Targeted therapies in Acute Myeloid Leukemia: a focus on FLT-3 inhibitors and ABT199

Meta‑analysis of the efficacy of venetoclax and azacitidine combination therapy and azacitidine monotherapy for treating acute myeloid leukemia

The present study aimed to compare the efficacy of combination therapy with venetoclax and azacitidine with that of azacytidine monotherapy in the treatment of acute myeloid leukemia (AML). The Web of Science, PubMed, Embase, The Cochrane Library, Weipu Database, Wanfang Digital Periodicals, Sinomed, China National Knowledge Infrastructure, ProQuest Dissertations and Theses and Cumulative Index to Nursing and Allied Health Literature were searched for publications on the treatment of AML with venetoclax combined with azacitidine or with azacitidine monotherapy. A total of 5,271 relevant studies were retrieved, of which 10 were included. Literature quality was evaluated according to the Cochrane systematic review methodology, and data were extracted for meta-analysis using Review Manager 5.4. The combination of venetoclax and azacitidine demonstrated greater overall efficacy than azacitidine monotherapy for AML treatment. Notably, combination therapy resulted in a higher frequency of complete remission. By contrast, combined treatment and monotherapy showed no significant differences in partial remission, whereas there was a statistically significant decrease in the frequency of no remission in the combination therapy group compared with in the monotherapy group. The results also revealed a significantly higher incidence of adverse reactions when venetoclax and azacitidine were combined in the treatment of AML compared with the observed rates in response to azacitidine monotherapy. Moreover, subgroup analyses showed that no statistically significant differences were observed between the two groups regarding adverse events, including hypokalemia and liver insufficiency. In conclusion, the combination of venetoclax and azacitidine was more effective than azacitidine alone, and had a good clinical application value in the treatment of AML. Although some adverse reactions occurred in response to the combination therapy, they did not significantly affect the prognosis of AML. To better evaluate the efficacy and safety of this treatment regimen, multicenter clinical studies with larger sample sizes are required.

Machine Learning–Based Exploratory Clinical Decision Support for Newly Diagnosed Patients With Acute Myeloid Leukemia Treated With 7 + 3 Type Chemotherapy or Venetoclax/Azacitidine

PURPOSE

There are currently limited objective criteria to help assist physicians in determining whether an individual patient with acute myeloid leukemia (AML) is likely to do better with induction with either standard 7 + 3 chemotherapy or targeted therapy with venetoclax plus azacitidine. The study goal was to address this need by developing exploratory clinical decision support methods.

PATIENTS AND METHODS

Univariable and multivariable analysis as well as comparison of a range of machine learning (ML) predictors were performed using cohorts of 120 newly diagnosed 7 + 3-treated AML patients compared with 101 venetoclax plus azacitidine–treated patients.

RESULTS

A variety of features in the two patient cohorts were identified that may potentially correlate with short- and long-term outcomes, toxicities, and other considerations. A subset of these diagnostic features was then used to develop ML-based predictors with relatively high areas under the curve of short- and long-term outcomes, hospital stays, transfusion requirements, and toxicities for individual patients treated with either venetoclax/azacitidine or 7 + 3.

CONCLUSION

Potential ML-based approaches to clinical decision support to help guide individual patients with newly diagnosed AML to either 7 + 3 or venetoclax plus azacitidine induction therapy were identified. Larger cohorts with separate test and validation studies are necessary to confirm these initial findings.

Role of Pharmacogenetics in the Treatment of Acute Myeloid Leukemia: Systematic Review and Future Perspectives

Acute myeloid leukemia (AML) is a heterogeneous disease characterized by remarkable toxicity and great variability in response to treatment. Plenteous pharmacogenetic studies have already been published for classical therapies, such as cytarabine or anthracyclines, but such studies remain scarce for newer drugs. There is evidence of the relevance of polymorphisms in response to treatment, although most studies have limitations in terms of cohort size or standardization of results. The different responses associated with genetic variability include both increased drug efficacy and toxicity and decreased response or resistance to treatment. A broad pharmacogenetic understanding may be useful in the design of dosing strategies and treatment guidelines. The aim of this study is to perform a review of the available publications and evidence related to the pharmacogenetics of AML, compiling those studies that may be useful in optimizing drug administration.

