A humanized mouse model suggests that head and neck cancer growth may stem from chronic stress. The study found that animals had immunophenotypic changes and a greater propensity towards tumor growth and metastasis.
Other studies have shown this may be caused by the lack of access to health care services or poor quality care. but the difference remains even after adjusting for these factors, according to researchers writing in Head and Neck.
Led by Heather A. Himburg, PhD, associate professor of radiation oncology with the Medical College of Wisconsin, Milwaukee, researchers conducted a study of head and neck cancer models in which tumor cells were implanted into a mouse with a humanized immune system.
Their theory was that psychosocial stress may contribute to the growth of head and neck tumors. The stress of poverty, social deprivation and social isolation can lead to the up-regulation of proinflammatory markers in circulating blood leukocytes, and this has been tied to worse outcomes in hematologic malignancies and breast cancer. Many such studies examined social adversity and found an association with greater tumor growth rates and treatment resistance.
Other researchers have used mouse models to study the phenomenon, but the results have been inconclusive. For example, some research linked the beta-adrenergic pathway to head and neck cancer, but clinical trials of beta-blockers showed no benefit, and even potential harm, for patients with head and neck cancers. Those results imply that this pathway does not drive tumor growth and metastasis in the presence of chronic stress.
Previous research used immunocompromised or nonhumanized mice. However, neither type of model reproduces the human tumor microenvironment, which may contribute to ensuing clinical failures. In the new study, researchers describe results from a preclinical model created using a human head and neck cancer xenograft in a mouse with a humanized immune system.
How the study was conducted
The animals were randomly assigned to normal housing of two or three animals from the same litter to a cage, or social isolation from littermates. There were five male and five female animals in each arm, and the animals were housed in their separate conditions for 4 weeks before tumor implantation.
The isolated animals experienced increased growth and metastasis of the xenografts, compared with controls. The results are consistent with findings in immunodeficient or syngeneic mice, but the humanized nature of the new model could lead to better translation of findings into clinical studies. “The humanized model system in this study demonstrated the presence of both human myeloid and lymphoid lineages as well as expression of at least 40 human cytokines. These data indicate that our model is likely to well-represent the human condition and better predict human clinical responses as compared to both immunodeficient and syngeneic models,” the authors wrote.
The researchers also found that chronic stress may act through an immunoregulatory effect, since there was greater human immune infiltrate into the tumors of stressed animals. Increased presence of regulatory components like myeloid-derived suppressor cells or regulatory T cells, or eroded function of tumor-infiltrating lymphocytes, might explain this finding. The researchers also identified a proinflammatory change in peripheral blood monocular cells in the stressed group. When they analyzed samples from patients who were low income earners of less than $45,000 in annual household income, they found a similar pattern. “This suggests that chronic socioeconomic stress may induce a similar proinflammatory immune state as our chronic stress model system,” the authors wrote.
Tumors were also different between the two groups of mice. Tumors in stressed animals had a higher percentage of cancer stem cells, which is associated with more aggressive tumors and worse disease-free survival. The researchers suggested that up-regulated levels of the chemokine SDF-1 seen in the stressed animals may be driving the higher proportion of stem cells through its effects on the CXCR4 receptor, which is expressed by stem cells in various organs and may cause migration, proliferation, and cell survival.
The study was funded by an endowment from Advancing a Healthier Wisconsin and a grant from the National Center for Advancing Translational Sciences. The authors reported no conflicts of interest.