Abstract: INTRODUCTION Endothelial cells (EC) play an important role in thrombosis and are increased in frequency in Myeloproliferative Neoplasms (MPN). Notably, the JAK2V617F mutation has been identified in micro-laser-dissected EC in peripheral vasculature (Sozer, 2009) and is present in a subset of endothelial progenitor cells (Teofili, 2011). Primary myelofibrosis (PMF) is also characterized by increased bone marrow vascularity. These data suggest that PMF clones could derive from a common precursor shared between CD34-hematopoietic stem cells (HSC) and EC. We explored this hypothesis with a prospective study aimed at comparing the mutational profiles of paired Circulating Endothelial Cells (CEC) and HSC in patients (pts) with PMF. METHODS 14 PMF pts not previously treated with JAK2 inhibitors, along with one healthy control, were enrolled in the MyCEC0617 study beginning in 2018. The study was approved by the local Ethical Committee and all pts gave written informed consent. HSC were selected using CD34+ immunomagnetic bead-column separation. CEC were detected using the CellSearch system, which uses immunomagnetic selection incorporating ferrofluid nanoparticles and fluorophore-labelled antibodies. The markers CD146, CD105, CD45, and DAPI were used to isolate CEC. We identified cells as CEC when we observed characteristic morphological features and a surface immunophenotype of CD146+, CD105 +, DAPI+ and CD45-. Putative CEC were then sorted using the DEPArray system, which uses a combination of di-electrophoresis technology and high-quality image-based cell selection to manipulate individual cells. Sequencing data was then assessed with the MiSeq Illumina NGS platform using a 54-gene custom panel focused on genes mutated in PMF. The cutoffs to confirm the presence of the mutations were identification of mutant alleles in 30 and 50 reads both in forward and reverse, for HSC and CEC, respectively. RESULTS The characteristics of pts are reported in Figure 1. Median age of pts was 69.5 ys (35-85) and male/female ratio was 9:6. Median time from diagnosis to sample collection was 4 (1-211) months. 2/14 pts had had a previous thrombosis, 78% had splenomegaly, and 29% presented with constitutional symptoms. Considering the molecular profile, 9 pts were JAK2V617F mutated, 3 were CALR mutated, and 1 was MPLW515L positive. 2 pts were triple-negative. Most of the pts (7) presented with an Intermediate-1 DIPSS score, while 5 were intermediate-2, and 2 were high risk DIPSS. CEC were collected for 12 of 15 subjects (including the normal control). No significative differences were found between pts from whom we isolated CEC and those we did not successfully recover CEC. A median of 26 (1-122) CEC in 4 ml of peripheral blood were recovered. Notably, no mutations were found in the CEC or HSC from healthy control whereas molecular alterations were discovered both on CEC and HSC in 11 pts (Fig. 1). The previously-identified MPN driver mutation was identified in MF HSC (except for one JAK2-mutated pt and for all CALR-mutated pts, consistent with the limitations of NGS in detecting these lesions). Interestingly, PMF pts demonstrated both shared and different mutations when comparing mutational profiles of HSC and CEC. In particular, 8 of 11 pts shared at least one mutation between EC and HSC. 2 pts harbored the same driver mutation (JAK2V617F), together with ABL1, IDH1, TET2, and ASXL1, respectively. The most frequently mutated genes shared between both CEC and HSC were JAK2, ASXL1, TET2, NOTCH1, and SRSF2. All of these mutations were observed as shared clonal events in at least 2 cases. We also identified individual paired HSC/CEC with shared mutations in TP53, KIT, KMT2A, IDH1, WT1 and ABL1. One pt shared 4 mutations between HSC and CEC, while 4 and 2 pts shared 1 and 2 mutations, respectively. CONCLUSION HSC and EC in PMF have in common one or more gene mutations implicated in the pathogenesis of PMF. For the first time, we show that mutations other than JAK2 can be identified in EC, and in most instances (70% of pts), these mutations are shared between CEC and HSC. Moreover, we present an analysis of mature cells of endothelial lineage including to the CEC. These preliminary findings using primary pts samples support the notion that PMF-initiating cells may be derived from a common HSC/EC precursor. Further data are needed to validate these findings and provide a rationale for additional studies exploring the antecedent cell of origin in MPN. Disclosures D'Adda: Pfizer: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees. Rossi:Celgene: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Jazz: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria; Mundipharma: Honoraria; BMS: Honoraria; Sandoz: Honoraria; Daiichi-Sankyo: Consultancy; Roche: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees. Levine:Qiagen: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy; Loxo: Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Research Funding; Prelude Therapeutics: Research Funding; Isoplexis: Membership on an entity's Board of Directors or advisory committees; C4 Therapeutics: Membership on an entity's Board of Directors or advisory committees; Imago Biosciences: Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy; Lilly: Honoraria; Amgen: Honoraria; Celgene: Consultancy, Research Funding.

