Deuterium Magnetic Resonance Spectroscopy of Early Treatment-Induced Changes in Tumour Lactate in Vitro

Elevated production of lactate is a key characteristic of aberrant tumour cell metabolism and can be non-invasively measured as an early marker of tumour response using deuterium ( 2 H) magnetic resonance spectroscopy (MRS). Following treatment, changes in the 2 H-labeled lactate signal could identify tumour cell death or impaired metabolic function, which precede morphological changes conventionally used to assess tumour response. In this work, the association between apoptotic cell death, extracellular lactate concentration, and early treatment-induced changes in the 2 H-labeled lactate signal was established in an in vitro tumour model. Experiments were conducted at 7 T on acute myeloid leukemia cells which had been treated with 10 µg/mL of the chemotherapeutic agent cisplatin. At 24 and 48 hours after cisplatin treatment, the cells were injected with 20 mM of [6,6’- 2 H 2 ]glucose and scanned over two hours using a two-dimensional 2 H MR spectroscopic imaging sequence. The resulting signals from 2 H-labeled glucose, lactate, and water were quantified using a spectral fitting algorithm implemented on the OXford Spectroscopy Analysis (OXSA) MATLAB toolbox. After scanning, the cells were processed for histological stains (TUNEL [terminal deoxynucleotidyl transferase UTP nick end labeling] and H&E [hematoxylin and eosin]) to assess apoptotic area fraction and cell morphology respectively, while a colorimetric assay was used to measure extracellular lactate concentrations in the supernatant. Significantly lower levels of 2 H-labeled lactate were observed in the 48-hour treated cells compared to the untreated and 24-hour treated cells, and these changes were significantly correlated with an increase in apoptotic fraction and a decrease in extracellular lactate. By establishing the biological processes associated with treatment-induced changes in the 2 H-labeled lactate signal, these findings suggest that 2 H MRS of lactate may be valuable in evaluating early tumour response.