Sarcoplasmic reticulum calcium release is stimulated and inhibited by daunorubicin and daunorubicinol

Drug-Related Lymphedema: Mysteries, Mechanisms, and Potential Therapies

The lymphatic circulation is an important component of the circulatory system in humans, playing a critical role in the transport of lymph fluid containing proteins, white blood cells, and lipids from the interstitial space to the central venous circulation. The efficient transport of lymph fluid critically relies on the rhythmic contractions of collecting lymph vessels, which function to “pump” fluid in the distal to proximal direction through the lymphatic circulation with backflow prevented by the presence of valves. When rhythmic contractions are disrupted or valves are incompetent, the loss of lymph flow results in fluid accumulation in the interstitial space and the development of lymphedema. There is growing recognition that many pharmacological agents modify the activity of ion channels and other protein structures in lymph muscle cells to disrupt the cyclic contraction and relaxation of lymph vessels, thereby compromising lymph flow and predisposing to the development of lymphedema. The effects of different medications on lymph flow can be understood by appreciating the intricate intracellular calcium signaling that underlies the contraction and relaxation cycle of collecting lymph vessels. For example, voltage-sensitive calcium influx through long-lasting (“L-type”) calcium channels mediates the rise in cytosolic calcium concentration that triggers lymph vessel contraction. Accordingly, calcium channel antagonists that are mainstay cardiovascular medications, attenuate the cyclic influx of calcium through L-type calcium channels in lymph muscle cells, thereby disrupting rhythmic contractions and compromising lymph flow. Many other classes of medications also may contribute to the formation of lymphedema by impairing lymph flow as an off-target effect. The purpose of this review is to evaluate the evidence regarding potential mechanisms of drug-related lymphedema with an emphasis on common medications administered to treat cardiovascular diseases, metabolic disorders, and cancer. Additionally, although current pharmacological approaches used to alleviate lymphedema are largely ineffective, efforts are mounting to arrive at a deeper understanding of mechanisms that regulate lymph flow as a strategy to identify novel anti-lymphedema medications. Accordingly, this review also will provide information on studies that have explored possible anti-lymphedema therapeutics.

Doxorubicin causes lesions in the electron transport system of skeletal muscle mitochondria that are associated with a loss of contractile function

Doxorubicin is an anthracycline-based chemotherapeutic that causes myotoxicity with symptoms persisting beyond treatment. Patients experience muscle pain, weakness, fatigue, and atrophy, but the underlying mechanisms are poorly understood. Studies investigating doxorubicin-induced myotoxicity have reported disrupted mitochondrial function. Mitochondria are responsible for regulating both cellular energy status and Ca²⁺ handling, both of which impact contractile function. Moreover, loss of mitochondrial integrity may initiate muscle atrophy. Skeletal muscle mitochondrial dysregulation may therefore contribute to an overall loss of skeletal muscle quality and performance that may be mitigated by appropriately targeted mitochondrial therapies. We therefore assessed the impact of doxorubicin on muscle performance and applied a multiplexed assay platform to diagnose alterations in mitochondrial respiratory control. Mice received a clinically relevant dose of doxorubicin delivered systemically and were euthanized 72 h later. We measured extensor digitorum longus and soleus muscle forces, fatigue, and contractile kinetics in vitro, along with Ca²⁺ uptake in isolated sarcoplasmic reticulum. Isolated skeletal muscle mitochondria were used for real-time respirometry or frozen for protein content and activity assays. Doxorubicin impaired muscle performance, which was indicated by reduced force production, fatigue resistance, and sarcoplasmic reticulum-Ca²⁺ uptake, which were associated with a substrate-independent reduction in respiration and membrane potential but no changes in the NAD(P)H/NAD(P)⁺ redox state. Protein content and dehydrogenase activity results corroborated these findings, indicating that doxorubicin-induced mitochondrial impairments are located upstream of ATP synthase within the electron transport system. Collectively, doxorubicin-induced lesions likely span mitochondrial complexes I-IV, providing potential targets for alleviating doxorubicin myotoxicity.