Abstract: Background . The identification of germline mutations in familial leukemia predisposition genes by next generation sequencing is of pivotal importance. Lately, some “blend pedigrees” characterized by both solid and hematologic malignancies have been described. Some genes were recognized as related to this double predisposition, while the involvement of others is still a matter of debate. ETV6 was associated with hematologic malignancies, in particular myeloid malignancies, and recently described as mutated also in oncologic patients. No clear evidences in its involvement in blend pedigrees are known. Case Presentation . We present our recent experience in the identification of an ETV6 -mutated “blend pedigree,” suggesting the involvement of ETV6 in the predisposition to both solid and hematologic neoplasia. The pedigree recognition started with a MDS case enrolled in the NEXT-Famly protocol. The patient presented 9 relatives affected by solid tumors and hematological malignancies. Following the clinical trial protocol, the patient underwent NGS analysis, which confirmed the presence of a mutation on the noncoding region of ETV6 both on tumor and on germline DNA. The mutation resulted was shared by the still alive affected relatives. Conclusion . This evidence supports the involvement of ETV6 in the predisposition to both solid and hematologic neoplasia and the importance of the investigation of the noncoding regions of the genes as recently suggested by different expert groups.

Abstract: In the setting of follicular lymphoma (FL), frontline therapy with rituximab, cyclophosphamide, doxorubicin, and prednisone (R-CHOP) has represented for many years the standard of care for patients with symptomatic advanced disease. More recently, the combination of bendamustine plus rituximab (R-B) has emerged as an alternative therapeutic option. We present a retrospective, multicenter, observational study aimed at comparing outcomes and toxicities observed in 145 patients diagnosed with grade 3A FL treated with a first line therapy in 15 Italian Fondazione Italiana Linfomi centers between the 1st of January 2014 and the 30th of May 2018. Seventy patients were treated with R-B and 75 with R-CHOP. In the R-B group, the median age at the time of diagnosis was 67 years compared with 59 years in the R-CHOP group. Patients in R-B group achieved a similar overall response rate (96% vs. 99%) and a better complete remission rate (87% vs. 80%, p=0.035 ) compared with patients in R-CHOP group. Progression free survival (PFS) was similar between individual treated with R-CHOP and R-B (48- month PFS 77.7% vs. 76.6% respectively, p=0.745 ). The overall survival was significantly longer with R-CHOP treatment (HR=0.16; 95% IC, 0.04-0.74; p=0.007 ); however, no statistical significant difference was observed after adjustment for age. With the limitations of the study design, our results suggest that both R-B and R-CHOP seem to be valid first-line treatment options in FL3A.

