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BACKGROUND: Patients (pts) with newly diagnosed chronic myeloid leukemia in chronic phase (CML-CP) may be treated with 1 of the 4 tyrosine kinase inhibitors (TKIs) approved for first-line (1L) use: the first-generation TKI imatinib and the second-generation (2G) TKIs bosutinib, dasatinib, and nilotinib. Deep molecular responses (DMRs) are important criteria for attempting treatment-free remission, an important goal for pts in 1L. However, in 1L, only about 30% of pts treated with imatinib and 30%-55% of pts treated with a 2G TKI achieve MR 4.5 (BCR-ABL1levels on the International Scale≤0.0032%). More than 50% of pts with CML-CP treated with imatinib develop resistance or intolerance to therapy. Among pts treated with a 2G TKI in 1L, 30%-40% need to change therapy by 5 years. Therefore, new treatment options are needed to help pts achieve their treatment goals in 1L. The main treatment goal for all pts is achievement of disease control, which potentially requires lifelong treatment. Therefore, highly potent, safe treatment options are needed for newly diagnosed pts with CML-CP. Asciminib is an investigational drug that inhibits the BCR-ABL1 oncoprotein through a novel mechanism of action: specifically targeting the ABL myristoyl pocket (STAMP). Due to asciminib's specifically targeting the ABL kinase family (ABL1, ABL2, BCR-ABL1), asciminib monotherapy offers the potential to improve safety and tolerability vs TKIs that target the adenosine triphosphate binding site of BCR-ABL1 and thus have varying degrees of selectivity toward ABL kinases. Asciminib has shown promising efficacy and safety in heavily pretreated adult pts with CML in phase I and III trials. In a phase III trial for pts with CML-CP treated with ≥2 prior TKIs, major molecular response (MMR) was achieved by 25.5% of pts on asciminib (40 mg twice daily [BID]) vs 13.2% on bosutinib at week 24. In the phase I trial of asciminib monotherapy at doses of 10-200 mg BID and 80-200 mg once daily (QD), 48% of pts with CML-CP treated with ≥2 prior TKIs without T315I mutations achieved or maintained MMR by 12 months. Here we present the upcoming phase III trial evaluating asciminib 80 mg QD monotherapy vs an investigator-selected approved TKI in newly diagnosed adult pts with CML-CP. OBJECTIVE: The primary objectives of this study are to assess the efficacy of asciminib vs an investigator-selected TKI (either imatinib, bosutinib, dasatinib, or nilotinib) in 1L and to compare the efficacy of asciminib within the stratum receiving investigator-selected imatinib in 1L through the primary end point of MMR rates at week 48. DMRs and; other long-term outcomes are also of interest. DESIGN: This is a multicenter, open-label, randomized, phase III study of asciminib at 80 mg QD compared with an approved, investigator-selected TKI (either imatinib, bosutinib, dasatinib, or nilotinib) for adult pts with newly diagnosed CML-CP in 1L (expected N=402; NCT04971226). Pts may not have received prior TKI therapy for CML, with the exception of ≤2 weeks of imatinib therapy and must have Eastern Cooperative Oncology Group performance status (ECOG PS) scores of 0 or 1. Pts who have previously received hydroxyurea or anagrelide may be included. Pts will be randomized 1:1 to the asciminib and investigator-selected TKI arms using 2 strata: European Treatment and Outcome Study (EUTOS) long-term survival (ELTS) risk score and the control arm TKI selected by the investigator prior to randomization (Figure 1). Pts randomized to the investigator-selected TKI arm will receive their selected TKIs at approved doses: imatinib, 400 mg QD; bosutinib, 400 mg QD; dasatinib, 100 mg QD; or nilotinib, 300 mg BID. Pts will remain on study for 5 years after the last pt first treatment has occurred, unless they have discontinued early due to treatment failure, disease progression, intolerance, or investigator or pt decision. Pts who discontinue early will continue to be followed up for survival and disease progression until the end of the study. MAIN OUTCOMES: The primary end point is MMR at week 48. Key secondary end