IGF1 and medulloblastoma: To confirm the biochemical activity of MMP9 and the bioactivity of free IGF1 cleaved from IGF1/IGFBP3 complexes in a medulloblastoma cell culture model system, we performed an MMP9 cleavage assay wherein IGF1/IGFBP3 complexes were exposed to MMP9 in a molar substrate:enzyme ratio of 1:1 and measured phospho-IGF1 by ELISA in D425 cells.