eIF4B Is a Novel Target of CAMK2G and Promotes Proliferation of Malignant Cells in Myelofibrosis

Background Myelofibrosis (MF) is a myeloproliferative neoplasm which is associated with megakaryocytic atypia, fibrosis in the bone marrow (BM), and extramedullary hematopoiesis, followed by progressive hematopoietic failure and leukemic transformation. JAK1/JAK2 inhibitors are currently available and reduce spleen volume, improve symptoms related to MF and prolong the overall survival (OS). Although the benefits associated with JAK1/JAK2 inhibitors are well established, not all patients respond to these inhibitors, and long-term exposure to these inhibitors results in the emergence of resistant clones based on the reactivation of the JAK-STAT pathway. Therefore, new therapeutic strategies targeting other molecules can provide additional benefits to patients with MF. In the previous study, we identified Calcium/Calmodulin Dependent Protein Kinase II Gamma (CAMK2G) as a new therapeutic target for MF by performing compound screening. Furthermore, CAMK2G inhibition can overcome drug-resistance against JAK2 inhibitors. Therefore, it is important to investigate the mechanisms underlying the therapeutic effect of CAMK2G inhibition. In this study, to explore the mechanism underlying the therapeutic effect of CAMK2G inhibition, we performed the immunoprecipitation mass spectrometry to find out the protein that has the direct interaction with CAMK2G. Methods Quantitative Proteomic Analysis of the Target Proteins of CAMK2G The protein complexes with FLAG-tagged CAMK2G (FLAG-CAMK2G) were trapped by anti-FLAG antibody. The eluted assay mixtures were reduced, alkylated and digested into peptides. Each peptide solution and control mixture were labeled with differential stable isotope tags. The samples were quantitatively analyzed using a Q Exactive mass spectrometer (Thermo Fisher Scientific). The spectra were searched against the SWISS-PROT databases using SEQUEST on Proteome Discoverer software 2.2 (Thermo Scientific). Results To reveal the , we conducted the immunoprecipitation assays by FLAG-CAMK2G or FLAG-tag alone, overexpressed in MF model cells. Because CAMK2G has kinase activity, we attempted to reveal the kinase-activity-dependent targets using unhydrolyzable ATP analog, AMP-PNP（5'-adenylyl-imidodiphosphate）that can maintain the strong-binding state of kinase with its target. The protein complexes with FLAG-CAMK2G were trapped by anti-FLAG antibody. After samples were digested into peptides and the candidate proteins were identified and quantitatively analyzed by mass spectrometry. As a result, we identified eukaryotic translation initiation factor 4B (eIF4B) as a protein that has a direct interaction with CAMK2G. eIF4B is a part of the complex involved in the initiation of translation. It has been reported that eIF4B plays a role in the translation of factors involved in anti-apoptosis (Bcl2, Bclxl, Mcl1), cell cycle (Cdc25c), and cell proliferation (c-Myc). We then checked whether knockdown of eIF4B decrease proliferation of MF model cell line. shRNA-mediated silencing of eIF4B decreased cell growth of these cells. Furthermore, the phosphorylation of eIF4B was increased by the ectopic expression of MPL W515L, one of the common mutations found in MF. Also, the phosphorylation of eIF4B was increased by the overexpression of CAMK2G. We then explored the proteins regulated by eIF4B in MF and identified that knockdown of eIF4B decreased the amount of Bcl2 protein. Conclusion In our study, we performed immunoprecipitation mass spectrometry and identified eIF4B as a partner protein of CAMK2G. Since CAMK2G inhibition was shown to be effective against MF in vitro and in vivo, we focused on eIF4B as a potential effector in MF. We also showed that overexpression of MPL W515L and CAMK2G phosphorylates eIF4B and that knockdown of eIF4B inhibited proliferation of MF cells. Furthermore, Bcl2 can be one of the target proteins regulated by eIF4B. Based on these, eIF4B plays an important role in MF. We further perform ribosome profiling to comprehensively understand the regulation of translation by eIF4B. Our research not only elucidate the pathogenesis of MF but also identify new therapeutic targets for MF. Disclosures Masamoto: MSD K.K.: Speakers Bureau; Eisai Co., Ltd.: Speakers Bureau; Otsuka Pharmaceutical Co., Ltd.: Speakers Bureau; ONO PHARMACEUTICAL CO., LTD.: Speakers Bureau; Takeda Pharmaceutical Company Limited.: Speakers Bureau; Chugai Pharmaceutical Company: Speakers Bureau; Kyowa Hakko Kirin Co., Ltd.: Speakers Bureau; Nippon Shinyaku Co., Ltd.: Speakers Bureau; AbbVie GK: Speakers Bureau; Janssen Pharmaceutical K.K.: Speakers Bureau; SymBio Pharmaceuticals: Speakers Bureau; Bristol Myers Squibb: Speakers Bureau. Kurokawa: Otsuka Pharmaceutical Co., Ltd.: Research Funding, Speakers Bureau; ONO PHARMACEUTICAL CO., LTD.: Research Funding, Speakers Bureau; Takeda Pharmaceutical Company Limited.: Research Funding, Speakers Bureau; Chugai Pharmaceutical Company: Research Funding, Speakers Bureau; Sumitomo Dainippon Pharma Co., Ltd.: Research Funding, Speakers Bureau; Kyowa Hakko Kirin Co., Ltd.: Research Funding, Speakers Bureau; Nippon Shinyaku Co., Ltd.: Research Funding, Speakers Bureau; Daiichi Sankyo Company.: Research Funding, Speakers Bureau; AbbVie GK: Research Funding, Speakers Bureau; Teijin Limited: Research Funding, Speakers Bureau; Pfizer Japan Inc.: Research Funding, Speakers Bureau; Eisai Co., Ltd.: Research Funding, Speakers Bureau; MSD K.K.: Research Funding, Speakers Bureau; Astellas Pharma Inc.: Research Funding, Speakers Bureau.

