Radical Hemithoracic Radiotherapy Induces Systemic Metabolomics Changes That Are Associated with the Clinical Outcome of Malignant Pleural Mesothelioma Patients

Abstract

Radical hemithoracic radiotherapy (RHRT) represents an advanced therapeutic option able to improve overall survival of malignant pleural mesothelioma patients. This study aims to investigate the systemic effects of this radiotherapy modality on the serum metabolome and their potential implications in determining the individual clinical outcome. Nineteen patients undergoing RHRT at the dose of 50 Gy in 25 fractions were enrolled. Serum targeted metabolomics profiles were investigated at baseline and the end of radiotherapy by liquid chromatography and tandem mass spectrometry. Univariate and multivariate OPLS-DA analyses were applied to study the serum metabolomics changes induced by RHRT while PLS regression analysis to evaluate the association between such changes and overall survival. RHRT was found to affect almost all investigated metabolites classes, in particular, the amino acids citrulline and taurine, the C14, C18:1 and C18:2 acyl-carnitines as well as the unsaturated long chain phosphatidylcholines PC ae 42:5, PC ae 44:5 and PC ae 44:6 were significantly decreased. The enrichment analysis showed arginine metabolism and the polyamine biosynthesis as the most perturbed pathways. Moreover, specific metabolic changes encompassing the amino acids and acyl-carnitines resulted in association with the clinical outcome accounting for about 60% of the interpatients overall survival variability. This study highlighted that RHRT can induce profound systemic metabolic effects some of which may have a significant prognostic value. The integration of metabolomics in the clinical assessment of the malignant pleural mesothelioma could be useful to better identify the patients who can achieve the best benefit from the RHRT treatment.

Keywords: biomarkers; cancers; mesothelioma; metabolomics; radiotherapy.

Figure 1

Orthogonal partial least squares discriminant analysis (OPLS-DA) score plot discriminated serum metabolomics profiles (n = 19) at baseline (T₀, blue) and post-radical hemithoracic radiotherapy (RHRT) (T₁, green) (a). Internal validation by permutation test showed R² (green) and Q² (blue) values from the permuted models (bottom left) significantly lower than the corresponding original model (top right) (b). Percentage variations of metabolites altered by RHRT (c). Heat map plot of the significantly changed serum metabolites between T₀ samples (left) and T₁ samples (right) ranked by t-test. Metabolites significantly decreased were in green, while metabolites significantly increased were in red. The brightness of the colour corresponded to the magnitude of the difference with the mean value (d).

Figure 2

Over Representation Analysis plot from enrichment analysis. Bars represent matched pathways coloured according to their significance values, with gradations from yellow (low significance) to red (high significance) (a). Metabolic pathways altered as effect of RHRT and relative metabolites concentrations prior- (T₀) and post-RHRT (T₁) in 19 malignant pleural mesothelioma (MPM) patients. p-values derive from the Student’s t-test, *** p < 0.001, ** p < 0.01, * p < 0.05 (b).

Figure 3

Partial least square (PLS) score plot for the first two latent variables t(1) and u(1), in which each point represents one patient, plotted as scores (or coefficients) from the metabolomics fold changes data (X block) vs. the score from the overall survival (OS) (Y block). Colour gradations from blue to red represents increasing values of OS (a). PLS loading plot. Each point is a metabolite plotted as the coefficient from PLS LV1 (first latent variable) vs. the coefficient from LV2 (second latent variable). Metabolites in the top right (highest positive coefficient) or in the bottom left (lowest negative coefficient) have a strong correlation with the OS (b). Metabolites fold changes most correlated with OS by Pearson correlation analysis (c).

Figure 4

Amino acids mean overall variations of long survival patients normalized to those of short survival patients. Long survival patients belong to IQ (interquartile) and Q4 OS groups; short survival patients belong to the Q1 OS group. Amino acids statistically significant (p < 0.05) are highlighted in grey *** p < 0.001; ** p < 0.01, * p < 0.05.