Fig. 3
Relationship between SPHK1 and SGPL1 expression and S1P and cisplatin resistance in gastroesophageal cancer cell lines. a In drug resistant cell lines that demonstrate increased SPHK1 together with decreased SGPL1 (AGSCIS5, AGSDOC6,OE33OX4, OE33CIS4), the fold change in the ratio of SPHK1:SGPL1 mRNA correlates with observed increase in cellular S1P in drug resistant cell lines relative to the respective parental cell lines (R = 0.981, p = 0.020). Data shown is mean for 3 independent replicates per cell line from three different passages measured by qRT-PCR (see also Additional file 1: Additional information 5). b In the drug resistant cell lines (Fig. 1a), cellular S1P correlates with IC50 to cisplatin, oxaliplatin and docetaxel, respectively (R = 0.690, p = 0.040). IC50 data determined by MTT assay with each data point in each cell line measured in triplicate with 3 independent replicate experiments. S1P measured using high performance liquid chromatography-tandem mass spectrometry as described in the text, mean value from duplicate assays