PROTAC: An Effective Targeted Protein Degradation Strategy for Cancer Therapy

Proteolysis targeting chimeric (PROTAC) technology is an effective endogenous protein degradation tool developed in recent years that can ubiquitinate the target proteins through the ubiquitin-proteasome system (UPS) to achieve an effect on tumor growth. A number of literature studies on PROTAC technology have proved an insight into the feasibility of PROTAC technology to degrade target proteins. Additionally, the first oral PROTACs (ARV-110 and ARV-471) have shown encouraging results in clinical trials for prostate and breast cancer treatment, which inspires a greater enthusiasm for PROTAC research. Here we focus on the structures and mechanisms of PROTACs and describe several classes of effective PROTAC degraders based on E3 ligases.

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

FLT3 internal tandem duplication (FLT3-ITD) mutations account for ~25% of adult acute myeloid leukemia cases and are associated with poor prognosis. Venetoclax, a selective BCL-2 inhibitor, has limited monotherapy activity in relapsed/refractory acute myeloid leukemia with no responses observed in a small subset of FLT3-ITD+ patients. Further, FLT3-ITD mutations emerged at relapse following venetoclax monotherapy and combination therapy suggesting a potential mechanism of resistance. Therefore, we investigated the convergence of FLT3-ITD signaling on the BCL-2 family proteins and determined combination activity of venetoclax and FLT3-ITD inhibition in preclinical models. In vivo, venetoclax combined with quizartinib, a potent FLT3 inhibitor, showed greater anti-tumor efficacy and prolonged survival compared to monotherapies. In a patient-derived FLT3-ITD+ xenograft model, cotreatment with venetoclax and quizartinib at clinically relevant doses had greater anti-tumor activity in the tumor microenvironment compared to quizartinib or venetoclax alone. Use of selective BCL-2 family inhibitors further identified a role for BCL-2, BCL-XL and MCL-1 in mediating survival in FLT3-ITD+ cells in vivo and highlighted the need to target all three proteins for greatest anti-tumor activity. Assessment of these combinations in vitro revealed synergistic combination activity for quizartinib and venetoclax but not for quizartinib combined with BCL-XL or MCL-1 inhibition. FLT3-ITD inhibition was shown to indirectly target both BCL-XL and MCL-1 through modulation of protein expression, thereby priming cells toward BCL-2 dependence for survival. These data demonstrate that FLT3-ITD inhibition combined with venetoclax has impressive anti-tumor activity in FLT3-ITD+ acute myeloid leukemia preclinical models and provides strong mechanistic rational for clinical studies.

The multi-tyrosine kinase inhibitor ponatinib for chronic myeloid leukemia: Real-world data

Development of the highly selective targeted tyrosine kinase inhibitors (TKIs) has expanded the therapeutic options for chronic myeloid leukemia (CML). Patients undergoing TKI therapy should be closely monitored to ensure that the best therapeutic response and quality of life are achieved, and to control suboptimal responses and adverse events. Despite the high rate of response using current first-line TKIs, treatment failure may still occur, and resistance is considered a challenge in the treatment of patients with CML. The third-generation TKI, ponatinib, is a potent orally bioavailable pan BCR-ABL inhibitor that inhibits both wild-type and mutant BCR-ABL1 kinase, including the "gatekeeper" T315I mutation, which is resistant to all other currently available TKIs. This paper reviews the effectiveness, feasibility, and safety of ponatinib in the real-life clinical management of CML. Potential prognostic factors in identifying patients most likely to benefit from ponatinib treatment will be discussed, and case presentations illustrating situations encountered in real-life clinical practice are described. Ponatinib is effective in patients who have received prior TKIs in clinical studies as well as under real-life conditions. Nevertheless, the risk/benefit balance must be evaluated for each patient, particularly considering disease state, mutational status, treatment line, intolerance/resistance to prior TKIs, age, frailty, and specific comorbidities.

