MMP9 and neoplasm: After inhibition of 3T3-A-EXO uptake by cytochalasin D, increased MMP9 activity in 3LL tumor cells could not be detected, suggesting that MMP3 in 3T3-A-EXO cannot directly induce MMP9 activation and fusion of 3T3-A-EXO and that 3LL tumor cells are required for this process.