FDA Approval Summary: Gilteritinib for Relapsed or Refractory Acute Myeloid Leukemia with a FLT3 Mutation

Lipopolymer/siRNA Complexes Engineered for Optimal Molecular and Functional Response with Chemotherapy in FLT3-Mutated Acute Myeloid Leukemia

Approximately 25% of newly diagnosed AML patients display an internal tandem duplication (ITD) in the fms-like tyrosine kinase 3 (FLT3) gene. Although both multi-targeted and FLT3 specific tyrosine kinase inhibitors (TKIs) are being utilized for clinical therapy, drug resistance, short remission periods, and high relapse rates are challenges that still need to be tackled. RNA interference (RNAi), mediated by short interfering RNA (siRNA), presents a mechanistically distinct therapeutic platform with the potential of personalization due to its gene sequence-driven mechanism of action. This study explored the use of a non-viral approach for delivery of FLT3 siRNA (siFLT3) in FLT3-ITD positive AML cell lines and primary cells as well as the feasibility of combining this treatment with drugs currently used in the clinic. Treatment of AML cell lines with FLT3 siRNA nanocomplexes resulted in prominent reduction in cell proliferation rates and induction of apoptosis. Quantitative analysis of relative mRNA transcript levels revealed downregulation of the FLT3 gene, which was accompanied by a similar decline in FLT3 protein levels. Moreover, an impact on leukemic stem cells was observed in a small pool of primary AML samples through significantly reduced colony numbers. An absence of a molecular response post-treatment with lipopolymer/siFLT3 complexes in peripheral blood mononuclear cells, obtained from healthy individuals, denoted a passive selectivity of the complexes towards malignant cells. The effect of combining lipopolymer/siFLT3 complexes with daunorubucin and FLT3 targeting TKI gilteritinib led to a significant augmentation of anti-leukemic activity. These findings demonstrate the promising potential of RNAi implemented with lipopolymer complexes for AML molecular therapy. The study prospectively supports the addition of RNAi therapy to current treatment modalities available to target the heterogeneity prevalent in AML. STATEMENT OF SIGNIFICANCE: We show that a clinically validated target, the FLT3 gene, can be eradicated in leukemia cells using non-viral RNAi. We validated these lipopolymers as effective vehicles to deliver nucleic acids to leukemic cells. The potency of the lipopolymers was superior to that of the 'gold-standard' delivery agent, lipid nanoparticles (LNPs), which are not effective in leukemia cells at clinically relevant doses. Mechanistic studies were undertaken to probe structure-function relationships for effective biomaterial formulations. Cellular and molecular responses to siRNA treatment have been characterized in cell models, including leukemia patient-derived cells. The use of the siRNA therapy with clinically used chemotherapy was demonstrated.

Deciphering the mechanism of HM43239 inhibiting the mutant F691L resistant to gilteritinib in FMS-like tyrosine kinase 3

FMS-like tyrosine kinase (FLT3) has become the legitimate molecular therapeutic target for acute myeloid leukemia therapy. Though FLT3 inhibitors have impact on disease progression, drug resistance induced by secondary point mutations is the primary mechanism and urgent to overcome. Herein, we sought to decipher the mechanism of HM43239 inhibiting the mutant F691L resistant to gilteritinib in FLT3. A series of molecular modeling studies, including molecular dynamics (MD) simulation, dynamic cross-correlation (DCC) analysis, binding free energy (MM-GBSA) and docking study were explored to elucidate the differential tolerance mechanisms of two inhibitors to the same mutant. The F691L mutation had relatively larger effect on gilteritinib than HM43239, which showed as the changed and fixed conformation, respectively. These observations rationalized that the binding affinity of gilteritinib decreased more than that of HM43239 in the F691L mutant.Communicated by Ramaswamy H. Sarma.

Perspectives and challenges of small molecule inhibitor therapy for FLT3-mutated acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous clonal disease characterized overall by an aggressive clinical course. The underlying genetic abnormalities present in leukemic cells contribute significantly to the AML phenotype. Mutations in FMS-like tyrosine kinase 3 (FLT3) are one of the most common genetic abnormalities identified in AML, and the presence of these mutations strongly influences disease presentation and negatively impacts prognosis. Since mutations in FLT3 were identified in AML, they have been recognized as a valid therapeutic target resulting in decades of research to develop effective small molecule inhibitor treatment that could improve outcome for these patients. Despite the approval of several FLT3 inhibitors over the last couple of years, the treatment of patients with FLT3-mutated AML remains challenging and many questions still need to be addressed. This review will provide an up-to-date overview of our current understanding of FLT3-mutated AML and discuss what the current status is of the available FLT3 inhibitors for the day-to-day management of this aggressive disease.

Advances in Drug Delivery Systems for the Treatment of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a common and catastrophic hematological neoplasm with high mortality rates. Conventional therapies, including chemotherapy, hematopoietic stem cell transplantation (HSCT), immune therapy, and targeted agents, have unsatisfactory outcomes for AML patients due to drug toxicity, off-target effects, drug resistance, drug side effects, and AML relapse and refractoriness. These intrinsic limitations of current treatments have promoted the development and application of nanomedicine for more effective and safer leukemia therapy. In this review, the classification of nanoparticles applied in AML therapy, including liposomes, polymersomes, micelles, dendrimers, and inorganic nanoparticles, is reviewed. In addition, various strategies for enhancing therapeutic targetability in nanomedicine, including the use of conjugating ligands, biomimetic-nanotechnology, and bone marrow targeting, which indicates the potential to reverse drug resistance, are discussed. The application of nanomedicine for assisting immunotherapy is also involved. Finally, the advantages and possible challenges of nanomedicine for the transition from the preclinical phase to the clinical phase are discussed.

