Hyperpolarized [1,3‐¹³C₂]ethyl acetoacetate is a novel diagnostic metabolic marker of liver cancer

Abstract

An increased prevalence of liver diseases such as hepatitis C and nonalcoholic fatty liver results in an augmented incidence of the most common form of liver cancer, hepatocellular carcinoma (HCC). HCC is most often found in the cirrhotic liver and it can therefore be challenging to rely on anatomical information alone when diagnosing HCC. Valuable information on specific cellular metabolism can be obtained with high sensitivity thanks to an emerging magnetic resonance (MR) technique that uses 13 C labeled hyperpolarized molecules. Our interest was to explore potential new high contrast metabolic markers of HCC using hyperpolarized 13 C-MR. This work led to the identification of a class of substrates, low molecular weight ethyl-esters, which showed high specificity for carboxyl esterases and proved in many cases to possess good properties for signal enhancement. In particular, hyperpolarized [1,3-13 C 2 ]ethyl acetoacetate (EAA) was shown to provide a metabolic fingerprint of HCC. Using this substrate a liver cancer implanted in rats was diagnosed as a consequence of an~4 times higher metabolic substrate-to-product ratio than in the surrounding healthy tissue, (p 5 0.009). Unregulated cellular uptake as well as cosubstrate independent enzymatic conversion of EAA, made this substrate highly useful as a hyperpolarized 13 C-MR marker. This could be appreciated by the signal-tonoise (SNR) obtained from EAA, which was comparable to the SNR reported in a literature liver cancer study with state-of-the-art hyperpolarized substrate, [1-13 C]pyruvate. Also, the contrast-to-noise (CNR) in the EAA based metabolic ratio images was significantly improved compared with the CNR in equivalent images reported using [1- Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer.1 Most HCC are found in cirrhotic livers. This is the underlying reason for a strong correlation seen between an increasing incidence of HCC and a large number of patients infected with hepatitis C several decades ago, which now present complications of cirrhosis.2 Due to the cirrhotic environment of most HCC, a common treatment of this disease is liver transplantation. This treatment is seen as the modality of choice because it removes the tumor along with the diseased liver. 3,4The diseased environment in which HCC is often found challenge its diagnosis. The highly heterogeneous arrangement of the diseased liver tissue makes the tumor detection difficult with conventional imaging modalities such as CT, MRI and ultrasound. Currently, the most helpful tool for detecting malignancy is gadolinium-enhanced MRI, though this approach is impeded by relatively poor specificity.5 Thus, more advanced imaging techniques are desirable to diagnose liver lesions. The MR technique is highly versatile and can provide information on functionality. In particular, MR spectroscopy is of interest since it can provide specific information on tumor pathogenesis and metabolism, including type, grade and stage of the tumor, which can assist in further manageme...

Metabolism of hyperpolarized 13C‐acetoacetate to β‐hydroxybutyrate detects real‐time mitochondrial redox state and dysfunction in heart tissue

“…HP 13 C‐AcAc was first reported as an imaging probe by Jensen et al In that study, ethyl [1,3‐ 13 C]AcAc was used as a marker for decreased esterase activity in liver tumors but HP‐β‐HB was not detected. Recently, Miller et al investigated the metabolism of HP‐[1‐ 13 C]AcAc and HP[1‐ 13 C]β‐HB in isolated, perfused rat hearts as well as in vivo .…”

“…HP 13 C-AcAc was first reported as an imaging probe by Jensen et al 43 In that study, ethyl [1,[3][4][5][6][7][8][9][10][11][12][13] 44 This study demonstrated that metabolism of HP 13 C-ketones can be detected in the heart, and several downstream metabolites of the HP 13 C-agents were observed. We first reported with preliminary results that it is possible to correlate altered mitochondrial redox in perfused rat hearts with the production of HP-β-HB from HP-AcAc.…”

Hyperpolarized ketone body metabolism in the rat heart

“…A small reagent impurity, ethyl‐[1‐ 13 C]acetoacetate, was visible in the batch of synthesized [1‐ 13 C]acetoacetate used for ex vivo experiments. Owing to the reported subsequent hepatic metabolism of ethyl‐[1‐ 13 C]acetoacetate to ethanol and [1‐ 13 C]acetoacetate, the presence of this impurity ex vivo was not considered to be significant for subsequent in vivo translation.…”

Design of a 15N Molecular Unit to Achieve Long Retention of Hyperpolarized Spin State

“…CE catalyzes phase I metabolism and a hydrolytic reaction by CE is used as an activation mechanism of several prodrugs2324. Therefore, CE has been an attractive target of hyperpolarized MR molecular sensors25.…”