Abstract IA14: Lymphatic metastasis and the lymph node microenvironment
Authors: Padera Timothy P. 
Published: May 2019

Abstract
Background: Lymph nodes are the most common sites of solid tumor metastases. Their presence signals a poorer prognosis and the recommendation for systemic therapy in most cancer patients. However, why lymph node metastases are such strong predictors of outcome in cancer patients is the subject of much debate. Furthermore, tumor draining LNs commonly have an environment which suppresses immune response. Here we will explore the microenvironment of metastatic lymph nodes and tumor draining lymphatic vasculature to determine how cancer cells can spread and grow in the lymph node.
Methods: We will measure lymphatic contractile function in tumor draining lymphatic vessels using intravital microscopy of an afferent lymphatic vessel to the popliteal lymph node (PLV). We will further use models that modify nitric oxide signaling to study how nitric oxide alters lymphatic pumping of tumor draining lymphatic vessels. Additionally, we will use our novel chronic lymph node window (CLNW) model to longitudinally image the growth and spread of lymph node metastases using intravital optical microscopy techniques. We use the CLNW in multiple models of spontaneous lymphatic metastases in mice to study the vasculature of metastatic lymph nodes. We further test our results in murine and patient samples using molecular and biochemical methods. Finally, we test the ability of antiangiogenic therapy to inhibit metastatic growth in the CLNW.
Results: We show that lymphatic pumping is impaired in tumor draining lymphatic vessels and is mediated by nitric oxide signaling. We also show that lymph node metastases originate from multiple tumor cells not a single clonal progenitor. We reveal the surprising lack of sprouting angiogenesis during metastatic growth in lymph nodes using both intravital microscopy and ex vivo methods. Vascular endothelial growth factor was not produced by the metastatic lesion despite the presence of hypoxia in some lesions. Treatment with two different antiangiogenic therapies showed no effect on the growth or vascular density of lymph node metastases in our models. We confirmed these findings in clinical specimens, including the lack of reduction in blood vessel density in lymph node metastases in patients treated with bevacizumab.
Conclusion: Tumors can impair the function of tumor draining lymphatic vessels, which may limit cancer cell dissemination as well the initiation of anti-tumor immunity. We provide pre-clinical and clinical evidence that sprouting angiogenesis does not occur during the growth of lymph node metastases, which reveals a mechanism of treatment resistance to antiangiogenic therapy in adjuvant settings. The targets of clinically approved angiogenesis inhibitors are not active during early cancer progression in the lymph node, suggesting that inhibitors of sprouting angiogenesis as a class will not be effective in treating lymph node metastases.
Citation Format: Timothy P. Padera. Lymphatic metastasis and the lymph node microenvironment. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr IA14.