Leukemia And Lymphoma Society Research Articles

Abstract P18: Splicing polymorphism rs12459419 modulates antibody-bound internalization of CD33 isoforms

Abstract P18: Splicing polymorphism rs12459419 modulates antibody-bound internalization of CD33 isoforms

A Patient-Centric Registry Dataset Generates Real-World Insights about Cause, Timing, Type, and Impact of Cardiotoxic Adverse Events in Chronic Lymphocytic Leukemia

INTRODUCTION Chronic Lymphocytic Leukemia (CLL) is a hematological malignancy characterized by a progressive accumulation of abnormal monoclonal B lymphocytes. The treatment landscape for CLL has undergone significant changes with the introduction of novel targeted agents, notably BTK inhibitors (BTKis). While BTKis have contributed to advancements in CLL management, the class effect of cardiac-related toxicity has emerged in several clinical trials, particularly associated with the first generation BTKi ibrutinib. Our study utilizes a real-world registry dataset to quantify cardiotoxic adverse events (CT AEs) across treatment classes, and explores resulting changes in the treatment journey and disease course for CT AEs associated with ibrutinib. METHODS 766 participants with CLL from the Leukemia and Lymphoma Society (LLS) registry had data extracted from collected medical records via the Invitae CiitizenⓇ platform, a patient-centric platform that leverages the HIPAA right-of-access to organize clinical data into a standardized, research-ready format using machine learning and human clinician review. Lines of therapy (LOTs) were generated using a proprietary logic-based algorithm, and defined as “ibrutinib” if they contained ibrutinib, “2nd-generation” if they contained a 2nd-generation BTKi (e.g. acalabrutinib), or “CD20” if they contained a CD20-targeting monoclonal antibody (e.g. rituximab). Categories were not mutually exclusive (e.g. LOT containing ibrutinib and rituximab counted as both “ibrutinib” and “CD20”). If the medical record stated that AEs resulted from only one medication in the LOT, the AE was assigned to that medication; if it was unclear which medication in a LOT caused the AE, that LOT and AE were excluded from analysis. A proprietary logic-based algorithm was used to calculate endpoints. Statistical significance was assessed using chi-square, with Bonferroni correction applied for multiple comparisons. RESULTS Out of 766 patients in the cohort, 411 received a total of 703 LOTs, of which 228 contained ibrutinib, 91 contained 2nd-generation BTKis, 358 contained CD20s, and 71 contained neither BTKis nor CD20s (“Other”). Ibrutinib-containing LOTs had a statistically significantly higher rate of at least one CT AE (21.5%; 49/228) as compared to LOTs containing 2nd-generation BTKis (5.5%; 5/91; p=0.002), CD20s (2.8%; 10/358; p<0.00001), or Other (8.5%; 6/71; p=0.005). The 49 individuals with an ibrutinib-associated cardiac AE experienced a total of 57 events, which were then characterized for timing, pre-existing cardiac comorbidities, treatment setting, and treatment impact ( Table 1). Ibrutinib CT AEs were not significantly concentrated in any numerical LOT, with a 22.5% (34/151) frequency in 1L, 28.6% (16/56) in 2L, and 22.6% (7/31) in 3+L settings. Individuals with a pre-existing cardiac comorbidity were neither more likely to experience an ibrutinib-associated CT AE, nor more likely to have a treatment impact if they did have a CT AE. Atrial fibrillation was more likely to result in a dose reduction, treatment hold, or discontinuation than hypertension (60% (12/20) vs. 18.2% (4/22), p=0.008); other differences were not statistically significant. We next explored outcomes and subsequent treatments for ibrutinib-containing LOTs that did or did not have any associated CT AE ( Table 2). Outcomes for LOTs associated with a CT AE were not statistically significantly different for ToT, TtNT, CRR, or ORR (see table 2). While the overall distribution of subsequent classes of therapy was similar for those who did or did not experience a CT AE, we note that for those who had treatment discontinued as a result of the CT AE, only 2/11 switched to a 2nd gen BTKi (the remainder switched to a BCL2i-containing regimen), suggesting a potential trend towards out-of-class switching. CONCLUSION Our data support the established higher rate of CT AEs associated with ibrutinib compared to 2nd-generation BTKis or non-BTKi LOTs. However, in this dataset the presence of an ibrutinib-associated CT AE did not significantly alter either the patient's treatment journey or disease course overall. Future analyses will characterize the real-world incidence and impact of other types of AEs at the level of individual medications, LOTs, and medication classes.

Real-World Patterns of MRD Testing and Impact on Treatment for Chronic Lymphocytic Leukemia Patients

INTRODUCTION Therapeutic options for Chronic Lymphocytic Leukemia (CLL) have advanced significantly over time, resulting in a heterogeneous treatment landscape. Insights into the depth of treatment response can be gained through highly-sensitive detection of residual cancer cells using measurable (also known as minimal) residual disease (MRD) testing. Initially, MRD testing was limited to prognostic use within clinical trials. However, in recent years it has expanded into various clinical settings, although the extent of real-world use is not well established. METHODS 766 individuals with CLL enrolled in the Leukemia and Lymphoma Society (LLS) registry had their medical records collected and data extracted via the Invitae Ciitizen® platform, a patient-centric platform that leverages HIPAA right-of-access to organize clinical data into a standardized, research-ready format, using a combination of machine learning and human clinician review. Proprietary logic-based algorithms were used to characterize lines of therapy (LOTs), MRD testing methods, outcomes and duration of therapy. Descriptive findings are reported below. RESULTS Of the 766 CLL participants, 117 (15%) received a total of 311 MRD tests (mean=3 tests/person, median=2, max=16). 67 individuals had one or more MRD negative results (134 negative results total) and 78 individuals had one or more MRD positive results (177 positive results total). 56/117 (47.9%) patients had one or more MRD tests as part of a clinical trial, for a total of 132/311 (42.2%) MRD tests performed during a trial. Total MRD tests included 260 (83.6%) evaluated by flow cytometry, 8 (2.6%) by next generation sequencing (NGS), with the remainder not having documented methods (43; 13.8%). Since 2014, when MRD testing was integrated as a prognostic indicator in clinical trials, there has been increasing use of MRD testing ( Figure 1) within this cohort, as assessed by percentage of individuals receiving one or more tests per year. Interestingly, there is a peak of percentage tested in a clinical trial setting in 2017, after which a continued increase in those tested outside of a clinical trial setting shifts the overall proportion down. We also note the appearance of NGS testing in 2018. The 117 individuals who were MRD tested received 40 unique LOTs (e.g., “obinutuzumab, venetoclax”). We then quantified the MRD outcomes as either “achieved MRD-negative” or “did not achieve MRD-negative” for the most commonly-used therapies (n≥5) ( Table 1). Ibrutinib and acalabrutinib monotherapies had the lowest proportion of MRD-negative outcomes (1/15 and 0/6, respectively), whereas obinutuzumab-venetoclax +/- ibrutinib combination therapies had the highest proportion of MRD-negative outcomes (4/5 and 17/17, respectively). In order to assess the impact of MRD outcome on treatment patterns, the duration of therapy following a MRD-positive and negative test were evaluated. Therapy continued a mean duration of 691 days (n=126, median=488) after a MRD-positive test and 419 days (n=66, median=230) after a MRD negative test. CONCLUSION In this real-world dataset of 766 individuals with CLL, we detect an increasing rate of MRD testing since 2014. Notably, this usage is not limited to the clinical trial setting, underscoring the growing significance of MRD testing as a more general tool for evaluating disease control. Exploration of which LOTs achieve proportionally more MRD-negative statuses highlights that venetoclax-containing fixed-duration regimens as well as venetoclax monotherapy have higher rates of MRD-negativity. Conversely, BTK monotherapies ibrutinib and acalabrutinib were associated with the lowest percentage of MRD-negative outcomes. Finally, we find that the duration of therapy from the time of MRD testing is shorter when the result is MRD-negative, suggesting that MRD testing as a component of outcomes assessment used in the real-world setting may be useful in deciding when to discontinue therapy. This aligns with ongoing clinical trials investigating fixed duration therapies and the use of MRD-negative status as an outcome measure to assess depth of remission. Future studies on larger datasets will explore how MRD testing is integrated into clinical practice and its impact on treatment decisions.

