The importance of what is on the inside: Metastasis from the inside-out and formation of a necrotic core is regulated by a peri-necrotic secreted factor

Abstract

Necrosis in the tumor interior is a common feature of aggressive cancers that is associated with poor clinical prognosis and the development of metastasis. However, how the necrotic core promotes tumor cell dissemination and metastasis remains unclear. Foundational models for cancer metastasis research include mouse, zebrafish, and chick embryo, but identifying tumor cells in transit is painstaking. In my thesis work, I used a rat model of breast cancer metastasis to increase detection of dissemination events. Owing to the large size and higher blood volume of rats, I collected 10 times more circulating tumor cells (CTCs) than from mice. In this model, tumor dissemination was temporally correlated with the emergence of necrosis in the tumor interior. These findings were corroborated by longitudinal study of CTC abundance and tissue necrosis markers in blood plasma from patients with metastatic breast cancer. Further, I observed that dilated blood vessels were located next to necrotic regions of the tumor and that their increase was concurrent with the initiation of intratumoral necrosis and increase in CTC abundance. Bulk RNA sequencing of mouse-to-rat xenograft tumor necrotic core compared to the non-necrotic rim revealed distinct tumor-specific and host-specific transcripts in the necrotic interior. We identified angiopoietin-like 7 (Angptl7) as a tumor-specific factor localized to the peri-necrotic zone. Functional studies showed that Angptl7 loss normalizes central necrosis, decreases peri-necrotic dilated vessels, reduces metastasis, and reduces circulating tumor cell counts to nearly zero. Taken together, these findings show that breast tumors actively produce factors controlling central necrosis formation and metastatic dissemination from the tumor core. Tumor dissemination events are localized spatially to dilated peri-necrotic vessels in the tumor interior, and tumor dissemination is dependent functionally on the expression of a factor, Angptl7, produced by peri-necrotic tumor cells. These findings provide strong evidence that the factors in the peri-necrotic zone in the center of the tumor regulate tumor cell dissemination and suggest that tumor dissemination originates from the tumor core. My thesis work informs a new perspective on the mechanism of tumor dissemination and reveal a potential therapeutic target to directly disrupt it.