Binding of Released Bim to Mcl-1 is a Mechanism of Intrinsic Resistance to ABT-199 which can be Overcome by Combination with Daunorubicin or Cytarabine in AML Cells

PIK-75 overcomes venetoclax resistance via blocking PI3K-AKT signaling and MCL-1 expression in mantle cell lymphoma

Therapeutic resistance is the major challenge in clinic for patients with mantle cell lymphoma (MCL), an aggressive subtype of B-cell lymphoma. In addition to the FDA-approved Bruton's tyrosine kinase (BTK) inhibitors, multiple clinical trials have demonstrated clinical benefits in targeting BCL-2 by venetoclax and reported to greatly improve clinical outcome for refractory/relapsed patients with MCL alone or in combination with BTK inhibitors. However, resistance to venetoclax is no exception and marks as a new clinic challenge. To decode the underlying mechanisms driving venetoclax resistance, we established two MCL cell lines, Mino-Re and Rec1-Re, with acquired resistance to venetoclax from sensitive Mino and Rec-1. Using reverse phase protein assay (RPPA), an agnostic proteomic approach, we identified targetable signaling pathways that are associated with acquired venetoclax resistance in Mino-Re and Rec1-Re cells. A panel of pro-survival signals was identified to correlate well with venetoclax-resistance, including increased expression of MCL-1, BCL-xL and AKT phosphorylation, and decreased expression of BIM, BAX and PTEN. Based on a high throughput drug screening of over 320 FDA-approved/investigational drugs in the paired venetoclax-sensitive and -resistant cell lines Mino-Re and Rec1-Re, we identified the top candidates that are capable to overcome acquired venetoclax resistance in these cells. The best candidate is PIK-75, a dual inhibitor targeting both PI3K and CDK9. Its action to overcome venetoclax resistance was further confirmed in additional cell lines with primary venetoclax resistance (n=4) and primary patient samples (n=21). Mechanistically, PIK75 treatment potently diminished the elevated MCL-1 expression and AKT activation in cells with acquired or primary venetoclax resistance and resulted in potent anti-MCL activity to overcome these resistances. In addition, PIK75 is also potent in overcoming tumor microenvironment (TME)-associated venetoclax resistance. Furthermore, PIK-75 treatment is efficacious in overcoming primary and acquired venetoclax resistance in xenograft models and inhibited tumor cell dissemination to spleen in mice. Altogether, our data demonstrated that PIK-75 is highly potent in overcoming primary, acquired, or stromal cells-induced venetoclax resistances in MCL cells and revealed a new tumor vulnerability that can be exploited clinically in difficult to treat MCL cases, especially those with venetoclax resistance.

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-based combinations for acute myeloid leukemia: optimizing their use in Latin-America

Objectives: Venetoclax combinations are a new standard for patients with acute myeloid leukemia (AML). We aimed to evaluate the safety and efficacy of these combinations in a period of accelerated approval in Latin-America.Methods: This observational study evaluated adults with acute myeloid leukemia who received venetoclax-based therapy in 11 public or private centers in Mexico and Peru for both newly diagnosed or relapsed and refractory AML.Results: Fifty patients were included; 28 with newly diagnosed (ND) AML and 22 with relapsed/refractory (RR) disease. ND patients were older (64 vs. 40 years; p < 0.001) with a lower functional capacity (ECOG ≥2 64.3% vs 9%; p < 0.001). Venetoclax was frequently combined with azacytidine (60%) and prophylactic azoles (82%) with a median maximum dose of 200 mg (range, 100-600 mg). Hematologic toxicities were common. Complete response rates including patients with incomplete hematopoietic recovery were 78.6% in ND and 45.5% in RR patients, with a median overall survival of 9.6 (95% CI 3.7-15.5) and 8 months (95% CI 4.8-11.2).Discussion: Our study showed a preferred use of venetoclax plus azacytidine over cyatrabine. Patients in the first-line setting were similar to those in the landmark studies, while most patients with relapsed disease had received prior intensive therapies. Responses were favorable, with a median survival in agreement to other reports, albeit shorter than that observed in the randomized phase-3 trials.Conclusion: Venetoclax-based therapy in AML was effective despite dose reductions and prophylactic antifungals in two middle-income countries outside of a clinical trial setting.

[Short-term efficacy of venetoclax combined with azacitidine in acute myeloid leukemia: a single-institution experience]

Objective: To explore the safety and short-term efficacy of venetoclax combined with azacitidine (Ven+AZA) in previously untreated patients unfit for standard chemotherapy and patients with relapsed/refractory (R/R) acute myeloid leukemia (AML) in China. Methods: A retrospective study was conducted in 60 previously untreated patients unfit for standard chemotherapy and patients with R/R AML who received Ven+ AZA (venetoclax, 100 mg D1, 200 mg D2, 400 mg D3-28; azacitidine, 75 mg/m(2) D1- 7) at the Peking University Institute of Hematology from June 1, 2019 to May 31, 2021. The incidence of adverse events, complete remission (CR) /CR with incomplete hematological recovery (CRi) rate, objective remission rate (ORR) , and minimal residual disease (MRD) status in patients with different risk stratification and gene subtypes were analyzed. Results: The median age of the patients was 54 (18-77) years, 33 (55.0%) were males, and the median follow-up time was 4.8 (1.4-26.3) months. Among the 60 patients, 24 (40.0%) were previously untreated patients unfit for standard chemotherapy, and 36 (60.0%) were R/R patients. The median mumber cycles of Ven+AZA in the two groups were both 1 (1-5) . According to the prognostic risk stratification of the National Comprehensive Cancer Network, it was divided into 8 cases of favorable-risk, 2 cases of intermediate risk, and 14 cases of poor-risk. In previously untreated patients unfit for standard chemotherapy, after the first cycle of Ven+AZA, 17/24 (70.8%) cases achieved CR/CRi, 3/24 (12.5%) achieved partial remission (PR) , and the ORR was 83.3%. Among them, nine patients received a second cycle chemotherapy and two received a third cycle. Among CR/CRi patients, 8/17 (47.1%) achieved MRD negativity after two cycles of therapy. In the R/R group, after the first cycle of Ven+AZA, 21/36 (58.3%) cases achieved CR/CRi (7/21 achieved MRD negativity) , 3 achieved PR, and the ORR was 66.7%. Among R/R patients, 12 were treated for more than two cycles. There were no new CR/CRi patients after the second treatment cycle, and 14 cases (66.7%) achieved MRD negativity. According to the time from CR to hematological recurrence, the R/R group was divided into 12 cases in the favorable-risk group (CR to hematological recurrence ≥18 months) and 24 in the poor-risk group (CR to hematological recurrence<18 months, no remission after one cycle of therapy, and no remission after two or more cycles of therapy) . Eleven of 24 (45.8%) cases achieved CR/CRi after one cycle of Ven+AZA in the poor-risk R/R group, and 10 of 12 (83.3%) achieved CR/CRi in the favorable-risk R/R group, which was significantly superior to the poor-risk group (P=0.031) . After one cycle of treatment, 13 patients with IDH1/2 mutations and 4 that were TP53-positive all achieved CR/CRi. The CR/CRi rate of 18 patients with NPM1 mutations was 77.8%. Five patients with RUNX1-RUNX1T1 combined with KIT D816 mutation (two initial diagnoses and three recurrences) had no remission. Ven+ AZA was tolerable for AML patients. Conclusion: Ven+AZA has acceptable safety in previously untreated patients unfit for standard chemotherapy, patients with R/R AML can achieve a high response rate, and some patients can achieve MRD negativity. It is also effective in NPM1-, IDH1/IDH2-, and TP53-positive patients. The long-term efficacy remains to be observed.