Patient-Associated Survival Modulators in Adolescent and Young Adult (AYA) Patients (Pts) with Acute Myeloid Leukemia (AML)

Background: AML is a highly aggressive hematologic malignancy, but the AYA pts [aged 18-39 years (y)] have improved survival, with ~50% of pts achieving long-term cure. Pt outcomes are known to be affected by disease-related factors including cytogenetic findings and gene mutations, which were established in large genomic studies. In addition, pt-related factors, such as self-reported race and socioeconomic contributors have been found to affect survival in population-based studies. Whereas population-based studies are performed on large pt cohorts to establish meaningful conclusions, they usually lack details with respect to additional pt-related factors, including complete comorbidities, insurance status as well as information on disease presentation, such as time from the first provider contact to confirmation of AML diagnosis (time to diagnosis) and treatment, which might also influence pt survival. Rationale and Methods: Thus, we set out to establish recent survival rates of AML AYA pts at the population level using pts reported to one of 12 Surveillance Epidemiology End Results (SEER) Program registries of the National Cancer Institute [n=1119; median age, 30 y,1992-2014; n=239; median age, 29 y, 2015-2020], and analyze possible factors influencing survival. In parallel, we performed an in-depth analysis of treatment response and survival, including time to diagnosis, and additional pt-associated variables pertinent to AYA pts (employment status, housing, insurance, comorbidities, distance to treatment center, research study enrollment, biobanking) based on retrospectively collected data of AYA AML pts cared for at a major US Comprehensive Cancer Center (CCC) in 2015-2020 (n=96, median age, 31 y), for whom detailed clinical information was available. Results: Generally, overall survival (OS) of AYA AML pts significantly improved over time, with a marked improvement of 3-y OS rates from 47% in pts diagnosed prior to 2009, to 63% in pts diagnosed in 2010-2014 and 69% in pts diagnosed in 2015-2020. Analysis of possible associations between demographic parameters and risk of death among AYA AML pts reported to SEER Program registries did not show any statistically significant impact of sex, age, county-level median household income or metro/rural status. The only factor affecting OS of AYA AML pts was race. Specifically, Black AML pts had a higher risk of death compared with that of White AML pts [HR 2.13 (95% CI 1.03 - 4.39)], with 3-y OS rates of 47% and 80% ( P=.04), respectively. Survival disparities did not improve over time. CCC AYA AML pts had similar OS rates to those seen in the population-based analyses, with a 3-y OS rate of 70%. Ninety-three percent of pts achieved a complete remission, and 31% of pts relapsed. Analyses of CCC AML pts allowed for preliminary assessment of additional parameters. Ninety-one percent of pts (77/85) received a diagnosis in ≤2 weeks after first provider contact. Although pt numbers were small, there was a trend for a longer diagnosis time in Black pts, 27% (3/11) of whom were diagnosed >2 weeks after first presentation, compared with only 8% (5/61; P=.10) of White pts. Interestingly, analysis of possible additional outcome modulators in CCC AYA pts suggested that presence of other medical conditions at diagnosis associated with lower relapse rates (16% vs 34%, P=.04), and unemployment tended to associate with higher relapse rates (34% vs 17%, P=.06). In addition, of pts approached for biobanking, fewer Black pts consented to sample collection than White pts (60% vs 87%, P=.06). Conclusion: Survival of AYA pts with AML significantly improved over time, likely driven by availability of allogeneic stem cell transplantation and improved supportive care. Black race still represents the most important negative survival prognosticator, without marked signs of improvement. An exploratory analyses of additional pt-associated variables suggested less recognized factors that may impact survival, such as trends for longer time to diagnosis and reduced participation in biobanking protocols in Black pts compared with White pts, and a higher relapse rate in pts who are unemployed. Although these differences were not yet statistically significant , we are currently in the process of increasing the sample size to further evaluate these potentially important trends. Support: American Cancer Society, Leukemia Lymphoma Society

Splicing Polymorphism rs12459419 Modulates Antibody-Bound Internalization of CD33 Isoforms

Background: While the standard regimen for AML has been intense chemotherapy followed by stem-cell transplantation (SCT), addition of immunotherapeutics such as gemtuzumab ozogamicin (GO) to this has shown to improve outcomes in multiple clinical trials. Since these trials, GO has been added to the National Comprehensive Cancer Network (NCCN) practice guidelines for use in AML therapy (NCCN., 2018). GO is a humanized monoclonal antibody conjugated to calicheamicin and targets the cell surface antigen CD33, observed on most AML blasts. Upon binding to GO, CD33 is internalized and the subsequent release of calicheamicin mediates cytotoxicity. CD33 contains two extracellular domains: IgV and IgC, the IgV domain is coded by CD33 exon 2 and is the binding site for GO. A splicing SNP, rs12459419 (C>T; A14V) in exon 2 results in a shorter isoform (CD33-D2) and has been previously associated with CD33 abundance on cell surface as well as clinical benefit from GO addition to standard chemotherapy. Patients with CC genotype (~50% of the cohort) expressed full length CD33 (CD33-FL) and benefited significantly from GO. However, heterozygous CT and homozygous TT genotype groups did not derive the same benefit. These results were perplexing as CT genotype group had intermediate levels of CD33-FL and CD33-D2 isoforms (Lamba et al., 2017). It is hypothesized that lack of IgV domain in CD33-D2 and putative CD33-FL/CD33-D2 dimerization prevents GO binding and subsequent internalization in rs12459419 CT/TT genotype cells, however this has never been tested. We have generated novel antibodies directed against the IgC domain that recognizes CD33-D2 in AML cell lines as well as primary AML cells (Gbadamosi et al., 2021) thus facilitating testing the above indicated hypothesis. Objective: In this study, we first tested the ability of antibody-bound CD33-D2 to internalize, followed by impact of the internalization status of CD33-FL and CD33-D2 in cells co-expressing both isoforms along with the concomitant impact on GO induced cytotoxicity. Methods: Using pMXs retroviral particles encoding CD33-FL or CD33-D2, we engineered CRISPR/Cas9 mediated CD33 KO in AML cell lines to overexpress either one or both CD33 isoforms to mimic cells expression varying proportions of CD33-FL/CD33-D2. Internalization of either CD33-FL or CD33-D2 over a duration of 4 hours in the presence of antibodies recognizing either of the two isoforms was performed. Cells were labeled with unconjugated mouse anti-CD33-FL P67.6 or anti-CD33-D2 HL2541 antibody on ice and incubated at 37°C for 0-4 hours, followed by staining with mouse anti-mouse IgG antibody conjugated with biotin. Surface CD33-FL or CD33-D2 was then detected using streptavidin-FITC conjugate. Percentage antibody-bound CD33-FL or CD33-D2 internalization was expressed as change in FITC MFI between each time point incubated and cells kept at 0°C post CD33 antibody labeling. Results: While P67.6-bound-CD33-FL internalized as expected in AML cell lines expressing CD33-FL only (Fig. 1A), we show for the first time that HL2541-bound-CD33-D2 also internalizes upon antibody binding in cell lines expressing CD33-D2 isoform only (Fig. 1B). In AML cell lines co-expressing both CD33-FL and CD33-D2 isoforms, a >2.5-3 fold decrease in this antibody-bound internalization was observed for each isoform (Figs. 1C and D). In response to GO exposure for 48 hours, cells co-expressing both CD33-FL and CD33-D2 isoforms had 7-9.5-fold higher IC50 values (233 nmol and 277 nmol) compared to cells expressing only CD33-FL (33.19 nmol and 29 nmol) (Figs. 1E and F). As expected, cells expressing CD33-D2 only did respond to GO. Discussion: Our finding that antibody-bound CD33-D2 internalizes like CD33-FL adds a novel piece of evidence in understanding the biology of this variant isoform and opens opportunities to develop antibody drug conjugate (ADC) such as GO using CD33-D2 antibody. This new CD33-D2 targeting ADC will provide a treatment option in patients with TT genotypes. Our results also provide a mechanistic insight on the previous clinical observation showing lack of benefit from GO in patients heterozygous for the splicing SNP. Our ongoing studies are focused on validating this result using live cell imaging and efforts towards design of new ADC or T cell engagers using CD33-D2 antibody. The study was supported by Leukemia Lymphoma Society, UFHealth Cancer Center, and the Frank A. Duckworth Endowment.

