AZD6244 promotes FNMA and decreases tumor cell detachment. MLL cells treated with DMSO as carrier control fail to assemble a fibronectin matrix, whereas MLL cells treated overnight with 1.5 μM AZD6244 assemble a matrix as revealed by immunofluorescnce assay (A). Matrix assembly was confirmed by differential solubilization assay and immunoblot analysis. The assembly of high molecular weight fibronectin multimers (HMWFM) is only evident in AZD62244-treated MLL cells. Actin in the soluble fraction was used as a loading control (B). AZD6244 treatment also resulted in increased aggregate cohesion as measured by TST. Treated aggregates were found to be significantly more cohesive than aggregates treated with the DMSO carrier (Student t-test, p < 0.0001) (C). The migration of DMSO and AZD6244-treated MLL cells was not significantly different when cells were sparsely plated into Boyden chambers containing control filters (Student t-test, p = 0.4604). However, when migration assays were conducted using 3D spheroids of DMSO and AZD6244-treated cells, detachment of cells from the aggregate was shown to be significantly delayed by treatment with the MEK inhibitor (Student t-test, p < 0.0008) (D).