Cardiotoxicity is understood as a clinical entity related to diminished heart function, which Beutner first described in 1946 in relation with the use of injectable anesthetics [
3]. Many pharmaceutical substances were recognized as cardiotoxic in the following decades [
4]. These drugs belong to different pharmacological groups and have been enumerated in a publication by the American Heart Association (Tables 1 and 2 in [
5]). Drugs that are effective in anti-cancer treatments can affect heart function in different ways [
6,
7,
8], leading to cardiac damage and heart failure [
9]. Cardiotoxic anti-cancer drugs include anthracyclines, alkylating agents, topoisomerase inhibitors, taxanes, and others [
10].
In 2022 Cardinale and coworkers described cardiotoxicity as a series of changes in the heart including cell injury, deformation, and left ventricular dysfunction (Figure 1 in [
11]). In a joint publication with Tsiouris et al., they stressed the relevance of left ventricular function evaluation [
12]. López-Sendón and coworkers described an incidence of cardiotoxicity of 37.5% among 865 patients included in a prospective study[
13]. Cardiotoxicity has been recently evaluated in the form of a Delphi study by Gavila et al. [
14]. The authors pointed out the need to identify affected patients using cardiological diagnostic criteria such as the periodic evaluation of the left ventricular ejection fraction. The authors praised their work as the first one to produce statements related to prevention, assessment, and monitoring of cardiac toxicity after chemotherapy. The publication, unfortunately, did not suggest a therapeutic procedure to achieve these goals. Belger and coworkers analyzed risk factors in relation to cardiotoxicity and concluded inconclusively that “a better understanding” would be desirable [
15]. The same applies to surveillance programs based on epidemiological data [
16,
17]. Epidemiology alone, cannot deliver treatment options.
In this review we will deal with cardiac side effects of anthracyclines and those due to external radiation therapy. We will focus on research and development work of daunomycin (adriamycin, doxorubicin) since this group of substances is relevant for treating breast cancer and other solid tumors.
1.1. Pharmaceutical Development of Natural Anti-Tumor Substances
A historical account of the early research of new anti-tumor substances in Italy was published by Cassinelli in 2016 [
20]. He described how in May 1960, a fruitful connection had been established by Dr. Bertini, CEO of Farmitalia, and Prof. Bucalossi, director of the Istituto Nazionale dei Tumori, to start research on new natural anti-tumor substances. Adriamycin was isolated as an antibiotic substance in the Farmitalia Research Laboratories working with a mutant strain Streptomyces peucetius bacterium (Streptomyces peucetius caesius). Dott. Aurelio Di Marco reported the discovery of daunomycin in 1964 [
21]. In the same year, Dubost et al., reported the discovery of rubidomycin, a substance related to daunomycin [
22]. A description of the therapeutical use of daunomycin followed in 1967 [
23]. In 1969 Arcamone et al. reported the production of the new anti-tumor substance 14-hydroxydaunomycicn (Adriamycin) [
24]. Phase I and preliminary Phase II studies with adriamycin were published in 1970 [
25]. The patent, describing the anti-tumoral activity of the compound, was granted in 1971 to Farmitalia Carlo Erba Spa [
26]. At that time, no cardiac side effects were mentioned.
In 1969 Bonadonna et al., described indeed ECG changes after treatment with adriamycin, i.e., doxorubicin [
27]. Previously, in 1967, Tan et al. had also reported cardiotoxicity after the administration of daunomycin [
28].
In 1981, Di Marco published a historical review on the discovery of daunorubicin [
29]. Readers interested in further historical aspects of these developments can also consult the publication by Waksman and Woodruf on the discovery of Actinomyces antibioticus [
30]. An important notion to be kept in mind is that actinomycin has a quinone structure as described by Dalgliesh and Todd in 1949 [
31]. Additional studies from the early past century had evaluated quinones concerning their structure and biochemistry and their role as disinfectants and antibiotics [
32,
33,
34,
35,
36].