Bak and Bcl-xL Participate in Regulating Sensitivity of Solid Tumor Derived Cell Lines to Mcl-1 Inhibitors

Simple Summary

Apoptosis is one of the best-known types of programmed cell death. This process is regulated by a number of genes and proteins, among which the Bcl-2 protein family plays a key role. This family includes anti- and proapoptotic proteins. Cancer cell resistance to apoptosis is commonly associated with overexpression of the antiapoptotic members of Bcl-2 family proteins, in particular, Bcl-2, Bcl-xL, and Mcl-1. Subsequently, these proteins represent perspective targets for anticancer therapy. Here, using an inhibitory approach, we found that Bak and Bcl-xL regulate sensitivity of cancer cells to Mcl-1 inhibition.

Abstract

BH3 mimetics represent a promising tool in cancer treatment. Recently, the drugs targeting the Mcl-1 protein progressed into clinical trials, and numerous studies are focused on the investigation of their activity in various preclinical models. We investigated two BH3 mimetics to Mcl-1, A1210477 and S63845, and found their different efficacies in on-target doses, despite the fact that both agents interacted with the target. Thus, S63845 induced apoptosis more effectively through a Bak-dependent mechanism. There was an increase in the level of Bcl-xL protein in cells with acquired resistance to Mcl-1 inhibition. Cell lines sensitive to S63845 demonstrated low expression of Bcl-xL. Tumor tissues from patients with lung adenocarcinoma were characterized by decreased Bcl-xL and increased Bak levels of both mRNA and proteins. Concomitant inhibition of Bcl-xL and Mcl-1 demonstrated dramatic cytotoxicity in six of seven studied cell lines. We proposed that co-targeting Bcl-xL and Mcl-1 might lead to a release of Bak, which cannot be neutralized by other anti-apoptotic proteins. Surprisingly, in Bak-knockout cells, inhibition of Mcl-1 and Bcl-xL still resulted in pronounced cell death, arguing against a sole role of Bak in the studied phenomenon. We demonstrate that Bak and Bcl-xL are co-factors for, respectively, sensitivity and resistance to Mcl-1 inhibition.

Venetoclax in Relapsed/Refractory Acute Myeloid Leukemia: Are Supporting Evidences Enough?

Simple Summary

Venetoclax (VEN) is a potent oral inhibitor of the anti-apoptotic molecule BCL2, approved for adults with chronic lymphocytic leukemia (CLL), and recently for naïve acute myeloid leukemia (AML) unfit for intensive chemotherapy. Therefore, VEN is not approved for relapsed/refractory (R/R) AML patients; consequently, this use falls within the so-called off-label use. This review provides evidence of the role of VEN-based therapy in R/R AML patients, including data from clinical trials and from retrospective studies.

Abstract

Despite the progress in the development of new therapeutic strategies, relapsed/refractory (R/R) acute myeloid leukemia (AML) still represents a high unmet medical need. Treatment options in this setting include enrollment into clinical trials, allogeneic stem cell transplantation and/or targeted therapy. Nevertheless, it is associated with poor outcomes. Thus, the development of new treatments, which could ameliorate the prognosis of these patients with a good safety profile are highly demanded. Recently, venetoclax (VEN) has been approved for naïve AML patients unfit for intensive chemotherapy. In this regard, regimens including VEN could represent a valuable treatment option even in those with R/R disease and several studies have been conducted to demonstrate its role in this clinical setting. This review aims to summarize the current evidence on the use of VEN regimens in the treatment of R/R AML.

Mitochondria and Their Relationship with Common Genetic Abnormalities in Hematologic Malignancies

Hematologic malignancies are known to be associated with numerous cytogenetic and molecular genetic changes. In addition to morphology, immunophenotype, cytochemistry and clinical characteristics, these genetic alterations are typically required to diagnose myeloid, lymphoid, and plasma cell neoplasms. According to the current World Health Organization (WHO) Classification of Tumors of Hematopoietic and Lymphoid Tissues, numerous genetic changes are highlighted, often defining a distinct subtype of a disease, or providing prognostic information. This review highlights how these molecular changes can alter mitochondrial bioenergetics, cell death pathways, mitochondrial dynamics and potentially be related to mitochondrial genetic changes. A better understanding of these processes emphasizes potential novel therapies.

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.

Synergistic effect of chidamide and venetoclax on apoptosis in acute myeloid leukemia cells and its mechanism

Background

Acute myeloid leukemia (AML) is a hematological malignancy with a low remission rate and high recurrence rate. Overexpression of the antiapoptotic protein Bcl-2 is associated with a lower overall survival rate in AML patients. Venetoclax (ABT199) is a selective inhibitor of Bcl-2 that has a significant effect in AML, but single-drug resistance often occurs due to the high expression of Mcl-1 protein. Studies have confirmed that chidamide can downregulate the expression levels of Bcl-2 and Mcl-1 and induce apoptosis.

Methods

This study aimed to use AML cell lines and primary cells to study the effects of venetoclax and chidamide combination therapy on AML cell apoptosis, the cell cycle, and changes in related signaling pathways in vitro; establish an AML mouse model to observe the efficacy and survival time of combination therapy in vivo; and analyze the drug effects with multi-omics sequencing technology. The changes in gene and protein expression before and after treatment were examined to clarify the molecular mechanism driving the synergistic effect of the two drugs.

Results

(I) Both venetoclax and chidamide promoted apoptosis in AML cell lines and primary cells in a time- and concentration-dependent manner. The effect was further enhanced when the two drugs were combined, and a synergistic effect was observed (combination index <1). (II) At both the mRNA and protein levels, the expression of Mcl-1 was upregulated by venetoclax and downregulated by chidamide, and the expression of Mcl-1 decreased further after combination treatment. (III) Transcriptome sequencing showed that differentially expressed genes in the combination group compared with the venetoclax monotherapy group were mainly enriched in the PI3K-AKT pathway and JAK2/STAT3 pathway. Moreover, qRT-PCR and Western blot confirmed these results. (IV) The combination therapy group exhibited significantly inhibited disease progression and a prolonged survival time among AML mice.

Conclusions

Chidamide combined with venetoclax synergistically promoted apoptosis in AML cell lines and primary cells by inhibiting activation of the PI3K/AKT pathway and JAK2/STAT3 pathway.

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.

Cotargeting of Bcl-2 and Mcl-1 shows promising antileukemic activity against AML cells including those with acquired cytarabine resistance

Acute myeloid leukemia (AML) remains a clinical challenge. Venetoclax is an effective Bcl-2 selective inhibitor approved by the U.S. Food and Drug Administration (FDA) for treatment of AML in patients who are 75 years and older or who have comorbidities. However, resistance to venetoclax limits its clinical efficacy. Mcl-1 has been identified as one determinant of resistance to venetoclax treatment. In this study, we investigate the Mcl-1 inhibitor S63845 in combination with venetoclax in AML cells. We found that S63845 synergizes with venetoclax in AML cell lines and primary patient samples. Bak/Bax double knockdown and treatment with the pan-caspase inhibitor Z-VAD-FMK revealed that the combination induces intrinsic apoptosis in AML cells. Inhibition of Mcl-1 using another Mcl-1 selective inhibitor, AZD5991, also synergistically enhanced apoptosis induced by venetoclax in a caspase-dependent manner. Importantly, S63845 in combination with venetoclax can effectively combat AML cells with acquired resistance to the standard chemotherapy drug cytarabine. In light of these facts, the combined inhibition of Mcl-1 and Bcl-2 shows promise against AML cells, including relapse/refractory AML.

