Chronic inflammation and cancer: the role of the mitochondria.

Accumulating evidence shows that chronic inflammation can promote all stages of tumorigenesis, including DNA damage, limitless replication, apoptosis evasion, sustained angiogenesis, self-sufficiency in growth signaling, insensitivity to anti-growth signaling, and tissue invasion/metastasis. Chronic inflammation is triggered by environmental (extrinsic) factors (eg, infection, tobacco, asbestos) and host mutations (intrinsic) factors (eg, Ras, Myc, p53). Extensive investigations over the past decade have uncovered many of the important mechanistic pathways underlying cancer-related inflammation. However, the precise molecular mechanisms involved and the interconnecting crosstalk between pathways remain incompletely understood. We review the evidence implicating a strong association between chronic inflammation and cancer, with an emphasis on colorectal and lung cancer. We summarize the current knowledge of the important molecular and cellular pathways linking chronic inflammation to tumorigenesis. Specifically, we focus on the role of the mitochondria in coordinating life- and death-signaling pathways crucial in cancer-related inflammation. Activation of Ras, Myc, and p53 cause mitochondrial dysfunction, resulting in mitochondrial reactive oxygen species (ROS) production and downstream signaling (eg, NFkappaB, STAT3, etc.) that promote inflammation-associated cancer. A recent murine transgenic study established that mitochondrial metabolism and ROS production are necessary for K-Ras-induced tumorigenicity. Collectively, inflammation-associated cancers resulting from signaling pathways coordinated at the mitochondrial level are being identified that may prove useful for developing innovative strategies for both cancer prevention and cancer treatment.

Quality of reporting of serious adverse drug events to an institutional review board: a case study with the novel cancer agent, imatinib mesylate.

PURPOSE: Serious adverse drug event (sADE) reporting to Institutional Review Boards (IRB) is essential to ensure pharmaceutical safety. However, the quality of these reports has not been studied. Safety reports are especially important for cancer drugs that receive accelerated Food and Drug Administration approval, like imatinib, as preapproval experience with these drugs is limited. We evaluated the quality, accuracy, and completeness of sADE reports submitted to an IRB. EXPERIMENTAL DESIGN: sADE reports submitted to an IRB from 14 clinical trials with imatinib were reviewed. Structured case report forms, containing detailed clinical data fields and a validated causality assessment instrument, were developed. Two forms were generated for each ADE, the first populated with data abstracted from the IRB reports, and the second populated with data from the corresponding clinical record. Completeness and causality assessments were evaluated for each of the two sources, and then compared. Accuracy (concordance between sources) was also assessed. RESULTS: Of 115 sADEs reported for 177 cancer patients to the IRB, overall completeness of adverse event descriptions was 2.4-fold greater for structured case report forms populated with information from the clinical record versus the corresponding forms from IRB reports (95.0% versus 40.3%, P < 0.05). Information supporting causality assessments was recorded 3.5-fold more often in primary data sources versus IRB adverse event descriptions (93% versus 26%, P < 0.05). Some key clinical information was discrepant between the two sources. CONCLUSIONS: The use of structured syndrome-specific case report forms could enhance the quality of reporting to IRBs, thereby improving the safety of pharmaceuticals administered to cancer patients.

Evaluation of serious adverse drug reactions: a proactive pharmacovigilance program (RADAR) vs safety activities conducted by the Food and Drug Administration and pharmaceutical manufacturers.

BACKGROUND: The Food and Drug Administration (FDA) and pharmaceutical manufacturers conduct most postmarketing pharmaceutical safety investigations. These efforts are frequently based on data mining of databases. In 1998, investigators initiated the Research on Adverse Drug events And Reports (RADAR) project to investigate reports of serious adverse drug reactions (ADRs) and prospectively obtain information on these cases. We compare safety efforts for evaluating serious ADRs conducted by the FDA and pharmaceutical manufacturers vs the RADAR project. METHODS: We evaluated the completeness of serious ADR descriptions in the FDA and RADAR databases and the comprehensiveness of notifications disseminated by pharmaceutical manufacturers and the RADAR investigators. A serious ADR was defined as an event that led to death or required intensive therapies to reverse. RESULTS: The RADAR investigators evaluated 16 serious ADRs. Compared with descriptions of these ADRs in FDA databases (2296 reports), reports in RADAR databases (472 reports) had a 2-fold higher rate of including information on history and physical examination (92% vs 45%; P<.001) and a 9-fold higher rate of including basic science findings (34% vs 4%; P = .08). Safety notifications were disseminated earlier by pharmaceutical suppliers (2 vs 4 years after approval, respectively), although notifications were less likely to include information on incidence (46% vs 93%; P = .02), outcomes (8% vs 100%; P<.001), treatment or prophylaxis (25% vs 93%; P<.001), or references (8% vs 80%; P<.001). CONCLUSION: Proactive safety efforts conducted by the RADAR investigators are more comprehensive than those conducted by the FDA and pharmaceutical manufacturers, but dissemination of related safety notifications is less timely.

