Synergy and antagonism between azacitidine and FLT3 inhibitors

Synergetic interactions between drugs can make a drug combination more effective. Alternatively, they may allow to use lower concentrations and thus avoid toxicities or side effects that not only cause discomfort but might also reduce the overall survival. Here, we studied whether synergy exists between agents that are used for treatment of acute myeloid leukaemia (AML). Azacitidine is a demethylation agent that is used in the treatment of AML patients that are unfit for aggressive chemotherapy. An activating mutation in the FLT3 gene is common in AML patients and in the absence of specific treatment makes prognosis worse. FLT3 inhibitors may be used in such cases. We sought to determine whether combination of azacitidine with a FLT3 inhibitor (gilteritinib, quizartinib, LT-850-166, FN-1501 or FF-10101) displayed synergy or antagonism. To this end, we calculated dose-response matrices of these drug combinations from experiments in human AML cells and subsequently analysed the data using a novel consensus scoring algorithm. The results show that combinations that involved non-covalent FLT3 inhibitors, including the two clinically approved drugs gilteritinib and quizartinib were antagonistic. On the other hand combinations with the covalent inhibitor FF-10101 had some range of concentrations where synergy was observed.

FLT3 tyrosine kinase inhibition modulates PRC2 and promotes differentiation in acute myeloid leukemia

Internal tandem duplication mutations in fms-like tyrosine kinase 3 (FLT3-ITD) are recurrent in acute myeloid leukemia (AML) and increase the risk of relapse. Clinical responses to FLT3 inhibitors (FLT3i) include myeloid differentiation of the FLT3-ITD clone in nearly half of patients through an unknown mechanism. We identified enhancer of zeste homolog 2 (EZH2), a component of polycomb repressive complex 2 (PRC2), as a mediator of this effect using a proteomic-based screen. FLT3i downregulated EZH2 protein expression and PRC2 activity on H3K27me3. FLT3-ITD and loss-of-function mutations in EZH2 are mutually exclusive in human AML. We demonstrated that FLT3i increase myeloid maturation with reduced stem/progenitor cell populations in murine Flt3-ITD AML. Combining EZH1/2 inhibitors with FLT3i increased terminal maturation of leukemic cells and reduced leukemic burden. Our data suggest that reduced EZH2 activity following FLT3 inhibition promotes myeloid differentiation of FLT3-ITD leukemic cells, providing a mechanistic explanation for the clinical observations. These results demonstrate that in addition to its known cell survival and proliferation signaling, FLT3-ITD has a second, previously undefined function to maintain a myeloid stem/progenitor cell state through modulation of PRC2 activity. Our findings support exploring EZH1/2 inhibitors as therapy for FLT3-ITD AML.

Sorafenib plus triplet therapy with venetoclax, azacitidine and homoharringtonine for refractory/relapsed acute myeloid leukemia with FLT3-ITD: A multicenter phase 2 study

BACKGROUND

Patients with relapsed or refractory acute myeloid leukemia (R/R AML) and FLT3-internal tandem duplication (FLT3-ITD) respond infrequently to salvage chemotherapy.

OBJECTIVE

To investigate the efficacy of sorafenib plus triplet therapy with venetoclax, azacitidine, and homoharringtonine (VAH) as a salvage therapy in this population.

METHODS

This multicenter, single-arm, phase 2 study was conducted at 12 hospitals across China. Eligible patients had R/R AML with FLT3-ITD (aged 18-65 years) who were treated with VAH. The primary endpoint was composite complete remission (CRc) after two cycles. Secondary outcomes included the overall response rate (ORR), safety, and survival.

RESULTS

Between July 9, 2020, and March 19, 2022, 58 patients were assessed for eligibility, 51 of whom were enrolled. The median patient age was 47 years (interquartile range [IQR] 31-57). CRc was 76.5% with ORR of 82.4%. At a median follow-up of 17.7 months (IQR, 8.7-24.7), the median duration of CRc was not reached (NR), overall survival was 18.1 months (95% confidence interval [CI], 11.8-NR) and event-free survival was 11.4 months (95% CI, 5.6-NR). Grade 3 or 4 adverse events occurring in ≥10% of patients included neutropenia in 47 (92.2%), thrombocytopenia in 41 (80.4%), anemia in 35 (68.6%), febrile neutropenia in 29 (56.9%), pneumonia in 13 (25.5%), and sepsis in 6 (11.8%) patients. Treatment-related death occurred in two (3.9%) patients.