BH3-mimetics: recent developments in cancer therapy

The hopeful outcomes from 30 years of research in BH3-mimetics have indeed served a number of solid paradigms for targeting intermediates from the apoptosis pathway in a variety of diseased states. Not only have such rational approaches in drug design yielded several key therapeutics, such outputs have also offered insights into the integrated mechanistic aspects of basic and clinical research at the genetics level for the future. In no other area of medical research have the effects of such work been felt, than in cancer research, through targeting the BAX-Bcl-2 protein-protein interactions. With these promising outputs in mind, several mimetics, and their potential therapeutic applications, have also been developed for several other pathological conditions, such as cardiovascular disease and tissue fibrosis, thus highlighting the universal importance of the intrinsic arm of the apoptosis pathway and its input to general tissue homeostasis. Considering such recent developments, and in a field that has generated so much scientific interest, we take stock of how the broadening area of BH3-mimetics has developed and diversified, with a focus on their uses in single and combined cancer treatment regimens and recently explored therapeutic delivery methods that may aid the development of future therapeutics of this nature.

Transcriptional inhibition by CDK7/9 inhibitor SNS-032 suppresses tumor growth and metastasis in esophageal squamous cell carcinoma

Metastasis is one of most lethal causes that confer a poor prognosis of patients with esophageal squamous cell carcinoma (ESCC), whereas there is no available target drug for metastatic ESCC currently. In this study, we aimed to determine whether the transcriptional inhibition by CDK7/9 inhibitor SNS-032 is activity against ESCC. MTT and soft agar assays were performed to examine the influence of SNS-032 on ESCC growth in vitro. Tumor xenograft in nude mice was used to assess the antitumor activity of SNS-032 in vivo. The roles of SNS-032 in ESCC metastasis were conducted by wound healing and transwell assays in vitro, and by a lung and a popliteal lymph node metastasis model in vivo. The results showed that CDK7 and CDK9 were highly expressed in ESCC cells; SNS-032 effectively inhibited cellular viability, abrogated anchorage-independent growth, and potentiated the sensitivity to cisplatin in ESCC cells in vitro and in vivo. In addition, SNS-032 induced a mitochondrial-dependent apoptosis of ESCC cells by reducing Mcl-1 transcription. SNS-032 also potently abrogated the abilities of ESCC cell migration and invasion through transcriptional downregulation of MMP-1. Importantly, SNS-032 remarkably inhibited the growth of ESCC xenograft, increased the overall survival, as well as diminished the lung and lymph node metastasis in nude mice. Taken together, our findings highlight that the CDK7/9 inhibitor SNS-032 is a promising therapeutic agent, and warrants a clinical trial for its efficacy in ESCC patients, even those with metastasis.

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.

Evolving Therapeutic Approaches for Older Patients with Acute Myeloid Leukemia in 2021

Simple Summary

The better understanding of disease biology, the availability of new effective drugs and the increased awareness of patients’ heterogeneity in terms of fitness and personal expectations has made the current treatment paradigm of AML in the elderly very challenging. Here, we discuss the evolving criteria used to define eligibility for induction chemotherapy and transplantation, the introduction of new agents in the treatment of patients with very different clinical conditions, the implications of precision medicine and the importance of quality of life and supportive care, proposing a simplified algorithm that we follow in 2021.

Abstract

Acute myeloid leukemia (AML) in older patients is characterized by unfavorable prognosis due to adverse disease features and a high rate of treatment-related complications. Classical therapeutic options range from intensive chemotherapy in fit patients, potentially followed by allogeneic hematopoietic cell transplantation (allo-HCT), to hypomethylating agents or palliative care alone for unfit/frail ones. In the era of precision medicine, the treatment paradigm of AML is rapidly changing. On the one hand, a plethora of new targeted drugs with good tolerability profiles are becoming available, offering the possibility to achieve a prolonged remission to many patients not otherwise eligible for more intensive therapies. On the other hand, better tools to assess patients’ fitness and improvements in the selection and management of those undergoing allo-HCT will hopefully reduce treatment-related mortality and complications. Importantly, a detailed genetic characterization of AML has become of paramount importance to choose the best therapeutic option in both intensively treated and unfit patients. Finally, improving supportive care and quality of life is of major importance in this age group, especially for the minority of patients that are still candidates for palliative care because of very poor clinical conditions or unwillingness to receive active treatments. In the present review, we discuss the evolving approaches in the treatment of older AML patients, which is becoming increasingly challenging following the advent of new effective drugs for a very heterogeneous and complex population.

Venetoclax plus low-dose cytarabine in Japanese patients with untreated acute myeloid leukaemia ineligible for intensive chemotherapy

Background

In a multinational phase 3 trial (VIALE-C), venetoclax plus low-dose cytarabine prolonged overall survival vs placebo plus low-dose cytarabine in patients with newly diagnosed acute myeloid leukaemia ineligible for intensive chemotherapy, although it was not statistically significant. Herein, we assess the benefit of venetoclax plus low-dose cytarabine in the Japanese subgroup of VIALE-C patients (n = 27).

Methods

VIALE-C, a randomized (2:1), double-blind study (NCT03069352), enrolled untreated patients (≥18 years) with acute myeloid leukaemia. Patients received venetoclax (600 mg days 1–28, 4-day ramp-up in cycle 1) or placebo in 28-day cycles with low-dose cytarabine (20 mg/m² days 1–10). The primary endpoint was median overall survival.

Results

In the Japanese subgroup, at a 6-month follow-up from the primary analysis, median overall survival for venetoclax (n = 18) and placebo (n = 9), plus low-dose cytarabine, was 4.7 and 8.1 months, respectively (hazard ratio, 0.928, 95% confidence intervals : 0.399, 2.156). The rate of complete remission plus complete remission with incomplete blood count recovery was higher with venetoclax plus low-dose cytarabine (44.4%) vs placebo plus low-dose cytarabine (11.1%). All patients experienced at least 1 adverse event. The most common grade ≥3 adverse events with venetoclax or placebo, plus low-dose cytarabine, were febrile neutropenia (50.0% vs 44.4%, respectively) and thrombocytopenia (27.8% vs 44.4%, respectively). Serious adverse events were reported in 50.0 and 33.3% of patients in the venetoclax and placebo, plus low-dose cytarabine arms, respectively; pneumonia was the most common (22.2% each).

Conclusions

Limited survival benefit in the Japanese subgroup can be attributed to small patient numbers and to baseline imbalances observed between treatment arms, with more patients in the venetoclax plus low-dose cytarabine arm presenting poor prognostic factors. Venetoclax plus low-dose cytarabine was well tolerated in Japanese patients with acute myeloid leukaemia ineligible for intensive chemotherapy.

BCL2 inhibitors and MCL1 inhibitors for hematological malignancies

BCL2 and MCL1 are commonly expressed pro-survival (anti-apoptotic) proteins in hematological cancers and play important roles in their biology either through dysregulation or by virtue of intrinsic importance to the cell-of-origin of the malignancy. A new class of small molecule anti-cancer drugs, BH3-mimetics, now enable specific targeting of these proteins in patients. BH3-mimetics act by inhibiting the pro-survival BCL2 proteins to enable the activation of BAX and BAK, apoptosis effectors which permeabilize the outer mitochondrial membrane, triggering apoptosis directly in many cells and sensitizing others to cell death when combined with other anti-neoplastic drugs. Venetoclax, a specific inhibitor of BCL2, is the first approved in class, demonstrating striking single agent activity in chronic lymphocytic leukemia (CLL) and in other lymphoid neoplasms, as well as activity against acute myeloid leukemia (AML), especially when used in combination. Key insights from the venetoclax experience include that responses occur rapidly, with major activity as monotherapy proving to be the best indicator for success in combination regimens. This emphasizes the importance of adequate single agent studies for drugs in this class. Furthermore, secondary resistance is common with long-term exposure and often mediated by genetic or adaptive changes in the apoptotic pathway, suggesting that BH3-mimetics are better suited to limited-duration, rather than continuous, therapy. The success of venetoclax has inspired development of BH3-mimetics targeting MCL1. Despite promising preclinical activity against MYC-driven lymphomas, myeloma and AML, their success may particularly depend on their tolerability profile given physiological roles for MCL1 in several non-hematological tissues.

