Inflammation and Metabolism in Cancer Cell-Mitochondria Key Player

Cancer metabolism is an essential aspect of tumorigenesis, as cancer cells have increased energy requirements in comparison to normal cells. Thus, an enhanced metabolism is needed in order to accommodate tumor cells' accelerated biological functions, including increased proliferation, vigorous migration during metastasis, and adaptation to different tissues from the primary invasion site. In this context, the assessment of tumor cell metabolic pathways generates crucial data pertaining to the mechanisms through which tumor cells survive and grow in a milieu of host defense mechanisms. Indeed, various studies have demonstrated that the metabolic signature of tumors is heterogeneous. Furthermore, these metabolic changes induce the exacerbated production of several molecules, which result in alterations that aid an inflammatory milieu. The therapeutic armentarium for oncology should thus include metabolic and inflammation regulators. Our expanding knowledge of the metabolic behavior of tumor cells, whether from solid tumors or hematologic malignancies, may provide the basis for the development of tailor-made cancer therapies.

Superior proapoptotic activity of curcumin-loaded mixed block copolymer micelles with mitochondrial targeting properties

Targeting tumor cell mitochondria is a prospective strategy for highly effective anticancer therapy. Consequently, the development of potent systems for the targeted delivery of mitochondria-acting therapeutics to mitochondria has the potential to boost this sector of nanomedicine. In this study, a functional mixed micellar system based on two co-assembled triblock copolymers, poly(2-(dimethylamino)ethyl methacrylate)-b-poly(ε-caprolactone)-b-poly(2-(dimethylamino)ethyl methacrylate) bearing triphenylphosphonium ligands (PDMAEMA(TPP+)20-b-PCL70-b-PDMAEMA(TPP+)20) and poly(ethylene oxide)-b-poly(ε-caprolactone)-b-poly(ethylene oxide) (PEO113-b-PCL70-b-PEO113), was assessed for the mitochondria targeted delivery of curcumin. The high proapoptotic activity of the system and the sub-cellular mechanisms of cytotoxicity were demonstrated using a chemosensitive HL-60 cell line and its resistant alternative HL-60/DOX. Next, the successful localization of nanocarriers in mitochondria was proved by fluorescence microscopy with the aid of DAPI (4',6-diamidino-2-phenylindole) as a cellular localization tracker. The in vitro experiments revealed the great potential of the functional system developed for the targeted delivery of curcumin to mitochondria, causing programmed tumor cell death.

An ingenious non-spherical mesoporous silica nanoparticle cargo with curcumin induces mitochondria-mediated apoptosis in breast cancer (MCF-7) cells

Curcumin delivery to cancer cells is challenging due to its hydrophobic nature, low bio distribution and low availability. Many nano vehicles suffer from low stability and toxicity, and hence the prerequisite of a non-toxic nano vehicle with effective drug delivery is still being delved. The present study investigates the delivery efficiency of curcumin with non-spherical mesoporous silica nanoparticles (MSNAs). Their mechanism of drug delivery and signalling proteins activated to induce apoptosis was further explored in MCF-7 cells. A non-spherical MSN was synthesised, functionalised with PEI (MSNAP) and analysed its intracellular behaviour. Our result indicates that MSNAP was non-toxic until 20 µg/mL and likely localizes in cytoplasmic vesicles. On contrast, well-known MCM-41P induced autophagosome formation, indicating cellular toxicity. Curcumin was loaded on MSNAP and its effectiveness in inducing cell death was studied in MCF-7 and in MCF-7R cells. Curcumin loading on MSNAP induces better cell death with 30 µM curcumin, better than unbounded curcumin. Western blot analysis suggest, curcumin induce apoptosis through the activation of caspase 9, 6, 12, PARP, CHOP and PTEN. The cell survival protein Akt1 was downregulated by curcumin with and without the nanostructure. Interestingly, cleaved caspase 9 was activated in higher amount in nano-conjugated curcumin compared to the free curcumin. But other ER resident protein like IRE1α, PERK and GRP78 were downregulated indicating curcumin disturbs ER homeostasis. Further, electron microscopic analysis reveled that nanocurcumin induced apoptosis by disrupting mitochondria and nucleus. Our results with doxorubicin resistant MCF-7 cell lines confirm nanodelivery of doxorubicin and curcumin sensitised cells effectively at lesser concentration. Further docking studies of curcumin indicate it interacts with the apoptotic proteins through hydrogen bonding formation and with higher binding energy.

