Age-driven changes in tumor-associated macrophages contribute to slower tumor growth in murine melanoma and breast cancer models.

Introduction: The global cancer incidences are significantly higher between 50 to 70 years of age and decline thereafter. The age-driven factors contributing to this decline beyond 70-75 years of age is unknown, but it can help identify novel anticancer targets. It is now well established that tumor-associated macrophages (TAMs) secrete angiogenic growth factors that promote an immunosuppressive tumor microenvironment (TME). While novel strategies try to modulate TAMs for anticancer benefits, the impact of aging is often neglected. We have previously characterized the changes in macrophage phenotype and functions with aging. Considering their significant role in the TME, this study further determines the changing landscape of TAMs with aging and their impact on melanoma and breast tumors. Objective: To elucidate the impact of age-driven changes in tumor-associated macrophages in murine melanoma and breast cancer models. Methods: Wildtype mice of four ages (2-3, 6-8, 12-14, and 22-24 months) were implanted with SM1 melanoma and 4T1 breast tumor cells. In addition to tumor growth kinetics, changes in macrophage, T cell, and NK cell populations within the aging tumors were determined. At the end of the study, single-cell transcriptomic and proteomic analyses were performed on CD45-positive and F4/80-positive cells, respectively, to characterize TAMs and their interactions with other immune cells with aging. To study the impact of cancer on macrophage aging, we compared RNA sequencing data from bone marrow-derived macrophages from tumor-bearing and healthy mice of the above four age groups. Using a multiplex ELISA, we also determined age-associated changes in the secretion profile of macrophage cytokines, chemokines, and growth factors. Results: The melanoma and breast tumor growth kinetics were significantly slower in aged mice compared to younger mice. The macrophage population within melanoma tumors increased, whereas that within breast tumors decreased with aging. The aged TAMs, however, exhibited dysfunctional properties, including reduced secretion of cytokines, chemokines, and growth factors. The transcriptomic analyses of tumor-associated and bone marrow-derived macrophages highlighted a unique age-driven signature that complements previously observed changes in macrophage function with aging and emphasized the potential cancer-driven acceleration of macrophage aging. In addition to the secretome profile, changes in the epigenetic and metabolic landscapes of aged macrophages further identified potential targets contributing to slower tumor growth. Conclusions: Aging of TAMs significantly affects tumor growth and the TME in murine melanoma and breast cancer models. The changes observed in transcriptomic and proteomic landscape further reveal the age- and cancer-driven impact on macrophages and their significance to cancer development.