MAPK8 and neuroblastoma: Blocking JNK activity by its pharmacological inhibitor (SP600125) alone was not able to attenuate the inhibitory effect of metformin on cell viability; however, addition of Rac1 inhibitor (NSC23766) or Cdc42 inhibitor (ML141) along with SP600126 (JNK inhibitor) significantly protected neuroblastoma cells against metformin toxicity (Fig. 6E).