Mitochondria as a Novel Target for Cancer Chemoprevention: Emergence of Mitochondrial-targeting Agents

Design, synthesis and antitumor effects of lupeol quaternary phosphonium salt derivatives

Lupeol is a natural pentacyclic triterpenoid with a wide range of biological activities. To improve the water solubility and targeting of lupeol, in the following study, we synthesized 27 lupeol derivatives in the first series by introducing lipophilic cations with lupeol as the lead compound. Through the screening of different cancer cells, we found that some of the derivatives showed better activity than cisplatin against human non-small cell lung cancer A549 cells, among which compound 6c was found to have an IC50 value of 1.83 μM and a selectivity index of 21.02 (IC50MRC-5/IC50A549) against A549 cells. To further improve the antiproliferative activity of the compounds, we replaced the ester linkage of the linker with a carbamate linkage and synthesized a second series of five lupeol derivatives which were screened for activity, among which compound 14f was found to have an IC50 value of 1.36 μM and a selectivity index of 15.60 (IC50MRC-5/IC50A549) against A549 cells. We further evaluated the bioactivity of compounds 6c and 14f and found that both compounds induced apoptosis in A549 cells, promoted an increase in intracellular reactive oxygen species and decrease in mitochondrial membrane potential, and inhibited the cell cycle in the S phase. Of the compounds, compound 14f showed stronger bioactivity than compound 6c. We then selected compound 14f for molecular-level Western blot evaluation and in vivo evaluation in the zebrafish xenograft A549 tumor cell model. Compound 14f was found to significantly downregulate Bcl-2 protein expression and upregulate Bax, Cyt C, cleaved caspase-9, and cleaved caspase-3 protein expression, and 14f was found to be able to inhibit the proliferation of A549 cells in the zebrafish xenograft model. The above results suggest that compound 14f has great potential in the development of antitumor drugs targeting mitochondria.

The ubiquitin-specific protease 21 is critical for cancer cell mitochondrial function and regulates proliferation and migration

Ubiquitin-specific proteases (USPs) are the main members of deubiquitinases (DUBs) that catalyze removing ubiquitin chains from target proteins, thereby modulating their half-life and function. Enzymatic activity of USP21 regulates protein degradation which is critical for maintaining cell homeostasis. USP21 determines the stability of oncogenic proteins and therefore is implicated in carcinogenesis. In this study, we investigated the effect of USP21 deletion on cancer cell metabolism. Transcriptomic and proteomic analysis of USP21 KO HAP-1 cells revealed that endogenous USP21 is critical for the expression of genes and proteins involved in mitochondrial function. Additionally, we have found that the deletion of USP21 reduced STAT3 activation and STAT3-dependent gene and protein expression in cancer cells. Genetic deletion of USP21 impaired mitochondrial respiration and disturbed ATP production. This resulted in cellular consequences such as inhibition of cell proliferation and migration. Presented results provide new insights into the biology of USP21, suggesting novel mechanisms for controlling STAT3 activity and mitochondrial function in tumor cells. Taken together, our findings indicate that targeting USP21 dysregulates the energy status of cancer cells offering new perspectives for anticancer therapy.

Synthesis, Characterization, In Vitro Anticancer Evaluation, ADMET Properties, and Molecular Docking of Novel 5-Sulfanyl Substituted (Thiazol-4-yl)-Phosphonium Salts

Seven TPP+ new 5-sulfanyl substituted (thiazol-4-yl) phosphonium salts functionalized with different substituents were designed, synthesized, and studied against the NCI-60 human cancer cell lines. Compounds 1-4 show the total average parameters GI50=0.7-2.7 μM, TGI=7.0-14.6 μM, and LC50=25.2-41.8 μM, and compounds 5-7 show GI50=0.3-0.5 μM, TGI=1.3-3.1 μM, and LC50=3.6-4.0 μM. The most active compound 7 demonstrated the best anticancer results against leukemia (K-562, GI50=0.141 μM; RPMI-8226, GI50=0.143 μM), ovarian cancer (NCI/ADR-RES, GI50=0.142 μM), breast cancer (HS578T, GI50=0.175 μM; MDA-MB-468, GI50=0.101 μM), melanoma (SK-MEL-5, GI50=0.155 μM), and colon cancer (COLO 205, GI50=0.163 μM). All compounds showed low cytotoxicity against the leukemia subpanel (LC50>100 μM). The SAR analysis reveals the critical role of the substitutes at the thiazole C2 and C5 positions. Adding the phenyl, p-tolyl, or 4-chlorophenyl group to the C2 position in compounds 5-7 increases anticancer effectiveness. According to the NCI COMPARE analysis, compounds 2-3 showed a very high (r=0.92, 0.81) correlation with morpholino-doxorubicin. Molecular docking-analyzing the antitumor mechanism of compounds 1-4 action demonstrated that the DNA chain is a probable biotarget. The ADMET analysis acknowledges the favorable prognosis using compounds as potential anticancer agents.

Targeted mitochondrial nanomaterials in biomedicine: Advances in therapeutic strategies and imaging modalities

Mitochondria, pivotal organelles crucial for energy generation, apoptosis regulation, and cellular metabolism, have spurred remarkable advancements in targeted material development. This review surveys recent breakthroughs in targeted mitochondrial nanomaterials, illuminating their potential in drug delivery, disease management, and biomedical imaging. This review approaches from various application perspectives, introducing the specific applications of mitochondria-targeted materials in cancer treatment, probes and imaging, and diseases treated with mitochondria as a therapeutic target. Addressing extant challenges and elucidating potential therapeutic mechanisms, it also outlines future development trajectories and obstacles. By comprehensively exploring the diverse applications of targeted mitochondrial nanomaterials, this review aims to catalyze innovative treatment modalities and diagnostic approaches in medical research. STATEMENT OF SIGNIFICANCE: This review presents the latest advancements in mitochondria-targeted nanomaterials for biomedical applications, covering diverse fields such as cancer therapy, bioprobes, imaging, and the treatment of various systemic diseases. The novelty and significance of this work lie in its systematic analysis of the intricate relationship between mitochondria and different diseases, as well as the ingenious design strategies employed to harness the therapeutic potential of nanomaterials. By providing crucial insights into the development of mitochondria-targeted nanomaterials and their applications, this review offers a valuable resource for researchers working on innovative treatment modalities and diagnostic approaches. The scientific impact and interest to the readership lie in the identification of promising avenues for future research and the potential for clinical translation of these cutting-edge technologies.

Small molecule inhibitors targeting heat shock protein 90: An updated review

As a molecular chaperone, heat shock protein 90 (HSP90) plays important roles in the folding, stabilization, activation, and degradation of over 500 client proteins, and is extensively involved in cell signaling, proliferation, and survival. Thus, it has emerged as an important target in a variety of diseases, including cancer, neurodegenerative diseases, and viral infections. Therefore, targeted inhibition of HSP90 provides a valuable and promising therapeutic strategy for the treatment of HSP90-related diseases. This review aims to systematically summarize the progress of research on HSP90 inhibitors in the last five years, focusing on their structural features, design strategies, and biological activities. It will refer to the natural products and their derivatives (including novobiocin derivatives, deguelin derivatives, quinone derivatives, and terpenoid derivatives), and to synthetic small molecules (including resorcinol derivatives, pyrazoles derivatives, triazole derivatives, pyrimidine derivatives, benzamide derivatives, benzothiazole derivatives, and benzofuran derivatives). In addition, the major HSP90 small-molecule inhibitors that have moved into clinical trials to date are also presented here.

