Background: Colorectal cancer liver metastasis (CRLM) is characterized by an immunosuppressive microenvironment and a blunted response to immunotherapy. Notably, tumor‐associated macrophages (TAMs) play a critical role in modulating immune responses and exhibit significant heterogeneity in CRLM. Sphingosine kinase 1 (SPHK1) serves as a pivotal kinase in maintaining the balance between ceramide and sphingosine‐1‐phosphate (S1P) levels. However, the effects of SPHK1 within TAMs on tumor immune evasion during CRLM remain elusive. This study aimed at investigating the role of TAM‐intrinsic SPHK1 in tumor immunosuppressive microenvironment in CRLM. Methods: SPHK1 expression levels in TAMs were estimated by immunofluorescence and bioinformatics analysis. Several animal models were established to elucidate the role of SPHK1 in tumor immunity reprogramming in vivo. Flow cytometry, cytokine assay, and transwell assay were conducted to investigate the effects of SPHK1 in TAMs in cell‐cell communication in vitro. RNA‐sequencing, Western blotting, and quantitative real‐time polymerase chain reaction were used to explore the molecular mechanism by which SPHK1 activated NLR family pyrin domain containing 3 (NLRP3) inflammasome in TAMs. Results: We found that SPHK1 was mainly expressed in TAMs and identified SPHK1 ⁺ TAMs as associated with CRLM and diminished efficacy of immunotherapy in human patients. These SPHK1 ⁺ TAMs exhibited strong immunosuppressive activities by inducing CD8 ⁺ T cell exhaustion with high programmed cell death 1 (PD‐1) expression via the interaction between TAMs and CRC cells. Mechanistically, SPHK1‐produced S1P exerted an autocrine effect to activate NLRP3 inflammasome and interleukin 1 beta (IL‐1β) release via nuclear factor‐kappa B (NF‐κB) and hypoxia inducible factor 1 subunit alpha (HIF‐1α) signaling in TAMs. Paracrine IL‐1β then upregulated the expression of monocyte chemoattractants and ADAM metallopeptidase domain 17 (ADAM17) sheddase in CRC cells, resulting in TAM infiltration and CD8 ⁺ T cell dysfunction in the liver microenvironment. Furthermore, combining SPHK1‐targeting treatments with anti‐PD‐1 therapy or radioimmunotherapy largely stalled liver metastasis and caused a significant extension of lifespan in preclinical mouse models. Conclusions: Our findings highlighted the role of SPHK1 of TAMs in facilitating CRLM by promoting CD8 ⁺ T cell dysfunction and immunosuppressive microenvironment. Combining SPHK1 blockade with anti‐PD‐1 therapy may be a promising treatment regimen for patients with CRLM.

Background: Radiotherapy (RT) is one of the major therapeutic approaches to hepatocellular carcinoma (HCC). Ionizing radiation (IR) inducing the generation of reactive oxygen species (ROS) leads to a promising antitumor effect. However, the dysregulation of the redox system often causes radioresistance and impairs the efficacy of RT. Increasing evidence indicates that nuclear protein 1 (NUPR1) plays a critical role in redox reactions. In this study, we aim to explore the role of NUPR1 in maintaining ROS homeostasis and radioresistance in HCC. Methods: The radioresistant role of NUPR1 was determined by colony formation assay, comet assay in vitro, and xenograft tumor models in vivo. Probes for ROS, apoptosis assay, and lipid peroxidation assay were used to investigate the functional effect of NUPR1 on ROS homeostasis and oxidative stress. RNA sequencing and co-immunoprecipitation assay were performed to clarify the mechanism of NUPR1 inhibiting the AhR/CYP signal axis. Finally, we analyzed clinical specimens to assess the predictive value of NUPR1 and AhR in the radiotherapeutic efficacy of HCC. Results: We demonstrated that NUPR1 was upregulated in HCC tissues and verified that NUPR1 increased the radioresistance of HCC in vitro and in vivo. NUPR1 alleviated the generation of ROS and suppressed oxidative stress, including apoptosis and lipid peroxidation by downregulating cytochrome P450 (CYP) upon IR. ROS scavenger N-acetyl-L-cysteine (NAC) and CYP inhibitor alizarin restored the viability of NUPR1-knockdown cells during IR. Mechanistically, the interaction between NUPR1 and aryl hydrocarbon receptor (AhR) promoted the degradation and decreased nuclear translation of AhR via the autophagy-lysosome pathway, followed by being incapable of CYP’s transcription. Furthermore, genetically and pharmacologically activating AhR abrogated the radioresistant role of NUPR1. Clinical data suggested that NUPR1 and AhR could serve as novel biomarkers for predicting the radiation response of HCC. Conclusions: Our findings revealed the role of NUPR1 in regulating ROS homeostasis and oxidative stress via the AhR/CYP signal axis upon IR. Strategies targeting the NUPR1/AhR/CYP pathway may have important clinical applications for improving the radiotherapeutic efficacy of HCC.

