Abstract 2957: Senescence of stromal, endothelial, and myeloid cells in the tumor microenvironment has distinct effects on cancer progression

Abstract Accumulation of senescent cells, undermining the function of vital organs, is a culprit of aging. The effects of senescence in different types of cells on tumor growth and metastasis remain incompletely characterized. Cell senescence has been shown to result from inactivation of Telomerase (TERT), an enzyme that maintains telomere length and has obscure roles in regulating gene expression and supporting mitochondrial function. As we reported previously, knockout (KO) of Tert gene in mesenchymal stromal cells (MSC) of Pdgfra+ or Pdgfrb+ lineages leads to premature replicative stromal cell senescence in adipose tissue. To assess the effect of senescence in endothelial and myeloid cells, we also created mice with Tert KO driven by the Tie2e promoter or the LysM promoter, respectively. Here, to investigate the effect of these three KOs on cancer, we used syngeneic graft models of breast, prostate, and pancreatic carcinoma. Overall, Tert KO in cells of Pdgfra+, Pdgfrb+, Tie2e+, or LysM+ lineage had a suppressive effect on tumor growth. The strongest tumor suppression effect of Tert KO was observed in female mice orthotopically grafted with E0771 breast cancer cells. Intermediate suppressive effects of Tert KO were observed in mice orthotopically grafted with KPC pancreatic ductal adenocarcinoma cells, whereas the effect on RM1 prostate cancer cells grafts in male mice was the least significant. MSC Tert KO and myeloid Tert KO also suppressed the growth of breast and prostate cells grafts. Importantly, spontaneous metastases to the liver were induced by Tie2e-Tert KO in all mice with pancreatic KPC grafts. Analysis of adipose tissue in this endothelial senescence model revealed vasculature abnormality, leakiness, and tissue hypoxia, which provides a mechanistic explanation for increased tumor dissemination. In contrast, LysM-Tert KO did not promote KPC metastases, consistent with the lack of contribution of myeloid cells to the vasculature. Pdgfrb-Tert KO in the KPC model resulted in liver metastases observed for some but not all mice, consistent with the role of MSC in supporting vascular integrity. To test an independent model of replicative MSC senescence, we exhausted their pool by several cycles of ganciclovir treatment in mice expressing thymidine kinase under the control of Pdgfrb promoter. Upon KPC grafting in this model, reduced primary pancreatic tumor growth was also observed and liver metastases were also induced. We conclude that senescence of distinct cells in the tumor microenvironment affects early and late stages of cancer progression differently. Specifically, our data indicate that vascular cell senescence suppresses tumor growth but promotes metastases. These findings are important to consider as new approaches designed to mitigate cell senescence are investigated in the context of cancer. Citation Format: Joseph Rupert, Zhanguo Gao, Yongmei Yu, Mikhail Kolonin. Senescence of stromal, endothelial, and myeloid cells in the tumor microenvironment has distinct effects on cancer progression abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2957.