Elevated Tumor Lactate and Efflux in High-grade Prostate Cancer demonstrated by Hyperpolarized 13C Magnetic Resonance Spectroscopy of Prostate Tissue Slice Cultures

Abstract

Non-invasive assessment of the biological aggressiveness of prostate cancer (PCa) is needed for men with localized disease. Hyperpolarized (HP) 13C magnetic resonance (MR) spectroscopy is a powerful approach to image metabolism, specifically the conversion of HP [1-13C]pyruvate to [1-13C]lactate, catalyzed by lactate dehydrogenase (LDH). Significant increase in tumor lactate was measured in high-grade PCa relative to benign and low-grade cancer, suggesting that HP 13C MR could distinguish low-risk (Gleason score ≤3 + 4) from high-risk (Gleason score ≥4 + 3) PCa. To test this and the ability of HP 13C MR to detect these metabolic changes, we cultured prostate tissues in an MR-compatible bioreactor under continuous perfusion. 31P spectra demonstrated good viability and dynamic HP 13C-pyruvate MR demonstrated that high-grade PCa had significantly increased lactate efflux compared to low-grade PCa and benign prostate tissue. These metabolic differences are attributed to significantly increased LDHA expression and LDH activity, as well as significantly increased monocarboxylate transporter 4 (MCT4) expression in high- versus low- grade PCa. Moreover, lactate efflux, LDH activity, and MCT4 expression were not different between low-grade PCa and benign prostate tissues, indicating that these metabolic alterations are specific for high-grade disease. These distinctive metabolic alterations can be used to differentiate high-grade PCa from low-grade PCa and benign prostate tissues using clinically translatable HP [1-13C]pyruvate MR.

Hyperpolarised 13C-MRI identifies the emergence of a glycolytic cell population within intermediate-risk human prostate cancer

“…3g , Supplementary Table 5 ), as demonstrated by a significant increase in the LDHA / LDHB ratio ( P = 0.006; Supplementary Table 5 ). Increased LDHA and MCT4 expression in aggressive prostate lesions are in agreement with previous studies 36 , 48 , and changes in LDHB have been reported previously 44 , 49 , 50 . However, the role of total LDH expression and individual isoenzyme pattern in the context of clinical hyperpolarised 13 C-MRI has not been elucidated in previous work and provides an important additional measure of metabolism that can be used in future studies.…”

“…3 ; Supplementary Table 9 ). Overall, these observations are consistent with the known increase in glycolysis in late-stage aggressive PCa 36 , 48 , while also in agreement with reports in which changes in glycolysis could not differentiate GP3 and GP4 disease, suggesting a step-change nature of the emergence of a more glycolytic phenotype in GP5 disease 54 – 56 . These findings provide further support for the importance of increased tumour epithelial LDH expression with more aggressive disease, which has direct implications for the clinical use of HP 13 C-MRI.…”

“…Several groups have investigated the effects of monocarboxylate transporter and lactate dehydrogenase expression and activity on [1- 13 C]pyruvate metabolism 21 , 22 , 48 , 59 , 65 – 67 . [1- 13 C]Lactate labelling has been shown to correlate significantly with MCT1 expression in breast and prostate cancer patients 21 , 59 , and experiments in vitro have demonstrated the importance of MCT1 for [1- 13 C]pyruvate-to-[1- 13 C]lactate conversion in selected cell lines 67 .…”

“…[1- 13 C]Lactate labelling has been shown to correlate significantly with MCT1 expression in breast and prostate cancer patients 21 , 59 , and experiments in vitro have demonstrated the importance of MCT1 for [1- 13 C]pyruvate-to-[1- 13 C]lactate conversion in selected cell lines 67 . Increased MCT4 expression and LDH expression or activity have also been shown to be distinct features of high-grade and metastatic prostate tumours 22 , 36 , 48 . Here we have shown that the key drivers of higher [1- 13 C]lactate labelling in the more aggressive subtype of intermediate-risk PCa are the combined tumour epithelial LDH (combined LDHA and LDHB ), and the associated increase in tumour epithelium-to-stroma MCT4 expression, with both markers demonstrating a much stronger relationship with lactate SNR compared to epithelial MCT1 and epithelial or stromal MCT4 alone.…”

Metabolic response to radiation therapy in cancer

“…HP‐NMRS has been successfully used to track metabolite conversion over time in cells cultured in NMR‐compatible bioreactors, providing a useful system for studying cancer cell organoids, 78 tissue slices, 79 or the effects of ionizing radiation in three‐dimensional alginate hydrogel cultures of cancer cells 80 . This method has successfully tracked the concentration and conversion of multiple metabolites in cancer cells, including the conversion of pyruvate to lactate, alanine, and bicarbonate 66,81 and the conversion of αKG to 2‐hydroxyglutarate 71 in cells with mutations in isocitrate dehydrogenase 1 (IDH1) 82 .…”