Microtubule Targeting Agents Induce Cell Cycle Phase‐Specific Death Pathways in Primary Acute Lymphoblastic Leukemia Cells

Abstract

Microtubule targeting agents (MTAs), such as taxanes (microtubule stabilizers) or vinca alkaloids (microtubule destabilizers), are important and widely used cancer chemotherapeutics which are thought to act primarily in mitosis. In addition to mitotic effects there is increasing evidence that MTAs also act in interphase which may be relevant to their clinical mode of action. Previously we discovered that vincristine (VCR), a microtubule destabilizer, is able to induce death in primary acute lymphoblastic leukemia (ALL) cells in G1 phase. In order to expand on this previous study, we sought to determine if other MTAs induced phase‐specific death and to investigate the associated cell death pathways. This was achieved through studies comparing primary ALL cells to HeLa cells after treatment with two microtubule destabilizers, vincristine and eribulin, and one microtubule stabilizer, paclitaxel, at varying concentrations. Consistent with previous studies, it was found that at high concentrations (>100 nM) of the microtubule destabilizers, death was induced in G1 phase of primary ALL cells. Interestingly, when treated with lower concentrations (<100 nM) of microtubule destabilizers, mitotic arrest followed by cell death occurred. However treatment with the microtubule stabilizer, paclitaxel, led to mitotic arrest followed by cell death at all tested concentrations. All three MTAs induced solely mitotic death in HeLa cells consistent with many other established cell lines. Furthermore, immunofluorescence studies indicated that G1 phase death in response to higher destabilizer concentrations was associated with complete loss of the microtubule network, while some intact microtubule structures remained after treatment with low destabilizer concentrations and paclitaxel. Finally preliminary experiments assessing phosphorylation and activation status of several Bcl‐2 proteins suggest that mitotic death is controlled through intrinsic apoptosis while death induced in G1 phase is not. These results suggest that microtubule destabilizers induce cell cycle phase specific‐death which is dependent on concentration while microtubule stabilizers do not and that the difference in these types of MTAs may arise from differential effects on the microtubule network. These findings advance our understanding of interphase microtubule function and have significant implications for the clinical use of MTAs particularly in the context of combination treatments.Support or Funding InformationThe present study was funded by a grant (to TCC) from the UAMS Chancellor's Circle.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.