CONCLUSIONS

The sorafenib plus VAH regimen was well tolerated and highly active against R/R AML with FLT3-ITD. This regimen may be a suitable therapeutic option for this population, but larger population trials are needed to be explored.

TRIAL REGISTRATION

Clinical Trials Registry: NCT04424147.

Identification of a Selective FLT3 Inhibitor with Low Activity against VEGFR, FGFR, PDGFR, c-KIT, and RET Anti-Targets

FLT3 is mainly expressed in immune and various cancer cells and is a drug target for acute myeloid leukemia (AML). Recently, FLT3 has also been identified as a potential target for treating chronic pain. Most FLT3 inhibitors (FLT3i) identified to date, including approved drugs such as gilteritinib, midostaurin, ponatinib, quizartinib, and FLT3i in clinical trials, such as quizartinib and crenolanib, also inhibit closely-related kinases that are important for immune (c-KIT), cardiovascular (KDR/VEGFR2, FGFR, PDGFR) or kidney (RET) functions. While the aforementioned FLT3i may increase survival rates in AML, they are neither ideal for AML maintenance therapy nor for non-oncology applications, such as for the treatment of chronic pain, due to their promiscuous inhibition of many kinase anti-targets. Here, we report the identification of new FLT3i compounds that have low activities against kinases that have traditionally been difficult to differentiate from FLT3 inhibition, such as KDR/VEGFR, FGFR, PGFR, c-KIT, and RET. These selective compounds could be valuable chemical probes for studying FLT3 biology in the context of chronic pain and/or may represent good starting points to develop well-tolerated FLT3 therapeutics for non-oncology indications or for maintenance therapy for AML.

Identifying novel therapeutic inhibitors to target FMS-like tyrosine kinase-3 (FLT3) against acute myeloid leukemia: a molecular docking, molecular dynamics, and DFT study

Around 30% of acute myeloid leukemia (AML) patients have triggering mutations in Feline McDonough Sarcoma (FMS)-like tyrosine kinase 3 (FLT3), which has been suggested as a possible therapeutic candidate for AML therapy. Many tyrosine kinase inhibitors are available and have a wide variety of applications in the treatment of cancer by inhibiting subsequent steps of cell proliferation. Therefore, our study aims to identify effective antileukemic agents against FLT3 gene. Initially, well-known antileukemic drug candidates have been chosen to generate a structure-based pharmacophore model to assist the virtual screening of 217,77,093 compounds from the Zinc database. The final hits compounds were retrieved and evaluated by docking against the target protein, where the top four compounds have been selected for the analysis of ADMET. Based on the density functional theory (DFT), the geometry optimization, frontier molecular orbital (FMO), HOMO-LUMO, and global reactivity descriptor values have been evaluated that confirming a satisfactory profile and reactivity order for the selected candidates. In comparison to control compounds, the docking results revealed that the four compounds had substantial binding energies (-11.1 to -11.5 kcal/mol) with FLT3. The physicochemical and ADMET (adsorption, distribution, metabolism, excretion, toxicity) prediction results corresponded to the bioactive and safe candidates. Molecular dynamics (MD) confirmed the better binding affinity and stability compared to gilteritinib as a potential FLT3 inhibitor. In this study, a computational approach has been performed that found a better docking and dynamics score against target proteins, indicating potent and safe antileukemic agents, furthermore in-vivo and in-vitro investigations are recommended.Communicated by Ramaswamy H. Sarma.

