Drugs Enhance SPECT Imaging of Metastatic Cancer

New drugs that bind to metastatic prostate cancer in soft tissue, lymph nodes and bone can enhance SPECT and planar imaging.

A new study represents the first time these target-specific radiopharmaceuticals have been shown to improve cancer detection in human patients. Previous in vitro studies showed that the drugs bind strongly to tumor cells containing prostate-specific membrane antigen (PSMA).

The drugs were tested in six healthy men and six men diagnosed with metastatic prostate cancer. After injection, whole-body images were obtained at 10 minutes and at one, two, four and 24 hours. Single-photon emission computed tomography (SPECT) was performed between three and four hours after injection.

Differences in urinary excretion between the two radiopharmaceuticals. The planar and SPECT images of one drug, 99mTc-MIP-1404 (A and B) show minimal urinary excretion and bladder (BL) activity, compared with that of the other drug, 99mTc-MIP-1405 (C and D). Images also identify metastasis in lymph node (LN) in pelvis and para-aortic lymph nodes (PLN). Courtesy of the Journal of Nuclear Medicine.

In men with metastatic prostate cancer, both agents were absorbed in bone and lymph node lesions in as little as one hour. The drugs helped identify most bone metastatic lesions and rapidly detected soft-tissue lesions, including in subcentimeter lymph nodes.

SPECT provided good lesion contrast, the researchers said. Paired with the two drugs, it may provide more sensitive detection of skeletal or marrow invasion than bone scans, which are the standard of care today.

“With respect to imaging, the lack of focal uptake in the normal prostate of healthy volunteers with both compounds further demonstrated that PSMA is a viable targeting mechanism for detection and visualization of prostate cancer and suggests that this imaging approach is highly sensitive and disease specific,” said Weill Cornell Medical College professor Dr. Shankar Vallabhajosula, lead author of the study.

A multicenter phase II study involving 100 patients was recently completed, and the data were presented at the annual meeting of the Society of Nuclear Medicine and Molecular Imaging in St. Louis. Progenics Pharmaceuticals plans to conduct a phase III trial soon.

The research was published in the Journal of Nuclear Medicine (doi: 10.2967/jnumed.114.140426).

For more information, visit www.weill.cornell.edu.