Prostate-specific membrane antigen (PSMA)–targeted imaging of metastatic prostate cancer (PCa) via small molecule inhibitors: Comparison to bone scan, CT/MRI, and 111In capromab.

Abstract

4658 Background: Accurate and sensitive visualization of metastatic PCa remains a clinical challenge. 123I-MIP-1072 is a radiolabeled small molecule that selectively binds the extracellular enzymatic region of PSMA and is internalized and retained in viable PCa cells. In contrast, the antibody, 111In capromab pendetide, targets the intracellular domain of PSMA. This investigation studied administered dose, imaging time and the comparison of 123I-MIP-1072 imaging to current standard of care for visualizing PCa (bone scan, CT/MRI and 111In capromab) in patients (Pts) with radiographic evidence of metastatic PCa (mets). Methods: Eligible Pts with biopsy confirmed PCa and radiographic evidence of mets received either 10 or 5 mCi of 123I-MIP-1072 and 5 mCi of 111In capromab within 30 days of each other. With 123I-MIP-1072, serial whole body planar images were collected over 1 day with SPECT/CT imaging at 4 and 24 hr post injection (PI). 111In capromab SPECT/CT imaging occurred 3-5 days PI with blood pool imaging as needed. Results: 12 Pts in each cohort (57-83 years) received 123I-MIP-1072 and 111In capromab. After IV injection, 123I-MIP-1072 rapidly localized in both soft tissue and bone lesions, as visualized on planar imaging. At 4hr PI using SPECT/CT, 123I-MIP-1072 detected (known) lesions in the prostate, lymph nodes and bone at both doses tested with signal to noise (SNR) of >5:1. High SNR persisted through 24 hr PI. In contrast, due to prolonged blood clearance, 111In capromab at 3-5 days PI detected lesions in the prostate but infrequently detect lesions in the bone and required additional blood pool imaging to confirm lesions in lymph nodes. 123I-MIP-1072 detected more lesions with a higher SNR than 111In capromab when compared to CT/MRI and bone scan (standard of care) and was able to detect disease prior to CT/MRI and/or bone scan becoming positive, based on 12 week follow up imaging. Conclusions: 123I-MIP-1072 SPECT/CT detected prostate cancer localized in the prostate bed, soft tissues and bone within 4 hr PI. 123I-MIP-1072 alone shows concordance with multiple modalities currently used as standard of care in the detection and staging of PCa.