No abstract

Cancer cells are usually under higher oxidative stress compared with normal cells. We hypothesize that introducing additional reactive oxygen species (ROS) insults or suppressing antioxidant capacity may selectively enhance cancer cell killing by oxidative stress-generating agents through stress overload or stress sensitization, whereas normal cells may be able to maintain redox homeostasis under exogenous ROS by adaptive response. Here, we show that parthenolide, a sesquiterpene lactone, selectively exhibits a radiosensitization effect on prostate cancer PC3 cells but not on normal prostate epithelial PrEC cells. Parthenolide causes oxidative stress in PC3 cells but not in PrEC cells, as determined by the oxidation of the ROS-sensitive probe H 2 DCFDA and intracellular reduced thiol and disulfide levels. In PC3 but not PrEC cells, parthenolide activates NADPH oxidase, leading to a decrease in the level of reduced thioredoxin, activation of phosphoinositide 3-kinase/Akt, and consequent FOXO3a phosphorylation, which results in the downregulation of FOXO3a targets antioxidant enzyme manganese superoxide dismutase and catalase. Importantly, when combined with radiation, parthenolide further increases ROS levels in PC3 cells whereas it decreases radiation-induced oxidative stress in PrEC cells, possibly by increasing reduced glutathione levels. Together, the results show that parthenolide selectively activates NADPH oxidase and mediates intense oxidative stress in prostate cancer cells by both increasing ROS generation and decreasing antioxidant defense capacity. The results support the concept of exploiting the intrinsic differences in the redox status of cancer cells and normal cells as targets for selective cancer killing. Cancer Res; 70(7); 2880-90. ©2010 AACR.

The relationship between NF-jB and resistance to radiation treatment in many tumor cell types has been generally well recognized. However, which members of the NF-jB family contribute to radiation resistance is unclear.In the present study, we demonstrate that RelB plays an important radioprotective role in aggressive prostate cancer cells, in part by the induction of antioxidant and antiapoptotic manganese superoxide dismutase (MnSOD) gene. RelB is both constitutively present and is inducible by radiation in aggressive prostate cancer cells. Using ectopically expressed dominant negative inhibitor, p100 mutant, and the siRNA approach, we demonstrate that selective inhibition of RelB significantly decreases the levels of MnSOD resulting in a significant increase in the sensitivity of prostate cancer cells to radiation treatment. These results demonstrate that RelB plays an important role in redox regulation of the cell and protects aggressive prostate cancer cells against radiation-induced cell death. Thus, inhibition of RelB could be a novel mechanism to radiosensitize prostate cancer.

Because of the importance of ROS in the response of normal and cancer tissues to ionizing radiation, methods that differentially modulate the ROS scavenging ability of cells may prove to be an important method to increase the radiation response in cancer tissues and simultaneously mitigate the damaging effects of ionizing radiation on normal tissues. Altering the expression or activity of SODs may prove valuable in maximizing the overall effectiveness of ionizing radiation.

Based on the biological significance of the redox state, we postulate that this system could potentially be used to create a new avenue for targeted therapy, including the potential to incorporate personalized redox therapy for cancer treatment.

The nuclear factor-KB (NF-KB) classic pathway is thought to be critical for tumorigenesis, but little is known about the role of the NF-KB alternative pathway in cancer development. Recently, high constitutive nuclear levels of RelB have been observed in human prostate cancer specimens with high Gleason scores. Here, we used four complementary approaches to test whether RelB contributes to tumorigenicity of prostate cancer. Inhibiting RelB in aggressive androgenindependent PC-3 cells by stable or conditional expression of a dominant-negative p100 mutant significantly reduced the incidence and growth rate of tumors. The decrease in tumorigenicity coincided with a reduction in the NF-KB target interleukin-8 (IL-8). Consistently, down-regulation of RelB by small interfering RNA targeting also reduced tumor growth and decreased levels of IL-8. Conversely, stable expression of RelB in androgen-responsive LNCaP tumors increased the circulating IL-8 levels. Taken together, these results reveal a tumor-supportive role of RelB, implicate the NF-KB alternative pathway as a potential target for preventing prostate cancer, and suggest the use of IL-8 as a marker for prostate cancer prognosis. [Cancer Res 2009;69(8):3267-71]

Aberrant micro RNA (miRNA) expression has been implicated in the pathogenesis of cancer. Recent studies have shown that the miR-17-92 cluster is overexpressed in many types of cancer. The oncogenic function of mature miRNAs encoded by the miR-17–92 cluster has been identified from the 5′ arm of six precursors. However, the function of the miRNAs produced from the 3′ arm of these precursors remains unknown. The present study demonstrates that miR-17* is able to suppress critical primary mitochondrial antioxidant enzymes, such as manganese superoxide dismutase (MnSOD), glutathione peroxidase-2 (GPX2) and thioredoxin reductase-2 (TrxR2). Transfection of miR-17* into prostate cancer PC-3 cells significantly reduces levels of the three antioxidant proteins and activity of the luciferase reporter under the control of miR-17* binding sequences located in the 3′-untranslated regions of the three target genes. Disulfiram (DSF), a dithiolcarbomate drug shown to have an anticancer effect, induces the level of mature miR-17* and cell death in PCa cells, which can be attenuated by transfection of antisense miR-17*. Increasing miR-17* level in PC-3 cells by a Tet-on based conditional expression system markedly suppresses its tumorigencity. These results suggest that miR-17* may suppress tumorigenicity of prostate cancer through inhibition of mitochondrial antioxidant enzymes.

The aim of this investigation was to study crypt fission, a process which may be instrumental in regulating crypt number in the intestine. Young Holtzman rats were killed at various times after parturition and samples of the small intestine and colon were removed and processed. A microdissection technique was used to separate crypts from other structures. Crypts were scored as normal or fissioning. the percentage of crypts in fission (PCF) reached peak values of 25% and 52% in the small bowel and colon, respectively, at 21 days post‐parturition. From this time onward, the PCF dropped until the adult value of approximately 7% was reached in each site. During this same period, the number of crypts increased from 1.9 × 106 to 3.3 × 106 in the small bowel and 2.2 × 105 to 6.5 × 105 in the colon. Thus an inverse relationship between the percentage of crypts in fission and crypt number was found. Distribution of fissure heights in fissioning crypts did not change as the animal aged. the majority of the fissures were found in the lower 1/4 of the fissioning crypts. This suggests that as soon as the fissure extends beyond the stem cell zone, division into two crypts soon occurs.