In vitro activity: LEE011, as dual CDK4/CDK6 inhibitor, significantly inhibits the growth of 12 of 17 neuroblastoma cell lines with mean IC50 of 307 nM. The growth inhibition of neuroblastoma cell lines is primarily cytostatic and is mediated by a G1 cell-cycle arrest and cellular senescence.

Kinase Assay: Ribociclib (formerly also known as LEE011, NVP-LEE011; trade name: Kisqali) is a potent, orally available and highly specific inhibitor of CDK4/6 (cyclin-dependent kinase) with IC50s of 10 nM and 39 nM, respectively. As of March 2017, Ribociclib was approved by FDA to treat postmenopausal women with a type of advanced breast cancer. Ribociclib functions via decreasing in phosphorylated RB and FOXM1. When tested with 17 human neuroblastoma cell lines, 12 of them were sensitive to Ribociclibtreatment with mean IC50=306±68 NM. Treatment with Ribociclib could dramatically decrease cell growth via arresting cell cycle G0-G1. In 12 of 17 human neuroblastoma-derived cell lines, treatment with LEE011 could significantly reduce cell proliferation.

Cell Assay: A panel of neuroblastoma cell lines, selected based upon prior demonstration of substrate adherent growth, is plated in triplicate on the Xcelligence Real-Time Cell Electronic Sensing system and treated 24 hours later with a four-log dose range of inhibitor or with a dimethyl sulfoxide (DMSO) control. Cell indexes are monitored continuously for ~100 hours, and IC50 values are determined as follows: growth curves are generated by plotting the cell index as a function of time and are normalized to the cell index at the time of treatment for a baseline cell index of 1. The area under the normalized growth curve from the time of treatment to 96 hours posttreatment is then calculated using a baseline area of 1 (the cell index at the time of treatment). Areas are normalized to the DMSO control, and the resulting data are analyzed using a nonlinear log inhibitor versus normalized response function. All experiments are repeated at least once.