Silibinin induced mast cell regulation: Potential immunomodulation via ODC1 in pancreatic cancer prevention and therapy

It has been estimated by the American Cancer Society that in the US in 2025, ~67,440 people (34,950 men; 32,490 women) will be diagnosed with, and ~51,980 people (27,050 men; 24,930 women) will die of pancreatic cancer (PC). Additionally, the average lifetime risk of developing PC has been estimated to be ~1 in 56 in men and ~1 in 60 in women. PC has been reported to be the 4th leading cause of cancer deaths in the US with a <5% overall 5-year survival rate. The role of immune system, particularly the primary cellular responders, the mast cells (MCs), in PC remains obscure. The natural flavonolignan silibinin (SB), has been effective in preclinical models of PC; however, its role in the immune modulation in PC has not been reported, to our knowledge, particularly with respect to MCs. We previously reported immunomodulation by SB in basal cell carcinoma, prostate cancer, colon cancer, and hepatocellular carcinoma. Thus, mechanistic aspects of SB treatment on MCs in PC were determined, leveraging bone marrow MCs (BMMCs) derived from C57BL/6 mice, in the presence of IL-3 and SCF (confirmed using flow cytometry [cKit/Fc€RI dual staining]). BMMCs were exposed to different doses of SB (25-100 µM) and two concentrations (25 µM; SB 25 and 100 µM; SB 100) were selected for further experiments. BMMCs treated with SB 25, SB 100, and untreated (control) were subjected to proteomics (LCMS on Fusion Lumos mass spectrometer); 3575 proteins were identified using the annotated mouse proteome. Statistical analysis (ANOVA followed by Fisher's posthoc analysis; p<0.05, FDR<0.01) and 166 proteins were found to have statistically significant differential expressions amongst the three groups (n=4/group). These 166 proteins were selected for further pathway analysis using Ingenuity Pathway Analysis (IPA; Qiagen). Only pathways specifically demonstrated experimentally in immune cells/cell lines in PC were selected for further analysis. Top canonical pathways associated with SB treatment of immune cell regulation via MCs were found to be folate signaling pathway, senescence-associated secretory phenotype, cyclins and cell cycle regulation, transcriptional regulation by RUNX2, as senescence pathway. Important upstream regulators were found to be ODC1, CDKN1A, SMAD2, PLAC8, TP53. Important nodes determined were KRAS, GLI1, and ODC1, with the main causal network implicated being polyamine synthesis, hinged on ornithine decarboxylase 1 (ODC1). ODC1 inhibition is proposed to be a potential therapeutic strategy, as pancreatic tumors particularly those resistant to conventional treatments are highly dependent on this enzyme for tumor progression. Thus, SB may play an important immunomodulatory role in PC via regulation of MCs and ODC1. Further studies are warranted to delineate these mechanisms leveraging SB in the form of a preventive or treatment option (supported by R01 CA140368).