In vitro modeling of the structure-activity determinants of anthracycline cardiotoxicity.

Doxorubicin and other anthracyclines rank among the most effective anticancer drugs ever developed. Unfortunately, the clinical use of anthracyclines is limited by a dose-related life-threatening cardiotoxicity. Understanding how anthracyclines induce cardiotoxicity is essential to improve their therapeutic index or to identify analogues that retain activity while also inducing less severe cardiac damage. Here, we briefly review the prevailing hypotheses on anthracycline-induced cardiotoxicity. We also attempt to establish cause-and-effect relations between the structure of a given anthracycline and its cardiotoxicity when administered as a single agent or during the course of multiagent chemotherapies. Finally, we discuss how the hypotheses generated by preclinical models eventually translate into phase I-II clinical trials.

Phase IB and pharmacological study of the novel taxane BMS-184476 in combination with doxorubicin.

The aim of this study was to define the maximum tolerated dose (MTD) and the pharmacological profile of the paclitaxel analogue BMS-184476 given once every 3 weeks, or on days 1 and 8 every 3 weeks (d1&8), in combination with a fixed dose of 50 mg/m(2) of Doxorubicin (Doxo) administered on day 1 of a 21-day cycle. Adult patients with advanced solid malignancies received escalating doses of BMS-184476 infused over 1 h after bolus Doxo. Pharmacokinetics (PK) of BMS-184476, Doxo and metabolites were investigated. The effect of BMS-184476 on doxorubicinol formation was studied in the cytosol from human myocardium. The MTD of 3-weekly BMS-184476 was 30 mg/m(2). The MTD/recommended Phase II dose was 35 mg/m(2)/week (70 mg/m(2) per cycle) in the d1&8 schedule. The dose-limiting toxicity was neutropenia for both schedules. Other toxicities were loss of appetite, asthenia, and mild, cumulative peripheral neuropathy. The objective response rate in 17 previously untreated or minimally pretreated patients with breast cancer treated at 35 mg/m(2)/week of BMS-184476 was 59% (95% Confidence Interval (CI): 33-82%). Two of the 7 patients not responding to the study regimen later responded to Doxo and paclitaxel. Plasma disposition of BMS-184476 at 30, 35 and 40 mg/m(2) was linear without evidence of a PK interaction with Doxo. In studies with cytosol from human myocardium, the formation of cardiotoxic doxorubicinol was not enhanced by BMS-184476. Dosing of BMS-184476 for 2 consecutive weeks allowed the administration of larger doses of the taxane with a promising antitumour activity in patients with untreated or minimally pretreated breast cancer. The higher than expected myelotoxicity of the 3-weekly schedule is unexplained by the investigated interactions. Lack of enhanced doxorubicinol formation in human myocardium is consistent with the cardiac safety of the regimen.

Doxorubicin irreversibly inactivates iron regulatory proteins 1 and 2 in cardiomyocytes: evidence for distinct metabolic pathways and implications for iron-mediated cardiotoxicity of antitumor therapy.

Changes in iron homeostasis have been implicated in cardiotoxicity induced by the anticancer anthracycline doxorubicin (DOX). Certain products of DOX metabolism, like the secondary alcohol doxorubicinol (DOXol) or reactive oxygen species (ROS), may contribute to cardiotoxicity by inactivating iron regulatory proteins (IRP) that modulate the fate of mRNAs for transferrin receptor and ferritin. It is important to know whether DOXol and ROS act by independent or combined mechanisms. Therefore, we monitored IRP activities in H9c2 rat embryo cardiomyocytes exposed to DOX or to analogues which were selected to achieve a higher formation of secondary alcohol metabolite (daunorubicin), a concomitant increase of alcohol metabolite and decrease of ROS (5-iminodaunorubicin), or a defective conversion to alcohol metabolite (mitoxantrone). On the basis of such multiple comparisons, we characterized that DOXol was able to remove iron from the catalytic Fe-S cluster of cytoplasmic aconitase, making this enzyme switch to the cluster-free IRP-1. ROS were not involved in this step, but they converted the IRP-1 produced by DOXol into a null protein which did not bind to mRNA, nor was it able to switch back to aconitase. DOX was also shown to inactivate IRP-2, which does not assemble or disassemble a Fe-S cluster. Comparisons between DOX and the analogues revealed that IRP-2 was inactivated only by ROS. Thus, DOX can inactivate both IRP through a sequential action of DOXol and ROS on IRP-1 or an independent action of ROS on IRP-2. This information serves guidelines for designing anthracyclines that spare iron homeostasis and induce less severe cardiotoxicity.

Impairment of myocardial contractility by anticancer anthracyclines: role of secondary alcohol metabolites and evidence of reduced toxicity by a novel disaccharide analogue.

1. The anticancer anthracycline doxorubicin (DOX) causes cardiotoxicity. Enzymatic reduction of a side chain carbonyl group converts DOX to a secondary alcohol metabolite that has been implicated in cardiotoxicity. We therefore monitored negative inotropism, assessed as inhibition of post-rest contractions, in rat right ventricle strips exposed to DOX or to analogues forming fewer amounts of their alcohol metabolites (epirubicin, EPI, and the novel disaccharide anthracycline MEN 10755). 2. Thirty microM EPI exhibited higher uptake than equimolar DOX, but formed comparable amounts of alcohol metabolite due to its resistance to carbonyl reduction. MEN 10755 exhibited also an impaired uptake, and consequently formed the lowest levels of alcohol metabolite. Accordingly, DOX and EPI inhibited post-rest contractions by approximately 40-50%, whereas MEN 10755 inhibited by approximately 6%. 3. One hundred microM EPI exhibited the same uptake as equimolar DOX, but formed approximately 50% less alcohol metabolite. One hundred microM MEN 10755 still exhibited the lowest uptake, forming approximately 60% less alcohol metabolite than EPI. Under these conditions DOX inhibited post-rest contractions by 88%. EPI and MEN 10755 were approximately 18% (P<0.05) or approximately 80% (P<0.001) less inhibitory than DOX, respectively. 4. The negative inotropism of 30-100 microM DOX, EPI, or MEN 10755 correlated with cellular levels of both alcohol metabolites (r=0.88, P<0.0001) and carbonyl anthracyclines (r=0.79, P<0.0001). Nonetheless, multiple comparisons showed that alcohol metabolites were approximately 20-40 times more effective than carbonyl anthracyclines in inhibiting contractility. The negative inotropism of MEN 10755 was therefore increased by chemical procedures, like side chain valeryl esterification, that facilitated its uptake and conversion to alcohol metabolite but not its retention in a carbonyl form. 5. These results demonstrate that secondary alcohol metabolites are important mediators of cardiotoxicity. A combination of reduced uptake and limited conversion to alcohol metabolite formation might therefore render MEN 10755 more cardiac tolerable than DOX and EPI.