Europeanpediatric Acute Leukemia (EuPAL) Registry

The Leukemia Lymphoma Society (LLS) Pediatric Acute Leukemia (PedAL) Initiative is a collaborative international effort that aims to improve the cure of children with relapsed/refractory (R/R) and other high-risk leukemias. Its comprehensive approach included preclinical and clinical research, standardization and improvement of diagnostics, quality management, and global data integration and analysis. The European Pediatric Acute Leukemia (EuPAL) Foundation was established as the PedAL Initiative partner to support European stakeholders in these efforts. A major focus of the EuPAL Registry and PedAL Initiative is to increase access to and test new drugs targeting leukemia-specific biologic and genetic characteristics in pediatric patients with R/R acute myeloid leukemia (AML). However, identification and recruitment of patients remains a challenge. For this purpose, the APAL2020SC screening trial (NCT04726241) in North America, Australia, and New Zealand and the EuPAL registry in Europe have been launched. In collaboration with national and international study groups, pediatric leukemia reference laboratories, and participating clinical trial sites, each child with R/R AML should be registered. In Europe, the EuPAL registry office identifies the best available trial for the patient based upon leukemia-associated genetic and immunophenotypic data and closest trial site(s) and coordinates contact between the treating physician/site and the trial site as needed. Results The EuPAL registry has been approved by the leading ethic committee in Germany with extension to several other European countries ongoing. To date, 35 children and adolescents with R/R AML have been enrolled since June 2022. The median age at initial diagnosis was 7.3 (range 0.2 to 17.7) years with median duration of remission 1.3 (0.3 to 5.3) years. Most patients were registered at first relapse (n=29) with 3 patients in second relapse and 1 patient in third relapse. Two children were diagnosed with a molecular relapse (n=2). Fourteen patients have been transplanted in 1 st CR (n=9) /2 nd CR (n=5) prior to registration Regarding the initial risk groups at diagnosis, most relapses occurred in the intermediate risk group (IR) n=19) and the high-rik group (HR; n=12). The others were standard risk, one isolated CNS relapse in APL and two in children with trisomy 21. Patients were treated at relapse on the AML-BFM 2017 registry (treatment recommendation: Idarubicin, fludarabine, cytarabine (IDA-FLA), FLA and HSCT), the AIEOP-BFM-AML 2020 trial (FLA- gemtuzumab ozogamicin (GO) or IDA-FLA t(8;21)), the AMORE 2017 trial (azacytidine and HSCT; n=2) or received off-label therapies (cytarabine/GO, venetoclax/cytarabine, or azacytidine). Conclusion The EuPAL registry has been successfully established and is beginning to generate relevant knowledge regarding the frequency and timing of pediatric AML relapse, leukemia-associated genetics, and immunophenotypic characteristics. In collaboration with the LLS PedAL Initiative, the EuPAL registry will continue to facilitate recruitment of children with R/R AML and other leukemias to clinical trials testing innovative therapies, as well as improve understanding of potential bias in clinical trial referrals. Current challenges include integration of more European countries into the EuPAL Registry and increasing the number of open early-phase PedAL/EuPAL clinical trials.

Validation of the transactional eHealth literacy instrument with cancer caregivers.

Family members are important sources of support for patients with cancer. They access, evaluate, and engage with online information and discuss it with a cancer clinician. This study validates the 4-dimensions, 18-item Transactional eHealth Literacy Instrument (TeHLI) and proposed to include Clinical eHealth Literacy as a 5th dimension. The Leukemia & Lymphoma Society (LLS) disseminated an online survey to 121 family member caregivers between March-June 2020. We conducted confirmatory factor analyses (1) to examine model fit for the 4-factor TeHLI in the cancer caregiver population, and (2) to examine the model fit when adding the 5th factor. The 4-dimension model yielded acceptable model fit (RMSEA = 0.09; 90% CI = 0.08-0.11; CFI = 0.98; TLI = 0.98; SRMR = 0.07). The 5-dimension model also yielded acceptable model fit (RMSEA = 0.08; 90% CI = 0.07-0.10; CFI = 0.97; TLI = 0.97; SRMR = 0.08), supporting the expansion of the TeHLI within this population. The five-dimension TeHLI is a valid and reliable measure of eHealth literacy among blood cancer caregiver populations. The TeHLI can be used as an outcome measure for communication skills training for caregivers, patients, and clinicians.

Activation of targetable inflammatory immune signaling is seen in myelodysplastic syndromes with SF3B1 mutations.

Mutations in the SF3B1 splicing factor are commonly seen in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML), yet the specific oncogenic pathways activated by mis-splicing have not been fully elucidated. Inflammatory immune pathways have been shown to play roles in the pathogenesis of MDS, though the exact mechanisms of their activation in splicing mutant cases are not well understood. RNA-seq data from SF3B1 mutant samples was analyzed and functional roles of interleukin-1 receptor-associated kinase 4 (IRAK4) isoforms were determined. Efficacy of IRAK4 inhibition was evaluated in preclinical models of MDS/AML. RNA-seq splicing analysis of SF3B1 mutant MDS samples revealed retention of full-length exon 6 of IRAK4, a critical downstream mediator that links the Myddosome to inflammatory NF-kB activation. Exon 6 retention leads to a longer isoform, encoding a protein (IRAK4-long) that contains the entire death domain and kinase domain, leading to maximal activation of NF-kB. Cells with wild-type SF3B1 contain smaller IRAK4 isoforms that are targeted for proteasomal degradation. Expression of IRAK4-long in SF3B1 mutant cells induces TRAF6 activation leading to K63-linked ubiquitination of CDK2, associated with a block in hematopoietic differentiation. Inhibition of IRAK4 with CA-4948, leads to reduction in NF-kB activation, inflammatory cytokine production, enhanced myeloid differentiation in vitro and reduced leukemic growth in xenograft models. SF3B1 mutation leads to expression of a therapeutically targetable, longer, oncogenic IRAK4 isoform in AML/MDS models. This work was supported by Cincinnati Children's Hospital Research Foundation, Leukemia Lymphoma Society, and National Institute of Health (R35HL135787, RO1HL111103, RO1DK102759, RO1HL114582), Gabrielle's Angel Foundation for Cancer Research, and Edward P. Evans Foundation grants to DTS. AV is supported by Edward P. Evans Foundation, National Institute of Health (R01HL150832, R01HL139487, R01CA275007), Leukemia and Lymphoma Society, Curis and a gift from the Jane and Myles P. Dempsey family. AP and JB are supported by Blood Cancer UK (grants 13042 and 19004). GC is supported by a training grant from NYSTEM. We acknowledge support of this research from The Einstein Training Program in Stem Cell Research from the Empire State Stem Cell Fund through New York State Department of Health Contract C34874GG. MS is supported by a National Institute of Health Research Training and Career Development Grant (F31HL132420).

