Targeted Deletion of Cxcl1 in MSCs Regulates Osteogenesis and Suppresses Bone-Metastatic Prostate Cancer.

Bone metastasis continues to be the greatest challenge in treating patients with prostate cancer despite ongoing research. In bone, prostate cancer tumors hijack normal bone remodeling processes to drive cancer progression. However, it is unclear how these interactions drive bone-metastatic prostate cancer growth in the bone environment. To understand the mechanisms associated with bone-metastatic prostate cancer regulation of mesenchymal stem cells (MSC), we previously identified that bone-metastatic prostate cancer induces MSC expression of the pro-inflammatory chemokine CXCL8 and its mouse functional homologue Cxcl1. To date, there has been little to no information about the role of CXCL1/8 in MSC biology and its impact in the tumor-bone environment. Using genetic deletion of Cxcl1, we discovered a novel role for Cxcl1/8 in regulating MSC osteoblast differentiation, such that targeted deletion of Cxcl1 enhanced MSC osteoblastogenesis. Despite the osteogenic nature of prostate cancer, co-injection of Cxcl1 knockout (KO) MSCs with bone-metastatic prostate cancer in bone significantly suppressed tumor growth compared with co-injection with scrambled control (non-targeting) MSCs, even in the presence of three times more prostate cancer to MSCs. Furthermore, bulk RNA sequencing revealed immune response pathways, both in Cxcl1-KO MSCs and bone-metastatic prostate cancer tumors containing Cxcl1-KO MSCs. In support of this, Cxcl1-KO MSCs reduced immature neutrophils in the bone environment, while increasing monocytes. These findings demonstrate the importance of MSC-derived Cxcl1 in the bone microenvironment and highlight the importance of Cxcl1 in bone-metastatic prostate cancer progression. IMPLICATIONS: MSC-derived Cxcl1 regulates prostate cancer progression in bone.