Unlike THZ1, which was highly cytotoxic at low nanomolar concentrations (IC50, 6-9 nM) in MYCN-amplified NB cells (4), YKL-5-124 appeared to be cytostatic (IC50, 8-60 nM), causing growth arrest rather than cell death in both MYCN-amplified and nonamplified NB cells (Figure 1B). Here, MYCN is linked to neuroblastoma.