Abstract: AML is a heterogeneous disease with a variety of structural and numerical chromosomal and genetic alterations that provided important prognostic information capable to guide therapy and predict outcome. The reported TP53 mutation rate in AML is low (2.1%). By contrast, the incidence of FLT3 disruption is frequent (20-30%) and is an independent predictor of unfavourable outcome of acquired clinical resistance to FLT3 inhibitors. TP53 mutations in AML with a complex karyotype (CK) is higher (69-78%), but few data are available for association between the most common AML associated lesions such as FLT3, NPM1, DNMT3A, IDH2 and TP53 mutation or CK. Aims: To investigate the frequency, the types of mutations, the associated cytogenetic, the molecular abnormalities, the correlation with known molecular alterations (FLT3, NPM, etc.) and the prognostic role TP53 mutations in adult AML pts. Patients and Methods: 886 AML patients were analysed for cytogenetic and for a panel of genetic alterations (FLT3, NPM, WT1, DNMT3A, IDH1-2 etc). Of these, 200 adult AML pts were also examined for TP53 mutations using several methods, including Sanger sequencing, NGS and HiSeq 2000 platform (38/200) and were correlated with cytogenetic analysis. Results: 55 pts (27.5%) showed 3 or more chromosome abnormalities (CK-AML), 83 (41.5%) presented one or two cytogenetic abnormalities (other-AML) and 43 pts (21.5%) have normal karyotype (nK). In 19 cases the karyotype was not available. Sanger sequencing analysis detected TP53 mutations on 29 patients with 36 different types of mutations (32 deleterious point mutations; 4 deletions); seven pts (4%) have 2 mutations. Mostly (23/29) of the TP53 mutated pts (79.3%) had CK while only 6/29 (21%) mutated pts have “no CK”. Overall, between pts with CK, TP53 frequency is 41.8% (P & gt;0,0001). 120 pts were analysed for concomitant presence of TP53 mutations and FLT3/NPM1 disruption/mutation: revealing a significant relation between pts with FLT3-ITD or NPM1 and TP53 wild-type (p = 0.043 and 0.022 respectively). As for clinical outcome alterations of TP53 were significantly associated with poor outcome (OS and EFS p & lt;0.0001). The very worsened outcome of TP53 mutations overcome the negative prognostic role of FLT3 mutations (P0.0001). WES analysis done in 38 pts (33 TP53 wt and 5 pts TP53 mutated) revealed no genes exclusively mutated in the 5 TP53 mutated pts. Conclusions: Our data demonstrated that TP53 mutations occur in 14.5% of AML with a higher frequency in the subgroup of CK-AML (p & lt;0.0001) and are mutually exclusive with FLT3 and/or NPM1; they predicted to be deleterious and significantly correlated with worse prognosis and may confer resistance to conventional and innovative therapy. For these reasons, TP53 mutation screening should be recommended at least in CK-AML pts. ELN, AIL, AIRC, PRIN, 2010-12 L. Bolondi, FP7 NGS-PTL project. Citation Format: Anna Ferrari, Cristina Papayannidis, Elisa Zuffa, Carmen Baldazzi, Antonella Padella, Eugenia Franchini, Ilaria Iacobucci, Stefania Paolini, Viviana Guadagnuolo, Margherita Perricone, Valentina Robustelli, Claudia Venturi, Maria Chiara Abbenante, Sarah Parisi, Chiara Sartor, Francesca Volpato, Federica Cattina, Giorgia Simonetti, Maria Chiara Fontana, Maria Teresa Bochicchio, Federica Frabetti, Elisa Lani, Katia Mancuso, Beatrice Zannetti, Simona Luatti, Emanuela Ottaviani, Nicoletta Testoni, Giovanni Martinelli. TP53 mutations are mutually exclusive with FLT3 and NPM mutations in AML patients and are strongly associated with complex karyotype and poor outcome. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4906. doi:10.1158/1538-7445.AM2015-4906

Abstract: Hedgehog (Hh) pathway activation contributes to leukemia development and growth, and that targeted pathway inhibition is likely to offer an efficient therapeutic opportunity. PF-04449913, a Hh pathway inhibitor, is a new selective and potent inhibitor of leukemia self-renewal and is currently being evaluated in phase I clinical trials. In order to identify new potential clinical biomarkers for the PF-04449913, we studied CD34+ leukemia stem cell population (LSC) collected before and after 28 days treatment in a phase I dose escalation protocol (Clinical Trial Gov. NTC00953758) enrolling selected hematological malignancies. This experimental clinical trial enrolled Myelofibrosis (MF), MDS, blastic phases CML, chronic myelomonocytic leukemia (CMML) and AML patients (pts). We were able to collect and separate highly purified (98%) bone marrow CD34+ cells from 5 AML, 1 MF and 2 CML pts by immunomagnetic separation, and analysed them for gene expression profile using Affimetrix HG-U133 Plus 2.0 platform. 