Targeting oncogenic kinases: Insights on FDA approved tyrosine kinase inhibitors

Protein kinases play pivotal roles in various biological functions, influencing cell differentiation, promoting survival, and regulating the cell cycle. The disruption of protein kinase activity is intricately linked to pathways in tumor development. This manuscript explores the transformative impact of protein kinase inhibitors on cancer therapy, particularly their efficacy in cases driven by targeted mutations. Focusing on key tyrosine kinase inhibitors (TKIs) like Bcr-Abl, Epidermal Growth Factor Receptor (EGFR), and Vascular Endothelial Growth Factor Receptor (VEGFR), it targets critical kinase families in cancer progression. Clinical trial details of these TKIs offer insights into their therapeutic potentials. Learning from FDA-approved kinase inhibitors, the review dissects trends in kinase drug development since imatinib's paradigm-shifting approval in 2001. TKIs have evolved into pivotal drugs, extending beyond oncology. Ongoing clinical trials explore novel kinase targets, revealing the vast potential within the human kinome. The manuscript provides a detailed analysis of advancements until 2022, discussing the roles of specific oncogenic protein kinases in cancer development and carcinogenesis. Our exploration on PubMed for relevant and significant TKIs undergoing pre-FDA approval phase III clinical trials enriches the discussion with valuable findings. While kinase inhibitors exhibit lower toxicity than traditional chemotherapy in cancer treatment, challenges like resistance and side effects emphasize the necessity of understanding resistance mechanisms, prompting the development of novel inhibitors like osimertinib targeting specific mutant proteins. The review advocates thorough research on effective combination therapies, highlighting the future development of more selective RTKIs to optimize patient-specific cancer treatment and reduce adverse events.

Comprehensive Review of ROS1 Tyrosine Kinase Inhibitors-Classified by Structural Designs and Mutation Spectrum (Solvent Front Mutation [G2032R] and Central β-Sheet 6 [Cβ6] Mutation [L2086F])

Despite ROS1 fusion-positive NSCLC accounting for approximately 1% to 2% of NSCLC, there is a long list of ROS1 tyrosine kinase inhibitors (TKIs) being developed in addition to three approved ROS1 TKIs, crizotinib, entrectinib and repotrectinib. Here, we categorized ROS1 TKIs by their structures (cyclic versus noncyclic) and inhibitory abilities (active against solvent front mutation G2032R or central β-sheet #6 [Cβ6] mutation L2086F) and summarized their reported clinical activity in order to provide a dashboard on how to use these ROS1 TKIs in various clinical situations. In addition, the less known Cβ6 mutation ROS1 L2086F confer resistances to next-generation ROS1 TKIs (repotrectinib, taletrectinib, and potentially NVL-520) that can be overcome by cabozantinib as documented in published patient reports and potentially by certain L-shaped type I ROS1 TKIs including ceritinib and gilteritinib, which is approved as a FLT3 inhibitor for relapsed refractory FLT3+ acute myeloid leukemia but have published preclinical activites against ROS1 (and ALK). Future clinical trials should investigate cabozantinib and gilteritinib to repurpose them as ROS1 TKIs that can target ROS1 L2086F Cβ6 mutation.

Paclitaxel mediates the PI3K/AKT/mTOR pathway to reduce proliferation of FLT3‑ITD+ AML cells and promote apoptosis

Acute myeloid leukemia (AML) with internal tandem duplication (ITD) mutations in the FLT3 tyrosine kinase tend to have a poor prognosis. FLT3-ITD can promote the progress of AML by activating the PI3K/AKT/mTOR pathway. Paclitaxel (PTX) is a natural anticancer drug that has been widely used in chemotherapy for multiple malignancies. The present study used the CCK-8 assay, flow cytometry, PCR and western blotting to explore the anti-leukemia effect and possible mechanisms of PTX on MV4-11 cells with the FLT3-ITD mutation and the underlying mechanism. As a result, it was found that PTX could inhibit proliferation of MV4-11 cells and promoted apoptosis by inhibiting the PI3K/AKT/mTOR pathway.

Advancements and Challenges in the Treatment of AML

The therapeutic arsenal for the management of AML has expanded significantly in recent years. Before 2017, newly diagnosed AML was treated with either standard cytarabine- and anthracycline-based induction chemotherapy (for all fit patients) or a single-agent hypomethylating agent (in unfit patients or those 75 years and older). While assessing patient fitness remains important, characterizing the disease biology has become critical to select the optimal initial therapy for each patient with more options available. FLT3 inhibitors, gemtuzumab ozogamicin, and CPX-351 have been shown to improve outcomes for specific subsets of patients. Venetoclax (VEN) with a hypomethylating agent (HMA) is the standard-of-care frontline regimen for most older patients, except perhaps for those with an IDH1 mutation where ivosidenib with azacitidine may also be considered. On the basis of the success seen with HMA/VEN in older patients, there is now increasing interest in incorporating VEN into frontline regimens in younger patients, with promising data from multiple early phase studies. This article focuses on recent updates and ongoing challenges in the management of AML, with a particular focus on the ongoing challenge of secondary AML and considerations regarding the selection of initial therapy in younger patients. An overview of common side effects and toxicities associated with targeted therapies is also presented here, along with recommended strategies to mitigate these risks.