Guanylate-binding proteins induce apoptosis of leukemia cells by regulating MCL-1 and BAK

Interferon-inducible guanylate-binding proteins (GBPs) are well-known for mediating host-defense mechanisms against cellular pathogens. Emerging evidence suggests that GBPs are also implicated in tumorigenesis; however, their underlying molecular mechanism is still unknown. In this study, we identified that GBP1 and GBP2 interact with MCL-1, the key prosurvival member of the BCL-2 family, via its BH3 domain. GBPs induce caspase-dependent apoptosis in chronic myeloid leukemia (CML) and acute myeloid leukemia (AML) cells, where the proapoptotic BCL-2 member, BAK, is an indispensable mediator. In particular, GBP2 completely inhibited the MCL-1-mediated promotion of the survival of CML cells through competitive inhibition, resulting in BAK liberation from MCL-1. Concurrently, GBP2 dramatically upregulates BAK expression via its inhibition of the PI3K/AKT pathway. Moreover, paclitaxel upregulates GBP2 expression, and paclitaxel-induced apoptotic activity was distinctively compromised by knockout of GBP2 in CML cells. Bioinformatics analyses of leukemia databases revealed that transcripts of GBPs were generally downregulated in leukemia patients and that GBPs were favorable prognosis markers. Thus, these findings provide molecular evidence of GBPs as apoptosis-inducing proteins of leukemia cells and suggest that GBPs are attractive targets for the development of chemotherapeutics.

Transcript-Level Dysregulation of BCL2 Family Genes in Acute Myeloblastic Leukemia

The expression of apoptosis-related BCL2 family genes, fine-tuned in normal cells, is dysregulated in many neoplasms. In acute myeloid leukemia (AML), this problem has not been studied comprehensively. To address this issue, RNA-seq data were used to analyze the expression of 26 BCL2 family members in 27 AML FAB M1 and M2 patients, divided into subgroups differently responding to chemotherapy. A correlation analysis, analysis of variance, and Kaplan-Meier analysis were applied to associate the expression of particular genes with other gene expression, clinical features, and the presence of mutations detected by exome sequencing. The expression of BCL2 family genes was dysregulated in AML, as compared to healthy controls. An upregulation of anti-apoptotic and downregulation of pro-apoptotic genes was observed, though only a decrease in BMF, BNIP1, and HRK was statistically significant. In a group of patients resistant to chemotherapy, overexpression of BCL2L1 was manifested. In agreement with the literature data, our results reveal that BCL2L1 is one of the key players in apoptosis regulation in different types of tumors. An exome sequencing data analysis indicates that BCL2 family genes are not mutated in AML, but their expression is correlated with the mutational status of other genes, including those recurrently mutated in AML and splicing-related. High levels of some BCL2 family members, in particular BIK and BCL2L13, were associated with poor outcome.

Kinome-wide RNAi screening for mediators of ABT-199 resistance in breast cancer cells identifies Wee1 as a novel therapeutic target

Antiapoptotic and proapoptotic BCL-2 protein family members regulate mitochondrial apoptotic pathway. Small molecule inhibitors of antiapoptotic BCL-2 proteins including BCL-2-specific inhibitor ABT-199 (Venetoclax) are in clinical development. However, the efficiency of ABT-199 as a single agent in solid tumors is limited. We performed a high-throughput RNAi kinome screen targeting 691 kinases to identify potentially targetable kinases to enhance ABT-199 response in breast cancer cells. Our studies identified Wee1 as the primary target kinase to overcome resistance to ABT-199. Depletion of Wee1 by siRNA-mediated knockdown or inhibition of Wee1 by the small molecule Wee1 inhibitor AZD1775 sensitized SKBR3, MDA-MB-468, T47D and CAMA-1 breast cancer cells to ABT-199 along with decreased MCL1. BH3-only proteins PUMA and BIM functionally contribute to apoptosis signaling following co-targeting BCL-2 and Wee1. Suppression of Wee1 function increased mitochondrial cell death priming. Furthermore, we found that Wee1 inhibition altered MCL1 phosphorylation and protein stability, which led to HUWE1-mediated MCL1 degradation. Our findings suggest that Wee1 inhibition can overcome resistance to ABT-199 and provide a rationale for further translational investigation of BCL-2 inhibitor/Wee1 inhibitor combination in breast cancer.

Bim transfer between Bcl-2-like protein and Hsp70 underlines Bcl-2/Hsp70 crosstalk to regulate apoptosis

The chaperone heat shock protein 70 (Hsp70) is crucial for avoiding protein misfolding under stress, but it is also upregulated in many kinds of cancers, where its ability to buffer cellular stress prevents apoptosis. Previous research has suggested that Bim, a BH3-only member of the Bcl-2 family proteins, also serves as a cochaperone for Hsp70, which modulates the folding and stabilization of many Hsp70 oncogenic substrates in tumor cells. However, a definitive demonstration of crosstalk between Bcl-2 and Hsp70 family proteins and molecular mechanism remain unclear. Herein, we examined the effects of pan-Bcl-2 inhibitor S1, Hsp70 inhibitor S1g-6 on the K562, U937, H23, HL-60 cell lines and these inhibitors synergistically induce mitochondrial apoptosis in cancer cell lines. Moreover, we identified that Bim transfer between Bcl-2-like protein and Hsp70 underlines Bcl-2/Hsp70 crosstalk in mitochondrial apoptosis pathway. Thus, the synergy of S1 and S1g-6 to induce a panel of cancer cell lines apoptosis by inhibiting free Bim and facilitating oncogenic client AKT folding and activation. Together, our results demonstrated the combination of Bcl-2 inhibitor and Hsp70 inhibitor showed synergistic effect in cancer cells and the potential to decrease tumor regression.

Venetoclax in combination with azacitidine in Japanese patients with acute myeloid leukaemia: phase 1 trial findings

BACKGROUND

Venetoclax plus azacitidine is indicated in the USA for the treatment of newly diagnosed acute myeloid leukaemia in older patients (≥75 years) or those ineligible for induction chemotherapy due to co-morbidities.

METHODS

In this phase 1/2 study (NCT02265731), Japanese patients (≥60 years) with untreated (ineligible for induction chemotherapy) or relapsed/refractory acute myeloid leukaemia received oral venetoclax 400 mg/day (3-day ramp up in cycle 1) plus subcutaneous or intravenous azacitidine 75 mg/m2 on days 1-7 per 28-day cycle until disease progression or unacceptable toxicity.

RESULTS

As of 10 December 2019, six patients were enrolled (median age: 75 years; untreated: n = 5; relapsed/refractory: n = 1); median treatment duration: 10.3 months (range, 0.7-29.4). Most common grade ≥ 3 adverse events were lymphopaenia and febrile neutropaenia (n = 4 each). Four patients reported serious adverse events; only an event of grade 3 fungal pneumonia was considered possibly related to both study drugs, requiring dose interruption of venetoclax and delay of azacitidine. Five (83%) patients had responses (complete remission: n = 3). Median time to first response of complete remission/complete remission with incomplete count recovery was 1.0 month (range, 0.8-5.5); median overall survival: 15.7 months (95% confidence interval: 6.2, not reached).

CONCLUSIONS

Venetoclax plus azacitidine was well tolerated and showed high response rates in Japanese patients with acute myeloid leukaemia.