Doxorubicin Activates Ryanodine Receptors in Rat Lymphatic Muscle Cells to Attenuate Rhythmic Contractions and Lymph Flow

Doxorubicin is a risk factor for secondary lymphedema in cancer patients exposed to surgery or radiation. The risk is presumed to relate to its cytotoxicity. However, the present study provides initial evidence that doxorubicin directly inhibits lymph flow and this action appears distinct from its cytotoxic activity. We used real-time edge detection to track diameter changes in isolated rat mesenteric lymph vessels. Doxorubicin (0.5-20 μmol/l) progressively constricted lymph vessels and inhibited rhythmic contractions, reducing flow to 24.2% ± 7.7% of baseline. The inhibition of rhythmic contractions by doxorubicin paralleled a tonic rise in cytosolic Ca²⁺ concentration in lymphatic muscle cells, which was prevented by pharmacological antagonism of ryanodine receptors. Washout of doxorubicin partially restored lymph vessel contractions, implying a pharmacological effect. Subsequently, high-speed optical imaging was used to assess the effect of doxorubicin on rat mesenteric lymph flow in vivo. Superfusion of doxorubicin (0.05-10 μmol/l) maximally reduced volumetric lymph flow to 34% ± 11.6% of baseline. Likewise, doxorubicin (10 mg/kg) administered intravenously to establish clinically achievable plasma concentrations also maximally reduced volumetric lymph flow to 40.3% ± 6.0% of initial values. Our findings reveal that doxorubicin at plasma concentrations achieved during chemotherapy opens ryanodine receptors to induce "calcium leak" from the sarcoplasmic reticulum in lymphatic muscle cells and reduces lymph flow, an event linked to lymph vessel damage and the development of lymphedema. These results infer that pharmacological block of ryanodine receptors in lymphatic smooth muscle cells may mitigate secondary lymphedema in cancer patients subjected to doxorubicin chemotherapy. SIGNIFICANCE STATEMENT: Doxorubicin directly inhibits the rhythmic contractions of collecting lymph vessels and reduces lymph flow as a possible mechanism of secondary lymphedema, which is associated with the administration of anthracycline-based chemotherapy. The inhibitory effects of doxorubicin on rhythmic contractions and flow in isolated lymph vessels were prevented by pharmacological block of ryanodine receptors, thereby identifying the ryanodine receptor family of proteins as potential therapeutic targets for the development of new antilymphedema medications.

First Insight on Small Molecules as Cardiac Calsequestrin Stabilizers

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is caused by mutations of cardiac calsequestrin (CASQ2) that impair its characteristic ability of Ca²⁺-induced polymerization-depolymerization. However, stabilizing the CASQ2 polymer by pharmacological agents to treat CPVT has not been reported so far. Here, we tested whether small molecules can stabilize CASQ2 polymers. We synthesized 24 glycinate/alaninate/acetate α-pyranone analogs and conducted the CASQ2 depolymerization assay. Most of the molecules of this class of compounds inhibited the depolymerization of the protein upon Ca²⁺ chelation by ethylene glycol tetraacetic acid. Structure-activity relationship studies revealed that the compounds with the 4-fluoro-phenyl group at the C-6 position of the pyranone ring and open-chain primary amine at C-4 are the most active of the class. This is the first report of an α-pyranone class of compounds with the ability to stabilize CASQ2 polymers and opens up the possibility to target Ca²⁺-release disorders via modulation of CASQ2 polymerization.