1197 genes were differentially expressed between CD34+ cells collected before and after 28 days of PF-04449913 dose finding oral therapy. Clustering of their expression profiles showed that mostly genes differentially expressed are mainly related to Hh signaling, this providing further evidences that PF-04449913 really therapeutically targets the Hh pathway. Regarding genes involved in Hh signaling pathway, Gas1 and Kif27 were strongly upregulated (fold change 1.0947 and 1.12757 respectively; p-value 0.01 and 0.02 respectively) in CD34+ LSC after 28 days exposure to PF-04449913 as compared to baseline, suggesting these two genes have potential as new biomarkers of activity. GAS-1 is a Sonic Hedgehog (Shh)-binding protein; it acts to sequester Shh and inhibit the Shh signalling pathway. Kif27 mainly acts as a negative regulator in the Hh signaling pathway, and inhibits the transcriptional activator activity of Gli1 by inhibiting its nuclear translocation. Other genes were differentially expressed after ‘ex- vivo’ treatment with PF-04449913 as compared to baseline: we observed a down regulation of Bcl2 (fold change -1.03004), ABCA2 (fold change -1.08966), LEF1 (fold change -1.28457), Gli1 (fold change -1.0775), Smo (fold change -1.07702), and an upregulation of Gli2 (fold change 1.08191). Conclusions: This data demonstrates that PF-04449913 specifically targets the Hh Pathway in CD34+ cells, suggesting that Hh inhibition may impair leukemia stem cell maintenance. In addition, we identify several new potential biomarkers (e.g. Gas1 and KIF27). Taken together, these data may be useful for pts selection strategies and subsequent eradication of the LSC. Acknowledgments: Work supported by Pfizer, European LeukemiaNet, FIRB 2006, AIRC, AIL, COFIN, University of Bologna and BolognAIL. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 906. doi:1538-7 445.AM2012-906

Abstract: Few data are available on the role of CHK inhibitors in Diffuse Large B cell Lymphoma (DLBCL). The checkpoint kinases 1 (CHK1) and 2 (CHK2) are serine-threonine kinases involved in the DNA damage response pathway. CHK inhibition enhances the efficacy of DNA damaging agents in a variety of tumors, including p53 deficient cells, that rely on the G2/M checkpoint, having a dysfunctional G1 checkpoint. DLBCL with dysfunctional p53 axis (harboring p53 mutations and/or CDKN2A loss) have been recently shown to have a dismal outcome. In this study we report the activity profile of the CHK1/2 inhibitor PF-0477736 (Pfizer) in a panel of B cell lymphoma cell lines and primary cells, and explore its mechanisms of action. Three Germinal center B cell (GCB) DLBCL derived cell lines (SUDHL-4, SHDHL-6, BJAB), 3 Activated B cell (ABC) DLBCL (HBL-1, U2932, TMD8), 2 mantle cell lymphoma (Mino, SP-53), and the Hodgkin Lymphoma cell line KM-H2 were first screened for p53 and CDKN2A mutations and deletions. P53 mutations were detected in the following cell lines: HBL-1, U2932, SUDHL-6, BJAB, Mino, SP-53. TMD8 was p53 wild-type but with an homozygous deletion of CDKN2A. Of note SUDHL-4 and KM-H2 were p53 wild type, with no deletion of CDKN2A. To assess the effect of PF-0477736 on cell proliferation, cells were incubated with increasing concentrations of PF-0477736 (from 5 to 2000 nM) for 24, 48 and 72 hours (hrs), and cell viability assessed by WST-1 assay (Roche). A significant growth inhibition was evident after 48 hrs, in all cell lines, excluding SUDHL-4 and KM-H2 that were resistant (IC50 8300 and 6800 nM at 48 hrs, respectively). The BJAB cell line showed the highest sensitivity (IC50 10 nM at 24 hrs). The IC50 ranged from 140 to 230 nM at 48 hrs in the other sensitive cell lines. Using Annexin V- propidium iodide staining, we found that PF-0477736 25-500 nM induced cell death by apoptosis in a time and dose dependent manner. Of note PF-0477736 100-1000 nM demonstrated activity also in primary DLBCL cells. We found no correlations between baseline levels of CHK1/2 activation and outcome. In the sensitive cell lines inhibition of the downstream target CDC25c ser216 phosphorylation coupled with a marked increase in levels of the DNA damage marker γH2AX was observed by western blot as soon as after 24 hrs of incubation with concentrations equal to the IC50 (25 - 250 nM). PF-0477736 at the dose of 50-100 nM synergistically enhanced the efficacy of Doxorubicin (0.1 to 1 μM) at 24 hrs. These data suggest that PF-0477736 has single agent activity and synergizes with chemotherapy in DLBCL. The drug shows high single agent activity in the subset of DLBCL with genomic lesions of the p53 pathway, that are resistant to conventional chemotherapy and associated with dismal outcome, providing the rationale for further clinical investigation of PF-0477736 in DLBCL alone or in combination with chemotherapy. PF-0477736 was provided by Pfizer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4694. doi:1538-7445.AM2012-4694