**4.4. Cytotoxic effect of doxorubicin on noncancerous tissues**

situation has been reported whereby heart tissue does not contain TOPIIα, but expresses TOPIIβ [20]. So, the TOPIIβ/DOX/DNA complex could only occur in the heart tissue [20, 28]. It is strongly supported that DOX's cardiotoxicity associates with TOPIIβ based on a TOPIIβ knockout mice study. When DNA damage occurs for some reason, e.g., by using DOX, the ataxia/telangiectasia-mutated protein is activated to trigger tumor suppressor protein p53. Activation of p53 by DOX has been indicated to elevate ROS production, double-strand DNA damage, and apoptotic cell death as well. Furthermore, another effect of p53 addresses one of the cardioprotective transcription factors, known as GATA-4. AMP-activated protein kinase (AMPK) plays the role of energy sensor to maintain enough available energy levels. If energy status drops too low by enhancing ROS production, and intracellular Ca2+ accumulates,

DOX utilization is limited due to its toxic effect [27]. There are well-established factors that pointed to an increase in DOX-related heart damage. These factors are total cumulative dose, one course or a day's full dose, radiation, especially mediastinal, age, gender, other cardio-

One of the riskiest factors for toxicity is the drug's cumulative dose [4]. Extensive reports are available in the literature. The mortality of congestive heart failure-induced DOX is

cancer type determines the risk ratio. For example, around 20% of lung cancer patients treated with DOX have been reported to develop heart failure [32]. DOX, an anthracycline antibiotic, therapy has been indicated to develop side effects in almost 35% of patients [33]. Its clinical utilization is, therefore, limited because many tissues become toxic when patients are treated

The detrimental effect of DOX is related to its dosage and treatment duration. Its utilization is recognized to develop into cachexia and cardiotoxic impact over time [4]. DOX can even cause cardiomyopathy after years of treatment [4]. Cardiomyopathy has been claimed to occur following final DOX treatment of 0–231 days (median 23 days) and final daunorubicin treatment of 9–192 days (median 60 days). Cardiotoxicity due to DOX therapy has been seen even after 20 years [10]. In other words, its toxic effect is mostly dose and time dependent [13]. DOX-

DOX is used not only for childhood cancer patient treatment, but also for adults cancer patients [35]. So, age is an important factor in the development of cardiotoxicity of DOX [9]. For example, it is reported that patients over 65 years and under 4 years treated with DOX are more susceptible to cardiomyopathy. Children, adolescents, and the elderly treated with

cumulative dose [17]. This side effect is related to

[10]. The risk of developing toxicity on noncancerous tissue

with 18–48% [4, 10, 20], or 950 mg/m2

cumulative dose [15]. DOXs toxicity can reach a 50% mortality rate at

DOX, the risk of heart damage is almost 100% [20]. Also,

, and the median dose of its

with 3–5% [4, 10, 20],

with 50%

[10]. When

AMPK can be activated and/or its phosphorylation can be elevated [20].

toxic drugs or chemicals, cardiovascular illness, and liver pathologies [17].

its dose, which is reported to be between 75 and 1095 mg/m2

with 7–26% [4, 10], 700 mg/m2

has been reported to enhance the cumulative dose, e.g., at 400 mg/m2

induced cardiotoxicity causes death in 50% of patients within 2 years [34].

[10]. Furthermore, the risk of toxicity has been reported to enhance at 550 mg/m2

**4.3. The risk factors of doxorubicin's toxicity**

around 50% at higher than a 500 mg/m2

toxicity is around 390 mg/m2

mice are given a total of 71 mg/m2

the highest cumulative dose [14].

with a 550–600 mg/m2

550 mg/m2

328 Mitochondrial Diseases

DOX is widely used for cancer therapy [38]. However, it has been recognized to have a toxic effect on noncancerous tissue such as the heart [13, 39], liver, kidneys [22], as well as the brain [40], and its poisonous effect is related to its dose [38]. This is why the drug's use for cancer treatment is limited based on its undesired impact on healthy tissue. Unfortunately, the mechanism of its toxic effect on noncancerous tissue has been not understood so far [38, 39].

DOX side effect symptoms are nausea, vomiting, alopecia, myelosuppression, stomatitis, and gastrointestinal disturbances [14], which are typical of cytotoxic chemotherapic agents [28]. The soft side effects of drugs include nausea, fever, and vomiting. Nausea, fever, and vomiting appear after DOX therapy as soft side effects. However, hypotension, arrhythmias, tachycardia, and congestive heart failure are also described after treatment as severe undesired side effects [17].

