Abstract A277: PF-06463922, a novel ROS1/ALK inhibitor, demonstrates sub-nanomolar potency against oncogenic ROS1 fusions and capable of blocking the resistant ROS1G2032R mutant in preclinical tumor models.

The oncogenic ROS1 gene fusion ( Fig-ROS1 ) was first identified in glioblastoma cells over two decades ago. Recently, ROS1 gene rearrangements were further discovered in a variety of human cancers, including lung adenocarcinoma, cholangiocarcinoma, ovarian cancer, gastric adenocarcinoma, colorectal cancer, inflammatory myofibroblastic tumor, angiosarcoma, and epithelioid hemangioendothelioma, providing additional evidence for ROS1 as an attractive cancer target. The 1st generation Met/ALK/ROS1 inhibitor XALKORI ® (crizotinib) has demonstrated promising clinical response in ROS1 fusion positive NSCLC. But similar to what was seen with acquired ALK secondary resistant mutations in XALKORI refractory patients, a ROS1 kinase domain mutant–ROS1G2032R has been identified in a ROS1 positive NSCLC patient who developed resistance to XALKORI. Therefore, there is an urgent need to develop agents that can overcome this type of resistance. PF-06463922 is a novel, orally available, ATP-competitive small molecule inhibitor of ROS1/ALK with exquisite potency against ROS1 kinase. PF-06463922 inhibited the catalytic activity of recombinant ROS1 with a mean Ki of < 0.005 nM, and inhibited ROS1 autophosphorylation at IC50 values ranging from 0.1 nM to 1 nM cross a panel of cell lines harboring oncogenic ROS1 fusion variants including CD74-ROS1, SLC34A2-ROS1 and Fig-ROS1. PF-06463922 also inhibited cell proliferation and induced cell apoptosis at sub- to low-nanomolar concentrations in the HCC78 human NSCLC cells harboring SLC34A2-ROS1 fusions and the BaF3-CD74-ROS1 cells expressing human CD74-ROS1. In the BaF3 cells engineered to express the XALKORI resistant CD74-ROS1G2032R mutant, PF-06463922 demonstrated nanomolar potency against either ROS1G2032R cellular activity or cell proliferation. In vivo, PF-06463922 demonstrated marked cytoreductive antitumor efficacy at low nanomolar concentration in the NIH3T3 xenograft models expressing human CD74-ROS1 and Fig-ROS1. The antitumor efficacy of PF-06463922 was dose dependent and strongly correlated to inhibition in ROS1 phosphorylation and the downstream signaling molecules pSHP1, pSHP2 and pErk1/2, as well as inhibition of the cell cycle protein Cyclin D1 in tumors. To our knowledge, PF-06463922 is the first reported ROS1 inhibitor that is capable of blocking the resistant ROS1G2032R mutant at predicted pharmacologically relevant concentrations. Our data indicate that PF-06463922 has great potential for treating ROS1 fusion positive cancers including those from patients who relapsed from XALKORI therapy due to acquired ROS1G2032Rmutation. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A277. Citation Format: Helen Y. Zou, Lars R. Engstrom, Qiuhua Li, Melissa West Lu, Ruth Wei Tang, Hui Wang, Konstantinos Tsaparikos, Sergei Timofeevski, Justine Lam, Shinji Yamazaki, Wenyue Hu, Hovhannes Gukasyan, Nathan Lee, Ted W. Johnson, Valeria Fantin, Tod Smeal. PF-06463922, a novel ROS1/ALK inhibitor, demonstrates sub-nanomolar potency against oncogenic ROS1 fusions and capable of blocking the resistant ROS1G2032R mutant in preclinical tumor models. [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 A277.