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Wednesday, 4 April 2012

Cancer and Inflammation

Tumor heterogeneity is a confusing finding in the assessment of neoplasms, potentially resulting in inaccurate diagnostic, prognostic and predictive tests. This tumor heterogeneity is not always a random and unpredictable phenomenon, whose knowledge helps designing better tests. The biologic reasons for this intratumoral heterogeneity would then be important to understand both the natural history of neoplasms and the selection of test samples for reliable analysis. The main factors contributing to intratumoral heterogeneity inducing gene abnormalities or modifying its expression include: the gradient ischemic level within neoplasms, the action of tumor microenvironment (bidirectional interaction between tumor cells and stroma), mechanisms of intercellular transference of genetic information (exosomes), and differential mechanisms of sequence-independent modifications of genetic material and proteins. The intratumoral heterogeneity is at the origin of tumor progression and it is also the byproduct of the selection process during progression. Any analysis of heterogeneity mechanisms must be integrated within the process of segregation of genetic changes in tumor cells during the clonal expansion and progression of neoplasms. The evaluation of these mechanisms must also consider the redundancy and pleiotropism of molecular pathways, for which appropriate surrogate markers would support the presence or not of heterogeneous genetics and the main mechanisms responsible. This knowledge would constitute a solid scientific background for future therapeutic planning.

Cancer and Inflammation

Central to the development of cancer are genetic changes that endow these “cancer cells” with many of the hallmarks of cancer, such as self-sufficient growth and resistance to anti-growth and pro-death signals. However, while
1. the genetic changes that occur within cancer cells themselves, such as activated oncogenes or dysfunctional tumor suppressors, are responsible for many aspects of cancer development, they are not sufficient.
2. Tumor promotion and progression are dependent on ancillary processes provided by cells of the tumor environment but that are not necessarily cancerous themselves.

      Inflammation has long been associated with the development of cancer.

This review will discuss the reflexive relationship between cancer and inflammation with particular focus on how considering the role of inflammation in physiologic processes such as the maintenance of tissue homeostasis and repair may provide a logical framework for understanding the connection between the inflammatory response and cancer.

Tocotrienols: inflammation and cancer

Inflammation is an organism's response to environmental assaults. It can be classified as acute inflammation that leads to therapeutic recovery or chronic inflammation, which may lead to the development of cancer and other ailments. Genetic changes that occur within cancer cells themselves are responsible for many aspects of cancer development but are dependent on ancillary processes for tumor promotion and progression. Inflammation has long been associated with the development of cancer. The distinct characteristics of cancer cells to proliferate, metastasize, evade apoptotic signals, and develop chemoresistance have been linked to the inflammatory response. Due to the involvement of multiple genes and various pathways, current drugs that target single genes have not been effective in providing a therapeutic cure. On the other hand, natural products target multiple genes and therefore have better success compared to drugs. Tocotrienols, the potent isoforms of vitamin E, are such a natural product. This review will discuss the relationship between cancer and inflammation with particular focus on the roles played by NF-κB, STAT3, and COX-2.

Increasing evidence from epidemiological, preclinical and clinical studies suggests that dysregulated inflammatory response plays a pivotal role in a multitude of chronic ailments including cancer. The molecular mechanism(s) by which chronic inflammation drives cancer initiation and promotion include increased production of pro-inflammatory mediators, such as cytokines, chemokines, reactive oxygen intermediates, increased expression of oncogenes, COX-2 (cyclo-oxygenase-2), 5-LOX (5-lipoxygenase) and MMPs (matrix metalloproteinases), and pro-inflammatory transcription factors such as NF-κB (nuclear factor κB), STAT3 (signal transducer and activator of transcription 3), AP-1 (activator protein 1) and HIF-1α (hypoxia-inducible factor 1α) that mediate tumour cell proliferation, transformation, metastasis, survival, invasion, angiogenesis, chemoresistance and radioresistance. These inflammation-associated molecules are activated by a number of environmental and lifestyle-related factors including infectious agents, tobacco, stress, diet, obesity and alcohol, which together are thought to drive as much as 90% of all cancers. The present review will focus primarily on the role of various inflammatory intermediates responsible for tumour initiation and progression, and discuss in detail the critical link between inflammation and cancer.