Review of Venetoclax in CLL, AML and Multiple Myeloma

Venetoclax is a highly selective and effective B-cell lymphoma-2 (BCL-2) inhibitor, which is able to reinstate the apoptotic potential of cancer cells. With its full repertoire yet to be explored, it has changed the therapeutic landscape in haematological malignancies, and most particularly chronic lymphocytic leukaemia (CLL), acute myeloid leukaemia (AML) and multiple myeloma (MM). In CLL, it has shown remarkable efficacy both as monotherapy and in combination therapy. Based on data from MURANO and CLL14 studies, fixed-duration combination therapy of venetoclax with anti-CD20 antibody is now the standard of care in numerous countries. In AML, although of limited efficacy as a single agent, venetoclax combination therapy has demonstrated encouraging outcomes including rapid, durable responses and acceptable toxicity, particularly in the older, unfit patient population. Multiple myeloma with translocation (t)(11;14) harbours high BCL-2/ myeloid cell leukaemia sequence-1 (MCL-1) and BCL-2/BCL-XL ratio and is, therefore, particularly suited for venetoclax-based therapy. Despite a wide ranging and evolving clinical role in these diseases, venetoclax treatment is not curative and, over time, clonal evolution and disease relapse appear to be the norm. While a variety of distinct resistance mechanisms have been identified, frequently emerging in a sub-clonal pattern, the full picture is yet to be characterised. Further illumination of the complex interplay of various factors is needed to pave the way for rational combination therapies aimed at circumventing resistance and improving durability of disease control. Serial molecular studies can aid in identification of new prognostically significant and/or targetable mutations.

NOXA-mediated degradation of MCL1 and BCL2L1 causes apoptosis of daunorubicin-treated human acute myeloid leukemia cells

Daunorubicin (DNR) is used clinically to treat acute myeloid leukemia (AML), while the signaling pathways associated with its cytotoxicity are not fully elucidated. Thus, we investigated the DNR-induced death pathway in the human AML cell lines U937 and HL-60. DNR-induced apoptosis in U937 cells accompanied by downregulation of MCL1 and BCL2L1, upregulation of Phorbol-12-myristate-13-acetate-induced protein 1 (NOXA), and mitochondrial depolarization. DNR induced NOX4-mediated reactive reactive oxygen species (ROS) production, which in turn inactivated Akt and simultaneously activated p38 mitogen-activated protein kinase (MAPK). Activated p38 MAPK and inactivated Akt coordinately increased GSK3β-mediated cAMP response element-binding protein (CREB) phosphorylation, which promoted NOXA transcription. NOXA upregulation critically increased the proteasomal degradation of MCL1 and BCL2L1. The same pathway was also responsible for the DNR-induced death of HL-60 cells. Restoration of MCL1 or BCL2L1 expression alleviated DNR-induced mitochondrial depolarization and cell death. Furthermore, ABT-199 (a BCL2 inhibitor) synergistically enhanced the cytotoxicity of DNR in AML cell lines. Notably, DNR-induced DNA damage was not related to NOXA-mediated degradation of MCL1 and BCL2L1. Collectively, these results indicate that the upregulation of NOXA expression through the NOX4-ROS-p38 MAPK-GSK3β-CREB axis results in the degradation of MCL1 and BCL2L1 in DNR-treated U937 and HL-60 cells. This signaling pathway may provide insights into the mechanism underlying DNR-triggered apoptosis in AML cells.

The HDAC and PI3K dual inhibitor CUDC-907 synergistically enhances the antileukemic activity of venetoclax in preclinical models of acute myeloid leukemia

Venetoclax is a promising agent in the treatment of acute myeloid leukemia, though its antileukemic activity is limited to combination therapies. Mcl-1 downregulation, Bim upregulation, and DNA damage have been identified as potential ways to enhance venetoclax activity. In this study, we combine venetoclax with the dual PI3K and histone deacetylase inhibitor CUDC-907, which can downregulate Mcl-1, upregulate Bim, and induce DNA damage, as well as downregulate c-Myc. We establish that CUDC-907 and venetoclax synergistically induce apoptosis in acute myeloid leukemia cell lines and primary acute myeloid leukemia patient samples ex vivo. CUDC-907 downregulates CHK1, Wee1, RRM1, and c-Myc, which were found to play a role in venetoclax-induced apoptosis. Interestingly, we found that venetoclax treatment enhances CUDC-907-induced DNA damage potentially through inhibition of DNA repair. In vivo results show that CUDC-907 enhances venetoclax efficacy in an acute myeloid leukemia cell line derived xenograft mouse model, supporting the development of CUDC-907 in combination with venetoclax for the treatment of acute myeloid leukemia.

Targeting epigenetic mechanisms to overcome venetoclax resistance

The BH-3 mimetic venetoclax overcomes apoptosis and therapy resistance caused by high expression of BCL2 or loss of BH3-only protein function. Although a promising therapy for hematologic malignancies, increased expression of anti-apoptotic MCL-1 or BCL-XL, as well as other resistance mechanisms prevent a durable response to venetoclax. Recent studies demonstrate that agents targeting epigenetic mechanisms such as DNA methyltransferase inhibitors, histone deacetylase (HDAC) inhibitors, histone methyltransferase EZH2 inhibitors, or bromodomain reader protein inhibitors may disable oncogenic gene expression signatures responsible for venetoclax resistance. Combination therapies including venetoclax and epigenetic therapies are effective in preclinical models and the subject of many current clinical trials. Here we review epigenetic strategies to overcome venetoclax resistance mechanisms in hematologic malignancies.

Inhibition of CPT1a as a prognostic marker can synergistically enhance the antileukemic activity of ABT199

Background

Fatty acid oxidation (FAO) provides an important source of energy to promote the growth of leukemia cells. Carnitine palmitoyltransferase 1a(CPT1a), a rate-limiting enzyme of the essential step of FAO, can facilitate cancer metabolic adaptation. Previous reports demonstrated that CPT1a acts as a potential molecular target in solid tumors and hematologic disease. However, no systematic study was conducted to explore the prognostic value of CPT1a expression and possible treatment strategies with CPT1a inhibitor on acute myeloid leukemia (AML).

Methods

The expression of CPT1a in 325 cytogenetically normal AML (CN-AML) patients was evaluated using RT-PCR. The combination effects of ST1326 and ABT199 were studied in AML cells and primary patients. MTS was used to measure the cell proliferation rate. Annexin V/propidium iodide staining and flow cytometry analysis was used to measure the apoptosis rate. Western blot was used to measure the expression of Mcl-1. RNAseq and GC-TOFMS were used for genomic and metabolic analysis.

Results

In this study, we found AML patients with high CPT1a expression (n = 245) had a relatively short overall survival (P = 0.01) compared to patients in low expression group (n = 80). In parallel, downregulation of CPT1a inhibits proliferation of AML cells. We also conducted genomic and metabolic interactive analysis in AML patients, and found several essential genes and pathways related to aberrant expression of CPT1a. Moreover, we found downregulation of CPT1a sentitized BCL-2 inhibitor ABT199 and CPT1a-selective inhibitor ST1326 combined with ABT199 had a strong synergistic effect to induce apoptosis in AML cells and primary patient blasts for the first time. The underlying synergistic mechanism might be that ST1326 inhibits pGSK3β and pERK expression, leading to downregulation of Mcl-1.

Conclusion

Our study indicates that overexpression of CPT1a predicts poor clinical outcome in AML. CPT1a-selective inhibitor ST1326 combined with Bcl-2 inhibitor ABT199 showed strong synergistic inhibitory effects on AML.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02848-9.

Mitochondrial metabolism as a target for acute myeloid leukemia treatment

Acute myeloid leukemias (AML) are a group of aggressive hematologic malignancies resulting from acquired genetic mutations in hematopoietic stem cells that affect patients of all ages. Despite decades of research, standard chemotherapy still remains ineffective for some AML subtypes and is often inappropriate for older patients or those with comorbidities. Recently, a number of studies have identified unique mitochondrial alterations that lead to metabolic vulnerabilities in AML cells that may present viable treatment targets. These include mtDNA, dependency on oxidative phosphorylation, mitochondrial metabolism, and pro-survival signaling, as well as reactive oxygen species generation and mitochondrial dynamics. Moreover, some mitochondria-targeting chemotherapeutics and their combinations with other compounds have been FDA-approved for AML treatment. Here, we review recent studies that illuminate the effects of drugs and synergistic drug combinations that target diverse biomolecules and metabolic pathways related to mitochondria and their promise in experimental studies, clinical trials, and existing chemotherapeutic regimens.

