Abstract 5402: Understanding the role of exercise in lymphatic vessel regulation in melanoma

Abstract

Abstract Exercise has been demonstrated to be an effective method to remodel tumor blood vessels and to improve immune cell infiltration in multiple tumor models in mice. However, it is unclear whether aerobic exercise alters lymphatic vasculature in tumors. The lymphatic system plays an important role in tumor growth and metastasis because it regulates interstitial fluid pressure via lymph flow and immune cell trafficking, in conjunction with blood vessels. Lymphatic vessels are particularly important during metastasis because tumor cells frequently escape the primary tumor through lymphatic vasculature to establish the first site of metastasis in the lymph nodes. Here, we evaluated the effect of aerobic exercise on lymphatic vessels and lymphatic endothelial cell junctions in melanoma in male C57BL/6J mice. BP melanoma cells derived from transgenic mice with BrafV600E/+ and Pten−/− mutations were injected subcutaneously. Mice were assigned to no exercise and exercise groups when tumors reached ~30 mm3. The exercise group completed treadmill running at 12 meters/minute for 45 minutes for 5 consecutive days with 2 days of rest per week for 2 weeks before tumor harvest. Tumor lymphatic endothelial cells were identified by LYVE-1, endothelial tight junctions by ZO-1, and nuclei were identified by DAPI using immunofluorescence staining on frozen tumors. The number of total lymphatic vessels, elongated vessels( >100 µm), open lumens, and co-localization of ZO-1 with LYVE-1 was quantified on 6 random images per tumor using NIH Image J software. ANOVA and t-test were used to conduct statistical analysis (p < 0.05). Tumors from exercised mice had higher lymphatic vessel density (p=0.002) and more open lumens (p=0.001). Surprisingly, tumors from exercised mice had fewer ZO-1 positive vessels (p=0.015) and lower co-localization of ZO-1 and LYVE-1 (p = 0.0185) than tumors from non-exercised mice, suggesting fewer stable endothelial cell junctions in lymphatic vessels. The higher lymphatic vessel density and higher number of open lumens present in tumors from exercised mice may contribute to an exercise-induced improved anti-tumor immune response, which has been previously reported. However, the lower ZO-1 expression on lymphatic endothelial cells in tumors from exercised mice may indicate lymphatic vasculature dysfunction and/or hyper-permeability. Further work is needed to assess the functional changes in tumor lymphatic vasculature by exercise, and how these changes impact the anti-tumor immune response and metastasis. Citation Format: Priya Tirumala, Jonghae Lee, Keri L. Schadler. Understanding the role of exercise in lymphatic vessel regulation in melanoma [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(6_Suppl):Abstract nr 5402.