Epidemiological and experimental evidence has emerged that a dysregulated inflammation is associated with most of the tumors. Recent studies have begun to unravel molecular pathways linking inflammation and cancer. The identification of transcription factors such as NF-kappaB, STAT3, HIF-1 alpha and their gene products such as COX-2, cytokines, chemokines and chemokine receptors have laid molecular foundation for the decisive role of inflammation in carcinogenesis. Inflammation contributes to survival and proliferation of malignant cells, tumor angiogenesis, metastasis and reduced response to chemotherapy. In view of their involvement at different stages of tumor development, inflammatory pathways represent attractive targets for cancer prevention and therapy. However, advances in this field have not been fully realized, and challenge remains to obtain clinical data from patients and then to utilize this information for optimal and personalized therapy. We present evidence that targeting inflammatory pathways have a potential role to improve chemotherapy of cancer.

Chronic infections, obesity, alcohol, tobacco, radiation, environmental pollutants, and high-calorie diet have been recognized as major risk factors for the most common types of cancer. All these risk factors are linked to cancer through inflammation. Although acute inflammation that persists for short-term mediates host defense against infections, chronic inflammation that lasts for long term can predispose the host to various chronic illnesses, including cancer. Linkage between cancer and inflammation is indicated by numerous lines of evidence; first, transcription factors nuclear factor-kappaB (NF-kappaB) and signal transducers and activators of transcription 3 (STAT3), two major pathways for inflammation, are activated by most cancer risk factors; second, an inflammatory condition precedes most cancers; third, NF-kappaB and STAT3 are constitutively active in most cancers; fourth, hypoxia and acidic conditions found in solid tumors activate NF-kappaB; fifth, chemotherapeutic agents and gamma-irradiation activate NF-kappaB and lead to chemoresistance and radioresistance; sixth, most gene products linked to inflammation, survival, proliferation, invasion, angiogenesis, and metastasis are regulated by NF-kappaB and STAT3; seventh, suppression of NF-kappaB and STAT3 inhibits the proliferation and invasion of tumors; and eighth, most chemopreventive agents mediate their effects through inhibition of NF-kappaB and STAT3 activation pathways. Thus, suppression of these proinflammatory pathways may provide opportunities for both prevention and treatment of cancer

Evidence has emerged in the last two decades that at the molecular level most chronic diseases, including cancer, are caused by a dysregulated inflammatory response. The identification of transcription factors such as NF-kB, AP-1 and STAT3 and their gene products such as tumor necrosis factor, interleukin-1, interleukin-6, chemokines, cyclooxygenase-2, 5 lipooxygenase, matrix metalloproteases, and vascular endothelial growth factor, adhesion molecules and others have provided the molecular basis for the role of inflammation in cancer. These inflammatory pathways are activated by tobacco, stress, dietary agents, obesity, alcohol, infectious agents, irradiation, and environmental stimuli, which together account for as much as 95% of all cancers. These pathways have been implicated in transformation, survival, proliferation, invasion, angiogenesis, metastasis, chemoresistance, and radioresistance of cancer, so much so that survival and proliferation of most types of cancer stem cells themselves appear to be dependent on the activation of these inflammatory pathways. Most of this evidence, however, is from preclinical studies. Whether these pathways have any role in prevention, progression, diagnosis, prognosis, recurrence or treatment of cancer in patients, is the topic of discussion of this review. We present evidence that inhibitors of inflammatory biomarkers may have a role in both prevention and treatment of cancer.

