Abstract 4758: Inhibition of checkpoint kinase 1 (Chk1) as a potential therapeutic for pediatric neuroblastoma

Neuroblastoma is a cancer derived from cells of the sympathetic nervous system that manifests with significant clinical heterogeneity. Although children diagnosed with low-risk neuroblastoma are very likely to be cured, high-risk patients are frequently resistant to even the most intensive of multi-modal regimens, and at least half of these children suffer relapse that is almost always fatal. To address the unmet need for novel therapeutic targets, our lab conducted an unbiased siRNA screen and determined that the loss of cell cycle checkpoint kinase 1 (Chk1) produced the most robust cytotoxic effect across multiple neuroblastoma cell lines. We subsequently confirmed that many neuroblastoma cell lines express constitutively phosphorylated Chk1 – a discovery that is supported by identical findings in tumors obtained from high-risk patients. Here we present evidence that the combination of a small molecule inhibitor of Chk1 with either irinotecan (SN-38) or cisplatin was synergistic or additive in vitro in cell lines sensitive to single agent Chk1 inhibition. Inhibition of Chk1 signaling as potential therapy in neuroblastoma is further supported by complimentary experiments in which we found that induction of shRNA specific for Chk1 results in marked cytotoxicity. To further understand the chemosensitizing aspect of Chk1 inhibition in neuroblastoma cells, we assayed the ATR/Chk1 pathway for potential biomarkers predictive of response. Candidate signaling partners in this pathway were isolated based upon either pharmacological inhibition or shRNA-induced silencing of Chk1, followed by hybridization to antibody microarrays. This technique has allowed for identification of Chk1-related signaling proteins involved in the DNA damage response pathway. Lastly, we have assessed the efficacy of Chk1 inhibition in an in vivo xenograft mouse model of pediatric neuroblastoma. We found that daily administration of a small molecule Chk1 inhibitor, currently undergoing Phase I clinical testing, was able to significantly impede the growth of NB1643 neuroblastoma xenografts (p=0.001). Efforts are currently underway in our laboratory to investigate a potentially synergistic effect in vivo through co-administration of this inhibitor with irinotecan or cisplatin. Taken together, these results provide a strong rationale for further studies to assess the use of Chk1 inhibition as either a single-agent or combinatorial therapy in pediatric neuroblastoma. Citation Format: {Authors}