Mitochondrial dysfunction route as a possible biomarker and therapy target for human cancer

Abstract

Mitochondria are vital organelles found within living cells and have signalling, biosynthetic, and bioenergetic functions. Mitochondria play a crucial role in metabolic reprogramming, which is a characteristic of cancer cells and allows them to ensure a steady supply of proteins, nucleotides, and lipids to enable rapid proliferation and development. Their dysregulated activities have been associated with the growth and metastasis of different kinds of human cancer, particularly ovarian carcinoma. In this review, we briefly demonstrated the modified mitochondrial function in cancer, including mutations in mitochondrial DNA (mtDNA), reactive oxygen species (ROS) production, dynamics, apoptosis of cells, autophagy, and calcium excess to maintain cancer genesis, progression, and metastasis. Furthermore, the mitochondrial dysfunction pathway for some genomic, proteomic, and metabolomics modifications in ovarian cancer has been studied. Additionally, ovarian cancer has been linked to targeted therapies and biomarkers found through various alteration processes underlying mitochondrial dysfunction, notably targeting (ROS), metabolites, rewind metabolic pathways, and chemo-resistant ovarian carcinoma cells.

Highlights

• •Living cells have mitochondria, important organelles that perform biosynthetic, energetic, and signaling tasks.
• •Different types of human cancer have been linked to mitochondrial dysfunction.
• •The altered mitochondrial function in cancer maintains cancer genesis, development, and metastasis.
• •Some alterations in ovarian cancer's genome, proteome, and metabolome have been linked to the mitochondrial dysfunction pathway.
• •Targeted treatments and biomarkers for ovarian cancer have been identified through multiple modification pathways underlying mitochondrial malfunction.

1. Introduction

The mitochondria constitute the “energy center” of the cell, producing over 90 % ATP. Most recently, it has been recognized that mitochondria, as a vital organelle in our bodies, play a vital function in controlling many different kinds of physiological and pathological processes, especially proliferation, growth, and migration, as well as functions related to cancer genesis, progression, and metastasis [[1], [2], [3]].

Mitochondria serve as the target core for multiple energy metabolism regulators. Multiple research investigations have confirmed that, throughout the development and spread of cancer, aberrant mitochondrial metabolism (e.g., alterations in glucose, fatty acid, and amino acid metabolism) is frequently seen [4]. In addition, mitochondria serve as the cellular factories that create reactive oxygen molecules, which will stimulate tumor malignancy through the reactive oxygen species (ROS) dysregulation pathway [5].

The Bcl-2 protein family regulates apoptosis by modulating mitochondrial permeability, which is a key route in the process of apoptosis. Proteins that suppress apoptosis, such as B-cell lymphoma-2 (Bcl-2) and B-cell lymphoma-extra-large (Bcl-xL), exist in mitochondrial outer membranes and block cytochrome c release [6]. However, the cytoplasmic proteins that promote apoptosis, particularly Bim, Bad, Bax, and Bid, translocate to mitochondria following getting a death signal and induce cytochrome c towards the cytoplasm. Released cytochrome c links to apoptotic protease activating factor-1 (Apaf-1) to generate an apoptosome, which enhances the apoptotic cascade [7], [8].

Internal calcium homeostasis can be controlled via a variety of calcium transport pathways found in mitochondria membranes, which make up the bulk of intracellular calcium pool management. Calcium homeostasis issues in the mitochondria are linked to mitochondrial dysfunction, in which the dysregulated calcium equilibrium is a major cause of cancer initiation and development [9]. As a result, Ca2+ signaling has emerged as a highly appealing target for the development of innovative anticancer medicines [10].

One of the key governing mechanisms is mitophagy, which is a particular kind of autophagy that specifically removes damaged mitochondria to maintain mitochondrial homeostasis [11,12]. It has been demonstrated that the Pink1-and Parkin-dependent mitophagy routes preserve mitochondrial homeostasis [13]. Therefore, dysregulation of mitophagy can be linked to a variety of clinical conditions, including cancer [14,15].

Ovarian cancer (OC) is the deadliest malignant tumor in women worldwide [16], whereas 90% of ovarian cancers are of epithelial origin, 7% are stromal forms [17], and germ cell tumors are discovered relatively rarely [18]. Basic cytoreductive surgery followed by platinum-based adjuvant chemotherapy is the usual therapy for women with ovarian cancer. Despite first-line treatment having high initial response rates, the majority of ovarian cancer patients relapse with a mere 46% 5-year survival rate, mainly due to delayed diagnosis and an elevated degree of chemotherapy resistance. Therefore, improving early ovarian cancer diagnosis has important clinical ramifications [19].

