RESUMEN
BACKGROUND: The dose-limiting toxicity of doxorubicin on hematopoietic stem cells reduces the maximum benefit from this powerful drug. Melatonin may play a role in reducing this toxicity. MATERIALS AND METHODS: Melatonin at 10 microM was used while challenging human peripheral blood stem cells (PBSC) with doxorubicin (0.6 microM and 1 microM), and colony formation was used to evaluate the protective effect of melatonin. RESULTS: Melatonin was protective for the myeloid and erythroid series when given during or 1 hour after, but not before, doxorubicin, as measured by colony assay. This protection was independent from its antioxidant function as measured by 2', 7'-dichlodihydro-fluorescein diacetate and was selective for PBSC when compared to the MCF-7 cancer cell line. CONCLUSION: The results suggest the importance of the time sequence for melatonin administration to exert its protective effect in relation to doxorubicin treatment, as well as its protective effect on both erythroid and myeloid elements independent from its antioxidant function.