PF-06463922, a novel brain-penetrating small molecule inhibitor of ALK/ROS1 with potent activity against a broad spectrum of ALK resistant mutations in preclinical models in vitro and in vivo

Oncogenic fusions of Anaplastic Lymphoma Kinase (ALK) define a subset of human lung adenocarcinomas. The 1st generation ALK inhibitor XALKORI ® (crizotinib) demonstrated impressive clinical benefit in ALK-fusion positive lung cancers and was approved by the FDA for the treatment of ALK-fusion positive NSCLC in 2011. However, as seen with most kinase inhibitors, patients treated with XALKORI eventually developed resistance to therapy. Acquired ALK kinase domain mutations and brain metastases are significant contributors to the relapse after XALKORI therapy. To date, multiple types of ALK kinase domain mutations have been identified in XALKORI refractory patients including ALKG1269A, ALKL1196M, ALKC1156Y, ALKL1152R, ALKF1174L, ALKS1206Y, ALK1151Tins and ALKG1202R, accounting for about 1/3 of patient samples tested. Currently, a number of 2nd generation ALK inhibitors are under development aiming to overcome XALKORI resistant mutations. Even though in preclinical models, some ALK mutants such as ALKG1202R and ALK1151Tins confer high-levels of resistance to almost all of the 2nd generation ALK inhibitors tested. Here we report PF-06463922, a novel ATP competitive small molecule inhibitor of ALK/ROS1, with potent and selective inhibitory activity against all known acquired XALKORI resistant mutations identified in patients. PF-06463922 is also capable of penetrating the blood brain barrier in preclinical animal models. In vitro, PF-06463922 demonstrated potent inhibition in catalytic activities of ALK and 8 different ALK mutant kinases in recombinant enzyme and cell based assays (cell IC50s = 1 to 65 nM). PF-06463922 also showed potent growth inhibitory activity and induced apoptosis in the NSCLC cells harboring either non-mutant ALK or mutant ALK fusions (IC50s = 1 to 30 nM). In vivo, PF-06463922 demonstrated marked cytoreductive activity in mice bearing tumor xenografts that express EML4-ALK, EML4-ALKL1196M, EML4-ALKG1269A, EML4-ALKG1202R or NPM-ALK at low nM free plasma concentrations. These effects were associated with significant inhibition in cellular Ki67 and increased cleaved-caspase3 levels in tumors. In addition, PF-06463922 achieved brain exposure of 20-30% of its plasma levels in mice, and significantly regressed the brain tumors and prolonged survival of mice bearing orthotopic EML4-ALK and EML4-ALKL1196M positive brain tumor implants. The antitumor efficacy of PF-06463922 was dose dependent and strongly correlated with inhibition of ALK phosphorylation and downstream signaling. Our data indicate that PF-06463922 is the most potent ALK inhibitor reported to date (to our knowledge, against both non-mutant or mutant ALK in cell assays), and it demonstrates great potential for treating ALK fusion positive cancers including patients who relapsed from XALKORI therapy due to various ALK kinase domain mutations and/or brain metastases. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C253. Citation Format: Helen Y. Zou, Lars R. Engstrom, Qiuhua Li, Melissa West Lu, Ruth Wei Tang, Hui Wang, Konstantinos Tsaparikos, Jinwei Wang, Sergei Timofeevski, Dac M. Dinh, Hieu Lam, Justine Lam, Shinji Yamazaki, Wenyue Hu, Timothy Affolter, Patrick B. Lappin, Hovhannes Gukasyan, Nathan Lee, Jennifer M. Tursi, Ted W. Johnson, Valeria Fantin, Tod Smeal. PF-06463922, a novel brain-penetrating small molecule inhibitor of ALK/ROS1 with potent activity against a broad spectrum of ALK resistant mutations in preclinical models in vitro and in vivo. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C253.