Anti-oxidant effect of bergamot polyphenolic fraction counteracts doxorubicin-induced cardiomyopathy: Role of autophagy and c-kitposCD45negCD31neg cardiac stem cell activation

Doxorubicin (DOXO) is one of the most widely used antineoplastic drugs. Despite its highly beneficial effects against several malignancies, the clinical use of DOXO is often associated to cardiomyopathy that leads to congestive heart failure. Here we investigated the antioxidant and cardioprotective effects of a polyphenol-rich fraction of citrus bergamot (BPF), in DOXO-induced cardiac damage in rats. Moreover, we evaluated the effect of BPF on cardiomyocyte survival and resident endogenous cardiac stem/progenitor cell (eCSC) activation. Adult male Wistar rats were i.p. injected with saline (serving as controls, CTRL, n = 10), BPF (20 mg/kg daily for 14 consecutive days, n = 10), DOXO (6 doses of 2,5 mg/Kg from day 1 to day 14, n = 10), and DOXO + BPF (n = 10). Animals were then sacrificed 7 days later (i.e., at 21 days). DOXO administration reduced cardiac function at 21 days, an adverse effect significantly attenuated in animals receiving DOXO + BPF. No changes were detected in rats receiving just saline or BPF alone. The cardioprotective effect of BPF on DOXO acute toxicity was also associated with a significant antioxidant effect coupled with protective autophagy restoration, and attenuation of cardiomyocyte apoptosis and reactive hypertrophy. Finally, treatment of rats with BPF prevented eCSCs attrition by DOXO which was followed by a limited but significant increase of newly-formed BrdU⁺ cardiomyocytes. In conclusion, BPF reduces DOXO-induced cardiotoxicity by counteracting reactive oxygen species (ROS) overproduction, thereby restoring protective autophagy and attenuating cardiomyocyte apoptosis and pathologic remodeling. This beneficial effects on the early toxicity of DOXO is associated with enhanced CSCs survival and regenerative potential. Overall these data point to a potential clinical role by diet supplementation with polyphenol-rich fraction of citrus bergamot in counteracting antracycline-induced cardiomyopathy.

Adverse effects of doxorubicin and its metabolic product on cardiac RyR2 and SERCA2A

The use of anthracycline chemotherapeutic drugs is restricted owing to potentially fatal cardiotoxic side effects. It has been hypothesized that anthracycline metabolites have a primary role in this cardiac dysfunction; however, information on the molecular interactions of these compounds in the heart is scarce. Here we provide novel evidence that doxorubicin and its metabolite, doxorubicinol, bind to the cardiac ryanodine receptor (RyR2) and to the sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA2A) and deleteriously alter their activity. Both drugs (0.01 μM-2.5 μM) activated single RyR2 channels, and this was reversed by drug washout. Both drugs caused a secondary inhibition of RyR2 activity that was not reversed by drug washout. Preincubation with the reducing agent dithiothreitol (DTT, 1 mM) prevented drug-induced inhibition of channel activity. Doxorubicin and doxorubicinol reduced the abundance of thiol groups on RyR2, further indicating that oxidation reactions may be involved in the actions of the compounds. Ca(2+) uptake into sarcoplasmic reticulum vesicles by SERCA2A was inhibited by doxorubicinol, but not doxorubicin. Unexpectedly, in the presence of DTT, doxorubicinol enhanced the rate of Ca(2+) uptake by SERCA2A. Together the evidence provided here shows that doxorubicin and doxorubicinol interact with RyR2 and SERCA2A in similar ways, but that the metabolite acts with greater efficacy than the parent compound. Both compounds modify RyR2 and SERCA2A activity by binding to the proteins and also act via thiol oxidation to disrupt SR Ca(2+) handling. These actions would have severe consequences on cardiomyocyte function and contribute to clinical symptoms of acute anthracycline cardiotoxicity.

Imaging of early modification in cardiomyopathy: the doxorubicin-induced model

Doxorubicin chemotherapy is effective and widely used to treat acute lymphoblastic leukemia. However, its effectiveness is hampered by a wide spectrum of dose-dependent cardiotoxicity including both morphological and functional changes, affecting primarily the myocardium. Non-invasive imaging techniques are used for the diagnosis and monitoring of these cardiotoxic effects. The purpose of this review is to summarize and compare the most common imaging techniques used in early detection and therapeutic monitoring of doxorubicin-induced cardiotoxicity and the suggested mechanisms of such side effects. Imaging techniques using echocardiography including conventional 2D and 3D echocardiography along with MRI sequences including Tagging, Cine, and quantitative MRI in detecting early myocardial damage are also reviewed. As there is a multitude of reported indices and imaging methods to assess particular functional alterations, we limit this review to the most relevant techniques based on their clinical application and their potential to early detection of doxorubicin-induced cardiotoxic effects.