A novel near-infrared triggered dual-targeted nanoplatform for mitochondrial combined photothermal-chemotherapy of cancer in vitro

A combination of photothermal-chemotherapy has received widespread attention in drug delivery systems for cancer treatment. However, the combination therapy operated in subcellular organelles, such as mitochondria, has been rarely reported. Herein, we designed a novel near-infrared (NIR) triggered dual-targeted nanoplatform (FA/TPP-DINPs) based on mitochondrial combined photothermal-chemotherapy by co-loading FDA-approved NIR dye indocyanine green (ICG) and anticancer drug doxorubicin (DOX). The resulting nanoparticles showed a monodispersed sphere and excellent colloidal stability. Specially, the simultaneous introduction of targeted ligands folic acid (FA) and triphenylphosphine (TPP) to nanoparticles significantly promoted the cellular internalization and mitochondrial co-localization of nanoparticles. Moreover, the encapsulated dye could convert NIR light into heat with high efficiency, which makes the FA/TPP-DINPs an effective platform for mitochondrial combination therapy with chemotherapy drug DOX. Meanwhile, the thermal expansion in response to the change of temperature after sustained 808 nm laser irradiation could cause the disintegration of nanoparticles, which triggered the rapid release of DOX from nanoparticles. As expected, the prepared FA/TPP-DINPs exhibited evidently enhanced cytotoxicity and preeminent combination therapy efficiency on MCF-7 cells. Thus, the NIR triggered dual-targeted nanoplatform provides a new drug delivery strategy for mitochondrial combined photothermal-chemotherapy of cancer.

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.

Enhanced Cytotoxic Activity of Mitochondrial Mechanical Effectors in Human Lung Carcinoma H520 Cells: Pharmaceutical Implications for Cancer Therapy

Cancer cell mitochondria represent an attractive target for oncological treatment as they have unique hallmarks that differ from their healthy counterparts, as the presence of a stronger membrane potential that can be exploited to specifically accumulate cytotoxic cationic molecules. Here, we explore the selective cytotoxic effect of 10-N-nonyl acridine orange (NAO) on human lung carcinoma H520 cells and compare them with healthy human lung primary fibroblasts. NAO is a lipophilic and positively charged molecule that promotes mitochondrial membrane adhesion that eventually leads to apoptosis when incubated at high micromolar concentration. We found an enhanced cytotoxicity of NAO in H520 cancer cells. By means Fluorescence lifetime imaging microscopy (FLIM) we also confirmed the formation of H-dimeric aggregates originating from opposing adjacent membranes that interfere with the mitochondrial membrane structure. Based on our results, we suggest the mitochondrial membrane as a potential target in cancer therapy to mechanically control the cell proliferation of cancer cells.

Mitochondria-targeting drug conjugates for cytotoxic, anti-oxidizing and sensing purposes: current strategies and future perspectives

Mitochondrial targeting is a promising approach for solving current issues in clinical application of chemotherapy and diagnosis of several disorders. Here, we discuss direct conjugation of mitochondrial-targeting moieties to anticancer drugs, antioxidants and sensor molecules. Among them, the most widely applied mitochondrial targeting moiety is triphenylphosphonium (TPP), which is a delocalized cationic lipid that readily accumulates and penetrates through the mitochondrial membrane due to the highly negative mitochondrial membrane potential. Other moieties, including short peptides, dequalinium, guanidine, rhodamine, and F16, are also known to be promising mitochondrial targeting agents. Direct conjugation of mitochondrial targeting moieties to anticancer drugs, antioxidants and sensors results in increased cytotoxicity, anti-oxidizing activity and sensing activity, respectively, compared with their non-targeting counterparts, especially in drug-resistant cells. Although many mitochondria-targeted anticancer drug conjugates have been investigated in vitro and in vivo, further clinical studies are still needed. On the other hand, several mitochondria-targeting antioxidants have been analyzed in clinical phases I, II and III trials, and one conjugate has been approved for treating eye disease in Russia. There are numerous ongoing studies of mitochondria-targeted sensors.

