RT Journal Article SR Electronic T1 Detection Threshold and Reproducibility of 68Ga-PSMA11 PET/CT in a Mouse Model of Prostate Cancer JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1392 OP 1397 DO 10.2967/jnumed.118.207704 VO 59 IS 9 A1 Katharina Lückerath A1 Andreea D. Stuparu A1 Liu Wei A1 Woosuk Kim A1 Caius G. Radu A1 Christine E. Mona A1 Jeremie Calais A1 Matthew Rettig A1 Robert E. Reiter A1 Johannes Czernin A1 Roger Slavik A1 Ken Herrmann A1 Matthias Eiber A1 Wolfgang P. Fendler YR 2018 UL http://jnm.snmjournals.org/content/59/9/1392.abstract AB To improve prostate-specific membrane antigen (PSMA)–targeted theranostic approaches, robust murine models of prostate cancer are needed. However, important characteristics of preclinical PSMA imaging—that is, the reproducibility of the imaging signal and the relationship between quantitative cell surface PSMA expression and lesion detectability with small-animal PET/CT—have not been defined yet. Methods: Murine prostate cancer RM1 sublines (ras myc transformed cells of C57BL/6 prostate origin) expressing varying levels of human PSMA were injected into the shoulder of C57BL/6 mice on day 0. 68Ga-PSMA11 PET/CT was performed on days 7 and 8 and interpreted by 2 masked readers to determine interday and interreader reproducibility. PSMA expression was quantified on days 7 and 8 by flow cytometry of fine-needle aspiration tumor biopsy samples. Cell surface PSMA expression was correlated with PET signal. The threshold for PET positivity was based on the clinical Prostate Cancer Molecular Imaging Standardized Evaluation (PROMISE) criteria. Results: The maximum and average percentages of injected 68Ga-PSMA11 activity per gram of tissue (%IA/g) correlated nearly perfectly as determined by 2 independent readers and on 2 separate days (intraclass correlation coefficient, 1.00/0.89 and 0.95/0.88, respectively). The number of PSMA molecules per cell increased from the RM1-yellow fluorescent protein subline (PSMA−; 2,000/cell) to the RM1-low subline (PSMA+; 17,000/cell), the RM1-medium subline (PSMA++; 22,000/cell), and the RM1-PGLS subline (PSMA-positive, green fluorescent protein–positive, and luciferase-positive; PSMA+++; 45,000/cell). Expression levels correlated with the visual positivity rate on 68Ga-PSMA11 PET and with the PSMA PET %IA/g. The PSMA threshold for PET positivity was approximately 20,000 per cell. Signal correlation was close at lower PSMA levels (RM1-low to RM1-medium; 10–23 %IA/g) but was lost at higher PSMA levels (RM1-medium to RM1-PGLS; 23–27 %IA/g). Conclusion: The in vivo relationship between 68Ga-PSMA11 PET/CT and PSMA expression level in a murine model of prostate cancer was robust for lower cell surface PSMA expression levels (≤22,000/cell). Thus, preclinical 68Ga-PSMA11 PET/CT can be used as an imaging biomarker to test PSMA-targeted interventions in murine models.