Prolonged activation of the spindle assembly checkpoint (SAC) due to mitotic spindle disruption
can result in p53 activation, centriole disengagement and cell death. Indeed, one
chemotherapeutic strategy frequently applied to aggressive and hormone-independent cancers
is to target the mitotic spindle, a microtubule-based structure that is required for proper
chromosome segregation and cell division. Drugs such as vinblastine or Paciltaxel suppress the
normal microtubule assembly dynamics, leading to mitotic arrest and eventual cell death by
apoptosis. However, despite their decades-long implementation in the clinic, the mechanisms by
which prolonged mitotic delay results in cell death remains unclear. Further, despite the
universality of the requirement of the mitotic spindle for cell division, there is still a great deal of
heterogeneity in how cells respond to spindle disruption, which may reduce the efficacy of anti-
mitotic chemotherapeutic strategies. Using a combination of biochemical and live cell imaging
approaches, our preliminary data reveals that targeting both Kinesin Spindle Protein (KSP), a
molecular motor required for spindle bipolarity, and the Phosphatidylinositide 3-kinase
(PI3K)/Akt/mTOR signaling pathway dramatically accelerates the kinetics of mitotic cell death
relative to mitotic arrest alone. Moreover, it elicits a more homogeneous response from the
treated cells. PI3K signaling is involved in a variety of regulatory pathways that regulate cell
survival, metabolism and proliferation, but the mechanism by which PI3K activity promotes cell
viability during mitotic arrest is unknown. To better understand how PI3K signaling is involved in
the timing of cell death and variability of cellular responses of mitotic delay, we will continue to
apply high-throughput timelapse imaging, high-resolution 4D imaging and biochemical
approaches to a battery of cell lines differ in their sensitivity to mitotic delay as well as
dependence on PI3K signaling. The Specific Aims of this project will 1) Define the protective
role of PI3K in normal and cancer cells; and 2) Determine the mechanism by which PI3K
promotes cell survival during mitotic delay. If successful, these studies will lay the foundation for
future translational studies to further develop adjuvant therapies that will target mitotically active
tumor cells without the side effects associated with other microtubule disruptors.