Systemic chemotherapy was considered of modest efficacy in prostate cancer until the recent introduction of taxanes. We took advantage of the known differential effect of camptothecin and docetaxel on human PC-3 and LNCaP prostate cancer cells to determine their effect on sphingosine kinase-1 (SphK1) activity and subsequent ceramide/sphingosine 1-phosphate (S1P) balance in relation with cell survival. In vitro, docetaxel and camptothecin induced strong inhibition of SphK1 and elevation of the ceramide/S1P ratio only in cell lines sensitive to these drugs. SphK1 overexpression in both cell lines impaired the efficacy of chemotherapy by decreasing the ceramide/S1P ratio. Alternatively, silencing SphK1 by RNA interference or pharmacologic inhibition induced apoptosis coupled with ceramide elevation and loss of S1P. The differential effect of both chemotherapeutics was confirmed in an orthotopic PC-3/green fluorescent protein model established in nude mice. Docetaxel induced a stronger SphK1 inhibition and ceramide/S1P ratio elevation than camptothecin. This was accompanied by a smaller tumor volume and the reduced occurrence and number of metastases. SphK1-overexpressing PC-3 cells implanted in animals developed remarkably larger tumors and resistance to docetaxel treatment. These results provide the first in vivo demonstration of SphK1 as a sensor of chemotherapy. (Cancer Res 2005; 65(24): 11667-75)

The mitochondrial enzyme monoamine oxidase (MAO), its isoform MAO-A, plays a major role in reactive oxygen species–dependent cardiomyocyte apoptosis and postischemic cardiac damage. In the current study, we investigated whether sphingolipid metabolism can account for mediating MAO-A– and reactive oxygen species–dependent cardiomyocyte apoptosis. In H9c2 cardiomyoblasts, MAO-A–dependent reactive oxygen species generation led to mitochondria-mediated apoptosis, along with sphingosine kinase-1 (SphK1) inhibition. These phenomena were associated with generation of proapoptotic ceramide and decrease in prosurvival sphingosine 1-phosphate. These events were mimicked by inhibition of SphK1 with either pharmacological inhibitor or small interfering RNA, as well as by extracellular addition of C ₂ -ceramide or H ₂ O ₂ . In contrast, enforced expression of SphK1 protected H9c2 cells from serotonin- or H ₂ O ₂ -induced apoptosis. Analysis of cardiac tissues from wild-type mice subjected to ischemia/reperfusion revealed significant upregulation of ceramide and inhibition of SphK1. It is noteworthy that SphK1 inhibition, ceramide accumulation, and concomitantly infarct size and cardiomyocyte apoptosis were significantly decreased in MAO-A–deficient animals. In conclusion, we show for the first time that the upregulation of ceramide/sphingosine 1-phosphate ratio is a critical event in MAO-A–mediated cardiac cell apoptosis. In addition, we provide the first evidence linking generation of reactive oxygen species with SphK1 inhibition. Finally, we propose sphingolipid metabolites as key mediators of postischemic/reperfusion cardiac injury.

The emerging role of FTY720 (Fingolimod) in cancer treatment

Activation of cardiac fibroblasts and their differentiation into myofibroblasts is a key event in the progression of cardiac fibrosis that leads to end-stage heart failure. Apelin, an adipocyte-derived factor, exhibits a number of cardioprotective properties; however, whether apelin is involved in cardiac fibroblast activation and myofibroblast formation remains unknown. The aim of this study was to determine the effects of apelin in activated cardiac fibroblasts, the potential related mechanisms and impact on cardiac fibrotic remodelling process. In vitro experiments were performed in mouse cardiac fibroblasts obtained from normal and pressure-overload hearts. Pretreatment of naive cardiac fibroblasts with apelin (1–100 nM) inhibited Transforming growth factor-β (TGF-β)-mediated expression of the myofibroblast marker α-smooth muscle actin (α-SMA) and collagen production. Furthermore, apelin decreased the spontaneous collagen production in cardiac fibroblasts isolated from hearts after aortic banding. Knockdown strategy and pharmacological inhibition revealed that prevention of collagen accumulation by apelin was mediated by a reduction in sphingosine kinase 1 (SphK1) activity. In vivo studies using the aortic banding model indicated that pretreatment with apelin attenuated the development of myocardial fibrotic remodelling and inhibited cardiac SphK1 activity and α-SMA expression. Moreover, administration of apelin 2 weeks after aortic banding prevented cardiac remodelling by inhibiting myocyte hypertrophy, cardiac fibrosis, and ventricular dysfunction. Our data provide the first evidence that apelin inhibits TGF-β-stimulated activation of cardiac fibroblasts through a SphK1-dependent mechanism. We also demonstrated that the administration of apelin during the phase of reactive fibrosis prevents structural remodelling of the myocardium and ventricular dysfunction. These findings may have important implications for designing future therapies for myocardial performance during fibrotic remodelling, affecting the clinical management of patients with progressive heart failure.

Radiotherapy is widely used as a radical treatment for prostate cancer, but curative treatments are elusive for poorly differentiated tumors where survival is just 15% at 15 years. Dose escalation improves local response rates but is limited by tolerance in normal tissues. A sphingosine analogue, FTY720 (fingolimod), a drug currently in phase III studies for treatment of multiple sclerosis, has been found to be a potent apoptosis inducer in prostate cancer cells. Using in vitro and in vivo approaches, we analyzed the impact of FTY720 on sphingolipid metabolism in hormone-refractory metastatic prostate cancer cells and evaluated its potential as a radiosensitizer on cell lines and prostate tumor xenografts. In prostate cancer cell lines, FTY720 acted as a sphingosine kinase 1 (SphK1) inhibitor that induced prostate cancer cell apoptosis in a manner independent of sphingosine-1-phosphate receptors. In contrast, γ irradiation did not affect SphK1 activity in prostate cancer cells yet synergized with FTY720 to inhibit SphK1. In mice bearing orthotopic or s.c. prostate cancer tumors, we show that FTY720 dramatically increased radiotherapeutic sensitivity, reducing tumor growth and metastasis without toxic side effects. Our findings suggest that low, well-tolerated doses of FTY720 could offer significant improvement to the clinical treatment of prostate cancer. Cancer Res; 70(21); 8651–61. ©2010 AACR.