Assessment of the sensitivity of 2H MR spectroscopy measurements of [2,3‐2H2]fumarate metabolism for detecting tumor cell death

Abstract

AbstractImaging the metabolism of [2,3‐2H2]fumarate to produce malate can be used to detect tumor cell death post‐treatment. Here, we assess the sensitivity of the technique for detecting cell death by lowering the concentration of injected [2,3‐2H2]fumarate and by varying the extent of tumor cell death through changes in drug concentration. Mice were implanted subcutaneously with human triple negative breast cancer cells (MDA‐MB‐231) and injected with 0.1, 0.3, and 0.5 g/kg [2,3‐2H2]fumarate before and after treatment with a multivalent TRAlL‐R2 agonist (MEDI3039) at 0.1, 0.4, and 0.8 mg/kg. Tumor conversion of [2,3‐2H2]fumarate to [2,3‐2H2]malate was assessed from a series of 13 spatially localized 2H MR spectra acquired over 65 min using a pulse‐acquire sequence with a 2‐ms BIR4 adiabatic excitation pulse. Tumors were then excised and stained for histopathological markers of cell death: cleaved caspase 3 (CC3) and DNA damage (terminal deoxynucleotidyl transferase dUTP nick end labeling [TUNEL]). The rate of malate production and the malate/fumarate ratio plateaued at tumor fumarate concentrations of 2 mM, which were obtained with injected [2,3‐2H2]fumarate concentrations of 0.3 g/kg and above. Tumor malate concentration and the malate/fumarate ratio increased linearly with the extent of cell death determined histologically. At an injected [2,3‐2H2]fumarate concentration of 0.3 g/kg, 20% CC3 staining corresponded to a malate concentration of 0.62 mM and a malate/fumarate ratio of 0.21. Extrapolation indicated that there would be no detectable malate at 0% CC3 staining. The use of low and nontoxic fumarate concentrations and the production of [2,3‐2H2]malate at concentrations that are within the range that can be detected clinically suggest this technique could translate to the clinic.