Abstract 2744: CDK4/CDK6 inhibition is potently active in a definable subset of human neuroblastomas.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Background: Neuroblastoma is a pediatric embryonal cancer for which the survival of patients with high-risk disease is less than 50% and has not dramatically changed over the last several years. Recently, a number of cell cycle genes\_particularly those within the Cyclin D/CDK4/CDK6/RB network\_have been identified as oncogenic vulnerabilities in neuroblastoma, suggesting that their therapeutic exploitation might improve survivability. Indeed, genomic amplifications of CDK4, CDK6, and CCND1 have been reported in primary neuroblastomas, and we have previously shown via an unbiased loss of function screen that CDK4 depletion is associated with potent anti-tumor activity (Cole, PNAS 2011). Here, we sought to translate these findings into novel therapies for children with neuroblastoma by evaluating the effect of pharmacologic Cdk4/Cdk6 inhibition on neuroblastoma viability. Methods: We analyzed the effect of combined Cdk4/6 inhibition in a comprehensive panel of human-derived neuroblastoma cell lines using LEE011, a highly specific Cdk4/6 small molecule inhibitor. Anti-tumor activity was also determined in vivo in three neuroblastoma xenograft models, and integrative genomics was used to identify biomarkers of drug sensitivity. Results: Treatment with LEE011 significantly inhibited proliferation in 10 of 15 human neuroblastoma-derived cell lines by inducing cytostasis at nanomolar concentrations (mean IC50 = 361 ± 97 nM, considering sensitive lines only), as evidenced by significant cell cycle arrest and senescence that were likely attributed to dose-dependent decreases in phosphorylated RB and FOXM1. In addition, responsiveness of neuroblastoma xenografts to LEE011 was reflective of in vitro data in that there was a direct correlation of IC50 values with degree of subcutaneous xenograft growth delay, with the most sensitive lines in vitro showing profound growth inhibition in vivo. While our data indicate that neuroblastomas sensitive to LEE011 were more likely to contain genomic amplification of MYCN (p= 0.04, student's t test), a supervised hierarchical clustering of gene expression data identified several potential gene signatures that could explain the observed differential sensitivity to Cdk4/6 inhibition. Conclusions: Our data show that LEE011 is highly active in a large subset of neuroblastoma cell lines and xenograft models, and therefore support the clinical development of LEE011 as a therapy for neuroblastoma as well as efforts to validate biomarkers of drug activity. Citation Format: JulieAnn Rader, Lori Hart, Mike Russell, Michael Nakazawa, Lili Belcastro, Daniel Martinez, Erica Carpenter, Sunkyu Kim, Sudha Parasuraman, Giordano Caponigro, Robert Schnepp, Andrew Wood, Bruce Pawel, Deborah Watson, Patrick Warren, Kristina Cole, John Maris. CDK4/CDK6 inhibition is potently active in a definable subset of human neuroblastomas. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2744. doi:10.1158/1538-7445.AM2013-2744