Predicting Drug-Drug Interactions Involving Rifampicin Using a Semi-mechanistic Hepatic Compartmental Model

AIMS

To develop a semi-mechanistic hepatic compartmental model to predict the effects of rifampicin, a known inducer of CYP3A4 enzyme, on the metabolism of five drugs, in the hope of informing dose adjustments to avoid potential drug-drug interactions.

METHODS

A search was conducted for DDI studies on the interactions between rifampicin and CYP substrates that met specific criteria, including the availability of plasma concentration-time profiles, physical and absorption parameters, pharmacokinetic parameters, and the use of healthy subjects at therapeutic doses. The semi-mechanistic model utilized in this study was improved from its predecessors, incorporating additional parameters such as population data (specifically for Chinese and Caucasians), virtual individuals, gender distribution, age range, dosing time points, and coefficients of variation.

RESULTS

Optimal parameters were identified for our semi-mechanistic model by validating it with clinical data, resulting in a maximum difference of approximately 2-fold between simulated and observed values. PK data of healthy subjects were used for most CYP3A4 substrates, except for gilteritinib, which showed no significant difference between patients and healthy subjects. Dose adjustment of gilteritinib co-administered with rifampicin required a 3-fold increase of the initial dose, while other substrates were further tuned to achieve the desired drug exposure.

CONCLUSIONS

The pharmacokinetic parameters AUCR and CmaxR of drugs metabolized by CYP3A4, when influenced by Rifampicin, were predicted by the semi-mechanistic model to be approximately twice the empirically observed values, which suggests that the semi-mechanistic model was able to reasonably simulate the effect. The doses of four drugs adjusted via simulation to reduce rifampicin interaction.

Design and synthesis of certain 7-Aryl-2-Methyl-3-Substituted Pyrazolo{1,5-a}Pyrimidines as multikinase inhibitors

Four new series 7a-e, 8a-e, 9a-e, and 10a-e of 7-aryl-3-substituted pyrazolo[1,5-a]pyrimidines were synthesized and tested for their RTK and STK inhibitory activity. Compound 7d demonstrated potent enzymatic inhibitory activity against TrkA and ALK2 with IC50 0.087and 0.105 μM, respectively, and potent antiproliferative activity against KM12 and EKVX cell lines with IC50 0.82 and 4.13 μM, respectively. Compound 10e showed good enzyme inhibitory activity against TrkA, ALK2, c-KIT, EGFR, PIM1, CK2α, CHK1, and CDK2 in submicromolar values. Additionally 10e revealed antiproliferative activity against MCF7, HCT116 and EKVX with IC50 3.36, 1.40 and 3.49 μM, respectively; with good safety profile. Moreover, 10e showed cell cycle arrest at the G1/S phase and G1 phase in MCF7 and HCT116 cells with good apoptotic effect. Molecular docking studies were fulfilled for compound 10e and illustrated good interaction with the hot spots of the active site of the tested enzymes.

Understanding the Role of Activation Loop Mutants in Drug Efficacy for FLT3-ITD

The type III receptor tyrosine kinase FLT3 is a pivotal kinase for hematopoietic progenitor cell regulation, with significant implications in acute myeloid leukemia (AML) through mutations like internal tandem duplication (ITD). This study delves into the structural intricacies of FLT3, the roles of activation loop mutants, and their interaction with tyrosine kinase inhibitors. Coupled with this, the research leverages molecular contrastive learning and protein language modeling to examine interactions between small molecule inhibitors and FLT3 activation loop mutants. Utilizing the ConPLex platform, over 5.7 million unique FLT3 activation loop mutants-small molecule pairs were analyzed. The binding free energies of three inhibitors were assessed, and cellular apoptotic responses were evaluated under drug treatments. Notably, the introduction of the Xepto50 scoring system provides a nuanced metric for drug efficacy. The findings underscore the modulation of molecular interactions and cellular responses by Y842 mutations in FLT3-KD, highlighting the need for tailored therapeutic approaches in FLT3-ITD-related malignancies.

FLT3 inhibitors and novel therapeutic strategies to reverse AML resistance: An updated comprehensive review

FMS-like tyrosine kinase 3 (FLT3) mutations occur in almost 30% of acute myeloid leukemia (AML) patients. Despite the initial clinical efficacy of FLT3 inhibitors, many treated AML patients with mutated FLT3 eventually relapse. This review critically discusses the opportunities and challenges of FLT3-targeted therapies and sheds light on their drug interactions as well as potential biomarkers. Furthermore, we focus on the molecular mechanisms underlying the resistance of FLT3 internal tandem duplication (FLT3-ITD) AMLs to FLT3 inhibitors alongside novel therapeutic strategies to reverse resistance. Notably, dynamic heterogeneous patterns of clonal selection and evolution contribute to the resistance of FLT3-ITD AMLs to FLT3 inhibitors. Ongoing preclinical research and clinical trials are actively directed towards devising rational "personalized" or "patient-tailored" combinatorial therapeutic regimens to effectively treat patients with FLT3 mutated AML.