A novel linked TCR: MyD88 receptor improves anti-tumor responses while maintaining antigen specificity

Abstract The treatment of malignant tumors utilizing engineered T cell receptor (TCR) therapies in the clinic have demonstrated encouraging therapeutic potential in a subset of patients. Limitations to T cell-based therapies include down-regulation of tumor-antigen presentation by the tumor cells, poor TCR activation, and the immunosuppressive effects of the tumor microenvironment (TME). Attempts to ameliorate these issues by utilizing T cells engineered with tumor-reactive TCRs with increased affinity showed enhanced responses. However, affinity-modified TCRs are more promiscuous and can lead to off-target toxicity. We and others have demonstrated that activating MyD88 signaling (a key adapter protein in toll-like receptor signaling) in T cells enhances effector function and expansion while simultaneously reducing their propensity to enter an exhausted state. In these studies, we designed novel receptors in which the death and intermediate domains of MyD88 are fused to the TCR. T cells engineered to express this novel TCR:MyD88 receptor showed improved responses in a tumor-antigen dependent manner, as demonstrated by increased proliferation and expression of effector molecules, without reducing the specificity of the TCR. In mouse models, TCR:MyD88 T cells conferred improved anti-tumor responses against tumors expressing suboptimal levels of target antigen which was associated with increased T cell infiltration, reduced T cell exhaustion, and an altered TME. These results demonstrate the ability of TCR:MyD88 to improve current therapies without sacrificing the specificity of the TCR which we believe can be utilized to improve the outcome of patients suffering from advanced cancer while reducing toxicities. Supported by -US Department of Veteran Affairs -Leukemia Lymphoma Society -University of Colorado -Shoots Medical Center -NCI (R01CA207913)

Heterologous SARS‐CoV‐2 vaccinations in patients with B‐cell lymphoid malignancies

Heterologous <scp>SARS‐CoV</scp>‐2 vaccinations in patients with B‐cell lymphoid malignancies

Sars-Cov-2 Antibody Levels in Blood Cancer Patients after a Third Sars-Cov-2 “Booster” Vaccination - Observational Data from the LLS National Registry

Immunosuppressed patients may be at high risk for breakthrough COVID-19 infection despite SARS-CoV-2 vaccination, due to an inadequate or negligible antibody response. Based on data from the Leukemia & Lymphoma Society (LLS) National Registry, 25% of patients with hematologic malignancies do not produce anti-Spike protein antibodies in response to mRNA vaccines, with B-cell malignancy patients at highest risk (Greenberger et al, 2021, Cancer Cell, on-line). While studies of T-cell immunity, antibody cocktails, and booster vaccinations are underway, some patients have elected to receive an additional “booster” vaccination after a full course of SARS-CoV-2 vaccination. The LLS National Registry (NCT04794387) has collected Patient Reported Outcomes and serology from 3300 patients with hematologic malignancies. This study was approved by the Western Institutional Review Board, and participants provided informed consent electronically.As of July 2021, the Registry includes 24 patients who obtained a 3 rd vaccination after full vaccination with mRNA vaccines. Twenty of these patients were seronegative >14 days post 2 nd vaccination (as measured by the Roche Elecsys assay). Four patients had low positive serology results. All patients were nucleocapsid antibody negative.Patient ages ranged from 51-79 years. Eleven had chronic lymphocytic leukemia (CLL), 7 non-Hodgkin's lymphoma (NHL), 5 Waldenstrom's macroglobulinemia (WM), and 1 multiple myeloma (MM). Six patients were not currently on anti-B cell therapy, 11 had received anti-CD20 therapy (8 within the last 6 months), 6 had received Bruton's tyrosine kinase (BTK) inhibitors within the last 6 months, and 1 patient had recently received chemotherapy. The booster vaccinations were obtained between April and June 2021, 21 to 114 days after completing the initial vaccination series between January and April 2021. Serology was performed 12-61 days post-booster vaccination. Fifteen patients received a heterologous adenovirus vaccine. Four patients received a heterologous mRNA vaccine, 5 patients received a homologous mRNA vaccine. Descriptive results are shown on the following table.All patients (4) who had some level of antibody response to the initial vaccines had an augmented antibody response after a booster (i.e. sero-enhanced). Patients who had prior anti-CD20 often failed to seroconvert after booster vaccination. Only 2 of 8 patients who received anti-CD20 antibody treatment in the 6 months prior to vaccination seroconverted after booster vaccination. Two out of 3 seronegative patients receiving anti-CD20 therapy in the last 2 years (but > 6 months) seroconverted after the booster. One patient with follicular lymphoma who received anti-CD20 therapy in 2019 remained seronegative despite a prolonged duration without therapy. Of the 6 seronegative patients taking BTK inhibitors, 3 seroconverted after the booster. Two of the 3 remaining seronegative patients were taking concomitant anti-CD20 therapy. Of the 4 seronegative patients not currently taking anti-B cell therapy, 3 seroconverted while one patient who currently required intravenous immunoglobulin remained seronegative. A patient currently receiving chemotherapy also did not respond to a booster.In this limited set of patients there was no evident pattern of antibody response amongst patients who received homologous versus heterologous vaccine nor between disease types. While anti-CD20 therapy appeared to reduce antibody response to booster vaccination, there was substantial heterogeneity. Although many patients with B-cell malignancies did not mount a robust response to full mRNA vaccine series, several patients demonstrated an antibody response to the booster vaccination.Clinical trials are needed to further understand who can benefit from a booster strategy as well as define the safety of the approach. The LLS Registry includes collection of Electronic Health Records, which will allow us to more specifically evaluate timing and dosage of boosters, the influence of prior therapeutics, as well as health and safety outcomes to better guide patients and physicians through the COVID-19 pandemic. [Display omitted] DisclosuresNo relevant conflicts of interest to declare. OffLabel Disclosure:Booster vaccination (after full vaccination) using BNT162b2, mRNA-1273, or Ad26.COV2.S

Inhibition of Cyclin Dependent Kinase 8(CDK8): A Novel Approach to Target the Leukemia Initiating Cells (LICs) in T-Cell Acute Lymphoblastic Leukaemia (T-ALL)

