Interestingly, valpromide (VPM), a VPA analog but devoid of HDAC inhibitory activity, did also potentiate STS-mediated NB cell death, through reduction in survivin and Akt levels, thus suggesting that HDAC inhibition might not be crucial for STS-induced apoptosis, and other mechanisms might be involved [224]. This evidence concerns the gene HDAC9 and neuroblastoma.