Fig. 1.

Selective antagonists of 5-HT5A inhibit tumorsphere formation by human breast tumor cells. a Panel of structurally distinct selective antagonists of 5-HT5A. b IC₅₀ curves (Graphpad Prism 7.0) generated from non-linear regression of sphere forming assays with enantiopure guanidine-like 5-HT5A antagonists. The blue curves show the effect of increasing doses of the (S) isomers on sphere formation whereas the red curves show the effect of the (R) isomers. Each point indicates the mean sphere forming efficiency +/− the standard error of the mean (SEM). c Bar graphs showing that the frequency of sphere initiating cells was unaffected by treatment with G1A-(R) and G1B-(R) (red) at the approximate IC₅₀ concentrations (2.7 μM) of their (S)-enantiomers (blue). Statistical significance was determined by one-way ANOVA and post-hoc Tukey’s tests [**** p < 0.0001; *** p = 0.006; ns p > 0.05]. d IC₅₀ curves of sphere forming assays using PDX derived cells lines exposed to increasing concentrations of SB-699551. A 0.1 nM concentration of each compound was used to represent the vehicle allowing for accurate IC₅₀ calculations