Intermittent Hypoxia During Sleep Promotes the Development of Colorectal Cancer Liver Metastases in a Murine Model of Sleep Apnea

Introduction: Obstructive sleep apnea (OSA) is a common condition affecting up to 1 billion people worldwide. OSA is associated with an increased incidence of various malignancies, including colorectal cancer (CRC). Despite the epidemiological data linking OSA with CRC, the mechanisms underlying this association are unclear. Previous research has suggested that hypoxia, oxidative stress, and the immune microenvironment play a role in the prognosis of CRC-related liver metastasis (CRLM). Here, we hypothesize that intermittent hypoxic (IH) exposure during sleep, a hallmark of OSA, creates a permissive microenvironment that promotes CRLM progression.

Methods: C57BL/6 and Balb/C mice were exposed to cycling levels of room air (RA) or IH during sleep (FIO₂ 6.5%–21%) for 14-28 days, mimicking chronic severe OSA. The CRLM model was induced by injecting MC-38 or CT-26 CRC cells intra-splenically. RA/IH exposures were initiated on the day of CRLM induction or two weeks prior. Liver samples were harvested 14 days after CRLM induction for histology and molecular analyses.

Results: IH exposure during metastatic establishment enhanced CRLM progression, increasing both the total number of tumors and specifically large tumors in IH compared to RA controls in two different CRC lines. IH-exposed livers exhibited increased cellular proliferation in the parenchyma and increased infiltration of CD8⁺ T cells and F4/80⁺ macrophages, indicating a direct effect of IH on the liver immune milieu. Interestingly, two weeks of IH preconditioning eliminated the differences in tumor number between IH and RA groups. However, a higher proportion of IH-exposed mice developed large tumors compared to RA-exposed mice (85% vs. 43%, p = 0.09). Tumor foci in IH were surrounded by a more prominent immune cell rim compared to RA controls, in addition to a higher density of CD8⁺ T cells within large tumors in IH.

Conclusion: Intermittent hypoxia during sleep directly accelerates the development of CRC liver metastasis seeding and growth. IH preconditioning activates hepatic immune cells, resulting in a paradoxical effect on CRLM progression. Future studies will characterize the effect of IH on hepatic immune cell function to further understand its role in CRLM progression.