Periostin+ Stromal Cells Guide Lymphovascular Invasion by Cancer Cells.

Cancer cell dissemination to sentinel lymph nodes is associated with poor patient outcomes, particularly in breast cancer. The process by which cancer cells egress from the primary tumor upon interfacing with the lymphatic vasculature is complex and driven by dynamic interactions between cancer cells and stromal cells, including cancer-associated fibroblasts (CAF). The matricellular protein periostin can distinguish CAF subtypes in breast cancer and is associated with increased desmoplasia and disease recurrence in patients. However, as periostin is secreted, periostin-expressing CAFs are difficult to characterize in situ, limiting our understanding of their specific contribution to cancer progression. Here, we used in vivo genetic labeling and ablation to lineage trace periostin+ cells and characterize their functions during tumor growth and metastasis. Periostin-expressing CAFs were spatially found at periductal and perivascular margins, were enriched at lymphatic vessel peripheries, and were differentially activated by highly metastatic cancer cells versus poorly metastatic counterparts. Surprisingly, genetically depleting periostin+ CAFs slightly accelerated primary tumor growth but impaired intratumoral collagen organization and inhibited lymphatic, but not lung, metastases. Periostin ablation in CAFs impaired their ability to deposit aligned collagen matrices and inhibited cancer cell invasion through collagen and across lymphatic endothelial cell monolayers. Thus, highly metastatic cancer cells mobilize periostin-expressing CAFs in the primary tumor site that promote collagen remodeling and collective cell invasion within lymphatic vessels and ultimately to sentinel lymph nodes. SIGNIFICANCE: Highly metastatic breast cancer cells activate a population of periostin-expressing CAFs that remodel the extracellular matrix to promote escape of cancer cells into lymphatic vessels and drive colonization of proximal lymph nodes.

Priming a vascular-selective cytokine response permits CD8+ T-cell entry into tumors.

Targeting DNA methyltransferase 1 (DNMT1) has immunomodulatory and anti-neoplastic activity, especially when paired with cancer immunotherapies. Here we explore the immunoregulatory functions of DNMT1 in the tumor vasculature of female mice. Dnmt1 deletion in endothelial cells (ECs) impairs tumor growth while priming expression of cytokine-driven cell adhesion molecules and chemokines important for CD8+ T-cell trafficking across the vasculature; consequently, the efficacy of immune checkpoint blockade (ICB) is enhanced. We find that the proangiogenic factor FGF2 promotes ERK-mediated DNMT1 phosphorylation and nuclear translocation to repress transcription of the chemokines Cxcl9/Cxcl10 in ECs. Targeting Dnmt1 in ECs reduces proliferation but augments Th1 chemokine production and extravasation of CD8+ T-cells, suggesting DNMT1 programs immunologically anergic tumor vasculature. Our study is in good accord with preclinical observations that pharmacologically disrupting DNMT1 enhances the activity of ICB but suggests an epigenetic pathway presumed to be targeted in cancer cells is also operative in the tumor vasculature.

Deadly DAaRTS destroy cancer cells via a tumor microenvironment-mediated trigger.

Stromal cells within the tumor microenvironment play a supportive role in tumor growth, progression, and treatment resistance; therefore, these nonmalignant cells are potential therapeutic targets. In this issue of the JCI, Szot et al. devised a strategy to exploit the cell-surface marker TEM8 (also known as ANTXR1), which is expressed by cancer-associated stromal cells, as a zip code to deliver an antibody-drug conjugate (ADC) linked to the potent cancer-killing drug monomethyl auristatin E (MMAE). In preclinical tumor and experimental metastasis models of multiple cancer types, TEM8-ADC targeted TEM8-expressing cancer-associated stromal cells, which processed and liberated membrane-permeable MMAE and released this drug via the P-glycoprotein (P-gp) drug transporter. Released MMAE killed cancer cells through a bystander mechanism that did minimal damage to the stromal cells themselves. P-gp-expressing tumor cells displayed MMAE resistance, suggesting that P-gp expression status may identify patients who might benefit the most from TEM8-ADC. This strategy, termed DAaRTS (drug activation and release through stroma), represents an elegant example of how selective expression of a cell-surface molecule on cancer-associated stroma can be exploited to facilitate drug delivery and shrink solid tumors.