Resistance to venetoclax and hypomethylating agents in acute myeloid leukemia

Despite the success of the combination of venetoclax with the hypomethylating agents (HMA) decitabine or azacitidine in inducing remission in older, previously untreated patients with acute myeloid leukemia (AML), resistance - primary or secondary - still constitutes a significant roadblock in the quest to prolong the duration of response. Here we review the proposed and proven mechanisms of resistance to venetoclax monotherapy, HMA monotherapy, and the doublet of venetoclax and HMA for the treatment of AML. We approach the mechanisms of resistance to HMAs and venetoclax in the light of the agents' mechanisms of action. We briefly describe potential therapeutic strategies to circumvent resistance to this promising combination, including alternative scheduling or the addition of other agents to the HMA and venetoclax backbone. Understanding the mechanisms of action and evolving resistance in AML remains a priority in order to maximize the benefit from novel drugs and combinations, identify new therapeutic targets, define potential prognostic markers, and avoid treatment failure.

Targeting AXL kinase sensitizes leukemic stem and progenitor cells to venetoclax treatment in acute myeloid leukemia

AXL activity is upregulated in AML stem/progenitor cells, so a novel AXL inhibitor with favorable pharmaceutical properties was developed.

AXL inhibition sensitizes AML cells to venetoclax, with strong synergistic effects via AXL/BCL-2–mediated oxidative phosphorylation signaling pathways.

The abundance of genetic abnormalities and phenotypic heterogeneities in acute myeloid leukemia (AML) poses significant challenges to the development of improved treatments. Here, we demonstrated that a key growth arrest-specific gene 6/AXL axis is highly activated in cells from patients with AML, particularly in stem/progenitor cells. We developed a potent selective AXL inhibitor that has favorable pharmaceutical properties and efficacy against preclinical patient-derived xenotransplantation (PDX) models of AML. Importantly, inhibition of AXL sensitized AML stem/progenitor cells to venetoclax treatment, with strong synergistic effects in vitro and in PDX models. Mechanistically, single-cell RNA-sequencing and functional validation studies uncovered that AXL inhibition, alone or in combination with venetoclax, potentially targets intrinsic metabolic vulnerabilities of AML stem/progenitor cells and shows a distinct transcriptomic profile and inhibits mitochondrial oxidative phosphorylation. Inhibition of AXL or BCL-2 also differentially targets key signaling proteins to synergize in leukemic cell killing. These findings have a direct translational impact on the treatment of AML and other cancers with high AXL activity.

Glucocorticoids enhance the antileukemic activity of FLT3 inhibitors in FLT3-mutant acute myeloid leukemia

FLT3 is a frequently mutated gene that is highly associated with a poor prognosis in acute myeloid leukemia (AML). Despite initially responding to FLT3 inhibitors, most patients eventually relapse with drug resistance. The mechanism by which resistance arises and the initial response to drug treatment that promotes cell survival is unknown. Recent studies show that a transiently maintained subpopulation of drug-sensitive cells, so-called drug-tolerant "persisters" (DTPs), can survive cytotoxic drug exposure despite lacking resistance-conferring mutations. Using RNA sequencing and drug screening, we find that treatment of FLT3 internal tandem duplication AML cells with quizartinib, a selective FLT3 inhibitor, upregulates inflammatory genes in DTPs and thereby confers susceptibility to anti-inflammatory glucocorticoids (GCs). Mechanistically, the combination of FLT3 inhibitors and GCs enhances cell death of FLT3 mutant, but not wild-type, cells through GC-receptor-dependent upregulation of the proapoptotic protein BIM and proteasomal degradation of the antiapoptotic protein MCL-1. Moreover, the enhanced antileukemic activity by quizartinib and dexamethasone combination has been validated using primary AML patient samples and xenograft mouse models. Collectively, our study indicates that the combination of FLT3 inhibitors and GCs has the potential to eliminate DTPs and therefore prevent minimal residual disease, mutational drug resistance, and relapse in FLT3-mutant AML.

Targeting BCL-2 in Cancer: Advances, Challenges, and Perspectives

Simple Summary

Apoptosis, a programmed form of cell death, represents the main mechanism by which cells die. Such phenomenon is highly regulated by the BCL-2 family of proteins, which includes both pro-apoptotic and pro-survival proteins. The decision whether cells live or die is tightly controlled by a balance between these two classes of proteins. Notably, the pro-survival Bcl-2 proteins are frequently overexpressed in cancer cells dysregulating this balance in favor of survival and also rendering cells more resistant to therapeutic interventions. In this review, we outlined the most important steps in the development of targeting the BCL-2 survival proteins, which laid the ground for the discovery and the development of the selective BCL-2 inhibitor venetoclax as a therapeutic drug in hematological malignancies. The limitations and future directions are also discussed.

Abstract

The major form of cell death in normal as well as malignant cells is apoptosis, which is a programmed process highly regulated by the BCL-2 family of proteins. This includes the antiapoptotic proteins (BCL-2, BCL-XL, MCL-1, BCLW, and BFL-1) and the proapoptotic proteins, which can be divided into two groups: the effectors (BAX, BAK, and BOK) and the BH3-only proteins (BIM, BAD, NOXA, PUMA, BID, BIK, HRK). Notably, the BCL-2 antiapoptotic proteins are often overexpressed in malignant cells. While this offers survival advantages to malignant cells and strengthens their drug resistance capacity, it also offers opportunities for novel targeted therapies that selectively kill such cells. This review provides a comprehensive overview of the extensive preclinical and clinical studies targeting BCL-2 proteins with various BCL-2 proteins inhibitors with emphasis on venetoclax as a single agent, as well as in combination with other therapeutic agents. This review also discusses recent advances, challenges focusing on drug resistance, and future perspectives for effective targeting the Bcl-2 family of proteins in cancer.

CS2164 and Venetoclax Show Synergistic Antitumoral Activities in High Grade B-Cell Lymphomas With MYC and BCL2 Rearrangements

High-grade B-cell lymphoma with concurrent MYC and BCL2 rearrangements (HGBL-DHL) is a rare, aggressive mature B-cell malignancy with a high likelihood of treatment failure following front-line immunochemotherapies. Patients with HGBL-DHL who develop a relapsed or refractory disease have little effective therapeutic strategies and show very poor clinical outcomes, thus calling for development of novel therapies for this specific patient population. In this study, we investigated the preclinical anti-lymphoma efficacies and potential mechanism of action of a novel treatment approach, combining the BCL2 inhibitor venetoclax with CS2164, a new orally active multitarget inhibitor, in HGBL-DHL models. This combination therapy exhibited a robust synergistic cytotoxicity against HGBL-DHL cells, evidenced by cooperatively inducing loss of cell viability and promoting cell apoptosis. Moreover, coadministration of CS2164 and venetoclax resulted in significant superior suppression of HGBL-DHL cell growth and remarkably abrogated tumor burden in a HGBL-DHL-xenografted mouse model. The synergistic lethality of CS2164 and venetoclax in HGBL-DHL cells was associated with induction of DNA damage and impairment of DNA repair ability. Of importance, the combined treatment almost abolished the expression of both BCL2 and MYC, two hallmark proteins of HGBL-DHL, and substantially blunted the activity of PI3K/AKT/mTOR signaling cascade. In addition, MCL1 and BCL-XL, two well-characterized contributors for venetoclax resistance, were significantly lessened in the presence of CS2164 and venetoclax, thus leading to the accumulation of proapoptotic proteins BAX and PUMA and then initiating the intrinsic apoptosis pathway. Taken together, these findings suggest that the regimen of CS2164 and venetoclax is highly effective to eliminate HGBL-DHL cells in the preclinical setting, warranting further clinical investigations of this regimen for the treatment of unfavorable HGBL-DHL patients.