Prior studies revealed that ovarian carcinoma is strongly linked to mitochondrial dysfunction [[19], [20], [21]]. For instance, in ovarian malignancies, the total amount of mitochondrial DNA (mtDNA) is much higher than in controls [22]. Also, earlier studies mentioned that analysis of a scanning electron microscope for ovarian cancer indicated that mitochondria were loose in the cytoplasm with a reduction in the width and junction diameter of cristae. Moreover, abnormalities in mitochondrial dynamics have been associated with metabolic abnormalities in cancer progression, as well as proteins responsible for chemosensitivity and chemotherapy resistance in OC [23]. Hence, mitochondrial dysfunction has been found to be a significant factor in ovarian cancer.

Accordingly, multiomics investigations have provided a novel method to generate tailored biomarkers for ovarian cancer therapies. Ovarian cancer is linked to numerous levels and multiple parameters of pathological alterations by employing a variety of genes, proteins, and metabolites separately or in combinations. Based on omics information, this article's review will help in clarifying the biological functions of mitochondrial dysfunction in ovarian cancer development, a possible connection between mitochondrial malfunction and oxidative stress, and the upcoming prospects of probable biomarkers and targeted therapies for ovarian cancer dependent on mitochondrial dysfunction pathways.

2. Mitochondria's vital role in cancer

Many mitochondrial characteristics have been reported to be modified in cancer to balance oxidative phosphorylation (OXPHOS) and glycolysis for ATP generation [24,25], including mtDNA alteration, mitochondrial-nuclear interaction, oxidative damage, cell apoptosis, autophagy, and calcium excess (Fig. 1).

Fig. 1.

Mitochondrial abnormalities in cancer show that various elements of cancer cells can be altered.

2.1. Mitochondrial metabolic pathways and cancer development

The usage of glucose and other sources of carbon in cancer is substantially more diverse than previously thought. Indeed, new research has discovered that cancer cells may employ both glycolytic and oxidative processes to maintain the generation of ATP [26]. Tumors with an identical clinical diagnosis may have mitochondrial metabolic heterogeneity, employing fatty acids or glutamine as additional oxidizable sources. ROS generated by mitochondrial metabolism and the availability of fuel is critical for interaction with cancer microenvironment constituents. Therefore, reprogramming of the metabolic system aids in the survival, migration, invasion, and multiplication of cancer cells.

2.1.1. Modification of the tricarboxylic acid (TCA) cycle pathway

Glucose, fatty acids, or glutamine-derived carbons enter the TCA pathway and generate NADH and FADH2, which then deliver their electrons to the electron transport network within the inner mitochondrial membrane for the production of CO₂ and ATP.

The TCA is a vital metabolic mechanism that takes place in the mitochondrial matrix. This cycle produces cellular energy as well as the building blocks for metabolic pathways.

Cancer cells can endure in a variety of energy-demanding settings as a result of the numerous substrates that are supplied by the TCA cycle and reprogramming of the metabolic process [27]. To maintain the TCA cycle's efficiency, two anaplerotic processes were observed: pyruvate carboxylation, which produces oxalacetate from glucose-derived pyruvate, and glutaminolysis [28], which produces α-ketoglutarate from glutamine.

TCA cycles enhance cellular proliferation by increasing ATP synthesis and contributing to nucleoside biosynthesis through mutations in TCA cycle enzymes which are linked to cancer occurrence and recurrence [29]. Particularly, fumarate hydratase, succinate dehydrogenase, and isocitrate dehydrogenase gene mutations have been linked to the advancement of cancer. These mutations result in an aberrant buildup of certain metabolites (succinate and fumarate), known as oncometabolites, leading to the dysregulation of signaling and promote the progression of cancer [30].

Targeting the TCA cycle in cancer therapy is one of several possible therapeutic approaches. To treat acute myelogenous leukemia with isocitrate dehydrogenase 2 or 1/2 mutations, for instance, AG-221 and AG881 [31] are both currently undergoing clinical trials.

2.1.2. Modification of the electron transport chain (ETC) and OXPHOS pathways

The OXPHOS route, which is linked to the oxidation processes in each fatty acid and the tricarboxylic acid cycle (TCA), generates more than 90% of ATP for cells. The process of OXPHOS takes place in the inner membrane of mitochondria and is made up of two-electron transfer carriers (cytochrome c and ubiquinone) and four complexes (CI-IV), which are arranged according to their different redox potentials to generate ATP [32].

Acute myeloid leukemia, ovarian cancer, colon and rectum adenocarcinoma, and glioblastoma are among the tumor types that have somatic mtDNA mutations that impact Complex I (ubiquinone oxidoreductase, oxidizing NADH), III (cytochrome c reductase), or IV (cytochrome c oxidase) pathways. Complex II (SDH) mutations lead to the formation of ROS and succinate buildup, which in turn inhibit HIF prolyl hydroxylase and activate the HIF pathway [33].