Synthesis and comparative analysis of the cytotoxicity and mitochondrial effects of triphenylphosphonium and F16 maslinic and corosolic acid hybrid derivatives

The cytotoxic profile and antiproliferative and mitochondrial effects of triterpene acid conjugates with mitochondriotropic lipophilic triphenylphosphonium (TPP+) and F16 cations were evaluated. Maslinic and corosolic acids chosen as the investigation objects were synthesized from commercially available oleanolic and ursolic acids. Study of the cytotoxic activity of TPP+ and F16 triterpenoid derivatives against six tumor cell lines demonstrated a comparable synergistic effect in the anticancer activity, which was most pronounced in the case of MCF-7 mammary adenocarcinoma cells and Jurkat and THP-1 leukemia cells. The corosolic and maslinic acid hybrid derivatives caused changes in the progression of tumor cell cycle phases when present in much lower doses than their natural triterpene acid precursors. The treatment of tumor cell lines with the conjugates resulted in the cell cycle arrest in the G1 phase and increase in the cell population in the subG1 phase. The cationic derivatives of the acids were markedly superior to their precursors as inducers of hyperproduction of reactive oxygen species and more effectively decreased the mitochondrial potential in isolated rat liver mitochondria. We concluded that the observed cytotoxic effect of TPP+ and F16 triterpenoid conjugates is attributable to the ability of these compounds to initiate mitochondrial dysfunctions. Their cytotoxicity, antiproliferative action, and mitochondrial effects depend little on the type of cationic groups used.

Triphenylphosphonium-linked derivative of hecogenin with enhanced antiproliferative activity: Design, synthesis, and biological evaluation

Hecogenin (HCG), a steroidal sapogenin, possesses good antitumor properties. However, the application of HCG for cancer treatment has been hindered primarily by its moderate potency. In this study, we incorporated triphenylphosphonium cation (TPP+) at the C-3 and C-12 positions through different lengths of alkyl chains to target mitochondria and enhance the efficacy and selectivity of the parent compound. Cytotoxicity screening revealed that most of the target compounds exhibited potent antiproliferative activity against five human cancer cell lines (MKN45, A549, HCT-116, MCF-7, and HepG2). Structure-activity relationship studies indicated that the TPP+ group significantly enhanced the antiproliferative potency of HCG. Among these compounds, 3c demonstrated remarkable potency against MKN45 cells with an IC50 value of 0.48 μM, significantly more effective than its parent compound HCG (IC50 > 100 μM). Further investigations into the mechanism of action revealed that 3c induced apoptosis of MKN45 cells through the mitochondrial pathway. In a zebrafish xenograft model, 3c inhibited the proliferation of MKN45 cells. Overall, these results suggest that 3c, with potent antiproliferative activity, may serve as a valuable scaffold for developing new antitumor agents.

Synthesis of Triphenylphosphonium-Linked Derivative of 3,5-Ditert-butyl-4-hydroxybenzylidene-malononitrile (SF6847) via Knoevenagel Reaction Yields an Effective Mitochondria-Targeted Protonophoric Uncoupler

Mitochondrial uncouplers are actively sought as potential therapeutics. Here, we report the first successful synthesis of mitochondria-targeted derivatives of the highly potent uncoupler 3,5-ditert-butyl-4-hydroxybenzylidene-malononitrile (SF6847), bearing a cationic alkyl(triphenyl)phosphonium (TPP) group. As a key step of the synthesis, we used condensation of a ketophenol with malononitrile via the Knoevenagel reaction. SF-C5-TPP with a pentamethylene linker between SF6847 and TPP, stimulating respiration and collapsing membrane potential of rat liver mitochondria at submicromolar concentrations, proved to be the most effective uncoupler of the series. SF-C5-TPP showed pronounced protonophoric activity on a model planar bilayer lipid membrane. Importantly, SF-C5-TPP exhibited rather low toxicity in fibroblast cell culture, causing mitochondrial depolarization in cells at concentrations that only slightly affected cell viability. SF-C5-TPP was more effective in decreasing the mitochondrial membrane potential in the cell culture than SF6847, in contrast to the case of isolated mitochondria. Like other zwitterionic uncouplers, SF-C5-TPP inhibited the growth of Bacillus subtilis in the micromolar concentration range.

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.

Ovarian cancer cells regulate their mitochondrial content and high mitochondrial content is associated with a poor prognosis

Most cancer patients ultimately die from the consequences of distant metastases. As metastasis formation consumes energy mitochondria play an important role during this process as they are the most important cellular organelle to synthesise the energy rich substrate ATP, which provides the necessary energy to enable distant metastasis formation. However, mitochondria are also important for the execution of apoptosis, a process which limits metastasis formation. We therefore wanted to investigate the mitochondrial content in ovarian cancer cells and link its presence to the patient's prognosis in order to analyse which of the two opposing functions of mitochondria dominates during the malignant progression of ovarian cancer. Monoclonal antibodies directed against different mitochondrial specific proteins, namely heat shock proteins 60 (HSP60), fumarase and succinic dehydrogenase, were used in immunohistochemistry in preliminary experiments to identify the antibody most suited to detect mitochondria in ovarian cancer cells in clinical tissue samples. The clearest staining pattern, which even delineated individual mitochondria, was seen with the anti-HSP60 antibody, which was used for the subsequent clinical study staining primary ovarian cancers (n = 155), borderline tumours (n = 24) and recurrent ovarian cancers (n = 26). The staining results were semi-quantitatively scored into three groups according to their mitochondrial content: low (n = 26), intermediate (n = 50) and high (n = 84). Survival analysis showed that high mitochondrial content correlated with a statistically significant overall reduced survival rate In addition to the clinical tissue samples, mitochondrial content was analysed in ovarian cancer cells grown in vitro (cell lines: OVCAR8, SKOV3, OVCAR3 and COV644) and in vivo in severe combined immunodeficiency (SCID) mice.In in vivo grown SKOV3 and OVCAR8 cells, the number of mitochondria positive cells was markedly down-regulated compared to the in vitro grown cells indicating that mitochondrial number is subject to regulatory processes. As high mitochondrial content is associated with a poor prognosis, the provision of high energy substrates by the mitochondria seems to be more important for metastasis formation than the inhibition of apoptotic cell death, which is also mediated by mitochondria. In vivo and in vitro grown human ovarian cancer cells showed that the mitochondrial content is highly adaptable to the growth condition of the cancer cells.

Small-molecule redox modulators with anticancer activity: A comprehensive mechanistic update

The pursuit of effective anticancer therapies has led to a burgeoning interest in the realm of redox modulation. This review provides a comprehensive exploration of the intricate mechanisms by which diverse anticancer molecules leverage redox pathways for therapeutic intervention. Redox modulation, encompassing the fine balance of oxidation-reduction processes within cells, has emerged as a pivotal player in cancer treatment. This review delves into the multifaceted mechanisms of action employed by various anticancer compounds, including small molecules and natural products, to disrupt cancer cell proliferation and survival. Beginning with an examination of the role of redox signaling in cancer development and resistance, the review highlights how aberrant redox dynamics can fuel tumorigenesis. It then meticulously dissects the strategies employed by anticancer agents to induce oxidative stress, perturb redox equilibrium, and trigger apoptosis within cancer cells. Furthermore, the review explores the challenges and potential side effects associated with redox-based treatments, along with the development of novel redox-targeted agents. In summary, this review offers a profound understanding of the dynamic interplay between redox modulation and anticancer molecules, presenting promising avenues to revolutionize cancer therapy and enhance patient outcomes.

