PC3 cells were cultured with regular RPMI 1640 medium ± 500 μM NAC or Cys/CySS-free RPMI 1640 medium ± 500 μM NAC for 3 hr. Cells or conditioned media were collected for redox western blot, cell invasion, and MMP activity assays. (A) Redox western blot assay. Oxy2= fully oxidized (two disulfides) Trx1, Oxy1= mixture of reduced and oxidized Trx1, R= fully reduced Trx1. PC3 cells were treated with DTT or H2O2 for 30 min and were used to determine fully reduced Trx1 or fully oxidized Trx1. (B) Cell invasion assay. (C) MMP9 zymography activity gel. (D) Relative quantification of MMP9 zymography activity gels. Lane 1 = regular RPMI 1640 medium, lane 2 = regular RPMI 1640 medium + NAC, lane 3 = Cys/CySS-free RPMI 1640 medium, lane 4 = Cys/CySS-free RPMI 1640 medium + NAC. *p-value ≤ 0.05 when compared with regular RPMI 1640 medium. **p-value = 0.06 when compared with Cys/CySS-free RPMI 1640 medium. Data represent average of at least three individual experiments