A hallmark of metastasis is the adaptation of tumor cells to new environments. Metabolic constraints imposed by the serine and glycine-limited brain environment restrict metastatic tumor growth. How brain metastases overcome these growth-prohibitive conditions is poorly understood. Here, we demonstrate that 3-phosphoglycerate dehydrogenase (PHGDH), which catalyzes the rate-limiting step of glucose-derived serine synthesis, is a major determinant of brain metastasis in multiple human cancer types and preclinical models. Enhanced serine synthesis proved important for nucleotide production and cell proliferation in highly aggressive brain metastatic cells. In vivo , genetic suppression and pharmacologic inhibition of PHGDH attenuated brain metastasis, but not extracranial tumor growth, and improved overall survival in mice. These results reveal that extracellular amino acid availability determines serine synthesis pathway dependence, and suggest that PHGDH inhibitors may be useful in the treatment of brain metastasis. SIGNIFICANCE:Using proteomics, metabolomics, and multiple brain metastasis models, we demonstrate that the nutrient-limited environment of the brain potentiates brain metastasis susceptibility to serine synthesis inhibition. These fi ndings underscore the importance of studying cancer metabolism in physiologically relevant contexts, and provide a rationale for using PHGDH inhibitors to treat brain metastasis.

Hyperpolarized micro-NMR nondestructively analyzes metabolic activities in scant cells.

The ever-changing tumor-microenvironment constantly challenges individual cancer cells to balance supply and demand, presenting tumor vulnerabilities and therapeutic opportunities. Everolimus and temsirolimus are inhibitors of mTOR (mTORi) approved for treating metastatic renal cell carcinoma (mRCC). However, treatment outcome varies greatly among patients. Accordingly, administration of mTORi in mRCC is diminishing, which could potentially result in missing timely delivery of effective treatment for select patients. Here we implemented a clinically applicable, integrated platform encompassing a single dose of [1-13C] pyruvate to visualize the in vivo effect of mTORi on the conversion of pyruvate to lactate using hyperpolarized MRI. A striking difference that predicts treatment benefit was demonstrated using two preclinical models derived from clear cell RCC (ccRCC) patients who exhibited primary resistance to VEGFRi and quickly succumbed to their diseases within 6 months after the diagnosis of metastasis without receiving mTORi. Our findings suggest that hyperpolarized MRI could be further developed to personalize kidney cancer treatment.

Although dissolution dynamic nuclear polarization is a robust technique to significantly increase magnetic resonance signal, the short T relaxation time of most C-nuclei limits the timescale of hyperpolarized experiments. To address this issue, we have characterized a non-synthetic approach to extend the hyperpolarized lifetime ofC-nuclei in close proximity to solvent-exchangeable protons. Protons exhibit stronger dipolar relaxation than deuterium, so dissolving these compounds in DO to exchange labile protons with solvating deuterons results in longer-lived hyperpolarization of the C-nucleus 2-bonds away.C T and T times were longer in DO versus HO for all molecules in this study. This phenomenon can be utilized to improve hyperpolarized signal-to-noise ratio as a function of longer T, and enhanced spectral and imaging resolution via longer T.

Alterations in arginase enzyme expression are linked with various diseases and have been shown to support disease progression, thus motivating the development of an imaging probe for this enzymatic target. 13 C-enriched arginine can be used as a hyperpolarized (HP) magnetic resonance (MR) probe for arginase flux since the arginine carbon-6 resonance (157 ppm) is converted to urea (163 ppm) following arginase catalyzed hydrolysis. However, scalar relaxation from adjacent 14 Nnuclei shortens cabon-6 T 1 and T 2 times, yielding poor spectral properties. To address these limitations, we report the synthesis of [6-13 C, 15 N 3 ]-arginine and demonstrate that 15 N-enrichment increases carbon-6 relaxation times, thereby improving signal-to-noise ratio and spectral resolution. By overcoming these limitations with this novel isotope-labeling scheme, we were able to perform in vitro and in vivo arginase activity measurements with HP MR. We present HP [6-13 C, 15 N 3 ]-arginine as a noninvasive arginase imaging agent for preclinical studies, with the potential for future clinical diagnostic use.