Background:

RBC8 inhibit Ral GTPase with IC50 values of 3.5 μM and 3.4 μM in Ral-dependent lines H2122 and H358 [1].

RalA and B are Ras-like GTPases. They are important drivers of metastasis and tumor growth [1].

RBC8 reduced the activation of RalA in living cells. Ral is required for spreading murine embryonic fibroblasts (MEFs) and lipid raft exocytosis on fibronectin-coated cover slips. In these cells, the spreading of WT MEFs was inhibited by the depletion of RalA via siRNA, whereas caveolin deficient (Cav1-/-) MEFs were resistant to RalA depletion. Treatment with RBC8 inhibited only the cell spreading in the WT MEFs, it did not inhibited the cell spreading in Cav1-/- MEFs. A Ral pull-down assay showed that RBC8 inhibited the activation of both RalA and RalB in both the H2122 and H358 cell lines. In H2122 and H358 cells with Ral knockdown by siRNA, treatment with RBC8 did not show further inhibition of colony formation [1].

In nude mice inoculated with H2122 human lung cancer cells subcutaneously, treatment with RBC8 at 50 mg/kg/d for 21 days (except weekends) intraperitoneally showed an inhibitory effect on tumor growth to a similar extent as dual knockdown of RalA and B. H358 is a lung cancer line. In this cell line, similar results were yielded [1].

Reference:
[1].  Yan C, Liu D, Li L, et al. Discovery and characterization of small molecules that target the Ral GTPase. Nature, 2014, 515(7527): 443-447.