points include MMR at week 96; exploratory end points include biomarker assessments. CONCLUSIONS: This study will assess the efficacy of asciminib 80 mg QD in adult pts with newly diagnosed CML-CP vs currently approved TKIs in 1L. This study is sponsored by Novartis. Figure 1 Figure 1. Disclosures Cortes: Bristol Myers Squibb, Daiichi Sankyo, Jazz Pharmaceuticals, Astellas, Novartis, Pfizer, Takeda, BioPath Holdings, Incyte: Consultancy, Research Funding; Sun Pharma: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Bio-Path Holdings, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding. Hochhaus: Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol-Myers Squibb: Research Funding; Pfizer: Research Funding; Incyte: Research Funding. Takahashi: Kyowahakko-Kirin: Research Funding; Ono: Research Funding; Asahikasei: Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Eizai: Research Funding; Toyamakagaku: Research Funding; Chugai: Research Funding; Otsuka Pharmaceutical: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Larson: CVS/Caremark: Consultancy; Gilead: Research Funding; Astellas: Consultancy, Research Funding; Rafael Pharmaceuticals: Research Funding; Epizyme: Consultancy; Takeda: Research Funding; Novartis: Research Funding; Cellectis: Research Funding. Issa: Syndax Pharmaceuticals: Research Funding; Kura Oncology: Consultancy, Research Funding; Novartis: Consultancy, Research Funding. Bombaci: CML Advocates Network: Consultancy, Current Employment, Membership on an entity's Board of Directors or advisory committees, Other: Organizational Grant Funding; MPN Advocates Network: Membership on an entity's Board of Directors or advisory committees, Other: Organizational Grant Funding; AIL - Associazione Italiana contro le Leucemie, i Linfomi e il Mieloma ONLUS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Organizational Grant Funding; CLL Advocate Network: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Organizational Grant Funding; Novartis: Consultancy, Other: Organizational Grant Funding; Jazz: Consultancy, Other: Organizational Grant Funding; Ceogene: Consultancy, Other: Organizational Grant Funding; Incyte: Consultancy, Other: Organizational Grant Funding; Takeda: Consultancy, Other: Organizational Grant Funding. Ramscar: Novartis: Current Employment. Kapoor: Novartis: Current Employment, Current equity holder in publicly-traded company. Ifrah: Novartis: Current Employment. Hughes: Novartis: Honoraria, Research Funding; BMS: Research Funding; Takeda: Honoraria.

Background In Chronic Myeloid Leukemia (CML), Treatment-free Remission (TFR) refers to having a stable deep molecular response without the need for ongoing Tyrosine Kinase Inhibitor (TKI) treatment. While first recommendations exist about how to manage stopping and re-starting therapy, based on data from the EURO-SKI study, much is still unknown about the experiences of those considering and undertaking TFR. Through this study, we sought to obtain quantitative evidence of patient experience that has previously only been anecdotal and to identify areas of unmet needs. One strong theme to emerge was patients' differing views on the need for psychological support. Method A global online survey was conducted, recruiting patients through CML patient associations, via online forums, social media and other methods. The questionnaire was designed by an expert panel of eight CML patients to capture the experiences of people along all phases of the TFR journey. The different phases were classified as: Phase I - Considerations around stopping treatment; Phase II - Probation period (experiences during the first 6 months of stopping treatment); Phase IIIA -Restarting treatment (experiences where treatment had to restart due to molecular reoccurrence), and Phase IIIB - Long-term remission (experiences of being in long-term, treatment-free remission). Once the question set was agreed, the questionnaire went through two rounds of testing by eight volunteers. This exercise contributed towards refining the questionnaire into a finished version. The questionnaire was translated into eleven languages: Arabic, Danish, English, Finnish, French, German, Hebrew, Italian, Japanese, Russian and Spanish. Fieldwork lasted 20 weeks. Results A total of 1016 responses were collected from CML patients across 68 countries. Patients only answered the sections of the questionnaire that were relevant for them. All 1016 had experience of Phase I, 494 (49%) had experience of Phase II, 159 (16%) had experience of Phase IIIA, and 203 (20%) had experience of IIIB. Of the 494 patients who stopped treatment, 32% said disease reoccurred and 41% reported being in long-term remission (this includes Conclusions There are opportunities for more communication and support around psychological issues to be given through the provision of information during the decision-making stage, and/or discussions between doctors and patients during the stopping stage. A considerable proportion of patients feel fear or anxiety at some level during stopping treatment, and not all patients who want psychological and/or emotional support receive it. The psychological well-being of patients should be a consideration of healthcare professionals and addressed at all stages of the TFR journey, to ensure patients receive support at the level they want through personalised care. Figure Disclosures Sharf: Incyte: Honoraria, Other: Advocacy Advisory Board, Research Funding; Abbvie: Other: Advocacy grants funding; Roche: Other: Advocacy grants funding; BMS: Other: Advocacy grants funding, Research Funding; Takeda: Other: Advocacy grants funding; Janssen: Other: Advocacy grants funding; Novartis: Honoraria, Other: Advocacy Advisory Board, Research Funding; Pfizer: Honoraria, Other: Advocacy Advisory Board, Research Funding. Hochhaus:Novartis: Research Funding; BMS: Research Funding; Pfizer: Research Funding; MSD: Research Funding; Incyte: Research Funding. Geissler:Pfizer: Consultancy, Research Funding, Speakers Bureau; Janssen: Consultancy, Speakers Bureau; Novartis: Consultancy, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Consultancy, Research Funding, Speakers Bureau; Biomarin: Consultancy; Takeda: Research Funding; Amgen: Consultancy; Incyte: Research Funding; Roche: Consultancy; Servier: Consultancy; UCB: Consultancy, Speakers Bureau. Marin:Leukemia Patient Advocates Foundation: Employment. Pemberton-Whiteley:Acute Leukemia Advocates Network (ALAN): Consultancy; CML Advocates Network: Membership on an entity's Board of Directors or advisory committees; Patient Evidence: Equity Ownership; Daiichi Sankyo: Other: Grant funding; Gilead: Other: Grant funding, Speakers Bureau; Incyte: Consultancy, Other: Grant funding; Jazz: Other: Grant funding, Speakers Bureau; Janssen: Consultancy, Other: Grant funding; Kyowa Kirin: Other: Grant funding; Novartis: Consultancy, Other: Grant funding, Speakers Bureau; Pfizer: Consultancy, Other: Grant Funding, Speakers Bureau; Takeda: Other: Grant funding; Shire: Other: Grant Funding; AbbVie: Other: Grant funding; Amgen: Consultancy, Other: Grant funding, Speakers Bureau; Bristol-Myers Squibb: Consultancy, Other: Grant funding, Speakers Bureau; Celgene: Consultancy, Other: Grant funding; Leukaemia Care: Employment. Bombaci:CLL Advocate: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: grant funding ; CML Advocate: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Grant funding ; Incyte: Consultancy; Onlus: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: grant funding; Novartis Pharma AG: Consultancy, Other: Advisory board ; MPN Advocate: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: grant funding ; Abbive: Consultancy, Other: grading funding; Bristol- Myers: Consultancy, Other: Grant Funding; Jazz: Consultancy, Other: Grant funding ; janssen: Consultancy, Other: grant funding. Christensen:Novartis: Consultancy, Other: Advisory Board; Incyte: Consultancy, Other: Advisory Board. Gouimi:AMAL: Membership on an entity's Board of Directors or advisory committees; Novartis Pharma: Consultancy, Other: Advisory Board; Bristol-Myers: Consultancy; Novartis: Consultancy, Other: funding grant; Takeda: Consultancy; Pfizer: Consultancy. Deekes:Novartis Pharma: Honoraria. Bradley:Quality Health: Employment.

