ALBERT

Description: Background : Anagrelide is a widely used therapeutic agent for patients with essential thrombocythemia. While other cytoreductive agents, such as hydroxyurea, influence multi-lineage blood cells, anagrelide exerts less effect on the white and red blood cell lineages. Although the clinical efficacy of anagrelide has been reported, the exact mechanism of action is unclear. Recently, immortalized megakaryocyte progenitor cell lines (imMKCLs) were established from human induced pluripotent stem (iPS) cells by the introduction of doxycycline-inducible lentiviral vectors harboring c-MYC, BMI1, and BCL-XL for the clinical application of artificially generated platelets. In this study, we aimed to elucidate the molecular mechanism of anagrelide on the inhibition of platelet production using imMKCLs as an ideal model for human megakaryogenesis and platelet formation. Materials and Methods : imMKCLs, established at Center for iPS Cell Research and Application, Kyoto University, Japan, were cultured in Iscove's modified Dulbecco's medium with thrombopoietin (TPO), stem cell factor (SCF), and doxycycline. The differentiation of imMKCLs and platelet generation were induced by doxycycline removal. The generation of mature platelets was observed approximately 7 days after the differentiation was initiated. Both undifferentiated and differentiated imMKCLs were treated with several different concentrations of anagrelide. The cell proliferation and number of generated platelets following anagrelide treatment were analyzed by BrdU cell proliferation assay and flow cytometry, respectively. To explore the molecular mechanism of anagrelide treatment in imMKCLs, we performed mRNA sequencing in imMKCLs treated with or without anagrelide followed by gene ontology (GO) analysis and gene set enrichment analysis (GSEA). The expression of genes related to megakaryogenesis and platelet formation was also analyzed utilizing quantitative real-time PCR. Results : Anagrelide exposure caused morphologically suppressive changes in the differentiation of imMKCLs. Anagrelide treatment also suppressed the mRNA expression of the megakaryocytic surface markers CD41 and CD61 in both undifferentiated (P 〈 0.01 and P 〈 0.001, respectively) and differentiated (P 〈 0.01 and P 〈 0.001, respectively) settings. The BrdU incorporation rate in differentiated imMKCLs decreased significantly following anagrelide treatment (P 〈 0.001, anagrelide 0 vs. 1 or 10 µM). The resultant generation of mature platelets (double positive for CD41 and CD42b) was significantly decreased by exposure to anagrelide, as analyzed by flow cytometry (P 〈 0.001). Regarding the molecular mechanism of anagrelide treatment on imMKCLs, GO analysis following RNA sequencing demonstrated that gene sets related to platelet activation and degranulation were significantly downregulated in both undifferentiated and differentiated conditions. Moreover, GSEA revealed that gene sets related to the cell cycle, such as mitosis and DNA replication, were decreased as well as platelet-specific genes. The mRNA expression levels of genes related to megakaryogenesis and platelet-formation, such as FLI1, TAL1, GATA1, and PF4, were significantly downregulated, especially in differentiated imMKCLs, by anagrelide treatment (P 〈 0.001, P = 0.013, P 〈 0.01, and P 〈 0.01, respectively). Conclusions : We successfully reproduced the platelet-lowering effect of anagrelide by using imMKCLs from human iPS cells that could generate functional platelets in culture. Our RNA sequencing results revealed that anagrelide specifically suppressed megakaryogenesis and platelet formation-related genes. Additional studies including an apoptosis assay and cell cycle analysis of imMKCLs following anagrelide exposure are ongoing to elucidate further molecular mechanisms of anagrelide treatment. Disclosures Takayama: Megakaryon co. Ltd.: Research Funding. Eto:Megakaryon co. Ltd.: Research Funding.

