Plk1 Inhibition Causes Post-Mitotic DNA Damage and Senescence in a Range of Human Tumor Cell Lines

Abstract

Plk1 is a checkpoint protein whose role spans all of mitosis and includes DNA repair, and is highly conserved in eukaryotes from yeast to man. Consistent with this wide array of functions for Plk1, the cellular consequences of Plk1 disruption are diverse, spanning delays in mitotic entry, mitotic spindle abnormalities, and transient mitotic arrest leading to mitotic slippage and failures in cytokinesis. In this work, we present the in vitro and in vivo consequences of Plk1 inhibition in cancer cells using potent, selective small-molecule Plk1 inhibitors and Plk1 genetic knock-down approaches. We demonstrate for the first time that cellular senescence is the predominant outcome of Plk1 inhibition in some cancer cell lines, whereas in other cancer cell lines the dominant outcome appears to be apoptosis, as has been reported in the literature. We also demonstrate strong induction of DNA double-strand breaks in all six lines examined (as assayed by γH2AX), which occurs either during mitotic arrest or mitotic-exit, and may be linked to the downstream induction of senescence. Taken together, our findings expand the view of Plk1 inhibition, demonstrating the occurrence of a non-apoptotic outcome in some settings. Our findings are also consistent with the possibility that mitotic arrest observed as a result of Plk1 inhibition is at least partially due to the presence of unrepaired double-strand breaks in mitosis. These novel findings may lead to alternative strategies for the development of novel therapeutic agents targeting Plk1, in the selection of biomarkers, patient populations, combination partners and dosing regimens.

Polo-like kinase 1 inhibition diminishes acquired resistance to epidermal growth factor receptor inhibition in non-small cell lung cancer with T790M mutations

“…PLK1 regulates the DNA damage response checkpoint [35, 36], and PLK1 inhibition can cause DNA damage [28, 29, 31]. To determine the extent to which PLK1 inhibition induces DNA damage in ER NSCLC cells, we incubated the cells with volasertib or erlotinib for 48 h and then subjected them to a comet assay which measures both single-strand and double-strand DNA breaks (Figure 5B).…”

“…PLK1 has a pivotal role in maintaining mitotic entry and progression as well as DNA damage checkpoints [42]. PLK1 depletion leads to varying lengths of mitotic delay and DNA damage [28, 29]. A previous in vitro study showed that inhibition or knock down of PLK1 in six cancer cell lines led to increased histone H3 phosphorylation (pHisH3) at 6 h followed by increased γ-H2AX expression at 24 h and increased PARP cleavage at 24–48 h, with senescence occurring in some of these cell lines after 2 weeks [29].…”

“…PLK1 depletion leads to varying lengths of mitotic delay and DNA damage [28, 29]. A previous in vitro study showed that inhibition or knock down of PLK1 in six cancer cell lines led to increased histone H3 phosphorylation (pHisH3) at 6 h followed by increased γ-H2AX expression at 24 h and increased PARP cleavage at 24–48 h, with senescence occurring in some of these cell lines after 2 weeks [29]. The timing of these changes suggests a model in which mitotic arrest leads to DNA damage and apoptosis and/or senescence.…”

In vitro study of the Polo‐like kinase 1 inhibitor volasertib in non‐small‐cell lung cancer reveals a role for the tumor suppressor p53

“…Similarly, Driscoll et al . () demonstrated more TIS in p53 wild‐type versus mutant colorectal and lung cancer cells after treatment with the Plk1 inhibitors MLN0905 or BI2536. From a therapeutic standpoint, it is noteworthy that cells that undergo cellular senescence are permanently growth arrested, but remain viable and metabolically active, thereby secreting multiple tumor‐promoting factors to adjacent tumor cells.…”

Mutations of the LIM protein AJUBA mediate sensitivity of head and neck squamous cell carcinoma to treatment with cell-cycle inhibitors

“…Our findings are also consistent with the results of multiple in vitro and in vivo laboratory studies of a small number of cell lines. These studies demonstrated diverse responses of cancer cells to PLK1 inhibition, with some cancer cell lines resistant to the effects of inhibition or knockdown of PLK1 expression [13, 18, 52]. However, predictive biomarkers have yet to be used to select cancer patients likely to experience responses to treatment with PLK1 inhibitors, and the mechanisms of resistance to PLK1 inhibitors have yet to be elucidated.…”