TP-0184 inhibits FLT3/ACVR1 to overcome FLT3 inhibitor resistance and hinder AML growth synergistically with venetoclax

We identified activin A receptor type I (ACVR1), a member of the TGF-β superfamily, as a factor favoring acute myeloid leukemia (AML) growth and a new potential therapeutic target. ACVR1 is overexpressed in FLT3-mutated AML and inhibition of ACVR1 expression sensitized AML cells to FLT3 inhibitors. We developed a novel ACVR1 inhibitor, TP-0184, which selectively caused growth arrest in FLT3-mutated AML cell lines. Molecular docking and in vitro kinase assays revealed that TP-0184 binds to both ACVR1 and FLT3 with high affinity and inhibits FLT3/ACVR1 downstream signaling. Treatment with TP-0184 or in combination with BCL2 inhibitor, venetoclax dramatically inhibited leukemia growth in FLT3-mutated AML cell lines and patient-derived xenograft models in a dose-dependent manner. These findings suggest that ACVR1 is a novel biomarker and plays a role in AML resistance to FLT3 inhibitors and that FLT3/ACVR1 dual inhibitor TP-0184 is a novel potential therapeutic tool for AML with FLT3 mutations.

PDP1 is a key metabolic gatekeeper and modulator of drug resistance in FLT3-ITD-positive acute myeloid leukemia

High metabolic flexibility is pivotal for the persistence and therapy resistance of acute myeloid leukemia (AML). In 20-30% of AML patients, activating mutations of FLT3, specifically FLT3-ITD, are key therapeutic targets. Here, we investigated the influence of FLT3-ITD on AML metabolism. Nuclear Magnetic Resonance (NMR) profiling showed enhanced reshuffling of pyruvate towards the tricarboxylic acid (TCA) cycle, suggesting an increased activity of the pyruvate dehydrogenase complex (PDC). Consistently, FLT3-ITD-positive cells expressed high levels of PDP1, an activator of the PDC. Combining endogenous tagging of PDP1 with genome-wide CRISPR screens revealed that FLT3-ITD induces PDP1 expression through the RAS signaling axis. PDP1 knockdown resulted in reduced cellular respiration thereby impairing the proliferation of only FLT3-ITD cells. These cells continued to depend on PDP1, even in hypoxic conditions, and unlike FLT3-ITD-negative cells, they exhibited a rapid, PDP1-dependent revival of their respiratory capacity during reoxygenation. Moreover, we show that PDP1 modifies the response to FLT3 inhibition. Upon incubation with the FLT3 tyrosine kinase inhibitor quizartinib (AC220), PDP1 persisted or was upregulated, resulting in a further shift of glucose/pyruvate metabolism towards the TCA cycle. Overexpression of PDP1 enhanced, while PDP1 depletion diminished AC220 resistance in cell lines and peripheral blasts from an AC220-resistant AML patient in vivo. In conclusion, FLT3-ITD assures the expression of PDP1, a pivotal metabolic regulator that enhances oxidative glucose metabolism and drug resistance. Hence, PDP1 emerges as a potentially targetable vulnerability in the management of AML.

A combinatorial therapeutic approach to enhance FLT3-ITD AML treatment

Internal tandem duplication mutations of the FMS-like tyrosine kinase-3 (FLT3-ITDs) occur in 25%-30% of patients with acute myeloid leukemia (AML) and are associated with dismal prognosis. Although FLT3 inhibitors have demonstrated initial clinical efficacy, the overall outcome of patients with FLT3-ITD AML remains poor, highlighting the urgency to develop more effective treatment strategies. In this study, we reveal that FLT3 inhibitors reduced protein stability of the anti-cancer protein p53, resulting in drug resistance. Blocking p53 degradation with proteasome inhibitors restores intracellular p53 protein levels and, in combination with FLT3-ITD inhibitors, shows superior therapeutic effects against FLT3-ITD AML in cells, mouse models, and patients. These data suggest that this combinatorial therapeutic approach may represent a promising strategy to target FLT3-ITD AML.

