Biosynthesis-Encoded Lipogenic Acetyl-CoA Measurement Using NMR Reveals Glucose-Driven Lipogenesis and Glutamine’s Alternative Roles in Kidney Cancer

Fatty acid de novo synthesis (FADNS)
is a critical
process in lipogenesis that is characteristically altered in clear
cell renal cell carcinoma (ccRCC), which is the major type of kidney
cancer. An important challenge in studying the FADNS process has been
the accurate measurement of cytosolic lipogenic acetyl-CoA (AcCoA),
the precursor in FADNS, due to its compartmentalization within cells.
Here, we describe a novel NMR-based method to decode the isotopic
enrichment of lipogenic AcCoA, which, as we demonstrated, is encoded
in the simple signal ratios of the geminal methyl groups of lanosterol
during its biosynthesis. The approach was validated based on the independence
of the tracer enrichment and species along with the expected FADNS
modulation using differentially enriched tracers and a well-studied
drug. Application of this technique to 786-O ccRCC cells showed that
glucose may serve as a major carbon source for lipogenic AcCoA in
FADNS at physiological nutrient concentrations, at odds with previous
studies that indicated glutamine’s dominant role through reductive
carboxylation under higher nutrient conditions. Further investigation
into glutamine’s alternative roles in ccRCC cells suggested
its major involvement in the bioenergetic TCA cycle, pyrimidine synthesis,
and glutathione synthesis, which is also critical in ccRCC growth.
The glutamine-dependent glutathione synthesis was also suggested as
a possible metabolic vulnerability compared to normal kidney cells
using a glutathione synthesis inhibitor. The current study provides
a simple tool for studying an important aspect of lipid metabolism
and suggests translational implications for targeting glucose-driven
lipogenesis and glutamine-supported glutathione synthesis in ccRCC.