Downregulation of CD 24 suppresses bone metastasis of lung cancer

Suppression of bone metastasis can improve patient quality of life. Current drugs for bone metastasis have been shown to prolong progression‐free survival but not overall survival; therefore, other potential therapeutic targets for bone metastasis should be investigated. Cell‐surface antigens, such as CD 24, have been recently shown to be involved in the metastasis of various cancers. However, whether CD 24 plays a role in bone metastasis of lung cancer remains unknown. To observe metastasis of lung cancer cells by imaging technology, we introduced a near‐infrared fluorescent protein, iRFP 720, into a bone‐seeking subclone established from lung cancer cells, HARA ‐B4 cells. The anchorage‐independent growth of these cells was then evaluated by colony formation assays. We also compared cancer cell tropism to bone tissue with HARA ‐B4 cells in the presence or absence of CD 24 by cell adhesion assays. To clarify the role of CD 24 in bone metastasis, we intracardially injected CD 24‐knockdown HARA ‐B4 cells into mice and monitored metastasis through detection of iRFP 720 using an in vivo imaging system. CD 24‐knockdown HARA ‐B4 cells in vitro showed reduced anchorage‐independent growth and cancer cell tropism to bone. Bone metastasis was diminished in mice inoculated with CD 24‐knockdown HARA ‐B4 cells, which was rescued by add‐back of CD 24 in cells. Our findings indicate that iRFP 720 is effective for in vivo imaging analysis of bone metastasis and that downregulation of CD 24 suppresses bone metastasis of lung cancer cells. These findings collectively indicate that CD 24 may be considered a promising new therapeutic candidate for the prevention of bone metastasis of lung cancer.