Detection of repair activity during the DNA damage-induced G2 delay in human cancer cells

Shin

Clinical Cancer Research

et al. 2006

Histone deacetylase inhibitors (HDI) are emerging as potentially useful components of the anticancer armamentarium and as useful tools to dissect mechanistic pathways. HDIs that globally inhibit histone deacetylases (HDAC) have radiosensitizing effects, but the relative contribution of specific HDAC classes remains unclear. Newly characterized HDIs are now available that preferentially inhibit specific HDAC classes, including SK7041 (inhibits class I HDACs) and splitomicin (inhibits class IIIHDACs). We investigated in human cancer cells the relative radiosensitizations that result from blocking specific HDAC classes. We found that trichostatin A (TSA; inhibitor of both class I and II HDACs) was the most effective radiosensitizer, followed by the class I inhibitor SK7041, whereas splitomicin (inhibitor of class III) had least effect. Interestingly, radiosensitization by TSA in cell lines expressing p53 was more pronounced than in isogenic lines lacking p53. Radiosensitization of cells expressing p53 by TSA was reduced by pifithrin-a, a small-molecule inhibitor of p53. In contrast, the radiosensitization by TSA of cells expressing low levels of p53 was enhanced by transfection of wild-type p53^expressing vector or pretreatment with leptomycin B, an inhibitor of nuclear export that increased intracellular levels of p53. These effects on radiosensitization were respectively muted or not seen in cells treated with SK7041or splitomicin. To our knowledge, this may be among the first systematic investigations of the comparative anticancer effects of inhibiting specific classes of HDACs, with results suggesting differences in the degrees of radiosensitization, which in some cell lines may be influenced by p53 expression.

Section: Discussionsupporting

confidence: 55%

Histone Deacetylase Inhibitor–Mediated Radiosensitization of Human Cancer Cells: Class Differences and the Potential Influence of p53

Shin

Clinical Cancer Research

et al. 2006

Prostate Cancer Prostatic Dis

“…Our own experiments illustrated that, even for similar levels of p53 induction/stabilization, the p21 WAF1/Cip1 response in PrEC is greatly attenuated in comparison to its stromal counterpart. While the p53/ p21 WAF1/Cip1 responses for our panel of malignant cell lines were as previously reported, the LNCaP cell line's 52 and cellular survival following radiation. 53 Indeed, although our results suggest increased survival for cells which lack the G1 checkpoint, defined studies in isogenic tissue culture or solid tumor models which differ in p53 status and specific G1, S and G2 checkpoint control experiments are required to prove this hypothesis, and are part of a current research program.…”

Section: Discussionmentioning

confidence: 70%

Cell death in irradiated prostate epithelial cells: role of apoptotic and clonogenic cell kill

Bromfield

Meng

Warde

et al. 2003

Dose-escalated conformal radiotherapy is increasingly being used to radically treat prostate cancer with encouraging results and minimal long-term toxicity, yet little is known regarding the response of normal or malignant prostate cells to ionizing radiation (IR). To clarify the basis for cell killing during prostate cancer radiotherapy, we determined the IR-induced expression of several apoptotic-(bax, bcl-2, survivin and PARP) and G1-cell cycle checkpoint-(p53 and p21 WAF1/Cip1 ) related proteins, in both normal (PrEC-epithelial and PrSC-stromal) and malignant (LNCaP, DU-145 and PC-3; all epithelial) prostate cells. For these experiments, we chose doses ranging from 2 to 10 Gy, to be representative of the 1.8 -2 Gy daily clinical fractions given during curative radiotherapy and the 8 -10 Gy single doses given in palliative radiotherapy. We observed that IR-induced bax and p21 WAF1/Cip1 protein expression were attenuated selectively in normal stromal and epithelial cell cultures, yet maintained their p53-dependency in malignant cell lines. For each cell culture, we also determined total apoptotic and overall radiation cell kill using a short-term nuclear morphologic assay and a long-term clonogenic survival assay, respectively. Clonogenic survival, as measured by the surviving fraction at 2 Gy (SF2), ranged from 0.05 (PrEC) to 0.55 (DU-145), suggesting that malignant prostate cells are more radioresistant than normal prostate cells, for this series. IR-induced apoptotic cell kill was minimal (less than 6% cell after a dose of 10 Gy at times of 24 -96 h) and was not dose-dependent. Furthermore, apoptotic kill was not correlated with either molecular apoptotic response or clonogenic cell kill. Using a flow cytometric proliferation assay with the PrSC (stromal) and representative cultures, we observed that a senescent-like phenotype (SLP) emerges within a sub-population of cells post-irradiation that is non-clonogenic. Terminal growth arrest was dose-responsive at 96 h following irradiation and associated with long-term expression of both p21 WAF1/Cip1 and p16 INK4a genes. Future strategies for prostate radiotherapy prediction or novel treatments should additionally focus on terminal growth arrest as an important endpoint in prostate cancer therapy.

“…For ZR-75-1 and H-466B cells, this global increase is, respectively, 41.4 and 41.5. Kao et al (2001) showed that DNA damage-induced G 2 delay was strongly associated with DNA repair activity in human cancer cells. We can hypothesize that, after irradiation, progesterone leads to the inhibition of the G 2 checkpoint that normally arrests the cell cycle and permits cells to repair DNA damage and/or to undergo apoptosis if the level of unrepaired DNA is too high.…”

Section: Discussionmentioning

confidence: 99%

Progesterone prevents radiation-induced apoptosis in breast cancer cells

Varès¹,

Ory²,

Lectard³

et al. 2004

Oncogene

Sex steroid hormones play an essential role in the control of homeostasis in the mammary gland. Although the involvement of progesterone in cellular proliferation and differentiation is well established, its exact role in the control of cell death still remains unclear. As dysregulation of the apoptotic process plays an important role in the pathogenesis of breast cancer, we investigated the regulation of apoptosis by progesterone in various breast cancer cell lines. Our results show that progesterone treatment protects against radiation-induced apoptosis. This prevention appears to be mediated by the progesterone receptor and is unrelated to p53 status. There is also no correlation with the intrinsic hormonal effect on cell proliferation, as the presence of cells in a particular phase of the cell cycle. Surprisingly, progesterone partly allows bypassing of the irradiation-induced growth arrest in G 2 /M in PgR þ cells, leading to an increase in cell proliferation after irradiation. One consequence of this effect is a higher rate of chromosome damage in these proliferating progesterone-treated cells compared to what is observed in untreated irradiated cells. We propose that progesterone, by inhibiting apoptosis and promoting the proliferation of cells with DNA damage, potentially facilitates the emergence of genetic mutations that may play a role in malignant transformation.