Cathepsin inhibition modulates metabolism and polarization of tumor-associated macrophages

Diana Oelschlaegel, Tommy Weiss Sadan, Seth Salpeter, Sebastian Krug, Galia Blum, Werner Schmitz, Almut Schulze, Patrick Michl*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


Stroma-infiltrating immune cells, such as tumor-associated macrophages (TAM), play an important role in regulating tumor progression and chemoresistance. These effects are mostly conveyed by secreted mediators, among them several cathepsin proteases. In addition, increasing evidence suggests that stroma-infiltrating immune cells are able to induce profound metabolic changes within the tumor microenvironment. In this study, we aimed to characterize the impact of cathepsins in maintaining the TAM phenotype in more detail. For this purpose, we investigated the molecular effects of pharmacological cathepsin inhibition on the viability and polarization of human primary macrophages as well as its metabolic consequences. Pharmacological inhibition of cathepsins B, L, and S using a novel inhibitor, GB111-NH2, led to changes in cellular recycling processes characterized by an increased expression of autophagy-and lysosome-associated marker genes and reduced adenosine triphosphate (ATP) content. Decreased cathepsin activity in primary macrophages further led to distinct changes in fatty acid metabolites associated with increased expression of key modulators of fatty acid metabolism, such as fatty acid synthase (FASN) and acid ceramidase (ASAH1). The altered fatty acid profile was associated with an increased synthesis of the pro-inflammatory prostaglandin PGE2, which correlated with the upregulation of numerous NFkB-dependent pro-inflammatory mediators, including interleukin-1 (IL-1), interleukin-6 (IL-6), C-C motif chemokine ligand 2 (CCL2), and tumor necrosis factor-alpha (TNFα). Our data indicate a novel link between cathepsin activity and metabolic reprogramming in macrophages, demonstrated by a profound impact on autophagy and fatty acid metabolism, which facilitates a pro-inflammatory micromilieu generally associated with enhanced tumor elimination. These results provide a strong rationale for therapeutic cathepsin inhibition to overcome the tumor-promoting effects of the immune-evasive tumor micromilieu.

Original languageAmerican English
Article number2579
Pages (from-to)1-22
Number of pages22
Issue number9
StatePublished - Sep 2020

Bibliographical note

Publisher Copyright:
© 2020 by the authors. Licensee MDPI, Basel, Switzerland.


  • Activity-based probes
  • Autophagy
  • Cathepsin
  • Inflammation
  • Lipid metabolism
  • Lysosome
  • Tumor-associated macrophage


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