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Cardiotoxicity is a concern in the development of microtubule-disassembling agents (MDAs) as vascular-disrupting agents of tumors. This study investigated cardiotoxicity in rats induced by a single-dose of combretastatin A4 disodium phosphate (CA4DP), an MDA and discussed the use of this rat model in nonclinical studies of MDAs. First, CA4DP (120 mg/kg) was administered to rats intravenously, and cardiac histopathology and blood biomarkers were examined after 0.5, 24, and 72 h. Next, CA4DP (120 mg/kg) was administered to rats intravenously, and the electrocardiography and echocardiography results were analyzed. The results showed that at 0.5 h after dosing, plasma creatine kinase (CK), CK-muscle/brain (CK-MB), and fatty acid binding protein 3 levels increased. At 24 h, lactate dehydrogenase (LDH)-1, CK, and CK-MB levels increased, and multifocal vacuolar degeneration of myocardial cells was observed in the apical inner layer. At 72 h, LDH-1 levels were increased, and multifocal myocardial necrosis was observed in the interventricular septum and inner layer of the apex of left ventricular wall. Furthermore, at 0.5 h, heart rate (HR), ejection fraction (EF), and cardiac output (CO) decreased. At 24 h, CO decreased. Finally, at 72 h, HR, EF, and CO decreased, and depression of the T-wave amplitude was observed. In conclusion, myocardial injury, bradycardia, and depressed cardiac function were induced in rats by a single-dose of CA4DP. The lesion distribution and electrocardiographic features suggested that myocardial injury was induced by ischemia. These findings are similar to MDA-induced cardiotoxicity in humans, and this rat model will prove useful in studies of the cardiotoxicity in humans.

The microtubule inhibitor colchicine is cardiotoxic and is suggested to impair impulse formation and conduction. However, little is known about the electrocardiographic (ECG) changes induced by colchicine in experimental animals and the detailed pathogenesis of its cardiotoxicity. Therefore, we analyzed cardiotoxicity in colchicine-treated rats using electrocardiographic, histopathological and blood-chemistry approaches. A telemetry device for transmitting ECG data was implanted into male Crl:CD(SD) rats, and ECG tracings were obtained. At 6 weeks of age, 1.25 mg/kg colchicine was injected intravenously once daily for 2 consecutive days, and ECG waveforms and heart rate variability were analyzed. Furthermore, 1.25 mg/kg colchicine or vehicle was injected for 1 or 2 consecutive days in other rats at 6 weeks of age. One day after the final dosing, heart and blood samples were taken for histopathological and bloodchemical examination. ECG analysis revealed a prolonged RR interval, QRS duration, PR interval and QT interval. Heart rate variability analysis showed an increase in high frequency (HF) components as an index of parasympathetic nervous activity. In blood chemical examinations, colchicine induced high levels of parameters of cardiac injury and low levels and/or variations in Ca, inorganic phosphorus, potassium and chloride. Histopathologically, colchicine-treated rats showed eosinophilic granular degeneration and cytoplasmic vacuolation of ventricular myocardial cells but no remarkable change in the atrioventricular node. Not only blood chemical and histopathological changes but also ECG changes were induced in colchicine-treated rats, which indicated a decrease in myocardium excitability and conductivity, and these changes might be related to increased parasympathetic nervous activity and low blood Ca levels.

Histopathological and electrocardiographic features of myocardial lesions induced by combretastatin A4 disodium phosphate (CA4DP) were evaluated, and the relation between myocardial lesions and vascular changes and the direct toxic effect of CA4DP on cardiomyocytes were discussed. We induced myocardial lesions by administration of CA4DP to rats and evaluated myocardial damage by histopathologic examination and electrocardiography. We evaluated blood pressure (BP) of CA4DP-treated rats and effects of CA4DP on cellular impedance-based contractility of human induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs). The results revealed multifocal myocardial necrosis with a predilection for the interventricular septum and subendocardial regions of the apex of the left ventricular wall, injury of capillaries, morphological change of the ST junction, and QT interval prolongation. The histopathological profile of myocardial lesions suggested that CA4DP induced a lack of myocardial blood flow. CA4DP increased the diastolic BP and showed direct effects on hiPS-CMs. These results suggest that CA4DP induces dysfunction of small arteries and capillaries and has direct toxicity in cardiomyocytes. Therefore, it is thought that CA4DP induced capillary and myocardial injury due to collapse of the microcirculation in the myocardium. Moreover, the direct toxic effect of CA4DP on cardiomyocytes induced myocardial lesions in a coordinated manner.

A subcutaneous tumor was found in the right abdomen of a 16-week-old male TCRβ and p53 double-knockout mouse. The tumor had indistinct borders with the surrounding tissue. The cut surface after formalin fixation was pale yellowish white, partially dark red and partly white. Histologically, the tumor was composed of three distinct regions. The first region showed pleomorphic cells arranged in sheets. The second region showed spindle cells arranged in interlacing fascicles. The final region contained a mixture of the above mentioned two types of cells. Furthermore, a small amount of collagen fibers, round cells, multinucleated giant cells, and cells with eosinophilic granules were observed between these tumor cells. Immunohistochemical examination and electron microscopy identified that the pleomorphic cells and spindle cells were histiocytes and fibroblasts, respectively, and that the round cells were undifferentiated mesenchymal cells. Based on these findings, the tumor was diagnosed as a malignant fibrous histiocytoma.

Microtubule disassembling agents (MDAs) such as colchicine (COL) and vincristine sulfate (VCR) are known to be cardiotoxic. However, few attempts have been made to histopathologically examine cardiac lesions induced by MDAs. In this study, we endeavored to induce myocardial injury in rats by administering MDAs and to clarify the morphological features of these myocardial lesions. Male rats were intravenously administered COL (1.00 or 1.25mg/kg for 2 days at single daily doses) or VCR (0.50 or 0.75 mg/kg for 2 days at single daily doses). The day after administration, hearts were excised and examined histopathologically, immunohistochemically and electron microscopically. Degeneration and necrosis of myocardial cells with vacuolation were observed in rats administered COL at 1.25mg/kg or VCR at 0.75 mg/kg. Electron microscopic examination revealed vacuoles in swollen mitochondria. Moreover, there were cells showing pyknosis and karyorrhexis in the interstitium. TUNEL and immunohistochemical staining for endothelial cells and electron microscopic examination identified the apoptotic cells in the interstitium to be vascular endothelial cells. These vascular endothelial lesions were induced by lower doses of MDAs than were myocardial lesions. Furthermore, common sites of cardiac lesions induced by MDAs had almost the same distribution as areas positive for pimonidazole, a marker of hypoxia. These findings indicate that MDAs occasionally damage mitochondria in myocardial cells, and suggest that these changes involve microcirculatory dysfunction induced by endothelial cell injury.