In the 1970s, scientific data relating adriamycin to mitochondrial function appeared. In 1974 Iwamoto, Hansen, Porter, and Folkers, working with beef heart mitochondria, described that adriamycin had an inhibitory action on cell respiration by affecting CoQ
10 enzymes related to the electron transfer processes [
37]. The rationale for their study was based on the quinoid and hydroquinoid structures of adriamycin and daunorubicin. In their conclusions, they described this potential inhibition of CoQ
10 by adriamycin. In 1976 Kishi et al. demonstrated a beneficial effect of CoQ
10 supplementation for preventing adriamycin-induced inhibition of myocardial mitochondria affecting the NADH-oxidase and the succinoxidase systems. A molar ratio of 3:1 of CoQ
10 to adriamycin prevented this inhibition [
38]. An additional mechanism of cardiotoxicity by doxorubicin is the alteration of fatty acid oxidation and interference of carnitine palmitoyltransferase [
39,
40].
In 1986 Davies and Doroshow identified Complex I of mitochondrial OXPHOS as an essential metabolic site for doxorubicin [
41]. An accompanying study showed that cardiac damage through doxorubicin was due to the production of a hydroxyl radical [
42]. Following this line of research, Schimmel et al., illustrated oxidative stress mechanisms arising from anthracyclines based on their quinone structure (Figure 1 in [
43]). A recent 2020 study on cardiotoxicity and doxorubicin involving respiratory Complex I and mitochondria was published by Wallace, Sardão, and Oliveira [
44].
In an experimental setting with male Sprague-Dawley rats weighing 180-200g, Folkers et al. showed in 1978 that the administration of CoQ
10 at a dose of 1mg/ml/kg resulted in "rescue" of electrocardiographic abnormalities caused by adriamycin cardiotoxicity [
45]. These experiments showed clearly a relation of the drug to CoQ
10 and placed CoQ
10 in the category of a therapeutical option. Saltiel and McGuire presented a similar line of thought in 1983, mentioning the use of CoQ
10, selenium sulfide, or α-tocopherol, among others, to prevent cardiotoxicity [
46].
In 1981 Ohhara, Kanaide, and Nakamura presented data on the protection against cardiotoxicity due to adriamycin achieved by administering CoQ
10. This effect was associated with a higher cardiac contractile tension and higher ATP stores [
47].
The beneficial effects of CoQ
10 or α-tocopherol had been previously shown by Lubawy, Whaley, and Hurley in an experimental setting in 1979 [
48].
In 1982 Takimoto et al., described a protective effect of CoQ
10 on the heart after the combined use of 500 rad irradiation with
60Co plus a mixture of adriamycin, cyclophosphamide and 5-FU can lead to cardiac toxicity [
49]. In 1984 Tsubaki et al. described a preventive effect of CoQ
10 administration on alterations of the ECG in patients treated either with adriamycin or daunorubicin [
50].
An elegant experiment by Sarvazyan in 1996 delivered imaging data that demonstrated oxidation-sensitive fluorescence in isolated cardiac myofibers after administration of 160µM of doxorubicin. They showed that an oxidative mechanism was seen already 20 minutes after exposure [
51]. Newer data from Doroshow complement these observations by demonstrating that quinones and anthracycline antibiotics can stimulate oxygen radical production in cardiac cells [
52]. In 2005 Conklin reported an alteration of mitochondrial function as the side effect of anthracyclines and proposed using CoQ
10 to prevent these changes [
53]. Recently, Botehlho et al., showed protective effects of CoQ
10 in an experimental model of doxorubicin-induced cardiotoxicity in 2020 [
54].
While these valuable studies show beneficial cardiac effects of CoQ
10 administration, they do not supply a full explanation of the underlying biochemical situation (Figure 3 in [
55]). This can also be seen in a proposed protocol for early detection of subclinical left ventricular dysfunction by Caspi and Aronson (Figure 1 in [
56]).