Background: T cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematopoietic malignancy characterized by an aberrant proliferation of immature thymocytes affecting preferentially children and adolescents. Approximately 70% of T-ALL cases have activating mutations of the NOTCH1 followed by oncogenic pathways PI3K/Akt, the anti-apoptotic BCL-2 family, and CDKN2A/2B cell cycle regulators 1, 2. Unlike other leukemias such as chronic myeloid leukemia (CML) and Philadelphia-positive ALL, which are kinase-driven malignancies 3, 4, the initiating events in T-ALL cause the ectopic expression of transcription factors that drive leukemogenesis, hence targeted therapies needed to focused on this field. Cyclin Dependent Kinase 8 (CDK8) and its paralog CDK19, restrain activation of super-enhancer-associated tumor suppressors and lineage commitment genes in leukemia. Moreover CDK8 phosphorylates intracellular domain (ICD) and regulates activation and turnover of NOTCH1 5, 6, indicating that targeting CDK8 with specific inhibitors may be considered as a novel therapeutic strategy for T-ALL. RVU120 is a first-in-class, specific and selective inhibitor of CDK8/CDK19, currently in phase Ib dose-escalation trial in patients with relapsed or refractory (R/R) AML and HR-MDS (NCT04021368).Objectives: The goals of these studies were to investigated the effectiveness of RVU120 and other non-related CDK8/19 inhibitors against T-ALL cell lines/PDXs, including GSI-resistant lines. Comprehensive analysis of target inhibition and apoptotic signatures were evaluated. The clinical relevance of RVU120 in LICs was confirmed in Patient derived xenografts (PDXs).Results:T-ALL cell lines and PDXs were treated with RVU120 and other chemically non-related CDK8/19 inhibitors in different concentration for 12-18 days, and the changes in cell number and apoptosis using flow cytometry analysis were determined. High differential efficacy in double-digit nM range has been observed for NOTCH1 PEST domain mutant cell lines including GSI-sensitive HPB-ALL cells and GSI-resistant cells PF-382, KOPT-K1, and MOLT4, where both inhibition of cell proliferation and induction of apoptosis were observed. GI-resistant cell lines SUP-T1, SUP-T11, MOLT16 and JURKAT were considered as moderately sensitive and LOUCY (early T-cell phenotype ALL), and CCRF-CEM devoid those phenotype, were considered as resistant to RVU120. Results form etsblished cell lines were further corroborated in patient-derived xenograft cells (PDX) treated with RVU120. In T-ALL PDX 6522288 (Notch1 HD /PEST mut, TET2 mut, U2AF1 mut, WT1 mut and CUL76- CDKN2A/B mut, PTEN-/-) treatment with RVU120 was followed by a reduction in cell number and induction of apoptosis in phenotypically defined leukemia initiating cells (LICs) CD34+CD7+CD19-, with calculated IC50s value for bulk and LICs as 92.8 nM and 141.8 nM, respectively. The clinical relevance of these findings and impact on LICs are under the evaluation in PDX mice model. Mechanistically, treatment with RVU120 reduced the phosphorylation of STAT5 and STAT1 as well as the level of MYC and anti-apoptotic proteins MCL1, but induced expression of BAX in sensitive cells. Hence, inhibition of CDK8 is a novel approach to target the LICs in T-ALL.Conclusion:Inhibition of CDK8 by RVU120 triggers inhibition of cell proliferation and apoptosis in cell lines and LICs in T-ALL. Further clinical study is warranted to study the efficacy of RVU120 and CDK8 inhibition in T-ALL.Keywords: CDK8, RVU120, apoptosis, T-ALL, LICs in PDX modelReference1 Girardi, T., Vicente, C., Cools, J. & De Keersmaecker, K. Blood129, 1113-1123, doi:10.1182/blood-2016-10-706465 (2017).2 Sanchez-Martin, M. & Ferrando, A. Blood 129, 1124-1133, doi:10.1182/blood-2016-09-692582 (2017).3 Braun, T. P., Eide, C. A. & Druker, B. J. Cancer cell 37, 530-542, doi:10.1016/j.ccell.2020.03.006 (2020).4 Gazeau, N. et al. Leukemia 34, 2230-2233, doi:10.1038/s41375-020-0715-2 (2020).5 Pelish, H. E. et al. Nature526, 273-276, doi:10.1038/nature14904 (2015).6 Fryer, C. J., White, J. B. & Jones, K. A. Molecular cell 16, 509-520, doi:10.1016/j.molcel.2004.10.014 (2004). DisclosuresGolas: Ryvu Therapeutics: Current Employment. Windak: Ryvu Therapeutics: Current Employment. Rzymski: Ryvu Therapeutics: Current Employment, Current equity holder in publicly-traded company. Andreeff: ONO Pharmaceuticals: Research Funding; AstraZeneca: Research Funding; Glycomimetics: Consultancy; Daiichi-Sankyo: Consultancy, Research Funding; Breast Cancer Research Foundation: Research Funding; Karyopharm: Research Funding; Reata, Aptose, Eutropics, SentiBio; Chimerix, Oncolyze: Current holder of individual stocks in a privately-held company; Amgen: Research Funding; Aptose: Consultancy; Medicxi: Consultancy; Oxford Biomedica UK: Research Funding; Novartis, Cancer UK; Leukemia & Lymphoma Society (LLS), German Research Council; NCI-RDCRN (Rare Disease Clin Network), CLL Foundation; Novartis: Membership on an entity's Board of Directors or advisory committees; Syndax: Consultancy; Senti-Bio: Consultancy. Borthakur: GSK: Consultancy; Astex: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees; Ryvu: Research Funding; University of Texas MD Anderson Cancer Center: Current Employment; Protagonist: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; ArgenX: Membership on an entity's Board of Directors or advisory committees.

Targeting Polo-like Kinase 4 Triggers Polyploidy and Apoptotic Cell Death in TP53-Mutant Acute Myeloid Leukemia

