Venetoclax combines synergistically with FLT3 inhibition to effectively target leukemic cells in FLT3-ITD+ acute myeloid leukemia models

Proteomic and phosphoproteomic measurements enhance ability to predict ex vivo drug response in AML

Acute Myeloid Leukemia (AML) affects 20,000 patients in the US annually with a five-year survival rate of approximately 25%. One reason for the low survival rate is the high prevalence of clonal evolution that gives rise to heterogeneous sub-populations of leukemic cells with diverse mutation spectra, which eventually leads to disease relapse. This genetic heterogeneity drives the activation of complex signaling pathways that is reflected at the protein level. This diversity makes it difficult to treat AML with targeted therapy, requiring custom patient treatment protocols tailored to each individual's leukemia. Toward this end, the Beat AML research program prospectively collected genomic and transcriptomic data from over 1000 AML patients and carried out ex vivo drug sensitivity assays to identify genomic signatures that could predict patient-specific drug responses. However, there are inherent weaknesses in using only genetic and transcriptomic measurements as surrogates of drug response, particularly the absence of direct information about phosphorylation-mediated signal transduction. As a member of the Clinical Proteomic Tumor Analysis Consortium, we have extended the molecular characterization of this cohort by collecting proteomic and phosphoproteomic measurements from a subset of these patient samples (38 in total) to evaluate the hypothesis that proteomic signatures can improve the ability to predict response to 26 drugs in AML ex vivo samples. In this work we describe our systematic, multi-omic approach to evaluate proteomic signatures of drug response and compare protein levels to other markers of drug response such as mutational patterns. We explore the nuances of this approach using two drugs that target key pathways activated in AML: quizartinib (FLT3) and trametinib (Ras/MEK), and show how patient-derived signatures can be interpreted biologically and validated in cell lines. In conclusion, this pilot study demonstrates strong promise for proteomics-based patient stratification to assess drug sensitivity in AML.

Impact of FLT3 Mutation on Outcomes after Venetoclax and Azacitidine for Patients with Treatment-Naïve Acute Myeloid Leukemia

PURPOSE

To evaluate efficacy and safety of venetoclax + azacitidine among treatment-naïve patients with FLT3-mutant acute myeloid leukemia.

PATIENTS AND METHODS

Data were pooled from patients enrolled in a phase III study (NCT02993523) that compared patients treated with venetoclax + azacitidine or placebo + azacitidine and a prior phase Ib study (NCT02203773) where patients were treated with venetoclax + azacitidine. Enrolled patients were ineligible for intensive therapy due to age ≥75 years and/or comorbidities. Patients on venetoclax + azacitidine received venetoclax 400 mg orally (days 1-28) and azacitidine (75 mg/m2; days 1-7/28-day cycle). FLT3 mutation was analyzed centrally on pretreatment bone marrow aspirates.

RESULTS

In the biomarker evaluable population, FLT3 mutation was detected in 42 (15%) and 22 (19%) patients in the venetoclax + azacitidine and azacitidine groups. Composite complete remission [CRc; complete remission (CR) + CR with incomplete hematologic recovery (CRi)] rates (venetoclax + azacitidine/azacitidine) for FLT3-mutant patients were 67%/36%, median duration of remission (DoR) was 17.3/5.0 months, and median OS was 12.5/8.6 months. The CRc rates among FLT3 wild-type patients were 67%/25%, median DoR 18.4/13.4 months, and median OS 14.7/10.1 months. In patients treated with venetoclax + azacitidine, CRc in patients with FLT3-ITD and FLT3-TKD was 63% and 77% and median OS was 9.9 and 19.2 months, and in comutated FLT3-ITD + NPM1 patients, CRc was 70%, median DoR was not reached, and median OS was 9.1 months. There were no unexpected toxicities in the venetoclax + azacitidine group.

CONCLUSIONS

When treated with venetoclax + azacitidine, patients with FLT3 mutations and FLT3 wild-type had similar outcomes. Future analyses in larger patient populations may further define the impact of venetoclax + azacitidine in patients harboring FLT3-ITD. See related commentary by Perl and Vyas, p. 2719.

Resistance to targeted therapies: delving into FLT3 and IDH

Recent advances in FLT3 and IDH targeted inhibition have improved response rates and overall survival in patients with mutations affecting these respective proteins. Despite this success, resistance mechanisms have arisen including mutations that disrupt inhibitor-target interaction, mutations impacting alternate pathways, and changes in the microenvironment. Here we review the role of these proteins in leukemogenesis, their respective inhibitors, mechanisms of resistance, and briefly ongoing studies aimed at overcoming resistance.

Outcomes following venetoclax-based treatment in therapy-related myeloid neoplasms

Therapy‐related myeloid neoplasms (t‐MN) are aggressive malignancies in need of effective therapies. The BCL‐2 inhibitor venetoclax represents a paradigm shift in the treatment of acute myeloid leukemia. However, the effectiveness of venetoclax has not been studied in a large cohort of t‐MN. We retrospectively analyzed 378 t‐MN patients, of which 96 (25.4%, 47 therapy‐related acute myeloid leukemia, 1 therapy‐related chronic myelomonocytic leukemia, 48 therapy‐related myelodysplastic syndrome) received venetoclax. Median interval from t‐MN to venetoclax initiation was 2.9 (Interquartile range [IQR] 0.7–12) months, and patients received a median of 3 (IQR 1–4) cycles. The composite complete remission (CRc) rate, median progression‐free survival (PFS), and overall survival (OS) were 39.1%, 4.9 months, and 7 months, respectively. The upfront use of venetoclax and achieving CRc were associated with improved survival, whereas the presence of Chromosome 7 abnormalities was associated with an inferior survival. Neither the TP53‐status nor the percent bone marrow blast predicted the likelihood of CRc or survival. Paired genetic analysis performed at venetoclax initiation and failure did not show the evidence of the selection of the TP53‐mutated clone. In a propensity‐matched analysis, the use of venetoclax‐based regimen as the first‐line therapy was associated with a superior survival compared to hypomethylating agent (HMA)‐based first‐line therapy (9.4 vs. 6.1 months, p = .01). We conclude that the upfront use of venetoclax with HMA improved survival, though PFS and OS remain poor. As the phenotype at diagnosis or the percent blasts did not predict outcomes, venetoclax should be studied in all t‐MN phenotypes.

