Vanderbilt-Ingram Cancer Center

Vanderbilt Department of Radiation Oncology

Preceptors

David Cortez, Ph.D.

My laboratory is dedicated to discovering the basic biological processes that govern cell growth and genome stability. Cancer arises as a result of genetic alterations. Cells deploy numerous genome surveillance systems to prevent and repair DNA damage and to coordinate repair with cell cycle transitions. However, cancer cells have lost some of these systems and are genetically unstable. We aim to define the components of genomic surveillance systems and understand how they work in a coordinated manner to prevent cancer by inhibiting the cell cycle, promoting DNA repair, or initiating apoptosis.

The DNA damage response pathway is a signal transduction pathway that functions within the cell nucleus. Proteins involved in these pathways include ATM, ATR, p53, Chk2, Brca1, FancD2, and Blms. Mutations in the genes encoding these proteins are linked to specific cancer predisposition, developmental, and premature aging syndromes. Our primary research goal is to understand how DNA damage response pathways function to maintain genome integrity and prevent cancer.

There are currently four specific focuses in the laboratory:

1. How does DNA damage activate the checkpoint kinases ATM and ATR?
2. What are the substrates of ATM and ATR that are involved in regulating cell division and DNA replication?
3. How is DNA replication regulated to ensure accurate duplication of the genome?
4. How does the DNA damage binding protein DDB1 regulate genome stability through ubiquitin-mediated proteolysis?

We use a variety of genetic and biochemical approaches in mammalian and yeast systems. RNA inhibition, gene knockouts, mass spectrometry, and yeast genetics all are employed as needed to understand the basic molecular mechanisms that maintain our genomes. We also collaborate with structural biologists to gain a more detailed understanding of how protein-protein interactions regulate DNA damage responses. An exciting new area of investigation involves the use of genetic screens in vertebrate cells to understand genome maintenance. We believe that our multidisciplinary approach to studying these topics will yield new insights into the molecular basis of cancer and aging.

 

Michael L. Freeman, Ph.D.

My laboratory focuses on 2 aspects of cancer drug development: 1) Development of efficacious sensitizers of ionizing radiation . 2-Indol-3-yl-methylenequinuclidin-3-ols are being used as the basis for development of novel radiation sensitizers. Defined DNA substrates, cell and animals models are used in the approach to design specific sensitizers. 2) Providing a rationale basis for development of chemoprevention agents. Expression of the genes that encode Phase II detoxification proteins is regulated by the transcription factor Nrf2, which itself is negatively regulated by association to the Cul-3 ubiquitin ligase adaptor protein Keap1. Proteomics, biochemical, biophysical and genetic approaches are used to determine if Keap1's activity is regulated by multiple Cys residues that exhibit differential chemical reactivity, allowing integration of different chemical input signals. Nrf2 also impacts inflammation and pulmonary fibrosis. We are investigating the mechanism by which TGF-beta suppresses Nrf2 signaling, thereby contributing to the development of radiation-induced inflammatory and fibrotic responses.

 

David Gius, M.D., Ph.D.

The central theme of the laboratory is the potential relationship of intracellular pro-proliferative / prosurvival factors and how tumor cells respond to therapeutic modalities. The overarching goal of my research is an extension of the hypothesis that tumor cells use pre-existing pro-survival signaling pathways, up-regulated as a result of transformation or tumor micro-environment, to evade the damaging and cytotoxic effects of anti-cancer agents. These signaling factors are involved in the transmission of inter- and intracellular information through multiple transduction cascades and it has been suggested that one function is the activation of preprogrammed reparative or protective cellular processes responding to intracellular stress. Tumor cells likely activate these pathways responding to dys-regulated cell division and the increased demands on multiple cellular processes including increased replication, transcription, translation, protein trafficking and the production of metabolites that must be scavenged to prevent cellular oxidative stress. Thus, the long term goal of this part of the laboratory is to develop both in vitro and in vivo model systems to investigate the genetic relationship between longevity, carcinogenesis, and tumor cell resistance. While preliminary work suggests fundamental intracellular roles for the Sirtuin gene family the work in this field has been limited to the basic biological mechanisms. The central theme of our research program proposes that cancer is a disease of aging and one major factor holding this research back is a lack of invitro and in vivo genetic models systems. However, the genes involved in longevity (aging) and the murine knockout models are either available or will be very soon. In this regard, the laboratory has recently constructed a Sirt3 knockout mouse to establish both in vitro and in vivo models of mitochondrial aging and the connection between mitochondrial aging, oxidative stress, and carcinogenesis.

