Bioactive Components of Ganoderma lucidum (W.Curt.:Fr.) Lloyd Can Induce Apoptosis of Tumor Cells

Abstract

The antitumor activity of Ling Zhi or Reishi mushroom Ganoderma lucidum has been studied widely in vivo and in vitro, and many reports show that polysaccharides are the main antitumor active substances in G. lucidum, acting by improvement of the host immunity. In addition, it was also reported that an extract of G. lucidum killed the tumor cells in vitro. In our experiment, it was also found that crude extracts of G. lucidum (named LZ) and their fractions significantly inhibited the proliferation of different tumor cells, and the fractions induced SW620 cell apoptosis in vitro. The antiproliferative capacity of LZ was tested using 11 tumor cell lines. LZ very strongly inhibited the growth of Jurkat, K562, SW620, LS180, and QGP-1 cell lines, and the IC50 of LZ to them was measured as 180, 200, 180, 320, and 360 μg/mL, respectively. Moreover, LZ showed the capacity to inhibit the growth of S180 cell lines, the IC50 is 420 μg/mL, and meanwhile it obviously inhibits the growth of MCF7 and Caco-2 only at 1000 μg/mL. However, LZ does not possess inhibitory capacity to BON, Panc-1, and HUH7 cell lines in the range of experimental concentrations. In order to find out the bioactive components from crude extracts, LZ were divided into two parts by dialysis, and then they were further fractionated using different chromatographic procedures. All fractions obtained were tested for their antiproliferative capacity to SW620 cells. LZ-2-2 and LZ-DW-2-a-3 were found to be active components of LZ. After incubation with LZ and LZ-2-2, SW620 cells were found to form apoptotic bodies in situ checked by light microscopy—their apoptosis activity was confirmed by staining with Annexin V-FITC conjugate. The apoptotic percentage of SW620 was quantified by flow cytometry. At the most effective concentration of 600 μg/mL, LZ induced 28% of cells to undergo apoptosis, 39.5% for LZ-2-2, and, at 1000 μg/mL, 51% for LZ-DW-2-a-3.The influence of LZ-2-2 and LZ-DW-2-a-3 on the cell cycle of SW620 cells during their apoptotic processes was analyzed by flow cytometry. Experimental results suggested that SW620 cells were arrested in the GO phase, and they could not transit from the G2/M phase to the G1 phase after treatment by LZ-2-2 or LZ-DW-2-a-3. Until now, there has been no final answer as to how the extract of G. lucidum inhibited and killed the tumor cells. Our results revealed that some fractions from G. lucidum induced apoptosis of tumor cells, which means that G. lucidum exerts its antitumor function by the apoptosis pathway as well as by the immune pathway, which is accepted widely as a new pathway.