Venetoclax resistance: mechanistic insights and future strategies

Acute myeloid leukemia (AML) is historically associated with poor prognosis, especially in older AML patients unfit for intensive chemotherapy. The development of Venetoclax, a potent oral BH3 (BCL-2 homology domain 3) mimetic, has transformed the AML treatment. However, the short duration of response and development of resistance remain major concerns. Understanding mechanisms of resistance is pivotal to devising new strategies and designing rational drug combination regimens. In this review, we will provide a comprehensive summary of the known mechanisms of resistance to Venetoclax and discuss Venetoclax-based combination therapies. Key contributing factors to Venetoclax resistance include dependencies on alternative anti-apoptotic BCL-2 family proteins and selection of the activating kinase mutations. Mutational landscape governing response to Venetoclax and strategic approaches developed considering current knowledge of mechanisms of resistance will be addressed.

Hypomethylating agent and venetoclax with FLT3 inhibitor "triplet" therapy in older/unfit patients with FLT3 mutated AML

In older/unfit newly diagnosed patients with FLT3 mutated acute myeloid leukemia (AML), lower intensity chemotherapy (LIC) in combination with either a FLT3 inhibitor or with venetoclax results in poor overall survival (median 8 to 12.5 months). We performed a retrospective analysis of 87 newly diagnosed FLT3 mutated AML patients treated on triplet (LIC + FLT3 inhibitor + Venetoclax, [N = 27]) and doublet (LIC + FLT3 inhibitor, [N = 60]) regimens at our institution. Data were collected from prospective clinical trials in 75% (N = 65) and 25% (N = 22) who received the same treatment regimens outside of a clinical trial. Triplet therapy was associated with significantly higher rates of complete remission (CR) (67% versus 32%, P = 0.002), CR/CRi (93% versus 70%, P = 0.02), FLT3-PCR negativity (96% versus 54%, P < 0.01), and flow-cytometry negativity (83% versus 38%, P < 0.01) than doublets. At the end of the first cycle, the median time to ANC > 0.5 (40 versus 21 days, P = 0.15) and platelet > 50 K (29 versus 25 days, P = 0.6) among responders was numerically longer with triplets, but 60-day mortality was similar (7% v 10%). With a median follow-up of 24 months (median 12 months for triplet arm, and 63 months for doublet arm), patients receiving a triplet regimen had a longer median overall survival (not reached versus 9.5 months, P < 0.01). LIC combined with FLT3 inhibitor and venetoclax (triplet) may be an effective frontline regimen for older/unfit FLT3 mutated AML that should be further validated prospectively.

Refining AML Treatment: The Role of Genetics in Response and Resistance Evaluation to New Agents

Simple Summary

Acute myeloid leukemia (AML) is an aggressive cancer of the hematopoietic system. At present, we know that AML is heterogeneous and varies from one patient to another, often characterized by specific changes in the DNA (mutations). Likewise, we know that the mutational landscape of the disease predicts its response to certain therapies and that it can change under the influence of therapy. Since 2017, the number of potential drugs intended to treat AML has substantially increased and so has our knowledge about the role of certain mutations in the prediction of disease response, relapse and resistance. In this article, we review the current state of knowledge of genetic aberrations with respect to clinical decision making.

Abstract

The number of treatment options for acute myeloid leukemia (AML) has greatly increased since 2017. This development is paralleled by the broad implantation of genetic profiling as an integral part of clinical studies, enabling us to characterize mutation–response, mutation–non-response, or mutation–relapse patterns. The aim of this review is to provide a concise overview of the current state of knowledge with respect to newly approved AML treatment options and the association of response, relapse and resistance with genetic alterations. Specifically, we will highlight current genetic data regarding FLT3 inhibitors, IDH inhibitors, hypomethylating agents (HMA), the BCL-2 inhibitor venetoclax (VEN), the anti-CD33 antibody conjugate gemtuzumab ozogamicin (GO) and the liposomal dual drug CPX-351.

Which FLT3 Inhibitor for Treatment of AML?

OPINION STATEMENT

Treatment options in acute myeloid leukemia (AML) have improved significantly over the last decade with better understanding of disease biology and availability of a multitude of targeted therapies. The use of FLT3 inhibitors (FLT3i) in FLT3-mutated (FLT3^mut) AML is one such development; however, the clinical decisions that govern their use and dictate the choice of the FLT3i are evolving. Midostaurin and gilteritinib are FDA-approved in specific situations; however, available data from clinical trials also shed light on the utility of sorafenib maintenance post-allogeneic stem cell transplantation (allo-SCT) and quizartinib as part of combination therapy in FLT3^mut AML. The knowledge of the patient's concurrent myeloid mutations, type of FLT3 mutation, prior FLT3i use, and eligibility for allo-SCT helps to refine the choice of FLT3i. Data from ongoing studies will further precisely define their use and help in making more informed choices. Despite improvements in FLT3i therapy, the definitive aim is to enable the eligible patient with FLT3^mut AML (esp. ITD) to proceed to allo-SCT with regimens containing FLT3i incorporated prior to SCT and as maintenance after SCT.

