PGE2-HIF1α reciprocal induction regulates migration, phenotypic alteration and immunosuppressive capacity of macrophages in tumor microenvironment.

Background: Very little is known about the role inflammation and mechanism(s) that enables the tumor to evade host's anti-tumor immune function during very initial days of tumor establishment. Our study focuses on the immune response and local inflammation specially the pro-inflammatory and immune modifier components that are responsible for tumor-induced immune-suppression, tumor-associated macrophages (TAM) at tumor microenvironment in mouse model from very early to late phase of tumor progression.

Methods: 1 × 10 Ascites tumor, EAC in Swiss albino or Sarcoma-180 (S-180) in Balb c mice strain were inoculated intra-peritonially and grouped into Control (0 day or no tumor), initial phase (3 day tumor), early (7 Day), Late (14 day) and terminal (21 day tumor) sets. T cell activity, tumor niche macrophage, inflammatory signatures were studied using Confocal microscopy, flowcytometry, ELISA, q-RT PCR and Western blot.

Results: We observed increased T cell infiltration at a very early stage of tumorigenesis in the tumor site with elevated percentage of activated/memory T cells. But increased cellular death and functional suppression of tumor site T cells during final stages. We observed increased infiltration of TAMs with skewed M2 phenotype. Increased chemokine receptor expression could be noted on these TAMs. Using HIF-1α inhibitor and prostaglandin receptor antagonists we demonstrated crucial role of these factor in functional alteration in TAMs. HIF-1α inhibition and also by prostaglandin receptor inhibition reduced signature pro-inflammatory gene expression, migration of macrophages and T cell suppression capacity of TAMs. We also demonstrated that PGE2 can induce HIF-1α activation in relatively less hypoxic microenvironment during early stages of tumor.

Conclusion: Altogether, these findings strongly suggest link between prostaglandin mediated early HIF-1α activation and subsequent hypoxia induced HIF-1α activation that further enhances prostaglandin synthesis driving the recruitment and functional alteration of tumor site macrophages.