Anaplastic lymphoma kinase (ALK) is a tyrosine kinase receptor involved in both 
solid and hematological tumors. About 80% of ALK-positive anaplastic large-cell 
lymphoma (ALCL) cases are characterized by the t(2;5)(p23;q35) translocation, 
encoding for the aberrant fusion protein nucleophosmin (NPM)-ALK, whereas 5% of 
non-small-cell lung cancer (NSCLC) patients carry the inv(2)(p21;p23) 
rearrangement, encoding for the echinoderm microtubule-associated protein-like 4 
(EML4)-ALK fusion. The ALK/c-MET/ROS inhibitor crizotinib successfully improved 
the treatment of ALK-driven diseases. However, several cases of resistance 
appeared in NSCLC patients, and ALK amino acid substitutions were identified as 
a leading cause of resistance to crizotinib. Second-generation ALK inhibitors 
have been developed in order to overcome crizotinib resistance. In this work, we 
profiled in vitro the activity of crizotinib, AP26113, ASP3026, alectinib, and 
ceritinib against six mutated forms of ALK associated with clinical resistance 
to crizotinib (C1156Y, L1196M, L1152R, G1202R, G1269A, and S1206Y) and provide a 
classification of mutants according to their level of sensitivity/resistance to 
the drugs. Since the biological activity of ALK mutations extends beyond the 
specific type of fusion, both NPM-ALK- and EML4-ALK-positive cellular models 
were used. Our data revealed that most mutants may be targeted by using 
different inhibitors. One relevant exception is represented by the G1202R 
substitution, which was highly resistant to all drugs (>10-fold increased IC50 
compared to wild type) and may represent the most challenging mutation to 
overcome. These results provide a prediction of cross-resistance of known 
crizotinib-resistant mutations against all second-generation tyrosine kinase 
inhibitors (TKIs) clinically available, and therefore could be a useful tool to 
help clinicians in the management of crizotinib-resistance cases.