Dkk3 rdkk3

NCI-H508, Caco-2, SW403, SW948, HT29, SK-CO-1, DLD-1, SW480, SW837, SW48, SW620, LoVo, COLO205, T84, LS174T, NCI-H716, HCT8, HCT15, SW1116, RKO, COLO320DM, HuTu80, LS123, and HCT116 cell lines were from the American Type Culture Collection (ATCC). HCA-7, its derivatives CC and CC-CR, DiFi, GEO, LIM1215, and LIM2405 were maintained in the Coffey lab. The SNUC4 cell line was from the Korean Cell Line Bank and the V9P cell line was provided by John Mariadason (Olivia Newton-John Cancer Research Institute, Melbourne, Australia). HNSCC cell lines SCC25, its derived cetuximab-resistant sublines (CTX-R1, R3, R4, R5, R7, and R8), and UNC10 were maintained in Christine Chung's laboratory. All cell lines were confirmed to be free of mycoplasma contamination. Cells were grown in Dulbecco's Modified Eagle's Medium (DMEM, Corning) supplemented with 10% bovine growth serum, glutamine, nonessential amino acids, 100 U/ml penicillin and 100 μg/ml streptomycin (HyClone) in 5% CO₂ at 37°C. 3D collagen cultures were set up using 3 layers of type-I collagen PureCol (Advanced BioMatrix) in triplicate as previously described^{14 (link),15 (link)}. Human recombinant DKK1 (rDKK1) and DKK3 (rDKK3) are from R&D Systems. Drugs are used as follows: cetuximab (Merck KGaA), Wnt pathway inhibitor ICG-001 and XAV-939 (Selleck Chemicals). Colonies were counted by GelCount colony counter (Oxford Optronix).