The key findings of this study are that stress-related biobehavioral factors were associated with both stromal and tumor expression of factors supporting angiogenesis and invasion in the tumor microenvironment of ovarian cancer patients. Specifically, depressed patients and patients reporting higher levels of chronic stress, current stress, and negative affect showed higher MMP-9 expression in tumor-associated macrophages. In contrast, patients with higher levels of social support had lower levels of VEGF and MMP-9 expression in tumor cells. MMP-2 expression by macrophages or tumor cells was not significantly associated with any of the biobehavioral factors examined. To the best of our knowledge, this is the first clinical study to demonstrate significant associations between biobehavioral factors and stromal macrophage production of matrix metalloproteinases.
These findings extend previous experiments demonstrating that chronic stress and social isolation increase expression of VEGF and MMP-9 by human ovarian tumors implanted orthotopically in mice (1
). The current findings also extend our previous report of relationships between greater social support and lower serum VEGF in ovarian cancer patients (37
) and demonstrate that similar relationships exist within the tumor microenvironment. The findings are also consistent with previously reported associations between elevated distress, poor social support, and elevations in the pro-angiogenic cytokine interleukin-6 (IL-6) in ascites and plasma of ovarian cancer patients (38
Mechanisms underlying these associations likely involve stress hormones such as norepinephrine (NE) and cortisol (hydrocortisone). In vitro
stimulation of isolated human macrophages with NE and hydrocortisone enhanced production of MMP-9, thus supporting the presence of causal pathways between stress and stimulation of this MMP. These findings extend previous in vitro
) and in vivo
) studies of ovarian carcinoma showing that NE induces an increase in MMP-9, MMP-2, and VEGF expression by ovarian tumor cells via β-adrenergic receptor signaling. Specific doses of cortisol have also been shown to enhance VEGF production by ovarian cancer cell lines (6
Macrophages are known to express β-adrenergic (17
) as well as α-adrenergic receptors (16
). Some data suggest that NE ligation of α1
- and β-adrenergic receptors on human monocytes can activate nuclear factor κ-B (NF-κB), which mediates the expression of several other angiogenic factors including VEGF and MMP-9 (39
) as well as IL-6 (40
). As elevated levels of stress (41
), depression (43
) and social isolation (46
) have been associated with elevations in NE and cortisol (36
), it is not surprising that these factors are associated with increased expression of MMP-9 by tumor associated macrophages and MMP-9 and VEGF by tumor cells in ovarian cancer patients (50
). Stress also induces an increase in NE in animal models (1
It is not clear why an association was seen between distress and macrophage-produced MMP-9 but not with tumor-produced MMP-9 or VEGF, which were associated with social support/isolation. Variations in the neuroendocrine factors in the tumor microenvironment and receptors associated with depression and social support/isolation have not been well characterized. Furthermore, the predominant source of MMP-9 in ovarian tumors is known to be from macrophages (10
); however, there may be compensatory pathways operating as well. The lack of a significant association between biobehavioral factors and MMP-2 was unanticipated. Additional studies will be required to fully define the mechanisms by which biobehavioral factors might influence MMPs within the tumor microenvironment.
These findings are significant in that they demonstrate another mechanism by which stress factors may facilitate tumor growth and invasion, that is, by stimulation of stromal cells such as macrophages in the tumor microenvironment. Under conditions of behavioral distress or low social support, it is plausible that elevated levels of stress hormones such as catecholamines and glucocorticoids may 1) stimulate TAM production of MMP-9, which promotes an environment supportive of angiogenesis and invasion and 2) directly stimulate tumor production of MMP-9 and VEGF. The net result is that the downstream effects of stress hormones on tumor growth would be amplified by both direct and indirect influences. Future studies examining levels of NE and/or cortisol within ovarian tumor samples would provide valuable insights into the role of adrenergic and glucocorticoid mechanisms in clinical tumor biology.
It should be noted that the clinical findings are correlational and thus limit causal inferences. However, in vitro data are consistent with an interpretation of stress-induced enhancement of macrophage production of MMP-9. Small sample size may also have resulted in under reporting of associations between distress and tumor production of MMP-9.
Depression and stress were associated with expression of MMP-9 by tumor associated macrophages and MMP-9 and VEGF by tumor cells in ovarian cancer patients. These findings identify new biological mechanisms that may underlie stress-induced progression of cancer, and could have implications for survival and treatment.