Midostaurin plus daunorubicin or idarubicin for young and older adults with FLT3-mutated AML: a phase 3b trial

The pivotal RATIFY study demonstrated midostaurin (50 mg twice daily) with standard chemotherapy significantly reduced mortality in adult patients (<60 years) with newly diagnosed (ND) FLT3mut acute myeloid leukemia (AML). Considering that AML often present in older patients who show poor response to chemotherapy, this open-label, multicenter phase 3b trial was designed to further assess safety and efficacy of midostaurin plus chemotherapy in induction, consolidation, and maintenance monotherapy in young (≤60 years) and older (>60 years) patients with FLT3mut ND-AML. Compared with RATIFY, this study extended midostaurin treatment from 14 days to 21 days, substituted anthracyclines (idarubicin or daunorubicin), and introduced variation in standard combination chemotherapy dosing ("7+3" or "5+2" in more fragile patients). Total 301 patients (47.2% >60 years and 82.7% with FLT3-ITDmut) of median age 59 years entered induction phase. Overall, 295 patients (98.0%) had at least 1 adverse event (AE), including 254 patients (84.4%) with grade ≥3 AE. The grade ≥3 serious AEs occurred in 134 patients. No difference was seen in AE frequency between age groups, but grade ≥3AE frequency was higher in older patients. Overall, complete remission (CR) rate including incomplete hematologic recovery (CR + CRi) (80.7% [95% confidence interval, 75.74-84.98]) was comparable between age groups (≤60 years [83.5%]; >60 to ≤70 years [82.5%]; in patients >70 years [64.1%]) and the type of anthracycline used in induction. CR + CRi rate was lower in males (76.4%) than females (84.4%). Overall, the safety and efficacy of midostaurin remains consistent with previous findings, regardless of age, sex, or induction regimen. The trial is registered at www.clinicaltrials.gov as #NCT03379727.

Clinical impact of the genomic landscape and leukemogenic trajectories in non-intensively treated elderly acute myeloid leukemia patients

To characterize the genomic landscape and leukemogenic pathways of older, newly diagnosed, non-intensively treated patients with AML and to study the clinical implications, comprehensive genetics analyses were performed including targeted DNA sequencing of 263 genes in 604 patients treated in a prospective Phase III clinical trial. Leukemic trajectories were delineated using oncogenetic tree modeling and hierarchical clustering, and prognostic groups were derived from multivariable Cox regression models. Clonal hematopoiesis-related genes (ASXL1, TET2, SRSF2, DNMT3A) were most frequently mutated. The oncogenetic modeling algorithm produced a tree with five branches with ASXL1, DDX41, DNMT3A, TET2, and TP53 emanating from the root suggesting leukemia-initiating events which gave rise to further subbranches with distinct subclones. Unsupervised clustering mirrored the genetic groups identified by the tree model. Multivariable analysis identified FLT3 internal tandem duplications (ITD), SRSF2, and TP53 mutations as poor prognostic factors, while DDX41 mutations exerted an exceptionally favorable effect. Subsequent backwards elimination based on the Akaike information criterion delineated three genetic risk groups: DDX41 mutations (favorable-risk), DDX41wildtype/FLT3-ITDneg/TP53wildtype (intermediate-risk), and FLT3-ITD or TP53 mutations (high-risk). Our data identified distinct trajectories of leukemia development in older AML patients and provide a basis for a clinically meaningful genetic outcome stratification for patients receiving less intensive therapies.

Targeting conditioned media dependencies and FLT-3 in chronic lymphocytic leukemia

The importance of the stromal microenvironment in chronic lymphocytic leukemia (CLL) pathogenesis and drug resistance is well established. Despite recent advances in CLL therapy, identifying novel ways to disrupt interactions between CLL and its microenvironment may identify new combination partners for the drugs currently in use. To understand the role of microenvironmental factors on primary CLL cells, we took advantage of an observation that conditioned media (CM) collected from stroma was protective of CLL cells from spontaneous cell death ex vivo. The cytokine in the CM-dependent cells that most supports CLL survival in short-term ex vivo culture was CCL2. Pretreatment of CLL cells with anti-CCL2 antibody enhanced venetoclax-mediated killing. Surprisingly, we found a group of CLL samples (9/23 cases) that are less likely to undergo cell death in the absence of CM support. Functional studies revealed that CM-independent (CMI) CLL cells are less sensitive to apoptosis than conventional stroma-dependent CLL. In addition, a majority of the CMI CLL samples (80%) harbored unmutated immunoglobulin heavy-chain variable (IGHV) region. Bulk-RNA sequence analysis revealed upregulation of the focal adhesion and RAS signaling pathways in this group, along with expression of fms-like tyrosine kinase 3 (FLT3) and CD135. Treatment with FLT3 inhibitors caused a significant reduction in cell viability among CMI samples. In summary, we were able to discriminate and target 2 biologically distinct subgroups of CLL based on CM dependence with distinct microenvironmental vulnerabilities.