With the creation of inhibitors for each ETC complex, the ETC has long been used in therapeutics. As shown in Table 1, there are several inhibitors for various ETC complexes, such as tamoxifen for inhibition Complex I [34], malonate and nitropropionic acid for inhibition Complex II [35], antimycin A and resveratrol for inhibition Complex III [36], doxorubicin and porphyrin for inhibition Complex IV [37], and oligomycin for inhibition Complex V [35].

Table 1.

Different inhibition drugs for the targeted pathway of the ETC.

	Complex I	Complex II	Complex III,	Complex IV	Complex V
Type of inhibitors	Tamoxifen increases hydrogen peroxide production [34].	Malonate and nitropropionic acid [35].	Antimycin A and resveratrol, targeting different types of cancer [36].	Doxorubicin, and the porphyrin, targeting esophageal cancer and NSCLC [37].	Oligomycin [35].

2.1.3. Modulation of the fatty acid oxidation (FAO) pathway

In many tumors, this pathway—which is a source of high quantities of ATP—is triggered to deal with stress and supports high proliferation rates [38]. The normal cells that exhibit fatty acid synthesis (FAS) decrease FAO by inhibiting carnitine palmitoyltransferases (CPT1) with malonyl-CoA generated by acetyl carboxylase 1 or 2 (ACC1 and ACC2), which is required for FAO to transport fatty acids to mitochondria [39].

In cancer cells, elevated FAO is linked to high ATP levels. This happens through a decrease in ACC1 and ACC2 expression, which leads to specific ACC2 downregulation and CPT1 overexpression [38]. Significant serous ovarian cancer and acute leukemia both have elevated levels of CPT1A, which is associated with poor survival. The rate-limiting CPT1 enzyme is the target of the majority of FAO inhibitors. As an illustration, Etomoxir, the most commonly used CPT1 inhibitor, stops tumor growth in a model of HGSOC [40].

2.1.4. Modification of glutamine metabolism pathway

The synthesis of various amino acids, proteins, nucleotides, and glutathione generally depends on glutamine, which is regarded as a non-essential amino acid [41]. The TCA cycle uses glutamine as an anaplerotic source in many cancer cells, which are said to be “glutamine addicted” [41]. Through the SCL1A5 transporter, glutamine can enter mitochondria, where it is changed to glutamate by glutaminases (GLS) and then to α-ketoglutarate by glutamate dehydrogenase.

Elevated α-ketoglutarate synthesis, triggered by high glutamate dehydrogenase, causes glutamine-derived carbon flow into the TCA cycle and increases anaplerosis and the generation of energy. Furthermore, increasing glutamate dehydrogenase concentrations cause more fumarate to be produced, which in turn triggers and binds the glutathione peroxidase enzyme, boosting the ROS detoxification process in different cancer cells. Additionally, tumor growth in vivo and proliferation in cancer cell lines are decreased by genetic suppression or glutaminase blockage employing the BPTES allosteric inhibitor [42].

2.2. Biomass generation and mitochondria

Nucleotides, fatty acids, and amino acids are synthesized by a large number of intermediates within the mitochondrial TCA cycle, and are increased in a wide range of cancers. The ability to produce aspartate in growing cancer cells is one of the vital functions carried by the mitochondrial electron transport chain (ETC). An important enzyme called dihydroorotate dehydrogenase (DHODH) is needed for the de novo synthesis of pyrimidines. It supplies the nucleotides needed for the production of RNA and DNA, which are vital for the proliferation of cells. It changes dihydroorotate into orotate and is found on the inner membrane of the mitochondria. Consequently, the proliferation of cancer cells is greatly inhibited by blocking the ETC. DHODH also transports electrons to ubiquinone, a substrate for the ETC complex III [43].

Mitochondrial production of proline is vital for tumor cell proliferation. Proline biosynthesis enzymes, such as the P5C biosynthetic enzyme delta-1-pyrroline-5-carboxylate synthase (P5CS) and the mitochondrial NAD(P)H-dependent enzyme pyrroline-5-carboxylate reductase, have been identified as being upregulated in malignancies [44].

2.3. Mitochondria and apoptosis

The significance of mitochondria is not confined to cellular metabolism; it has also been shown to be directly involved in maintaining cell viability by controlling cell death through apoptosis and maintaining cell viability through autophagy. Apoptosis is a closely regulated physiological process required for appropriate embryonic development, genomic integrity preservation, immune system function, and tissue homeostasis maintenance. As the cell contents are finally removed by phagocytic cells, the apoptotic process does not cause inflammation [45].

The permeability of the mitochondrial outer membrane and resulting release of cytochrome C towards the cytoplasm to trigger caspase activation is a significant apoptotic mechanism. The mitochondrial structural integrity of the membrane is tightly regulated by the interaction and balance between proapoptotic BAX and BAK and antiapoptotic BCL-2 proteins. Studies have shown associations between BAK and BCL-2 and proteins related to mitochondrial dynamics, suggesting that the dynamics of mitochondria and the apoptotic mechanism interact extensively [46]. Deregulated apoptosis may be a cause of cancer cells' increased resistance against apoptosis, allowing for rapid growth and drug resistance.