The role of metabolism and tunneling nanotube-mediated intercellular mitochondria exchange in cancer drug resistance

Intercellular communications play a major role in tissue homeostasis. In pathologies such as cancer, cellular interactions within the tumor microenvironment (TME) contribute to tumor progression and resistance to therapy. Tunneling nanotubes (TNTs) are newly discovered long-range intercellular connections that allow the exchange between cells of various cargos, ranging from ions to whole organelles such as mitochondria. TNT-transferred mitochondria were shown to change the metabolism and functional properties of recipient cells as reported for both normal and cancer cells. Metabolic plasticity is now considered a hallmark of cancer as it notably plays a pivotal role in drug resistance. The acquisition of cancer drug resistance was also associated to TNT-mediated mitochondria transfer, a finding that relates to the role of mitochondria as a hub for many metabolic pathways. In this review, we first give a brief overview of the various mechanisms of drug resistance and of the cellular communication means at play in the TME, with a special focus on the recently discovered TNTs. We further describe recent studies highlighting the role of the TNT-transferred mitochondria in acquired cancer cell drug resistance. We also present how changes in metabolic pathways, including glycolysis, pentose phosphate and lipid metabolism, are linked to cancer cell resistance to therapy. Finally, we provide examples of novel therapeutic strategies targeting mitochondria and cell metabolism as a way to circumvent cancer cell drug resistance.

Diverse Roles of Mitochondria in Immune Responses: Novel Insights Into Immuno-Metabolism

Lack of immune system cells or impairment in differentiation of immune cells is the basis for many chronic diseases. Metabolic changes could be the root cause for this immune cell impairment. These changes could be a result of altered transcription, cytokine production from surrounding cells, and changes in metabolic pathways. Immunity and mitochondria are interlinked with each other. An important feature of mitochondria is it can regulate activation, differentiation, and survival of immune cells. In addition, it can also release signals such as mitochondrial DNA (mtDNA) and mitochondrial ROS (mtROS) to regulate transcription of immune cells. From current literature, we found that mitochondria can regulate immunity in different ways. First, alterations in metabolic pathways (TCA cycle, oxidative phosphorylation, and FAO) and mitochondria induced transcriptional changes can lead to entirely different outcomes in immune cells. For example, M1 macrophages exhibit a broken TCA cycle and have a pro-inflammatory role. By contrast, M2 macrophages undergo β-oxidation to produce anti-inflammatory responses. In addition, amino acid metabolism, especially arginine, glutamine, serine, glycine, and tryptophan, is critical for T cell differentiation and macrophage polarization. Second, mitochondria can activate the inflammatory response. For instance, mitochondrial antiviral signaling and NLRP3 can be activated by mitochondria. Third, mitochondrial mass and mobility can be influenced by fission and fusion. Fission and fusion can influence immune functions. Finally, mitochondria are placed near the endoplasmic reticulum (ER) in immune cells. Therefore, mitochondria and ER junction signaling can also influence immune cell metabolism. Mitochondrial machinery such as metabolic pathways, amino acid metabolism, antioxidant systems, mitochondrial dynamics, mtDNA, mitophagy, and mtROS are crucial for immune functions. Here, we have demonstrated how mitochondria coordinate to alter immune responses and how changes in mitochondrial machinery contribute to alterations in immune responses. A better understanding of the molecular components of mitochondria is necessary. This can help in the development of safe and effective immune therapy or prevention of chronic diseases. In this review, we have presented an updated prospective of the mitochondrial machinery that drives various immune responses.

