How is glycine associated with cancer?

Glycine is Fundamentally Linked to Cancer Through Multiple Metabolic Pathways That Support Rapid Cell Proliferation

Glycine consumption and biosynthesis are strongly correlated with cancer cell proliferation rates, with rapidly dividing cancer cells becoming dependent on glycine for survival and growth 1. This relationship represents both a metabolic vulnerability and a potential therapeutic target in cancer treatment.

Core Metabolic Roles in Cancer

Glycine serves critical functions in cancer cell metabolism through several interconnected pathways 2:

• Serine and glycine metabolism is among the key metabolic pathways differentially activated in cancer cells, alongside the Warburg effect and glutamine metabolism
• Cancer cells rewire these pathways to maintain continuous supplies of anabolic precursors, reducing equivalents, and energy for proliferation
• The pathways allow cancer cells to extract cellular building blocks from substrates and adapt to changing microenvironments

Specific Metabolic Functions

Glycine supports four essential cancer cell functions:

• Macromolecule synthesis: Glycine primarily directs toward protein and nucleotide synthesis (100% of glycine output), supporting the high biosynthetic demands of proliferating cells 3
• One-carbon metabolism: Serine converts to glycine while donating one-carbon units for nucleotide synthesis and methylation reactions 4
• Oxidative stress management: The serine-glycine pathway helps neutralize high levels of reactive oxygen species in cancer cells 4
• Epigenetic regulation: These amino acids regulate methylation and tRNA formylation processes 4

Quantitative Metabolic Flux

In cancer cells, the metabolic flux reveals striking dependencies 3:

• Serine input flux exceeds glycine by 7.3-fold
• Glycine inputs derive from: uptake (45.6%), conversion from serine (45.1%), and other sources like protein degradation (9.4%)
• Serine predominantly directs to phospholipid, sphingolipid, and protein synthesis (94.7%), with only 5.3% converting to glycine and one-carbon units
• Serine deprivation primarily impairs phospholipid and sphingolipid synthesis, which are crucial for cell growth

Proliferation Dependency

The mitochondrial glycine biosynthetic pathway expression correlates strongly with proliferation rates across cancer cell lines 1. Key findings include:

• Antagonizing glycine uptake and mitochondrial biosynthesis preferentially impairs rapidly proliferating cells
• Higher expression of this pathway associates with greater mortality in breast cancer patients
• This represents a metabolic vulnerability for selectively targeting rapid cancer cell proliferation

Clinical and Prognostic Implications

The relationship between glycine levels and cancer outcomes shows important nuances:

Protective effects of circulating glycine:

• Higher serum glycine levels associate with reduced pancreatic cancer risk (21.4% reduction, HR: 0.786) 5
• Elevated glycine shows >70% risk reduction for pancreatic cancer development 6
• This protective effect persists even in individuals with highest genetic susceptibility 5

Treatment response modulation:

• Higher serine/glycine ratio associates with lower rectal cancer recurrence risk (HR 0.47 per doubling) 7
• The ratio indicates SHMT enzyme activity, suggesting this pathway's importance in treatment outcomes
• Glutamine, serine, and glycine at increasing concentrations regulate cisplatin sensitivity through KDM4A posttranslational modifications 8

Therapeutic Targeting Considerations

Cancer subtypes with high serine/glycine pathway expression may benefit from adjuvant targeting compounds 9. However, critical caveats exist:

• The pathway shows immunosuppressive potential 4
• Serine and glycine are essential for survival of non-transformed neighboring cells 4
• Enzymes in these pathways have emerging moonlighting functions beyond metabolism 4

Key Clinical Pitfall

The paradox: While cancer cells depend on glycine for proliferation (making it a therapeutic target), higher circulating glycine levels in patients associate with reduced cancer risk and better outcomes. This suggests:

• Intracellular cancer cell glycine metabolism differs fundamentally from systemic glycine homeostasis
• Therapeutic strategies must distinguish between blocking cancer cell glycine utilization versus maintaining adequate systemic glycine levels
• Patient stratification based on serine/glycine pathway expression is essential before considering metabolic targeting 9

The relationship between glycine and cancer is bidirectional: cancer cells hijack glycine metabolism to fuel proliferation, while adequate systemic glycine levels may provide protective effects against cancer development 6, 5.