Gilteritinib and the risk of intracranial hemorrhage: a case series of a possible, under-reported side effect

Gilteritinib is currently approved for patients with relapsed/refractory AML with FLT3 mutations, based on the positive results of the pivotal ADMIRAL study. In ADMIRAL trial, no increased risk of bleeding was reported, but in the previous dose finding study, a single event of intracranial hemorrhage (ICH) was registered after exposure to subtherapeutic doses of gilteritinib. Here, we report the first case series on five ICHs diagnosed in patients with FLT3-mutated AML, occurred within the first month of exposure to gilteritinib. Our cohort included 24 patients treated in three Italian centers. Most of these ICH cases were non-severe and self-limiting, while one was fatal. This link with ICHs remains in any case uncertain for the presence of active AML. We further reported that an analysis of the post-marketing surveillance data (EudraVigilance) retrieved other 11 cases of ICHs present in the database after gilteritinib treatment. A causality assessment was performed according to the Dx3 method to evaluate the possibility that ICHs might be an actual side effect of gilteritinib. In conclusion, further research is needed to elucidate the potential role of gilteritinib in the pathogenesis of ICHs.

Differentiation Syndrome in Acute Leukemia: APL and Beyond

Differentiation syndrome (DS) is a frequent and potentially life-threatening clinical syndrome first recognized with the advent of targeted therapeutics for acute promyelocytic leukemia (APL). DS was subsequently observed more broadly with targeted therapeutics for acute myeloid leukemia (AML). DS is typically characterized by fever, dyspnea, hypotension, weight gain, pleural or pericardial effusions, and acute renal failure. The incidence in patients with APL ranges from 2 to 37%, with the wide variation likely attributed to different diagnostic criteria, use of prophylactic treatment, and different treatment regimens. Treatment with corticosteroids +/- cytoreductive therapy should commence as soon as DS is suspected to reduce DS-related morbidity and mortality. The targeted anti-leukemic therapy should be discontinued in patients with severe DS. Here, we discuss the pathogenesis of DS, clinical presentations, diagnostic criteria, management strategies, and implementation of prospective tracking on clinical trials.

PLM-101 is a novel and potent FLT3/RET inhibitor with less adverse effects in the treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) is a prevalent form of leukemia in adults. As its survival rate is low, there is an urgent need for new therapeutic options. In AML, FMS-like tyrosine kinase 3 (FLT3) mutations are common and have negative outcomes. However, current FLT3-targeting agents, Midostaurin and Gilteritinib, face two significant issues, specifically the emergence of acquired resistance and drug-related adverse events leading to treatment failure. Rearranged during transfection (RET), meanwhile, is a proto-oncogene linked to various types of cancer, but its role in AML has been limited. A previous study showed that activation of RET kinase enhances FLT3 protein stability, leading to the promotion of AML cell proliferation. However, no drugs are currently available that target both FLT3 and RET. This study introduces PLM-101, a new therapeutic option derived from the traditional Chinese medicine indigo naturalis with potent in vitro and in vivo anti-leukemic activities. PLM-101 potently inhibits FLT3 kinase and induces its autophagic degradation via RET inhibition, providing a superior mechanism to that of FLT3 single-targeting agents. Single- and repeated-dose toxicity tests conducted in the present study showed no significant drug-related adverse effects. This study is the first to present a new FLT3/RET dual-targeting inhibitor, PLM-101, that shows potent anti-leukemic activity and fewer adverse effects. PLM-101, therefore, should be considered for use as a potential therapeutic agent for AML.

Oral therapy for myelodysplastic syndromes/neoplasms and acute myeloid leukemia: a revolution in progress

INTRODUCTION

Patients with myeloid neoplasms such as myelodysplastic syndromes/neoplasms (MDS) and acute myeloid leukemia (AML) are generally older, and many are not eligible for curative intent intensive therapies and/or allogeneic hematopoietic stem cell transplantation. While lower intensity, hypomethylating agent (HMA)-based therapies such as azacitidine+venetoclax have improved patient outcomes significantly, responses are not durable, and most patients die from disease-related complications. The approvals of oral HMAs such as cedazuridine-decitabine (C-DEC) and oral azacitidine (CC-486) have kindled the hope that myeloid malignancies may soon be treated with total oral therapy.

AREAS COVERED

We review all-oral therapies including the approvals of C-DEC and CC-486 in MDS and AML, respectively, in addition to emerging all-oral therapies, both monotherapy and combination, in higher-risk (HR) MDS and AML.

EXPERT OPINION

Oral HMAs have the potential to be a convenient and efficacy-equivalent treatment option for patients with HR-MDS or AML and improve their quality of life by reducing clinic visits for medication administration. Total-oral therapy combinations, largely including an oral HMA 'backbone,' are in the early phases of clinical development, and it is our hope that well-designed trials employing these agents may soon allow the identification of optimal regimens that deliver effective disease-directed therapy with good tolerability.

Cardiotoxicities of Novel Therapies in Hematological Malignancies: Monoclonal Antibodies and Enzyme Inhibitors

Monoclonal antibodies (mAB) selectively target leukemia surface antigens and work by either blocking cell surface receptors or triggering the target cell's destruction. Similarly, enzyme inhibitors bind to complex molecular platforms and induce downstream mechanisms that trigger cell death. These are used in a variety of hematologic malignancies. Yet, they also elicit severe immune-mediated reactions as biological agents that require careful monitoring. Cardiovascular effects include cardiomyopathy, ventricular dysfunction, cardiac arrest, and acute coronary syndrome. While there have been scattered reviews of mAB and enzyme inhibitors, a consolidated resource regarding their cardiovascular risk profile is lacking. We provide general recommendations for initial screening and serial monitoring based on the literature.

