Oral administration of Manuka honey modulates gut microbiota composition and enhances anti-tumor immunity in a preclinical model of colorectal cancer

Abstract Background : There is increasing interest in exploring alternative natural products for cancer prevention and treatment. Among these, we recently highlighted the potential utilization of Manuka honey (MH) as an immunomodulatory agent. In the present study, we characterized mechanistically the immunomodulatory properties of MH in a preclinical model of colorectal cancer (CRC). Methods : MH was administered orally over a 4 week-period. A solution containing equivalent concentrations of the main sugars in MH was used as a control (SC). Mucosal and systemic lymphoid tissues were examined for alterations in cellular composition and activation status by multi-color flow cytometry (FACS). Fecal pellets were collected before and after treatment and used for bacterial 16S rRNA sequencing. Pretreated mice were implanted with CRC cells and followed for tumor growth. Tumors, lymph nodes, and spleens were analyzed by FACS, immunohistochemistry, and qRT-PCR 3-weeks post-implantation. Results : Pretreatment with MH, but not SC solution, induced type I/II IFN response in mucosal and systemic lymphoid tissues, resulting in enhanced expression of IFN-inducible stem cell antigen-1 (Sca-1) and MHC class II proteins. In an implantable model of CRC, tumor growth was significantly retarded in MH-pretreated mice. These tumors had increased infiltration of immune cells, ~2.0-fold increase in the percentage of intratumoral CD4 + and CD8 + T cells, and a 50% decrease in the percentage of Ly6G + myeloid cells. Immunohistochemical analysis of tumor tissues revealed an increase in CD4 + and CD8 + T cells and granzyme-B-expressing cells following MH treatment. Moreover, FACS analysis showed significantly elevated expression of MHC class I on tumors of MH-treated mice. qRT-PCR analysis of purified tumor-infiltrating leucocytes highlighted changes in the expression of various chemokines and inflammatory cytokines that underlie the increased tumor immunogenicity. Finally, bacterial 16S rRNA sequencing revealed unique enrichment of >20 bacterial genera in MH-treated mice. Conclusions : Our findings demonstrate that oral administration of MH induces specific alterations in the gut microbiota and triggers innate and adaptive mucosal immune responses through the activation of type I/II IFN signaling pathways. This culminates in rendering the tumors more immunogenically responsive. Our data highlight the immunostimulatory properties of MH and demonstrate its potential utilization in cancer prevention.