Description: Background:Myelodysplastic Syndrome (MDS) is a clonal bone marrow disorder characterized by ineffective and clonal hematopoiesis accompanied by morphological dysplasia and variable cytopenia. There are few treatment options for MDS, and allogenic hematopoietic stem cell transplantation is the only curative option. Dihydroorotate dehydrogenase (DHODH) catalyzes a rate-limiting step in de novo pyrimidine synthesis, the conversion of DHO to orotate. DHODH inhibition has been described recently as a new approach for treating acute myeloid leukemia (AML) by inducing differentiation of diverse AML subclasses. PTC299 represents a novel potent DHODH inhibitor and recently clinical development of PTC299 as a potential treatment option for acute leukemia was initiated. Here, we explored the efficacy of DHODH inhibitor PTC299 for MDS. Methods:Anti-MDS efficacy of PTC299 was studied using human MDS cell lines and primary MDS cells in vitro. PTC299 was synthesized at PTC Therapeutics Inc. Mechanistic studies were conducted via flow cytometric analysis and RNA-sequencing (RNA-seq). Gene expression levels were analyzed by quantitative PCR (qPCR). Results:PTC299 inhibited proliferation of AML cell lines and induced their differentiation. As previously reported in other DHODH inhibitors, upregulation of CD11b was observed after PTC299 treatment in both HL-60 and THP-1 cells. In addition, PTC299 inhibited the proliferation of MDS cell lines, MDSL and SKM-1 cells, with EC50s of 12.6 nM in MDSL cells and 19.7 nM in SKM-1 cells. The inhibitory effect was reversed by the exogenous addition of 100 µM uridine, which bypasses the requirement for de novo pyrimidine synthesis by feeding into the salvage pathway, thereby negating the need for DHODH. Because the basal expression levels of CD11b are high in MDS cells, we examined the expression levels of CD38. Both cell lines showed dose-dependent upregulation of CD38 after PTC299 treatment. To investigate the possible synergism between PTC299 and decitabine, we treated MDSL and SKM-1 cells with increasing concentrations of PTC299 and decitabine as single agents or in combination. After 3 days of culture, cells were analyzed by MTS assays. PTC299 and decitabine exerted a enhanced cytotoxic effect on MDSL and SKM-1 cells. Similar results were obtained with primary MDS samples. In Annexin/PI assays, the percentage of apoptotic cells was increased by combination of PTC299 with decitabine in both cell lines. Mechanistically, treatment with PTC299 induced an intra-S-phase arrestfollowed by entry intoapoptotic cell death. It has also been reported that the expression of p53 is increased in response to the intra-S-phase arrest. To understand the genome-wide effects and target genes of PTC299 and the combination with decitabine, we performed RNA-seq of MDSL and SKM-1 cells treated with PTC299, decitabine, or the combination of both agents versus DMSO-treated cells. Gene set enrichment analysis (GSEA) using our RNA-seq data confirmed that MYC target gene sets were negatively enriched in both PTC299-, decitabine- and combination- treated cells. KEGG pathway enrichment analysis revealed activation of genes associated with apoptosis in both cell lines. To better elucidate a synergistic effect of PTC299 and decitabine, we performed qPCR of CDKN1A, which is a major target of p53 activity. The mRNA expression levels of CDKN1A were upregulated after treatment with PTC299, which was further enhanced by the combination with decitabine. Conclusions:Our result indicate that the DHODH inhibitor PTC299 suppresses the growth of MDS cells in vitro and acts in at least an additive and possibly synergistic manner with decitabine in this process. This combination therapy could be a new therapeutic option for the treatment of MDS. Disclosures Lennox: PTC Therapeutics: Employment. Weetall:PTC Therapeutics: Employment. Sheedy:PTC Therapeutics: Employment.