π Bridge Engineering-Boosted Dual Enhancement of Type-I Photodynamic and Photothermal Performance for Mitochondria-Targeting Multimodal Phototheranostics of Tumor

Designing mitochondria-targeting phototheranostic agents (PTAs), which can simultaneously possess exceptional and balanced type-I photodynamic therapy (PDT) and photothermal therapy (PTT) performance, still remains challenging. Herein, benzene, furan, and thiophene were utilized as π bridges to develop multifunctional PTAs. STB with thiophene as a π bridge, in particular, benefiting from stronger donor-accepter (D-A) interactions, reduced the singlet-triplet energy gap (ΔES1-T1), allowed more free intramolecular rotation, and exhibited outstanding near-infrared (NIR) emission, effective type-I reactive oxygen species (ROS) generation, and relatively high photothermal conversion efficiency (PCE) of 51.9%. In vitro and in vivo experiments demonstrated that positive-charged STB not only can actively target the mitochondria of tumor cells but also displayed strong antitumor effects and excellent in vivo imaging ability. This work subtly established a win-win strategy by π bridge engineering, breaking the barrier of making a balance between ROS generation and photothermal conversion, boosting a dual enhancement of PDT and PTT performance, and stimulating the development of multimodal imaging-guided precise cancer phototherapy.

GSH-Responsive Prodrug Nanoassembly as a Carrier-Free Nanoplatform for Tumor-Targeting Delivery and Chemo-Photothermal Therapy

Photothermal therapy, combined with chemotherapy, holds promising prospects for the therapeutic outcome of malignant tumors. However, the synergistic therapeutic effect suffers from low coloading capacity and inefficient synchronous tumor-targeting delivery of chemodrug and photothermal photosensitizers. Herein, we designed a versatile carrier-free nanoplatform to seek improvement for chemo-photothermal therapy. An NIR photosensitizer IR-808 was used for noninvasive cancer imaging, diagnosis, and imaging-guided photothermal therapy. A reduction-sensitive paclitaxel prodrug (PTX-SS-PEG2k) was rationally synthesized by covalently linking paclitaxel with polyethylene glycol 2000 via a disulfide bond. Then, the carrier-free nanoassemblies were constructed with an inner core of IR-808 and an amphiphilic paclitaxel prodrug shell. PTX-SS-PEG2k served as a stabilizer and chemodrug and could facilitate the self-assembly of IR-808 nanoparticles with high coloading efficiency and reduction-sensitive drug release. The versatile nanoplatform exhibited multiple advantages, including high drug payload, reduction-sensitive drug release, tumor-targeting drug delivery, and potent synergistic antitumor effect. We provide a versatile theranostic nanoplatform, which improves the effectiveness of synergetic chemo-photothermal therapy and reduces the off-target toxicity.

OXPHOS-targeting drugs in oncology: new perspectives

INTRODUCTION

Drugs targeting mitochondria are emerging as promising antitumor therapeutics in preclinical models. However, a few of these drugs have shown clinical toxicity. Developing mitochondria-targeted modified natural compounds and US FDA-approved drugs with increased therapeutic index in cancer is discussed as an alternative strategy.

AREAS COVERED

Triphenylphosphonium cation (TPP+)-based drugs selectively accumulate in the mitochondria of cancer cells due to their increased negative membrane potential, target the oxidative phosphorylation proteins, inhibit mitochondrial respiration, and inhibit tumor proliferation. TPP+-based drugs exert minimal toxic side effects in rodents and humans. These drugs can sensitize radiation and immunotherapies.

EXPERT OPINION

TPP+-based drugs targeting the tumor mitochondrial electron transport chain are a new class of oxidative phosphorylation inhibitors with varying antiproliferative and antimetastatic potencies. Some of these TPP+-based agents, which are synthesized from naturally occurring molecules and FDA-approved drugs, have been tested in mice and did not show notable toxicity, including neurotoxicity, when used at doses under the maximally tolerated dose. Thus, more effort should be directed toward the clinical translation of TPP+-based OXPHOS-inhibiting drugs in cancer prevention and treatment.

The Finally Rewarding Search for A Cytotoxic Isosteviol Derivative

Acid hydrolysis of stevioside resulted in a 63% yield of isosteviol (1), which served as a starting material for the preparation of numerous amides. These compounds were tested for cytotoxic activity, employing a panel of human tumor cell lines, and almost all amides were found to be non-cytotoxic. Only the combination of isosteviol, a (homo)-piperazinyl spacer and rhodamine B or rhodamine 101 unit proved to be particularly suitable. These spacered rhodamine conjugates exhibited cytotoxic activity in the sub-micromolar concentration range. In this regard, the homopiperazinyl-spacered derivatives were found to be better than those compounds with piperazinyl spacers, and rhodamine 101 conjugates were more cytotoxic than rhodamine B hybrids.

Mitochondria-targeted organic sonodynamic therapy agents: concept, benefits, and future directions

Sonodynamic therapy (SDT) is an emerging and potentially less invasive therapeutic approach for cancer that employs ultrasound (US)-sensitive agents combined with US irradiation to generate cytotoxic reactive oxygen species (ROS) in deep tumor regions. Among various cellular organelles, the mitochondria are particularly susceptible to ROS, making them an attractive target for SDT. Organic-based SDT agents with mitochondria-targeting affinity have gained considerable interest as potential alternatives to conventional SDT agents, offering significant advantages in the field of SDT. However, to date, a comprehensive review focusing on mitochondria-targeted SDT agents has not yet been published. In this review, we provide an overview of the general concept, importance, benefits, and limitations of mitochondria-targeted organic SDT agents in comparison to conventional SDT methods. Finally, we discuss the current challenges and future directions for the design and development of efficient SDT agents. By addressing these issues, we aim to stimulate further research and advancements in the field of mitochondria-targeted SDT, ultimately facilitating the translation of these agents into clinical applications.

A novel multifunctional mitochondrion-targeting NIR fluorophore probe inhibits tumour proliferation and metastasis through the PPARγ/ROS/β-catenin pathway

Recent advancements in tumour-targeted therapies and immunotherapy offer hope to patients with various malignancies. However, the uncontrolled growth and metastatic infiltration of malignant tumours remain a huge therapeutic challenge. Therefore, this study aimed to develop an integrated multifunctional diagnostic and treatment reagent IR-251 that can not only be used for tumour imaging but also to inhibit tumour growth and metastasis. Besides, our results showed that IR-251 targeted and damaged the mitochondria in cancer cells via organic anion-transporting polypeptides. Mechanistically, IR-251 induced ROS overproduction by inhibiting PPARγ and then inhibiting the β-catenin signalling pathway and downstream protein molecules related to the cell cycle and metastasis. Moreover, the excellent anti-tumour proliferation and metastasis ability of IR-251 were verified in vitro/in vivo. And histochemistry staining revealed that IR-251 inhibited tumour proliferation and metastasis, which showed no significant side effect. In conclusion, this novel, multifunctional, mitochondria-targeting near-infrared fluorophore probe IR-251 has great potential in achieving accurate tumour imaging and inhibiting tumour proliferation and metastasis, and the underlying mechanism of action of IR-251 is mainly via the PPARγ/ROS/β-catenin pathway.

