%0 Journal Article %A Wolfgang Fendler %A Andreea Stuparu %A Liu Wei %A Roger Slavik %A Ken Herrmann %A Johannes Czernin %A Matthias Eiber %A Katharina Lückerath %T Detection threshold and reproducibility of 68Ga-PSMA11 PET/CT in a mouse model of prostate cancer %D 2018 %J Journal of Nuclear Medicine %P 320-320 %V 59 %N supplement 1 %X 320Objectives: 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, i.e. reproducibility of the imaging signal and the relationship between quantitative cell surface PSMA expression and lesion detectability with microPET/CT, have not been defined yet. Methods: Murine prostate cancer RM1 sublines 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 blinded readers to determine inter-day and inter-reader reproducibility. PSMA expression was quantified on days 7 and 8 by flow cytometry of fine needle aspiration tumor biopsies. Cell surface PSMA expression was correlated with PET signal. The threshold for PET positivity was determined based on clinical PROMISE criteria. Results: Maximum and average %IA/g 68Ga-PSMA11 were near perfectly correlated when determined by 2 independent readers and on 2 separate days (ICC 1.00/0.89 and 0.95/0.88, respectively). PSMA/cell increased from RM1-YFP (PSMA-; 2,000/cell) to -LOW (PSMA+; 17,000/cell), -MEDIUM (PSMA++; 22,000/cell), and -PGLS (PSMA+++; 45,000/cell). Expression levels correlated with the visual positivity rate on 68Ga-PSMA11 PET and the PSMA PET activity (%IA/g). Threshold for PET positivity was ~20,000 PSMA/cell. Signal correlation was close at lower (LOW to MEDIUM; 10 to 23 %IA/g), but lost at higher PSMA levels (MEDIUM to PGLS; 23 to 27 %IA/g). Conclusions: The in vivo relationship between 68Ga-PSMA11 PET/CT and PSMA expression level in a murine model of prostate cancer is robust for lower cell surface expression levels (≤22,000 PSMA/cell). Thus, preclinical 68Ga-PSMA11 PET/CT can be used as an imaging biomarker to test PSMA targeted interventions in murine models. %U