Abstract
<title>Abstract</title> <p>Pyruvate kinase M2 (PKM2) is a key glycolytic enzyme that regulates immune cell activation, and PKM2 activators such as the literature tool compound, TEPP-46, have shown that targeting PKM2 is immunomodulatory. However, previous studies reveal a disconnect between TEPP-46 potency in cellular assays and efficacy in animal models of inflammation or autoimmunity. This study identifies serine demand as a factor responsible for this disconnect and the key determinant of the cellular and tissue-level response to PKM2 modulation. SYX-PKM-A is a novel orally bioavailable PKM2 modulator that induced tetramer formation and increased pyruvate kinase activity in human lymphocytes. PKM2 activation redirects 3-phosphoglycerate (3-PG) away from serine biosynthesis, limiting one-carbon metabolism and nucleotide production. This induces a state of serine auxotrophy in activated human CD4⁺ T cells, Th2 cells, Th17 cells, and B cells, leading to reduced proliferation, cytokine release and immunoglobulin production. These effects are dependent on serine concentration and fully rescued by exogenous formate, confirming one-carbon pathway restriction as the primary mechanism. Skin from atopic dermatitis (AD) patients exhibits reduced serine, increased PKM2, and upregulation of serine transporters and one-carbon metabolism genes, indicating a high serine-demand environment with PKM2-driven metabolic vulnerability. Consistent with this, SYX-PKM-A demonstrates robust efficacy in DNFB-induced dermatitis, KLH delayed-type hypersensitivity, and chronic house dust mite models, reducing lymphocytes, Th2 cytokines, and tissue inflammation to levels comparable with JAK inhibition. These findings establish serine-dependent metabolic restriction as a mechanism for tissue-targeted immunoregulation and highlight PKM2 modulation as a promising oral therapeutic strategy for AD and other T cell–driven inflammatory diseases.</p>