No abstract

The peroxisome proliferator-activated receptor gamma (PPARγ) plays an important role in vascular regulation. However, the impact of oxidative stress on PPARγ expression and activity has not been clearly defined. Human umbilical vein endothelial cells (HUVECs) were exposed to graded concentrations of H 2 O 2 for 0.5-72 h, or bovine aortic endothelial cells (BAECs) were exposed to alterations in extracellular thiol/disulfide redox potential (E h ) of the cysteine (Cys)/cystine (CySS) couple. Within 2 h, H 2 O 2 reduced HUVEC PPARγ mRNA and activity and reduced the expression of two PPARγ-regulated genes without altering PPARγ protein levels. After 4 h H 2 O 2 exposure, mRNA levels remained reduced while PPARγ activity returned to control levels. PPARγ mRNA levels remained depressed for up to 72 h after exposure to H 2 O 2 , without any change in PPARγ activity. Catalase prevented H 2 O 2 -induced reductions in PPARγ mRNA and activity. H 2 O 2 1) reduced luciferase expression in HUVECs transiently transfected with a human PPARγ promoter reporter, 2) failed to alter PPARγ mRNA half-life, and 3) transiently increased expression and activity of c-Fos and phospho-c-Jun. Treatment with the AP-1 inhibitor, curcumin, prevented H 2 O 2 -mediated reductions in PPARγ expression. In addition, media having an oxidized E h reduced BAEC PPARγ mRNA and activity. These findings demonstrate that oxidative stress, potentially through activation of inhibitory redox-regulated transcription factors, attenuates PPARγ expression and activity in vascular endothelial cells through suppression of PPARγ transcription.

Purpose: X-ray therapy (XRT) remains one of the major modalities used to treat patients diagnosed with locally advanced pancreatic adenocarcinoma. However, the effect of XRT on metastatic tumors outside the field of irradiation (abscopal effect) remains largely unknown. In the current study, we examined the effect of XRT alone and in combination with capecitabine and/or celecoxib in both irradiated and lead-shielded contralateral BxPC-3 pancreatic cancer xenografts. This chemoradiation regimen was chosen based on our molecular analysis of pancreatic adenocarcinoma. Experimental Design: Athymic mice were injected bilaterally with BxPC-3 cells and treatment was initiated 28 days postimplant. During XRT (2 Gy for 5 consecutive days, administered on days 0 and 24), one flank was irradiated whereas the rest of the body (including the contralateral tumor) was lead shielded. Capecitabine (350 mg/kg) was administered on days 0 to 13 and 24 to 37. Celecoxib was initiated in the diet at 100 ppm (equivalent to 20 mg/kg/d p.o.) and administered throughout the study. Results: In irradiated xenografts, capecitabine and XRT showed synergistic anitiumor efficacy (P = 0.008), which was further improved with the addition of celecoxib (P < 0.001). In contralateral shielded xenografts, abscopal effects were observed. Whereas monotherapy with XRT showed significant reduction in tumor area in irradiated xenografts, growth was promoted by 23% (P < 0.001) in contralateral lead-shielded tumors in the same animals relative to untreated tumors. Interestingly, synergistic antiproliferative efficacy occurred in these contralateral tumors when capecitabine was administered (P < 0.001), despite being outside the irradiated field. The addition of celecoxib further inhibited tumor growth (P < 0.001). This trimodal combination most effectively stabilized disease in both shielded and irradiated tumors; however, tumor eradication was not observed. There were no significant changes in thymidine phosphorylase, dihydropyrimidine dehydrogenase, or cyclooxygenase-2 mRNA levels in irradiated or lead-shielded tumors, suggesting that efficacy cannot be predicted solely from these previously identified indicators of response. Immunohistochemistry examining the proliferation marker Ki-67 showed concordance with tumor response in both irradiated and contralateral shielded xenografts. Conclusions:These results have implications in the rational design of treatment paradigms for pancreatic cancer where metastatic disease remains the primary cause of patient morbidity and abscopal effects in tumors outside the field of irradiation may affect tumor response.Pancreatic cancer, the fourth leading cause of cancer mortality in the United States (1, 2), is characterized by an unusual resistance to both radiation [X-ray therapy (XRT)] and chemotherapy. Despite highly aggressive therapeutic approaches, the overall median survival of 3 to 5 months and a 5-year survival rate of 0.4% to 3% have not appreciably changed in the last 80 years (3). Surgery remains the ...