ASP3026, a Selective ALK Inhibitor, Induces Tumor Regression against Crizotinib Resistant EML4-ALK-Dependent Tumor Models in Mice

ABSTRACT EML4-ALK translocation has been validated as a therapeutic target in a subset of non-small-cell lung cancer (NSCLC) patients. In clinical settings, crizotinib has shown promising response rates in patients with EML4-ALK-positive NSCLC. However, disease relapse has been observed after an initial favorable response and several resistance mechanisms, including the gatekeeper L1196M mutation, have been reported to date. We have discovered ASP3026, a selective inhibitor for the ALK kinase. ASP3026 potently inhibited ALK kinase activity with an IC50 value of 3.5 nmol/L and showed more selective inhibition in a Tyr-kinase panel than crizotinib. Using NCI-H2228, a human NSCLC cell line endogenously expressing EML4-ALK, we determined the anti-proliferative effect of ASP3026. ASP3026 inhibited the in vitro proliferation with an IC50 value of 64.8 nmol/L and induced dose-dependent anti-tumor effects starting at 1 mg/kg with marked regression at 10, 30 and 100 mg/kg in a subcutaneous tumor model. Body weights were unaffected. ASP3026 at 100 mg/kg also showed tumor regression against EML4-ALK-driven tumor model with gatekeeper mutation while crizotinib at 100 mg/kg was ineffective. In an NCI-H2228 orthotopic lung model, ASP3026 at 30 mg/kg induced sustained tumor regression during the experimental period. In contrast, crizotinib at 30 mg/kg induced initial regression during the first 7 days but regrowth of the tumor was observed despite continuous crizotinib administration. After tumor regrowth had been established in crizotinib-treated mice, substantial tumor regression was achieved by subsequent administration of ASP3026 at 30 mg/kg. Taken together, these results suggest that ASP3026 in the non-clinical setting shows superior efficacy to crizotinib in crizotinib-resistant models.