Plasma Metabolomic Profiles in Hepatocellular Carcinoma Patients Before and After Stereotactic Body Radiation Therapy

Grade 1 and 2 toxicities such as fatigue and nausea are common following stereotactic body radiation therapy (SBRT) for hepatocellular carcinoma (HCC). Less commonly, grade 3 or higher hepatic (e.g., non-classic radiation-induced liver toxicity in 30% of patients) and non-hepatic (e.g., luminal gastrointestinal) toxicities develop following HCC SBRT, and are often associated with irreversible injury, and high morbidity and mortality. There is a need to identify biomarkers that can detect radiation-induced liver/luminal gastrointestinal injury early for appropriate medical intervention or radiation dose reduction, and predict tumor response, allowing tailoring of SBRT to improve the therapeutic ratio for individual patients, ideally prior to completion of SBRT. The objectives of this study are two-fold: a) to identify the profile of changes in metabolite levels in the plasma of HCC patients at baseline and following the first or second fraction of SBRT, and b) to correlate such changes with clinical liver/luminal gastrointestinal toxicities and radiologic tumor response. HCC patients were treated with SBRT to a total dose of 30-54 Gy in 6 fractions on a previously published clinical trial (Bujold et al., J Clin Oncol, 2013). Plasma samples were collected from fifty HCC patients at baseline and after completion of the first or second fraction (within 5 days from the first fraction) of SBRT on an institutional review board approved companion protocol. Targeted metabolomic profiling was performed using the Biocrates p180 kit and liquid chromatography/tandem mass spectrometry, while untargeted metabolomic profiling was conducted using gas chromatography/mass spectrometry (GC/MS). GC/MS metabolite annotation was performed with comparing the mass spectrum and retention time to commercially available libraries such as Fiehn, GOLM, and NIST. Paired t-test and spearman correlation were used for statistical analyses. Four hundred eighty-three metabolites were detected, of which 293 were annotated. Significant differences were seen following SBRT from baseline in 34 annotated metabolites (P-values < 0.05) and 39 non-annotated spectral signatures (P-values < 0.05). Methyl linoleate, cysteine, tryptophan, and tyrosine were amongst the metabolites that demonstrated the highest fold increases, while succinic acid, campesterol and complex lipids with low degree of unsaturation in their fatty acid chains were amongst those that showed the highest fold decreases following one or two fractions of SBRT compared to baseline. This study demonstrated significant fold changes in groups of plasma metabolites following one or two SBRT fractions for HCC. Some of the identified plasma metabolites were shown to be associated with liver injury in previous preclinical studies. Correlation analyses are underway to determine if these metabolites are associated with clinical radiation-induced liver/luminal gastrointestinal toxicities and tumor response.