Crinum Latifolium Leave Extracts Suppress Immune Activation Cascades in Peripheral Blood … 327 extract almost completely suppressed mitogen-induced IDO activity (kyn/trp; Fig. 1A). Measurement of neopterin concentrations showed, that the extract only slightly, but significantly reduced neopterin production in unstimulated PBMC supernatants, whereas PHA-stimulated neopterin formation was suppressed in a dose-dependent manner with an IC50 of 453 ± 86 µg/ml (~2.3 µg/ml total alkaloids; 0.13 µg/ml crinamidine; Fig. 1B). No influence on the viability of PBMC, even at the highest concentrations tested, could be detected after 48 hours of treatment (data not shown). Antiproliferative activity Treatment of human prostate carcinoma PC3 and LNCaP cells, and also benign prostate hyperplasia BPH-1 cells with water extracts of Crinum latifolium, showed a significant and dose-dependent inhibition of cell growth after a culture period of 72 hours (Fig. 2A). Parallel measurements of growth inhibition after treatment of cells with cisplatin were used as a positive control (Figure 2B). The most sensitive cell line affected by these treatments were BPH-1 cells, whose proliferation was inhibited with an IC50 of 2120 ± 41 µg/ml (~10.6 µg/ml total alkaloids; 0.6 µg/ml crinamidine) after treatment with Crinum latifolium extract and with an IC50 of 2.3 ± 0.3 nM after treatment with cisplatin. Fig. 2. Viability of PC3- (open triangles), BPH-1- (open squares) and LNCaP-cells (open circles) after treatment with or without increasing concentrations of Crinum latifolium leave extract (A) or cisplatin (B) for 72 hours, expressed as % of baseline. Results shown are the mean values ± S.E.M. of three independent experiments run in duplicates (*p <0.05). The growth of PC3 and LNCaP cells was suppressed by the Crinum latifolium extract at IC50-doses of 4540 ± 791 µg/ml (~22.7 µg/ml total alkaloids; 1.3 µg/ml crinamidine) and 2344 ± 148 µg/ml (~11.7 µg/ml total alkaloids; 0.7 µg/ml crinamidine), respectively. Cisplatin showed potent antiproliferative effects on PC3 and LNCaP cells at IC50-doses of 6.3 ± 0.8 nM and 5.5 ± 0.9 nM, respectively. It is unclear, which compounds of the Crinum latifolium leave extract are responsible for the effects on stimulated PBMC or proliferation of prostate cells. Obviously, the active compounds present in our leave extract of Crinum latifolium, were well soluble in water Sci Pharm. 2011; 79: 323–335