Drug combinations can improve the efficacy of anticancer therapy and reduce the side effects. Our preliminary data suggest that clinically used antibiotics such as azithromycin (AZI) reduce proliferative capacity and induce apoptosis in human glioblastoma (GBM) cells U87. Hence, the present study explored the cytotoxicity of cotreatment with temozolomide (TMZ) and AZI on U87 cells. The cells were treated with each drug individually and in combination in a series of concentrations (0.5225.0 μg/ml) for 48 h synchronously. Cell viability was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and data were analyzed with the Code for the Identification of Synergism Numerically Efficient software. The cytotoxicity was potentiated when the cells were cotreated with TMZ and AZI compared to TMZ alone, but was markedly lower than AZI alone. Moreover, it was shown that TMZ + AZI exerted a competitive inhibition of cell growth and TMZ partially repressed the cytotoxicity of AZI. These findings delineate that the TMZ and AZI cotreatment behaves antagonistically in human GBM cells U87. A further chapter on the pretreatment of cells with AZI prior to TMZ or a so-called sensitization strategy may provide valuable insight into the fight against GBM.
Key words: Temozolomide, Azithromycin, Co-treatment, Cytotoxicity, Glioblastoma cells
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