(a) Effects of 6-thioguanine on PTHrP content in the media of cultured MDA-MB-231 cells plated onto 48-well plates and grown to near confluence. Cells were washed and treated with serum-free media containing 6-thioguanine in the indicated concentrations for 48 hours. PTHrP concentrations in conditioned media were corrected for cell number. The detection limit of the assay is ∼0.5 pM/L. (b) Effects of 6-thioguanosine on PTHrP content in the media of cultured MDA-MB-231 cells plated onto 48-well plates and treated as described in a. (c) Effects of purine on PTHrP content in the media of cultured MDA-MB-231 cells plated onto 48-well plates and treated as described in a. (d) Effects of dexamethasone on PTHrP content in the media of cultured MDA-MB-231 cells plated onto 48-well plates and treated as described in a. Values in all panels represent means ± SEM (n = 3 per group). Ctrl, control. *P < 0.05.