Peritoneal dissemination requires an Sp1-dependent CXCR4/CXCL12 signaling axis and extracellular matrix-directed spheroid formation

Peritonitis carcinomatosa is an advanced and intractable state of gastrointestinal and ovarian cancer, where mechanistic elucidation might enable the development of more effective therapies. Peritoneal dissemination of this type of malignancy has been generally thought to initiate from "milky spots" of primitive lymphoid tissues in the peritoneal cavity. In this study, we offer evidence challenging this idea, based on the finding that tumor implantation and directional dissemination was not required for the presence of milky spots, but rather SCF/CXCL12-expressing niche-like cells located at the border regions of perivascular adipose tissue. Interestingly, we found that peritoneal cavity lavage fluid, which specifically contains peritoneal collagen type IV and plasma fibronectin, dramatically facilitated spheroid formation of murine and human colon cancer cells. Spheroid formation strongly induced the expression of CXCR4 in an Sp1-dependent manner to promote niche-directed metastasis. Notably, disrupting sphere formation or inhibiting Sp1 activity was sufficient to suppress tumor dissemination and potentiated chemosensitivity to 5-fluorouracil. Our findings illuminate mechanisms of peritoneal cancer dissemination and highlight the Sp1/CXCR4/CXCL12 signaling axis as a rational target for the development of therapeutics to manage this intractable form of malignancy.