Both historically and contemporarily, cancer is seen as an inflammatory process. Evidence has emerged in the last two decades that at the molecular level most chronic diseases, including cancer, are caused by a dysregulated inflammatory response. The identification of transcription factors such as nuclear factor-kappa B and signal transducer and activator of transcription 3 and their gene products such as tumor necrosis factor, interleukin-1, interleukin-6, chemokines, cyclooxygenase-2, and vascular endothelial growth factor, adhesion molecules and others has provided the molecular basis for the role of inflammation in cancer. Tumor initiation, its progression and metastasis and the failure of immune suppression of tumors all can be attributed in part to chronic and systemic inflammation. Chinese herbs have a long history in both treatment of cancer and suppression of inflammation. This paper looks at recent research on cancer and inflammation and Chinese herbs and compounds, which can be used in the treatment of cancer

Both inflammation and angiogenesis are exacerbated by increased production of chemokines/cytokines, growth factors, proteolytic enzymes, proteoglycans, lipid mediators and prostaglandins. It has been reported that approximately 15-20% of all malignancies are initiated or exacerbated by inflammation. Initiation and progression of cancer are also closely linked to angiogenesis. Infiltration of macrophages is a dramatic and common feature of inflammation, angiogenesis and cancer, and has been recently highlighted in an attempt to develop novel strategies for treating cancer. The recruitment and infiltration of macrophages in the tumor microenvironment activates them to support the malignant progression of cancer cells, and these macrophages are called tumor-associated macrophages. In a model of experimental angiogenesis using mouse corneas, macrophages infiltrated tissue in response to inflammatory cytokines and produced chemokines and angiogenesis-promoting factors, such as vascular endothelial growth factor-A, interleukin-8, matrix metalloproteinases, prostanoids and reactive oxygen species. Moreover, in a cancer xenograft model, inflammatory stimuli by a representative inflammatory cytokine, interleukin-1beta, enhanced tumor growth and angiogenesis with infiltration and activation of macrophages. Co-culture of cancer cells with macrophages synergistically stimulated production of various angiogenesis-related factors when stimulated by the inflammatory cytokine. This inflammatory angiogenesis in both mouse cornea and a tumor model was mediated, in part, by activation of nuclear factor kappaB and activator protein 1 (Jun/Fos). Administration of either nuclear factor kappaB-targeting drugs or cyclooxygenase 2 inhibitors or depletion of macrophages could block both inflammatory angiogenesis and tumor angiogenesis. Thus, both inflammatory and angiogenic responses in tumor stroma could be targets for development of anticancer therapeutic drugs.

J Nucleic Acids. 2011;2011:102431. Epub 2011 Aug 10.
It is now well established that inflammation is associated with the induction or the aggravation of nearly 25% of cancers. Therefore, the above microRNAs are thought to link inflammation and cancer.  Recently, resveratrol (trans-3,4',5-trihydroxystilbene), a natural polyphenol with antioxidant, anti-inflammatory, and anticancer properties, currently at the stage of preclinical studies for human cancer prevention, has been shown to induce the expression of miR-663, a tumor-suppressor and anti-inflammatory microRNA, while downregulating miR-155 and miR-21. In this paper we will discuss how the use of resveratrol in therapeutics may benefit from the preanalyses on the status of expression of miR-155 or miR-21 as well as of TGFβ1. In addition, we will discuss how resveratrol activity might possibly be enhanced by simultaneously manipulating the levels of its key target microRNAs, such as miR-663.

Int J Cancer. 2007 Dec 1;121(11):2373-80.

Infection and chronic inflammation contribute to about 1 in 4 of all cancer cases. Mediators of the inflammatory response, e.g., cytokines, free radicals, prostaglandins and growth factors, can induce genetic and epigenetic changes including point mutations in tumor suppressor genes, DNA methylation and post-translational modifications, causing alterations in critical pathways responsible for maintaining the normal cellular homeostasis and leading to the development and progression of cancer. Recent discovery of an interaction between microRNAs and innate immunity during inflammation has further strengthened the association between inflammation and cancer