Cardiotoxicity in childhood cancer survivors: strategies for prevention and management

Advances in cancer treatment have greatly improved survival rates of children with cancer. However, these same chemotherapeutic or radiologic treatments may result in long-term health consequences. Anthracyclines, chemotherapeutic drugs commonly used to treat children with cancer, are known to be cardiotoxic, but the mechanism by which they induce cardiac damage is still not fully understood. A higher cumulative anthracycline dose and a younger age of diagnosis are only a few of the many risk factors that identify the children at increased risk of developing cardiotoxicity. While cardiotoxicity can develop at anytime, starting from treatment initiation and well into adulthood, identifying the best cardioprotective measures to minimize the long-term damage caused by anthracyclines in children is imperative. Dexrazoxane is the only known agent to date, that is associated with less cardiac dysfunction, without reducing the oncologic efficacy of the anthracycline doxorubicin in children. Given the serious long-term health consequences of cancer treatments on survivors of childhood cancers, it is essential to investigate new approaches to improving the safety of cancer treatments.

Anthracycline-associated cardiotoxicity in survivors of childhood cancer

Anthracycline chemotherapeutic agents are widely used to treat childhood cancers, helping to create an increasing population of childhood cancer survivors. Cardiac complications can occur years after exposure to anthracyclines and are a leading cause of noncancerous morbidity and mortality in this population. The mechanism of its cardiotoxicity is not completely known, although oxidative stress is believed to play a significant role. This pathway and other nonoxidative mechanisms are reviewed. Several risk factors such as age, dose, female gender, and concomitant radiation therapy are known, but the relative risks of many comorbidities such as diabetes and hypertension are not well studied. No standard, evidence-based guidelines for appropriate screening methods to detect cardiotoxicity exist. Periodic imaging with echocardiography or radionuclide angiography is appropriately recommended for long-term survivors but is of limited use during therapy. Biomarkers such as cardiac troponins and brain natriuretic peptides may aid in detecting cardiotoxicity. Studies investigating the use of agents such as angiotensin-converting enzyme (ACE)-inhibitors and beta-blockers to treat anthracycline cardiotoxicity have shown promise, but more data are needed. Structural analogs such as epirubicin were developed to minimize cardiotoxicity but have not sufficiently reduced it. Liposome-encapsulated anthracyclines have shown a considerable decrease of cardiotoxicity in adults without sacrificing efficacy, but the data related to children are sparse. The only agent proven to be cardioprotective is the iron chelator, dexrazoxane. Studies have shown that dexrazoxane is safe and significantly reduces the incidence of cardiotoxicity. Dexrazoxane should be considered for pediatric oncology protocols using anthracyclines that include longitudinal assessment.

Synthesis of 3-[(N-carboalkoxy)ethylamino]-indazole-dione derivatives and their biological activities on human liver carbonyl reductase

A series of indazole-dione derivatives were synthesized by the 1,3-dipolar cycloaddition reaction of appropriate substituted benzoquinones or naphthoquinones and N-carboalkoxyamino diazopropane derivatives. These compounds were evaluated for their effects on human carbonyl reductase. Several of the analogs were found to serve as substrates for carbonyl reductase with a wide range of catalytic efficiencies, while four analogs display inhibitory activities with IC(50) values ranging from 3-5 microM. Two of the inhibitors were studied in greater detail and were found to be noncompetitive inhibitors against both NADPH and menadione with K(I) values ranging between 2 and 11 microM. Computational studies suggest that conformation of the compounds may determine whether the indazole-diones bind productively to yield product or nonproductively to inhibit the enzyme.