Mitophagy is a selective form of autophagy, allowing for the degradation of damaged or dysfunctional mitochondria. Dysfunctional mitochondria are unable to carry out OXPHOS properly due to mitochondrial membrane depolarization and further accumulation of ROS, resulting in a significant increase in overall cellular oxidative stress [47]. Mitophagy plays a dual role in cancer and may either promote or suppress tumorigenesis, depending on the tumor type and molecular context [48]. Thus, the loss of function of several mitophagy-related genes results in the inhibition of mitophagy and further accumulation of dysfunctional mitochondria, thereby contributing to tumorigenesis. On the other hand, mitophagy may act as a tumor-promoting mechanism and thus contribute to cancer cell survival under stress conditions [49]. Autophagy induction prevents cancer progression in the early stages by activating cell death signaling. But, in the later phases of cancer, autophagy activation triggers additional signaling pathways to promote tumor involving p53, Vascular endothelial growth factor (VEGF), the microRNAs, and Epidermal growth factor receptor (EGFR), all of which promote the development of chemotherapy resistance [50].

2.4. Relation between mitochondria and reactive oxygen species (ROS) in cancer

Several compounds formed from oxygen that possess additional electrons along with the ability to undergo oxidation in other molecules are commonly referred to as reactive oxygen species [51]. The majority of intracellular ROS are generated by just one electron in the reduction of oxygen (O₂), resulting in the radical superoxide (O₂^•−). Superoxide dismutases then convert two superoxide molecules into a single molecule of hydrogen peroxide (H₂O₂) and one molecule of water. The Fenton reaction can potentially receive an additional electron from free Fe₂⁺ to form a hydroxyl radical (HO·). All of these ROS can be reactivated through various mechanisms, which can result in different consequences on cellular physiology. Most cellular ROS is produced by the mitochondria. Cellular signaling can be influenced by ROS produced by Complexes I, II, and III, as has been demonstrated [52]. Contrary to Complexes I and II, Complex III may release ROS on either side of the mitochondrial inner membrane.

ROS that derive from mitochondria (mROS) are becoming recognized as signaling molecules that influence the functioning of cells. ROS generation has been known to be a characteristic of several cancer cell types. Initial investigations revealed that ROS may trigger protein, lipid, and DNA damage, leading to tumorigenesis by encouraging genomic disorder [53]. Thus, ROS can promote cancer by triggering signaling pathways that control the proliferation of cells, metabolic changes, and angiogenesis.

2.4.1. Pathways that promote mitochondrial reactive oxygen molecules in cancer

2.4.1.1. Tumorigenic alterations elevate mROS levels

Numerous cancer cells have elevated ROS levels, as well as signaling events and mutations that promote ROS, including various oncogenes that are associated with higher ROS generation. Since exogenous expression of the c- Myc protein increased ROS production and caused alteration in certain cells while causing apoptosis in alternate cells, it has been shown that deregulated expression of the c- Myc protein alters ROS levels [54]. This suggests that the effects of ROS may differ according to the type of cell, genetic alterations, and levels of oncogenic expression. However, even if cancer cells themselves generate extra ROS, these quantities are still beyond those that are clearly harmful.

2.4.1.2. Mitochondrial abnormalities enhance mROS levels

Mutations in ETC proteins encoded by mtDNA were found in a wide range among human tumors. Given that cells possess several hundred copies of mtDNA, these alterations normally occur in just a percentage of total mtDNA, a phenomenon termed as heteroplasmy. Heteroplasmic alterations were found to be more prevalent in tumors than in healthy tissues, suggesting that they may provide a selection advantage in carcinogenesis [55]. Complex I heteroplasmic alterations have been shown to increase mROS, colony growth in soft agar, and in vivo growth of tumors.

2.4.2. Role of ROS in cancer 2.4.2.1. ROS trigger phosphoinositide 3-kinase- protein kinase B (PI3K-Akt) signaling pathway

The PI3K-Akt pathway is an internal signal transduction system that stimulates proliferation, metabolism, cell survival, and angiogenesis in association with external signals. In brief, the binding of growth factors to the receptor tyrosine kinase activates the receptor complex, which in turn activates PI3K. Activated PI3K converts PIP2 to PIP3, which subsequently mediates the phosphorylation of Akt through PDK1. Phosphorylated Akt is active on a wide range of substrates, but one of its most important targets is mTOR, which is involved in cell growth, proliferation, and survival. PTEN is a tumor suppressor that negatively regulates the pathway by removing the 3-phosphate from PIP3, converting it back to PIP2. Loss of PTEN leads to over-activation of Akt, which, in turn, is associated with uncontrolled cell proliferation, decreased apoptosis, and enhanced tumor angiogenesis. In many cancers, the PI3K-Akt pathway has been reported to increase cellular mobility, survival, and proliferation [56]. Akt stimulation is a key modulator in the PI3K pathway that promotes the proliferation of cells while suppressing apoptosis. In human ovarian carcinoma cells, hydrogen peroxide produced by epithelial growth factor (EGF) triggers Akt, which modulates the synthesis of proteins [57]. Furthermore, mROS were demonstrated to preferentially inhibit phosphatase and tensin homolog deleted on chromosome ten (PTEN), a negative modulator of the PI3K pathway, causing Akt activation [58]. Furthermore, ROS block phosphatases, causing PI3K signaling to be dysregulated, leading to greater Akt signaling and higher proliferation and survival.

