title: Polo-like kinase 1 as predictive marker and therapeutic target for radiotherapy in rectal cancer.
abstract: The ability to predict tumor sensitivity toward radiotherapy may significantly impact the selection of patients for preoperative combined-modality therapy. The aim of the present study was to test the predictive value of Polo-like kinase 1 (PLK1) in rectal cancer patients and to investigate whether PLK1 plays a direct role in mediating radiation sensitivity. PLK1 expression was evaluated by immunohistochemistry (n = 76) or Affymetrix HG133 microarray (n = 20) on pretreatment biopsies of patients with advanced rectal cancer. Expression was correlated with both tumor regression in the resected specimen and long-term clinical outcome. Furthermore, we used small interfering RNAs (siRNAs) to down-regulate PLK1 expression in colorectal cancer cells and analyzed the effects of PLK1-specific siRNAs by Western blot and quantitative real-time PCR analysis, FACScan analysis, caspase 3/7 assays, and colony-forming assays. We observed that increased PLK1 protein expression was significantly related to a poorer tumor regression and a higher risk of local recurrence in uni- and multivariate analysis. A significant decrease of PLK1 expression by siRNAs in combination with ionizing radiation induced an increased percentage of apoptotic cells and increased caspase 3/7 activity. Furthermore, enhanced G(2)-M levels, decreased cellular viability, and reduced clonogenic survival were demonstrated, indicating a radiosensitizing effect of PLK1 depletion. Therefore, PLK1 may be a novel predictive marker for radiation response as well as a promising therapeutic target in rectal cancer patients.
authors.affiliation: Department of Radiation Therapy and Oncology, University of Frankfurt/Main, Frankfurt, Germany. franz.roedel@kgu.de
authors.forename: Franz
authors.initials: F
authors.lastname: Rödel
authors.forename: Sarah
authors.initials: S
authors.lastname: Keppner
authors.forename: Gianni
authors.initials: G
authors.lastname: Capalbo
authors.forename: Robina
authors.initials: R
authors.lastname: Bashary
authors.forename: Manfred
authors.initials: M
authors.lastname: Kaufmann
authors.forename: Claus
authors.initials: C
authors.lastname: Rödel
authors.forename: Klaus
authors.initials: K
authors.lastname: Strebhardt
authors.forename: Birgit
authors.initials: B
authors.lastname: Spänkuch
mesh_terms: D014408:Biomarkers, Tumor / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D006801:Humans; D046228:Microarray Analysis; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism / Q000627:therapeutic use; D011836:Radiation Tolerance / Q000502:physiology*; D012004:Rectal Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000532:radiotherapy; D000097869:Polo-Like Kinase 1
chemical_list: D014408:Biomarkers, Tumor; D018797:Cell Cycle Proteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D000097869:Polo-Like Kinase 1