Translating recent advances in the pathogenesis of acute myeloid leukemia to the clinic

Despite FDA approval of nine new drugs for patients with acute myeloid leukemia (AML) in the United States over the last 4 years, AML remains a major area of unmet medical need among hematologic malignancies. In this review, we discuss the development of promising new molecular targeted approaches for AML, including menin inhibition, novel IDH1/2 inhibitors, and preclinical means to target TET2, ASXL1, and RNA splicing factor mutations. In addition, we review progress in immune targeting of AML through anti-CD47, anti-SIRPα, and anti-TIM-3 antibodies; bispecific and trispecific antibodies; and new cellular therapies in development for AML.

SOHO State of the Art Updates and Next Questions:Harnessing Apoptosis in AML

The treatment landscape for acute myeloid leukemia has expanded significantly in the past 5 years with the approval of several therapeutic small molecules. While agents such as FLT3 inhibitors and IDH inhibitors are restricted for patients with specific mutations, the selective BCL-2 inhibitor venetoclax combined with a hypomethylating agent or low-dose cytarabine was approved after demonstrating frontline efficacy across a molecularly heterogenous group of patients. Currently, venetoclax is being investigated in combination with multiple other therapies as the role of the intrinsic apoptotic pathway in acute myeloid leukemia continues to be explored.

Venetoclax combination therapy in acute myeloid leukemia and myelodysplastic syndromes

PURPOSE OF REVIEW

Venetoclax is a BCL-2 inhibitor that was approved in combination therapy with hypomethylating agents or low dose cytarabine for newly diagnosed acute myeloid leukemia (AML). The purpose of this review is to outline the most recent venetoclax-based combination therapies in newly diagnosed or relapsed myelodysplastic syndrome (MDS) and AML patients.

RECENT FINDING

Venetoclax has been incorporated in various therapeutic regimens - either with chemotherapy, immunotherapy or targeted therapies. These combinations achieve high remission rates with deep molecular responses, as suggested by measurable residual disease measurements. There are concerns regarding the incomplete count recovery, prolonged cytopenia and infection rates, especially when combined with chemotherapy. There is also limited data concerning durability of these remissions, and the effectiveness in high-risk population (i.e. p53-mutated AML patients).

SUMMARY

Venetoclax-based combination therapies encompass novel therapeutic possibilities in MDS and AML with encouraging initial results. However, the exact role of each combination therapy and the long-term effects on patients' outcome are yet to be defined.

A review of FLT3 inhibitors in acute myeloid leukemia

FLT3 mutations are the most common genetic aberrations found in acute myeloid leukemia (AML) and associated with poor prognosis. Since the discovery of FLT3 mutations and their prognostic implications, multiple FLT3-targeted molecules have been evaluated. Midostaurin is approved in the U.S. and Europe for newly diagnosed FLT3 mutated AML in combination with standard induction and consolidation chemotherapy based on data from the RATIFY study. Gilteritinib is approved for relapsed or refractory FLT3 mutated AML as monotherapy based on the ADMIRAL study. Although significant progress has been made in the treatment of AML with FLT3-targeting, many challenges remain. Several drug resistance mechanisms have been identified, including clonal selection, stromal protection, FLT3-associated mutations, and off-target mutations. The benefit of FLT3 inhibitor maintenance therapy, either post-chemotherapy or post-transplant, remains controversial, although several studies are ongoing.

Exploring the Metabolic Landscape of AML: From Haematopoietic Stem Cells to Myeloblasts and Leukaemic Stem Cells

Despite intensive chemotherapy regimens, up to 60% of adults with acute myeloid leukaemia (AML) will relapse and eventually succumb to their disease. Recent studies suggest that leukaemic stem cells (LSCs) drive AML relapse by residing in the bone marrow niche and adapting their metabolic profile. Metabolic adaptation and LSC plasticity are novel hallmarks of leukemogenesis that provide important biological processes required for tumour initiation, progression and therapeutic responses. These findings highlight the importance of targeting metabolic pathways in leukaemia biology which might serve as the Achilles' heel for the treatment of AML relapse. In this review, we highlight the metabolic differences between normal haematopoietic cells, bulk AML cells and LSCs. Specifically, we focus on four major metabolic pathways dysregulated in AML; (i) glycolysis; (ii) mitochondrial metabolism; (iii) amino acid metabolism; and (iv) lipid metabolism. We then outline established and emerging drug interventions that exploit metabolic dependencies of leukaemic cells in the treatment of AML. The metabolic signature of AML cells alters during different biological conditions such as chemotherapy and quiescence. Therefore, targeting the metabolic vulnerabilities of these cells might selectively eradicate them and improve the overall survival of patients with AML.

Emerging Targeted Therapy for Specific Genomic Abnormalities in Acute Myeloid Leukemia

We describe recent updates of existing molecular-targeting agents and emerging novel gene-specific strategies. FLT3 and IDH inhibitors are being tested in combination with conventional chemotherapy for both medically fit patients and patients who are ineligible for intensive therapy. FLT3 inhibitors combined with non-cytotoxic agents, such as BCL-2 inhibitors, have potential therapeutic applicability. The menin-MLL complex pathway is an emerging therapeutic target. The pathway accounts for the leukemogenesis in AML with MLL-rearrangement, NPM1 mutation, and NUP98 fusion genes. Potent menin-MLL inhibitors have demonstrated promising anti-leukemic effects in preclinical studies. The downstream signaling molecule SYK represents an additional target. However, the TP53 mutation continues to remain a challenge. While the p53 stabilizer APR-246 in combination with azacitidine failed to show superiority compared to azacitidine monotherapy in a phase 3 trial, next-generation p53 stabilizers are now under development. Among a number of non-canonical approaches to TP53-mutated AML, the anti-CD47 antibody magrolimab in combination with azacitidine showed promising results in a phase 1b trial. Further, the efficacy was somewhat better in patients with the TP53 mutation. Although clinical evidence has not been accumulated sufficiently, targeting activating KIT mutations and RAS pathway-related molecules can be a future therapeutic strategy.

