Abstract
PurposeProstate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRP-R) are expressed in prostate cancer and can be targeted with radiolabeled inhibitors and antagonists. Their performances for the initial characterization of prostatic tumors have been barely evaluated but never compared. We aimed to gather comparative preclinical data of the role of PSMA and GRP-R targeting in prostate cancer.ProceduresWe retrospectively studied 20 frozen prostatectomy samples with various metastatic risks of the D’Amico classification. Tissue samples were investigated by tissular microimaging using the radiolabeled PSMA inhibitor 111In-PSMA-617 and the radiolabeled GRP-R antagonist 111In-RM2. Bindings of the two radiopharmaceuticals were compared to histology and clinico-biological data (Gleason score, PSA values, metastatic risks).ResultsBinding of 111In-PSMA-617 was high whatever the metastatic risk (p = 0.665), Gleason score (p = 0.555), or PSA value (p = 0.404) while 111In-RM2 exhibited a significantly higher binding in the low metastatic risk group (p = 0.046), in the low PSA value group (p = 0.001), and in samples with Gleason 6 score (p = 0.006).ConclusionPSMA and GRP-R based imaging might have complementary performances for the initial characterization of prostatic tumors. Prospective clinical studies comparing the two tracers in this setting are needed.
Highlights
Prostate cancer is the most common cancer in men and the third cause of cancer deaths [1]
78.5 ± 4.6%, radiochemical purity of 99.9 ± 0.2%, and specific activity of 1.4 ± 0.4 GBq/μmol. 111In-Prostate-specific membrane antigen (PSMA)-617 was produced with a radiolabeling yield of 85.6 ± 0.2%, radiochemical purity of 100.0 ± 0.0%, and specific activity of 2.2 ± 0.5 GBq/μmol
In the low Prostate-specific antigen (PSA) group, there was only a trend for higher 111In-PSMA-617 binding compared to 111In-RM2 (64.60 ± 4.83% vs 14.67 ± 3.96%, p = 0.0625)
Summary
Prostate cancer is the most common cancer in men and the third cause of cancer deaths [1]. It is a multifocal disease as cancerous cells may arise from different locations within the prostatic gland. Attractive targets for a more specific and sensitive imaging of primary prostate cancer are the prostate-specific membrane antigen (PSMA) and the gastrin-releasing peptide receptor (GRP-R). They can be effectively targeted with radiolabeled inhibitors [3] and antagonists [4], respectively
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