Abstract 1287: Targeting pleckstrin-2 for the JAK2-STAT and PI3K-Akt pathways in cancer therapy
Authors: Han Xu , Mei Yang , Schiltz Gary E. , Mishra Rama K. , Jain Atul D. , Ji Peng 
Published: August 2019

Abstract
Pleckstrin-2 (Plek2) is a widely expressed PH domain containing protein that binds to phosphoinositide with unclear functions. Our published reports reveal that Plek2 is overexpressed in JAK2 V617F mutation positive myeloproliferative neoplasms (MPNs). We identified that Plek2 is a downstream effector of the JAK2-STAT5 pathway. Furthermore, through a mouse genetic approach, we discovered that knockout of Plek2 significantly ameliorated the MPN phenotypes and reverted lethality and thrombosis in JAK2 V617F knockin mice. These studies demonstrate that Plek2 is critical for the pathogenesis of MPNs with the activated JAK2-STAT5 pathway, and form a strong foundation for the development of Plek2 inhibitors for the treatment of MPNs. Importantly, our published study shows that Plek2 knockout mice do not develop anemia or cytopenia, indicating Plek2’s oncogenic potential is only in the disease background, which makes Plek2 inhibitors less likely to cause severe side effects compared to JAK inhibitor ruxolitinib.
Based on these studies, we used an in silico approach to screen for putative Plek2 binding small molecules and identified hit compounds that bind to the DEP domain of Plek2. Further medicinal chemistry studies identified lead compound NUP-17d that inhibited proliferation of the hyperproliferative hematopoietic cells with potency comparable to ruxolitinib. In addition, NUP-17d also blocked proliferation of several Plek2-overexpressing solid tumor cell lines. Our biochemical assays showed that NUP-17d inhibited Akt phosphorylation. Further mechanistic studies revealed that Plek2 functions as a central hub to mediate the JAK2-STAT and PI3K-Akt pathways to promote tumor cell proliferation. Specifically, Plek2 binds to and recruits PI3K-produced PtdIns(3,4)P2 and PI3K effector proteins including Akt, PDK1, PDK2, and mTOR, which forms a complex and significantly enhances the PI3K signaling. In addition to the biochemical assays, we also demonstrated Plek2’s function through a mouse genetic approach using a Pten hematopoietic specific knockout mouse model. Knockout of Plek2 significantly reverted the myeloproliferative phenotype in these mice and markedly extended their survival. Therefore, NUP-17d blocks tumor cell proliferation through the disruption of the Plek2 complex and inhibition of the PI3K-Akt pathway. Indeed, treatment of an erythropoietin-induced myeloproliferative mouse model with NUP-17d also demonstrated its potent inhibitory effect in myeloproliferation in vivo.
These study establishes Plek2 as a oncoprotein mediating JAK2-STAT and PI3K-Akt signaling pathways. In addition to hematologic malignancies, Plek2 is also found to be highly upregulated with an associated worse prognosis in many solid tumors (oncomine, kmplot). Therefore, our Plek2 inhibitors will have a broad impact in cancer therapy, especially cancers with upregulated JAK2-STAT or PI3K-Akt pathway.
Citation Format: Xu Han, Yang Mei, Gary E. Schiltz, Rama K. Mishra, Atul D. Jain, Peng Ji. Targeting pleckstrin-2 for the JAK2-STAT and PI3K-Akt pathways in cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1287.