SHMT2-mediated mitochondrial serine metabolism drives 5-FU resistance by fueling nucleotide biosynthesis

5-Fluorouracil (5-FU) is a key component of chemotherapy for colorectal cancer (CRC). 5-FU efficacy is es-tablished by intracellular levels of folate cofactors and DNA damage repair strategies. However, drug resis-tance still represents a major challenge. Here, we report that alterations in serine metabolism affect 5-FU sensitivity in in vitro and in vivo CRC models. In particular, 5-FU-resistant CRC cells display a strong serine dependency achieved either by upregulating endogenous serine synthesis or increasing exogenous serine uptake. Importantly, regardless of the serine feeder strategy, serine hydroxymethyltransferase-2 (SHMT2)-driven compartmentalization of one-carbon metabolism inside the mitochondria represents a specific adap-tation of resistant cells to support purine biosynthesis and potentiate DNA damage response. Interfering with serine availability or affecting its mitochondrial metabolism revert 5-FU resistance. These data disclose a relevant mechanism of mitochondrial serine use supporting 5-FU resistance in CRC and provide perspec-tives for therapeutic approaches.

Automated summary

The study reveals that alterations in serine metabolism affect the sensitivity of colorectal cancer cells to 5-FU. Resistant cells become dependent on serine by increasing its synthesis or uptake. Mitochondrial compartmentalization of one-carbon metabolism supports purine biosynthesis and DNA damage response in resistant cells.