p53 is not directly relevant to the response of Polo-like kinase 1 inhibitors

Abstract

Polo-like kinase 1 (Plk1) is elementary for cell proliferation and its deregulation is involved in tumorigenesis. Plk1 has been established as one of the most attractive targets for molecular cancer therapy. In fact, multiple small molecule inhibitors targeting either the kinase domain or the Polo-box binding domain (PBD) of Plk1 have been identified and intensively investigated. Intriguingly, Plk1 depletion affects more cancer cells than normal cells. It is also reported that the cytotoxicity induced by Plk1 inhibition is elevated in cancer cells with defective p53. The data lead to the hypothesis that p53 might be a predictive marker for the response of Plk1 inhibition. In this study, we demonstrate that there is no obvious different cytotoxic response between cancer cells with and without functional p53, including the isogenic colon cancer cell lines HCT116p53(+/+) and HCT116p53(-/-), breast cancer cell line MCF7, lung cancer cell line A549 and cervical carcinoma cell line HeLa, after treatment with either siRNA against Plk1, the kinase domain inhibitors BI 2536 and BI 6727 or the PBD inhibitor Poloxin. We suggest that the p53 status is not a predictor for the response of Plk1 inhibition, at least not directly. Yet, the long-term outcomes of losing p53, such as genome instability, could be associated with the cytotoxicity of Plk1 inhibition. Further studies are required to investigate whether other circumstances of cancer cells, such as DNA replication/damage stress, mitotic stress, and metabolic stress, which make possibly the survival of cancer cells more dependent on Plk1 function, are responsible for the sensitivity of Plk1 inhibition.

B-cell lymphoma 6 promotes proliferation and survival of trophoblastic cells

“…Western blot analysis was performed, as previously described. 7,36,53 The following antibodies were used for Western blot analysis: mouse monoclonal antibody against BCL6 (1:500, DAKO), mouse monoclonal antibody against Plk1 (1:1000, Santa Cruz Biotechnology, Heidelberg), rabbit polyclonal antibodies against phospho-p53 (S15) (1:500) and against poly(ADP-ribose) polymerase (PARP) (1:1000, Cell Signaling, Danvers), rabbit polyclonal antibody against phospho-HH3 (S10, 1:750, Merck Millipore), rabbit polyclonal antibody against HIF1-a (1:1000, Bethyl, Montgomery), and mouse monoclonal antibodies against Flag tag and b-actin (1: 1000 and 1:100,000, respectively, SigmaAldrich).…”

“…3H). Moreover, the tumor suppressor p53 and the cyclin-dependent kinase inhibitor p21, on which we have worked, [32][33][34][35][36] are multiple functional and greatly impact the cell cycle. Intriguingly, while the gene expression of p21, an important inhibitor of the interphase and functionally also active in mitosis, 35,36 remained nearly unchanged (Fig.…”

“…[53][54][55] In brief, control or treated cells were fixed for 15 min with 4% PFA containing 0.1% Triton X-100 at room temperature. The following primary antibodies were used for staining: polyclonal rabbit antibody against pericentrin (1:800, Abcam, Cambridge), mouse monoclonal antibody against BCL6 (1:500, Santa Cruz Biotechnology), immune serum against centromere (1:400, anti-centromere antibody, ACA, ImmunoVision, Springdale), mouse monoclonal antibody against Flag tag and FITC-conjugated mouse monoclonal antibody against a-tubulin (1:200 and 1:500, respectively, SigmaAldrich).…”

Polo-like kinase 1 inhibitors, mitotic stress and the tumor suppressor p53

“…[20][21][22][23][24][25] Poloxin, the first reported non-peptidic inhibitor of the PBD of Plk1, shows its specificity and anti-proliferative activity in vitro as well as in vivo. [15][16][17] While the preclinical data of Plk1 inhibitors are encouraging, the clinical results are rather less inspiring, showing limited anticancer activity. 20,23,26,27 It is of importance to identify the molecules and mechanisms responsible for the sensitivity of Plk1 inhibitors.…”

“…In fact, multiple small-molecule inhibitors targeting the enzymatic kinase domain and the regulatory Polobox binding domain (PBD) have been recently developed and characterized. 1,[7][8][9][10][11][12][13][14][15][16][17][18][19] In particular, BI 2536 and BI 6727 are the most intensively investigated Plk1 inhibitors. [20][21][22][23][24][25] Poloxin, the first reported non-peptidic inhibitor of the PBD of Plk1, shows its specificity and anti-proliferative activity in vitro as well as in vivo.…”