Carbon Flux as a Measure of Prostate Cancer Aggressiveness: [ ¹¹C]-Acetate PET/CT

Abstract

Purpose: Dynamic [ ¹¹C]-acetate positron emission tomography (PET) can be used to study tissue perfusion and carbon flux simultaneously. In this study, the feasibility of the quantification of prostate cancer aggressiveness using parametric methods assessing [ ¹¹C]-acetate kinetics was investigated in prostate cancer subjects. The underlying uptake mechanism correlated with [ ¹¹C]-acetate influx and efflux measured in real-time in vitro in cell culture.

Methods: Twenty-one patients with newly diagnosed low-to-moderate risk prostate cancer underwent magnetic resonance imaging (MRI) and dynamic [ ¹¹C]-acetate PET/CT examinations of the pelvis. Parametric images of K ₁ (extraction × perfusion), k ₂ (oxidative metabolism) and V _T (=K ₁/k ₂, anabolic metabolism defined as carbon retention) were constructed using a one-tissue compartment model with an arterial input function derived from pelvic arteries. Regions of interest (ROIs) of the largest cancer lesion in each patient and normal prostate tissue were drawn using information from MRI (T2 and DWI images), biopsy results, and post-surgical histopathology of whole prostate sections (n=7). In vitro kinetics of [ ¹¹C]-acetate were studied on DU145 and PC3 cell lines using LigandTracer ^® White equipment for the measurement of the radioactivity uptake in real-time at 37°C.

Results: Mean prostate specific antigen (PSA) was 8.33±3.92 ng/mL and median Gleason Sum 6 (range 5-7). K ₁, V _T and standardized uptake values (SUVs) were significantly higher in cancerous prostate tissues compared to normal ones for all patients (p<0.001), while k ₂ was not (p=0.26). PSA values correlated to early SUVs (r=0.50, p=0.02) and K ₁ (r=0.48, p=0.03). Early and late SUVs correlated to V _T (r>0.76, p<0.001) and K ₁ (r>0.64, p<0.005). In vitro studies demonstrated higher extraction and retention (p<0.01) of [ ¹¹C]-acetate in the more aggressive PC3 cells.

Conclusion: Parametric images could be used to visualize the [ ¹¹C]-acetate kinetics of the prostate cancer exhibiting elevated extraction associated with the cancer aggressiveness. The influx rate of [ ¹¹C]-acetate studied in cell culture also showed dependence on the cancer aggressiveness associated with elevated lipogenesis. Dynamic [ ¹¹C]-acetate/PET demonstrated potential for prostate cancer aggressiveness estimation using parametric-based K ₁ and V _T values.