DeeDee Smart

SIRT2 Interacts with β-Catenin to Inhibit Wnt Signaling Output in Response to Radiation-Induced Stress

Wnt signaling is critical to maintaining cellular homeostasis via regulation of cell division, mitigation of cell stress, and degradation. Aberrations in Wnt signaling contribute to carcinogenesis and metastasis, whereas sirtuins have purported roles in carcinogenesis, aging, and neurodegeneration. Therefore, the hypothesis that sirtuin 2 (SIRT2) directly interacts with β-catenin and whether this interaction alters the expression of Wnt target genes to produce an altered cellular phenotype was tested. Coimmunoprecipitation studies, using mouse embryonic fibroblasts (MEF) from Sirt2 wild-type and genomic knockout mice, demonstrate that β-catenin directly binds SIRT2. Moreover, this interaction increases in response to oxidative stress induced by ionizing radiation. In addition, this association inhibits the expression of important Wnt target genes such as survivin (BIRC5), cyclin D1 (CCND1), and c-myc (MYC). In Sirt2 null MEFs, an upregulation of matrix metalloproteinase 9 (MMP9) and decreased E-cadherin (CDH1) expression is observed that produces increased cellular migration and invasion. Together, these data demonstrate that SIRT2, a tumor suppressor lost in multiple cancers, inhibits the Wnt signaling pathway in nonmalignant cells by binding to β-catenin and that SIRT2 plays a critical role in the response to oxidative stress from radiation. Implications: Disruption of the SIRT2–β-catenin interaction represents an endogenous therapeutic target to prevent transformation and preserve the integrity of aging cells against exogenous stressors such as reactive oxygen species. Mol Cancer Res; 12(9); 1244–53. ©2014 AACR.

Thermal stress and the disruption of redox-sensitive signalling and transcription factor activation: possible role in radiosensitization

In spite of ongoing research efforts, the specific mechanism(s) of heat-induced alterations in the cellular response to ionizing radiation (IR) remain ambiguous, in part because they likely involve multiple mechanisms and potential targets. One such group of potential targets includes a class of cytoplasmic signalling and/or nuclear transcription factors known as immediate early response genes, which have been suggested to perform cytotoxic as well as cytoprotective roles during cancer therapy. One established mechanism regulating the activity of these early response elements involves changes in cellular oxidation/reduction (redox) status. After establishing common alterations in early response genes by oxidative stress and heat exposure, one could infer that heat shock may have similarities to other forms of environmental antagonists that induce oxidative stress. In this review, recent evidence supporting a mechanistic link between heat shock and oxidative stress will be summarized. In addition, the hypothesis that one mechanism whereby heat shock alters cellular responses to anticancer agents (including hyperthermic radiosensitization) is through heat-induced disruption of redox-sensitive signalling factors will be discussed.

Radiation-Induced Alteration of the Brain Proteome: Understanding the Role of the Sirtuin 2 Deacetylase in a Murine Model

Whole brain radiotherapy (WBRT) produces unwanted sequelae, albeit via unknown mechanisms. A deacetylase expressed in the central nervous system, Sirtuin 2 (SIRT2), has been linked to neurodegeneration. Therefore, we sought to challenge the notion that a single disease pathway is responsible for radiation-induced brain injury in Sirt2 wild-type (WT) and knockout (KO) mice at the proteomic level. We utilized isobaric tag for relative and absolute quantitation to analyze brain homogenates from Sirt2 WT and KO mice with and without WBRT. Selected proteins were independently verified, followed by ingenuity pathway analysis. Canonical pathways for Huntington’s, Parkinson’s, and Alzheimer’s were acutely affected by radiation within 72 h of treatment. Although loss of Sirt2 preferentially affected both Huntington’s and Parkinson’s pathways, WBRT most significantly affected Huntington’s-related proteins in the absence of Sirt2. Identical protein expression patterns were identified in Mog following WBRT in both Sirt2 WT and KO mice, revealing a proteomic radiation signature; however, long-term radiation effects were found to be associated with altered levels of a small number of key neurodegeneration-related proteins, identified as Mapt, Mog, Snap25, and Dnm1. Together, these data demonstrate the principle that the presence of Sirt2 can have significant effects on the brain proteome and its response to ionizing radiation.