2.4.2.1. Hypoxia-inducible factors are triggered by mitochondrial ROS

The hypoxia-response pathway represents one of the most well-known pathways that has been demonstrated as being responsive to mROS. Hypoxia, which is a major characteristic of solid tumor cells in vivo, is caused by an imbalance between the tumor cells' rapid rate of reproduction and the blood's capacity to give oxygen and other nutrients. Hypoxia-inducible factors (HIFs) are activated by tumor cells, triggering a transcriptional network that allows the cells to adjust to their reduced oxygen environment. In hypoxia, a higher release of superoxide from Complex III is crucial for the suppression of prolyl hydroxylase domain 2 proteins (PHD2) along with the stability of HIF subunits [59]. Consequently, treating cells with mitochondria-targeted antioxidants suppresses the generation of mitochondrial ROS as well as inhibition the stabilization of HIF subunits during hypoxia. Additionally, antioxidants have been shown to suppress the growth of tumor cells when tested in vitro and in vivo via inhibiting HIF1 [60].

2.4.2.2. Mitochondrial ROS and deregulated metabolism

The relationship between the amounts of ROS and cell metabolism is tightly controlled. Because metabolic processes generate ROS, particularly in the mitochondria, the flow of metabolic products must be tightly regulated to preserve ROS balance. HIF1 stimulation by mROS promotes the production of glycolysis enzymes as well as transporters, triggering an increase in glycolytic flow [61]. A further manner in which ROS may modify metabolism is through activating Nuclear factor erythroid 2 related factor 2 (Nrf2). Induction of Nrf2 enhances anabolic enzyme production and promotes tumor development through increased NADPH generation and purine synthesis. Additionally, ROS have been shown to influence metabolism through oxidizing the glycolytic pyruvate kinase M2 enzyme [62]; this oxidation resulted in enhanced the pathway of pentose phosphate flow, glutathione concentration, and cell development under hypoxia.

3. The mitochondrial alterations in ovarian cancer

Modifications in genomics, proteomics, and metabolomics are the overall state of numerous omics associated with the mitochondrial dysfunction route in ovarian cancer.

3.1. Genomic studies

Cancer originates and develops as a result of modifications in a genetic sequence. Mitochondria have multiple functions that regulate metabolic signaling, generation of energy, oxidative damage, and apoptosis, and so occupy vital roles in cancer. The mtDNA is a circular DNA containing genetic sequences that express important proteins within mitochondria [63], including oxidative phosphorylation, regulatory proteins, and a noncoding regulatory section called the displacement loop (D-loop). Most healthy individuals carry a low point mutation load (<1%) in their mtDNA; however, up to 60% of mtDNA genes in ovarian tumors have mutations that may be the outcome of mitochondrial malfunction; the cytochrome b genes, the D-loop area, and the genes of 12S and 16S rRNA are the central sites for mtDNA alterations in ovarian carcinoma [64]. The etiology of ovarian cancer may be attributed to SNP abnormalities in the nDNA and mtDNA; SNPs that occur at different nucleotide locations, such as 207G/A, 73A/G, and 523C/del, have been linked to an elevated risk of ovarian cancer. A research study of 89 individuals suffering from primary ovarian carcinoma discovered that particular SNPs within the D-loop sections may predict age-at-onset in ovarian cancer women. A large ovarian cancer research study found that 2839 SNPs in 138 nuclear encoding genes, 128 SNPs in 22 mitochondrial DNA sections, as well as 2839 SNPs in 138 nuclear encoding genes, have been associated with ovarian cancer susceptibility. Particularly, CO1 (cytochrome c oxidase 1) has been strongly associated with ovarian cancer risk [65].

According to earlier reports, the amount of mtDNA in ovarian cancer was much higher than in normal ovaries. However, it has been found that the average number of mtDNA copies in high-grade ovarian cancers is substantially lower than that of low-grade ovarian tumors [66], reflecting the enhanced mitochondrial activity associated with tumor development [67].

A quantitative study of the number of mtDNA copies in the blood of advanced ovarian carcinoma patients shows that the mtDNA copy number in the tested blood of healthy controls differs greatly than patients having epithelial ovarian carcinoma [68].

