Data from Differential Protein Stability and ALK Inhibitor Sensitivity of EML4-ALK Fusion Variants

Abstract

<div>Abstract<p><b>Purpose:</b><i>ALK</i> rearrangement–positive lung cancers can be effectively treated with ALK inhibitors. However, the magnitude and duration of response is heterogeneous. In addition, acquired resistance limits the efficacy of ALK inhibitors, with most upfront resistance mechanisms being unknown.</p><p><b>Experimental Design:</b> By making use of the Ba/F3 cell line model, we analyzed the cytotoxic efficacy of ALK kinase inhibitors as a function of different <i>EML4-ALK</i> fusion variants <i>v1</i>, <i>v2, v3a</i>, and <i>v3b</i> as well as of three artificially designed <i>EML4-ALK</i> deletion constructs and the <i>ALK</i> fusion genes <i>KIF5b-ALK</i> and <i>NPM1-ALK</i>. In addition, the intracellular localization, the sensitivity to HSP90 inhibition and the protein stability of <i>ALK</i> fusion proteins were studied.</p><p><b>Results:</b> Different <i>ALK</i> fusion genes and <i>EML4-ALK</i> variants exhibited differential sensitivity to the structurally diverse ALK kinase inhibitors crizotinib and TAE684. In addition, differential sensitivity correlated with differences in protein stability in <i>EML4-ALK</i>–expressing cells. Furthermore, the sensitivity to HSP90 inhibition also varied depending on the ALK fusion partner but differed from ALK inhibitor sensitivity patterns. Finally, combining inhibitors of ALK and HSP90 resulted in synergistic cytotoxicity.</p><p><b>Conclusions:</b> Our results might explain some of the heterogeneous responses of <i>ALK</i>-positive tumors to ALK kinase inhibition observed in the clinic. Thus, targeted therapy of <i>ALK</i>-positive lung cancer should take into account the precise <i>ALK</i> genotype. Furthermore, combining ALK and HSP90 inhibitors might enhance tumor shrinkage in <i>EML4-ALK</i>–driven tumors. <i>Clin Cancer Res; 18(17); 4682–90. ©2012 AACR</i>.</p></div>