PSMA agents pinpoint prostate cancer throughout the body with SPECT, planar imaging

Two novel technetium-99m agents, when used with SPECT or planar imaging, have been found to effectively target prostate specific membrane antigen (PSMA) in advanced prostate cancer within bone, lymph nodes and soft tissues, according to a study published in the November issue of the Journal of Nuclear Medicine.

SNMMI officials are highlighting the study of these particular drugs because they are the first-ever agents to be able to thoroughly detect metastatic prostate cancer in bone, lymph nodes and soft tissues with a single biomarker that can be married with technetium-99m. This way, the agents, known as MIP-1404 and MIP-1405, can be used in conjunction with SPECT and planar imaging to find prostate cancer in a variety of tissues.

One of the confounding factors in the detection of prostate cancer in bone is the uptake of imaging agents in degenerative bone tissues, but no uptake of this kind was found in the pharmacokinetic and biodistribution study. Shankar Vallabhajosula, PhD, a professor of radiochemistry at Weill Cornell Medical College, and colleagues led the research.

“The results of the present study demonstrate that targeting PSMA with both Tc-99m MIP-1404 and Tc-99m MIP-1405 facilitates the detection of radiologically proven prostate cancer in bone, lymph nodes, and the prostate gland,” wrote Vallabhajosula et al. “Also the radiation dosimetry from a single administration of a diagnostic dose for either of these agents is only around 6 mSv, which is similar to the radiation dose from the conventional bone scan in nuclear medicine.”

There were some subtle differences between the two agents. Tc-99m MIP-1404 clearance from the kidneys was less rapid than for MIP-1405 and the latter’s urinary activity was significantly higher. This suggests that MIP-1404 may be better suited for pelvic imaging, whereas MIP-1405 could be the better choice for imaging other regions besides the pelvis.

“Although both of these agents showed minimal or no uptake in the prostate of healthy male subjects, only Tc-99m MIP-1404 showed minimal urinary excretion,” wrote the researchers. “This finding suggested that Tc-99m MIP-1404 may have distinct advantage for detecting prostate cancer in the gland and in the pelvis at early stages of the disease.”

More than 2 million men are believed to be living with prostate cancer in the U.S. Besides skin cancer, prostate cancer is the most commonly diagnosed malignancy in the country and only lung cancer is associated with more fatalities. An estimated 233,000 new cases of prostate cancer will be diagnosed in America in 2014, and approximately 29,000 are expected to die from the disease, according to the American Cancer Society.

A multi-center phase II study will soon be underway and a phase III trial is expected to be conducted by Progenics Pharmaceuticals, based in Tarrytown, N.Y.