| Summary: | Cancer is one of the leading causes of death worldwide and only modest progress has been achieved in decreasing the mortality and incidence of this disease. Combined therapy in cancer treatment is one of the main approaches used to treat this disease and enhance the therapeutic index. Doxorubicin (DOX) is one of the most important anticancer drugs used in the treatment of many tumours; however, its usefulness is compromised by severe cardiotoxicity. Melatonin (MEL), the pineal hormone has been reported to display antiproliferative activity against many tumours. In addition, MEL is a free radical scavenger. These two properties make MEL as an interestining candidate for combination with DOX. PPARy-ligands appeared as another eligible candidate for combination with DOX since they also have been reported to have antiproliferative activity against some tumours, in addition to being able to protect myocytes form oxidative stress induced by H202. This project focused on the assessment of the effects of combining DOX with MEL or PPARy-ligands to enhance the antiproliferative activity of DO X and protect from its cardiotoxicity. Cytotoxicity assessment by MTT -assay did not show the antiproliferative activity of MEL against MCF-7 cells, while the effect was significant with the PPARy-ligands, rosiglitazone (Rosi), ciglitazone (Cig) and troglitazone (Tro) on both MCF -7 cells and MCF-7IDX (a DOX resistant phenotype of MCF-7 cells). Interestingly, the combination of DO X (at the ICso) with the glitazones (at the ICso) showed a synergistic activity, combination index < 1. F ACS was used to demonstrate the effect of DO X and the glitazones (separately and in combination) on the cell cycle ofMCF-7 cells. It was found that these drugs held the MCF-7 cells in the Go/G) phase of the cell cycle, an effect which had been confirmed by the significant decrease in the expression of cyclin Dl by using western blotting. Assessment of cytotoxicity of DOX, MEL and the glitazones against primary cardiac cells (myocytes and fibroblasts) showed different responses. For the myocytes, it was found that Rosi did not affect the viability, while Cig produced a dose dependent decrease, additionally; the combination of glitazones with DOX showed enhanced toxicity only with Cig at 20 ~M. Rosi did not affect the integrity of the sarcomeres significantly, while Cig decreased the integrity of the sarcomeres significantly at 20 ~M. On the other hand, with fibroblasts, both glitazones did not affect the viability but after combination with DOX (lCso), Cig potentiated DOX toxicity at 1 0 ~M and 20 ~M. The expression of cyclin D 1 revealed a significant decrease in expression after DOX and glitazone treatments which explain the static behavior of the fibroblasts during the assessment of cell viability for 72 h after DOX treatment. Rosi decreased the expression of procollagen in fibroblasts at 20 ~M, while Cig decreased pro collagen expression significantly at (1 0 ~M). On the other hand MEL showed enhanced toxicity to DOX at supraphysiological concentrations (1 ~M, 10 ~M) against fibroblasts. The tracking of CLOCK (a protein involved in regulation of circadian rhythm) expression within the different subcellular fractions of the fibroblasts showed that the above mentioned effects did not involve the incorporation of the CLOCK protein. Taken together, these results showed that the combination of DOX with Rosi constitutes a promising approach in the treatment of breast cancer, since they displayed a synergistic antiproliferative activity at concentrations that did not affect the cardiac cells. Further studies are needed to establish the value ofthis combination in vivo.
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