Radiation Toxicity in the Central Nervous System: Mechanisms and Strategies for Injury Reduction

The potential for radiation-induced toxicities in the brain produces significant anxiety, both among patients receiving radiation therapy and those radiation oncologists providing treatment. These concerns often play a significant role in the medical decision-making process for most patients with diseases in which radiotherapy may be a treatment consideration. Although the precise mechanisms of neurotoxicity and neurodegeneration after ionizing radiation exposure continue to be poorly understood from a biological perspective, there is an increasing body of scientific and clinical literature that is producing a better understanding of how radiation causes brain injury; factors that determine whether toxicities occur; and potential preventative, treatment, and mitigation strategies for patients at high risk or with symptoms of injury. This review will focus primarily on injuries and biological processes described in mature brain.

Radioprotection as a Method to Enhance the Therapeutic Ratio of Radiotherapy

Radiotherapy is a commonly used local and regional treatment for cancer. Although important advances in radiation treatment delivery have been made in recent years, normal tissue damage remains a major cause of toxicity from radiotherapy and chemoradiotherapy regimens. Efforts to reduce normal tissue injury have included technical improvements to minimize normal tissue exposure to high doses of irradiation. Extensive preclinical research and a growing field of clinical research are focusing on the development of agents to protect normal tissues from the deleterious effects of irradiation. In this review, we discuss the characteristics of these agents, the research required to translate these agents into clinical trials, and highlight some challenges and successes in these efforts.

Differentiating pseudoprogression from true progression: analysis of radiographic, biologic, and clinical clues in GBM

IntroductionPseudoprogression (PsP) is a diagnostic dilemma in glioblastoma (GBM) after chemoradiotherapy (CRT). Magnetic resonance imaging (MRI) features may fail to distinguish PsP from early true progression (eTP), however clinical findings may aid in their distinction.MethodsSixty-seven patients received CRT for GBM between 2003 and 2016, and had pre- and post-treatment imaging suitable for retrospective evaluation using RANO criteria. Patients with signs of progression within the first 12-weeks post-radiation (P-12) were selected. Lesions that improved or stabilized were defined as PsP, and lesions that progressed were defined as eTP.ResultsThe median follow up for all patients was 17.6 months. Signs of progression developed in 35/67 (52.2%) patients within P-12. Of these, 20/35 (57.1%) were subsequently defined as eTP and 15/35 (42.9%) as PsP. MRI demonstrated increased contrast enhancement in 84.2% of eTP and 100% of PsP, and elevated CBV in 73.7% for eTP and 93.3% for PsP. A decrease in FLAIR was not seen in eTP patients, but was seen in 26.7% PsP patients. Patients with eTP were significantly more likely to require increased steroid doses or suffer clinical decline than PsP patients (OR 4.89, 95% CI 1.003–19.27; p = 0.046). KPS declined in 25% with eTP and none of the PsP patients.ConclusionsMRI imaging did not differentiate eTP from PsP, however, KPS decline or need for increased steroids was significantly more common in eTP versus PsP. Investigation and standardization of clinical assessments in response criteria may help address the diagnostic dilemma of pseudoprogression after frontline treatment for GBM.

Radiation and Altering Clinical Pharmacology

Ionizing radiation is a widely used therapeutic option in both curative and palliative cancer treatments, as well as in specialized benign conditions. Because the majority of cancer patients will receive radiation at some point in their treatment course, and because radiation is often given concurrently or sequentially with chemotherapy, it is critically important to understand the biology of how ionizing radiation affects tumor cells as well as normal tissue, how pharmacotherapy may alter the effectiveness of radiation, and how radiotherapy may augment standard pharmacologic interventions.

Abstract 1682: Radiation-induced autophagy is dependent on Sirtuin 3.

