Background:
Cancer cachexia is characterized by a significant reduction in body weight which impacts patient morbidity and mortality. Several factors are proposed to play a role in the pathogenesis of cancer cachexia, including systemic inflammation. Various studies have demonstrated a link between tumor-derived factors, muscle wasting, and lipolysis, but the potential impact of tumor factors on immunometabolism has remained largely unexplored. We hypothesized that tumor factors from cachectic pancreatic cancer patients induce a pro-inflammatory response in macrophages accompanied by a shift towards glycolysis to meet their metabolic demand.

Methods:
Pancreatic tumor organoids from cachectic (n=3) and non-cachectic patients (n=3) were incubated with RPMI for 24 hours to generate conditioned medium (CM). Human monocytes were isolated from peripheral blood mononuclear cells by positive selection using magnetic CD14 microbeads and differentiated to macrophages. The macrophages were incubated with RPMI or CM (50% v/v) for 24 hours. We then analyzed mitochondrial respiration using the Agilent Seahorse XF96 extracellular flux analyzer (Seahorse Bioscience) and pro-inflammatory cytokine levels in the culture medium by ELISA. Furthermore, apoptosis, lipid uptake, and phagocytosis assays were conducted for functional analysis.

Results:
CM from pancreatic tumor organoids strongly suppressed basal mitochondrial respiration of macrophages (120.2±21.6 vs. 91.6±26.9 pmol/min, p=0.017). Moreover, there was a significant difference in the basal oxygen consumption rate of macrophages exposed to CM from the cachectic vs the non-cachectic group (100.8±21.4 vs. 81.7±29.0 pmol/min). Similar observations were made for the spare respiratory capacity (control: 309.6±92.1 vs. non-cachectic: 142.0±53.7 vs. cachectic: 111.0±51.5 pmol/min). However, there were no significant differences in functionality of macrophages that were exposed to CM from cachectic vs non-cachectic organoids.

Conclusion:
Factors released by pancreatic tumor organoids from cachectic patients suppress macrophage respiration, but this does not majorly affect key macrophage functions.