In breast cancer, radiation has a central role in the treatment of brain metastasis, although tumor sensitivity might be limited. The tumor cell defense response to ionizing radiation involves activation of cell cycle checkpoint signaling. Histone deacetylase (HDAC) inhibitors, agents that cause hyperacetylation of histone proteins and thereby aberrations in the chromatin structure, may also override the DNA damage defense response and facilitate the radiation-induced mitotic cell death. In experimental metastasis models, the human breast carcinoma cell line MA-11 invariably disseminates to the central nervous system. We compared profiles of in vitro MA-11 cell cycle response to ionizing radiation and HDAC inhibition. After radiation exposure, the G 2 -M phase accumulation and the preceding repression of the G 2 phase regulatory factors Polo-like kinase-1 and cyclin B1 required intact G 2 checkpoint signaling through the checkpoint kinase CHK1, whereas the similar phenotypic changes observed with HDAC inhibition did not. MA-11 cells did not show radiation-induced expression of the G 1 cell cycle inhibitor

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Objective.The aim of this study was to assess treatment-related changes in prostate-specific antigen (PSA), total and bone alkaline phosphatase (total ALP, bone ALP), and changes on conventional bone scans in patients with metastatic castration-resistant prostate cancer (mCRPC) with bone metastases who received six cycles of radium-223 (Ra-223). Materials and methods. Changes in PSA, total ALP and bone ALP ( ‡30% increase or decrease), and changes on bone scans were assessed before and after six monthly cycles of Ra-223 therapy (50 kBq/kg body weight) in 14 patients with mCRPC with bone metastases and four patients on placebo. Results.Post-treatment PSA increased by at least 30% in 11 out of 14 patients and remained stable in three. Total ALP and bone ALP decreased in six and nine patients, respectively. In 10 out of 12 evaluable patients the uptake on post-treatment bone scan was reduced in lesions with high pretreatment uptake, in 11 patients accompanied by the development of new or expanded bone lesions. FACBC position emission tomography/computed tomography scans confirmed the growth of new or expanded bone metastases in two patients. Conclusions.These observations support the notion that Ra-223 kills tumour cells in metastases surrounded by highly proliferating osteoblasts, consistent with the reported survival benefit. The radiation effect in small tumour deposits not surrounded by increased osteoblast activity seems, however, insufficient, thus allowing continuous tumour growth. Long-lasting PSA reductions are the exception rather than the rule during Ra-223 treatment, whereas alkaline phosphatases decrease more frequently. To improve the overall anticancer effect, Ra-223 might be a valuable component of combination treatment.

Background: The tumor response to preoperative radiotherapy of locally advanced rectal cancer varies greatly, warranting the use of experimental models to assay the efficacy of molecular targeting agents in rectal cancer radiosensitization. Histone deacetylase (HDAC) inhibitors, agents that cause hyperacetylation of histone proteins and thereby remodeling of chromatin structure, may override cell cycle checkpoint responses to DNA damage and amplify radiation-induced tumor cell death.