Host CD39 Deficiency Affects Radiation-Induced Tumor Growth Delay and Aggravates Radiation-Induced Normal Tissue Toxicity

MiR-378a-5p exerts a radiosensitizing effect on CRC through LRP8/β-catenin axis

BACKGROUND

MiRNAs are closely related to tumor radiosensitivity. MiR-378a-5p level is down-regulated in colorectal cancer (CRC). Therefore, this study intends to explore the role of miR-378a-5p in CRC, especially radiosensitivity.

METHODS

The expression of miR-378a-5p was analyzed in CRC samples. CRC cell lines were treated with different doses of X-rays. Bioinformatics analysis, dual-luciferase reporter assay and RT-qPCR were used to detect the expressions and binding relationship of miR-378a-5p and low-density lipoprotein receptor-related protein 8 (LRP8). MiR-378a-5p inhibitor or/and siLRP8 were transfected into CRC cells with or without irradiation. Subsequently, clonogenic assay, flow cytometry and in vivo experiments including tumorigenesis assay, immunohistochemistry, RT-qPCR and Western blot were performed to clarify the role of miR-378a-5p/LRP8 axis in the radiosensitivity of CRC.

RESULTS

The down-regulated expression of miR-378a-5p in CRC is related to histological differentiation and tumor-node-metastasis (TNM) stage. After irradiation, the survival fraction of CRC cells was decreased, while the apoptotic rate and the level of miR-378a-5p were increased. Restrained miR-378a-5p repressed apoptosis and apoptosis-related protein expressions, yet promoted the proliferation and the radioresistance of cells by regulating β-catenin in CRC cells. LRP8 was highly expressed in CRC, and targeted by miR-378a-5p. SiLRP8 improved radiosensitivity and reversed the effect of miR-378a-5p down-regulation on CRC cells. Overexpressed miR-378a-5p and irradiation enhanced the level of miR-378a-5p, yet suppressed the expressions of Ki67 and LRP8 as well as tumorigenesis.

CONCLUSION

MiR-378a-5p may exert a radiosensitizing effect on CRC through the LRP8/β-catenin axis, which may be a new therapeutic target for CRC radioresistance.

CD39 inhibition and VISTA blockade may overcome radiotherapy resistance by targeting exhausted CD8+ T cells and immunosuppressive myeloid cells

Although radiotherapy (RT) has achieved great success in the treatment of non-small cell lung cancer (NSCLC), local relapses still occur and abscopal effects are rarely seen even when it is combined with immune checkpoint blockers (ICBs). Here, we characterize the dynamic changes of tumor-infiltrating immune cells after RT in a therapy-resistant murine tumor model using single-cell transcriptomes and T cell receptor sequencing. At the early stage, the innate and adaptive immune systems are activated. At the late stage, however, the tumor immune microenvironment (TIME) shifts into immunosuppressive properties. Our study reveals that inhibition of CD39 combined with RT preferentially decreases the percentage of exhausted CD8+ T cells. Moreover, we find that the combination of V-domain immunoglobulin suppressor of T cell activation (VISTA) blockade and RT synergistically reduces immunosuppressive myeloid cells. Clinically, high VISTA expression is associated with poor prognosis in patients with NSCLC. Altogether, our data provide deep insight into acquired resistance to RT from an immune perspective and present rational combination strategies.

CD39 - A bright target for cancer immunotherapy

The ATP-adenosine pathway functions as a key modulator of innate and adaptive immunity within the tumor microenvironment, and cancer immune evasion largely involves the generation of high amounts of immunosuppressive extracellular adenosine (eADO). Consequently, inhibition of eADO-generating enzymes and/or eADO receptors can effectively restore the antitumor immunity of multiple immune cells. With several clinical strategies currently being explored to modulating the eADO pathway in patients with cancer, recent clinical data with antagonists targeting CD73 and A_2A receptor have demonstrated a promising therapeutic potential in cancer. Recent findings reveal that the ectonucleotidase CD39, the limiting enzyme been viewed as "immunological switch", converts ATP-driven pro-inflammatory milieu to an anti-inflammatory state mediated by adenosine. Owing to its superior feature of CD39 antagonism that rely not only on preventing the accumulation of adenosine but also on the stabilization of extracellular ATP to restore antitumor immunity, several inhibitors and clinical trials based on CD39 are being evaluated. Consequently, there is currently a focus on understanding the role of CD39 in governing immunity and how therapeutic strategies targeting this pathway alter the antitumor potential. We herein review the impact of CD39 on tumor microenvironment with a focus on treatment preference. Additionally, we also discuss the implication for rational combination therapies, molecular regulation, as well as potential limitations.