Degree Name

PhD (Doctor of Philosophy)

Program

Biomedical Sciences

Date of Award

5-2003

Committee Chair or Co-Chairs

Balvin H.L. Chua

Committee Members

Donald B. Hoover, Race L. Kao, Richard M. Kostrzewa, William E. Stone

Abstract

The current studies were designed to explore the protective effects of pifithrin-α and melatonin against doxorubicin-induced cardiotoxicity. Doxorubicin was injected at a dose of 22.5 mg/kg (i.p.) in mice to induce cardiotoxic effects. Meanwhile, doxorubicin caused a significant increase of cardiac cell apoptosis following injection (14.2 ± 1.1% for doxorubicin-5 d vs. 1.8 ± 0.12% for control, P < 0.01). Ribonuclease protection assays and Western blot analyses revealed that doxorubicin upregulated the p53-dependent genes Bax, BclxL, and MDM2 at least 2-fold. p53 was phosphorylated at Ser 15 in mouse hearts 1 h following doxorubicin injection, and p38 and ERK1/2 MAPKs mediated the phosphorylation of p53. In addition, caspases-3 and -9 were activated 24 h after doxorubicin injection. A p53 inhibitor, pifithrin-α, inhibited doxorubicin-induced apoptosis when administered at a dose of 2.2 mg/kg. Pifithrin-α abolished p53 transactivation activity, but did not influence doxorubicin-induced phosphorylation at Ser 15. By effectively inhibiting the expression of p53-dependent genes, pifithrin-α blocked doxorubicin-induced activation of caspases-3 and -9, thereby preventing cardiac apoptosis. In addition, pifithrin-α attenuated doxorubicin-induced structural and functional damages, without diminishing its anti-tumor efficacy on p53-null PC-3 cancer cells. The protective effects of melatonin and its metabolite 6-hydroxymelatonin on doxorubicin-induced cardiac dysfunction were evaluated in an isolated perfused mouse hearts and in vivo doxorubicin-treated mice. While perfusion of mouse hearts with 5 μM doxorubicin for 60 min resulted in a 50% suppression of HRxLVDP and a 50% reduction of coronary flow, pre-exposure of hearts to 1 μM melatonin or 6-hydroxymelatonin eased the cardiac dysfunction. In addition, administration of melatonin or 6-hydroxymelatonin (2 mg/kg/d) significantly attenuated doxorubicin-induced cardiac dysfunction, myocardial lesions, and cardiac cell apoptosis. Melatonin and 6-hydroxymelatonin significantly improved the survival rate of doxorubicin-treated mice. Another melatonin analog, 8-methoxy-2-propionamidotetralin, did not show any convincing protection on either animal survival or on in vitro cardiac function, presumably due to its lack of free radical-scavenging activity. Finally, neither melatonin nor 6-hydroxymelatonin compromised the anti-tumor activity of doxorubicin in cultured PC-3 cells. These studies suggest that pifithrin-α and melatonin have significant therapeutic potential for patients suffering doxorubicin-induced cardiotoxicity.

Document Type

Dissertation - Open Access

Copyright

Copyright by the authors.

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