Abstract

Significance Enzymes of the folate cycle are among the most consistently overexpressed proteins in cancer. Whereas multiple clinical agents inhibit thymidylate synthase, no current drugs target the incorporation of one-carbon into folates via serine hydroxymethyltransferase (SHMT). Using genetics, we show that cancer cells require SHMT to generate tumors. We then describe small-molecule SHMT inhibitors, and show that they block the growth of many human cancer cells, with B-cell lymphomas particularly sensitive to SHMT inhibition. We find that this sensitivity arises from the lymphomas’ inability to import the amino acid glycine, which is made as a byproduct of the SHMT reaction. Thus, B-cell lymphomas have an intrinsic defect in amino acid import, which causes a therapeutically targetable metabolic vulnerability.