Panobinostat and venetoclax enhance the cytotoxicity of gemcitabine, busulfan, and melphalan in multiple myeloma cells

Gemcitabine (Gem), busulfan (Bu), and melphalan (Mel) are used for hematopoietic stem cell transplantation. To further improve their efficacy, a preclinical study on their synergism with the histone deacetylase inhibitor panobinostat (Pano) and the BCL2 inhibitor venetoclax/ABT199 was performed. Multiple myeloma cell lines MM.1R and MC/CAR were exposed to ∼IC₂₀ levels of the drugs. Synergistic cytotoxicity was observed in cells exposed to the five-drug combination as indicated by combination indexes <1, supported by ∼86% inhibition of proliferation and ∼84% annexin V positivity in MM.1R and ∼58% inhibition of proliferation and ∼46% annexin V positivity in MC/CAR cells. Activation of the DNA damage response and apoptosis were suggested by a modest increase in the phosphorylation of ATM and its substrates; significant cleavage of PARP1, caspase 3, and heat shock protein 90; DNA fragmentation; mitochondrial membrane depolarization; and reactive oxygen species production. The five-drug combination significantly decreased the levels of PI3K, AKT, mTOR, RAPTOR, P-P70S6K, and eIF2α, with concomitant increases in P-AMPK and its substrate Tuberin/TSC2, suggesting that the mTOR signaling pathway was compromised. Endoplasmic reticulum stress through activation of the unfolded protein response was also observed as suggested by increases in the levels of calnexin, BiP/GRP78, ERO1-Lα, and protein disulfide isomerase, which may relate to venetoclax-mediated inhibition of BCL2 in the endoplasmic reticulum. This is the first report on the effects of a venetoclax-containing regimen on the unfolded protein response. These results provide a rationale to propose a clinical trial on use of Gem + Bu + Mel + Pano + Venetoclax as part of a conditioning regimen for multiple myeloma patients undergoing autologous hematopoietic stem cell transplantation.

Novel treatments for relapsed/refractory acute myeloid leukemia with FLT3 mutations

Introduction: Mutations in the gene encoding for the FMS-like tyrosine kinase 3 (FLT3) are present in about 30% of adults with AML and are associated with shorter disease-free and overall survival after initial therapy. Prognosis of relapsed/refractory AML with FLT3 mutations is even more dismal with median overall survival of a few months only. Areas covered: This review will cover current and emerging treatments for relapsed/refractory AML with FLT3 mutations, preclinical rationale and clinical trials with new encouraging data for this particularly challenging population. The authors discuss mechanisms of resistance to FLT3 inhibitors and how these insights serve to identify current and future treatments. As allogeneic stem cell transplant in the first remission is the preferred therapy for newly diagnosed AML patients with FLT3 mutations, the authors discuss the role of maintenance after SCT for the prevention of relapse. Expert opinion: Relapsed/refractory AML with FLT3 mutations remains a therapeutic challenge with currently available treatments. However, the evolution of targeted therapies with next-generation FLT3 inhibitors and their combinations with chemotherapy is showing much promise. Moreover, growing understanding of the pathways of resistance to treatment has led to the identification of various targeted therapies currently being explored, which in time will improve outcomes.

Impact of elevated anti-apoptotic MCL-1 and BCL-2 on the development and treatment of MLL-AF9 AML in mice

Many acute myeloid leukaemias (AMLs) express high levels of BCL-2 and MCL-1, especially after therapy. To test the impact of these anti-apoptotic proteins on AML development and treatment, we used haemopoietic reconstitution to generate MLL-AF9 AMLs expressing BCL-2 or Mcl-1 transgenes. AMLs with elevated BCL-2 or MCL-1 had a higher proportion of mature myeloid cells but, like conventional MLL-AF9 AMLs, were readily transplantable. Short-term cell lines established from multiple primary AMLs of each genotype were tested in vitro for susceptibility to chemotherapeutics currently used for treating AML (daunorubicin, etoposide, cytarabine); the proteasome inhibitor bortezomib; CDK7/9 inhibitors; and BH3 mimetics, which bind and inhibit pro-survival proteins. The BH3 mimetics tested, alone and in combination with the other drugs, were: ABT-737 which, like its clinical counterpart navitoclax, targets BCL-2, BCL-X_L and BCL-W; BCL-2-specific ABT-199 (venetoclax); BCL-X_L-specific A-1331852; and S63845, a new MCL-1-specific BH3 mimetic. As single agents, daunorubicin and bortezomib had the greatest efficacy. Elevated MCL-1 or BCL-2 reduced sensitivity to daunorubicin but, surprisingly, not to bortezomib. MCL-1 markedly enhanced resistance to ABT-737 and ABT-199 but not S63845, and BCL-2 increased resistance to S63845 but not to ABT-737 or ABT-199. Notable synergies were achieved by combining BH3 mimetics with daunorubicin: S63845 increased the sensitivity of both MCL-1 and BCL-2 overexpressing MLL-AF9 AMLs, and ABT-737 aided in killing those overexpressing BCL-2. Synergy between daunorubicin and ABT-199 was also apparent in vivo, although not curative. Impressive synergistic responses were achieved for human MLL-fusion AML cell lines treated with daunorubicin plus either ABT-737, ABT-199 or S63845, and with ABT-199 plus S63845, with or without daunorubicin. Our data suggest that AML patients may benefit from combining conventional cytotoxic drugs with BH3 mimetics targeting BCL-2 or MCL-1 or, if tolerated, both these agents.