Real-time detection of the early event of cytotoxicity of herbal ingredients on single leukemia cells studied in a microfluidic biochip

A microfluidic approach has been developed for the real-time detection of drug effects, based on the quantitative measurement of calibrated cytosolic calcium ([Ca(2+)](i)) on single cancer cells. This microfluidic method is rapid by detecting the early event of cytotoxicity of drug candidates on cancer cells, without waiting for a couple of days needed for cell seeding and drug treatment by conventional assays. The miniaturized biochip consists of a V-shaped structure for the single-cell selection and retention. Various test reagents such as the chemotherapy drug (daunorubicin), an ionophore (ionomycin), and herbal ingredients from licorice (isoliquiritigenin or IQ) were investigated for their abilities to stimulate sustained cellular [Ca(2+)](i) elevations. The microfluidic results obtained in hours have been confirmed by conventional cytotoxicity assays which take days to complete. Moreover, any color or chemical interference problems found in the conventional assays of herbal compounds could be resolved. Using the microfluidic approach, IQ (50 microM) has been found to cause a sustained [Ca(2+)](i) elevation and cytotoxic effects on leukemia cells. The microfluidic single-cell analysis not only reduces reagent cost, and demands less cells, but also reveals some phenomena due to cellular heterogeneity that cannot be observed in bulk analysis.

Real-time monitoring of intracellular calcium dynamic mobilization of a single cardiomyocyte in a microfluidic chip pertaining to drug discovery

A microfluidic method for real-time quantitative measurement of cellular response pertaining to drug discovery is reported. This method is capable of multiple-step liquid delivery for measuring the drug response of a single cardiomyocyte, due to the improved cell retention by a newly designed chip. The chip, which consists of a cell-retention chamber with a weir structure, was fabricated just by a one-photomask microfabrication procedure followed by on-chip etching. This method differs from the conventional method, which uses two-mask photolithography to fabricate the microchannel (deep etch) and the weir structure (shallow etch). The dimensions of the weir structure have been predicted by a mathematical model, and confirmed by confocal microscopy. Using this microfluidic method, the dynamic [Ca2+]i mobilization in a single cardiomyocyte during its spontaneous contraction was quantified. Furthermore, we measured the cellular response of a cardiomyocyte on (i) a known cardiotonic agent (caffeine), (ii) a cardiotoxic chemotherapeutic drug (daunorubicin), and (iii) an herbal anticancer drug candidate - isoliquiritigenin (IQ) based on the fluorescent calcium measurement. It was found that IQ had produced a less pronounced effect on calcium mobilization( )of the cardiomyocytes whereas caffeine and daunorubicin had much stronger effects on the cells. These three experiments on cardiomyocytes pertaining to drug discovery were only possible after the improved cell retention provided by the new chip design (MV2) required for multiple-step real-time cellular analysis on a microchip, as compared with our old chip design (MV1).

An introduction to the metabolic determinants of anthracycline cardiotoxicity

Antitumor therapy with doxorubicin and other anthracyclines is limited by the possible development of cardiomyopathy upon chronic administration. Several lines of evidence suggest that a close link exists between cardiotoxicity and the amount of anthracycline that accumulates in the heart and then undergoes one- or two- electron reduction to toxic metabolites or by-products. Alternative metabolic pathways lead to an oxidative degradation of anthracyclines, possibly counteracting anthracycline accumulation and reductive bioactivation; unfortunately, however, the actual role of anthracycline oxidation is only partially characterized. Here, we briefly review the biochemical foundations of reductive versus oxidative anthracycline metabolism. We show that multiple links exist between one pathway of toxic biactivation and another, limiting the search and clinical development of "better anthracyclines" that retain antitumor activity but induce less cardiotoxicity than the available analogues.

