Figure 5. The rS3-PA induced downregulation of P-STAT3, which affects the proliferation and survival of cancer cells, but not of normal cells. (A) Different tumors and normal cells (NIH-3T3 and MCF-10A) were cultured in the presence of 1 µM Flag-hTrxΔcys (hTrx), rS3-PA or an equal volume of PBS. The medium was exchanged daily and the cells were photographed after 96 h of treatment. (B) Cancer cells and normal cells were transduced for 72 h with 1 µM hTrx or rS3-PA. The viability of PBS-treated control cells was considered 100% at 72 h for each cell line. (C) Cells were treated with rS3-PA, hTrx or PBS, for 24 h or 48 h. Cells were lysed and the enrichment of nucleosomes in the cytoplasm was determined in an ELISA-based assay (Cell Death Detection ELISA, Roche). The nucleosome enrichment factor was calculated according to the formula: Treated cells (A405nm – A490nm)/PBS control cells (A405nm – A490nm). The absorbance (A405) of control treated cells (PBS) was set to 1. Error bars in (B and C) represent SD. NS, not significant, *p < 0.05, **p < 0.01.