After tumors have been treated successfully, childhood cancer survivors face the risk of developing chronic heart diseases in adult age. Oeffinger et al., have called this a chronic health condition where the most common diseases are second cancers, cardiovascular disease, renal disease, musculoskeletal problems, and endocrine diseases [
57]. Robison and Hudson described a complex health situation for childhood cancer survivors arising from the use of radiation, chemotherapy, or surgery (Figure 2 in [
55]). The appearance of disease seems to have a variable latency time. Tumor types at the primary diagnosis can be leukemia, lymphoma, central nervous system tumors, Wilms tumor, neuroblastoma, rhabdomyosarcoma, and bone cancer [
58]. Another medical situation associated with cardiotoxicity in adult life is hematopoietic stem cell transplantation [
59].
A clinical description of Hodgkin’s lymphoma, published by Brice, de Kerviler, and Friedberg, pointed out that many patients died because of late toxic effects of the treatment [
60]. Maraldo et al. approached the topic of cardiovascular disease after therapy for Hodgkin’s lymphoma in 2015 using a questionnaire approach. The authors found 19% of cases reporting ischemic heart disease, 12% with congestive heart failure, as well as arrhythmia and valvular disease [
61]. Bergom et al., analyzed radiation-induced cardiac changes in 2021. They proposed that the goal of screening should be the detection of cardiac injury before it becomes clinically evident, expecting that dosimetry and advanced imaging would answer this problem [
62].
1.2. Investigating Cardiotoxicity in Pediatric Oncology
Cardiotoxicity related to the administration of adriamycin is known as a syndrome that affects cardiac function leading to functional changes of the left ventricle. In 1973 Lefrak, Pitha, Rosenheim, and Gottlieb published an analysis of clinical and pathological characteristics found in patients who presented cardiotoxicity due to adriamycin [
63]. Their study included 399 patients who presented advanced carcinomas. They observed cardiotoxic effects such as transient changes in the ECG in 45 cases and severe congestive heart failure in 11. Eight patients with heart failure died because of cardiac decompensation. Cardiac involvement was suggested by diminution of QRS voltage, ventricular failure and cardiac dilatation, and lack of response to inotropic drugs. Postmortem studies showed a decrease in cardiomyocytes, loss of contractile elements, mitochondrial swelling, and intramitochondrial dense inclusion bodies. Electron microscopy studies showed alterations in mitochondria, including swelling and absence or degeneration of cristae (Fig. 12 in [
63]). Since a therapeutic approach to this problem was not available at that time, they simply suggested to limit the total dose to less than 550mg/m2.
An early diagnostic approach to adriamycin cardiotoxicity and irradiation was the endomyocardial biopsy, as reported by Billingham in 1977 [
64]. In 1979 Ulmer, Ludwig, and Geiger presented the assessment of systolic time intervals to detect cardiotoxicity [
65]. Potential benefits and limitations in the use of M-mode echocardiography for the diagnosis of doxorubicin cardiotoxicity were presented by Markiewicz et al. in 1980 [
66]. Ritchie et al. advocated radionuclide angiography as a basis and follow-up examination when anthracyclines were administered [
67]. Lahtinen et al., introduced radionuclide ventriculography in 1982 and found the method better than echocardiography and systolic time intervals [
68]. In 1981, Lewis et al. described the application of echocardiography [
69]. In 2000, Agarwala et al., described multiple gated acquisition scans (MUGA) [
70]. A recent publication by Leerink et al. described changes of ejection fraction values in cases of cardiotoxicity. Surveillance intensity was adapted to the EF values [
71].
In 1995, Shulkin et al., described the use of Nuclear Medicine diagnostic imaging using
18F-fluorodeoxyglucose positron emission tomography (
18F-FDG) [
72]. In 2007 an updated version of this topic appeared [
73]. Two Figures in this publication showed cardiac uptake:
Figure 2 shows the initial staging for a patient with an embryonal sarcoma; Figure 7 showed a similar pattern in follow-up examinations in a young patient with recurrent neuroblastoma. The authors did not explain the meaning of these cardiac images.