Molecular specific contrast agent can be used in combination with the appropriate imaging systems to detect the three dimensional distribution of molecular changes in living tissue.  For example, sensing cancer specific biomolecular signatures can significantly improve cancer screening, diagnosis and prognosis, and facilitate selection and monitoring of therapy.    Currently  these  biomolecular  signatures  can  only  be  assessed  through  invasive,  painful biopsy.  Through  collaboration  between  Professors  Korgel,  Sokolov,  Anslyn  and  Ellington, we are developing  optically  interrogated  contrast  agents  based  on  metal  nanocrystals,  quantum  dots  and fluorescent dyes attached to probe molecules with a high affinity to a specific biomarker on the surface of cancer  cells.    Optical interrogation provides non-invasive real time assessment of tissue pathology, while contrast agents give molecular specificity and selectivity.  Through collaboration with Professors Richards-Kortum and Follen, we are testing the hypothesis that the combination of optical imaging  techniques  with  cancer  specific  contrast  agents  can  provide  useful  molecular-specific information to assist clinicians in earlier detection of pre-cancers.

This interdisciplinary interaction provides a unique opportunity to train graduate students in this field.  In this program, we bring together the most recent advances of in vivo optical imaging, modern nano-chemistry,  combinatorial  chemistry  and  molecular  engineering  to  permit  optical  imaging  with molecular specificity.  Two IGERT students, Betsy Hsu and Kristen Carlson, are currently involved in the development and evaluation of these contrast agents.  The optical imaging techniques they are  developing  can  significantly  benefit  health  care  by  reducing  the  number  of  unnecessary  biopsies, enabling combined diagnosis and therapy, and reducing the need for clinical expertise.  The activities of this  competitive  renewal  will  provide  programs  to  help  IGERT  trainees  understand  and  appreciate  the process  of medical  technology  development  and  adoption,  better  preparing  them  for  a  wide  variety  of career opportunities.

Building  on  the  interactions  between  science  and  engineering  faculty  in  our  current  IGERT program, we will expand our contrast agent development training program to include the development of ‘active imaging agents’ that only signal in the presence of their cognate analytes.   Such imaging agents would be extremely useful to determine the real-time in vivo or intracellular concentrations of analytes of interest.  Well-known examples of  ‘active imaging  agents’  include  calcium-sensitive  dyes  that  allow  a direct  readout  of  intracellular  calcium  concentrations.    However, the ability to control the conformations and activities of organic receptors and biopolymers can potentially allow the development of 'active imaging agents'.  For example, Eric Anslyn has developed a series of 'smart dyes' in which a fluorescent  label  is  displaced  by  a  particular  analyte,  and  subsequently  fluoresces.   Organic receptors that can recognize a variety of analytes of biological interest, including cAMP, have been identified by screening targeted combinatorial chemical libraries, and during the course of the renewal we will  work  closely  with  participating  cell  biologists  to  generate  additional  sensors  for  monitoring  cell physiology.    Similarly, the Ellington lab has developed a variety of nucleic acid biosensors that can specifically recognize analytes ranging from small ions to supramolecular structures such as viruses, cells, and tissues, and in response produce an optical signal.  The capabilities of these biosensors are being further augmented in collaboration with Jon Sessler. Chemical  modifications  have  been  designed  that will increase the hydrophobicity of the nucleic acids, making them cell permeable (and in some instances, specifically  permeable  to  individual  cell  types,  such  as  transformed  or  tumor  cells). In addition, the Sessler lab’s pioneering work on porphyrin derivatives should provide a ready source of dyes, contrast agents, and even radionuclide labels that can be conjugated to the nucleic acid biosensors.

An  approach undertaken  by  the Ellington lab involves the transduction  of chemical signals  not  by  individual chemical  or  biopolymer receptors,  but  by  the signaling pathways in cells  themselves.  It has proven  possible  to generate  effector activated,  self-splicing introns;  these  introns  can be  placed  inside  reporter genes,  such  as  beta-galactosidase,  luciferase, or  GFP.    Analyte-mediated activation of the mRNA-embedded  intron by  its  analyte  will  thereby  lead  to  the  expression  and  observation  of  the  reporter  protein.    By making introns that are sensitive to particular intracellular analytes, such as phosphoproteins, or to extracellular analytes  that make  their  way  inside  of  cells,  such  as  steroid hormones,  it  should  be  possible  to follow cellular  responses  in  almost  real-time  in  a  completely  non-invasive  manner. Nicholas  Peppas  has developed  biomimetic  molecular  recognition  nanoparticles  based  on  configuration  biomimesis;  these agents  exhibit  fluorescence  and  can  trigger  simultaneous  therapeutic  action.    The  design  of  a  precise chemical architecture that can recognize target molecules from an ensemble of closely related molecules has  a  large  number  of  potential  applications.  Configurational  biomimesis  and  nanoimprinting  (CBIP) create  stereo-specific  three-dimensional  binding  cavities  based  on  the  template  of  interest.    The  CBIP network  structure  depends  upon  the  type  of  monomer  chemistry,  the  association  interactions  between monomers and pendent groups,  the  solvent,  and  the  relative  amounts  of  comonomers  in  the  feed from which the structure is formed. Since recognition requires 3D orientation, most techniques limit movement of the memory site via macromolecular chain relaxation, swelling phenomena, and other processes, by using high ratios of crosslinking agent to functional monomers.  

As  part  of this  renewal,  we will work with faculty  at  the Texas Medical  Center  to  expand  our efforts  to  develop  molecular-specific  contrast  agents  for  multi-modal  clinical  imaging.    We will work closely with Professor Chun Li.   Dr.  Li’s group has used nuclear imaging methods to track polymeric carriers for targeted delivery of both diagnostic and therapeutic agents. Recently, Dr. Li has shifted his efforts to the emerging field of near-infrared optical imaging. He has developed several near-infrared dyes to target tumor-associated receptors and other molecular processes for the early detection of tumor progression as well as therapy-induced responses. These molecular targets include epidermal growth factor receptors, integrins, matrix metalloproteinases, and tumor apoptosis.  These  dyes  are  now  being evaluated  for  their  in  vivo  imaging  properties  such  as  specificity  and  sensitivity.   In addition, we will collaborate with Professor K.S. Clifford Chao at the MD Anderson Cancer Center.    Dr.  Chao  is developing  and  evaluating  tools  for  molecular  imaging  of  hypoxia  signal  transduction  pathways.  His group is developing important 3D validation tools for molecular imaging which are relevant to many of the proposed imaging projects described here.  Through this expansion of collaborative activities, we will develop  new  training  opportunities  for  graduate  students  to  experience  and  participate  in  the  entire spectrum of contrast agent development and testing.  While the primary focus of this program is optical imaging,  these  expanded  interactions  will  enable  students  to  better  appreciate  the  strengths  and weaknesses  of  optical  imaging,  to  appreciate  the  benefits  and  challenges  of  multi-modal  imaging applications and to participate in and better appreciate the challenges in taking contrast agents from bench to bedside.  These interactions are designed to help students place their research in context with broader efforts, better preparing them for a wide variety of future career opportunities.