Sirtuin family members (Sirtuin 1 to 7) are highly conserved proteins, both structurally and functionally, and have either NAD+ dependent enzymatic activity (Sirtuin 1,2, 3, 5 and 7) for deacetylation of proteins or ADP ribosyl transferase activity (Sirtuin 4 and 6). Their functions in metabolic processes and chromatin remodeling have been conserved throughout evolution. Sirtuin 1 and Sirtuin 2 have been shown to be linked with several neurological disorders. The role of other Sirtuins in neurodegenerative disorders is not known. Radiation therapy (RT), one of the preferred and widely accepted treatments for intracranial primary and secondary metastatic tumors, may lead to long-term irreversible neurotoxicity in susceptible individuals with cognitive dysfunction similar to that observed in other neurodegenerative disorders. There are ample data which demonstrate that aberrant autophagic process and dysfunctional mitochondria are important factors leading to several neurological diseases, such as Huntington9s disease and Parkinson9s dementia. Among the Sirtuins, Sirtuin 3, 4 and 5 are localized within mitochondria, however, their role in radiation-induced neurotoxicity has not been evaluated. Using Sirtuin 3 knockout (KO) mice generated through genomic deletion allowed us the opportunity to study its role in autophagy and mitochondrial function during exposure to radiation. Preliminary reports show Sirtuin 3 in the adult mouse brain to be localized primarily within hippocampus and subcortical plate. Through flow cytometry and immunofluorescence stainin of mouse embryonic fibroblasts (MEFs) derived from Sirtuin 3 KO mice, we demonstrate that loss of Sirtuin 3 alters rates of basal autophagy. Furthermore, immunoblot analysis of autophagic marker LC3B I I 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1682. doi:10.1158/1538-7445.AM2013-1682

Radiation Therapy of CNS Metastases

Radiation treatment of central nervous system (CNS) metastases, particularly brain metastasis, is changing. The role of radiation for intraaxial disease was originally limited to palliation. However, now there is an increasing expectation by both patients and physicians to integrate radiotherapy in an overall strategy for eradication of disease. Recent innovations in radiobiology and technical advances in radiotherapy have proven beneficial to many extracranial sites. Nevertheless, these advances have lagged behind in the treatment of brain and spinal metastases and have not kept pace with changing expectations. We aim to explain the scientific basis of radiotherapy for CNS metastasis, current treatment options and techniques, controversies, and future goals for potential improvement.

Abstract 4354: Proteomic analysis of acute radiation response following whole brain irradiation: Is Sirt2 a key player of radiation-induced neurotoxicity

Radiation therapy (RT) is one of the most effective and widely used treatments of both primary and metastatic intracranial tumors. Recent technical advances in RT and multimodality approach to treatment have increased the life span of patients. However, a major concern remains as to radiation9s effect on long term neurotoxicity and cognitive impairment. Acute and sub acute effects of RT following whole brain RT appear to be reversible, but we hypothesize that these acute changes provide a platform for alteration of the central nervous system (CNS) microenvironment that is responsible for delayed irreversible neurotoxicity. To improve the quality of life of patients and to improve efficacy of whole brain RT, we require effective and targeted approaches to minimize cognitive dysfunction. In order to understand the acute molecular events involved after RT and to identify potential markers that lead to long-term neurotoxicity and dementia, we performed quantitative mass spectroscopy using the iTRAQ (isobaric tag of relative and absolute quantitation) technique on C57 Bl/6 mouse brain tissue extract 72 hours following whole brain RT versus sham-irradiated controls. We found significant changes up- and down-regulation of critical proteins in multiple canonical pathways to be affected, but interestingly some of the most significant changes were in proteins vital to Huntington and Parkinson9s signaling pathways. Additionally, we explored the role of Sirtuin 2 (Sirt2), a Class III histone deacetylase which is abundant in CNS and has been shown to mediate oxidative stress response in animal models of neurodegeneration which produce dementia, within the context of whole brain RT. Our aim was to investigate if Sirt2 might be a potential target to mitigate neurotoxic effects induced by RT. Our proteomic analysis of the brain tissue extracts of Sirt2 genomic knockout mice shows that the absence of Sirt2 affects several metabolic and signaling pathways including Huntington, Parkinson9s, as well as mitochondrial-mediated signaling. Several factors were found to be uniquely and differentially expressed in Sirt2 knockout tissues under radiation condition. This study indicates that Sirt2 might be a key player in radio sensitization of the CNS and a potential clinical target for minimizing radiation-induced neurocognitive dysfunction. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4354. doi:1538-7445.AM2012-4354