Second-Generation Jak2 Inhibitors for Advanced Prostate Cancer: Are We Ready for Clinical Development?

Androgen deprivation therapy (ADT) for metastatic and high-risk prostate cancer (PC) inhibits growth pathways driven by the androgen receptor (AR). Over time, ADT leads to the emergence of lethal castrate-resistant PC (CRPC), which is consistently caused by an acquired ability of tumors to re-activate AR. This has led to the development of second-generation anti-androgens that more effectively antagonize AR, such as enzalutamide (ENZ). However, the resistance of CRPC to ENZ develops rapidly. Studies utilizing preclinical models of PC have established that inhibition of the Jak2-Stat5 signaling leads to extensive PC cell apoptosis and decreased tumor growth. In large clinical cohorts, Jak2-Stat5 activity predicts PC progression and recurrence. Recently, Jak2-Stat5 signaling was demonstrated to induce ENZ-resistant PC growth in preclinical PC models, further emphasizing the importance of Jak2-Stat5 for therapeutic targeting for advanced PC. The discovery of the Jak2V617F somatic mutation in myeloproliferative disorders triggered the rapid development of Jak1/2-specific inhibitors for a variety of myeloproliferative and auto-immune disorders as well as hematological malignancies. Here, we review Jak2 inhibitors targeting the mutated Jak2V617F vs. wild type (WT)-Jak2 that are currently in the development pipeline. Among these 35 compounds with documented Jak2 inhibitory activity, those with potency against WT-Jak2 hold strong potential for advanced PC therapy.

Recent Advances in Molecular Diagnostics and Targeted Therapy of Myeloproliferative Neoplasms

Somatic mutations in JAK2, calreticulin, and MPL genes drive myeloproliferative neoplasms (MPN), and recent technological advances have revealed a heterogeneous genomic landscape with additional mutations in MPN. These mainly affect genes involved in epigenetic regulation and splicing and are of diagnostic and prognostic value, predicting the risk of progression and informing decisions on therapeutic management. Thus, genetic testing has become an integral part of the current state-of-the-art laboratory work-up for MPN patients and has been implemented in current guidelines for disease classification, tools for prognostic risk assessment, and recommendations for therapy. The finding that JAK2, CALR, and MPL driver mutations activate JAK2 signaling has provided a rational basis for the development of targeted JAK2 inhibitor therapies and has fueled their translation into clinical practice. However, the disease-modifying potential of JAK2 inhibitors remains limited and is further impeded by loss of therapeutic responses in a substantial proportion of patients over time. Therefore, the investigation of additional molecular vulnerabilities involved in MPN pathogenesis is imperative to advance the development of new therapeutic options. Combination of novel compounds with JAK2 inhibitors are of specific interest to enhance therapeutic efficacy of molecularly targeted treatment approaches. Here, we summarize the current insights into the genetic basis of MPN, its use as a diagnostic and prognostic tool in clinical settings, and the most recent advances in targeted therapies for MPN.