Mixed-ligand Cu(II) hydrazone complexes designed to enhance anticancer activity

The ligand quantity, ligand type, and coordination geometry have important influences on the anticancer activity of metal-based complexes. On the basis of the structures of previously reported 1:1 Cu(II)/ligand complexes ([Cu(L1)Cl]·2H₂O 1a, [Cu(L2)Cl]·H₂O 2a, and [Cu(L2)NO₃]·H₂O 3a), we subsequently designed, developed, and characterized a series of corresponding 1:1:1 Cu(II)/ligand/co-ligand complexes ([Cu(L1)(Py)Cl]·H₂O 1b, [Cu(L2)(Py)Cl] 2b, and [Cu(L2)(Py)NO₃] 3b), where L1 = (E)-N'-(2-hydroxybenzylidene)acetohydrazide, L2 = (E)-N'-(2- hydroxybenzylidene)benzohydrazide, and Py = pyridine. All six Cu(II) complexes were assessed for their in vitro anticancer properties against a panel of human cancer cells, including cisplatin-resistant A549cisR cell lines. Interestingly, we observed that the 1:1:1 Cu/ligand/co-ligand mixed-ligand Cu(II) complexes exhibited higher anticancer activity than the corresponding 1:1 Cu(II)/ligand complexes. In particular, the 1:1:1 Cu(II)/ligand/co-ligand complex 3b displayed the greatest toxicity toward several cancer cells with better IC₅₀ (1.12-3.77 μM) than cisplatin. Further mechanistic explorations showed that the 3b complex induced DNA damage, thus resulting in mitochondria-mediated apoptotic cell death. Furthermore, the 3b complex displayed pronounced cytostatic effects in the MCF-7 3D spheroid model.

Measurement of Oxygen Consumption Rate (OCR) and Extracellular Acidification Rate (ECAR) in Culture Cells for Assessment of the Energy Metabolism

Mammalian cells generate ATP by mitochondrial (oxidative phosphorylation) and non-mitochondrial (glycolysis) metabolism. Cancer cells are known to reprogram their metabolism using different strategies to meet energetic and anabolic needs ( Koppenol et al., 2011 ; Zheng, 2012). Additionally, each cancer tissue has its own individual metabolic features. Mitochondria not only play a key role in energy metabolism but also in cell cycle regulation of cells. Therefore, mitochondria have emerged as a potential target for anticancer therapy since they are structurally and functionally different from their non-cancerous counterparts (D'Souza et al., 2011). We detail a protocol for measurement of oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) measurements in living cells, utilizing the Seahorse XF24 Extracellular Flux Analyzer (Figure 1). The Seahorse XF24 Extracellular Flux Analyzer continuously measures oxygen concentration and proton flux in the cell supernatant over time ( Wu et al., 2007 ). These measurements are converted in OCR and ECAR values and enable a direct quantification of mitochondrial respiration and glycolysis. With this protocol, we sought to assess basal mitochondrial function and mitochondrial stress of three different cancer cell lines in response to the cytotoxic test lead compound mensacarcin in order to investigate its mechanism of action. Cells were plated in XF24 cell culture plates and maintained for 24 h. Prior to analysis, the culture media was replaced with unbuffered DMEM pH 7.4 and cells were then allowed to equilibrate in a non-CO₂ incubator immediately before metabolic flux analysis using the Seahorse XF to allow for precise measurements of Milli-pH unit changes. OCR and ECAR were measured under basal conditions and after injection of compounds through drug injection ports. With the described protocol we assess the basic energy metabolism profiles of the three cell lines as well as key parameters of mitochondrial function in response to our test compound and by sequential addition of mitochondria perturbing agents oligomycin, FCCP and rotenone/antimycin A. Figure 1.Overview of seahorse experiment.