Effects of angiotensin II receptor blocker (candesartan) in daunorubicin-induced cardiomyopathic rats

BACKGROUND

Daunorubicin is an anthracycline anti-tumor agent; anthracycline chemotherapy in cancer can cause severe cardiomyopathy leading to a frequently fatal congestive heart failure; the first-line treatment is diuretics and digoxin. Recently, angiotensin-converting enzyme inhibitors have been shown to be effective in the treatment of such toxicity. The purpose of this study was to investigate the effects of angiotensin II type-1 receptor antagonist (candesartan) in a rat model of daunorubicin-induced cardiomyopathy.

METHODS

Rats were treated with a cumulative dose of 9 mg/kg body weight daunorubicin (i.v.). 28 days later, after the development of cardiomyopathy, animals were randomly assigned to candesartan-treated (5 mg/kg/day, p.o.) or vehicle-treated groups; age-matched normal rats were used as the control group. Candesartan treatment was continued for 28 days. Hemodynamic and echocardiographic parameters were measured, cardiac protein and mRNA were analyzed, and histopathological analyses of myocardial fibrosis, cell size and apoptosis were conducted.

RESULTS

Following cardiomyopathy, left ventricular end diastolic pressure and left ventricular systolic dimension were significantly elevated; while % fractional shortening and Doppler E/A ratio were significantly reduced. Cardiomyopathic hearts showed significant increases in % fibrosis, % apoptosis, and myocyte diameter/body weight ratio; candesartan treatment reversed these changes. Fas-L protein overexpression in myopathic hearts was significantly suppressed by treatment with candesartan. Moreover, SERCA2 mRNA and protein expression were both down-regulated in myopathic hearts and restored to normal by candesartan treatment, significantly.

CONCLUSIONS

Our findings suggest that candesartan treatment significantly improved the left ventricular function and reversed the myocardial pathological changes investigated in this model of daunorubicin-induced cardiomyopathy; suggesting its potentials in limiting daunorubicin cardiotoxicity.

Effects of drugs with muscle-related side effects and affinity for calsequestrin on the calcium regulatory function of sarcoplasmic reticulum microsomes

The tight regulation of Ca2+ release to and clearance from the cytosol is essential for normal excitation-contraction coupling in both skeletal and cardiac muscles. Calsequestrin (CSQ) is one of the major components in the sarcoplasmic reticulum (SR) of both skeletal and cardiac muscle. Previously, we showed that several pharmaceutical drugs, such as phenothiazine derivatives, tricyclic antidepressants, anthracycline derivatives, and other hydrophobic compounds bind CSQ with K(d) values in the micromolar range and significantly reduce the Ca2+ binding capacity of cardiac CSQ (Mol Pharmacol 67:97-104, 2005). Because of its key role in Ca2+ regulation, this interference with CSQ function could well produce adverse physiological consequences and potentially be linked to the known muscle-related side effects of these drugs. To further understand the molecular mechanism of undesirable drug effects or adverse drug reactions among those compounds, we examined their effect on the SR microsome. The results clearly showed that these compounds affect Ca2+ release and reduce the total Ca2+ content of the purified SR microsomes, matching well with our previous results with purified recombinant CSQ. Liquid chromatography-mass spectrometry/mass spectrometry showed that the antipsychotic drug trifluoperazine penetrates well into the SR microsome as expected from the reported and calculated log S (aqueous solubility) and log P (partition coefficient) values among the phenothiazine derivatives. We therefore propose that a certain portion of the muscle-related (both cardiac and skeletal) complications of these drugs is caused by the altered Ca2+ regulation of the SR mediated by their adverse interaction with CSQ.