Inhibition of BCL2A1 by STAT5 inactivation overcomes resistance to targeted therapies of FLT3-ITD/D835 mutant AML

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BCL2A1 is upregulated and exerts a pro-survival function in FLT3-ITD/D835 AML cells.

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Upregulation of BCL2A1 attenuates sensitivity to quizartinib in FLT3-ITD/D835 cells.

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Gilteritinib decreases BCL2A1 through inactivation of STAT5 in FLT3-ITD/D835 cells.

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Gilteritinib/Venetoclax has a synergistic anti-tumor activity in FLT3-ITD/D835 cells.

Tyrosine kinase inhibitors (TKIs) are established drugs in the therapy of FLT3-ITD mutated acute myeloid leukemia (AML). However, acquired mutations, such as D835 in the tyrosine kinase domain (FLT3-ITD/D835), can induce resistance to TKIs. A cap analysis gene expression (CAGE) technology revealed that the gene expression of BCL2A1 transcription start sites was increased in primary AML cells bearing FLT3-ITD/D835 compared to FLT3-ITD. Overexpression of BCL2A1 attenuated the sensitivity to quizartinib, a type II TKI, and venetoclax, a selective BCL2 inhibitor, in AML cell lines. However, a type I TKI, gilteritinib, inhibited the expression of BCL2A1 through inactivation of STAT5 and alleviated TKI resistance of FLT3-ITD/D835. The combination of gilteritinib and venetoclax showed synergistic effects in the FLT3-ITD/D835 positive AML cells. The promoter region of BCL2A1 contains a BRD4 binding site. Thus, the blockade of BRD4 with a BET inhibitor (CPI-0610) downregulated BCL2A1 in FLT3-mutated AML cells and extended profound suppression of FLT3-ITD/D835 mutant cells. Therefore, we propose that BCL2A1 has the potential to be a novel therapeutic target in treating FLT3-ITD/D835 mutated AML.

Rapid and Efficient Response to Gilteritinib and Venetoclax-Based Therapy in Two AML Patients with FLT3-ITD Mutation Unresponsive to Venetoclax Plus Azacitidine

The presence of FLT3-ITD mutation is associated with relapse and poor survival in AML patients. Venetoclax combined with hypomethylating agents (VEN+HMA) was approved for the frontline treatment of elderly or unfit AML patients, which leads to noteworthy impacts on AML management. The combination therapy is associated with encouraging efficacy in FLT3-mutated AML among both newly diagnosed unfit and relapsed/refractory patients. However, we found that two AML patients with FLT3-ITD mutation did not respond to venetoclax plus azacitidine (VEN+AZA). Given that the combined efficacy of venetoclax and the FLT3 inhibitor has been proved in pre-clinical models of FLT3+ AML, it is a scientific rationale to investigate venetoclax combined with the FLT3 inhibitor in AML patients with FLT3-ITD mutation. This is the first report of assessing the safety and response of gilteritinib (the first and only targeted second-generation FLT3 tyrosine kinase inhibitor approved by the US FDA) and venetoclax-based therapy in two AML patients with FLT3-ITD mutation unresponsive to VEN+AZA, which may bring new hope to FLT3 mutated patients who are unresponsive to VEN+HMA.

Clinical experience with venetoclax in patients with newly diagnosed, relapsed, or refractory acute myeloid leukemia

Background

Diagnosis of acute myeloid leukemia (AML) is associated with poor outcome in elderly and unfit patients. Recently, approval of the BCL-2 inhibitor venetoclax (VEN) in combination with hypo-methylating agents (HMA) led to a significant improvement of response rates and survival. Further, application in the relapsed or refractory (r/r) AML setting or in context of allogeneic stem cell transplantation (alloHSCT) seems feasible.

Methods and patients

Fifty-six consecutive adult AML patients on VEN from January 2019 to June 2021 were analyzed retrospectively. Patients received VEN either as first-line treatment, as subsequent therapy (r/r AML excluding prior alloHSCT), or at relapse after alloHSCT. VEN was administered orally in 28-day cycles either combined with HMA or low-dose cytarabine (LDAC).

Results

After a median follow-up of 11.5 (range 6.1–22.3) months, median overall survival (OS) from start of VEN treatment was 13.3 (2.2–20.5) months, 5.0 (0.8–24.3) months and 4.0 (1.5–22.1) months for first-line, subsequent line treatment and at relapse post-alloHSCT, respectively. Median OS was 11.5 (10–22.3) months from start of VEN when subsequent alloHSCT was carried out. Relapse-free survival (RFS) for the total cohort was 10.2 (2.2 – 24.3) months. Overall response rate (composite complete remission + partial remission) was 51.8% for the total cohort (61.1% for VEN first-line treatment, 52.2% for subsequent line and 42.8% at relapse post-alloHSCT). Subgroup analysis revealed a significantly reduced median OS in FLT3-ITD mutated AML with 3.4 (1.9–4.9) months versus 10.4 (0.8–24.3) months for non-mutated cases, (HR 4.45, 95% CI 0.89–22.13, p = 0.0002). Patients harboring NPM1 or IDH1/2 mutations lacking co-occurrence of FLT3-ITD showed a survival advantage over patients without those mutations (11.2 (5–24.3) months versus 5.0 (0.8–22.1) months, respectively, (HR 0.53, 95% CI 0.23 – 1.21, p = 0.131). Multivariate analysis revealed mutated NPM1 as a significant prognostic variable for achieving complete remission (CR) (HR 19.14, 95% CI 2.30 – 436.2, p < 0.05). The most common adverse events were hematological, with grade 3 and 4 neutropenia and thrombocytopenia reported in 44.6% and 14.5% of patients, respectively.

Conclusion

Detailed analyses on efficacy for common clinical scenarios, such as first-line treatment, subsequent therapy (r/r AML), and application prior to and post-alloHSCT, are presented. The findings suggest VEN treatment combinations efficacious not only in first-line setting but also in r/r AML. Furthermore, VEN might play a role in a subgroup of patients with failure to conventional chemotherapy as a salvage regimen aiming for potential curative alloHSCT.

