Dual <i>ALK</i> and <i>CDK4/6</i> Inhibition Demonstrates Synergy against Neuroblastoma

<b>Purpose:</b> Anaplastic lymphoma kinase (<i>ALK</i>) is the most frequently mutated oncogene in the pediatric cancer neuroblastoma. We performed an <i>in vitro</i> screen for synergistic drug combinations that target neuroblastomas with mutations in <i>ALK</i> to determine whether drug combinations could enhance antitumor efficacy.<b>Experimental Design:</b> We screened combinations of eight molecularly targeted agents against 17 comprehensively characterized human neuroblastoma-derived cell lines. We investigated the combination of ceritinib and ribociclib on <i>in vitro</i> 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 <i>in vivo</i> 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.<b>Results:</b> The combination of ribociclib, a dual inhibitor of cyclin-dependent kinase (CDK) 4 and 6, and the ALK inhibitor ceritinib demonstrated higher cytotoxicity (<i>P</i> = 0.008) and synergy scores (<i>P</i> = 0.006) in cell lines with <i>ALK</i> mutations as compared with cell lines lacking mutations or alterations in <i>ALK</i> Compared with 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 <i>ALK</i>-F1174L and F1245C <i>de novo</i> resistance mutations and prevented the emergence of resistance. Murine ribociclib and ceritinib plasma concentrations were unaltered by combination therapy.<b>Conclusions:</b> This preclinical combination drug screen with <i>in vivo</i> validation has provided the rationale for a first-in-children trial of combination ceritinib and ribociclib in a molecularly selected pediatric population. <i>Clin Cancer Res; 23(11); 2856-68. ©2016 AACR</i>.