Hematopoietic stem cells (HSC) in higher vertebrate species, especially in mammals, maintain hematopoiesis throughout adult life and require critical cell cycle regulation for their self-renewal and cell fate decisions. Although cell cycle pathways are quite conserved across animal species, it is unknown whether a higher vertebrate specific cell cycle regulation exists in adult mammalian HSCs. Recently, we have published that Ribonuclease inhibitor (RNH1) regulates erythropoiesis by controlling GATA1 mRNA translation. Here, we report that RNH1, which is present only in higher vertebrates regulates HSC cell cycle and HSC function. To study the role of RNH1 in hematopoiesis, we generated hematopoietic-specific knockout mice by backcrossing Rnh1FL/FL mice with Vav1-iCre and Mx1-Cre mice, respectively. Rnh1-deficiency (Rnh1FL/FLVav1-iCre mice) resulted in hematopoietic alterations resembling emergency myelopoiesis. At 15 weeks of age Rnh1-deficient mice had reduced hemoglobin levels (144.4 ± 2.6 vs 165.0 ± 4.2 g/L, p = 0.005), decreased lymphocytes (4.1 ± 0.8 vs 9.6 ± 1.6 K/µL, p = 0.023), increased neutrophils (3.2 ± 0.6 vs 1.5 ± 0.2 K/µL, p = 0.046) and monocytes (0.65 ± 0.05 vs 0.09 ± 0.02 K/µL, p = 0.0001) in the peripheral blood. Total bone-marrow (BM) cellularity was similar in wild type andRnh1-deficient mice, however the number of erythroid cells and lymphoid cells (T and B cells) was significantly decreased, whereas myeloid cells were significantly increased. Rnh1-deficient spleens were significantly larger than wild type controls and showed extramedullary hematopoiesis. Surprisingly, although Rnh1-deficient mice showed myeloproliferation they survived normally and did not show progression to leukemia. However, they did not tolerate even little stress, such as 35 µg LPS administration, which lead to early mortality. We analysed the progenitor populations in the BM. In line with the myelopoiesis dominant phenotype granulocyte-monocyte progenitor (GMP) cell numbers were increased but common lymphoid progenitor (CLP) and megakaryocyte-erythrocyte progenitor (MEP) cell numbers were decreased. Cell extrinsic factors such as growth factors and the bone marrow niche play a critical role in shaping lineage choice. To exclude this, we performed bone marrow transplantation experiments (BMT) by transplanting wild type (Rnh1FL/FL) and Rnh1-deficient (Rnh1FL/FLMx1-Cre+) bone marrow into lethally irradiated CD45.1 congenic mice. After reconstitution Rnh1 was deleted by administration of polyinosinic:polycytidylic acid (polyI:C). We observed a similar myelopoiesis dominant phenotype in Rnh1-deleted mice. Interestingly, we found increased numbers of long term HSCs (LT-HSCs) and short term HSCs (ST-HSCs) in Rnh1-deficient mouse BM, suggesting that RNH1 could affect HSC function. Supporting this Rnh1-deficient HSCs failed to engraft lethally irradiated mice in competitive BMT experiments. Furthermore, Rnh1-deficient HSCs produced significantly less and smaller colonies in in-vitro colony forming cell (CFC) assays. Transcriptome analysis showed increased expression of genes related to cell cycle, kinetochore, DNA damage and decreased expression of genes related to stem cell function in Rnh1-deficient LT-HSCs and ST-HSCs. Corroborating this, Rnh1-deficient LT-HSCs and ST-HSCs showed increased S/G2/M phase in cell cycle analysis. In line with this, at the molecular level, we found that RNH1 directly binds to cell-cycle related proteins such as cyclin-dependent kinase 1 (CDK1), cell-division cycle protein 20 (CDC20) and mitotic checkpoint protein BUB3, suggesting direct involvement of RNH1 in cell cycle regulation. Confirming this, pharmacological inhibition of CDK1 (RO-3306, 10 µM) in Rnh1-deficinet ST-HSCs restored colony size in CFC assays, suggesting that RNH1 and CDK1 inhibition have a synergistic effect in ST-HSCs. In summary, our results demonstrate that RNH1, which is present only in higher vertebrates, is essential for HSC cell cycle regulation and steady state hematopoiesis. Disclosures No relevant conflicts of interest to declare.

