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ProxiScan Completes First Animal Tests

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The first animal studies made using a 2009 R&D 100 Award-winning technology were recently performed at Molecular Insight Pharmaceuticals (MIP) in Cambridge, Mass. A new small molecule drug, Trofex, was successfully tested for its effectiveness as a biomarker for the detection of prostate cancer.

According to Terry Lyall of Hybridyne, the ProxiScan tests, performed on mice which had cancerous tumors, were able to clearly show the kidneys (and liver) and the location and extent of the cancer, demonstrating the usefulness of ProxiScan for more accurate imaging of radiotracers.

ProxiScan was engineered by Hybridyne Imaging Technologies Inc., Toronto, Canada, and is a compact, high-resolution gamma camera for the detection of cancer and other abnormalities in the body. Specifically, the system is useful for imaging the distribution of radionuclides in the human body using planar imaging techniques.

The unique component of the technology is a small cadmium zinc telluride (CZT)-based compact gamma camera developed by Hybridyne in collaboration with scientists at Brookhaven National Laboratory.

“The compact size of the instrument allows placement of the camera close to the objects of interest, thus creating the possibility of reductions in the radiation dose to patients,” says co-developer Yonggang Cui of Brookhaven.

R&D Magazine reported in April 2010 of final FDA clearance for ProxiScan to be used intra-operatively, on pathological specimens, and for endocavity applications if a protective sheath is used. It is the first gamma camera to receive this clearance, and the camera was soon put to use on model models.

The measurements made at MIP in August 2010 were performed on mice that had received prostate cancer cells and had subsequently developed xenographic tumors. Trofex (123I-MIP-1072) is a small molecule targeting the extracellular domain of prostate specific membrane antigen (PSMA). It was developed as a biomarker for the detection of primary and metastatic prostate cancer. Trofex is now undergoing Phase-I clinical trials at multiple institutions.

ProxiScan 2

Test results demonstrate high spatial resolution imaging. The measurement time in the results above was two minutes for one kidney and a tumor of a live mouse. The relative activity of the kidney to the tumor is 4.6:1. Image: ProxiScan

A total of 23 images were captured during the tests. Trofex, which is an I-123-based radiopharmaceutical, was injected into the mouse. I-123 emits 159-keV gamma rays. ProxiScan’s linearity range covers this energy, so the camera was expected to produce images of the uptake of Trofex. In fact, the results did capture this uptake in the organs and tumor.

The only area of concern that was identified during the animal tests was that the amount of side shielding on the device should be increase for systems used in clinical settings.

Based on ProxiScan’s performance during the measurements, says Lyall, Hybridyne has been invited to be a part of the Phase-I studies.

“This plan to include ProxiScan in the clinical protocol ensures Hybridyne’s ability to collect human data faster and cheaper, and we are rapidly becoming a critical link in research efforts to explore development of new drugs,” he says.

In addition to validating the high spatial resolution performance of Hybridyne’s gamma camera, and its readiness for clinical use on humans, MIP was also interested in the ability of ProxiScan to simultaneously image the kidneys and tumor of a mouse, which is not possible with conventional gamma cameras due to their relatively poor spatial resolution.

According to Ralph B. James, a senior scientist at Brookhaven and another co-developer of ProxiScan, Brookhaven’s pre-clinical laboratory experiments demonstrated the high-spatial-resolution and high-contrast capabilities of the instrument.

“Images of shaped phantoms have shown spatial resolutions as low as 1-2 mm, potentially allowing more precise information about the distribution of radionuclides in nuclear medical applications,” says James.

Further measurements will test its potential for quantifying the biological potential of prostate tumors, which could pave the way for new directed therapy (e.g., chemo- or radio- therapy) and for innovative, minimally invasive therapies as treatment options.

Source: R&D Mag