Tricarboxylic Acid (TCA) cycle, also known as the Citric Acid cycle or Krebs cycle, is a key metabolic pathway that plays a central role in cellular energy production.
The TCA cycle is a series of chemical reactions that occur in the mitochondria and involve the breakdown of acetyl-CoA, a molecule produced from the breakdown of carbohydrates, fats, and proteins. The TCA cycle produces:
1. NADH and FADH2
2. ATP
3. GTP
Expression of TCA cycle enzymes is often downregulated in cancer cells.
Since cancer cells often exhibit rewired metabolism, including alterations in the use of the TCA cycle, researchers are exploring potential therapeutic interventions that target metabolic enzymes or pathways.
TCA cycle is essential for normal cellular metabolism, its role in cancer is multifaceted. Cancer cells often reprogram their metabolism—including the TCA cycle—to support rapid growth, adapt to hypoxia, and manage oxidative stress. Mutations in key TCA cycle enzymes generate oncometabolites that further contribute to cancer progression by disrupting normal cellular regulation.
Rather than saying the TCA cycle is globally over- or underexpressed in cancer, it is more accurate to say that cancer cells reprogram the cycle—with selective upregulation of parts important for biosynthesis and survival and mutations or downregulation of other parts—to best support their growth and survival in a challenging microenvironment.
Oncometabolites
-Some metabolites in the Krebs cycle, when accumulated to abnormal levels due to genetic mutations or enzyme deficiencies, are termed “oncometabolites” because they can promote tumorigenesis.
-Mutations in succinate dehydrogenase (SDH) can lead to accumulation of succinate.
-Mutations in fumarate hydratase (FH) result in an accumulation of fumarate.
-Mutations in isocitrate dehydrogenase (IDH1 and IDH2) result in a neomorphic enzyme activity that converts α-ketoglutarate (α-KG) to 2-hydroxyglutarate:
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