Background Adherence to the prescribed dose of tyrosine kinase inhibitors (TKIs) is critical to maximize treatment effectiveness in chronic myeloid leukemia (CML). While patient-centered outcome studies are lacking in this area, literature has shown that a significant proportion of patients report both intentional and unintentional non-adherence. Objective The main objective of this multivariate analysis was to identify risk factors that might predict intentional non-adherence to TKIs in CML. Methods The CML Advocates Network, connecting 79 CML patient groups from 63 countries, conducted an international project investigating patterns of medication-taking behaviors of CML patients, supported by CML investigator groups in Germany, Italy and France. We sought to demonstrate the relationship between 16 factors and adherence in this multinational cohort. A web-based survey was launched in 12 languages, enrolling CML patients from Sept 2012 to Jan 2013. The identical questionnaire was provided to a cohort of patients recruited in clinics in France, Germany and Italy, returned by patients in a pre-stamped envelope to an independent data center. Questions included potential factors associated with non-adherence as well as on patients' perception of disease and treatment burden. Based on previous literature and on clinical relevance, a pool of 16 candidate factors, potentially predicting intentional non-adherence, was selected for analysis. These included: frequency of CML medication, co-payment for CML treatment, and current TKI therapy. Patients who reported having skipped intentionally one or more doses over the last year were considered as “intentional non-adherers”. Univariate logistic regression analysis was performed to examine the impact of pre-selected candidate factors on the probability of intentional non-adherence. Two multivariate models were fitted based on line of therapy received by patients (i.e. first line and second or greater lines of therapy). Results This patient-led study is the largest study conducted to date on the influencers of non-adherence in CML. Overall, 2546 adult CML patients (47.6% female) under TKI treatment from 79 countries responded to the survey. 2151 patients responded online, 395 questionnaires were returned on paper. No significant difference on intentional non-adherence was observed between paper or online responses. Median age of patients was 51 years (range 18-96) and median time from diagnosis was 4 years (0-27). Overall, 51.6% of all respondents reported having missed at least one dose unintentionally over the last year, and 19.5% did so intentionally. This analysis regards the intentional non-adherent population (n=490). Of those, 60% were on imatinib, 20% on nilotinib, 14% on dasatinib, 6% on other TKIs. Several factors predicted intentional non-adherence in univariate analysis, including education level (P=0.016) and co-payment for TKIs (P=0.005). For patients on first line TKI (n=1551), the following factors independently predicted a higher likelihood of being intentional non-adherers: younger age (P=0.015), longer time since diagnosis (P Discussion Despite there is clear evidence that survival is close to that of the general population when CML is treated effectively in chronic phase with current therapies, every fifth CML patient deliberately skips doses. Key factors predicting intentional non-adherence can potentially help physicians and patient organisations to identify patients early who should be monitored more closely and informed about the importance of adherence. Managing side effects proactively also reduces reasons for intentional non-adherence. Disclosures: Geissler: Novartis: Membership on an entity’s Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity’s Board of Directors or advisory committees; Pfizer: Membership on an entity’s Board of Directors or advisory committees; Ariad: Membership on an entity’s Board of Directors or advisory committees. Efficace:Novartis: Consultancy; Bristol-Myers Squibb: Consultancy. Bombaci:Ariad: Consultancy; Bristol-Myers Squibb: Consultancy; Novartis: Consultancy. de Jong:Novartis: Membership on an entity’s Board of Directors or advisory committees. Gavin:Celgene: Membership on an entity’s Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity’s Board of Directors or advisory committees; Ariad: Membership on an entity’s Board of Directors or advisory committees; Novartis: Membership on an entity’s Board of Directors or advisory committees. Daban:Ariad: Membership on an entity’s Board of Directors or advisory committees; Pfizer: Membership on an entity’s Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity’s Board of Directors or advisory committees; Novartis: Membership on an entity’s Board of Directors or advisory committees. Pelouchová:Bristol-Myers Squibb: Membership on an entity’s Board of Directors or advisory committees; Ariad: Membership on an entity’s Board of Directors or advisory committees; Novartis: Membership on an entity’s Board of Directors or advisory committees. Sharf:Pfizer: Membership on an entity’s Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity’s Board of Directors or advisory committees; Ariad: Membership on an entity’s Board of Directors or advisory committees; Novartis: Membership on an entity’s Board of Directors or advisory committees.