DOX's cytotoxicity includes two molecular mechanisms: intercalation of nuclear DNA and elevation of ROS production [41]. A cancer cell's DNA replication is well known to be faster than normal cells [41]. If DOX generates normal levels of ROS, it might selectively destroy heart pump function [41]. The most accepted mechanism leading to DOX's toxicity is oxidative stress, which causes damage to membrane lipid peroxidation products and decreases antioxidants as well. The most severe ROS generation by DOX is in the heart vs. other organs or tissues, e.g., kidneys, liver, etc. [10]. Extensive research has been suggested as to why DOX's cardiotoxicity relies on oxidative stress, mitochondrial dysfunction, and mitochondrial energy-forming disruption [16]. DOX treatment after 3 h has been reported to cause oxidative stress, lipid peroxidation, as well as lipid aldehydes in cardiac tissue [42]. Selective toxicity of the heart by DOX will explain these reasons. There is strong evidence supporting a critical role of oxidative stress on DOX's toxicological effect, though the molecular mechanism of its toxicity is still a mystery. According to study results from animal and human tissue, DOX disrupts the myofibril, mitochondrial membrane [13].

DOX's anticancer activity is associated with intercalation to DNA by decreasing TOPII activity after double-strand breakage, resulting in alleviation of DNA replication and protein synthesis. However, it is accepted that DOX's toxicity and anticancer efficiency are different from each other. The cytotoxic effect of DOX is produced by a mechanism such as ceramide synthesis by CREB3L1 activation, oxidative damage to DNA, losing mitochondrial membrane potential (MMP), caspase-3 activation, and p53 and c-Jun NH2-terminal kinase (JNK) activations. Nuclear factor-kappa B (NF-κB), a proapoptotic factor, could participate in DOX's cytotoxicity [33].

The clinical utilization of DOX is limited because of its toxic impact, especially on heart tissues, e.g., heart failure, cardiomyopathy [20]. The mortality rate of congestive heart failure induced by DOX is estimated at around 20%. There is no explanation for how DOX causes its toxicity on noncancerous tissue. However, it is thought to be multiple and complex mechanisms, nitrosative and nitrative stress, DNA damage, dysregulation of metabolites, and inflammation [16] involving DOX's toxicity, eventually triggering apoptotic cell loss [43]. The dysfunction of energy production has played a critical role in the development of both acute and chronic DOX toxicity and is related to time-dependent mitochondrial dysfunction [43]. Also, there is limited knowledge of its toxic mechanism, including disruption of calcium homeostasis by activation of calcium-dependent kinases, phospholipases, proteases [15], myofibrillar disruption, apoptotic cell death, as well as mitochondrial dysfunction. The mitochondrial toxic effect of DOX relates to the generation of ROS, destroying energy production [44]. The impact on its mitochondrial toxicity is caused by blocking the ETC associated with cardiolipin, which is an inner mitochondrial membrane protein [44]. DOX's toxicity is mainly associated with enhancing mitochondrial ROS production and decreasing mitochondrial biogenesis [38].

**5. Cardiospecific toxicity of doxorubicin**

The most severe toxic effect of DOX is on the heart [17]. This toxic effect is related to mitochondria because DOX targets cellular mitochondria, resulting in mitochondrial damage and cell death [20]. Cardiomyocytes are differentiated and nondividing cells, so they would not be a direct target of the drug since it blocks DNA replication and synthesis [28]. Therefore, cardiomyocytes have an insufficient regenerative ability after significant injury [46, 47]. In case of severe damage, the majority of heart muscle functions can be terminally lost. DOX could selectively oxidize mtDNA associated with heart failure [28]. For some reasons the most

Mitochondrial Dysfunction Associated with Doxorubicin http://dx.doi.org/10.5772/intechopen.80284 331

**2.** There is a high affinity for cardiolipin in the mitochondrial inner membrane of the heart.

**4.** There is lower antioxidant capacity in the cardiac tissue. The opening of the mitochondrial permeability transition (MPT) pore initiates apoptosis by releasing a proapoptotic factor, such as cytochrome, SMAC/DIABLO, and the apoptosis-inducing factor (AIF). MPT can form with the voltage-dependent anion channel (VDAC) and the adenine nucleotide translocase (ANT) matrix chaperon cyclophilin D (Cyp D). The open probabilities of MPT can be enhanced by DOX, so mitochondriopathy has been related to DOX's cardiotoxicity [23].

