Due to the high incidence of breast cancer in the population and also the high mortality rate in women, we investigated the sensitivity of the spheroids of hormone-positive breast cancer MCF-7 to tamoxifen, which is a common chemotherapeutic agent in hormone therapy, and cannabidiol, which is a common part of palliative treatment. Spheroids were treated with selected concentrations of tamoxifen (7.5 μM, 15 μM, 22.5 μM), ordinary or water-soluble cannabidiol (30 μM, 60 μM, 90 μM) and their combinations. The spheroids were monitored with the Cytation1 device until the seventh day after exposure and their daily growth was determined. We performed a test of the metabolic activity of cells in spheroids with the PrestoBlue reagent. We determined the proportions of mitosis, apoptosis and necrotic area in spheroids by examining histological slides. We also conducted a migration test and an invasion test. The exposure to test substances produced a dose-dependent effect on spheroid growth. Exposure to the combination of the highest tested concentrations of tamoxifen and water-soluble cannabidiol inhibited spheroid growth the most. This exposure also reduced the metabolic activity of cells in the spheroids the most, resulted in the highest proportion of apoptotic cells in the spheroids and the highest proportion of necrosis of all exposures. For reducing the migratory abilities of cells, both cannabidiols in combination with tamoxifen proved to be equally good, and of all the tested exposures, the most effective. Of the exposures to individual active substances in selected concentrations, the spheroids of hormone-positive breast cancer MCF-7 were the most sensitive to water-soluble cannabidiol.
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