New magnetic resonance (MR) molecular imaging techniques offer the potential for non-invasive, simultaneous quantification of metabolic and perfusion parameters in tumors. This study applied a 3D dynamic dual-agent hyperpolarized 13C magnetic resonance spectroscopic imaging (MRSI) approach with 13C-pyruvate and 13C-urea to investigate differences in perfusion and metabolism between low and high grade tumors in the TRAMP transgenic mouse model of prostate cancer. Dynamic MR data were corrected for T1 relaxation and RF excitation and modeled to provide quantitative measures of pyruvate to lactate flux (kPL) and urea perfusion (urea AUC) that correlated with TRAMP tumor histologic grade. kPL values were relatively higher for high-grade TRAMP tumors. The increase in kPL flux correlated significantly with higher lactate dehydrogenase activity and mRNA expression of Ldha, Mct1 and Mct4 as well as with more proliferative disease. There was a significant reduction in perfusion in high-grade tumors that associated with increased hypoxia and mRNA expression of Hif1α and Vegf and increased ktrans, attributed to increased blood vessel permeability. In 90% of the high-grade TRAMP tumors, a mismatch in perfusion and metabolism measurements was observed, with low perfusion being associated with increased kPL. This perfusion-metabolism mismatch was also associated with metastasis. The molecular imaging approach we developed could be translated to investigate these imaging biomarkers for their diagnostic and prognostic power in future prostate cancer clinical trials.

Optimal treatment selection for localized renal tumors is challenging due to their variable biological behavior and limited ability to pre-operatively assess their aggressiveness. We investigated hyperpolarized (HP) 13C pyruvate MRI to noninvasively assess tumor lactate production and compartmentalization, which are strongly associated with renal tumor aggressiveness. Orthotopic tumors were created in mice using human renal cell carcinoma (RCC) lines (A498, 786-O, UOK262) with varying expression of lactate dehydrogenase A (LDHA) which catalyzes the pyruvate-to-lactate conversion, and varying expression of monocarboxylate transporter 4 (MCT4) which mediates lactate export out of the cells. Dynamic HP 13C pyruvate MRI showed that the A498 tumors had significantly higher 13C pyruvate-to-lactate conversion than the UOK262 and 786-O tumors, corresponding to higher A498 tumor LDHA expression. Additionally, diffusion-weighted HP 13C pyruvate MRI showed that the A498 tumors had significantly higher 13C lactate apparent diffusion coefficients compared to 786-O tumors, with corresponding higher MCT4 expression, which likely reflects more rapid lactate export in the A498 tumors. Our data demonstrate the feasibility of HP 13C pyruvate MRI to inform on tumor lactate production and compartmentalization, and provide the scientific premise for future clinical investigation into the utility of this technique to noninvasively interrogate renal tumor aggressiveness and to guide treatment selection.

Acute kidney injury (AKI) is a major risk factor for the development of chronic kidney disease (CKD). Persistent oxidative stress and mitochondrial dysfunction are implicated across diverse forms of AKI and in the transition to CKD. In this study, we applied hyperpolarized (HP) 13C dehydroascorbate (DHA) and 13C pyruvate MR spectroscopy to investigate the renal redox capacity and mitochondrial pyruvate dehydrogenase (PDH) activity, respectively, in a murine model of AKI at baseline, and 7 days after unilateral ischemia reperfusion injury (IRI). Compared to the contralateral sham-operated kidneys, the kidneys subjected to IRI showed a significant decrease in the HP 13C Vitamin C/(Vitamin C+DHA) ratio, consistent with a decrease in redox capacity. The kidneys subjected to IRI also showed a significant decrease in the HP 13C bicarbonate/pyruvate ratio, consistent with impaired PDH activity. The IRI kidneys showed a significantly higher HP 13C lactate/pyruvate ratio at day 7 compared to baseline, although the 13C lactate/pyruvate ratio was not significantly different between the IRI and the contralateral sham-operated kidneys at day 7. Arterial spin labeling MRI demonstrated significantly reduced perfusion in the IRI kidneys. Renal tissue analysis showed corresponding increased reactive oxygen species (ROS), and reduced PDH activity in the IRI kidneys. Our results show the feasibility of HP 13C MR for the noninvasive assessment of oxidative stress and mitochondrial PDH activity following renal ischemia reperfusion injury.

The detection and treatment monitoring of inflammatory states remain challenging in part due to the multifactorial mechanisms of immune activation and spectrum of clinical manifestations. Currently, diagnostic strategies tend to be subjective and limited quantitative tools exist to monitor optimal treatment strategies. Pro-inflammatory M1 polarized macrophages exhibit a distinct metabolic glycolytic phenotype compared to the continuum of M2 polarization states. In the present study, the distinct metabolic phenotypes of resting and activated macrophages were successfully characterized and quantified using hyperpolarized carbon-13 (13C) labeled pyruvate and its metabolic products, i.e. lactate, as a biomarker of resting, disease and treated states.Methods: Mouse macrophage J774A.1 cells were used as a model system in an NMR compatible bioreactor to facilitate dynamic hyperpolarized 13C measurements. The glycolytic metabolism of the cells in the quiescent or resting state were compared with macrophages stimulated by lipopolysaccharide, a classical M1 activator using hyperpolarized 13C labeled pyruvate. Additionally, the activated macrophages were also treated with a non-steroidal anti-inflammatory drug to assess the changes in hyperpolarized lactate signal. The hyperpolarized lactate signals were then correlated using biochemical and molecular assays.Results: We first validated our model system of inflammatory cells by the hallmarks of M1 polarization using steady state metabolic profiling with high resolution NMR in conjunction with nitric oxide Greiss assay, enzyme activity, and mRNA expression. Subsequently, we clearly showed that the cutting edge technology of hyperpolarized 13C NMR can be used to detect elevated lactate levels in M1 polarized macrophages in comparison to control and non-steroidal anti-inflammatory drug treated M2 states.Conclusion: Hyperpolarized 13C lactate has the potential to serve as a biomarker to non-invasively detect and quantify pro-inflammatory state of immune regulatory cells and its response to therapy.