ABSTRACT
Correct interpretation of tumor progression data, including the influence of host biology, in mouse models of breast cancer requires models and conditions that faithfully recapitulate human disease and human host status. Our previous attempts to investigate the effects of social isolation have proven inconclusive due to premature mortality in tumor-bearing animals. Those studies were completed in standard temperature (ST), which commonly is 70-72°F (21-22°C) for in vivo murine research based on laboratory animal care and use guidelines. Previous work from the Repasky lab (Kokulus, 2013), which we have validated (Gaymon, 2020), demonstrates that ST housing results in chronic cold stress and immune suppression mediated by an increase in norepinrephrine (NE) levels, leading to increased tumor aggressiveness. Based on these findings, we investigated the effects of social isolation on BALB/cJ-4T1-luc and C57BL/6J/E0771 tumor progression and metastasis in thermoneutral housing conditions (84-85°F). Mice were first acclimatized to thermoneutral temperature and/or isolation for two weeks in cages that were unilaterally draped to provide physical and visual isolation. In BALB/cJ mice, 4T1-luc tumors were significantly larger in isolated mice compared to group-housed (GH) mice at day 18 (p<.0001). Statistically larger tumors were observed in isolated mice compared to GH mice through day 24 and final tumor masses were Salso significantly different (p=.004). Spleen masses were not statistically different. In C57BL/6J mice, E0771 tumors were significantly larger in isolates at Day 25 (p=.002). Final tumor masses were statistically (p=.002) different while no difference in spleen sizes were observed. Data on metastasis will be presented at the meeting. We hypothesized that social isolation may perturb immune function and next investigated the growth of 4T1-luc xenograft tumors in NSG mice. 4T1-luc/NSG tumor progression and metastasis data will also be presented at the meeting. We conclude that syngeneic breast tumor growth in immunocompetent BALB/cJ and C57BL/6J mice demonstrates that social isolation is a bona fide stress with sufficient influence to exacerbate breast cancer growth. These data are potentially clinically important due the known relationship of social support to survivorship outcomes in patients and the high-risk of depression and isolation in patients following breast cancer diagnosis. The data may provide additional insight into possible effects of COVID-19 isolation on breast cancer progression.