With technological advancements, radiotherapy (RT) has become an effective non-surgical treatment for hepatocellular carcinoma (HCC), comprehensively improving the local control rate of patients with HCC. However, some patients with HCC still experience radio-resistance, cancer recurrence, and distant metastasis following RT. Our previous study has revealed that hexokinase 2 (HK2), a potent oncogene, was overexpressed in radio-resistant HCC cell lines; however, its role in HCC radio-resistance remains elusive. Here, we confirmed the upregulation of HK2 in HCC tissue, which is related to unfavorable prognosis in patients with HCC, and demonstrated that HK2 exerts a radio-resistant role by attenuating apoptosis and promoting proliferation in HCC cell lines. HK2 downregulation combined with ionizing radiation showed an excellent synergistic lethal effect. Mechanistically, HK2 alleviated ionizing radiation-mediated apoptosis by complexing with pro-apoptotic protein aminoacyl tRNA synthetase complex interacting multifunctional protein 2 (AIMP2) while enhancing its autophagic lysosomal-dependent degradation, thereby increasing radio-resistance of HCC. Pharmacologically, ketoconazole, an FDA-approved antifungal drug, served as an inhibitor of HK2 and synergistically enhanced the efficacy of RT. Our results indicated that HK2 played a vital role in radio-resistance and could be a potential therapeutic target for improving RT efficacy in HCC.

Aberrant gene expression plays critical roles in the development of colorectal cancer (CRC). Here we show that POTEE, which was identified as a member E of POTE ankyrin domain family, was significantly upregulated in colorectal tumors and predicted poor overall survival of CRC patients. In CRC cells, POTEE could act as an oncogene and could promote cell growth, cell-cycle progression, inhibit apoptosis, and elevates xenograft tumor growth. Mechanically, we used microarray analysis and identified a POTEE/SPHK1/p65 signaling axis, which affected the biological functions of CRC cells. Further evaluation showed that overexpression of POTEE could increase the protein expression of SPHK1, followed by promoting the phosphorylation and activation of p65 protein. Altogether, our findings suggested a POTEE/SPHK1/p65 signaling axis could promote colorectal tumorigenesis and POTEE might potentially serve as a novel biomarker for the diagnosis and an intervention of colorectal cancer.

Colorectal cancer (CRC) is a leading global health issue, ranking third in incidence and second in cancer mortality. Immunotherapy, effective mainly in mismatch repair-deficient CRC, may benefit from dietary interventions. This study investigates caffeine’s potential to boost programmed death-1 (PD-1) immunotherapy efficacy in CRC, revealing that caffeine significantly reduces tumor growth, extends survival, and enhances CD8⁺ T cell activity in CRC by suppressing kynurenine pathway. Mechanistically, caffeine decreases kynurenine via the Krüppel-like factor 4 (KLF4)- Collagen type XII alpha 1 (COL12A1)- Mitogen-Activated Protein Kinase (MAPK)-Indoleamine 2,3-dioxygenase 1 (IDO1) axis, mitigating CD8⁺ T cell exhaustion. Combining caffeine with PD-1 therapy further prolongs survival, highlighting the value of integrating nutritional strategies into cancer treatment to improve outcomes and broaden therapeutic options. Here, we show caffeine can enhance PD-1 immunotherapy in CRC by suppressing kynurenine pathway, suggesting its potential as an adjunctive dietary therapy.