Greater expectations: meeting clinical needs through broad and rapid genomic testing

Cancer describes a group of diseases driven by genetic and genomic changes that can occur across hundreds of different genes. Knowledge of the specific variants present in a patient's cancer can help to predict response to different treatment options, confirm disease diagnosis, and understand a patient's prognosis and risks, which ultimately leads to improved survival outcomes. The advent of next-generation sequencing (NGS) technology has allowed pathologists to simultaneously profile the sequences of many genes in a single reaction, but not all NGS assays are built the same. While those used for broad genomic profiling are useful to probe large regions of the genome and gather more information about a patient's tumor, it comes at the cost of relatively long turnaround times (TAT), which may be detrimental to patient care. Conversely, NGS assays used for rapid genomic profiling provide faster results, but may miss detection of variants that are clinically informative. Determining which type of genomic profiling to order depends on a number of factors including the severity of a patient's illness, standard of care paradigms, and success or failure of previous therapies. Ultimately, the ideal clinical diagnostic laboratory will be able to offer both options to best meet the clinical needs of its patients.

Itraconazole-Induced Increases in Gilteritinib Exposure Are Mediated by CYP3A and OATP1B

Gilteritinib, an FDA-approved tyrosine kinase inhibitor approved for the treatment of relapsed/refractory FLT3-mutated acute myeloid leukemia, is primarily eliminated via CYP3A4-mediated metabolism, a pathway that is sensitive to the co-administration of known CYP3A4 inhibitors, such as itraconazole. However, the precise mechanism by which itraconazole and other CYP3A-modulating drugs affect the absorption and disposition of gilteritinib remains unclear. In the present investigation, we demonstrate that pretreatment with itraconazole is associated with a significant increase in the systemic exposure to gilteritinib in mice, recapitulating the observed clinical drug–drug interaction. However, the plasma levels of gilteritinib were only modestly increased in CYP3A-deficient mice and not further influenced by itraconazole. Ensuing in vitro and in vivo studies revealed that gilteritinib is a transported substrate of OATP1B-type transporters, that gilteritinib exposure is increased in mice with OATP1B2 deficiency, and that the ability of itraconazole to inhibit OATP1B-type transport in vivo is contingent on its metabolism by CYP3A isoforms. These findings provide new insight into the pharmacokinetic properties of gilteritinib and into the molecular mechanisms underlying drug–drug interactions with itraconazole.

Microtubule-affinity regulating kinase 4: A potential drug target for cancer therapy

The human genome encodes more than 500 protein kinases that work by transferring the γ-phosphate group from ATP to serine, threonine, or tyrosine (Ser/Thr/Tyr) residues. Various kinases are associated with the onset of cancer and its further progression. The recent advancements in developing small-molecule kinase inhibitors to treat different cancer types have shown noticeable results in clinical therapies. Microtubule-affinity regulating kinase 4 (MARK-4) is a Ser/Thr protein kinase that relates structurally to AMPK/Snf1 subfamily of the CaMK kinases. The protein kinase modulates major signalling pathways such as NF-κB, mTOR and the Hippo-signalling pathway. MARK4 is associated with various cancer types due to its important role in regulating microtubule dynamics and subsequent cell division. Aberrant expression of MARK4 is linked with several pathologies such as cancer, Alzheimer's disease, obesity, etc. This review provides detailed information on structural aspects of MARK4 and its role in various signalling pathways related to cancer. Several therapeutic molecules were designed to inhibit the MARK4 activity from controlling associated diseases. The review further highlights kinase-targeted drug discovery and development in oncology and cancer therapies. Finally, we summarize the latest findings regarding the role of MARK4 in cancer, diabetes, and neurodegenerative disease path to provide a solid rationale for future investigation and therapeutic intervention.

Understanding gilteritinib resistance to FLT3-F691L mutation through an integrated computational strategy

FMS-like tyrosine kinase 3 (FLT3) serves as an important drug target for acute myeloid leukemia (AML), and gene mutations of FLT3 have been closely associated with AML patients with an incidence rate of ~ 30%. However, the mechanism of the clinically relevant F691L gatekeeper mutation conferred resistance to the drug gilteritinib remained poorly understood. In this study, multiple microsecond molecular dynamics (MD) simulations, end-point free energy calculations, and dynamic correlated and network analyses were performed to investigate the molecular basis of gilteritinib resistance to the FLT3-F691L mutation. The simulations revealed that the resistant mutation largely induced the conformational changes of the activation loop (A-loop), the phosphate-binding loop, and the helix αC of the FLT3 protein. The binding abilities of the gilteritinib to the wild-type and the F691L mutant were different through the binding free energy prediction. The simulation results further indicated that the driving force to determine the binding affinity of gilteritinib was derived from the differences in the energy terms of electrostatic and van der Waals interactions. Moreover, the per-residue free energy decomposition suggested that the four residues (Phe803, Gly831, Leu832, and Ala833) located at the A-loop of FLT3 had a significant impact on the binding affinity of gilteritinib to the F691L mutant. This study may provide useful information for the design of novel FLT3 inhibitors specially targeting the F691L gatekeeper mutant.