Targeting Mitochondria with ClpP Agonists as a Novel Therapeutic Opportunity in Breast Cancer

Breast cancer is the most frequently diagnosed malignancy worldwide and the leading cause of cancer mortality in women. Despite the recent development of new therapeutics including targeted therapies and immunotherapy, triple-negative breast cancer remains an aggressive form of breast cancer, and thus improved treatments are needed. In recent decades, it has become increasingly clear that breast cancers harbor metabolic plasticity that is controlled by mitochondria. A myriad of studies provide evidence that mitochondria are essential to breast cancer progression. Mitochondria in breast cancers are widely reprogrammed to enhance energy production and biosynthesis of macromolecules required for tumor growth. In this review, we will discuss the current understanding of mitochondrial roles in breast cancers and elucidate why mitochondria are a rational therapeutic target. We will then outline the status of the use of mitochondria-targeting drugs in breast cancers, and highlight ClpP agonists as emerging mitochondria-targeting drugs with a unique mechanism of action. We also illustrate possible drug combination strategies and challenges in the future breast cancer clinic.

A novel lonidamine derivative targeting mitochondria to eliminate cancer stem cells by blocking glutamine metabolism

Cancer stem cells (CSCs) have been blamed as the main culprit of tumor initiation, progression, metastasis, chemoresistance, and recurrence. However, few anti-CSCs agents have achieved clinical success so far. Here we report a novel derivative of lonidamine (LND), namely HYL001, which selectively and potently inhibits CSCs by targeting mitochondria, with 380-fold and 340-fold lower IC₅₀ values against breast cancer stem cells (BCSCs) and hepatocellular carcinoma stem cells (HCSCs), respectively, compared to LND. Mechanistically, we reveal that HYL001 downregulates glutaminase (GLS) expression to block glutamine metabolism, blunt tricarboxylic acid cycle, and amplify mitochondrial oxidative stress, leading to apoptotic cell death. Therefore, HYL001 displays significant antitumor activity in vivo, both as a single agent and combined with paclitaxel. Furthermore, HYL001 represses CSCs of fresh tumor tissues derived from liver cancer patients. This study provides critical implications for CSCs biology and development of potent anti-CSCs drugs.

Recent Development of Advanced Fluorescent Molecular Probes for Organelle-Targeted Cell Imaging

Fluorescent molecular probes are very powerful tools that have been generally applied in cell imaging in the research fields of biology, pathology, pharmacology, biochemistry, and medical science. In the last couple of decades, numerous molecular probes endowed with high specificity to particular organelles have been designed to illustrate intracellular images in more detail at the subcellular level. Nowadays, the development of cell biology has enabled the investigation process to go deeply into cells, even at the molecular level. Therefore, probes that can sketch a particular organelle's location while responding to certain parameters to evaluate intracellular bioprocesses are under urgent demand. It is significant to understand the basic ideas of organelle properties, as well as the vital substances related to each unique organelle, for the design of probes with high specificity and efficiency. In this review, we summarize representative multifunctional fluorescent molecular probes developed in the last decade. We focus on probes that can specially target nuclei, mitochondria, endoplasmic reticulums, and lysosomes. In each section, we first briefly introduce the significance and properties of different organelles. We then discuss how probes are designed to make them highly organelle-specific. Finally, we also consider how probes are constructed to endow them with additional functions to recognize particular physical/chemical signals of targeted organelles. Moreover, a perspective on the challenges in future applications of highly specific molecular probes in cell imaging is also proposed. We hope that this review can provide researchers with additional conceptual information about developing probes for cell imaging, assisting scientists interested in molecular biology, cell biology, and biochemistry to accelerate their scientific studies.

Mitochondriotropic Derivative of Ethyl Ferulate, a Dietary Phenylpropanoid, Exhibits Enhanced Cytotoxicity in Cancer Cells via Mitochondrial Superoxide-Mediated Activation of JNK and AKT Signalling

Specific targeting of anti-cancer drugs to mitochondria is an emerging strategy to enhance cancer cell killing whilst simultaneously overcoming the problem of drug resistance, low bioavailability and limited clinical success of natural products. We have synthesized a mitochondria targeted derivative of Ethyl Ferulate (EF, a naturally occurring ester of ferulic acid), by conjugating it with triphenylphosphonium ion and compared its cytotoxicity with the parent molecule. Mito-Ethyl Ferulate (M-EF) was found to be more potent than EF (~ 400-fold) in inhibiting the growth of A549 and MCF-7 cells and suppressing the clonogenic potential of A549 cells. Notably, M-EF did not induce any cytotoxicity in normal cells (mouse normal fibroblast cells) up to a concentration of 25 μM. Furthermore, M-EF treatment induced significantly higher cell death in MCF-7 and A549 cells, as compared to EF via induction of apoptosis. M-EF treatment increased mitochondrial superoxide production and induced mitochondrial DNA damage and phosphorylation of JNK and AKT in A549 cells. Furthermore, M-EF induced increase in mitochondrial superoxide production and cytotoxicity was attenuated on pre-treatment with mitochondria-targeted antioxidant (mitoTEMPO) indicating the involvement of mitochondrial ROS in the cytotoxic effects of M-EF. Finally, in silico prediction revealed putative mitochondrial targets of M-EF which are known to regulate mitochondrial ROS and cell viability. In conclusion, the improved cytotoxic efficacy of M-EF exemplifies the use of mitochondria-specific drug delivery in future development of natural product based mitochondrial pharmacology.

Comparative proteomics reveals anticancer compounds from Lansium domesticum against NSCLC cells target mitochondrial processes

Lansium domesticum is identified as a potential source of anticancer compounds. However, there are minimal studies on its anti-lung cancer properties as well as its mechanism of action. Here, we show the specificity of lanzones hexane (LH) leaf extracts to non-small cell lung cancer cells (A549) compared to normal lung fibroblast cells (CCD19-Lu) and normal epithelial prostate cells (PNT2). Subsequent bioassay-guided fractionation of the hexane leaf extracts identified two bioactive fractions with IC₅₀ values of 2.694 μg/ml (LH6-6) and 2.883 μg/ml (LH7-6). LH 6-6 treatment (1 μg/ml concentration) also showed a significantly reduced migration potential of A549 relative to the control. Thirty-one phytocompounds were isolated and identified using gas chromatography-mass spectrometric (MS) analysis and were then subjected to network pharmacology analysis to assess its effects on lung cancer target proteins. Using liquid chromatography-tandem mass spectrometry proteomics experiments, we were able to show that these compounds cause cytotoxic effects through targeting mitochondrial processes in A549 lung cancer cells.

