“These results identify CTHRC1 as a key driver of CRC that may suppress the immune system, allowing for easier immune evasion by tumor cells, highlighting CTHRC1 as a potential new target for therapy.”
Colorectal cancer does not develop in isolation. Cancer cells exist within a complex tumor microenvironment made up of fibroblasts, immune cells, blood vessels, and extracellular matrix. Increasing evidence suggests that these surrounding cells and structures can influence whether tumors grow, regress, or evade the immune system.
A research paper published in Volume 17 of Oncotarget, titled “Microenvironmental CTHRC1 has a pro-tumorigenic role in colorectal cancer,” investigated the role of collagen triple helix repeat containing 1 (CTHRC1), a secreted protein found in cancer-associated stroma.
Looking Beyond the Cancer Cell
CTHRC1 is a secreted protein involved in tissue remodeling, extracellular matrix organization, cell migration, and other physiological processes. Previous research has associated elevated CTHRC1 with metastasis and poor prognosis in several cancers, including colorectal cancer. However, an important question has remained: where is the CTHRC1 within a tumor actually coming from?
Some previous studies have suggested that cancer cells themselves produce CTHRC1. The researchers behind the new study instead found CTHRC1 in the tumor-associated stroma. Using a highly specific antibody, they examined human colorectal cancer samples and observed strong CTHRC1 staining in cancer-associated fibroblasts surrounding and infiltrating the tumor, while the colorectal tumor cells themselves were negative. They also found no detectable CTHRC1 production by the MC38 mouse colon cancer cells used in their experiments.
These observations allowed the researchers to investigate a different question: rather than asking what CTHRC1 produced by cancer cells does, they could examine whether host-derived CTHRC1 in the tumor microenvironment helps colorectal tumors grow.
Testing CTHRC1’s Role in Tumor Growth
To investigate this possibility, the researchers compared normal wild-type mice with genetically modified mice lacking the CTHRC1 gene throughout the body. Both groups received subcutaneous injections of MC38 mouse colon cancer cells.
The experiments were performed across three independent cohorts, each containing 20 mice: 10 wild-type mice and 10 CTHRC1 knockout mice. Tumor progression was followed using bioluminescence imaging and direct tumor measurements. One cohort was followed for survival, while two additional cohorts were used to examine tumors and other tissues at defined endpoints.
The results showed a clear difference between the groups. Across the independent experiments, mice lacking CTHRC1 developed substantially less tumor burden than wild-type mice. In some knockout animals, tumors initially grew but subsequently regressed, whereas tumors in most wild-type animals continued to progress.
Removing CTHRC1 Was Associated With Longer Survival
The difference extended beyond tumor size.
In the survival experiment, the median time to the predefined survival endpoint was approximately 28 days after tumor inoculation in wild-type mice compared with 69 days in CTHRC1-deficient mice—an approximately 2.5-fold increase. Notably, 60% of the knockout mice had still not reached the study’s endpoint criteria when the experiment ended on day 69.
The researchers reproduced the reduced tumor burden in two additional independent cohorts. In one endpoint experiment, knockout mice showed significantly lower tumor burden by day 13, with regression occurring around days 9 to 13 while tumors in wild-type animals continued growing. A third cohort again demonstrated reduced tumor burden and tumor regression in mice lacking CTHRC1.
Together, these findings provided evidence that CTHRC1 originating from the host microenvironment can promote tumor progression in this mouse model, even though the implanted cancer cells themselves did not produce the protein.
CTHRC1 Was Also Linked to the Immune Environment
The researchers next examined whether the dramatic differences in tumor growth were accompanied by changes in immune cells.
Compared with wild-type mice, CTHRC1 knockout mice had a higher percentage of CD3-positive T cells in both their tumors and spleens. They also had a lower percentage of Gr-1-positive myeloid cells in the spleen.