Cardiomyocytes contain high mitochondrial density, and one cardiomyocyte occupies 40–45% of mitochondria [21, 34]. The organelle has a function to maintain standard cardiac capacity due to a high-demanding, high-energy substrate for contractile function [21]. DOX accumulates in mitochondria 100 times more than plasma [34]. After binding DOX, cardio-

DOX tends to accumulate in the nucleus and mitochondria. In heart tissue, mitochondria make up around 50% of its volume [48]. DOX has a high affinity to bind the inner mitochondrial membrane and is collected on the matrix side [3]. One of DOX's similarities in the inner mitochondrial membrane is cardiolipin, which has a much higher affinity vs. other lipids in mitochondria (around 80 times). Phosphatidylethanolamine and cardiolipin are adaptors in the hexagonal (HII) phase in existent divalent cations, e.g., DOX, leading to changes in fluidity and functionality of mitochondrial membranes. DOX inactivates mitochondrial lipiddependent enzymes, such as NADH dehydrogenase, cytochrome-*c* oxidase, and cytochrome*c* reductase. DOX binds to cardiolipin, causing inactivation of complex I–III. DOX and NADH/ NADH dehydrogenase incubations have been suggested to reduce sequestration at the SR by around 80% [48]. Also, mitochondrial TOPI is also found to relate to anthracyline-based

The heart's mitochondria have two NADH dehydrogenases. One, known as cytosolic or intermembranous, is located at the outer surface of the inner mitochondrial membrane. However, the other one, known as matrix NADH dehydrogenase, is placed at the matrix surface of the inner mitochondrial membrane. Complex I relates to cytosolic NADH dehydrogenase as a

**3.** Existing cardiospecific NADH dehydrogenase results in elevated ROS production.

severe detrimental effect of DOX is seen as heart based. These reasons are:

**1.** The heart contains a high volume of mitochondria per cardiomyocyte.

lipin loses the cofactor role in mitochondrial enzymes [34].

cardiac toxicity [11].

However, its clinical utility is limited due to irreversible myocardial damage and dysfunction. Apoptosis mediated by DOX contributes to heart failure. DOX's main intracellular target is mitochondria, causing mitochondrial damage and ROS elevation, and initiating apoptosis [21]. So, DOX gives rise to degrading contractile proteins [29]. However, limited knowledge of how mitochondrial dysfunction triggers cardiac apoptotic cell death-mediated DOX is still a mystery. Therefore, further studies are needed to increase knowledge [21].

DOX has detrimental effects, classified as acute and chronic abnormalities, including arrhythmias, heart failure, and ventricular dysfunction. The primary issue for DOX therapy is to overcome and minimize its toxic effect without altering its therapeutic impact on cells with cancer. Knowledge of its detrimental effect remains a mystery. There are, however, disorders that may explain its side effect, such as mitochondrial dysfunction and ROS production. Mitochondria have an essential function, including energy metabolism, cellular apoptosis, and cell death pathways, apoptosis, and necrosis [35]. The cardiotoxicity of DOX relies on its dosage. For example, electrocardiologic abnormalities have been reported to occur at a low dose, although dilated cardiomyocytes and congestive heart failure have been reported at a high dose [13]. After left ventricular end diastolic pressure and left ventricular ejection fraction are suppressed, DOX dilates cardiomyopathy because of the decline in heart pump function. Besides cardiomyopathy, DOX also leads to the development of cardiac remodeling, including cytoplasmic vacuolization, myofibrillar clutter, or sarcoplasmic reticulum (SR) swelling. This is why further studies are required to evaluate DOX's toxic effects on noncancerous tissue [4]. There is no defined specific therapy to cope with DOX's cardiomyopathy yet, except receiving traditional treatment of congestive heart failure, e.g., angiotensin converting enzyme blockers, etc. [24].

Based on our best knowledge of the mechanisms associated with apoptosis, oxidative stress, and mitochondrial dysfunction, to avoid undesired toxicity it has been suggested to use some form of antioxidant. Unfortunately, antioxidant therapy has failed to accomplish the drug's toxicity effect in many tissues, particularly the heart and liver according to clinical data [39]. This is why any approaches to use the drug clinically may reduce its toxic effects on noncancerous mass. Therefore, further studies are needed to evaluate the molecular mechanism of DOX's toxicity [45].
