PSMA-based imaging identifies even treatment-resistant prostate cancer

Anti-androgen hormonal therapy, also known as chemical castration, can be an important defence against further disease progression for patients with prostate cancer that has metastasized. However some cases simply do not respond to the treatment. In an effort to improve clinical decision making, a ground-breaking molecular imaging agent has been developed to identify whether prostate cancer is responding favorably or not to therapy, according to work presented by a group from Johns Hopkins University at the recent US Society of Nuclear Medicine and Molecular Imaging’s 2014 Annual Meeting.

The patients were examined by PET/CT imaging using a F-18 labelled ligand known as DCFBC. This is a unique small-molecule that binds to prostate-specific membrane antigen (PSMA), which is more expressed on malignant prostate cells than on normal cells. The study showed the effectiveness of the imaging agent by providing substantial clinical data for both castration-sensitive and castration-resistant prostate cancer patients.

“Currently there is a great unmet need in prostate cancer management and drug development for a functional imaging agent that is able to detect prostate cancer and monitor response to therapy,” said Dr S Cho from the department of radiology at Johns Hopkins. “Unfortunately, a truly reliable functional imaging agent for prostate cancer does not exist. However several exciting metastatic cancer imaging agents have been in development over the last several years. We are working toward improvements beyond the current capabilities of conventional bone and CT imaging, and a small-molecule PSMA-based PET radiopharmaceutical such as F-18 DCFBC is one such possibility.”

This study included the first 12 patients from an ongoing trial, including five cases of castration-sensitive and seven cases of castration-resistant cancer, both with rising PSMA levels and evidence of metastases. Hot spots representing tumor uptake were correlated with serum prostate-specific antigen and folate levels as well as castration-resistant status. Results of the study showed F-18 DCFBC uptake was comparable to conventional imaging in relation to the lymph nodes, some bone and viscera, including the adrenal glands and pancreas. Lower DCFBC uptake was seen in highly scarred bone metastases when compared to other kinds of growths, but DCFBC PET was found to be more sensitive than conventional imaging for detecting bone metastases, especially within the cervical spine and areas showing degenerative changes, as well as in subcentimeter-sized lymph nodes. Additionally, a higher uptake of the agent was observed in castration-resistant bone metastases, and a direct link was found between PSMA levels and tumor-agent uptake.