Investigations of Calsequestrin as a Target for Anthracyclines: Comparison of Functional Effects of Daunorubicin, Daunorubicinol, and Trifluoperazine

Anthracycline therapy is associated with a life-threatening but poorly understood cardiotoxicity. Effects of treatment are consistent with drug-induced disruption of cardiac sarcoplasmic reticulum (SR) calcium homeostasis, including inhibition of calcium release by anthracyclines. This effect, which depends on luminal SR calcium concentration, is hypothesized to involve interactions of anthracyclines with the calcium binding protein calsequestrin (CSQ). This study was designed to test the hypothesis that an interaction between CSQ and anthracyclines could be related to alterations in SR calcium release and cardiac function. The effects of the anthracycline, daunorubicin, and its metabolite daunorubicinol were compared with those of a known CSQ inhibitor, trifluoperazine (TFP). Protein fluorescence quenching studies demonstrated that TFP, daunorubicin, and daunorubicinol bind to CSQ with apparent binding affinities in the low micromolar range. The presence of calcium decreases the drug-dependent fluorescence quenching, probably because of calcium-induced CSQ conformational changes. TFP also inhibited SR calcium release. Although the TFP IC50 value is somewhat larger than for anthracyclines, the TFP effect is also dependent on luminal SR calcium concentration. In a muscle preparation, micromolar TFP decreased cardiac contractility in a manner that implicates the involvement of SR calcium and resembles the effects of anthracyclines. These data are consistent with a mechanism in which TFP or anthracyclines impair SR calcium release and cardiac function through a mechanism involving disruption of CSQ function. Such a mechanism may contribute to anthracycline cardiotoxicity.

Interaction between cardiac calsequestrin and drugs with known cardiotoxicity

Ca(2+) regulation is coupled to critical signals in eucaryotic cells, and calsequestrin is one of the crucial components for this calcium regulation. Our previous observations of calsequestrins revealed the existence of three thioredoxin-like folds, a basic motif that often provides the platform for small molecule binding. Therefore, we have examined the previously reported trifluoperazine and other pharmaceuticals that have similar heart-related side effects (such as tachycardia; bradycardia; palpitation; changing PR, QRS, QTc intervals in electrocardiogram; heart failure) for their binding affinity to cardiac calsequestrin (cCSQ) using isothermal titration calorimetry. Our results showed that several antipsychotic phenothiazine derivatives, tricyclic antidepressants, and anthracycline derivatives bind cCSQ with K(d) in the micromolar range. For these compounds that have a significantly low K(d), their effect on Ca(2+) binding capacity of cCSQ was checked using equilibrium dialysis and atomic absorption spectroscopy, which clearly showed a significant reduction in Ca(2+) binding capacity of cCSQ as a result of this interaction. Furthermore, 8-anilino-1-naphthalene sulfonate (ANS) binding to cCSQ closely resembles ANS binding to flavine or nucleotide binding sites. The combination of this information with the high abundance of CSQ in SR and the high membrane permeability of those drugs led us to the specific hypothesis that there are undesirable and damaging interactions between cCSQ and tricyclic antidepressants, phenothiazine derivatives, anthracyclines, and many other pharmaceutical compounds and to the corollary hypothesis that better understanding of the molecular details of cCSQ-drug interactions could lead to modified drug molecules with reduced heart-related side effects.

Anthracyclines: Molecular Advances and Pharmacologic Developments in Antitumor Activity and Cardiotoxicity

The clinical use of anthracyclines like doxorubicin and daunorubicin can be viewed as a sort of double-edged sword. On the one hand, anthracyclines play an undisputed key role in the treatment of many neoplastic diseases; on the other hand, chronic administration of anthracyclines induces cardiomyopathy and congestive heart failure usually refractory to common medications. Second-generation analogs like epirubicin or idarubicin exhibit improvements in their therapeutic index, but the risk of inducing cardiomyopathy is not abated. It is because of their janus behavior (activity in tumors vis-à-vis toxicity in cardiomyocytes) that anthracyclines continue to attract the interest of preclinical and clinical investigations despite their longer-than-40-year record of longevity. Here we review recent progresses that may serve as a framework for reappraising the activity and toxicity of anthracyclines on basic and clinical pharmacology grounds. We review 1) new aspects of anthracycline-induced DNA damage in cancer cells; 2) the role of iron and free radicals as causative factors of apoptosis or other forms of cardiac damage; 3) molecular mechanisms of cardiotoxic synergism between anthracyclines and other anticancer agents; 4) the pharmacologic rationale and clinical recommendations for using cardioprotectants while not interfering with tumor response; 5) the development of tumor-targeted anthracycline formulations; and 6) the designing of third-generation analogs and their assessment in preclinical or clinical settings. An overview of these issues confirms that anthracyclines remain "evergreen" drugs with broad clinical indications but have still an improvable therapeutic index.