P53 mediates amosite asbestos-induced alveolar epithelial cell mitochondria-regulated apoptosis.

Asbestos causes pulmonary toxicity in part by generating reactive oxygen species that cause DNA damage. We previously showed that the mitochondria-regulated (intrinsic) death pathway mediates alveolar epithelial cell (AEC) DNA damage and apoptosis. Because p53 regulates the DNA damage response in part by inducing intrinsic cell death, we determined whether p53-dependent transcriptional activity mediates asbestos-induced AEC mitochondrial dysfunction and apoptosis. We show that inhibitors of p53-dependent transcriptional activation (pifithrin and type 16-E6 protein) block asbestos-induced AEC mitochondrial membrane potential change (DeltaPsim), caspase 9 activation, and apoptosis. We demonstrate that asbestos activates p53 promoter activity, mRNA levels, protein expression, and Bax and p53 mitochondrial translocation. Further, pifithrin, E6, phytic acid, or rho(0)-A549 cells (cells incapable of mitochondrial reactive oxygen species production) block asbestos-induced p53 activation. Finally, we show that asbestos augments p53 expression in cells at the bronchoalveolar duct junctions of rat lungs and that phytic acid prevents this. These data suggest that p53-dependent transcription pathways mediate asbestos-induced AEC mitochondria-regulated apoptosis. This suggests an important interactive effect between p53 and the mitochondria in the pathogenesis of asbestos-induced pulmonary toxicity that may have broader implications for our understanding of pulmonary fibrosis and lung cancer.

Clostridium perfringens enterotoxin elicits rapid and specific cytolysis of breast carcinoma cells mediated through tight junction proteins claudin 3 and 4.

Clostridium perfringens enterotoxin (CPE) induces cytolysis very rapidly through binding to its receptors, the tight junction proteins CLDN 3 and 4. In this study, we investigated CLDN 3 and 4 expression in breast cancer and tested the potential of CPE-mediated therapy. CLDN 3 and 4 proteins were detected in all primary breast carcinomas tested (n = 21) and, compared to normal mammary epithelium, were overexpressed in approximately 62% and 26%, respectively. Treatment of breast cancer cell lines in culture with CPE resulted in rapid and dose-dependent cytolysis exclusively in cells that expressed CLDN 3 and 4. Intratumoral CPE treatment of xenografts of T47D breast cancer cells in immunodeficient mice resulted in a significant reduction in tumor volume (P = 0.007), with accompanying necrosis. Necrotic reactions were also seen in three freshly resected primary breast carcinoma samples treated with CPE for 12 hours, while isolated primary breast carcinoma cells underwent rapid and complete cytolysis within 1 hour. Thus, expression of CLDN 3 and 4 sensitizes primary breast carcinomas to CPE-mediated cytolysis and emphasizes the potential of CPE in breast cancer therapy.

Mitochondrial-derived free radicals mediate asbestos-induced alveolar epithelial cell apoptosis.

Asbestos causes pulmonary toxicity by mechanisms that in part involve reactive oxygen species (ROS). However, the precise source of ROS is unclear. We showed that asbestos induces alveolar epithelial cell (AEC) apoptosis by a mitochondrial-regulated death pathway. To determine whether mitochondrial-derived ROS are necessary for causing asbestos-induced AEC apoptosis, we utilized A549-rho(omicron) cells that lack mitochondrial DNA and a functional electron transport. As expected, antimycin, which induces an oxidative stress by blocking mitochondrial electron transport at complex III, increased dichlorofluoroscein (DCF) fluorescence in A549 cells but not in A549-rho(omicron) cells. Compared with A549 cells, rho(omicron) cells have less asbestos-induced ROS production, as assessed by DCF fluorescence, and reductions in total glutathione levels as well as less caspase-9 activation and apoptosis, as assessed by TdT-mediated dUTP nick end labeling staining and DNA fragmentation. A mitochondrial anion channel inhibitor that prevents ROS release from the mitochondria to the cytoplasm also blocked asbestos-induced A549 cell caspase-9 activation and apoptosis. Finally, a role for nonmitochondrial-derived ROS with exposure to high levels of asbestos (50 microg/cm(2)) was suggested by our findings that an iron chelator (phytic acid or deferoxamine) or a free radical scavenger (sodium benzoate) provided additional protection against asbestos-induced caspase-9 activation and DNA fragmentation in rho(omicron) cells. We conclude that asbestos fibers affect mitochondrial DNA and functional electron transport, resulting in mitochondrial-derived ROS production that in turn mediates AEC apoptosis. Nonmitochondrial-associated ROS may also contribute to AEC apoptosis, particularly with high levels of asbestos exposure.