Targeting Oncogenic Signaling in Mutant FLT3 Acute Myeloid Leukemia: The Path to Least Resistance

The identification of recurrent driver mutations in genes encoding tyrosine kinases has resulted in the development of molecularly-targeted treatment strategies designed to improve outcomes for patients diagnosed with acute myeloid leukemia (AML). The receptor tyrosine kinase FLT3 is the most commonly mutated gene in AML, with internal tandem duplications within the juxtamembrane domain (FLT3-ITD) or missense mutations in the tyrosine kinase domain (FLT3-TKD) present in 30–35% of AML patients at diagnosis. An established driver mutation and marker of poor prognosis, the FLT3 tyrosine kinase has emerged as an attractive therapeutic target, and thus, encouraged the development of FLT3 tyrosine kinase inhibitors (TKIs). However, the therapeutic benefit of FLT3 inhibition, particularly as a monotherapy, frequently results in the development of treatment resistance and disease relapse. Commonly, FLT3 inhibitor resistance occurs by the emergence of secondary lesions in the FLT3 gene, particularly in the second tyrosine kinase domain (TKD) at residue Asp835 (D835) to form a ‘dual mutation’ (ITD-D835). Individual FLT3-ITD and FLT3-TKD mutations influence independent signaling cascades; however, little is known about which divergent signaling pathways are controlled by each of the FLT3 specific mutations, particularly in the context of patients harboring dual ITD-D835 mutations. This review provides a comprehensive analysis of the known discrete and cooperative signaling pathways deregulated by each of the FLT3 specific mutations, as well as the therapeutic approaches that hold the most promise of more durable and personalized therapeutic approaches to improve treatments of FLT3 mutant AML.

The irreversible ERBB1/2/4 inhibitor neratinib interacts with the BCL-2 inhibitor venetoclax to kill mammary cancer cells

The irreversible ERBB1/2/4 inhibitor, neratinib, down-regulates the expression of ERBB1/2/4 as well as the levels of MCL-1 and BCL-XL. Venetoclax (ABT199) is a BCL-2 inhibitor. At physiologic concentrations neratinib interacted in a synergistic fashion with venetoclax to kill HER2 + and TNBC mammary carcinoma cells. This was associated with the drug-combination: reducing the expression and phosphorylation of ERBB1/2/3; in an eIF2α-dependent fashion reducing the expression of MCL-1 and BCL-XL and increasing the expression of Beclin1 and ATG5; and increasing the activity of the ATM-AMPKα-ULK1 S317 pathway which was causal in the formation of toxic autophagosomes. Although knock down of BAX or BAK reduced drug combination lethality, knock down of BAX and BAK did not prevent the drug combination from increasing autophagosome and autolysosome formation. Knock down of ATM, AMPKα, Beclin1 or over-expression of activated mTOR prevented the induction of autophagy and in parallel suppressed tumor cell killing. Knock down of ATM, AMPKα, Beclin1 or cathepsin B prevented the drug-induced activation of BAX and BAK whereas knock down of BID was only partially inhibitory. A 3-day transient exposure of established estrogen-independent HER2 + BT474 mammary tumors to neratinib or venetoclax did not significantly alter tumor growth whereas exposure to [neratinib + venetoclax] caused a significant 7-day suppression of growth by day 19. The drug combination neither altered animal body mass nor behavior. We conclude that venetoclax enhances neratinib lethality by facilitating toxic BH3 domain protein activation via autophagy which enhances the efficacy of neratinib to promote greater levels of cell killing.