Description: Introduction: Recent studies based on next-generation sequencing revealed the genetic landscape of diffuse large B cell lymphoma (DLBCL). A new genetic classification system was proposed, including four groups; the BCL2 and SGK1 groups that were both associated with germinal center B-cell like (GCB) DLBCL, an MYD88 group that was associated with non-GCB DLBCL, and a NOTCH2 group that was not associated with a specific cell-of-origin (COO). Unfortunately, this classification method is somewhat complex and thus not fully accepted in clinical practice. Furthermore, part of all cases remained unclassified; as such, it is clear that the diversity of the genetic landscape of DLBCL is not yet fully understood. In this study, we performed a retrospective analysis of genetic abnormalities and their correlations with clinical characteristics in a Japanese cohort of patients diagnosed with DLBCL. Materials and Methods: We collected clinical data from 224 of a total of 234 patients who were diagnosed with DLBCL between 2013 and 2018 at Chiba University Hospital. We also collected formalin-fixed paraffin-embedded (FFPE) specimens obtained from 204 patients via standard diagnostic procedures. The COO for each sample was assessed using the Hans algorithm with immunohistochemical staining; rearrangements of BCL2, BCL6, and MYC were evaluated by fluorescence in situ hybridization. Targeted DNA sequencing was performed using a 144-gene custom panel. Results: Of the 224 DLBCL patients evaluated in our study, the median age at diagnosis was 69 years (range, 18 - 92 years). The median follow-up time was 34 months; three-year progression-free survival (PFS) was 63.2%, and three-year overall survival was 78.0%. COO was determined in 218 cases; 93 of these cases (41.5%) were classified as GCB type and 125 cases (55.8%) as non-GCB type. We successfully performed targeted DNA sequencing in 167 of the 204 FFPE samples. Compared to previous reports, our cohort included relatively higher frequencies of mutations in PIM1 (44.3%), KMT2D (40.7%), MYD88L265P (37.7%), and CD79B (24.5%); by contrast, we detected comparatively lower mutation frequencies in B2M (6.6%), ETV6 (5.4%), CDKN2A (4.7%), and TNFAIP3 (4.1%). Multivariate adjustment of genes extracted by univariate analysis and factors identified by International Prognostic Index score revealed that genetic mutations of MYD88L265P (Hazard ratio [HR] = 2.045), IL16 (HR = 4.848), and BCOR (HR = 6.295) were significant prognostic factors. Mutations in IL16 and BCOR are novel factors that will be used to predict poor prognosis. In the 167 sequenced cases, 110 were classified into the aforementioned four subtypes based on mutations detected in 23 genes together with rearrangements of BCL2 and BCL6; specifically, 47 cases were classified as members of the MYD88 group, 28 in the BCL2 group, 19 in the NOTCH2 group, and 16 in the SGK1 group. We identified a trend toward differential PFSs among the four groups (p = 0.18); three-year PFS was 51.2% among patients with MYD88 group, 59.6% in the BCL2 group, 63.2% in the NOTCH2 group, and 75.0% for the SGK1 group. When compared outcomes of patients in the BCL6 group, patients in the MYD88 group had significantly inferior PFS (p = 0.043) among the non-GCB DLBCL patients; those in the BCL2 group revealed a trend toward inferior PFS compared with those in the SGK1 group (p = 0.34) among the GCB DLBCL patients. We next focused on 28 cases of CD5-positive DLBCL; this is a distinct DLBCL subtype with poor prognosis that is identified more frequently among Asians. We observed significantly higher frequencies of frameshift or nonsense mutations in CD58 and missense mutations in MYD88L265P. Furthermore, evaluation of gene expression data for CD5-positive DLBCL reported in a published database (Miyazaki K et al. Int J Hematol. 2015) revealed diminished expression of CD58 (p = 0.01) and augmented expression of MYD88L265P (p 〈 0.001). These results suggest that there may be a specific correlation between genetic mutations and gene expression. Intriguingly, these specific genes are key regulators of the immune response, suggesting that inflammation contribute to the unfavorable outcome of CD5-positive DLBCL. Conclusion: Our study provides support for the genetic classification of DLBCL using targeted DNA sequencing to evaluate outcomes in our Japanese cohort. We also identified mutations in novel candidate genes that may be used to predict clinical outcomes. Disclosures Nakaseko: Novartis Pharma KK: Speakers Bureau; Pfizer Japan Inc.: Speakers Bureau. Kaneda:SRL Inc.: Research Funding; SCRUM Inc.: Research Funding; Tsubakimoto Chain Co.: Research Funding; Takeda Foundation: Research Funding; Princess Takamatsu Cancer Research Fund.: Research Funding; Wedge Co Ltd: Research Funding.