Venetoclax enhances NK cell killing sensitivity of AML cells through the NKG2D/NKG2DL activation pathway

BACKGROUND

Venetoclax, a selective B-cell lymphoma-2 (BCL2) inhibitor, has a potential therapeutic effect when combined with demethylating agents in the first-line setting of unfit elderly patients with acute myeloid leukaemia (AML); however, efficacy is still limited in refractory/recurrent AML. Therefore, exploration of a suitable novel treatment scheme is urgently needed.However, combining venetoclax with NK cell-based immunotherapy has not been studied.

METHODS

The cytotoxicity of NK cell combined with venetoclax was assessed in vitro using flow cytometry. Venetoclax-induced natural killer group 2 member D (NKG2D) ligand (NKG2DL) expression was detected by flow cytometry and western blotting. Mechanisms underlying venetoclax-induced NKG2DL expression were found by GSE127200 analysis and investigated using real-time PCR (Q-PCR) and western blotting.

RESULTS

Flow cytometric analysis showed that combining venetoclax with NK cells produced synergistic anti-leukaemia effects similar to those of venetoclax + azacitidine. Venetoclax could render AML cell lines and primary AML cells sensitive to NK cell killing by promoting NK cell degranulation, NK-AML cell recognition and NK cell secretion of interferon (IFN)-γ and granzyme B. The synergistic effect resulted from venetoclax-induced NKG2DL upregulation in AML cells and could be undermined by blocking NKG2D on NK cells. This finding suggests that venetoclax enhances NK cell killing activity by activating the NKG2D/NKG2DL ligand-receptor pathway. Furthermore, the nuclear factor-kappa-B (NFKB) signalling pathway was involved in venetoclax-induced NKG2DL upregulation.

CONCLUSIONS

Collectively, our data confirm that venetoclax combined with NK cells induces synergistic AML cell cytolysis and preliminarily revealed that venetoclax could selectively induce NKG2DLs on AML cells via NFKB signalling pathway.

Reverse phase protein arrays in acute leukemia: investigative and methodological challenges

INTRODUCTION

Acute leukemia results from a series of mutational events that alter cell growth and proliferation. Mutations result in protein changes that orchestrate growth alterations characteristic of leukemia. Proteomics is a methodology appropriate for study of protein changes found in leukemia. The high-throughput reverse phase protein array (RPPA) technology is particularly well-suited for the assessment of protein changes in samples derived from clinical trials.

AREAS COVERED

This review discusses the technical, methodological, and analytical issues related to the successful development of acute leukemia RPPAs.

EXPERT COMMENTARY

To obtain representative protein sample lysates, samples should be prepared from freshly collected blood or bone marrow material. Variables such as sample shipment, transit time, and holding temperature only have minimal effects on protein expression. CellSave preservation tubes are preferred for cells collected after exposure to chemotherapy, and incorporation of standardized guidelines for antibody validation is recommended. A more systematic biological approach to analyze protein expression is desired, searching for recurrent patterns of protein expression that allow classification of patients into risk groups, or groups of patients that may be treated similarly. Comparing RPPA protein analysis between cell lines and primary samples shows that cell lines are not representative of patient proteomic patterns.

Molecular determinants of therapy response of venetoclax-based combinations in acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous, highly malignant disease of the bone marrow. After decades of slow progress, recent years saw a surge of novel agents for its treatment. The most recent advancement is the registration of the Bcl-2 inhibitor ventoclax in combination with a hypomethylating agent (HMA) in the US and Europe for AML patients not eligible for intensive chemotherapy. Treatment of newly diagnosed AML patients with this combination results in remission rates that so far could only be achieved with intensive treatment. However, not all AML patients respond equally well, and some patients relapse early, while other patients experience longer periods of complete remission. A hallmark of AML is its remarkable genetic, molecular and clinical heterogeneity. Here, we review the current knowledge about molecular features of AML that help estimate the probability of response to venetoclax-containing therapies. In contrast to other newly developed AML therapies that target specific recurrent molecular alterations, it seems so far that responses are not specific for a certain subgroup. One exception is spliceosome mutations, where good response has been observed in clinical trials with venetoclax/azacitidine. These mutations are rather associated with a more unfavorable outcome with chemotherapy. In summary, venetoclax in combination with hypomethylating agents represents a significant novel option for AML patients with various molecular aberrations. Mechanisms of primary and secondary resistance seem to overlap with those towards chemotherapy.

Keeping up with venetoclax for leukemic malignancies: key findings, optimal regimens and clinical considerations

INTRODUCTION

Venetoclax has transformed the treatment landscape in hematologic malignancies, especially in elderly population. With high rates of remission, deep and durable responses, and safe toxicity profile, venetoclax in combination therapy has been extremely effective, garnering accelerated approval and becoming standard of care in lymphoid and myeloid malignancies.

AREAS COVERED

The role of venetoclax in the intrinsic apoptotic pathway is covered. This includes preclinical and clinical experience of venetoclax monotherapy and combination therapy in relapsed/refractory and frontline CLL, AML, ALL and high-risk MDS, with an emphasis on key clinical trials and efficacy of combination regimens in distinct mutational landscapes. Strategies to mitigate myelosuppression, manage dose adjustments and infectious complications are addressed.

EXPERT OPINION

Targeting BCL-2 offers a safe and highly effective adjunct to available therapies in hematologic malignancies. Despite success and frequent utilization of venetoclax, several resistance mechanisms have been elucidated, prompting development of novel combinatorial strategies. Further, on-target myelosuppression of venetoclax is a key obstacle in clinical practice, requiring diligent monitoring and practice-based knowledge of dose modifications. Despite these limitations, venetoclax has gained tremendous popularity in hematologic-oncology, becoming an integral component of numerous combination regimes, with ongoing plethora of clinical trials encompassing standard chemotherapy, targeted agents and immune-based approaches.

