Background: A complex of Zn and carnosine, called Zinc-L-carnosine (ZnC), enjoys a wide application as part of a Zn supplement therapeutic method as well as in treating peptic ulcers. However, researches fail to confirm the biological functions possessed by ZnC as well as tumor immune microenvironment in colorectal cancer (CRC).

Methods: Cell counting kit 8(CCK8), 5-ethynyl-2'-deoxyuridine (EdU), transwell and wound healing assays were conducted to study the influence of ZnC in the proliferating, invading and migrating processes of CRC cell lines (HCT116, LOVO) in vitro. The antitumor activity ZnC as well as its effects on tumor immune microenvironment were then assessed using CRC subcutaneous tumors in the C57BL/6 mouse model.

Results: According to CCK8, EdU, transwell and wound healing assays, ZnC inhibited CRC cell lines in terms of proliferation, invasion and migration. ZnC could inhibit miR-570 for up-regulating PD-L1 expression. In vivo experiments showed that gavage (100 mg/kg, once every day) of ZnC inhibited the tumor growth of CRC, and the combination of ZnC and anti-PD1 therapy significantly improved the efficacy exhibited by anti-PD1 in treating CRC. In addition, mass cytometry results showed that immunosuppressive cells including regulatory T cells (tregs), bone marrow-derived suppressor cells (MDSC), and M2 macrophages decreased whereas CD8+ T cells elevated after adding ZnC.

Conclusions: The present study reveals that ZnC slows the progression of CRC by inhibiting CRC cells in terms of proliferation, invasion and migration, meanwhile up-regulating PD-L1 expression via inhibiting miR-570. The ZnC-anti-PD1 co-treatment assists in synergically increasing anti-tumor efficacy in CRC therapy.