Is Trofex a possible “replacement” imaging agent for Combidex?

According to a media release issued on Thursday this week by Molecular Insight Pharmaceuticals, Inc. (MIP), an investigational imaging agent known as Trofex™ (a.k.a, 123I-MIP-1072) may offer a new opportunity to identify the presence of early signs of metastatic prostate cancer in the prostate bed, soft tissues, and bone within 4 hours after injection.

Data from a series of three Phase I clinical trials were presented this week at the annual congress of the European Association of Nuclear Medicine in Vienna. Trofex is a small, radio-labeled molecule capable of binding to prostate-specific membrane antigen (PSMA). PSMA is a well-studied protein that is highly expressed by prostate cancer cells. MIP has announced that the uptake and retention of Trofex in prostate cancer cells makes possible the non-invasive molecular imaging of metastatic prostate cancer.

According to the data presented in Vienna, two completed Phase 1 studies enrolled a total of 13 subjects (7 prostate cancer patients and 6 healthy volunteers) and 12 more patients have been enrolled to date in a third, ongoing Phase I study. In this small group of patients Trofex (given at a dose of 370 MBq) was able to visualize prostate cancer lesions in in several tissue types, thus confirming that the extracellular domain of PSMA can be effectively targeted with small molecules as a way to image metastatic prostate cancer. Imaging of the tumors after injection of Trofex was carried out by serial whole-body planar imaging and by SPECT/CT scanning. The company also claims that the use of Trofex was significantly faster and more accurate than ProstaScint when used as a prostate cancer imaging agent. Trofex was eliminated from the blood stream relatively soon after initial injection.

What is not clear from the available data at this time is just how small (or large) the metastatic tumors need to be before they can be accurately visualized as a consequence of Trofex binding. From a clinical point of view, one would like to be able to clearly identify small metastatic tumors that can not be accurately imaged using any currently available technology. (For comparative purposes, one might like to think of Trofex as a possible replacement for the earlier Combidex imaging agent that had been approved in Europe — but not in America.)

There will be considerable work necessary to demonstrate that Trofex can accurately and safely be used as an imaging agent for extraprostatic and metastatic prostate cancer. If MIP can demonstrate such accuracy and safety, then Trofex has the potential to significantly enhance the management of locally advanced forms of prostate cancer and even of minimally metastatic disease. The conduct of necessary Phase II and Phase III clinical trials may, however, require several years of work before Trofex can be brought to market — even if everything goes according to plan.

MIP is also working on a therapeutic analog of Trofex (known as 131I-MIP-1375) which may have potential as a treatment for locally advanced and metastatic forms of prostate cancer (as opposed to as an imaging agent), but no clinical data is available on the use of this product to date.

2 Responses

  1. I guess you are talking about Combinex, not Combidex. I believe it is not approved in Europe too.

  2. Jean:

    In Europe, ferumoxtran-10 (Combidex) was known as Sinerem (at least in the Netherlands and perhaps some other European nations). It was available until early this year, when the manufacturer stopped making the product. It was an imaging agent.

    Combinex (as far as I am aware) is an antiinfective used in the treatment of worms in animals.

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