PARP1 and neoplasm: Desmaison et al. (2018) have also shown that physically confining tumor spheroids in agarose gels induced prometaphase delay as compared to freely growing spheroids (Desmaison et al., 2018). We have also verified that PARP, which is involved in DNA repair and inactivated by caspase cleavage during apoptosis (Morales et al., 2014), is increasingly cleaved as matrix rigidity is increased (Figures 3D, F), providing evidence that increasing matrix rigidity increases rate of cell apoptosis.