174P - Targeting SPHK1 in macrophages suppresses liver metastasis of colorectal cancer and decouples anti-tumor immunity from immunotherapy toxicity

Background

Colorectal cancer (CRC) is the second leading cause of cancer deaths, and liver metastasis accounts for most fatalities in CRC patients. Developing more effective treatments for patients with metastatic CRC is an urgent unmet need. Sphingosine kinase 1 (SPHK1) is selectively expressed in tumor-associated macrophages (TAMs) and SPHK1⁺ TAMs are abundant in metastatic tumor microenvironment. Here, we aimed to reveal the role of SPHK1⁺ TAMs in regulating immunosuppression and develop novel therapeutic strategies to enhance the efficacy of immune checkpoint blockade (ICB) therapy and mitigate ICB-induced toxicity.

Methods

The expression of SPHK1 in TAMs was determined using laser scanning microscopy and single-cell sequencing databases. The inhibitory effect of SPHK1 blockade alone or combined with ICB on liver metastasis was assessed using an orthotopic mouse model or intrasplenic injection of tumor cells. Flow cytometry and mass cytometry were used to analyze the immune microenvironment in SPHK1^-/- knockout mice. The effect of SPHK1 inhibitor PF543 on the ICB-induced toxicity was verified by DSS-induced colitis or humanized mouse model in a combination of ICB. RNA sequencing and western blot were used to further explore the molecular mechanism by which SPHK1 promoted inflammasome activation and IL-1β release.

Results

SPHK1 was selectively expressed by TAMs in CRC, and the abundance of SPHK1⁺ TAMs was associated with adverse clinical outcomes in CRC patients. In vivo, SPHK1 knockout and inhibition suppressed liver metastasis of CRC and enhanced the anti-tumor activity of ICB. Blocking SPHK1 reduced the infiltration of TAMs and exhausted T cells, and promoted cytotoxicity of CD8⁺ T cells. Mechanistically, SPHK1/S1P axis led to IL-1β secretion in response to AIM2 and NLRP3 inflammasome activation. SPHK1 inhibitor PF543 and anti-IL-1R alleviated ICB-induced toxicity, including colitis and liver damage. PF543 plus anti-PD-1 therapy could induce complete regression of liver metastasis and mitigate liver dysfunction when further combined with radiotherapy.

Conclusions

Targeting SPHK1 in macrophages could inhibit liver metastasis of CRC and decouple ICB anti-tumor immunity and toxicity.

Legal entity responsible for the study

The authors.

Funding

National Natural Science Foundation of China (No.82103595).

Disclosure

All authors have declared no conflicts of interest.