Background: TP53 mutations in acute myeloid leukemia (AML) are associated with complex karyotype, high incidence of minimal residual disease (MRD), and high risk of relapse (Döhner et al., 2017; Giacomelli et al., 2018). While numerous novel treatment regimens, including the combination of the BCL2 inhibitor venetoclax (VEN) and hypomethylating agents (HMA), have emerged as partially effective treatments and resulted in higher remission rates in patients with TP53-mutant AML, full clearance of the mutant TP53 clone is rarely achieved and the majority of patients relapse (Short et al., 2021; Takahashi et al., 2016). The mechanisms responsible for response and relapse in TP53-mutant AML remain unclear and investigating novel mechanisms is critical to develop more effective therapies.Results: In order to shed light on the defective p53 signaling pathways underlying TP53 mutant AML, and to better understand mechanisms of resistance, we performed RNA-sequencing (RNA-seq) on FACS-sorted subpopulations using samples collected from TP53-mutant or TP53-wt high-risk AML patients. Samples were collected at diagnosis (DX) and post-treatment (POSTTX) (total number of samples n= 67, TP53-mutant=36, TP53-wt=31). Diagnostic samples include bulk AML, leukemic stem cells (LSCs), and post-treatment samples including bulk mononuclear cells (MNCS) and patient specific MRD (total n= 67, DX_Bulk=15, DX_LSCs=15, POSTTX_MNCs=14, POSTTX_MRD=23). Differential gene expression analysis of TP53-mutant samples indicates a positive enrichment of the following pathways: G2/M checkpoint, MYC targets, and mitotic spindle, among others. We focused here on genes associated with TP53-mutant AML enriched pathways, and identified a key regulator of centriole biogenesis, one of E2F targets: Polo-like kinase 4 (PLK4) as a potential target highly expressed in TP53-mutant AML samples . Previous publications showed that PLK4 is transcriptionally repressed by p53 and induces apoptosis upon RNAi silencing (Fischer et al., 2014; Li et al., 2005). Here we show that TP53-mutant AML samples lack the p53-dependent PLK4 repression and have higher levels of PLK4 compared to TP53-wt AML.To test the rigor of this finding, we interrogated the Munich Leukemia Laboratory (MLL) data base and analyzed their clinically annotated (e.g. karyotype, survival, complete blood counts, previous treatments ... etc) RNA-seq dataset of 726 AML samples (TP53-mutant=72, TP53-wt=654). TP53-mutant AML samples consistently showed significant PLK4 upregulation (p= 0.0003). We analyzed PLK4 expression and its correlation with TP53 mutations in The Cancer Dependency Map project dataset (1375 cell lines in 35 different types of cancers) (p= 0.004). Furthermore, we found significantly higher PLK4 protein levels in TP53-mutant AML MOLM13 cell lines when compared with syngeneic TP53-wt AML MOLM13 cells. Experimentally, we found that PLK4 inhibition using 25nM CFI-400945 in TP53-mutant AML MOLM13 cell lines triggers polyploidy > 2-fold higher than in TP53-wt AML MOLM13 cell lines 72 hours post treatment (Fig.1A p< 0.0001). Finally, we show that polyploidy is not reversible after drug removal and results in significantly increased levels of apoptotic cell death in TP53-mutant AML MOLM13 cells (Fig.1B).Conclusion: Our data suggest that TP53-mutant AML expresses higher levels of PLK4 in comparison to TP53-wt AML, and targeting PLK4 triggers polyploidy and apoptotic cell death in TP53-mutant AML. A clinical trial is ongoing testing the efficacy of PLK4 inhibition (CFI-400945) in AML (Clinical Trial ID: NCT04730258, TWT-202). [Display omitted] DisclosuresIssa: Kura Oncology: Consultancy, Research Funding; Syndax Pharmaceuticals: Research Funding; Novartis: Consultancy, Research Funding. Borthakur: Takeda: Membership on an entity's Board of Directors or advisory committees; ArgenX: Membership on an entity's Board of Directors or advisory committees; Ryvu: Research Funding; Astex: Research Funding; University of Texas MD Anderson Cancer Center: Current Employment; Protagonist: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy. Konopleva: Ascentage: Other: grant support, Research Funding; Novartis: Other: research funding pending, Patents & Royalties: intellectual property rights; Stemline Therapeutics: Research Funding; KisoJi: Research Funding; Eli Lilly: Patents & Royalties: intellectual property rights, Research Funding; Sanofi: Other: grant support, Research Funding; AstraZeneca: Other: grant support, Research Funding; Ablynx: Other: grant support, Research Funding; AbbVie: Consultancy, Honoraria, Other: Grant Support, Research Funding; F. Hoffmann-La Roche: Consultancy, Honoraria, Other: grant support; Reata Pharmaceuticals: Current holder of stock options in a privately-held company, Patents & Royalties: intellectual property rights; Rafael Pharmaceuticals: Other: grant support, Research Funding; Genentech: Consultancy, Honoraria, Other: grant support, Research Funding; Cellectis: Other: grant support; Calithera: Other: grant support, Research Funding; Agios: Other: grant support, Research Funding; Forty Seven: Other: grant support, Research Funding. Haferlach: MLL Munich Leukemia Laboratory: Other: Part ownership. Andreeff: Senti-Bio: Consultancy; ONO Pharmaceuticals: Research Funding; Glycomimetics: Consultancy; Aptose: Consultancy; Breast Cancer Research Foundation: Research Funding; Oxford Biomedica UK: Research Funding; Karyopharm: Research Funding; Medicxi: Consultancy; Amgen: Research Funding; AstraZeneca: Research Funding; Daiichi-Sankyo: Consultancy, Research Funding; Syndax: Consultancy; Novartis, Cancer UK; Leukemia & Lymphoma Society (LLS), German Research Council; NCI-RDCRN (Rare Disease Clin Network), CLL Foundation; Novartis: Membership on an entity's Board of Directors or advisory committees; Reata, Aptose, Eutropics, SentiBio; Chimerix, Oncolyze: Current holder of individual stocks in a privately-held company.

Venetoclax Combined with FLAG-IDA Induction and Consolidation in Newly Diagnosed Acute Myeloid Leukemia

Venetoclax Combined with FLAG-IDA Induction and Consolidation in Newly Diagnosed Acute Myeloid Leukemia

Co-Targeting E-Selectin/CXCR4 with GMI-1359 Facilitates AML Stem Cell Mobilization and Protects BM Niches from Anti-Leukemia Therapy

Acute myeloid leukemia (AML) is characterized by the heterogeneous clonal expansion of undifferentiated myeloid cells in the bone marrow (BM). AML cells compete with normal hematopoietic cells and rewire the BM microenvironment into niches that selectively support leukemia stem cells (LSC). The leukemic niche produces soluble factors that facilitate the retention of LSC and provide protection from cytotoxic and targeted agents. The vascular adhesion molecule, E-selectin is expressed on endothelial cells (EC) in the perivascular niche where therapy-resistant AML cells have an increased affinity to E-selectin compared to normal hematopoietic stem cells (HSC) (Winkler et al., 2020). We previously demonstrated (Chang et al., ASH 2020) that E-selectin blockade by the pharmacological antagonist, GMI-1271 (uproleselan; GlycoMimetics, Inc) sensitized therapy-resistant LSC to Bcl-2 targeted therapy. Efficacious eradication of LSC in the BM however requires blocking multiple receptors and/or associated signaling pathways. A more optimal dislodgement of LSC from the BM could be attained by combining an E-selectin antagonism with blockade of the CXCR4/SDF-1α axis. The dual antagonist of E-selectin and CXCR4, GMI-1359 (GlycoMimetics, Inc.), has been tested in a phase 1 clinical trial (NCT02931214). Previously, we showed that GMI-1359 in combination with a FLT3-ITD inhibitor, improved survival in a xenograft model of FLT3-ITD + AML (Zhang et al., 2016). Hence, we hypothesized that co-targeting E-selectin/CXCR4 more efficiently mobilizes AML cells from BM niches and synergizes with the anti-leukemia activity of venetoclax/hypomethylating agent (Ven/HMA).Intra-vital 2-photon imaging and tracking of individual leukemia cells in triple reporter mice (Blood: dextran-TRITC; Host T-cells: DsRed; Host myeloid CD11 cells: EYFP) injected with AML cells carrying a turquoise fluorescent protein reporter gene suggested that dual inhibition of E-selectin/CXCR4 with GMI-1359 significantly enhanced AML cell motility (Fig 1. from 2.2 um/min to 5.4 um/min, p<0.001). Individual cells were dislodged from the niche and traveled long-distance. The combined inhibition of E-selectin and CXCR4 depleted BM leukemia cells in vascular niche areas. In a patient-derived primary AML xenograft (PDX) model (harboring mutations in JAK2 and c-Kit), combinatorial treatment of GMI-1359 with Ven/HMA significantly reduced BM retention of LSC compared to control cohorts or to Ven/HMA alone (p = 0.02 and p=0.003, respectively).In order to better understand how the augmented AML mobilization improves the efficacy of AML therapy, BM cells from PDX mice treated for 2 weeks with GMI-1271, GMI-1359, Ven/HMA, and their combinations were analyzed by single-cell proteomics (CyTOF). Blockade of E-selectin alone or dual E-selectin/CXCR4 inhibition in combination with Ven/HMA diminished levels of E-selectin ligand, mTOR, pFAK, pRb, cMyc, while increasing p21 and cleaved caspase3, which was associated with significant reduction of BM-resident LSC compared to Ven/HMA alone (CD45+34+CD38-CD123+, p= 0.03). AML blasts from the BM of the combinatorial treatment groups showed altered signaling including decreased Ki67, pRb, pNFkB, pPI3K, and E-selectin ligand, and increased levels of cleaved caspase 3. We further found that Ven/HMA significantly diminished CD31+ EC in the BM compared to control cohorts (p= 0.009). However, pharmacological antagonists of E-selectin or E-selectin/CXCR4 protected EC from Ven/HMA-induced detrimental insults through upregulation of survival signaling cascades including pAKT, pERK, pMAPK and decreased eNOS expression in EC compared to Ven/HMA treatment alone. Both EC and MSC were protected by dual inhibition of E-selectin/CXCR4 with GMI-1359. We also observed upregulated pro-survival signaling pathways such as phosphorylation of AKT-MAPK-ERK along with increased Bcl-xL, Bcl-2, and Idu expression in MSC from the GMI-1359 + Ven/HMA treated PDX mice compared to Ven/HMA single treatment cohorts.Collectively, our results provide strong evidence that co-targeting E-selectin/CXCR4 with GMI-1359 profoundly reduces BM retention of LSC as well as protects BM niche component cells from apoptosis induced by targeted therapy, resulting in improving the anti-leukemia activity of Ven/HMA therapy in AML. [Display omitted] DisclosuresFogler: GlycoMimetics Inc.: Current Employment, Current equity holder in publicly-traded company, Patents & Royalties. Magnani: GlycoMimetics Inc.: Current Employment, Current equity holder in publicly-traded company, Patents & Royalties. Carter: Ascentage: Research Funding; Syndax: Research Funding. Andreeff: Oxford Biomedica UK: Research Funding; ONO Pharmaceuticals: Research Funding; AstraZeneca: Research Funding; Reata, Aptose, Eutropics, SentiBio; Chimerix, Oncolyze: Current holder of individual stocks in a privately-held company; Karyopharm: Research Funding; Breast Cancer Research Foundation: Research Funding; Syndax: Consultancy; Daiichi-Sankyo: Consultancy, Research Funding; Novartis, Cancer UK; Leukemia & Lymphoma Society (LLS), German Research Council; NCI-RDCRN (Rare Disease Clin Network), CLL Foundation; Novartis: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding; Aptose: Consultancy; Glycomimetics: Consultancy; Medicxi: Consultancy; Senti-Bio: Consultancy.