In Pursuit of Genetic Prognostic Factors and Treatment Approaches in Secondary Acute Myeloid Leukemia—A Narrative Review of Current Knowledge

Secondary acute myeloid leukemia can be divided into two categories: AML evolving from the antecedent hematological condition (AHD-AML) and therapy related AML (t-AML). AHD-AML can evolve from hematological conditions such as myelodysplastic syndromes, myeloproliferative neoplasms, MDS/MPN overlap syndromes, Fanconi anemia, and aplastic anemia. Leukemic transformation occurs as a consequence of the clonal evolution—a process of the acquisition of mutations in clones, while previous mutations are also passed on, leading to somatic mutations accumulation. Compared de novo AML, secondary AML is generally associated with poorer response to chemotherapy and poorer prognosis. The therapeutic options for patients with s-AML have been confirmed to be limited, as s-AML has often been analyzed either both with de novo AML or completely excluded from clinical trials. The treatment of s-AML was not in any way different than de novo AML, until, that is, the introduction of CPX-351—liposomal daunorubicin and cytarabine. CPX-351 significantly improved the overall survival and progression free survival in elderly patients with s-AML. The only definitive treatment in s-AML at this time is allogeneic hematopoietic cell transplantation. A better understanding of the genetics and epigenetics of s-AML would allow us to determine precise biologic drivers leading to leukogenesis and thus help to apply a targeted treatment, improving prognosis.

Resistance to targeted therapies: delving into FLT3 and IDH

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

Trial Watch: combination of tyrosine kinase inhibitors (TKIs) and immunotherapy

The past decades witnessed the clinical employment of targeted therapies including but not limited to tyrosine kinase inhibitors (TKIs) that restrain a broad variety of pro-tumorigenic signals. TKIs can be categorized into (i) agents that directly target cancer cells, (ii) normalize angiogenesis or (iii) affect cells of the hematologic lineage. However, a clear distinction of TKIs based on this definition is limited by the fact that many TKIs designed to inhibit cancer cells have also effects on immune cells that are being discovered. Additionally, TKIs originally designed to target hematological cancers exhibit bioactivities on healthy cells of the same hematological lineage. TKIs have been described to improve immune recognition and cancer immunosurveillance, providing the scientific basis to combine TKIs with immunotherapy. Indeed, combination of TKIs with immunotherapy showed synergistic effects in preclinical models and clinical trials and some combinations of TKIs normalizing angiogenesis with immune checkpoint blocking antibodies have already been approved by the FDA for cancer therapy. However, the identification of appropriate drug combinations as well as optimal dosing and scheduling needs to be improved in order to obtain tangible progress in cancer care. This Trial Watch summarizes active clinical trials combining TKIs with various immunotherapeutic strategies to treat cancer patients.

Therapeutic Management of Patients with FLT3 + Acute Myeloid Leukemia: Case Reports and Focus on Gilteritinib Monotherapy

Acute myeloid leukemia is a malignant disorder of the bone marrow, characterized by differentiation, clonal expansion, and uncontrolled proliferation of malignant myeloid progenitor cells and by several molecular and genetic abnormalities. A mutation of FMS-like tyrosine kinase 3 gene can be observed in about one-third of cases of acute myeloid leukemia. Two FLT3 inhibitors are actually approved for FLT3 mutated acute myeloid leukemia: midostaurin, a multikinase first generation inhibitor with lower affinity for FLT3 binding, and gilteritinib fumarate, a potent second-generation inhibitor of both FLT3-ITD and TKD. Gilteritinib is a new effective and well-tolerated drug for patients with relapsing or refractory FLT3-positive acute myeloid leukemia. Thanks to its efficacy, low toxicity, its good manageability (oral formulation), this drug is suitable for all the patients, including elderly frail patient with concomitant therapies or pre-existing or underlying diseases, and can be used also in the outpatient setting, reducing risks and costs related to the hospitalization. We report and discuss seven cases of different patients with FLT3 positive acute myeloid leukemia successfully managed with gilteritinib in the real clinical practice.

Design, synthesis, and biological evaluation of novel pyrido-dipyrimidines as dual topoisomerase II/FLT3 inhibitors in leukemia cells

Dual inhibition of topoisomerase (topo) II and FLT3 kinase, as in the case of C-1311, was shown to overcome the shortcomings of using topo II inhibitors solely. In the present study, we designed and synthesized two series of pyrido-dipyrimidine- and pseudo-pyrido-acridone-containing compounds. The two series were evaluated against topo II and FLT3 as well as the HL-60 promyelocytic leukemia cell line in vitro. Compounds 6, 7, and 20 showed higher potency against topo II than the standard amsacrine (AMSA), whereas compounds 19 and 20 were stronger FLT3 inhibitors than the standard DACA. Compounds 19 and 20 showed to be dual inhibitors of both enzymes. Compounds 6, 7, 19, and 20 were more potent inhibitors of the HL-60 cell line than the standard AMSA. The results of the in vitro DNA flow cytometry analysis assay and Annexin V-FITC apoptosis analysis showed that 19 and 20 induced cell cycle arrest at the G2/M phase, significantly higher total percentage of apoptosis, and late-stage apoptosis in HL-60 cell lines than AMSA. Furthermore, 19 and 20 upregulated several apoptosis biomarkers such as p53, TNFα, caspase 3/7 and increased the Bax/Bcl-2 ratio. These results showed that 19 and 20 deserve further evaluation of their antiproliferative activities, particularly in leukemia. Molecular docking studies were performed for selected compounds against topo II and FLT3 enzymes to investigate their binding patterns. Compound 19 exerted dual fitting inside the active site of both enzymes.

The Multi-Kinase Inhibitor EC-70124 Is a Promising Candidate for the Treatment of FLT3-ITD-Positive Acute Myeloid Leukemia

Simple Summary

Patients with AML harboring constitutively active mutations in the FLT3 receptor generally have a poor prognosis (FLT3-ITD^MUT). Despite the fact that several FLT3 inhibitors have been developed, clinical responses are commonly partial or not durable, highlighting the need for new molecules targeting FLT3-ITD^MUT. Here, we tested EC-70124, a hybrid indolocarbazole analog from the same chemical space as midostaurin (a well-known FLT3 inhibitor). Our in vitro and in vivo experiments showed that EC-70124 exerts a robust and specific antileukemia activity against FLT3-ITD^MUT AML cells while sparing healthy hematopoietic cells. Collectively, EC-70124 is a promising and safe agent for the treatment of this aggressive type of AML.

