In vitro activity: Cyclopamine inhibits the Hedgehog signaling pathway with an IC50 of 46 nM, and blocks the activity of human Smo receptor expressed in CHO-K1 cells in [3H]Hh-Ag binding assay with an IC50 of 280 nM. Cyclopamine significantly inhibits Hedgehog pathway activity in a dose-dependent manner in gut-derived tumor cell lines expressing Patched (PTCH) mRNA, and induces growth inhibition of those tumor cell lines by 75-95% at the concentration of 3 μM, but ineffective towards the colon tumor cells without PTCH mRNA expression, suggesting the effects of Cyclopamine treatment are Hedgehog pathway related rather than generally cytotoxic. By blocking Hedgehog signaling through direct interaction with Smo, Cyclopamine (10 μM) inhibits the proliferation of SMOhigh Cyclopamine-responsive cell lines L3.6sl and Panc 05.04 by 75-80%, and increases the apoptosis by 2.5- to 3.5-fold, without affecting the BxPC3-SMOlow cell line. Cyclopamine treatment significantly decreases of Snail mRNA and increasea E-cadherin transcripts in the E3LZ10.7 cell line. Independent of inhibition of cell growth, Cyclopamine treatment significantly inhibits the invasive phenotype of Hedgehog-dependent L3.6pl cells, causing a >500-fold reduction in the number of transmigrating cells, but not that of the Hedgehog-independent cell line Panc-1.

Kinase Assay: This assay measures the end stage of the Hh signaling pathway, that is, the transcriptional modulation of Gli, using Luciferase as readout (Gli-Luc assay). Cyclopamine is prepared for assay by serial dilution in DMSO and then added to empty assay plates. TM3Hh12 cells (TM3 cells containing Hh-responsive reporter gene construct pTA-8xGli-Luc) are resuspended in F12 Ham's/DMEM (1:1) containing 5% FBS and 15 mM Hepes pH 7.3, added to assay plates and incubated with Cyclopamine for approximately 30 minutes at 37 °C in 5% CO2. 1 nM Hh-Ag 1.5 is then added to assay plates and incubated at 37 °C in the presence of 5% CO2. After 48 hours, either Bright-Glo or MTS reagent is added to the assay plates and luminescence or absorbance at 492 nm is determined. IC50 value, defined as the inflection point of the logistic curve, is determined by non-linear regression of the Gli-driven luciferase luminescence or absorbance signal from MTS assay vs log10 (concentration) of Cyclopamine using the R statistical software pack. 

Cell Assay: Cells (SEG1, OE33, KYAE, KYSE180, SNU1, AGS, SNU16, NCI-N-87, HUCCT1, PANC1, PL5, PL6, BXPC3, HS766T, KYSE150, GBD1, DLD1, and HCT116) are exposed to Cyclopamine in 96-well plates. Cell viability is measured by MTS (soluble tetrazolium salt) assay. Viable cell mass is determined by optical density measurements at 490 nm (OD490) at 2 and 4 days using the CellTiter96 colorimetric assay. Relative growth is calculated as OD (day 4)﹣OD (day 2)/OD (day 2).