Mitochondrial dysfunction-targeted nanosystems for precise tumor therapeutics

Mitochondria play critical roles in the regulation of the proliferation and apoptosis of cancerous cells. Targeted induction of mitochondrial dysfunction in cancer cells by multifunctional nanosystems for cancer treatment has attracted increasing attention in the past few years. Numerous therapeutic nanosystems have been designed for precise tumor therapy by inducing mitochondrial dysfunction, including reducing adenosine triphosphate, breaking redox homeostasis, inhibiting glycolysis, regulating proteins, membrane potential depolarization, mtDNA damage, mitophagy dysregulation and so on. Understanding the mechanisms of mitochondrial dysfunction would be helpful for efficient treatment of diseases and accelerating the translation of these therapeutic strategies into the clinic. Then, various strategies to construct mitochondria-targeted nanosystems and induce mitochondrial dysfunction are summarized, and the recent research progress regarding precise tumor therapeutics is highlighted. Finally, the major challenges and an outlook in this rapidly developing field are discussed. This review is expected to inspire further development of novel mitochondrial dysfunction-based strategies for precise treatments of cancer and other human diseases.

Mitochondrial-Targeted Triphenylphosphonium-Hydroxycamptothecin Conjugate and Its Nano-Formulations for Breast Cancer Therapy: In Vitro and In Vivo Investigation

Mitochondria are involved in various stages of cancer cell diffusion and metastasis. Therefore, targeting tumor mitochondria with antineoplastic medicines to cause mitochondria to initiate apoptosis may be an effective strategy for cancer therapy. Here, in order to enhance the anti-tumor efficacy of the antineoplastic agent hydroxycamptothecin (HCPT), the mitochondrial targeting ligand 4-(carboxybutyl) triphenylphosphine bromide (TPP) was attached to HCPT by an ester linkage. The resultant TPP-HCPT (TH) conjugate could self-assemble into nano-aggregates, with a mean particle size of 203.2 nm and a polydispersity index (PDI) value of 0.312. The TH conjugate could also co-assembly with mPEG₃₀₀₀-PLGA₅₀₀₀ into nanoparticles (TH-NPs), with a mean diameter of 86.41 nm, a PDI value of 0.256 and a zeta potential of -0.125 mV. In contrast to HCPT injections, TH aggregates displayed enhanced cellular uptake, mitochondria-targetability and cytotoxicity against 4T1 cells, while TH-NPs showed even better improvement than TH aggregates. In the in vivo study, TH aggregates displayed higher anti-tumor efficacy in 4T1 tumor-bearing mice than HCPT injections (tumor inhibition rate, 55.71% vs. 69.17%), and TH-NPs displayed more superior anti-tumor effects (tumor inhibition rate, 80.02%). In conclusion, our research demonstrated that the TPP-HCPT conjugate and its nano-formulations, including TH aggregates and TH-NPs, may be a promising mitochondria-targeting anticancer medicine for cancer therapy. As far as we know, this is the first report in which TPP and HCPT have been conjugated directly for this aim.

Mitochondrial Targeting and Imaging with Small Organic Conjugated Fluorophores: A Review

The last decade has seen an increasingly large number of studies reporting on the development of novel small organic conjugated systems for mitochondrial imaging exploiting optical signal transduction pathways. Mitochondria are known to play a critical role in a number of key biological processes, including cellular metabolism. Importantly, irregularities on their working function are nowadays understood to be intimately linked to a range of clinical conditions, highlighting the importance of targeting mitochondria for therapeutic benefits. In this work we carry out an in-depth evaluation on the progress to date in the field to pave the way for the realization of superior alternatives to those currently existing. The manuscript is structured by commonly used chemical scaffolds and comprehensively covers key aspects factored in design strategies such as synthetic approaches as well as photophysical and biological characterization, to foster collaborative work among organic and physical chemists as well as cell biologists.

Mitochondrion-Targeted NIR Therapeutic Agent Suppresses Melanoma by Inducing Apoptosis and Cell Cycle Arrest via E2F/Cyclin/CDK Pathway

Malignant melanoma is the most fatal form of skin cancer worldwide, and earlier diagnosis and more effective therapies are required to improve prognosis. As a possible solution, near-infrared fluorescent heptamethine cyanine dyes have been shown to be useful for tumor diagnosis and treatment. Here, we synthesized a novel theranostic agent, IR-817, a multifunctional bioactive small-molecule that has near-infrared emission, targets mitochondria in cancer cells, and has selective anti-cancer effects. In in vitro experiments, IR-817 preferentially accumulated in melanoma cells through organic anion transporting polypeptide transporters but also selectively inhibited the growth of tumor cells by inducing mitochondrial-dependent intrinsic apoptosis. Mechanistically, IR-817 caused G0/G1 cell cycle arrest by targeting the E2F/Cyclin/CDK pathway. Finally, IR-817 significantly suppressed the growth of xenograft tumors in zebrafish and mice. Immunohistochemical staining and hematoxylin and eosin staining revealed that IR-817 induced apoptosis and inhibited tumor cell proliferation without notable side effects. Therefore, mitochondrial-targeting theranostic agent IR-817 may be promising for accurate tumor diagnosis, real-time monitoring, and safe anti-cancer treatments.

An N-heterocyclic carbene iridium(III) complex as a potent anti-cancer stem cell therapeutic

Cancer stem cells (CSCs) represent a difficult to treat cellular niche within tumours due to their unique characteristics, which give them a high propensity for resistance to classical anti-cancer treatments and the ability to repopulate the tumour mass. An attribute that may be implicated in the high rates of recurrence of certain tumours. However, other characteristics specific to these cells, such as their high dependence on mitochondria, may be exploited for the development of new therapeutic agents that are effective against the niche. As such, a previously described phosphorescent N-heterocyclic carbene iridium(III) compound which showed a high level of cytotoxicity against classical tumour cell lines with mitochondria-specific effects was studied for its potential against CSCs. The results showed a significantly higher level of activity against several CSC lines compared to non-CSCs. Mitochondrial localisation and superoxide production were confirmed. Although the cell death involved caspase activation, their role in cell death was not definitive, with a potential implication of other, non-apoptotic pathways shown. A cytostatic effect of the compound was also displayed at low mortality doses. This study thus provides important insights into the mechanisms and the potential for this class of molecule in the domain of anti-CSC therapeutics.

MitoQ demonstrates connexin- and p53-mediated cancer chemoprevention in N-nitrosodiethylamine-induced hepatocarcinogenesis rodent model

Cancer chemoprevention is an approach that offers huge potential for preventing/retarding carcinogenesis. MitoQ is well-known and extensively studied mitochondria-targeted antioxidants for its applications in diseases linked with oxidative stress. In the present study chemopreventive potential of mitoQ was studied with a focus on the role of gap-junctions and p53 at an advanced stage of HCC. BALB/c mice model of hepatocarcinogenesis was established using N-nitrosodiethylamine as a carcinogen (200 mg/kg b. w., cumulative dose, intraperitoneally). The chemopreventive effect of mitoQ was studied by pre-protecting animals with mitoQ (0.125 mg/kg b. w., orally once a week) till the termination of the study. The tumors developed in the course of the study were histopathologically analyzed and statistically evaluated. The mechanistic role of mitoQ was investigated in terms of mitochondrial oxidative stress, expression of 8-OHdG, Cx26, Cx32, p53 and status of gap-junctional intercellular communication (GJIC) in tumors. Chemopreventive activity of mitoQ was evident from improved survival of animals, significantly (p ≤ 0.05) lower tumor multiplicity, tumor incidence and a total number of tumors. MitoQ treatment significantly (p ≤ 0.05) decreased mitochondrial oxidative stress as indicated by reduced mtROS and mtLPO. Increased staining intensity of 8-OHdG and internalization of Cx26, Cx32 which was observed in hepatic tumors was reduced upon mitoQ treatment. Furthermore, the expression of Cx26, Cx32 and p53 was significantly increased along with improvement in GJIC in mitoQ treatment group. MitoQ demonstrated its chemopreventive potential probably by regulating mtROS, connexins and p53 in hepatocarcinogenesis.