Abstract

Acute myeloid leukemia (AML) is the most common acute leukemia in adults. Patients with AML harboring a constitutively active internal tandem duplication mutation (ITD^MUT) in the FMS-like kinase tyrosine kinase (FLT3) receptor generally have a poor prognosis. Several tyrosine kinase/FLT3 inhibitors have been developed and tested clinically, but very few (midostaurin and gilteritinib) have thus far been FDA/EMA-approved for patients with newly diagnosed or relapse/refractory FLT3-ITD^MUT AML. Disappointingly, clinical responses are commonly partial or not durable, highlighting the need for new molecules targeting FLT3-ITD^MUT AML. Here, we tested EC-70124, a hybrid indolocarbazole analog from the same chemical space as midostaurin with a potent and selective inhibitory effect on FLT3. In vitro, EC-70124 exerted a robust and specific antileukemia activity against FLT3-ITD^MUT AML primary cells and cell lines with respect to cytotoxicity, CFU capacity, apoptosis and cell cycle while sparing healthy hematopoietic (stem/progenitor) cells. We also analyzed its efficacy in vivo as monotherapy using two different xenograft models: an aggressive and systemic model based on MOLM-13 cells and a patient-derived xenograft model. Orally disposable EC-70124 exerted a potent inhibitory effect on the growth of FLT3-ITD^MUT AML cells, delaying disease progression and debulking the leukemia. Collectively, our findings show that EC-70124 is a promising and safe agent for the treatment of AML with FLT3-ITD^MUT.

Response Rate, Event-Free Survival, and Overall Survival in Newly Diagnosed Acute Myeloid Leukemia: US Food and Drug Administration Trial-Level and Patient-Level Analyses

PURPOSE

To explore trial-level and patient-level associations between response (complete remission [CR] and CR + CR with incomplete hematologic [CRi] or platelet [CRp] recovery), event-free survival (EFS), and overall survival (OS) in newly diagnosed acute myeloid leukemia (AML) trials of intensive chemotherapy.

METHODS

We identified data from eight randomized, active-controlled trials of intensive chemotherapy submitted to the US Food and Drug Administration for treatment of newly diagnosed AML (N = 4,482). Associations between trial-level odds ratios (ORs) for CR and CR + CRi or CRp, and hazard ratios (HRs) for EFS and OS were analyzed using weighted linear regression models. We performed patient-level responder analyses to compare OS by response using pooled data from all studies.

RESULTS

In trial-level analyses, association between HR for OS and OR for CR was moderate (R² = 0.49; 95% CI, 0.05 to 0.86), as was the association with OR for CR + CRi or CRp (R² = 0.48; 95% CI, 0.05 to 0.99). For OS versus EFS, a strong association was observed (R² = 0.87; 95% CI, 0.47 to 0.98) when EFS definitions were harmonized across trials using raw data. In the patient-level responder analyses, patients who achieved CR had better OS compared with CRi or CRp responders (0.73; 95% CI, 0.64 to 0.84) and nonresponders (HR, 0.33; 95% CI, 0.31 to 0.37).

CONCLUSION

On a trial level, there is a moderate association between OS and CR rate. A strong association between EFS and OS was observed. However, CIs were wide, and results became moderate using alternative definitions for EFS. Patient-level analyses showed CR responders have better OS compared with CRi or CRp responders and nonresponders. A therapy in newly diagnosed AML with benefit in EFS or substantial benefit in CR rate would be likely to have an OS effect.

Small Molecule Induced FLT3 Degradation

Target protein degrader is a new paradigm in the small molecule drug discovery field and relates to the term ‘event-driven pharmacology’. Fms-like tyrosine kinase 3 (FLT3) is a significant target for treating acute myeloid leukemia (AML). A few FLT3 kinase inhibitors are currently used in the clinic for AML patients. However, resistance to current FLT3 inhibitors has emerged, and strategies to overcome this resistance are required. Small molecules downregulating FLT3 protein level are reported, exhibiting antileukemic effects against AML cell lines. Small molecules with various mechanisms such as Hsp90 inhibition, proteasome inhibition, RET inhibition, and USP10 inhibition are explained. In addition, reports of FLT3 as a client of Hsp90, current knowledge of the ubiquitin proteasome system for FLT3 degradation, the relationship with FLT3 phosphorylation status and susceptibility of FLT3 degradation are discussed.

Holistic View of ALK TKI Resistance in ALK-Positive Anaplastic Large Cell Lymphoma

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase expressed at early stages of normal development and in various cancers including ALK-positive anaplastic large cell lymphoma (ALK+ ALCL), in which it is the main therapeutic target. ALK tyrosine kinase inhibitors (ALK TKIs) have greatly improved the prognosis of ALK+ALCL patients, but the emergence of drug resistance is inevitable and limits the applicability of these drugs. Although various mechanisms of resistance have been elucidated, the problem persists and there have been relatively few relevant clinical studies. This review describes research progress on ALK+ ALCL including the application and development of new therapies, especially in relation to drug resistance. We also propose potential treatment strategies based on current knowledge to inform the design of future clinical trials.