The application of BH3 mimetics in myeloid leukemias

Execution of the intrinsic apoptotic pathway is controlled by the BCL-2 proteins at the level of the mitochondrial outer membrane (MOM). This family of proteins consists of prosurvival (e.g., BCL-2, MCL-1) and proapoptotic (e.g., BIM, BAD, HRK) members, the functional balance of which dictates the activation of BAX and BAK. Once activated, BAX/BAK form pores in the MOM, resulting in cytochrome c release from the mitochondrial intermembrane space, leading to apoptosome formation, caspase activation, and cleavage of intracellular targets. This pathway is induced by cellular stress including DNA damage, cytokine and growth factor withdrawal, and chemotherapy/drug treatment. A well-documented defense of leukemia cells is to shift the balance of the BCL-2 family in favor of the prosurvival proteins to protect against such intra- and extracellular stimuli. Small molecule inhibitors targeting the prosurvival proteins, named 'BH3 mimetics', have come to the fore in recent years to treat hematological malignancies, both as single agents and in combination with standard-of-care therapies. The most significant example of these is the BCL-2-specific inhibitor venetoclax, given in combination with standard-of-care therapies with great success in AML in clinical trials. As the number and variety of available BH3 mimetics increases, and investigations into applying these novel inhibitors to treat myeloid leukemias continue apace the need to evaluate where we currently stand in this rapidly expanding field is clear.

Venetoclax plus LDAC for newly diagnosed AML ineligible for intensive chemotherapy: a phase 3 randomized placebo-controlled trial

Effective treatment options are limited for patients with acute myeloid leukemia (AML) who cannot tolerate intensive chemotherapy. Adults age ≥18 years with newly diagnosed AML ineligible for intensive chemotherapy were enrolled in this international phase 3 randomized double-blind placebo-controlled trial. Patients (N = 211) were randomized 2:1 to venetoclax (n = 143) or placebo (n = 68) in 28-day cycles, plus low-dose cytarabine (LDAC) on days 1 to 10. Primary end point was overall survival (OS); secondary end points included response rate, transfusion independence, and event-free survival. Median age was 76 years (range, 36-93 years), 38% had secondary AML, and 20% had received prior hypomethylating agent treatment. Planned primary analysis showed a 25% reduction in risk of death with venetoclax plus LDAC vs LDAC alone (hazard ratio [HR], 0.75; 95% confidence interval [CI], 0.52-1.07; P = .11), although not statistically significant; median OS was 7.2 vs 4.1 months, respectively. Unplanned analysis with additional 6-month follow-up demonstrated median OS of 8.4 months for the venetoclax arm (HR, 0.70; 95% CI, 0.50-0.98; P = .04). Complete remission (CR) plus CR with incomplete blood count recovery rates were 48% and 13% for venetoclax plus LDAC and LDAC alone, respectively. Key grade ≥3 adverse events (venetoclax vs LDAC alone) were febrile neutropenia (32% vs 29%), neutropenia (47% vs 16%), and thrombocytopenia (45% vs 37%). Venetoclax plus LDAC demonstrates clinically meaningful improvement in remission rate and OS vs LDAC alone, with a manageable safety profile. Results confirm venetoclax plus LDAC as an important frontline treatment for AML patients unfit for intensive chemotherapy. This trial was registered at www.clinicaltrials.gov as #NCT03069352.

Venetoclax for the treatment of elderly or chemotherapy-ineligible patients with acute myeloid leukemia: a step in the right direction or a game changer?

INTRODUCTION

Acute myeloid leukemia (AML) is an aggressive malignancy with poor prognosis and high rates of relapse, especially in elderly patients who are ineligible to receive intensive chemotherapy. Venetoclax, an oral BCL-2 inhibitor, is approved by the Food and Drug Administration in combination with hypomethylating agents or low-dose cytarabine in newly-diagnosed AML patients who are ineligible to receive intensive chemotherapy. Confirmatory phase III VIALE-A and VIALE-C trials showed a composite complete remission rate of 66.4% and 48%, respectively. Thus, further validating venetoclax as an attractive therapeutic option in the AML treatment landscape.

AREAS COVERED

A review of venetoclax in AML, focusing on preclinical and clinical data, toxicity profile, and mechanisms of resistance; and its strengths and weaknesses in regards to its current and future role in AML treatment is discussed. To find relevant studies, authors searched PubMed/Medline and ClinicalTrials.gov.

EXPERT OPINION

The introduction of venetoclax-based combination therapies has greatly expanded the therapeutic options for elderly and chemotherapy-ineligible AML patients. Additional studies with extended follow-up are necessary to address remaining open questions such as (I) durability of responses, (II) head-to-head comparisons with intensive chemotherapy in selected patients (e.g. TP53 mutations), and (III) novel triplet combinations using an HMA-venetoclax backbone.

Targeting MCL-1 dysregulates cell metabolism and leukemia-stroma interactions and resensitizes acute myeloid leukemia to BCL-2 inhibition

MCL-1 and BCL-2 are both frequently overexpressed in acute myeloid leukemia (AML) and critical for the survival of AML cells and AML stem cells. MCL-1 is a key factor in venetoclax resistance. Using genetic and pharmacological approaches, we discovered that MCL-1 regulates leukemia cell bioenergetics and carbohydrate metabolisms, including the TCA cycle, glycolysis and pentose phosphate pathway and modulates cell adhesion proteins and leukemia-stromal interactions. Inhibition of MCL-1 sensitizes to BCL-2 inhibition in AML cells and AML stem/progenitor cells, including those with intrinsic and acquired resistance to venetoclax through cooperative release of pro-apoptotic BIM, BAX, and BAK from binding to anti-apoptotic BCL- 2 proteins and inhibition of cell metabolism and key stromal microenvironmental mechanisms. The combined inhibition of MCL-1 by MCL-1 inhibitor AZD5991 or CDK9 inhibitor AZD4573 and BCL-2 by venetoclax greatly extended survival of mice bearing patient-derived xenografts established from an AML patient who acquired resistance to venetoclax/decitabine. These results demonstrate that co-targeting MCL-1 and BCL-2 improves the efficacy of and overcomes pre-existing and acquired resistance to BCL-2 inhibition. Activation of metabolomic pathways and leukemia-stroma interactions are newly discovered functions of MCL-1 in AML, which are independent from canonical regulation of apoptosis by MCL-1. Our data provide new mechanisms of synergy and a rationale for co-targeting MCL-1 and BCL-2 clinically in patients with AML and potentially other cancers.

225Ac-labeled CD33-targeting antibody reverses resistance to Bcl-2 inhibitor venetoclax in acute myeloid leukemia models

Purpose

Despite the availability of new drugs, many patients with acute myeloid leukemia (AML) do not achieve remission and outcomes remain poor. Venetoclax is a promising new therapy approved for use in combination with a hypomethylating agent or with low‐dose cytarabine for the treatment of newly diagnosed older AML patients or those ineligible for intensive chemotherapy. ²²⁵Actinium‐lintuzumab (²²⁵Ac‐lintuzumab) is a clinical stage radioimmunotherapy targeting CD33 that has shown evidence of single‐agent activity in relapsed/refractory AML. Increased expression of MCL‐1 is a mediator of resistance to venetoclax in cancer.

Experimental design

Here we investigated the potential for ²²⁵Ac‐lintuzumab‐directed DNA damage to suppress MCL‐1 levels as a possible mechanism of reversing resistance to venetoclax in two preclinical in vivo models of AML.

Results

We demonstrated that ²²⁵Ac‐lintuzumab in combination with venetoclax induced a synergistic increase in tumor cell killing compared to treatment with either drug alone in venetoclax‐resistant AML cell lines through both an induction of double‐stranded DNA breaks (DSBs) and depletion of MCL‐1 protein levels. Further, this combination led to significant tumor growth control and prolonged survival benefit in venetoclax‐resistant in vivo AML models.