Repositioning chlorpromazine for treating chemoresistant glioma through the inhibition of cytochrome c oxidase bearing the COX4-1 regulatory subunit

Patients with glioblastoma have one of the lowest overall survival rates among patients with cancer. Standard of care for patients with glioblastoma includes temozolomide and radiation therapy, yet 30% of patients do not respond to these treatments and nearly all glioblastoma tumors become resistant. Chlorpromazine is a United States Food and Drug Administration-approved phenothiazine widely used as a psychotropic in clinical practice. Recently, experimental evidence revealed the anti-proliferative activity of chlorpromazine against colon and brain tumors. Here, we used chemoresistant patient-derived glioma stem cells and chemoresistant human glioma cell lines to investigate the effects of chlorpromazine against chemoresistant glioma. Chlorpromazine selectively and significantly inhibited proliferation in chemoresistant glioma cells and glioma stem cells. Mechanistically, chlorpromazine inhibited cytochrome c oxidase (CcO, complex IV) activity from chemoresistant but not chemosensitive cells, without affecting other mitochondrial complexes. Notably, our previous studies revealed that the switch to chemoresistance in glioma cells is accompanied by a switch from the expression of CcO subunit 4 isoform 2 (COX4-2) to COX4-1. In this study, chlorpromazine induced cell cycle arrest selectively in glioma cells expressing COX4-1, and computer-simulated docking studies indicated that chlorpromazine binds more tightly to CcO expressing COX4-1 than to CcO expressing COX4-2. In orthotopic mouse brain tumor models, chlorpromazine treatment significantly increased the median overall survival of mice harboring chemoresistant tumors. These data indicate that chlorpromazine selectively inhibits the growth and proliferation of chemoresistant glioma cells expressing COX4-1. The feasibility of repositioning chlorpromazine for selectively treating chemoresistant glioma tumors should be further explored.

Subcellular co-delivery of two different site-oriented payloads based on multistage targeted polymeric nanoparticles for enhanced cancer therapy

Smart nanoparticles which encapsulated two different site-oriented therapeutic agents for multistage targeted delivery and enhanced antitumor therapy.

Mitochondria-localizing BODIPY–copper(ii) conjugates for cellular imaging and photo-activated cytotoxicity forming singlet oxygen

BODIPY–copper(ii) conjugates are prepared and characterized and the complexes showed mitochondrial localization with singlet oxygen mediated visible light-induced apoptotic cell death.

Mitochondrial dysfunction activates lysosomal-dependent mitophagy selectively in cancer cells

Molecules designed to target and accumulate in the mitochondria are an emerging therapeutic approach for cancer and other indications. Mitochondria-targeted redox agents (MTAs) induce mitochondrial damage and autophagy in cancer cells. However, the mechanisms for these molecules to induce mitophagy, the clearance of damaged mitochondria, are largely unknown. Using breast derived cell lines and a series of targeted molecules, mitochondrial dysfunction and autophagy was established to be selective for MDA-MB-231 cancer cells as compared to the non-cancerous MCF-12A cells. Kinetic analyses revealed that mitochondrial dysfunction precedes the activation of autophagy in these cancer cells. To determine the onset of mitophagy, stably expressing mitochondrial mKeima, a mitochondrial pH sensor, cell lines were generated and revealed that these drugs activate lysosomal dependent mitochondrial degradation in MDA-MB-231 cells. Mitophagy was confirmed by identifying the accumulation of a PINK1, mitochondria located in autophagosomes, and the formation of an autophagosome-mitochondria protein (MFN2-LC3-II) complex. These results are the first to demonstrate that mitochondrial redox agents selectively induce mitophagy in a breast cancer cell line and their potential application both as tools for investigating mitochondrial biomechanics and as therapeutic strategies that target mitochondrial metabolism.

The natural product mensacarcin induces mitochondrial toxicity and apoptosis in melanoma cells