3.2. Transcriptomes studies

A transcriptome serves as a connection between the genome and the proteome. The human transcriptome contains an extensive amount of protein-coding mRNAs along with noncoding RNAs [69].

Gene expression studies found substantial associations between biomarkers of ovarian carcinoma (such as CD44) and biomarkers of glycolysis [hexokinase 2 (HK2) and lactate dehydrogenase A (LDHA)]. This suggests that mitochondrial malfunction is linked to energy metabolism reprogramming, triggering carcinogenesis and tumor growth. MicroRNAs (miRNA) are also important participants in the regulation of gene expression of proteins within tumor-connected pathways [70]. The major miRNA in ovarian carcinoma, miR-450a, restricts the spreading capacity of ovarian cancerous cells through targeting a series of mitochondrial mRNAs to decrease glutaminolysis and glycolysis [71]. As a result, miRNAs can influence mitochondrial gene expression through modulating miRNA-targeted genes.

The tumor microenvironment (TME) also has a significant role in the origin and progression of ovarian malignancies that may be a target for therapy. A previous study showed that SKVO3 decreases the expression of glycolysis genes in CD8⁺ T lymphocytes, whether the cells are grown with or without it. CD8⁺ Treg are obviously dependent on the glycolysis pathway [72].

3.3. Proteomics studies

To describe the process of tumor growth, proteomics can reflect the status of cell activity. Because of its speed and sensitivity, mitochondrial proteomics has been widely utilized for protein detection and quantification in the mitochondrial proteome. In mitochondrial samples collected from tissues of human ovarian carcinoma, about 5115 expressed proteins in mitochondrial (mtEPs) have been discovered. About 262 mtEPs are significantly associated with ovarian carcinoma patients' survival rates, which may recognize various critical signaling pathways ovarian malignancies biomarkers [73]. PDHB (pyruvate dehydrogenase subunit b), for instance, is an enzyme that catalyzes the transformation of pyruvate to acetyl CoA, which triggers OXPHOS; its levels of expression are minimal in ovarian malignancies. However, citrate synthases (CS), elevated in ovarian malignancies and enhancing cancer cell growth, migration and invasion, could be a viable target for ovarian cancer therapy [74].

Posttranslational modification (PTM) is commonly characterized as the enzymatic alteration of proteins after production, including glycosylation, phosphorylation, and others [75]. Phosphorylation is a frequent PTM that usually results in a protein's changed function. Phosphorylation of a mitochondrial protein has been confirmed to possibly modify mitochondrial function, which offers a fresh understanding of the relationship between mitochondrial protein phosphorylation and a potential role in ovarian cancers. Phosphorylated cofilin 1 (p-CFL1), for example, is highly expressed in cisplatin-resistant ovarian cancer 317 cell line p-CFL1 and taxol-resistant ovarian carcinoma cells [76]. In addition, p-CFL1 expression is substantially higher in chemoresistant patients compared to chemosensitive individuals.

3.4. Metabolomics studies

Metabolomics, the study of metabolites and biofluids inside cells, is important in the investigation of pathways that trigger carcinogenesis, the identification of new diagnostics biomarkers, and the development of potential therapeutic targets. One of the characteristics of cancer is the remodeling of energy metabolism, in which cancer cells cause alterations of their metabolism to accomplish rapid and aggressive multiplication [77]. These metabolic changes allow for the early detection of cancer. Earlier studies found that the rate of metabolism within ovarian carcinoma tissues differed greatly from normal tissues, with higher concentrations of amino acids in comparison to normal controls [78].

Mitochondrial dynamics (modification of mitochondria morphology), which largely describes the processes of fusion and fission, can lead to mitochondrial dysfunction and thus serve as a significant mechanism driving metabolic reprogramming in cancers [79]. MIEF2, mitochondrial elongation factor 2, which is found in the outer membrane of mitochondria, regulates mitochondrial fission and is overexpressed in ovarian carcinoma. Metabolomic research has discovered that overexpression of MIEF2 in ovarian cancer cells caused an increase in the metabolites of the glycolytic pathway while decreasing the metabolites concentration of the TCA cycle [80], suggesting that alerted MIEF2 mitochondrial dynamics promotes ovarian cancer growth by switching from OXPHOS to glycolysis.

4. Ovarian cancer biomarkers and treatment targets depend on the mitochondrial malfunctioning pathway

The altered molecules in defective mitochondrial pathways can be used to detect particular mitochondrial biomarkers. These key biomarkers in ovarian carcinoma have lately been discovered and are being employed to understand the fundamental causes and potential therapy targets.

