LL-37 Limits the Therapeutic Efficacy of 1,25(OH) 2 D 3 and Suramin for HCC by Enhancing M2 Macrophage Polarization

Abstract Background: Supplementation with 1,25(OH)2D3 alone doesn't benefit hepatocellular carcinoma (HCC) patients. LL-37, part of innate immunity, and its impact on HCC progression via macrophages, as well as its interaction with 1,25(OH)2D3, remain unclear. Methods: HCC/macrophage co-cultures in vitro was applied and the M1/M2 polarization from THP-1-derived macrophages was identified by qRT-PCR, Western blot, immunofluorescence staining and ELISA assays. The effect of 1,25(OH)2D3 -LL-37 axis on HCC cells (PLC/PRF-5 and Huh7) was detected by proliferation, colony formation, and invasion assays. A HCC/macrophage co-xenograft model tested suramin's targeting of TAMs for 1,25(OH)2D3 therapy. Results: LL-37 expression rose in HCC/macrophage co-culture. LL-37 overexpression boosted macrophage recruitment, M2 polarization, and Akt/mTOR, JAK/STAT3 pathway activation, enhancing HCC cell viability, migration, invasion. 1,25(OH)2D3 increased hCAP18/LL-37 levels in vitro and in xenografted mice, involving the vitamin D receptor. 1,25(OH)2D3 also increased macrophage recruitment, M2 polarization. Suramin blockade of LL-37 eliminated 1,25(OH)2D3-induced effects, enhancing its anticancer activity in vivo. Conclusions: LL-37 contributes to a 1,25(OH)2D3-induced immunosuppressive microenvironment by TAM regulation, limiting 1,25(OH)2D3 efficacy in HCC. Combining 1,25(OH)2D3 with suramin may enhance anticancer effects, potentially benefiting HCC patients.