Investigating the Addition of Ianalumab (VAY736) to Ibrutinib in Patients with Chronic Lymphocytic Leukemia (CLL) on Ibrutinib Therapy: Results from a Phase Ib Study

Investigating the Addition of Ianalumab (VAY736) to Ibrutinib in Patients with Chronic Lymphocytic Leukemia (CLL) on Ibrutinib Therapy: Results from a Phase Ib Study

FLT3 Inhibitors Upregulate CXCR4 and E-Selectin Ligands and CD44 Via ERK Suppression in AML Cells, and Blockade of CXCR4 and E-Selectin Signaling with GMI-1359 Overcomes AML Resistance to Quizartinib in Vitro and In Vivo

FLT3 Inhibitors Upregulate CXCR4 and E-Selectin Ligands and CD44 Via ERK Suppression in AML Cells, and Blockade of CXCR4 and E-Selectin Signaling with GMI-1359 Overcomes AML Resistance to Quizartinib in Vitro and In Vivo

Mdm2 Maintains Cholesterol Biosynthesis in Hematopoietic Stem/Progenitor Cells Independent of p53

Background: The Mdm2 protein is an E3 ubiquitin ligase that directly interacts with p53 protein leading to its degradation. The expression of MDM2 is controlled by p53 activity through an autoregulatory feedback loop. In addition, a single nucleotide polymorphism (SNP) in the MDM2 promoter modulates its expression and is associated with the risk of cancer. Emerging evidence emphasizes the metabolic activities of MDM2 to be essential for the maintenance of cellular homeostasis. We hypothesized that MDM2 maintains the metabolic homeostasis of hematopoietic stem cells (HSCs) and its downregulation in TP53-mutant leukemias leads to metabolic vulnerabilities independent of p53. Investigation of the metabolic role of MDM2 in hematopoietic stem cells can provide valuable insight into the pathology of TP53 mutant leukemias.Methods: To understand the function of Mdm2 in HSCs, we generated a conditional mouse model driven by Vav-Cre to genetically label and trace the fate of HSCs after heterozygous deletion of Mdm2 in early development and adult bone marrow. We utilized fluorescence microscopy, flow cytometry, apoptosis assays and RNA-seq to functionally characterize the fate of HSCs after heterozygous deletion of Mdm2. Using Trp53 floxed allele and a new Trp53 mutant allele that switches from wildtype to Trp53R172H mutant, we deleted and/or mutated Trp53 gene concomitantly in Mdm2 haplo-insufficient HSCs. Additionally, MDM2 copy number as well as MDM2 SNP309 status were determined in 95 samples from p53 mutant AML patients and 24 controls.Results: Heterozygous deletion of Mdm2 in hematopoietic stem cells (Vav-Cre;mTmG;Mdm2 fl/+) resulted in massive apoptosis of emerging hematopoietic progenitor cells in the aorta-gonad-mesonephros (AGM) region at E11.5. Strikingly, hematopoietic cells residing in fetal liver displayed minimal apoptosis evident by a few TUNEL positive cells. Colony forming assays revealed a myeloid biased hematopoiesis in Mdm2 haplo-insufficient HSCs. Vav-Cre;Mdm2 fl/+ mice displayed a marked reduction in Lin -/CD150 +/c-Kit +/Sca-1 + HSCs cells and significant decrease in peripheral blood counts. Deletion of Trp53 in these mice (Vav-Cre;Trp53 fl/fl;Mdm2 fl/+) resulted in marked decrease in CD19+ B lymphocytes cells whereas the population of CD11b+ myeloid cells did not change. The population of Lin neg-c-Kit + hematopoietic stem/progenitor cells isolated from the bone marrow of Vav-Cre;Mdm2 fl/+ mice displayed marked downregulation of cholesterol biosynthesis and mevalonate pathway (-log2 pvalue=20). Strikingly, 85% of genes involved in cholesterol biosynthesis (29 genes) were downregulated in Vav-Cre;Mdm2 fl/+ mice. Homozygous deletion of Trp53 in Vav-Cre;Mdm2 fl/+ mice did not rescue the metabolic alterations driven by Mdm2 haplo-insufficiency. In addition, the gene signature of oxidative phosphorylation(oxphos), was remarkably upregulated in Vav-Cre;Mdm2 fl/+ mice independent of p53. We further demonstrate that Cre-mediated induction of a Trp53R172 mutation in Mdm2 haplo-insufficient mice resulted in malignant transformation of HSCs leading to acute myeloid leukemia (AML). Of note, mice with homozygote Trp53 mutation and/or deletion without Mdm2- haplo-insufficiency developed lymphoma and not leukemia. In human, MDM2 loss of heterozygosity (MDM2 LOH) in AML was always concomitant with TP53 missense mutations (log2 odds ratio>3, p<.001), and not TP53 deletions or truncations whereas in lymphomas, MDM2 LOH and TP53 mutations were mutually exclusive.Conclusion: Using a genetic model, we have shown that Mdm2 haplo-insufficiency in HSCs leads to apoptosis and clonal selection towards myeloid biased hematopoiesis. Mechanistically, Mdm2 haplo-insufficiency resulted in a metabolic switch from cholesterol biosynthesis to oxphos in HSCs. Notably, this metabolic reprograming is not rescued by deletion of Trp53. However, mutation of Trp53 in Mdm2 haplo-insufficient hematopoietic stem cells resulted in leukemic transformation of HSCs leading to acute myeloid leukemia. Lastly, we demonstrate that MDM2 SNP309 is associated with TP53 mutation in AML and provide clinical evidence that MDM2 loss of heterozygosity is concomitant with TP53 mutations in AML with lower survival compared to TP53 mutant patients with diploid MDM2. Our findings demonstrate a p53-independent role for Mdm2 in metabolic maintenance of hematopoietic stem/progenitor cells. [Display omitted] DisclosuresKhoury: Kiromic: Research Funding; Angle: Research Funding; Stemline Therapeutics: Research Funding. Andreeff: Glycomimetics: Consultancy; Medicxi: Consultancy; Karyopharm: Research Funding; ONO Pharmaceuticals: Research Funding; Senti-Bio: Consultancy; Reata, Aptose, Eutropics, SentiBio; Chimerix, Oncolyze: Current holder of individual stocks in a privately-held company; Syndax: Consultancy; Amgen: Research Funding; Daiichi-Sankyo: Consultancy, Research Funding; Breast Cancer Research Foundation: Research Funding; Novartis, Cancer UK; Leukemia & Lymphoma Society (LLS), German Research Council; NCI-RDCRN (Rare Disease Clin Network), CLL Foundation; Novartis: Membership on an entity's Board of Directors or advisory committees; Oxford Biomedica UK: Research Funding; AstraZeneca: Research Funding; Aptose: Consultancy.