4.1. Targeting ROS molecules, energy metabolites, and permeabilization of dysfunctional mitochondrial membranes

Mitochondrial-targeted therapy relies on various molecular pathways, and comprises the permeability of the transition pore complex, mitochondrial permeabilization of the outer membrane, and energy metabolism. Numerous investigations have demonstrated that mitochondria-targeting medicines have good prospects as prospective therapies in the clinical treatment of ovarian cancer [81]. As represented in Table 2, there are several drugs for treating human ovarian carcinoma through targeting mitochondrial dysfunction, such as Gentisyl alcohol [82], chrysophanol [83], methiothepin [84], piperine [85], FA-SnO2 NPs [86], quercetin [87], the methanolic leaf extract of Stevia [88], Doxorubicin [89], epoxycytochalasin H [90], FA-SnO2 NPs [86], elesclomol sodium [91], Ivermectin [92], FDA-approved antibiotics [93], and tigecycline [94].

Table 2.

Different targeted drugs for mitochondrial dysfunction that are utilized in treatment human ovarian carcinoma.

Calcium overload and autophagy	Cell apoptosis	Oxidative stress	Energy metabolism
Gentisyl alcohol [82], chrysophanol [83], methiothepin [84], ect	Piperine [85], FA-SnO2 NPs [86], quercetin [87], methanolic leaves extract of Stevia [88], ect	Doxorubicin [89], epoxycytochalasin H [90], FA-SnO2 NPs [86], elesclomol sodium [91], ect	Ivermectin [92], FDA-approved antibiotics [93], tigecycline [94], ect
Targeting mitochondrial OXPHOS and inhibit ovarian cancer cell lines.	Activation of apoptotic pathways is a predominant antitumor mechanism.	Targeting mitochondrial drugs elevates the levels of ROS, which stimulates the intricacy cytoplasmic release of cytochrome C and triggers apoptosis.	Targeting the mitochondria with alteration of mitochondrial proteins or changes in energy metabolism

4.2. Targeting of chemoresistant ovarian cancer development

Ovarian cancer is still the leading cause of death among gynecological malignancies, owing to its delayed diagnosis. The main cause of its dismal prognosis is chemotherapy resistance. As a result, research aimed at providing better knowledge of the process of chemoresistance might aid in the creation of more effective targets for chemoresistant ovarian cancer cells.

Cullin 4A/B scaffold protein (CUL4A/B) and DNA damage-binding protein 1 (DDB1) are the two components of the CRL4 (Cullin-RING ubiquitin ligases) complex. Recent evidence suggests that CRL4(CU2L4/DDBI) is important in the regulation of mitochondrial shape and function [95]. Since cisplatin-resistant ovarian cancer exhibits overexpression of CRL4, it has been identified as a potential target for ovarian cancer treatment. The anti-apoptotic protein BIRC3 serves as one of several inhibitors of apoptosis proteins that are necessary for preserving cell survival, and prior research has demonstrated that CRL4 mediates OC chemoresistance by targeting this protein [96]. A better prognosis for patients with ovarian cancer and restoration of cisplatin sensitivity were the outcomes of the lowering of CRL4 and BIRC3 levels [96]. As a result, CRL4 and BIRC3 may be possible targets for individuals with recurrent ovarian cancer after treatment.

CRL4 can modulate OC cell's chemoresistance by modulating the dynamics of mitochondria and mitophagy, and CRL4 inhibition suppresses the proliferation of chemoresistant ovarian cancer through triggering mitophagy. The amount, quality, and structure of mitochondria are governed by mitochondrial dynamics, which also regulate other cellular functions such as metabolism, proliferation, and migration. The phosphorylation state of dynamin-related protein 1 (Drp1) controls mitochondrial fission, which may form dysfunctional daughter mitochondria that are utilized by mitophagy [97]. Therefore, in mitotic cells, phosphorylation of Drp1 at Ser585 by CDK/Cyclin B initiates mitochondrial fission, but phosphorylation of Ser637 suppresses fission. It has been found that inhibiting CRL4CUL4A/DDB1 enhanced DRP1 expression with diminishing phosphorylation of DRP1Ser637, which is associated with greater mitochondrial fission. This suggests a mechanistic relationship between CRL4CUL4A/DDB1 and the Parkin/PINK1 signaling pathway in OCC mitophagy.

4.3. Targeting of Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway

Inappropriate activation of the crucial signaling system JAK/STAT has been closely associated with tumor growth and a poorer prognosis for ovarian cancer. Tumor growth via the JAK/STAT pathway is primarily caused by the expression of several kinds of cytokines and proteins associated with survival, stemness, cellular proliferation, self-renewal, and antitumor immune evasion [98]. Ruxolitinib, a JAK inhibitor, has been shown to diminish cell survival in ovarian cancer. Interleukin-6 (IL6) receptor inhibition significantly decreases the activity of the effector IL6/JAK1/STAT3 signaling, which lowers the growth of tumor cells [99].

