Neuroblastomas (NBs) harboring activating point mutations in Anaplastic Lymphoma Kinase (ALK) are differentially sensitive to the ALK inhibitor crizotinib, with certain mutations conferring intrinsic crizotinib resistance. To overcome this clinical obstacle, our goal was to identify inhibitors with improved potency that can target intractable ALK variants such as F1174L. We find that PF-06463922 has high potency across ALK variants, and inhibits ALK more effectively than crizotinib in vitro. Most importantly, PF-06463922 induces complete tumor regression in both crizotinib-resistant and sensitive xenograft mouse models of NB, as well as in PDXs harboring the crizotinib-resistant F1174L or F1245C mutations. These studies demonstrate that PF-06463922 has the potential to overcome crizotinib resistance, and exerts unprecedented activity as a single targeted agent against F1174L and F1245C ALK-mutated xenograft tumors, while also inducing responses in a R1275Q xenograft model. Taken together, these results provide the rationale to move PF-06463922 into clinical trials for treatment of patients with ALK-mutated NB.

Purpose The presence of an ALK aberration correlates with inferior survival for patients with high-risk neuroblastoma. The emergence of ALK inhibitors such as crizotinib has provided novel treatment opportunities. However, certain ALK mutations result in de novo crizotinib resistance, and a phase I trial of crizotinib showed a lack of response in patients harboring those ALK mutations. Thus, understanding mechanisms of resistance and defining circumvention strategies for the clinic is critical. Experimental Design The sensitivity of human neuroblastoma-derived cell lines, cell line-derived and patient-derived xenograft (PDX) models with varying ALK statuses to crizotinib combined with topotecan and cyclophosphamide (topo/cyclo) was examined. Cultured cells and xenografts were evaluated for effects of these drugs on proliferation, signaling, and cell death, and assessment of synergy. Results In neuroblastoma murine xenografts harboring the most common ALK mutations, including those mutations associated with resistance to crizotinib (but not in those with wild-type ALK), crizotinib combined with topo/cyclo enhanced tumor responses and mouse event-free-survival. Crizotinib + topo/cyclo showed synergistic cytotoxicity and higher caspase-dependent apoptosis than crizotinib or topo/cyclo alone in neuroblastoma cell lines with ALK aberrations (mutation or amplification). Conclusions Combining crizotinib with chemotherapeutic agents commonly used in treating newly diagnosed patients with high-risk neuroblastoma restores sensitivity in preclinical models harboring both sensitive ALK aberrations and de novo resistant ALK mutations. These data support clinical testing of crizotinib and conventional chemotherapy with the goal of integrating ALK inhibition into multi-agent therapy for ALK-aberrant neuroblastoma patients.

Stem cells remember Tissue stem cells sense their surroundings, and this perception influences subsequent fate and function. Gonzales et al . observed that stem cells accumulate epigenetic memories of diverse environmental events (see the Perspective by Hoste). By wounding skin and monitoring the temporal steps involved in mobilizing stem cells of the hair follicle to repair the epidermis, the authors found that stem cells bear memories of their original niche, migration, encounters with inflammation, and adaptation to the new fate and tasks. During homeostasis, immigrant stem cells are functionally and transcriptionally analogous to native cells, but upon future assaults, they unleash discrete epigenetic memories to heighten physiological response and affect tissue fitness. —BAP

Purpose Anaplastic Lymphoma Kinase (ALK) is the most frequently mutated oncogene in the pediatric cancer neuroblastoma. We performed an in vitro screen for synergistic drug combinations that target neuroblastomas with mutations in ALK to determine if drug combinations could enhance anti-tumor efficacy. Experimental Design We screened combinations of eight molecularly targeted agents against seventeen comprehensively characterized human neuroblastoma-derived cell lines. We investigated the combination of Ceritinib and Ribociclib on in vitro proliferation, cell cycle, viability, caspase activation, and the Cyclin D/CDK4/CDK6/RB and pALK signaling networks in cell lines with representative ALK status. We performed in vivo trials in CB17 SCID mice bearing conventional and patient-derived xenograft models comparing Ceritinib alone, Ribociclib alone, and the combination, with plasma pharmacokinetics to evaluate for drug-drug interactions. Results The combination of Ribociclib, a dual inhibitor of cyclin-dependent kinase (CDK) 4 and 6, and the ALK inhibitor Ceritinib demonstrated higher cytotoxicity (p=0.008) and synergy scores (p=0.006) in cell lines with ALK mutations as compared to cell lines lacking mutations or alterations in ALK. Compared to either drug alone, combination therapy enhanced growth inhibition, cell cycle arrest, and caspase-independent cell death. Combination therapy achieved complete regressions in neuroblastoma xenografts with ALK-F1174L and F1245C de novo resistance mutations, and prevented the emergence of resistance. Murine Ribociclib and Ceritinib plasma concentrations were unaltered by combination therapy. Conclusions This preclinical combination drug screen with in vivo validation has provided the rationale for a first in children trial of combination Ceritinib and Ribociclib in a molecularly selected pediatric population.