Increased chemosensitivity of SKBR3 in MSC-CM or AT-MSCs cocultures. A) Doxorubicin decreased relative fluorescence of the EGFP-SKBR3 in the presence of MSC secreted factors, indicative of increased chemosensitivity of EGFP-SKBR3 cells in the MSC-CM to doxorubicin concentrations of 12.5 ng/ml and 25 ng/ml, *p < 0.05. B) Relative viability of MSC-CM-exposed tumor cells is significantly lower in the presence of 25 ng/ml doxorubicin in comparison to doxorubicin treatment in culture medium, *p < 0.05. C) Direct comparison of the doxorubicin sensitivity revealed shift in IC50(SKBR3) = 27 ng/ml DOX to IC50(SKBR3 in MSCs-CM) = 13 ng/ml DOX, as determined by luminescent viability assay, *p < 0.05. D) Cytotoxic treatment with doxorubicin induced significantly higher Caspase-3/7 activation in the SKBR3/MSC-CM cultures as determined by a Casp-3/7 luminescence assay. Each experiment was performed three times with four different MSCs isolates and one representative evaluation is shown. Data are expressed as means ± SD, *p < 0.05. E) Flow cytometric analysis of the directly cocultured cells unraveled significantly increased proportion of apoptotic and necrotic tumor cells as determined by the Annexin V and/or DAPI positivity in cocultures. Tumor cells were mixed with AT-MSCs (2:1) and treated with 50 ng/ml doxorubicin for 48 hrs. Representative data derived from one experiment were shown, *p < 0.05.