Abstract 5453: FCN-289, a novel, potent and selective PI3Kδ inhibitor for the treatment of B-cell malignancies
Authors: Lin Shu , Zhou Zuwen , Tan Rui , Xu Hua , Zhang Huajie , Zhang Weipeng , Chen Ling , Yang Lijun , Zhao Xingdong , Liu Yanxin , Zou Zongyao , Gao Yuwei , Zhou Jiashu , Wang Weibo 
Published: June 2022

Abstract
Phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway plays critical roles in cell growth, differentiation, motility, survival, and intracellular trafficking, and is one of the most frequently dysregulated pathways in human cancers including B-cell malignancies. There are 3 classes of PI3K, among which Class I PI3Ks including PI3Kα, β, γ, and δ isoforms are the mostly studied and plays key roles in physiological functions. PI3Kα has a role in insulin-dependent signaling, PI3Kβ functions in platelet aggregation, thrombosis and insulin signaling, and PI3Kγ/δ are expressed mainly in leukocytes and regulate lymphocyte activation, mast cell degranulation, and chemotaxis. Early PI3K inhibitors such as idelalisib are effective against B-cell malignancies such as chronic lymphocytic leukemia, but their clinical use is largely limited due to intolerable toxicities. More selective PI3Kδ inhibitors such as umbralisib (TGR-1202) demonstrates improved clinical efficacy and safety profile compared to current standard of care and was recently approved as a monotherapy for follicular lymphoma and marginal zone lymphoma. However, there is still unmet medical need for novel PI3Kδ inhibitors with improved safety profile and better efficacy to be used as monotherapy and in suitable combination strategies. Here we introduce FCN-289, a novel and oral next-generation PI3Kδ inhibitor. FCN-289 demonstrates potent kinase activity against PI3Kδ with single-digit nanomolar IC50 and remarkably improved selectivity over other PI3K isoforms compared with TGR-1202. FCN-289 exhibits significant anti-proliferating activity against various human diffuse large B-cell lymphoma (DLBCL)-derived cancer cell lines (OCI-LY10, TMD-8 and WSU-NHL) with superior activity compared with TGR-1202. Consistently, FCN-289 shows dose-dependent anti-tumor growth activity superior to that of TGR-1202 at the same and higher dose in TMD-8 DLBCL xenograft models. FCN-289 shows significantly improved anti-tumor activity when combined with BTK inhibitor ibrutinib in TMD-8 and OCI-LY10 DLBCL xenograft models. In non-clinical settings, FCN-289 exhibits good pharmacokinetic (PK) and safety properties with shorter Tmax and higher bioavailability in both rats and dogs, higher exposure in rats, improved CYP450 inhibition profile, and less plasma protein bound ratio compared with TGR-1202.Together, FCN-289 is a novel PI3Kδ inhibitor that possesses more potent in vitro and in vivo anti-cancer activities in B-cell malignancies-derived models with improved selectivity against other PI3K isoforms compared with TGR-1202. Combination with ibrutinib further improves anti-tumor activity compared with monotherapy. FCN-289 shows favorable PK and safety profiles compared with TGR-1202. Our findings highlight the therapeutic potential of FCN-289 as a novel targeted approach as monotherapy or in combination for treating B-cell malignancies.
Citation Format: Shu Lin, Zuwen Zhou, Rui Tan, Hua Xu, Huajie Zhang, Weipeng Zhang, Ling Chen, Lijun Yang, Xingdong Zhao, Yanxin Liu, Zongyao Zou, Yuwei Gao, Jiashu Zhou, Weibo Wang. FCN-289, a novel, potent and selective PI3Kδ inhibitor for the treatment of B-cell malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5453.