Sphingosine-1-phosphate (S1P) as a potential biomarker for multiple myeloma: determination of plasma S1P by ELISA using a monoclonal antibody to S1P.

B11

This study was undertaken to use a recently-developed ELISA-based assay to evaluate plasma sphingosine-1-phosphate (S1P) as a potential biomarker for malignant myeloma (MM). The bioactive lipid signaling mediator, S1P, is the only product of an oncogene, sphingosine kinase1 (Sphk1), and is S1P is known to promote tumorigenesis and angiogensis. S1P is produced by cancer cells for release into the extracellular space to activate its cognate GPCRs. While S1P has been proposed as a cancer biomarker, but a simple, inexpensive assay for its measurement as not been available until now. We have generated a monoclonal antibody (mAb) that has been shown to retard tumor progression in experimental animals (Visentin et al. 2006), and report here that it can be used to assess S1P as a biomarker in the plasma of cancer patients. The detection limit, assay linearity, and inter- and intra-assay precision were satisfactory for the assay development and optimization. The S1P ELISA operates in a dynamic range from 10 pM to 2 uM S1P. S1P level in cancer-free, control human plasma was 0.215 ± 0.094 uM (n=41). Importantly, the plasma S1P levels were significantly (p<0.0001) higher at 0.406 ± 0.214 uM (n=26) in MM patients compared to healthy controls. Multivariate analyses are being conducted to evaluate S1P levels with other surrogate markers of disease. These findings suggest that patients with active or asymptomatic disease whose S1P levels are elevated could be candidates for anti-S1P therapy such as use of the humanize mAb (ASONEP) which Lpath currently has in Phase 1 clinical trials for cancer.