Management of Acute Myeloid Leukemia: Current Treatment Options and Future Perspectives

Treatment of acute myeloid leukemia (AML) has improved in recent years and several new therapeutic options have been approved. Most of them include mutation-specific approaches (e.g., gilteritinib for AML patients with activating FLT3 mutations), or are restricted to such defined AML subgroups, such as AML-MRC (AML with myeloid-related changes) or therapy-related AML (CPX-351). With this review, we aim to present a comprehensive overview of current AML therapy according to the evolved spectrum of recently approved treatment strategies. We address several aspects of combined epigenetic therapy with the BCL-2 inhibitor venetoclax and provide insight into mechanisms of resistance towards venetoclax-based regimens, and how primary or secondary resistance might be circumvented. Furthermore, a detailed overview on the current status of AML immunotherapy, describing promising concepts, is provided. This review focuses on clinically important aspects of current and future concepts of AML treatment, but will also present the molecular background of distinct targeted therapies, to understand the development and challenges of clinical trials ongoing in AML patients.

Venetoclax in Acute Myeloid Leukemia: Molecular Basis, Evidences for Preclinical and Clinical Efficacy and Strategies to Target Resistance

Venetoclax is a BH3-mimetics agent specifically interacting with the antiapoptotic protein BCL-2, facilitating cytochrome c release from mitochondria, subsequent caspases activation, and cell death. Utilization of venetoclax has profoundly changed the landscape of treatment for the poor-prognosis category of AML patients unfit for intensive chemotherapy. In the phase III VIALE-A study, Venetoclax, in combination with the hypomethylating agent azacitidine, showed a 65% overall response rate and 14.7-month overall survival, in comparison with 22% and 8 months in the control arm. These results led to the widespread use of venetoclax in this indication. Other combination regimens, consisting of low-intensity, intensive, or targeted therapies are currently under evaluation. Despite promising results, preventing relapses or resistance to venetoclax is still an unmet clinical need. Numerous studies have been conducted to identify and overcome venetoclax resistance in preclinical models or in clinical trials, including the inhibition of other antiapoptotic proteins, the induction of proapoptotic BH3-only proteins, and/or the targeting of the mitochondrial metabolism and machinery.

FLT3 inhibition by olverembatinib (HQP1351) downregulates MCL-1 and synergizes with BCL-2 inhibitor lisaftoclax (APG-2575) in preclinical models of FLT3-ITD mutant acute myeloid leukemia

Introduction

FLT3-ITD mutations occur in approximately 25% of patients with acute myeloid leukemia (AML) and are associated with poor prognosis. Despite initial efficacy, short duration of response and high relapse rates limit clinical use of selective FLT3 inhibitors. Combination approaches with other targeted therapies may achieve better clinical outcomes.

Materials and methods

Anti-leukemic activity of multikinase inhibitor olverembatinib (HQP1351), alone or in combination with BCL-2 inhibitor lisaftoclax (APG-2575), was evaluated in FLT3-ITD mutant AML cell lines in vitro and in vivo. A patient-derived FLT3-ITD mutant AML xenograft model was also used to assess the anti-leukemic activity of this combination.

Results

HQP1351 potently induced apoptosis and inhibited FLT3 signaling in FLT3-ITD mutant AML cell lines MV-4-11 and MOLM-13. HQP1351 monotherapy also significantly suppressed growth of FLT3-ITD mutant AML xenograft tumors and prolonged survival of tumor-bearing mice. HQP1351 and APG-2575 synergistically induced apoptosis in FLT3-ITD mutant AML cells and suppressed growth of MV-4–11 xenograft tumors. Combination therapy improved survival of tumor bearing-mice in a systemic MOLM-13 model and showed synergistic anti-leukemic effects in a patient-derived FLT3-ITD mutant AML xenograft model. Mechanistically, HQP1351 downregulated expression of myeloid-cell leukemia 1 (MCL-1) by suppressing FLT3-STAT5 (signal transducer and activator of transcription 5) signaling and thus enhanced APG-2575-induced apoptosis in FLT3-ITD mutant AML cells.

Conclusions

FLT3 inhibition by HQP1351 downregulates MCL-1 and synergizes with BCL-2 inhibitor APG-2575 to potentiate cellular apoptosis in FLT3-ITD mutant AML. Our findings provide a scientific rationale for further clinical investigation of HQP1351 combined with APG-2575 in patients with FLT3-ITD mutant AML.

Efficacy of Venetoclax Combined with Decitabine-Based Treatment for Heavily Pre-Treated Relapsed or Refractory AML Patients in a Real-World Setting

Purpose

We report the efficacy and safety of venetoclax plus decitabine-based treatment in heavily pre-treated relapsed or refractory acute myeloid leukaemia (RR-AML) in a real-world setting.

Patients and Methods

There were 22 patients in this study and the median age was 47.5 (12–84) years old, including 11 males and 11 females. Among them, 8 patients were relapsed AML including 2 patients relapsed after HSCT and 14 patients with primary refractory AML including 4 secondary AML. The median number of cycles of previous chemotherapy was 4 (range, 2–10).

Results

After a course of venetoclax plus decitabine-based treatment, 9 patients achieved complete remission (CR) and 1 patient achieved complete remission with incomplete haematological recovery (CRi). The overall response rate (ORR) was 45.5% and the CR rate was 40.9%, and the median time to reach CR/CRi was 21 (13–46) days. Four of the 10 CR/CRi patients relapsed again, and the median time of relapse was 5 (1.0–24) months. The one-year overall survival rate was 31.8%, and the median survival time was 6 months (95% CI, 1–9 months). The one-year overall survival rate of 10 CR/CRi patients was 59.1%, and the 12 NR patients was 10.4% (p=0.001). Nausea and vomiting occurred in 11 patients (50.0%). All patients had grade IV neutropenia and IV thrombocytopenia (100%). Pneumonia occurred in 14 patients (63.6%) and septicaemia occurred in 2 patients (9.0%). The cause of death in all patients was primary disease progression, and no patients died due to the side effects.