Constitutively Synergistic Multiagent Drug Formulations Targeting MERTK, FLT3, and BCL-2 for Treatment of AML

PURPOSE

Although high-dose, multiagent chemotherapy has improved leukemia survival rates, treatment outcomes remain poor in high-risk subsets, including acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) in infants. The development of new, more effective therapies for these patients is therefore an urgent, unmet clinical need.

METHODS

The dual MERTK/FLT3 inhibitor MRX-2843 and BCL-2 family protein inhibitors were screened in high-throughput against a panel of AML and MLL-rearranged precursor B-cell ALL (infant ALL) cell lines. A neural network model was built to correlate ratiometric drug synergy and target gene expression. Drugs were loaded into liposomal nanocarriers to assess primary AML cell responses.

RESULTS

MRX-2843 synergized with venetoclax to reduce AML cell density in vitro. A neural network classifier based on drug exposure and target gene expression predicted drug synergy and growth inhibition in AML with high accuracy. Combination monovalent liposomal drug formulations delivered defined drug ratios intracellularly and recapitulated synergistic drug activity. The magnitude and frequency of synergistic responses were both maintained and improved following drug formulation in a genotypically diverse set of primary AML bone marrow specimens.

CONCLUSIONS

We developed a nanoscale combination drug formulation that exploits ectopic expression of MERTK tyrosine kinase and dependency on BCL-2 family proteins for leukemia cell survival in pediatric AML and infant ALL cells. We demonstrate ratiometric drug delivery and synergistic cell killing in AML, a result achieved by a systematic, generalizable approach of combination drug screening and nanoscale formulation that may be extended to other drug pairs or diseases in the future.

Improved efficacy of quizartinib in combination therapy with PI3K inhibition in primary FLT3-ITD AML cells

Acute myeloid leukemia is a heterogeneous hematopoietic malignancy, characterized by uncontrolled clonal proliferation of abnormal myeloid progenitor cells, with poor outcomes. The internal tandem duplication (ITD) mutation of the Fms-like receptor tyrosine kinase 3 (FLT3) (FLT3-ITD) represents the most common genetic alteration in AML, detected in approximately 30% of AML patients, and is associated with high leukemic burden and poor prognosis. Therefore, this kinase has been regarded as an attractive druggable target for the treatment of FLT3-ITD AML, and selective small molecule inhibitors, such as quizartinib, have been identified and trialled. However, clinical outcomes have been disappointing so far due to poor remission rates, also because of acquired resistance. A strategy to overcome resistance is to combine FLT3 inhibitors with other targeted therapies. In this study, we investigated the preclinical efficacy of the combination of quizartinib with the pan PI3K inhibitor BAY-806946 in FLT3-ITD cell lines and primary cells from AML patients. We show here that BAY-806946 enhanced quizartinib cytotoxicity and, most importantly, that this combination increases the ability of quizartinib to kill CD34+ CD38-leukemia stem cells, whilst sparing normal hematopoietic stem cells. Because constitutively active FLT3 receptor tyrosine kinase is known to boost aberrant PI3K signaling, the increased sensitivity of primary cells to the above combination can be the mechanistic results of the disruption of signaling by vertical inhibition.

Successful Pre- and Post-transplant Administration of Gilteritinib in a Patient with Relapsed and Refractory Acute Myeloid Leukemia Undergoing Allogeneic Peripheral Blood Stem Cell Transplantation

Patients with acute myeloid leukemia (AML) harboring FMS-like tyrosine kinase 3 (FLT3)-internal tandem duplication mutation are associated with a poor survival outcome, even those receiving allogeneic stem cell transplantation (Allo-SCT). An additional treatment strategy with allo-SCT is therefore required to reduce relapse in these patients. Gilteritinib is a specific FLT3 inhibitor that has shown clinical benefit for patients with relapsed and refractory (R/R) AML harboring FLT3 mutation. We herein report a 49-year-old woman with R/R AML who was successfully treated with pre- and post-transplant gilteritinib. Post-transplant gilteritnib yielded a durable response with possible exacerbation of graft-versus-host disease.

