CD24+ Ovarian Cancer Cells Are Enriched for Cancer-Initiating Cells and Dependent on JAK2 Signaling for Growth and Metastasis

Ovarian cancer is known to be composed of distinct populations of cancer cells, some of which demonstrate increased capacity for cancer initiation and/or metastasis. The study of human cancer cell populations is difficult due to long requirements for tumor growth, interpatient variability, and the need for tumor growth in immune-deficient mice. We therefore characterized the cancer initiation capacity of distinct cancer cell populations in a transgenic murine model of ovarian cancer. In this model, conditional deletion of Apc, Pten, and Trp53 in the ovarian surface epithelium (OSE) results in the generation of high-grade metastatic ovarian carcinomas. Cell lines derived from these murine tumors express numerous putative stem cell markers, including CD24, CD44, CD90, CD117, CD133, and ALDH. We show that CD24(+) and CD133(+) cells have increased tumor sphere-forming capacity. CD133(+) cells demonstrated a trend for increased tumor initiation while CD24(+) cells versus CD24(-) cells had significantly greater tumor initiation and tumor growth capacity. No preferential tumor-initiating or growth capacity was observed for CD44(+), CD90(+), CD117(+), or ALDH(+) versus their negative counterparts. We have found that CD24(+) cells, compared with CD24(-) cells, have increased phosphorylation of STAT3 and increased expression of STAT3 target Nanog and c-myc. JAK2 inhibition of STAT3 phosphorylation preferentially induced cytotoxicity in CD24(+) cells. In vivo JAK2 inhibitor therapy dramatically reduced tumor metastases, and prolonged overall survival. These findings indicate that CD24(+) cells play a role in tumor migration and metastasis and support JAK2 as a therapeutic target in ovarian cancer.