Metabolic imaging with hyperpolarized pyruvate is a noninvasive and well-tolerated method for visualizing prostate tumors, US scientists have shown.
Writing in Science Translational Medicine, the team says their findings “will be valuable for noninvasive cancer diagnosis and treatment monitoring in future clinical trials.”
Sarah Nelson (University of California, San Francisco) and colleagues conducted a first-in-man study to evaluate the safety and feasibility of hyperpolarized [1-13C]pyruvate as an imaging agent in prostate cancer.
“Hyperpolarized 13C MRI is a new molecular imaging technique with an unprecedented gain in signal intensity of 10,000- to 100,000-fold that can be used to monitor uptake and metabolism of endogenous biomolecules,” explain Nelson et al.
The technique is based on the rationale that cancer cells consume more pyruvate during glycolysis than noncancerous cells. Following injection, patients are rapidly imaged using hyperpolarized 13C magnetic resonance (MR) to provide dynamic information as well as three-dimensional (3D) data at a single time point.
They studied 31 patients with biopsy-proven prostate cancer who received doses of [1-13C]pyruvate ranging from 0.14 to 0.43 ml/kg. No dose-limiting toxicities were observed and the highest dose (0.43 ml/kg) gave the best signal-to-noise ratio.
MRI revealed tumors in all 31 patients; moreover, 3D imaging revealed cancer in regions of the prostate that had been deemed tumor-free using conventional imaging methods.
For instance, one patient who was believed to have cancer only on the right side of the gland was found to also have tumor in a region of the central gland, which was confirmed on subsequent MR-guided biopsy.
“The fact that the hyperpolarized imaging method was able to detect bilateral cancer, whereas conventional anatomic imaging methods were only able to visualize unilateral cancer, is an exciting finding, which may be especially important in monitoring patients like this who are thought to have slow-growing cancers and are being followed with active surveillance before starting treatment,” write Nelson et al.
They conclude: “When combined with findings from preclinical studies, the results of this first-in-man study suggest that hyperpolarized 13C metabolic imaging may be valuable for initial diagnosis and for monitoring therapy.”
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