It has been previously published that SIRT3 localizes in the inner mitochondrial membrane that also contains the complexes of electron transport. Thus, our research group hypothesized that SIRT3 may be a mitochondria watchdog overseeing the efficient function of oxidative phosphorylation. In this regard, we have recently published that SIRT3 is mitochondrial localized tumor suppress in vitro (tissue culture), in vivo (SIRT3 knockout mice), and in human breast cancer samples. It was also determined that at least one mechanisms accounting for the tumor permissive phenotype in the SIRT3 knockout mice is due to aberrant mitochondrial metabolism. To investigate the role of SIRT3 in ductal mammary tumors our laboratory uses a series of cell biological, biochemical, and molecular biological techniques that are applied to murine models that are more physiologically relevant than work limited to tissue culture models.

 

Lynn M. Matrisian, Ph.D.

My laboratory is interested in understanding the molecular mechanism that underlie cancer development, growth, and metastasis. Our approach involves a combination of cell biology, molecular biology, and whole animal techniques.

We have determined that growth factors and cancer-causing oncogenes induce the expression of genes for extracellular matrix-degrading metalloproteinases (MMPs). These enzymes are capable of degrading basement membrane and connective tissue proteins, and have been associated with tumor invasion and metastasis. More recently, it has become clear that these enzymes contribute to many stages of tumor progression, including the growth and development of early stage tumors and angiogenesis. In addition, their substrates are much broader than matrix components alone, and include growth factors and their receptors, chemokines, apoptosis factors, and adhesion molecules. We are using in vitro and in vivo model systems, including chemical carcinogenesis protocols and genetically altered transgenic or "knock-out" mice, to examine the role of metalloproteinases in specific stages of cancer.

Our experiments have led us to question the normal function of the metalloproteinase proteins. We are currently using rodent and human model systems and a combination of cellular, molecular, and developmental biology techniques to examine these questions. We hypothesize that the regulation of these matrix-degrading enzymes by growth factors is an important component of many normal biological processes, and that mis-regulation can contribute to the development of a variety of pathological conditions.

We have recently been exploring the application of MMP-sensitive protease switch as a component of multifunctional nanoparticles for the detection and treatment of cancer. Near infrared optical "beacons" and MRI contrast agents have been attached to peptide sequences that are cleaved by specific MMP family members, resulting in enhanced visualization of tumors based on elevated proteolytic activity. These probes have been attached to dendrimer backbones, resulting in nanostructures that detect proteolytic activity. We are extending these nanoparticles to include toxic drugs that are activated in the presence of tumor proteolytic activity.

 

Fen Xia, M.D., Ph.D.

Research in my laboratory focuses on elucidating the mechanisms that regulate the repair of chromosomal double-strand breaks (DSB) that arise during physiological DNA metabolism and after radiation therapy or chemotherapy. We aim to understand 1) the impact of deregulated DSB repair on carcinogenesis and the development of tumor resistance to therapy and 2) to explore novel avenues of cancer treatment targeting the DSB repair pathways. We have developed an array of intrachromosomal and extrachromosomal repair substrates that allow analysis of the quantity and quality of DSB repair by different mechanisms in mammalian cells. An understanding of the defects of DNA repair and its interplay with apoptosis in tumors may offer novel avenues for both cancer prevention and tailored therapy.

Project 1: There are several DSB repair subpathways, each with different impacts on mutagenesis and cell viability. Our main interests in this area are 1) understanding how cells determine which subpathway to use and 2) how regulation of these subpathways may be altered during carcinogenesis and cancer and determine tumor response to cancer therapies.

Project 2: Another major goal of our lab is to understand how DNA repair machinery communicates with cell death machinery in order to maintain genomic stability. We have begun these studies by examining BRCA1, a tumor suppressor involved in DSB repair and able to induce apoptosis, and Bid, a proapoptotic protein recently discovered to be involved in the DNA damage response. Brain tumors are among the model systems used for this project.

Project 3: Our research group has made an intriguing finding that indicates genetically wild type BRCA1 function can be disrupted by its mislocalization within the cell. We have also found another important tumor suppressor p53 is involved in regulating BRCA1's nuclear/cytoplasmic shuttling.

We are currently studying the molecular mechanism that regulates this shuttling and the potential use of BRCA1 mislocalization as a biomarker for tailored cancer therapy.

 

Thomas E. Yankeelov, PhD.

The long term goal of the Cancer Imaging Group (CIG) at the Vanderbilt University Institute of Imaging Research, is to be an international leader in the development and application of imaging techniques that can be used to quantitatively probe fundamental cancer biology as well to assess and predict the responses of tumors to treatment. CIG researchers currently employ MRI, optical, x-ray radiography and CT, SPECT, PET, and ultrasound to conduct studies in anatomical, physiological, cellular, and molecular imaging of cancer. These approaches are applied in both pre-clinical small animal models of cancer, as well as clinical trials. The CIG places special emphasis is placed on the techniques that readily lend themselves to image co-registration and clinical translation. Thus, we focus much of our effort on MRI, PET, SPECT, CT, and ultrasound to provide quantitative information on status of tumors and their response to treatment. Optical imaging is also used for developing new targeted agents and for high throughput studies. In addition to developing new methods of interrogating tumor characteristics (as our current activities below indicate), we offer a large range of services for external users.