The xCELLigence system (ACEA Biosciences, Inc. San Diego, CA) was used for quantifying changes in real-time cell proliferation in NGP and SK-N-BE(2) cells as previously described.8 (link),9 (link) IMR-32 cells exhibited clumping when cultured, thus, proliferation of IMR-32 cells was determined by counting cell number daily using a Z1 Coulter Counter (Beckman Coulter, Indianapolis, IN) as previously described.26 (link)