Differential Inhibitor Sensitivity of Anaplastic Lymphoma Kinase Variants Found in Neuroblastoma

Neuroblastoma sensitivity to crizotinib depends on the ATP-binding affinity of ALK variants, suggesting that higher doses may overcome resistance. A Boost for Neuroblastoma Therapy Neuroblastoma, a malignancy of the autonomic nervous system, is the most common cancer in children under 1 year of age. Nearly 10% of spontaneous neuroblastoma patients house mutations in the gene that encodes anaplastic lymphoma kinase (ALK). The U.S. Food and Drug Administration recently approved crizotinib—a small-molecule inhibitor of ALK’s tyrosine kinase activity and thus its cell signaling function—for the treatment of non–small cell lung carcinomas, and the drug is in early clinical trials for neuroblastoma. However, tumors with certain ALK mutations do not appear to respond to crizotinib. Bresler et al. now dissect the molecular mechanisms behind the differential crizotinib sensitivities of individual ALK mutations. Crizotinib inhibits kinase activity by competing for binding with the enzyme’s adenosine triphosphate (ATP) substrate. The authors used human neuroblastoma cell lines and xenografts in mice to show that cancers with the two most common ALK mutations, F1174L and R1275Q, are unresponsive to and effectively inhibited by crizotinib therapy, respectively. This reduced sensitivity was caused by a heightened ATP-binding affinity in F1174L-mutated ALK. These observations suggest that either increasing the dose of crizotinib or engineering higher-affinity inhibitors should improve therapy for patients with this common ALK mutation. Although careful toxicity studies need to be performed to find the maximum tolerated dose in the pediatric population, this mechanistic study provides more than a baby step toward improving crizotinib therapy in the clinic. Activating mutations in the anaplastic lymphoma kinase (ALK) gene were recently discovered in neuroblastoma, a cancer of the developing autonomic nervous system that is the most commonly diagnosed malignancy in the first year of life. The most frequent ALK mutations in neuroblastoma cause amino acid substitutions (F1174L and R1275Q) in the intracellular tyrosine kinase domain of the intact ALK receptor. Identification of ALK as an oncogenic driver in neuroblastoma suggests that crizotinib (PF-02341066), a dual-specific inhibitor of the ALK and Met tyrosine kinases, will be useful in treating this malignancy. Here, we assessed the ability of crizotinib to inhibit proliferation of neuroblastoma cell lines and xenografts expressing mutated or wild-type ALK. Crizotinib inhibited proliferation of cell lines expressing either R1275Q-mutated ALK or amplified wild-type ALK. In contrast, cell lines harboring F1174L-mutated ALK were relatively resistant to crizotinib. Biochemical analyses revealed that this reduced susceptibility of F1174L-mutated ALK to crizotinib inhibition resulted from an increased adenosine triphosphate–binding affinity (as also seen in acquired resistance to epidermal growth factor receptor inhibitors). Thus, this effect should be surmountable with higher doses of crizotinib and/or with higher-affinity inhibitors.