Ex vivo SPECT/CT imaging of prostate cancer via 111In-J591 monoclonal antibody

Objectives We have previously demonstrated targeting of metastatic prostate cancer lesions with 111In-J591, a radiolabeled monoclonal antibody (mAb) that binds to the prostate specific membrane antigen (PSMA), in human subjects. The goal of this study is to assess the efficacy of 111In-J591mAb as a pre-surgical imaging agent by examining excised prostate specimens with SPECT/CT.

Methods Eight patients with abnormal digital rectal exam and biopsy proven prostate cancer (PCa) were enrolled in the study. Each patient received an endo-rectal MRI, which showed an abnormal prostatic lesion. They also received bone and CT scan, both of which showed the absence of metastatic disease. Each patient was injected intravenously with two milligrams of J591 labeled with 5 mCi of 111In. SPECT/CT imaging was performed 2 to 5 days post injection. Prostatectomy was performed on the day of imaging and the excised prostate was imaged with SPECT/CT and planar scintigraphy before being sent to surgical pathology. Phantom images were acquired to determine the approximate resolution of the technique and to determine intraprostatic binding.

Results 111In-J591 immunoscintigraphic images were consistent with the pathologic diagnoses for all of the patients. Antibody imaging confirmed localization of potentially resectable disease without regional or metastatic spread. 111In-J591 showed high tumor to background ratio, and showed normal distribution.

Conclusions Acceptable toxicity and excellent targeting of localized PC was demonstrated, highlighting a potential role for the anti-PSMA antibody J591 as a vascular-targeting agent. Our results provide insight into the potential of SPECT quantitative imaging for prostate cancer using 111In-J591, which is highly specific for PSMA and will enable individual tailoring of therapies, and surgical decision making.