Conclusion

The efficacy of venetoclax plus decitabine-based treatment in the real-world treatment of heavily pre-treated RR-AML is similar to that in clinical trials, and the side effects are controllable.

FLT3 Tyrosine Kinase Inhibitors for the Treatment of Fit and Unfit Patients with FLT3-Mutated AML: A Systematic Review

FLT3-mutated acute myeloid leukemia accounts for around 30% of acute myeloid leukemia (AML). The mutation carried a poor prognosis until the rise of tyrosine kinase inhibitors (TKIs). New potent and specific inhibitors have successfully altered the course of the disease, increasing the complete response rate and the survival of patients with FLT3-mutated AML. The aim of this article is to review all the current knowledge on these game-changing drugs as well as the unsolved issues raised by their use for fit and unfit FLT3-mutated AML patients. To this end, we analyzed the results of phase I, II, III clinical trials evaluating FLT3-TKI both in the first-line, relapse monotherapy or in combination referenced in the PubMed, the American Society of Hematology, the European Hematology Association, and the Clinicaltrials.gov databases, as well as basic science reports on TKI resistance from the same databases. The review follows a chronological presentation of the different trials that allowed the development of first- and second-generation TKI and ends with a review of the current lines of evidence on leukemic blasts resistance mechanisms that allow them to escape TKI.

FLT3 mutated acute myeloid leukemia: 2021 treatment algorithm

Approximately 30% of patients with newly diagnosed acute myeloid leukemia (AML) harbor mutations in the fms-like tyrosine kinase 3 (FLT3) gene. While the adverse prognostic impact of FLT3-ITDmut in AML has been clearly proven, the prognostic significance of FLT3-TKDmut remains speculative. Current guidelines recommend rapid molecular testing for FLT3mut at diagnosis and earlier incorporation of targeted agents to achieve deeper remissions and early consideration for allogeneic stem cell transplant (ASCT). Mounting evidence suggests that FLT3mut can emerge at any timepoint in the disease spectrum emphasizing the need for repetitive mutational testing not only at diagnosis but also at each relapse. The approval of multi-kinase FLT3 inhibitor (FLT3i) midostaurin with induction therapy for newly diagnosed FLT3mut AML, and a more specific, potent FLT3i, gilteritinib as monotherapy for relapsed/refractory (R/R) FLT3mut AML have improved outcomes in patients with FLT3mut AML. Nevertheless, the short duration of remission with single-agent FLT3i's in R/R FLT3mut AML in the absence of ASCT, limited options in patients refractory to gilteritinib therapy, and diverse primary and secondary mechanisms of resistance to different FLT3i's remain ongoing challenges that compel the development and rapid implementation of multi-agent combinatorial or sequential therapies for FLT3mut AML.

New Treatment Options for Older Patients with Acute Myeloid Leukemia

OPINION STATEMENT

The treatment of acute myeloid leukemia (AML) has evolved considerably over the past several years. Advances in the field have historically benefited younger patients; however, a growing understanding of the molecular basis of leukemogenesis has brought multiple targeted agents to the clinic for patients of all ages. These therapies have expanded the therapeutic landscape for elderly patients from more than best supportive care and low-intensity monotherapy. In general, we currently utilize a backbone regimen of a hypomethylating agent (HMA) or low-intensity chemotherapy with the BCL-2 inhibitor venetoclax for the majority of elderly patients with newly diagnosed AML. For patients with targetable mutations, we employ a doublet/triplet strategy of HMA + a targeted inhibitor +/- venetoclax, often in the context of a clinical trial. CPX-351 is reserved for patients with secondary or therapy-related AML. In this review, we will outline our approach to the treatment of elderly patients with AML, with particular emphasis on recently approved agents and emerging novel therapies.

Targeting Bcl-2 Family Proteins: What, Where, When?

Proteins of the Bcl-2 family are known as regulators of apoptosis, one of the most studied forms of programmed cell death. The Bcl-2 protein family is represented by both pro- and antiapoptotic members. Antiapoptotic proteins are often exploited by tumor cells to avoid their death, thus playing an important role in carcinogenesis and in acquisition of resistance to various therapeutic agents. Therefore, antiapoptotic proteins represent attractive targets for cancer therapy. A detailed investigation of interactions between Bcl-2 family proteins resulted in the development of highly selective inhibitors of individual antiapoptotic members. These agents are currently being actively studied at the preclinical and clinical stages and represent a promising therapeutic strategy, which is highlighted by approval of venetoclax, a selective inhibitor of Bcl-2, for medical use. Meanwhile, inhibition of antiapoptotic Bcl-2 family proteins has significant therapeutic potential that is yet to be revealed. In the coming era of precision medicine, a detailed study of the mechanisms responsible for the sensitivity or resistance of tumor cells to various therapeutic agents, as well as the search for the most effective combinations, is of great importance. Here, we discuss mechanisms of how the Bcl-2 family proteins function, principles of their inhibition by small molecules, success of this approach in cancer therapy, and, eventually, biochemical features that can be exploited to improve the use of Bcl-2 family inhibitors as anticancer drugs.

Mechanisms for resistance in AML insights into molecular pathways mediating resistance to venetoclax

Resistance to therapy continues to pose hurdles in the therapeutic management of acute myeloid leukemia (AML). Although the approval and development of therapies such as venetoclax, was expected to overcome this issue, resistance remains a common occurrence in AML treatment. This review has summarized evidence that will provide insights into acquired mutations that influence response to venetoclax therapy and the utility of novel combination approaches in improving outcomes.