Curcumin Sensitises Cancerous Kidney Cells to TRAIL Induced Apoptosis via Let-7C Mediated Deregulation of Cell Cycle Proteins and Cellular Metabolism

Targeted therapies are the most attractive options in the treatment of different tumours, including kidney cancers. Such therapies have entered a golden era due to advancements in research, breakthroughs in scientific knowledge, and a better understanding of cancer therapy mechanisms, which significantly improve the survival rates and life expectancy of patients. The use of tumour necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL) as an anticancer therapy has attracted the attention of the scientific community and created great excitement due to its selectivity in targeting cancerous cells with no toxic impacts on normal tissues. However, clinical studies disappointingly showed the emergence of resistance against TRAIL. This study aimed to employ curcumin to sensitise TRAIL-resistant kidney cancerous ACHN cells, as well as to gain insight into the molecular mechanisms of TRAIL sensitization. Curcumin deregulated the expression of apoptosis-regulating micro Ribonucleic Acid (miRNAs), most notably, let-7C. Transfecting ACHN cells with a let-7C antagomir significantly increased the expression of several cell cycle protein, namely beta (β)-catenin, cyclin dependent kinase (CDK)1/2/4/6 and cyclin B/D. Further, it overexpressed the expression of the two key glycolysis regulating proteins including hypoxia-inducible factor 1-alpha (HIF-1α) and pyruvate dehydrogenase kinase 1 (PDK1). Curcumin also suppressed the expression of the overexpressed proteins when added to the antagomir transfected cells. Overall, curcumin targeted ACHN cell cycle and cellular metabolism by promoting the differential expression of let-7C. To the best of our knowledge, this is the first study to mechanistically report the cancer chemosensitisation potential of curcumin in kidney cancer cells via induction of let-7C.

Aspirin blocks AMPK/SIRT3-mediated glycolysis to inhibit NSCLC cell proliferation

Non-small cell lung cancer (NSCLC) has the highest incidence and mortality in the world. Aspirin has been reported to promote apoptosis, inhibit proliferation, stemness, angiogenesis, cancer-associated inflammation and migration in NSCLC. But the effect of aspirin on aerobic glycolysis in NSCLC is less reported. In the present study, we investigated whether aspirin blocked aerobic glycolysis of NSCLC cells to inhibit proliferation. Our results showed that aspirin inhibited viability, PCNA expression, ability of colony formation, dimished extracellular acidification rate (ECAR), oxygen consumption rate (OCR) and production of pyruvic acid and lactic acid, accompanied with reduced mitochondrial membrane potential (MMP), PGC-1α expression and ROS production, indicating mitochondrial dysfunction in NSCLC cells. AMPK and mitochondrial-localized deacetylase sirtuin 3 (SIRT3) were identified as the relevant molecular targets in glycolysis, but mechanism and relationship between AMPK and SIRT3 for aspirin induced glycolysis inhibition remain unknown in cancer cells. The investigation of underlying mechanism indicated that aspirin activated AMPK pathway to inhibit aerobic glycolysis and proliferation by upregulating SIRT3 after application of compound C (CC), an inhibitor of AMPK activity or SIRT3 siRNA. Upon activation of SIRT3, aspirin promoted the release of hexokinase-II (HK-II) from mitochondrial outer membrane to cytosol by deacetylating cyclophilin D (CypD). Consistently, aspirin significantly inhibited the growth of NSCLC xenografts and exhibited antitumor activity probably through AMPK/SIRT3/HK-II pathway in vivo. Collectively, AMPK/SIRT3/HK-II pathway plays a critical role in anticancer effects of aspirin, and our findings might serve as potential target for clinical practice and chemoprevention of aspirin in NSCLC.

An Epigenetic Role of Mitochondria in Cancer

Mitochondria are not only the main energy supplier but are also the cell metabolic center regulating multiple key metaborates that play pivotal roles in epigenetics regulation. These metabolites include acetyl-CoA, α-ketoglutarate (α-KG), S-adenosyl methionine (SAM), NAD⁺, and O-linked beta-N-acetylglucosamine (O-GlcNAc), which are the main substrates for DNA methylation and histone post-translation modifications, essential for gene transcriptional regulation and cell fate determination. Tumorigenesis is attributed to many factors, including gene mutations and tumor microenvironment. Mitochondria and epigenetics play essential roles in tumor initiation, evolution, metastasis, and recurrence. Targeting mitochondrial metabolism and epigenetics are promising therapeutic strategies for tumor treatment. In this review, we summarize the roles of mitochondria in key metabolites required for epigenetics modification and in cell fate regulation and discuss the current strategy in cancer therapies via targeting epigenetic modifiers and related enzymes in metabolic regulation. This review is an important contribution to the understanding of the current metabolic-epigenetic-tumorigenesis concept.

A Mitochondria-Targeted Phenylbutyric Acid Prodrug Confers Drastically Improved Anticancer Activities

Phenylbutyric acid (PBA) has been reported as a dual inhibitor of pyruvate dehydrogenase kinases (PDKs) and histone deacetylases (HDACs), exhibiting anticancer effects. However, the low membrane permeability and poor cellular uptake limit its access to the target organelle, resulting in weak potencies against the intended targets. Herein, we report the design and identification of a novel 4-CF₃-phenyl triphenylphosphonium-based PBA conjugate (53) with improved in vitro and in vivo anticancer activities. Compound 53 exhibited an IC₅₀ value of 2.22 μM against A375 cells, outperforming the parent drug PBA by about 4000-fold. In the A375 cell-derived xenograft mouse model, 53 reduced the tumor growth by 76% at a dose of 40 mg/kg, while PBA only reduced the tumor growth by 10% at a dose of 80 mg/kg. On the basis of these results, 53 may be considered for further preclinical evaluations for cancer therapy.

Synergic Effect of Metformin and Everolimus on Mitochondrial Dynamics of Renal Cell Carcinoma

Renal cell carcinoma (RCC) frequently recurs or metastasizes after surgical resection. Everolimus, an mTOR inhibitor, is used as a second-line treatment, but the response of RCC to everolimus is insufficient. Metformin is an antidiabetic drug; recent reports have indicated its anti-cancer effects in various cancers, and it is known to have synergistic effects with other drugs. We investigated the possibility of coadministering everolimus and metformin as an effective treatment for RCC. RCC cells treated with a combination of the two drugs showed significantly inhibited cell viability, cell migration, and invasion, and increased apoptosis compared to those treated with each drug alone. An anti-cancer synergistic effect was also confirmed in the xenograft model. Transcriptome analysis for identifying the underlying mechanism of the combined treatment showed the downregulation of mitochondrial fusion genes and upregulation of mitochondrial fission genes by the combination treatment. Changes in mitochondrial dynamics following the combination treatment were observed using LysoTracker, LysoSensor, and JC-1 staining. In conclusion, the combination of everolimus and metformin inhibited RCC growth by disrupting mitochondrial dynamics. Therefore, we suggest that a treatment combining metformin and everolimus disrupts mitochondrial dynamics in RCC, and may be a novel strategy for RCC treatment.

