OBJECTIVE: To provide in vitro evidence of Psorinum treatment against cancer cells in a controlled study. METHODS: Effects of homeopathic Psorinum 6× on cell viability were initially determined in several cancer cell lines, including A549, Hep G2 and MCF-7, using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and an ethanol 6× control. The cell line that exhibited highest inhibition was selected and used in the following experiments. A range of Psorinum 6× doses was used to explore treatment effects on cell cycle arrest, cell death(apoptosis), generation of reactive oxygen species(ROS) and change in mitochondrial membrane potential(MMP) using fl ow cytometry and fl uorescence microscopy, respectively. Expression of several signal proteins related to apoptosis and cell survival were quantified with Western blotting and confocal microscopy. Further, circular dichroism(CD) spectroscopy was used to determine possible drug-DNA interactions, as well as the induction of conformational changes. RESULTS: Treatment of cancer cell lines with Psorinum showed greater anticancer effects in A549 cells than in others. In A549 cells Psorinum treatment inhibited cell proliferation at 24 h after treatment, and arrested cell cycle at sub-G1 stage. It also induced ROS generation, MMP depolarization, morphological changes and DNA damage, as well as externalization of phosphatidyl serine. Further, increases in p53 expression, Bax expression, cytochrome c release, along with reduction of Bcl-2 level and caspase-3 activation were observed after Psorinum 6× treatment, which eventually drove A549 cells towards the mitochondria-mediated caspase-3-dependent pathway. CD spectroscopy revealed direct interaction of Psorinum with DNA, using calf thymus-DNA as target.CONCLUSION: Psorinum 6× triggered apoptosis in A549 cells via both up- and down-regulations of relevant signal proteins, including p53, caspase-3, Bax and Bcl-2. METHODS: Effects of homeopathic Psorinum 6 × on cell viability were pretermined in several cancer cell lines, including A549, Hep G2 and MCF-7, using 3 - (4,5-dimethylthiazol-2-yl) -2,5-diphenyltetrazolium bromide assay, and an ethanol 6 × control. The cell line that won highest inhibition was selected and used in the following experiments. A range of Psorinum 6 × doses was used to explore treatment effects on cell cycle arrest, cell death (apoptosis), generation of reactive oxygen species (ROS) and change in mitochondrial membrane potential (MMP) using fl ow cytometry and fl uorescence microscopy, respectively. Expression of several signals proteins related to apoptosis and cell survival were quantified with Western blotting and confocal microscopy. Further, circular dichroism (CD) spectroscopy was used to determine possible drug-DNA interactions, as well as the induction o fConformational changes. RESULTS: Treatment of cancer cell lines with Psorinum showed greater anticancer effects in A549 cells than in others. In A549 cells Psorinum treatment inhibited cell proliferation at 24 h after treatment, and arrested cell cycle at sub-G1 stage. Further, increases in p53 expression, Bax expression, cytochrome c release, along with reduction of Bcl-2 level and caspase-3 activation were observed after Psorinum 6 × treatment, which eventually drove A549 cells towards the mitochondria-mediated caspase-3-dependent pathway. CD spectroscopy revealed direct interaction of Psorinum with DNA, using calf thymus-DNA as target. CONCLUSION: Psorinum 6 × triggered apoptosis in A549 cells via both up- and down-regulations of relevant signal proteins, including p53, caspase-3, Bax and Bcl-2.