The mitochondria-regulated death pathway mediates asbestos-induced alveolar epithelial cell apoptosis.

The mechanisms underlying asbestos-induced pulmonary toxicity are not fully understood. Alveolar epithelial cell (AEC) apoptosis by iron-derived reactive oxygen species (ROS) is one important mechanism implicated. The two major pathways regulating apoptosis include (i) the mitochondrial death (intrinsic) pathway caused by DNA damage, and (ii) the plasma-membrane death receptor (extrinsic) pathway. However, it is unknown whether asbestos activates either death pathway in AEC. We determined whether asbestos triggers AEC mitochondrial dysfunction by exposing cells (A549 and rat alveolar type II) to amosite asbestos and assessing mitochondrial membrane potential changes (deltapsi(m)) using a fluorometric technique involving tetremethylrhodamine ethyl ester (TMRE) and mitotracker green. Unlike inert particulates (titanium dioxide and glass beads), amosite asbestos caused dose- and time-dependent reductions in deltapsi(m). Asbestos-induced deltapsi(m) was associated with the release of cytochrome c from the mitochondria to the cytoplasm as well as activation of caspase 9, a mitochondrial-activated caspase. In contrast, a lower level of caspase 8, the death receptor-activated caspase, was detected in asbestos-exposed AEC. An iron chelator (phytic acid or deferoxamine) or a hydroxyl radical scavenger (sodium benzoate) each blocked asbestos-induced reductions in deltapsi(m) and caspase 9 activation, suggesting a role for iron-derived ROS. Finally, Bcl-X(L), a mitochondrial antiapoptotic protein that prevents cell death by preserving the outer mitochondrial membrane integrity, blocked asbestos-induced decreases in A549 cell deltapsi(m) and reduced apoptosis as assessed by DNA fragmentation. We conclude that asbestos-induced AEC apoptosis results from mitochondrial dysfunction, in part due to iron-derived ROS, which is followed by the release of cytochrome c and caspase 9 activation. Our findings suggest an important role for the mitochondria-regulated death pathway in the pathogenesis of asbestos-associated pulmonary toxicity.

Asbestos-induced alveolar epithelial cell apoptosis: role of mitochondrial dysfunction caused by iron-derived free radicals.

Asbestos causes asbestosis and malignancies by mechanisms that are not fully understood. Alveolar epithelial cell (AEC) injury by iron-derived reactive oxygen species (ROS) is one important mechanism implicated. We previously showed that iron-catalyzed ROS in part mediate asbestos-inducedAEC DNA damage and apoptosis. Mitochondria have a critical role in regulating apoptosis after exposure to agents causing DNA damage but their role in regulating asbestos-induced apoptosis is unknown. To determine whether asbestos causes AEC mitochondrial dysfunction, we exposed A549 cells to amosite asbestos and assessed mitochondrial membrane potential changes (delta(psi)m) using a fluorometric technique involving tetremethylrhodamine ethyl ester (TMRE) and mitotracker green. We show that amosite asbestos, but not an inert particulate, titanium dioxide, reduces delta(psi)m after a 4 h exposure period. Further, the delta(psi)m after 4 h was inversely proportional to the levels of apoptosis noted at 24 h as assessed by nuclear morphology as well as by DNA nucleosome formation. A role for iron-derived ROS was suggested by the finding that phytic acid, an iron chelator, blocked asbestos-induced reductions in A549 cell delta(psi)m and attenuated apoptosis. Finally, overexpression of Bcl-xl, an anti-apoptotic protein that localizes to the mitochondria, prevented asbestos-induced decreases in A549 cell delta(psi)m after 4 h and diminished apoptosis. We conclude that asbestos alters AEC mitochondrial function in part by generating iron-derived ROS, which in turn can result in apoptosis. This suggests that the mitochondrial death pathway is important in regulating pulmonary toxicity from asbestos.

Chronic inflammation and cancer.

A substantial body of evidence supports the conclusion that chronic inflammation can predispose an individual to cancer, as demonstrated by the association between chronic inflammatory bowel diseases and the increased risk of colon carcinoma. Chronic inflammation is caused by a variety of factors, including bacterial, viral, and parasitic infections, chemical irritants, and nondigestible particles. The longer the inflammation persists, the higher the risk of associated carcinogenesis. This review describes some of the underlying causes of the association between chronic inflammation and cancer. Inflammatory mediators contribute to neoplasia by inducing proneoplastic mutations, adaptive responses, resistance to apoptosis, and environmental changes such as stimulation of angiogenesis. All these changes confer a survival advantage to a susceptible cell. In this article, we discuss the contribution of reactive oxygen and nitrogen intermediates, prostaglandins, and inflammatory cytokines to carcinogenesis. A thorough understanding of the molecular basis of inflammation-associated neoplasia and progression can lead to novel approaches to the prevention and treatment of cancer.