Deficiency of SR-B1 reduced the tumor load of colitis-induced or APC min /+ -induced colorectal cancer.

Background: Colorectal cancer (CRC) is one of the most common tumors in the world. Cholesterol plays an important role in the pathogenesis of tumors. One of the cholesterol transporters, scavenger receptor class B type 1 (SR-B1), a multi-ligand membrane receptor protein, is expressed in the intestines which also highly expressed in various tumors. But the potential mechanism of SR-B1 in CRC development has not been reported.
Aims: This study aimed to clarify the importance of SR-B1 in the development and prognosis of CRC as much as possible to provide a possible strategy in CRC treatment.
Materials & Methods: In this study, we used SR-B1 gene knockdown mice to study the effect of SR-B1 on colitis-induced or APC ^min/+ -induced CRC. The expression of related molecules were detected through the immunohistochemistry and hematoxylin-eosin staining, western blot analysis, and Flow cytometry. The gene expression and microbiota in microenvironment of CRC mice were analyzed through eukaryotic mRNA sequencing and 16S rRNA high-throughput sequencing.
Results: The results showed that SR-B1 knockdown reduced the tumor load of colitis-induced or APC ^min/+ -induced CRC. SR-B1 knockdown improved the immune microenvironment by affecting the level of tumor-associated macrophage (TAM), mononuclear myeloid-derived suppressor cells (M-MDSCs), granulocytic myeloid-derived suppressor cells (G-MDSCs), programmed cell death-ligand 1 (PD-L1), and human leukocyte antigen class I-B (HLA-B), and also reduced the level of low-density lipoprotein receptor (LDL-R), and increased the level of ATP binding cassette transporter A1 (ABCA1) to regulate the cholesterol metabolism, and regulated the expression of related genes and intestinal microbiota. SR-B1 knockdown can also trigger the anti-CRC effect of anti-PD 1 in colitis-induced CRC.
Discussion: SR-B1 deficiency significantly improved the immunity in tumor microenvironment of colitis-induced or APC ^min/+ -induced CRC. In addition, the microbiota changes caused by SR-B1 deficiency favor improving the immune response to chemotherapeutic drugs and anti-PD1 therapy. The mechanism of action of SR-B1 deficiency on the development of CRC still needs further in-depth research.
Conclusion: This study provides a new treatment strategy for treating CRC by affecting the expression of SR-B1 in intestine.
(© 2023 The Authors. Cancer Medicine published by John Wiley & Sons Ltd.)