Anthracycline cardiotoxicity in transgenic mice overexpressing SR Ca2+-ATPase

Chronic anthracycline administration results in a time- and dose-dependent cardiomyopathy. The Ca-ATPase of the sarcoplasmic reticulum, SERCA2, has been implicated as a principal target for anthracycline-induced cardiotoxicity. This hypothesis predicts that improved SERCA2 function would provide protection from cardiotoxic effects of anthracycline administration. Doxorubicin was administered (1.7 mg/kg three times weekly; cumulative dose of 20 mg/kg) to 10 transgenic mice that overexpressed SERCA2 and to 10 isogenic littermates. Survival was monitored for 60 days and histologic comparisons were made of cardiac tissue. Survival in the transgenic mice was worse (1/10 60-day survivors) compared to isogenic control mice (7/10 60-day survivors). There was a greater degree of histologic damage exhibited in hearts from transgenic mice compared to isogenic controls when all available hearts were examined. These data do not support a role of SERCA2 in ameliorating anthracycline cardiotoxicity.

Doxorubicin and C-13 deoxydoxorubicin effects on ryanodine receptor gene expression

Chronic anthracycline administration to rabbits causes impairment of cardiac contractility and decreased gene expression of the calcium-induced calcium release channel of sarcoplasmic reticulum (SR), the ryanodine receptor (RYR2). The C-13 hydroxy metabolite (doxorubicinol), formed in the heart, has been hypothesized to contribute to anthracycline cardiotoxicity. C-13 deoxydoxorubicin is an analog unable to form the C-13 hydroxy metabolite. Therefore, doxorubicin, C-13 deoxydoxorubicin, or saline was administered to rabbits (1 mg/kg iv twice weekly for 8 weeks). Left ventricular fractional shortening (LVFS) was decreased by chronic treatment with doxorubicin (28 +/- 2%; P < 0.05), but not C-13 deoxydoxorubicin (33 +/- 2%) compared to age-matched pair-fed controls. Doxorubicin, but not C-13 deoxydoxorubicin, caused a significant reduction (P < 0.02) in the ratio of RYR2/Ca-Mg ATPase (SERCA2) mRNA levels (0.57 +/- 0.1 vs 1.22 +/- 0.2, respectively) in the left ventricle. This suggests that doxorubicinol may contribute to the downregulation of cardiac RYR2 expression in chronic doxorubicin cardiotoxicity.

P-glycoprotein inhibitors enhance saturable uptake of idarubicin in rat heart: pharmacokinetic/pharmacodynamic modeling

Little is known about cardiac uptake kinetics of idarubicin, including a possible protective role of P-glycoprotein (Pgp)-mediated transport. This study therefore investigated uptake and negative inotropic action of idarubicin in the single-pass isolated perfused rat heart by using a pharmacokinetic/pharmacodynamic modeling approach. Idarubicin was administered as a 10-min constant infusion of 0.5 mg followed by a 70-min washout period in the absence and presence of the Pgp antagonists verapamil or amiodarone. Outflow concentration and left ventricular developed pressure were measured and the model parameters were estimated by simultaneous nonlinear regression. The results indicate the existence of a saturable, Michaelis-Menten type uptake process into the heart (K(m) = 3.06 microM, V(max) = 46.0 microM/min). Verapamil and amiodarone significantly enhanced the influx rate (V(max) increased 1.8-fold), suggesting that idarubicin is transported by Pgp directly out of the membrane before it gets into the cell. Verapamil and amiodarone attenuated the negative inotropic action of idarubicin, which was linked to the intracellular concentration of idarubicin.