4.4. MUC16/CA125 as an ovarian cancer-specific target

The MUC16 gene-encoded CA125 antigen has been licensed for clinical applications in OC screening and has been recommended as an indicator of prognosis in preinvasive OC. Despite its lack of specificity and sensitivity, the CA125 antigen has been associated with epithelial OC [100]. Mab-B3.13, a murine monoclonal antibody, possesses a high affinity for binding the CA125 antigen. Murine antibodies that target CA125 have therefore been used as potential therapeutics.

4.5. Targeting of angiogenesis and vascular endothelial growth factor (VEGF) signaling pathway

Angiogenesis is the process of growing new vessels in the bloodstream that allow nutrients and oxygen to reach the tissue around the tumor, enabling metastasis, cell invasion, and tumor growth. Earlier investigations revealed that VEGF and its receptor (VEGFR) have critical roles in pathological angiogenesis, notably cancer neovascularization, resulting in the emergence of numerous treatment techniques that target the VEGF system [101]. Bevacizumab acts as an anti-VEGF antibody that is being researched as the most effective VEGF-targeting therapy against ovarian carcinoma [101].

5. Ovarian cancer therapy using drug delivery systems (DDSs)

Traditional chemotherapy has major limitations in treating OC, such as medication clearance, improper distribution, and unwanted side effects. To overcome these constraints, scientists have focused on a variety of DDSs that are capable of encapsulating chemotherapy drugs and delivering them specifically to tumor cells through multiple surface modifications to either control drug release or improve loaded drug stability [102]. The advantages of utilizing a DDS over traditional chemotherapy were lesser nonspecific toxic effects, higher drug uptake within cancer cells, avoidance of drug resistance, and enhanced drug solubility [102].

5.1. Delivery systems with a single agent

To improve cancer treatment efficiency, a chemotherapeutic chemical is embedded into nanoparticles, such as cisplatin, which is utilized as the initial treatment for ovarian carcinoma but suffers from a dose limitation owing to its nephrotoxicity when free. As a result, scientists have used surface enhancement and nanoparticle technology to increase cisplatin distribution and prevent renal damage [103]. A polymer comprising glucosamine and polyisobutylene-maleic acid was combined with platinum (Pt) complexes to create cisplatin nanoparticles [103]. This carrier demonstrates toxicity towards cancer cells with an IC₅₀ value (4.25 ± 0.16 μM) similar to that of free cisplatin (3.87 ± 0.37 μM) and releases cisplatin in a pH-dependent manner. Additionally, the administration of nanoparticles led to a decrease in systemic and nephrotoxicity, as seen by a reduction in the kidney's biodistribution of platinum.

5.2. Nanoparticles for Co-delivery systems (NDCDSs)

To optimize the effects of single-drug delivery in chemotherapy, administration systems are being developed to improve efficacy. NDCDSs use a mixture of at least two chemotherapeutic medicines with differing physicochemical and physiological characteristics [104]. Paclitaxel and ceramide, for example, were co-administrated employing a poly (ethylene oxide)-modified poly (epsilon-caprolactone) nano-particle delivery system to combat resistance to drugs in ovarian carcinoma [105]. This single-dose co-administration of PTX (20 mg/kg) and CER (100 mg/kg) in nanoparticle formulations resulted in significant (p < 0.05) inhibition of tumor growth in both wild-type SKOV-3 and multidrug resistant SKOV-3(TR) models when compared to the individual drugs.

6. Conclusions

The growth, metastasis, and carcinogenesis of cancer cells depend on mitochondrial metabolism. Tumor growth and stemness may be supported by the fusion and fission dynamics of mitochondria, which carry out mitophagy to eliminate damaged mitochondria. Mitophagy is crucial for preserving tissue and cell homeostasis because it prevents the buildup of damaged mitochondria, which can cause a rise in ROS and damage to cells. Because mitochondria perform a variety of tasks in cancer cells, targeting specific molecules in the mitochondrial or mitochondria-related pathways, such as TCA enzymes and OXPHOS-related genes, may offer new and potential treatment methods. Furthermore, the regulation of intracellular mitochondrial ROS signaling to efficiently prevent ROS-induced events that promote tumor growth and shift the equilibrium in favor of ROS-induced apoptotic signaling would present a challenge for innovative treatment approaches. Therefore, this review covers the production of ROS in tumor cells, their detoxification, their biological consequences, and the main signaling cascades they use. It also offers an insight into how these ROS might be modulated in therapies.

Several mitochondrial features have been found to be strongly linked to ovarian cancer in numerous investigations. Several ovarian cancer cells may have elevated mitochondrial function, which could make the tumors more susceptible to blockage of the respiratory chain complex. An additional important factor in the development, progression, and chemoresistance of cancer is the dysregulation of mitochondrial dynamics and apoptosis. It appears that mitochondrial dynamics play a significant role in ovarian cancer and also influence chemoresistance and chemosensitivity. Therefore, understanding their molecular pathways may help pick new viable targets for chemotherapeutic agents, as well as stratify patients based on molecular traits and/or specific cancer types.