Mensacarcin is a highly oxygenated polyketide that was first isolated from soil-dwelling Streptomyces bacteria. It exhibits potent cytostatic properties (mean of 50% growth inhibition = 0.2 μm) in almost all cell lines of the National Cancer Institute (NCI)-60 cell line screen and relatively selective cytotoxicity against melanoma cells. Moreover, its low COMPARE correlations with known standard antitumor agents indicate a unique mechanism of action. Effective therapies for managing melanoma are limited, so we sought to investigate mensacarcin's unique cytostatic and cytotoxic effects and its mode of action. By assessing morphological and biochemical features, we demonstrated that mensacarcin activates caspase-3/7-dependent apoptotic pathways and induces cell death in melanoma cells. Upon mensacarcin exposure, SK-Mel-28 and SK-Mel-5 melanoma cells, which have the BRAF^V600E mutation associated with drug resistance, showed characteristic chromatin condensation as well as distinct poly(ADP-ribose)polymerase-1 cleavage. Flow cytometry identified a large population of apoptotic melanoma cells, and single-cell electrophoresis indicated that mensacarcin causes genetic instability, a hallmark of early apoptosis. To visualize mensacarcin's subcellular localization, we synthesized a fluorescent mensacarcin probe that retained activity. The natural product probe was localized to mitochondria within 20 min of treatment. Live-cell bioenergetic flux analysis confirmed that mensacarcin disturbs energy production and mitochondrial function rapidly. The subcellular localization of the fluorescently labeled mensacarcin together with its unusual metabolic effects in melanoma cells provide evidence that mensacarcin targets mitochondria. Mensacarcin's unique mode of action suggests that it may be a useful probe for examining energy metabolism, particularly in BRAF-mutant melanoma, and represent a promising lead for the development of new anticancer drugs.

Centrifugation-Free Magnetic Isolation of Functional Mitochondria Using Paramagnetic Iron Oxide Nanoparticles

Subcellular fractionation techniques are essential for cell biology and drug development studies. The emergence of organelle-targeted nanoparticle (NP) platforms necessitates the isolation of target organelles to study drug delivery and activity. Mitochondria-targeted NPs have attracted the attention of researchers around the globe, since mitochondrial dysfunctions can cause a wide range of diseases. Conventional mitochondria isolation methods involve high-speed centrifugation. The problem with high-speed centrifugation-based isolation of NP-loaded mitochondria is that NPs can pellet even if they are not bound to mitochondria. We report development of a mitochondria-targeted paramagnetic iron oxide nanoparticle, Mito-magneto, that enables isolation of mitochondria under the influence of a magnetic field. Isolation of mitochondria using Mito-magneto eliminates artifacts typically associated with centrifugation-based isolation of NP-loaded mitochondria, thus producing intact, pure, and respiration-active mitochondria. © 2017 by John Wiley & Sons, Inc.

Charge-Reversible Multifunctional HPMA Copolymers for Mitochondrial Targeting

Mitochondrial-oriented delivery of anticancer drugs has been considered as a promising strategy to improve the antitumor efficiency of chemotherapeutics. However, the physiological and biological barriers from the injection site to the final mitochondrial action site remain great challenges. Herein, a novel mitochondrial-targeted multifunctional nanocomplex based on N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers (MPC) is designed to enhance drug accumulation in mitochondria. MPC possesses various functions such as extracellular pH response, superior cellular uptake, lysosomal escape, and mitochondrial targeting. In detail, MPC was formed by two oppositely charged HPMA copolymers, that is, positively charged mitochondrial-targeting guanidine group-modified copolymers and charge-reversible 2,3-dimethylmaleic anhydride (DMA)-modified copolymers (P-DMA). It was validated that MPC could remain stable in the blood circulation (pH 7.4) but could be cleaved to expose the positive charge of the guanidine group immediately in response to the mild acidity of tumor tissues (pH 6.5). The gradual exposure of positively charged guanidine will simultaneously facilitate endocytosis, endosomal/lysosomal escape, and mitochondrial targeting. The in vitro experiments showed that compared with copolymers without guanidine modification, the cellular uptake and mitochondrial-targeting ability of MPC in the simulated tumor environment (MPC@pH6.5) separately increased 4.3- and 23.8-fold, respectively. The in vivo experiments were processed on B16F10 tumor-bearing C57 mice, and MPC showed the highest accumulation in the tumor site and a peak tumor inhibition rate of 82.9%. In conclusion, multifunctional mitochondrial-targeting HPMA copolymers provide a novel and versatile approach for cancer therapy.