Conclusions

There results suggest that the combination of ²²⁵Ac‐lintuzumab with venetoclax is a promising therapeutic strategy for the treatment of patients with venetoclax‐resistant AML.

Clinical trial of this combination therapy (NCT03867682) is currently ongoing.

Targeting multiple signaling pathways: the new approach to acute myeloid leukemia therapy

Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults and the second most common form of acute leukemia in children. Despite this, very little improvement in survival rates has been achieved over the past few decades. This is partially due to the heterogeneity of AML and the need for more targeted therapeutics than the traditional cytotoxic chemotherapies that have been a mainstay in therapy for the past 50 years. In the past 20 years, research has been diversifying the approach to treating AML by investigating molecular pathways uniquely relevant to AML cell proliferation and survival. Here we review the development of novel therapeutics in targeting apoptosis, receptor tyrosine kinase (RTK) signaling, hedgehog (HH) pathway, mitochondrial function, DNA repair, and c-Myc signaling. There has been an impressive effort into better understanding the diversity of AML cell characteristics and here we highlight important preclinical studies that have supported therapeutic development and continue to promote new ways to target AML cells. In addition, we describe clinical investigations that have led to FDA approval of new targeted AML therapies and ongoing clinical trials of novel therapies targeting AML survival pathways. We also describe the complexity of targeting leukemia stem cells (LSCs) as an approach to addressing relapse and remission in AML and targetable pathways that are unique to LSC survival. This comprehensive review details what we currently understand about the signaling pathways that support AML cell survival and the exceptional ways in which we disrupt them.

The Heme-Regulated Inhibitor Pathway Modulates Susceptibility of Poor Prognosis B-Lineage Acute Leukemia to BH3-Mimetics

Antiapoptotic MCL1 is one of the most frequently amplified genes in human cancers and elevated expression confers resistance to many therapeutics including the BH3-mimetic agents ABT-199 and ABT-263. The antimalarial, dihydroartemisinin (DHA) translationally represses MCL-1 and synergizes with BH3-mimetics. To explore how DHA represses MCL-1, a genome-wide CRISPR screen identified that loss of genes in the heme synthesis pathway renders mouse BCR-ABL⁺ B-ALL cells resistant to DHA-induced death. Mechanistically, DHA disrupts the interaction between heme and the eIF2α kinase heme-regulated inhibitor (HRI) triggering the integrated stress response. Genetic ablation of Eif2ak1, which encodes HRI, blocks MCL-1 repression in response to DHA treatment and represses the synergistic killing of DHA and BH3-mimetics compared with wild-type leukemia. Furthermore, BTdCPU, a small-molecule activator of HRI, similarly triggers MCL-1 repression and synergizes with BH3-mimetics in mouse and human leukemia including both Ph⁺ and Ph-like B-ALL. Finally, combinatorial treatment of leukemia bearing mice with both BTdCPU and a BH3-mimetic extended survival and repressed MCL-1 in vivo. These findings reveal for the first time that the HRI-dependent cellular heme-sensing pathway can modulate apoptosis in leukemic cells by repressing MCL-1 and increasing their responsiveness to BH3-mimetics. This signaling pathway could represent a generalizable mechanism for repressing MCL-1 expression in malignant cells and sensitizing them to available therapeutics. IMPLICATIONS: The HRI-dependent cellular heme-sensing pathway can modulate apoptotic sensitivity in leukemic cells by repressing antiapoptotic MCL-1 and increasing their responsiveness to BH3-mimetics.

Targeting Apoptosis in Acute Myeloid Leukemia: Current Status and Future Directions of BCL-2 Inhibition with Venetoclax and Beyond

Acute myeloid leukemia (AML) is a disease of the hematopoietic system that remains a therapeutic challenge despite advances in our understanding of the underlying cancer biology over the past decade. Recent developments in molecular targeting have shown promising results in treating leukemia, paving the way for novel treatment strategies. The discovery of drugs that promote apoptosis in leukemic cells has translated to encouraging activity in clinical trials. B-cell lymphoma (BCL)-2 inhibition has been at the center of drug development efforts to target apoptosis in AML. Remarkable clinical success with venetoclax has revolutionized the ways we treat hematological malignancies. Several landmark trials have demonstrated the potent antitumor activity of venetoclax, and it is now frequently combined with traditional cytotoxic agents to treat AML. However, resistance to BCL-2 inhibition is emerging, and alternative strategies to address resistance mechanisms have become an important focus of research. A number of clinical trials are now underway to investigate a plurality of novel agents that were shown to overcome resistance to BCL-2 inhibition in preclinical models. Some of the most promising data come from studies on drugs that downregulate myeloid cell leukemia (MCL)-1, such as cyclin-dependent kinases (CDK) inhibitors. Furthermore, innovative approaches to target apoptosis via extrinsic pathways and p53 regulation have added new cytotoxic agents to the arsenal, including drugs that inhibit inhibitor of apoptosis protein (IAP) family proteins and murine double minute 2 (MDM2). This review provides a perspective on past and current treatment strategies harnessing various mechanisms of apoptosis to target AML and highlights some important promising treatment combinations in development.

Current Understandings of Myeloid Differentiation Inducers in Leukemia Therapy

Differentiation therapy using all-trans retinoic acid for acute promyelocytic leukemia (APL) is well established. Several attempts have been made to treat non-APL, AML patients by employing differentiation inducers, such as hypomethylating agents (HMAs), and low-dose cytarabine (Ara-C) (LDAC), with encouraging results. Other than HMAs and LDAC, various inducers of myeloid cell differentiation have been identified. This review describes and categorizes these inducers, which include glycosylation modifiers, epigenetic modifiers, vitamin derivatives, cytokines, and chemotherapeutic agents. Some of these inducers are currently being used in clinical trials. I highlight the potential applications of glycosylation modifiers and epigenetic modifiers, which are attracting increasing attention in their use as differentiation therapy against AML. Among the agents described in this review, epigenomic modifiers seem particularly promising, and particular attention should also be paid to glycosylation modifiers. These drugs may signal a new era for AML differentiation therapy.

Targeting Bcl-2 Proteins in Acute Myeloid Leukemia

B cell lymphoma 2 (BCL-2) family proteins play an important role in intrinsic apoptosis. Overexpression of BCL-2 proteins in acute myeloid leukemia can circumvent resistance to apoptosis and chemotherapy. Considering this effect, the exploration of anti-apoptotic BCL-2 inhibitors is considered to have tremendous potential for the discovery of novel pharmacological modulators in cancer. This review outlines the impact of BCL-2 family proteins on intrinsic apoptosis and the development of acute myeloid leukemia (AML). Furthermore, we will also review the new combination therapy with venetoclax that overcomes resistance to venetoclax and discuss biomarkers of treatment response identified in early-phase clinical trials.

Venetoclax-Based Combinations in Acute Myeloid Leukemia: Current Evidence and Future Directions

The past decade has witnessed major advances in our understanding of molecular biology, which led to breakthrough novel therapies, importantly including the B-cell lymphoma-2 (BCL-2) inhibitor venetoclax. Notably, venetoclax-based combinations have improved outcomes, including both remission rates and overall survival, of older patients with acute myeloid leukemia (AML) deemed "unfit" for intensive chemotherapy due to age or comorbidities. This has translated into a rapid and widespread use of venetoclax-based combinations in both academic and community-based settings. Other venetoclax-based combinations are being investigated in AML with the ultimate goal of improving cure rates across many subgroups; frontline and relapsed/refractory, in combination with intensive chemotherapy, in the post-transplant setting, or as maintenance strategy. In this article, we summarize the current available data on venetoclax-based combinations. We also highlight areas of unmet medical need, and we offer practical clinical pearls for management of patients receiving such therapy.