This finding is particularly interesting because the Gr-1-positive population includes myeloid-derived suppressor cells, or MDSCs. These cells can inhibit T-cell activation and proliferation and contribute to an immunosuppressive tumor environment.
The authors therefore propose that CTHRC1 could contribute to immune suppression in colorectal cancer. In its absence, reduced myeloid-mediated suppression could allow a stronger T-cell response against the tumor. However, the researchers emphasize that the precise mechanism remains unknown and is likely to involve several interacting processes.
Tumors Without CTHRC1 Looked Different
The investigators also examined tumor tissue under the microscope.
Histological analysis showed that tumors from CTHRC1 knockout mice had significantly lower cellularity than tumors from wild-type animals. Some knockout tumors contained abundant collagen-rich extracellular matrix but relatively few remaining cells, which the researchers suggest could represent residual matrix left after tumor-cell regression.
CTHRC1 staining was primarily found within the tumor stroma of wild-type mice and was absent from both the tumors and surrounding stroma of knockout mice. This provided further evidence that the relevant CTHRC1 was produced by the host rather than the implanted MC38 cancer cells.
Interestingly, staining for CD31, a marker used to visualize blood vessels, did not reveal an apparent difference in tumor vascularization between wild-type and knockout mice. This suggests that the pronounced differences in tumor growth observed in the study cannot simply be attributed to an obvious change in the presence of tumor blood vessels.
Why the Tumor Microenvironment Matters
The findings reinforce an increasingly important concept in cancer biology: tumor progression depends not only on mutations within malignant cells but also on signals coming from their surrounding environment.
Cancer-associated fibroblasts can reshape the extracellular matrix and communicate with cancer and immune cells through secreted molecules. In this study, removing one such molecule—CTHRC1—from the host environment was associated with slower tumor growth, tumor regression, longer survival, and a shift toward a less immunosuppressive immune profile.
The researchers therefore conclude that both stromal and circulating CTHRC1 could contribute to the immunosuppressive conditions that allow colorectal cancer cells to escape immune control.
Importantly, these findings do not establish that blocking CTHRC1 would have the same effect in people with colorectal cancer. Rather, they identify CTHRC1 as a promising biological target that warrants further investigation.
Important Questions Remain
The study has several important limitations.
Most notably, the experiments used a subcutaneous mouse model, meaning that colon cancer cells were implanted beneath the skin rather than growing within the colon. The authors point out that subcutaneous and orthotopic colorectal tumors can have substantially different immune environments. Because immune-cell infiltration is particularly important when studying tumor immunity, these differences could affect how well the results translate to human colorectal cancer.
The researchers also used a global CTHRC1 knockout, meaning CTHRC1 was absent throughout the animals rather than being selectively removed from a particular cell population. Future experiments using inducible or cell-specific knockout models could help determine exactly which cells produce the tumor-promoting CTHRC1 and when its activity becomes important during cancer progression.
Looking Ahead
The study provides the first experimental evidence reported by the authors that host-derived CTHRC1 promotes colon cancer progression, with reduced tumor burden consistently observed across three independent mouse cohorts. The accompanying increases in T-cell percentages and reductions in splenic Gr-1-positive myeloid cells suggest that CTHRC1 may help create an immune environment that favors tumor growth.
The authors propose CTHRC1 as a potential therapeutic target, but considerable work remains before this possibility could be translated into treatment. The receptor or receptors through which CTHRC1 produces its effects still need to be identified, and suitable inhibitors would then need to be developed and tested. Future studies in orthotopic colorectal cancer models will also be important for establishing whether the effects observed beneath the skin are reproduced when tumors grow in their native intestinal environment.
Taken together, the findings show how a protein produced outside the cancer cell itself can substantially influence tumor behavior. By shifting attention from malignant cells alone to the biological environment that supports them, studies such as this could reveal new approaches for disrupting the conditions that allow colorectal tumors to grow and evade immune control.
Click here to read the full research paper published in Oncotarget.
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