Fig. 2
Seemingly pro-survival metabolic effects of 1,25(OH)2D3 do not hamper the efficacy of metabolism-targeting therapeutic regimens. a Kaplan-Meier plots demonstrating the significant inverse correlation between G6PD mRNA expression and overall survival in ER+ (left) and total (right) BCa patients. b Knocking-down G6PD in MCF-7 cells significantly reduces cell survival, independent of 1,25(OH)2D3 (100 nM; 72 h). Statistical comparison between DMSO- and 1,25(OH)2D3-treated cells was made using a two-tailed Student’s t test. P values less than or equal to 0.05, 0.01 and 0.001 are depicted by *, **, and ***, respectively. Error bars ± SD; n = 3. Cellular survival was assessed using SRB assay, and % survival is calculated by normalizing the absorbance value obtained with the different experimental conditions to DMSO-treated cells transfected with negative control (NC) siRNA. 1,25(OH)2D3 significantly enhances the anti-tumor effects of DHEA assessed by SRB assay. MCF-7 cells were treated for 72 h with increasing concentrations of DHEA in the presence of either DMSO or 1,25(OH)2D3, and % survival is calculated by normalizing the absorbance value obtained with the different experimental conditions to DMSO-treated cells. c Schematic overview of cellular serine uptake, synthesis, and metabolism. 3PS 3-phosphoserine. d 72 h treatment of MCF-7 cells with 1,25(OH)2D3 differentially influences the mRNA expression of enzymes involved in serine synthesis but upregulates the expression of those involved in serine metabolism. Relative expression was calculated using the ∆∆Ct method, with vinculin as the housekeeping gene. e 1,25(OH)2D3 significantly influences cellular survival in response to amino acid deprivation. MCF-7 cells were cultivated in medium lacking serine, glycine, or both, in the presence of either DMSO or 1,25(OH)2D3 for 72 h, after which SRB assay was performed. 1,25(OH)2D3 was found to mildly however significantly dampen the reduction in survival of MCF-7 cells in response to serine deprivation. 1,25(OH)2D3 was also found to enhance the efficacy of CBR-5884 and 5-FU, inhibitors of PHGDH and TYMS, respectively, assessed by SRB assay