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

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

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

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

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

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

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

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

Deciphering the Mechanism of Gilteritinib Overcoming Lorlatinib Resistance to the Double Mutant I1171N/F1174I in Anaplastic Lymphoma Kinase

Anaplastic lymphoma kinase (ALK) is validated as a therapeutic molecular target in multiple malignancies, such as non-small cell lung cancer (NSCLC). However, the feasibility of targeted therapies exerted by ALK inhibitors is inevitably hindered owing to drug resistance. The emergence of clinically acquired drug mutations has become a major challenge to targeted therapies and personalized medicines. Thus, elucidating the mechanism of resistance to ALK inhibitors is helpful for providing new therapeutic strategies for the design of next-generation drug. Here, we used molecular docking and multiple molecular dynamics simulations combined with correlated and energetical analyses to explore the mechanism of how gilteritinib overcomes lorlatinib resistance to the double mutant ALK I1171N/F1174I. We found that the conformational dynamics of the ALK kinase domain was reduced by the double mutations I1171N/F1174I. Moreover, energetical and structural analyses implied that the double mutations largely disturbed the conserved hydrogen bonding interactions from the hinge residues Glu1197 and Met1199 in the lorlatinib-bound state, whereas they had no discernible adverse impact on the binding affinity and stability of gilteritinib-bound state. These discrepancies created the capacity of the double mutant ALK I1171N/F1174I to confer drug resistance to lorlatinib. Our result anticipates to provide a mechanistic insight into the mechanism of drug resistance induced by ALK I1171N/F1174I that are resistant to lorlatinib treatment in NSCLC.

Haploidentical Stem Cell Transplantation for Acute Myeloid Leukemia: Current Therapies, Challenges and Future Prospective

Haploidentical stem cell transplantation (haplo-SCT), an alternative donor source, offers a curative therapy for patients with acute myeloid leukemia (AML) who are transplant candidates. Advances in transplantation techniques, such as donor selection, conditioning regimen modification, and graft-versus-host disease prophylaxis, have successfully improved the outcomes of AML patients receiving haplo-SCT and extended the haploidentical transplant indictions for AML. Presently, treating de novo AML, secondary AML, therapy-related AML and refractory and relapsed AML with haplo-SCT can achieve comparable outcomes to those of human leukocyte antigen (HLA)-matched sibling donor transplantation (MSDT), unrelated donor transplantation or umbilical cord blood transplantation. For some subgroups of AML subjects, such as patients with positive pretransplantation minimal/measurable residual disease, recent studies suggest that haplo-SCT might be superior to MSDT in decreasing relapse and improving survival. Unfortunately, for patients with AML after haplo-SCT, relapse and infections remain the causes of death that restrict further improvement in clinical outcomes. In this review, we discuss the recent advances and challenges in haplo-SCT for AML treatment, mainly focusing on unmanipulated haplo-SCT protocols. We provide an outlook on future prospects and suggest that relapse prophylaxis, intervention, and treatment, as well as infection prevention and therapy, are areas of active research in AML patients who receive haploidentical allografts.

Project 2025: Proposals for the Continued Success of Drug Development in Acute Myeloid Leukemia

The Food and Drug Administration Oncology Center of Excellence initiated Project 2025 to develop five-year goals in specific areas of oncology drug development. This meeting, in October 2020, brought together a panel of regulators and academic experts in acute myeloid leukemia (AML) to discuss opportunities to maximize the success that has recently occurred in AML drug development. The panel discussed challenges and opportunities in clinical trial design and novel endpoints, and outlined key considerations for drug development to facilitate continued growth in the field.

Inhibitors of class I HDACs and of FLT3 combine synergistically against leukemia cells with mutant FLT3

Acute myeloid leukemia (AML) with mutations in the FMS-like tyrosine kinase (FLT3) is a clinically unresolved problem. AML cells frequently have a dysregulated expression and activity of epigenetic modulators of the histone deacetylase (HDAC) family. Therefore, we tested whether a combined inhibition of mutant FLT3 and class I HDACs is effective against AML cells. Low nanomolar doses of the FLT3 inhibitor (FLT3i) AC220 and an inhibition of class I HDACs with nanomolar concentrations of FK228 or micromolar doses of the HDAC3 specific agent RGFP966 synergistically induce apoptosis of AML cells that carry hyperactive FLT3 with an internal tandem duplication (FLT3-ITD). This does not occur in leukemic cells with wild-type FLT3 and without FLT3, suggesting a preferential toxicity of this combination against cells with mutant FLT3. Moreover, nanomolar doses of the new FLT3i marbotinib combine favorably with FK228 against leukemic cells with FLT3-ITD. The combinatorial treatments potentiated their suppressive effects on the tyrosine phosphorylation and stability of FLT3-ITD and its downstream signaling to the kinases ERK1/ERK2 and the inducible transcription factor STAT5. The beneficial pro-apoptotic effects of FLT3i and HDACi against leukemic cells with mutant FLT3 are associated with dose- and drug-dependent alterations of cell cycle distribution and DNA damage. This is linked to a modulation of the tumor-suppressive transcription factor p53 and its target cyclin-dependent kinase inhibitor p21. While HDACi induce p21, AC220 suppresses the expression of p53 and p21. Furthermore, we show that both FLT3-ITD and class I HDAC activity promote the expression of the checkpoint kinases CHK1 and WEE1, thymidylate synthase, and the DNA repair protein RAD51 in leukemic cells. A genetic depletion of HDAC3 attenuates the expression of such proteins. Thus, class I HDACs and hyperactive FLT3 appear to be valid targets in AML cells with mutant FLT3.