Current Concepts of Pathogenesis and Treatment of Philadelphia Chromosome-Negative Myeloproliferative Neoplasms

Philadelphia chromosome-negative myeloproliferative neoplasms are hematopoietic stem cell disorders characterized by dysregulated proliferation of mature myeloid blood cells. They can present as polycythemia vera, essential thrombocythemia, or myelofibrosis and are characterized by constitutive activation of JAK2 signaling. They share a propensity for thrombo-hemorrhagic complications and the risk of progression to acute myeloid leukemia. Attention has also been drawn to JAK2 mutant clonal hematopoiesis of indeterminate potential as a possible precursor state of MPN. Insight into the pathogenesis as well as options for the treatment of MPN has increased in the last years thanks to modern sequencing technologies and functional studies. Mutational analysis provides information on the oncogenic driver mutations in JAK2, CALR, or MPL in the majority of MPN patients. In addition, molecular markers enable more detailed prognostication and provide guidance for therapeutic decisions. While JAK2 inhibitors represent a standard of care for MF and resistant/refractory PV, allogeneic hematopoietic stem cell transplantation remains the only therapy with a curative potential in MPN so far but is reserved to a subset of patients. Thus, novel concepts for therapy are an important need, particularly in MF. Novel JAK2 inhibitors, combination therapy approaches with ruxolitinib, as well as therapeutic approaches addressing new molecular targets are in development. Current standards and recent advantages are discussed in this review.

Integrated Ligand and Structure based approaches towards developing novel Janus Kinase 2 inhibitors for the treatment of myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs) are a group of diseases affecting hematopoiesis in humans. Types of MPNs include Polycythemia Vera (PV), Essential Thrombocythemia (ET) and myelofibrosis. JAK2 gene mutation at 617th position act as a major causative factor for the onset and progression of MPNs. So, JAK2 inhibitors are widely used for the treatment of MPNs. But, increased incidence of adverse drug reactions associated with JAK2 inhibitors acts as a paramount challenge in the treatment of MPNs. Hence, there exists an urgent need for the identification of novel lead molecules with enhanced potency and bioavailability. We employed ligand and structure-based approaches to identify novel lead molecules which could act as JAK2 inhibitors. The dataset for QSAR modeling (ligand-based approach) comprised of 49 compounds. We have developed a QSAR model, which has got statistical as well as biological significance. Further, all the compounds in the dataset were subjected to molecular docking and bioavailability assessment studies. Derivative compounds with higher potency and bioavailability were identified for the best lead molecule present in the dataset by employing chemical space exploration. Dataset and models are available at https://github.com/giribio/agingdataAbstract FigureGraphical abstract

Trial in Progress: Phase Ib/II Study of Bcl-2/Bcl-Xl Inhibitor Pelcitoclax (APG-1252) in Patients with Myelofibrosis (MF) That Progressed after Initial Therapy