Ferroptosis vulnerability in FLT3-mutant leukemia

Resistance to FLT3 inhibition is a prevalent challenge in managing FLT3-mutant acute myeloid leukemia (AML). A recent study by Sabatier et al. discovered ferroptosis vulnerability in FLT3-mutant AML and they propose a promising therapeutic approach of combining FLT3 inhibitors with ferroptosis inducers for treating this type of cancer.

Outcomes in Patients with FLT3-Mutated Relapsed/ Refractory Acute Myelogenous Leukemia Who Underwent Transplantation in the Phase 3 ADMIRAL Trial of Gilteritinib versus Salvage Chemotherapy

The fms-like tyrosine kinase 3 (FLT3) inhibitor gilteritinib improved the survival of patients with relapsed or refractory (R/R) FLT3-mutated acute myelogenous leukemia (AML) in the phase 3 ADMIRAL trial. In this study, we assessed survival and relapse rates of patients in the ADMIRAL trial who underwent hematopoietic stem cell transplantation (HSCT), as well as safety outcomes in patients who received post-transplantation gilteritinib maintenance therapy. ADMIRAL was a global phase 3 randomized controlled trial that enrolled adult patients with FLT3-mutated R/R AML. Patients with R/R AML who harbored FLT3 internal tandem duplication mutations in the juxtamembrane domain or D835/I836 point mutations in the tyrosine kinase domain were randomized (2:1) to gilteritinib (120 mg/day) or to preselected high- or low-intensity salvage chemotherapy (1 or 2 cycles). Patients in the gilteritinib arm who proceeded to HSCT could receive post-transplantation gilteritinib maintenance therapy if they were within 30 to 90 days post-transplantation and had achieved composite complete remission (CRc) with successful engraftment and no post-transplantation complications. Adverse events (AEs) during HSCT were recorded in the gilteritinib arm only. Survival outcomes and the cumulative incidence of relapse were assessed in patients who underwent HSCT during the trial. Treatment-emergent AEs were evaluated in patients who restarted gilteritinib as post-transplantation maintenance therapy. Patients in the gilteritinib arm underwent HSCT more frequently than those in the chemotherapy arm (26% [n = 64] versus 15% [n = 19]). For all transplantation recipients, 12- and 24-month overall survival (OS) rates were 68% and 47%, respectively. Despite a trend toward longer OS after pretransplantation CRc, post-transplantation survival was comparable in the 2 arms. Patients who resumed gilteritinib after HSCT had a low relapse rate after pretransplantation CRc (20%) or CR (0%). The most common AEs observed with post-transplantation gilteritinib therapy were increased alanine aminotransferase level (45%), pyrexia (43%), and diarrhea (40%); grade ≥3 AEs were related primarily to myelosuppression. The incidences of grade ≥III acute graft-versus-host disease and related mortality were low. Post-transplantation survival was similar across the 2 study arms in the ADMIRAL trial, but higher remission rates with gilteritinib facilitated receipt of HSCT. Gilteritinib as post-transplantation maintenance therapy had a stable safety and tolerability profile and was associated with low relapse rates. Taken together, these data support a preference for bridging therapy with gilteritinib over chemotherapy in transplantation-eligible patients.