Chemoprevention of Lung Cancer with a Combination of Mitochondria-Targeted Compounds

Simple Summary

Previous reports showed that mitochondria-targeted honokiol and mitochondria-targeted lonidamine potently inhibit complex-I- and complexes-I/II-induced respiration and cancer cell proliferation. In this study, we investigated the efficacy of combining mitochondria-targeted honokiol and mitochondria-targeted lonidamine treatments for lung cancer prevention. We found that their combination exhibited striking tumor inhibition in the benzo[a]pyrene-induced murine lung tumor model without causing detectable side effects. Using single-cell RNA sequencing, we found combined treatment has a clear advantage in that it can significantly inhibit two oncogenic pathways—STAT3 signaling and AKT/mTOR/p70S6K signaling. Such dual inhibition may contribute to the greater efficacy of the combined drug treatment. Therefore, the combination provides a novel option for lung cancer chemoprevention.

Abstract

Combined treatment targeting mitochondria may improve the efficacy of lung cancer chemoprevention. Here, mitochondria-targeted honokiol (Mito-HNK), an inhibitor of mitochondrial complex I and STAT3 phosphorylation, and mitochondria-targeted lonidamine (Mito-LND), an inhibitor of mitochondrial complexes I/II and AKT/mTOR/p70S6K signaling, were evaluated for their combinational chemopreventive efficacy on mouse lung carcinogenesis. All chemopreventive treatments began one-week post-carcinogen treatment and continued daily for 24 weeks. No evidence of toxicity (including liver toxicity) was detected by monitoring serum levels of alanine aminotransferase and aspartate aminotransferase enzymes. Mito-HNK or Mito-LND treatment alone reduced tumor load by 56% and 48%, respectively, whereas the combination of Mito-HNK and Mito-LND reduced tumor load by 83%. To understand the potential mechanism(s) of action for the observed combinatorial effects, single-cell RNA sequencing was performed using mouse tumors treated with Mito-HNK, Mito-LND, and their combination. In lung tumor cells, Mito-HNK treatment blocked the expression of genes involved in mitochondrial complex ǀ, oxidative phosphorylation, glycolysis, and STAT3 signaling. Mito-LND inhibited the expression of genes for mitochondrial complexes I/II, oxidative phosphorylation, and AKT/mTOR/p70S6K signaling in lung tumor cells. In addition to these changes, a combination of Mito-HNK with Mito-LND decreased arginine and proline metabolism, N-glycan biosynthesis, and tryptophan metabolism in lung tumor cells. Our results demonstrate that Mito-LND enhanced the antitumor efficacy of Mito-HNK, where both compounds inhibited common targets (oxidative phosphorylation) as well as unique targets for each agent (STAT3 and mTOR signaling). Therefore, the combination of Mito-HNK with Mito-LND may present an effective strategy for lung cancer chemoprevention.

Targeting Energy Metabolism in Cancer Treatment

Cancer is the second most common cause of death worldwide after cardiovascular diseases. The development of molecular and biochemical techniques has expanded the knowledge of changes occurring in specific metabolic pathways of cancer cells. Increased aerobic glycolysis, the promotion of anaplerotic responses, and especially the dependence of cells on glutamine and fatty acid metabolism have become subjects of study. Despite many cancer treatment strategies, many patients with neoplastic diseases cannot be completely cured due to the development of resistance in cancer cells to currently used therapeutic approaches. It is now becoming a priority to develop new treatment strategies that are highly effective and have few side effects. In this review, we present the current knowledge of the enzymes involved in the different steps of glycolysis, the Krebs cycle, and the pentose phosphate pathway, and possible targeted therapies. The review also focuses on presenting the differences between cancer cells and normal cells in terms of metabolic phenotype. Knowledge of cancer cell metabolism is constantly evolving, and further research is needed to develop new strategies for anti-cancer therapies.

Prevention of Tumor Growth and Dissemination by In Situ Vaccination with Mitochondria-Targeted Atovaquone

Atovaquone, an FDA-approved drug for malaria, is known to inhibit mitochondrial electron transport. A recently synthesized mitochondria-targeted atovaquone increased mitochondrial accumulation and antitumor activity in vitro. Using an in situ vaccination approach, local injection of mitochondria-targeted atovaquone into primary tumors triggered potent T cell immune responses locally and in distant tumor sites. Mitochondria-targeted atovaquone treatment led to significant reductions of both granulocytic myeloid-derived suppressor cells and regulatory T cells in the tumor microenvironment. Mitochondria-targeted atovaquone treatment blocks the expression of genes involved in oxidative phosphorylation and glycolysis in granulocytic-myeloid-derived suppressor cells and regulatory T cells, which may lead to death of granulocytic-myeloid-derived suppressor cells and regulatory T cells. Mitochondria-targeted atovaquone inhibits expression of genes for mitochondrial complex components, oxidative phosphorylation, and glycolysis in both granulocytic-myeloid-derived suppressor cells and regulatory T cells. The resulting decreases in intratumoral granulocytic-myeloid-derived suppressor cells and regulatory T cells could facilitate the observed increase in tumor-infiltrating CD4+ T cells. Mitochondria-targeted atovaquone also improves the anti-tumor activity of PD-1 blockade immunotherapy. The results implicate granulocytic-myeloid-derived suppressor cells and regulatory T cells as novel targets of mitochondria-targeted atovaquone that facilitate its antitumor efficacy.

Anticancer activity of ruthenium(II) plumbagin complexes with polypyridyl as ancillary ligands via inhibiting energy metabolism and GADD45A-mediated cell cycle arrest

To study the antitumor activity and action mechanism of Ru(II) polypyridyl plumbagin (PLN) complexes, four complexes [Ru(PLN)(DMSO)₂]Cl (Ru1), [Ru(bpy)₂(PLN)](PF₆) (bpy is bipyridine) (Ru2), [Ru(phen)₂(PLN)](PF₆) (phen is 1,10-phenanthroline) (Ru3), and [Ru(DIP)₂(PLN)](PF₆) (DIP is 4,7-diphenyl-1,10-phenanthroline) (Ru4) were obtained and fully characterized. Lipophilicity, cellular uptake and cytotoxicity of these Ru(II) complexes are in the order of: Ru1<Ru2<Ru3<Ru4. The ancillary polypyridyl ligands affected the bioactivity and action mechanisms of these Ru(II) complexes. Ru3 and Ru4 inhibited energy metabolism by severely impairing mitochondrial respiration and glycolysis processes. Moreover, Ru3 and Ru4 induced DNA damage and the increased expression of GADD45A, which led to cell cycle arrest in G0/G1 phase in MGC-803 cells, while the inactivation of GADD45A attenuated these effects; however, Ru3 or Ru4-induced GADD45A did not affect cell apoptosis. Further studies revealed that Ru3 and Ru4 induced ROS-dependent and caspase-dependent apoptotic cell death by mitochondrial dysfunction, and Ru4 displayed higher potency than Ru3. The in vivo results in MGC-803 xenograft nude mice model also confirmed that Ru4 obviously inhibited tumor growth. Ru4 is a promising candidate to be developed as a chemotherapeutic agent.

