A new (and better?) prostate cancer-specific imaging agent

With the failure of Combidex (ferumoxtran-10) to achieve FDA approval as an imaging agent for  lymph node-positive prostate cancer and the recognized limitations of the ProstaScint (capromab pendetide) scan, there is a widely acknowledged need for a much more specific and accurate prostate cancer imaging agent than anything currently available.

Availability of the right imaging agent would assist clinicians to:

  • Better identify the presence of prostate cancer outside the prostate prior to implementation of treatment of localized disease
  • Target salvage radiation and other salvage therapies to specific tissues when salvage therapy was needed
  • Monitor patients at risk for progressive disease much more accurately than can be carried out at present.

In addition, such an agent would also be useful in the conduct of clinical trials of new drugs if it could be applied to demonstrate delay in the onset of micrometastasis in men with high-risk or progressive disease.

The prostate-specific membrane antigen or PSMA has long been recognized as the potential target molecule to which researchers would like to be able to attach appropriate small molecule imaging agents that could then be visualized using some form of scanning technology. Researchers at Purdue University, now working in concert with Endocyte, believe they may have come up with just such a small molecule: a new radio-imaging agent that appears to be able to bind to PSMA and that can then be visualized on a CT scan.

The agent under development is supposed to be 150 times smaller than the molecule used in the ProstaScint scan, and clinical trials of this agent have just been started.

It may be a while before we get full details of the clinical trials needed to test this new agent, but there is no doubt that such an agent is badly needed. There is no concrete information available as yet on either ClinicalTrials.gov or on the Endocyte web sites. However, according to the information on the Purdue University web site, three patients have already been treated with the new agent and they expect to treat 25 patients in total in the Phase I trial of the new molecule. Research on the development of this agent started some time ago. Here is a link to a media release issued by Purdue in July 2009.

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