Zhang et al. reported the results of a very small pilot study using a synthetic molecule that targets two different receptor proteins at the same time (also see this link). One part of the molecule (bombesin - BBN) targets the GRPR protein. The other part, called RGD, targets a protein called αvβ3. αvβ3 is a member of a family of proteins called integrins. These proteins are responsible for maintaining the structural integrity of cells. αvβ3 promotes cell adhesion, spreading and blood supply -- qualities vital to metastatic progression.
They used both the single Ga-68-BBN PET/CT and the dual Ga-68-BBN-RGD PET/CT to detect prostate cancer among 13 patients (4 newly diagnosed, 9 recurrent) with biopsy-proven prostate cancer. The dual PET radiotracer found cancer:
- In the prostates of 3 of the 4 men with newly diagnosed prostate cancer vs. 2 of the 4 men using the BBN-only radiotracer.
- 14 metastatic lymph nodes vs. 5 metastatic lymph nodes using the BBN-only radiotracer.
- 20 bone metastases vs. 12 metastatic bone metastases using the BBN-only radiotracer.
There were no toxic reactions.
While encouraging, it is still very early to draw conclusions. There is no confirmation that the extra "metastases" discovered were indeed metastases - they may be false positives. And there are no clues as to which kinds of prostate cancer the dual PET radiotracer is sensitive to, and which kinds are undetectable.
If confirmed by larger studies, it may be possible to not just detect the cancer, but to kill the detectable cancer cells as well with beta emitters like Lu-177 or alpha emitters like Ac-225.