FLT3 Mutations in Acute Myeloid Leukemia: Key Concepts and Emerging Controversies

The FLT3 receptor is overexpressed on the majority of acute myeloid leukemia (AML) blasts. Mutations in FLT3 are the most common genetic alteration in AML, identified in approximately one third of newly diagnosed patients. FLT3 internal tandem duplication mutations (FLT3-ITD) are associated with increased relapse and inferior overall survival. Multiple small molecule inhibitors of FLT3 signaling have been identified, two of which (midostaurin and gilteritinib) are currently approved in the United States, and many more of which are in clinical trials. Despite significant advances, resistance to FLT3 inhibitors through secondary FLT3 mutations, upregulation of parallel pathways, and extracellular signaling remains an ongoing challenge. Novel therapeutic strategies to overcome resistance, including combining FLT3 inhibitors with other antileukemic agents, development of new FLT3 inhibitors, and FLT3-directed immunotherapy are in active clinical development. Multiple questions regarding FLT3-mutated AML remain. In this review, we highlight several of the current most intriguing controversies in the field including the role of FLT3 inhibitors in maintenance therapy, the role of hematopoietic cell transplantation in FLT3-mutated AML, use of FLT3 inhibitors in FLT3 wild-type disease, significance of non-canonical FLT3 mutations, and finally, emerging concerns regarding clonal evolution.

Venetoclax-based chemotherapy in acute and chronic myeloid neoplasms: literature survey and practice points

Venetoclax (VEN), a small-molecule inhibitor of B cell leukemia/lymphoma-2, is now FDA approved (November 2018) for use in acute myeloid leukemia (AML), specific to newly diagnosed elderly or unfit patients, in combination with a hypomethylating agent (HMA; including azacitidine or decitabine) or low-dose cytarabine. A recent phase-3 study compared VEN combined with either azacitidine or placebo, in the aforementioned study population; the complete remission (CR) and CR with incomplete count recovery (CRi) rates were 28.3% and 66.4%, respectively, and an improvement in overall survival was also demonstrated. VEN-based chemotherapy has also shown activity in relapsed/refractory AML (CR/CRi rates of 33-46%), high-risk myelodysplastic syndromes (CR 39% in treatment naïve, 5-14% in HMA failure), and blast-phase myeloproliferative neoplasm (CR 25%); in all instances, an additional fraction of patients met less stringent criteria for overall response. Regardless, venetoclax-induced remissions were often short-lived (less than a year) but long enough to allow some patients transition to allogeneic stem cell transplant. Herein, we review the current literature on the use of VEN-based combination therapy in both acute and chronic myeloid malignancies and also provide an outline of procedures we follow at our institution for drug administration, monitoring of adverse events and dose adjustments.

Molecular Mechanisms of Resistance to FLT3 Inhibitors in Acute Myeloid Leukemia: Ongoing Challenges and Future Treatments

Treatment of FMS-like tyrosine kinase 3 (FLT3)-internal tandem duplication (ITD)-positive acute myeloid leukemia (AML) remains a challenge despite the development of novel FLT3-directed tyrosine kinase inhibitors (TKI); the relapse rate is still high even after allogeneic stem cell transplantation. In the era of next-generation FLT3-inhibitors, such as midostaurin and gilteritinib, we still observe primary and secondary resistance to TKI both in monotherapy and in combination with chemotherapy. Moreover, remissions are frequently short-lived even in the presence of continuous treatment with next-generation FLT3 inhibitors. In this comprehensive review, we focus on molecular mechanisms underlying the development of resistance to relevant FLT3 inhibitors and elucidate how this knowledge might help to develop new concepts for improving the response to FLT3-inhibitors and reducing the development of resistance in AML. Tailored treatment approaches that address additional molecular targets beyond FLT3 could overcome resistance and facilitate molecular responses in AML.

Deciphering the Therapeutic Resistance in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a clonal hematopoietic disorder characterized by abnormal proliferation, lack of cellular differentiation, and infiltration of bone marrow, peripheral blood, or other organs. Induction failure and in general resistance to chemotherapeutic agents represent a hindrance for improving survival outcomes in AML. Here, we review the latest insights in AML biology concerning refractoriness to therapies with a specific focus on cytarabine and daunorubicin which still represent milestones agents for inducing therapeutic response and disease eradication. However, failure to achieve complete remission in AML is still high especially in elderly patients (40-60% in patients >65 years old). Several lines of basic and clinical research have been employed to improve the achievement of complete remission. These lines of research include molecular targeted therapy and more recently immunotherapy. In terms of molecular targeted therapies, specific attention is given to DNMT3A and TP53 mutant AML by reviewing the mechanisms underlying epigenetic therapies' (e.g., hypomethylating agents) resistance and providing critical points and hints for possible future therapies overcoming AML refractoriness.

Ex vivo cultures and drug testing of primary acute myeloid leukemia samples: Current techniques and implications for experimental design and outcome

New treatment options of acute myeloid leukemia (AML) are rapidly emerging. Pre-clinical models such as ex vivo cultures are extensively used towards the development of novel drugs and to study synergistic drug combinations, as well as to discover biomarkers for both drug response and anti-cancer drug resistance. Although these approaches empower efficient investigation of multiple drugs in a multitude of primary AML samples, their translational value and reproducibility are hampered by the lack of standardized methodologies and by culture system-specific behavior of AML cells and chemotherapeutic drugs. Moreover, distinct research questions require specific methods which rely on specific technical knowledge and skills. To address these aspects, we herein review commonly used culture techniques in light of diverse research questions. In addition, culture-dependent effects on drug resistance towards commonly used drugs in the treatment of AML are summarized including several pitfalls that may arise because of culture technique artifacts. The primary aim of the current review is to provide practical guidelines for ex vivo primary AML culture experimental design.