Description: Background: Myelodysplastic Syndrome (MDS) is a clonal bone marrow disorder characterized by ineffective and clonal hematopoiesis accompanied by morphological dysplasia and variable cytopenia. There are few treatment options for MDS, and allogenic hematopoietic stem cell transplantation is the only curative option. Tubulin belongs to protein superfamily of globular proteins. Monomeric tubulin can polymerize into microtubules, which play an important role in the attachment and segregation of chromosomes in various phases of cell division. Therefore, the targeting of microtubules represents a therapeutic strategy against both solid and hematological cancers. The first approved tubulin binding agent by the FDA was vincristine, which has been clinically used to treat multiple types of cancers, particularly hematological malignancies. Over the past few decades, additional tubulin binding agents have been developed and received FDA approval, mostly for applications to cancer therapy. These agents have been classified by their binding sites on tubulin, which influences their roles in the inhibition or stabilization of polymerized microtubules. We herein investigated the efficacy of PTC-028, a novel microtubule polymerization inhibitor for MDS. Method: Anti-MDS efficacy of PTC-028 was studied using human MDS cell lines and primary MDS cells in vitro. The efficacy of PTC-028 was also assessed in a xenograft mouse model of MDS using an MDS cell lines. PTC-028 was synthesized at PTC Therapeutics Inc. Mechanistic studies were conducted via flow cytometry and RNA sequencing. Results: A previous study reported that PTC596 suppressed cell proliferation and induced apoptosis in AML cell lines. Since MDS is regarded as a pre-leukemic stage, we examined the effects of PTC-028, another novel microtubule polymerization inhibitor, on MDS cells. PTC-028 induced a dose-dependent inhibition of cell proliferation on MDS cell lines, such as MDS-L and SKM-1 cells. Caspase 3/7 activity was also significantly induced in MDS-L and SKM-1 cells in the presence of PTC-028, suggesting the induction of apoptotic cell death by PTC-028. We then isolated CD34+ cells from primary MDS BM samples and investigated the efficacy of PTC-028 on primary MDS cells. The efficacy of PTC-028 in CD34+ MDS cells was also confirmed by cell proliferation assays. To enhance the therapeutic benefit of PTC-028 on MDS cells, we investigated synergism between PTC-028 and DNA hypomethylating agents. We treated MDS-L and SKM-1 cells with PTC-028 in combination with DNA hypomethylating agents. After 3 days of culture, cell growth was analyzed by MTS and Annexin V assays. PTC-028 synergized with hypomethylating agents, such as decitabine and azacitidine, to inhibit the growth and induce apoptosis of MDS cells. We assessed the efficacy of PTC-028 in a xenograft mouse model of MDS using an MDS cell line. Recipient mice were treated with PTC-028 for 7 weeks. PTC-028 significantly inhibited the growth of MDS-L cells and prolonged the overall survival of recipient mice. Furthermore, a significant synergistic effect was observed between PTC-028 and decitabine. Mice that received combination therapy showed moderate weight loss 11 days after the initiation of the treatment, but subsequently recovered. Mechanistically, a treatment with PTC-028 induced G2/M arrest followed by apoptotic cell death. We then investigated the effect of PTC-028 on the levels of soluble (unpolymerized) versus polymerized tubulin in MDS-L cells. Cells were treated with PTC-028 and paclitaxel for 4 hours, and cell lysates were then separated into soluble and polymerized fractions by centrifugation. The visualization of tubulin fractions by Western blotting demonstrated that the PTC-028 treatment for 4 hours resulted in the near-complete loss of polymerized microtubules. In contrast, polymerized microtubules increased in cells treated with paclitaxel, which stabilizes microtubules against depolymerization. These result indicates that PTC-028 also acts as a microtubule polymerization inhibitor. Conclusion: Our data reveal a possible chemotherapeutic strategy for PTC-028 and PTC-596 in MDS by disruption of microtubule dynamics as a single agent and in combination with hypomethylating agents. The present study provides a preclinical framework for the clinical evaluation of this promising therapeutic approach to improve outcomes in MDS patients. Disclosures Lennox: PTC therapeutics: Current Employment. Sheedy:PTC therapeutics: Current Employment. Weetall:PTC Therapeutic: Current Employment.