Background: Pelcitoclax (APG-1252), a novel dual inhibitor of Bcl-2/Bcl-xL, is active as monotherapy in patients with advanced solid tumors and well tolerated up to 240 mg twice weekly (NCT03387332). Preclinical data suggest that cells with Janus-associated kinase-2 (JAK2) mutations, including those associated with bone marrow fibrosis, are dependent on Bcl-2/Bcl-xL for survival and that addition of BH3 mimetics targeting Bcl-2/Bcl-xL induces apoptosis. Furthermore, in JAK2‒mutated cell models, apoptotic synergy is demonstrated when a JAK2 inhibitor and Bcl-2/Bcl-xL inhibitor are combined, as inhibition of Bcl-xL overcomes resistance to JAK2 inhibitors. Taken together, APG-1252 could overcome resistance to JAK2 inhibitors, and the combination could augment clinical benefit in patients with suboptimal responses to JAK2 inhibitor‒based therapy. Study Objectives: The primary objective of this open-label trial is to evaluate the safety and efficacy of APG-1252, as monotherapy and when combined with ruxolitinib, in adults with histologically or cytologically confirmed MF who require therapy and are ineligible for JAK2 inhibitors (and can receive single-agent APG-1252) or have had inadequate responses to ruxolitinib-based therapy (and can receive this treatment plus APG-1252). Secondary objectives include APG-1252 pharmacokinetics, time to response, and duration of response. Exploratory objectives include changes in cytogenetics and molecular mutations, bone marrow fibrosis, and cytokines on treatment. Study Design: The study is divided into Part 1 (APG-1252 monotherapy) and Part 2 (APG-1252 plus ruxolitinib). For Part 1, the key inclusion criterion is ineligibility for JAK2 inhibitors and for Part 2, inadequate responses to prior ruxolitinib-based therapy. A standard 3+3 dose-escalation design is being implemented to determine the maximum tolerated dose (MTD) of APG-1252 monotherapy in Part 1 and APG-1252 combined with ruxolitinib in Part 2. APG-1252 will initially be administered at 160 mg intravenously by 30-minute injection once weekly in a 28-day cycle. The dose can be escalated to a maximum of 240 mg or reduced to a minimum of 80 mg, depending on tolerability. Part 2 will begin once the MTD and recommended phase 2 dose (RP2D) of APG-1252 monotherapy have been determined. In Part 2, ruxolitinib will be administered orally twice daily per the package insert. After the MTD for APG-1252 monotherapy has been determined, no additional patients will be enrolled in Part 1; however, up to 15 to 30 additional patients can be enrolled in Part 2, to further evaluate the safety and anticancer activity of the combination at MTD or RP2D. Patients will continue treatment until disease progression or unacceptable toxicity. Clinical responses are being assessed every 12 weeks according to criteria from the International Working Group‒Myeloproliferative Neoplasms Research and Treatment and European LeukemiaNet panels, while optimal clinical benefit will be evaluated at 24 weeks. Enrollment will be from September 2020 and preliminary results estimated in October 2022. For further information, contact: [email protected]. Registration: ClinicalTrials.gov Identifier NCT04354727. Disclosures Pemmaraju: Pacylex Pharmaceuticals: Consultancy; Roche Diagnostics: Honoraria; LFB Biotechnologies: Honoraria; Stemline Therapeutics: Honoraria, Research Funding; Celgene: Honoraria; AbbVie: Honoraria, Research Funding; MustangBio: Honoraria; Affymetrix: Other: Grant Support, Research Funding; Cellectis: Research Funding; Daiichi Sankyo: Research Funding; Plexxikon: Research Funding; Samus Therapeutics: Research Funding; DAVA Oncology: Honoraria; Blueprint Medicines: Honoraria; Novartis: Honoraria, Research Funding; Incyte Corporation: Honoraria; SagerStrong Foundation: Other: Grant Support. Mudenda:Ascentage Pharma Group Inc.: Current Employment, Current equity holder in publicly-traded company. Wang:Ascentage Pharma Group Inc.: Current Employment, Current equity holder in publicly-traded company. JI:Ascentage Pharma (Suzhou) Co., Ltd.: Current Employment, Current equity holder in publicly-traded company. Lu:Ascentage Pharma Group: Current Employment, Current equity holder in publicly-traded company. Fu:Ascentage Pharma Group Inc.: Current Employment, Current equity holder in publicly-traded company. Liang:Ascentage Pharma Group Inc.: Current Employment, Current equity holder in publicly-traded company. McClain:Ascentage Pharma Group Inc.: Current Employment, Current equity holder in publicly-traded company. Sheladia:Ascentage Pharma Group Inc.: Current Employment, Current equity holder in publicly-traded company. Verstovsek:Novartis: Consultancy, Research Funding; Sierra Oncology: Consultancy, Research Funding; Blueprint Medicines Corp: Research Funding; PharmaEssentia: Research Funding; ItalPharma: Research Funding; AstraZeneca: Research Funding; Protagonist Therapeutics: Research Funding; Promedior: Research Funding; Celgene: Consultancy, Research Funding; NS Pharma: Research Funding; Genentech: Research Funding; CTI Biopharma Corp: Research Funding; Incyte Corporation: Consultancy, Research Funding; Roche: Research Funding; Gilead: Research Funding. Yang:Ascentage Pharma (SuZhou) Co., Ltd: Current Employment, Current equity holder in publicly-traded company, Other: Leadership and other ownership interests. Zhai:Ascentage Pharma (SuZhou) Co., Ltd: Current Employment, Current equity holder in publicly-traded company, Other: Leadership and other ownership interests.