Abstract 2010: SPHK1 promotes lung metastasis of breast cancer

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Breast cancer is the second most commonly diagnosed cancer and second leading cause of cancer death in American women. The majority of cancer-related fatalities are a result of metastases to distant organs, rather than due to the primary tumors themselves. The role of the lipid metabolic pathways in breast cancer progression and metastasis has become a focal point of interest in recent years and our work is mainly focused on sphingolipids. Sphingosine-1-phosphate (S1P) is a lipid signaling mediator that functions both intracellularly, as a second messenger signaling molecule, and extracellularly, as a ligand for G-protein coupled S1P receptors (S1PRs). S1P plays important roles in modulating diverse cellular functions involved in cancer, i.e. cell growth, survival, and motility. Sphingosine Kinase 1 (SPHK1) catalyzes the phosphorylation of sphingosine, an amino alcohol, to generate S1P. Recently, studies have shown that SPHK1 is overexpressed in breast cancer and correlates with poor prognosis; thus, its role in breast cancer has received substantial attention. It is still unclear if SPHK1 plays any role in spontaneous metastasis of breast cancer to the lungs, and if so, the underlying mechanism behind it. To study this, we used the highly metastatic human triple negative breast cancer cell line MDA-MB-435, as it expressed high levels of endogenous SPHK1. We generated SPHK1 knockdown (435 shSPHK1) and control (435 shScramble) cells using SPHK1-targeting shRNA and scrambled shRNA, respectively. Knocking down SPHK1 decreased the invasive and migration potential of MDA-MB-435 cells in vitro, but had no significant effect on in vitro cell proliferation. Then, the control and knockdown cells were orthotopically injected into mammary fat pads (MFP) of nude mice to form MFP tumors. MFP tumors were excised from mice with survival surgery at day 30. Consistent with our in vitro proliferation data, there was no significant difference in MFP tumor proliferation, indicated by Ki-67 staining, between control and SPHK1 knockdown cells by day 30. However, TUNEL staining of MFP tumors showed that tumors formed by 435 shSPHK1 cells have increased apoptosis compared to tumors formed by 435 shScramble cells. After tumor excision at day 30, mice were monitored for another 4 weeks for spontaneous metastases. Remarkably, although ∼100% of mice injected with 435 shScramble developed spontaneous lung metastasis, only ∼20% of mice injected with 435 shSPHK1 had spontaneous lung metastasis. No metastasis was detected in the liver and the brain in this time frame. These data suggest that SPHK1 might play an important role in promoting spontaneous lung metastasis of breast cancer. Currently, we are investigating the specific step(s) of the metastatic cascade regulated by SPHK1. An understanding of the molecular mechanism of SPHK1-mediated breast cancer lung metastasis may enable SPHK1 to be developed as a molecular marker and a therapeutic target of metastatic breast cancer. Citation Format: Sunil Acharya, Chenyu Zhang, Frank L. Lowery, Qingling Zhang, Dihua Yu. SPHK1 promotes lung metastasis of breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2010. doi:10.1158/1538-7445.AM2014-2010