Potential of In-room PET for Image Guided Proton Therapy

6.30.2009 SPEAKER: Martin Pomper, PhD, Johns Hopkins University MODERATOR: Clare Tempany, Brigham and Women's Hospital Video not available.

Forum Summary

One man dies of hormone-refractory prostate disease every twenty minutes in the United States, and thus, a molecular imaging technique capable of identifying prostate tumors is highly desirable.  Many radiopharmaceuticals exist for identifying prostate tumors, but most of these compounds operate via mechanisms that are not fully understood.  A group of scientists including Martin Pomper, PhD, are currently attempting to design new radiopharmaceuticals to target a protein specific to prostate tumors.

Their target protein is called prostate-specific membrane antigen (PSMA).  PSMA is membrane protein found on prostate tumors and on tumor neovasculature.  It has been targeted by emerging therapies such as Prostascint, the only FDA-approved agent with a known mechanism.  Unlike most membrane proteins, PSMA is an enzyme with an active site outside the cell.  Pomper’s group is attempting to target this active site.  X-ray crystallography of PSMA provides detailed information about the geometry of the active site, and researchers are trying to use this information to design labeled molecules capable of binding to the active site.  Pomper’s group has designed a number of urea-based PSMA inhibitors.  Tagging these low-molecular weight agents with radioactive atoms allows one to visualize prostate tumors using positron emission tomography (PET).  These new radiopharmaceuticals are still being developed, but they seem to bind to prostate tumors with great specificity, making the identification of tumors a relatively easy task for radiologists.

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