Co-Targeting Intrinsic and Extrinsic Apoptosis to Maximize Cell Death Induction in Venetoclax-Resistant AML Cells

Bcl-2 family protein-regulated intrinsic and IAP-family protein-regulated extrinsic pathways are two major apoptotic cell death mechanisms. Components of both pathways are regulated by the tumor suppressor p53. Although combinations of Bcl-2 inhibitor venetoclax (VEN) and a hypomethylating agent induce high response rates in AML, most patients ultimately relapse. In addition, pre-clinical and clinical studies have shown that TP53-mutant AML cells are less sensitive to VEN (Carter BZ, ASH 2019 and 2020; DiNardo CD, Blood 2020). We investigated if simultaneous inhibition of Bcl-2 and IAPs and activation of p53, via MDM2 inhibition could maximize apoptosis induction in AML cells with acquired resistance to VEN-based therapy or in those carrying TP53 mutations.We treated MV4-11 cells with acquired resistance to VEN (VEN-R) with the Bcl-2 inhibitor APG2575, IAP inhibitor APG1387, or MDM2 inhibitor APG115, and with their combinations. As expected, VEN-R cells were more resistant to APG2575 compared to control cells. APG1387 alone had limited activity in both VEN-R and in control cells and the combination of APG2575 and APG1387 enhanced cell killing (P < 0.05 compared to each single agent). APG115 was active in both VEN-R and control cells and its activity was only increased by APG2575 in the control cells, but minimally affected by either APG2575 or APG1387 in VEN-R cells. However, maximal apoptosis induction was observed in both VEN-R and control cells when all three compounds were combined (P < 0.05 compared to any of the double combinations or single agent treatments).We next treated NSG mice harboring PDX cells derived from an AML patient who relapsed on the VEN/decitabine therapy with APG2575 (50 mg/kg, p.o., daily), APG1387 (10 mg/kg, i.v., once/wk), APG115 (50 mg/kg, p.o., daily at wk 1 and 5), or combinations. At the end of a 5-wk treatment, significant reductions of human CD45 + cells were observed in all treatment groups. At 4 wks post treatment, decreased circulating leukemia cells were found in the triple and APG115+APG2575 combination groups. APG115 (139 d, p=0.009), APG1387 (130 d, p=0.004), or APG2575 (132 d, p=0.004) significantly extended mouse survival compared to controls (116 d). Among two drug combinations, APG115 plus APG1387 did not further prolong survival, APG2575 plus APG1387 (144 d, p<0.01) was more effective, and APG2575 plus APG115 (180 d, p<0.01) most effectively extended survival compared to each drug alone. Triple combination treated mice lived longest (185 d), which was significantly longer than APG115 plus APG1387 and APG2575 plus APG1387 but did not reach statistical significance compared to APG2575 plus APG115. Data showed that triple and APG115+APG2575 combinations were most effective, followed by APG2575+APG1387, then APG115+APG1387, APG2575, or APG115, and finally APG1387.Finally, we treated Molm13 cells lacking TP53 or carrying TP53 mutations (R248W/R213*, R248Q, R175H, R282W, Y220C) with the three agents and their combinations. All mutant cells were insensitive to single drugs. Enhanced activity was observed when any of two agents were combined and combined inhibition of Bcl-2, IAPs, and MDM2 most effectively induced cell death in TP53 knockout and all TP53 mutant cells (P < 0.05 for the triple combination compared to any of the double combinations or single agent treatments, and double combinations compared to their respective single agent treatments). Western blot analysis showed that decreased cIAP1, cIAP2, XIAP, or p21 was observed in single agent or combination-treated cells. Only in the triple combination group, cIAP1, cIAP2, and XIAP as well as MDM2 were largely diminished and p21 was marked decreased.In conclusion, our study demonstrates that co-targeting intrinsic and extrinsic apoptosis maximizes cell death induction in AML cells with acquired resistance to VEN or with TP53 deletion/mutations by antagonizing Bcl-2, eliminating cIAPs and XIAP, as well as MDM2 and p21, a finding that needs to be validated clinically. DisclosuresCarter: Syndax: Research Funding; Ascentage: Research Funding. Zhai: Ascentage Pharma Group Inc.: Current Employment, Current equity holder in publicly-traded company, Other: Leadership and other ownership interests, Patents & Royalties, Research Funding; Ascentage Pharma (Suzhou) Co., Ltd.: Current Employment, Current equity holder in publicly-traded company, Other: Leadership and other ownership interests, Patents & Royalties, Research Funding. Yang: Ascentage Pharma (Suzhou) Co., Ltd.: Current Employment, Current equity holder in publicly-traded company, Other: Leadership and other ownership interests, Patents & Royalties, Research Funding. Andreeff: Reata, Aptose, Eutropics, SentiBio; Chimerix, Oncolyze: Current holder of individual stocks in a privately-held company; Karyopharm: Research Funding; Oxford Biomedica UK: Research Funding; AstraZeneca: Research Funding; Syndax: Consultancy; Daiichi-Sankyo: Consultancy, Research Funding; Breast Cancer Research Foundation: Research Funding; Glycomimetics: Consultancy; Senti-Bio: Consultancy; Aptose: Consultancy; ONO Pharmaceuticals: Research Funding; Amgen: Research Funding; Medicxi: Consultancy; Novartis, Cancer UK; Leukemia & Lymphoma Society (LLS), German Research Council; NCI-RDCRN (Rare Disease Clin Network), CLL Foundation; Novartis: Membership on an entity's Board of Directors or advisory committees.

Phase II Study of Venetoclax Added to Cladribine (CLAD) and Low Dose AraC (LDAC) Alternating with 5-Azacytidine (AZA) in Older and Unfit Patients with Newly Diagnosed Acute Myeloid Leukemia (AML)

Phase II Study of Venetoclax Added to Cladribine (CLAD) and Low Dose AraC (LDAC) Alternating with 5-Azacytidine (AZA) in Older and Unfit Patients with Newly Diagnosed Acute Myeloid Leukemia (AML)