Carboranes as unique pharmacophores in antitumor medicinal chemistry

Carborane is a carbon-boron molecular cluster that can be viewed as a 3D analog of benzene. It features special physical and chemical properties, and thus has the potential to serve as a new type of pharmacophore for drug design and discovery. Based on the relative positions of two cage carbons, icosahedral closo-carboranes can be classified into three isomers, ortho-carborane (o-carborane, 1,2-C2B10H12), meta-carborane (m-carborane, 1,7-C2B10H12), and para-carborane (p-carborane, 1,12-C2B10H12), and all of them can be deboronated to generate their nido- forms. Cage compound carborane and its derivatives have been demonstrated as useful chemical entities in antitumor medicinal chemistry. The applications of carboranes and their derivatives in the field of antitumor research mainly include boron neutron capture therapy (BNCT), as BNCT/photodynamic therapy dual sensitizers, and as anticancer ligands. This review summarizes the research progress on carboranes achieved up to October 2021, with particular emphasis on signaling transduction pathways, chemical structures, and mechanistic considerations of using carboranes.

Tumor Acidity and Near-Infrared Light Responsive Drug Delivery MoS2-Based Nanoparticles for Chemo-Photothermal Therapy

The rational design of tumor microenvironment (TME)- multifunctional stimuli-responsive nanocomposites is appealing for effective cancer treatment. However, multidrug resistance remains the main obstacles to construct responsive oncotherapy. Herein, a novel MoS₂/PDA-TPP nanocomposite loaded with chemotherapy drug of doxorubicin (DOX) is designed for TME dual-response and synergistically enhanced anti-tumor therapy based on the tumor-specific mitochondria accumulation ability and photothermal (PTT) therapy. In detail, the designed MoS₂/PDA-TPP nanoplatform can act as a pH-responsive dissociation to endow fast release of DOX under an acidic TME and simultaneously improve the efficiency of PTT. Moreover, the mechanism shows that MoS₂/PDA-TPP trigger mitochondrial-dependent apoptosis by producing reactive oxygen species (ROS) and reducing mitochondrial membrane potential (MMP). Most importantly, during PTT procedure, hyperthermia up to 50°C can effectively induce tumor cell death without causing severe inflammation to adjacent tissues. Tumor targeting double stimulation response of nanocomposites is a novel idea to overcome drug resistance, which will provide a more effective strategy for solving practical problems.

Mito-Bomb: Targeting Mitochondria for Cancer Therapy

Cancer has been one of the most common life-threatening diseases for a long time. Traditional cancer therapies such as surgery, chemotherapy (CT), and radiotherapy (RT) have limited effects due to drug resistance, unsatisfactory treatment efficiency, and side effects. In recent years, photodynamic therapy (PDT), photothermal therapy (PTT), and chemodynamic therapy (CDT) have been utilized for cancer treatment owing to their high selectivity, minor resistance, and minimal toxicity. Accumulating evidence has demonstrated that selective delivery of drugs to specific subcellular organelles can significantly enhance the efficiency of cancer therapy. Mitochondria-targeting therapeutic strategies are promising for cancer therapy, which is attributed to the essential role of mitochondria in the regulation of cancer cell apoptosis, metabolism, and more vulnerable to hyperthermia and oxidative damage. Herein, the rational design, functionalization, and applications of diverse mitochondria-targeting units, involving organic phosphine/sulfur salts, quaternary ammonium (QA) salts, peptides, transition-metal complexes, guanidinium or bisguanidinium, as well as mitochondria-targeting cancer therapies including PDT, PTT, CDT, and others are summarized. This review aims to furnish researchers with deep insights and hints in the design and applications of novel mitochondria-targeting agents for cancer therapy.

Research Progress in the Synthesis of Targeting Organelle Carbon Dots and Their Applications in Cancer Diagnosis and Treatment

With increasing knowledge about diseases at the histological, cytological to sub-organelle level, targeting organelle therapy has gradually been envisioned as an approach to overcome the shortcomings of poor specificity and multiple toxic side effects on tissues and cell-level treatments using the currently available therapy. Organelle carbon dots (CDs) are a class of functionalized CDs that can target organelles. CDs can be prepared by a "synchronous in situ synthesis method" and "asynchronous modification method." The superior optical properties and good biocompatibility of CDs can be preserved, and they can be used as targeting particles to carry drugs into cells while reducing leakage during transport. Given the excellent organelle fluorescence imaging properties, targeting organelle CDs can be used to monitor the physiological metabolism of organelles and progression of human diseases, which will provide advanced understanding and accurate diagnosis and targeted treatment of cancers. This study reviews the methods used for preparation of targeting organelle CDs, mechanisms of accurate diagnosis and targeted treatment of cancer, as well as their application in the area of cancer diagnosis and treatment research. Finally, the current difficulties and prospects for targeting organelle CDs are prospected.

Metabolic Response to the Mitochondrial Toxin 1-Methyl-4-phenylpyridinium (MPP+) in LDH-A/B Double-knockout LS174T Colon Cancer Cells

BACKGROUND/AIM

Rapid glycolytic substrate-level phosphorylation (SLP) and accumulation of lactic acid are characteristics of diverse cancers. Recent advances in drug discovery have included the use of glycolytic inhibitors with mitochondrial targeting drugs to attempt to invoke an energy crisis in aggressive metabolically active chemo-resistant cancers. In this work, we examine the consequences of inhibiting mitochondrial oxidative phosphorylation (OXPHOS) with 1-methyl-4-phenylpyridinium (MPP+) in LS14T colon cancer cells containing a genetic double knock out (DKO) of lactic acid dehydrogenase (LDHA and LDHB).

MATERIALS AND METHODS

Several metabolic parameters were evaluated concomitant to whole transcriptomic (WT) mRNA, microRNA, and long intergenic non-coding RNAs using Affymetrix 2.1 human ST arrays.

RESULTS

MPP+ effectively blocked OXPHOS where a compensatory shift toward anaerobic SLP was only observed in the control vector (CV), and not observed in the LDH-A/B DKOs (lacking the ability to produce lactic acid). Despite this, there was an unexpected resilience to MPP+ in the latter in terms of energy, which displayed significantly higher resting baseline respiratory OXPHOS capacity relative to controls. At the transcriptome level, MPP+ invoked 1738 differential expressed genes (DEGs) out of 48,226; LDH-A/B DKO resulted in 855 DEGs while 349 DEGs were found to be overlapping in both groups versus respective controls, including loss of mitochondrial complex I (subunits 3 and 6), cell cycle transcripts and fluctuations in epigenetic chromatin remodeling systems. In terms of energy, the effects of MPP+ in the CV transcripts reflect the funneling of carbon intermediates toward glycolysis. The LDH-A/B DKO transcripts reflect a flow of carbons away from glycolysis toward the production of acetyl-CoA.

CONCLUSION

The findings from this study suggest a metabolic resilience to MPP+ in cancer cells devoid of LDH-A/B, explainable in-part by higher baseline OXPHOS respiratory ATP production, necessitating more toxin to suppress the electron transport chain.