Beta Elemene induces cytotoxic effects in FLT3 ITD-mutated acute myeloid leukemia by modulating apoptosis

OBJECTIVE: β-Elemene, a sesquiterpene with a broad anti-cancer spectrum, is particularly effective against drug-resistant and complex tumors. It can also be efficient against FLT3-expressed acute myeloid leukemia. This research aims to determine whether β-Elemene has cytotoxic effects on FLT3 ITD-mutated AML cells. MATERIALS AND METHODS: Cytotoxicity, cell morphology, mRNA analysis with apoptotic markers, and analysis of 43 distinct protein markers related to cell death, survival, and resistance were all performed to elucidate its mechanism. Additionally, in order to understand how β-Elemene and FLT3 interact, molecular docking, molecular dynamics simulations, and computational ADME investigations were performed. RESULTS: β-Elemene exhibited cytotoxic activity against FLT3-mutated MV4-11 and FLT3 wild-type THP-1 cells, with an IC50 of around 25 µg/ml. The molecular studies revealed that β-Elemene inhibited cell proliferation by inducing p53, and the involvement of p21, p27, HTRA, and HSPs were also demonstrated. The interactive inhibition in proliferation was confirmed via molecular docking and dynamics analyses. β-Elemene occupied the FLT3 enzymatic pocket with good stability at the FLT3 active site. CONCLUSIONS: We concluded from our observations that β-Elemene causes cell death in ITD mutant AML cells, together with the effects of stress factors and inhibiting cell division.

BMX kinase mediates gilteritinib resistance in FLT3-mutated AML through microenvironmental factors

Despite the clinical benefit associated with gilteritinib in relapsed/refractory acute myeloid leukemia (AML), most patients eventually develop resistance through unknown mechanisms. To delineate the mechanistic basis of resistance to gilteritinib, we performed targeted sequencing and scRNASeq on primary FLT3-ITD-mutated AML samples. Co-occurring mutations in RAS pathway genes were the most common genetic abnormalities, and unresponsiveness to gilteritinib was associated with increased expression of bone marrow-derived hematopoietic cytokines and chemokines. In particular, we found elevated expression of the TEK-family kinase, BMX, in gilteritinib-unresponsive patients pre- and post-treatment. BMX contributed to gilteritinib resistance in FLT3-mutant cell lines in a hypoxia-dependent manner by promoting pSTAT5 signaling, and these phenotypes could be reversed with pharmacological inhibition and genetic knockout. We also observed that inhibition of BMX in primary FLT3-mutated AML samples decreased chemokine secretion and enhanced the activity of gilteritinib. Collectively, these findings indicate a crucial role for microenvironment-mediated factors modulated by BMX in the escape from targeted therapy and have implications for the development of novel therapeutic interventions to restore sensitivity to gilteritinib.

Development and Validation of an LC-MS/MS Method to Quantify Gilteritinib and Its Clinical Application in Patients With FLT3 Mutation-Positive Acute Myelogenous Leukemia

BACKGROUND

Gilteritinib, a novel oral tyrosine kinase inhibitor, is used to treat acute myeloid leukemia (AML) with FMS-like tyrosine kinase-3 (FLT3) mutations. Therapeutic drug monitoring (TDM) of gilteritinib is important for improving clinical outcomes and ensuring safety. Therefore, this study aimed to develop a simplified method for quantifying gilteritinib in human plasma using liquid chromatography-tandem mass spectrometry.

METHODS

Liquid chromatography was performed by using an Acquity BEH C18 column (50 mm × 2.1 mm, 1.7 μm) and a gradient elution with 0.1% formic acid in water (A) and acetonitrile (B). Detection was performed by using a Shimadzu tandem mass spectrometer through multiple reaction monitoring in the positive-ion mode.

RESULTS

The developed method enabled quantification of gilteritinib in 4 minutes and was validated by evaluating selectivity, calibration curve (10-1000 ng/mL, r 2 > 0.99), a lower limit of quantification (LLOQ), accuracy (overall bias -4.2% to 1.9%), precision (intraday CV ≤ 7.9%; interday CV ≤ 13.6%), carryover, recovery, matrix effect, dilution integrity, and stability according to the US Food and Drug Administration (FDA) guidelines. This method was successfully applied to the TDM of gilteritinib trough concentrations in 3 patients with AML.

CONCLUSIONS

The developed method fulfilled the FDA guideline criteria and can easily be implemented to facilitate TDM in patients receiving gilteritinib in a clinical setting.

O-methylated flavonol as a multi-kinase inhibitor of leukemogenic kinases exhibits a potential treatment for acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia (AML) is a heterogeneous disease with poor overall survival characterized by various genetic changes. The continuous activation of oncogenic pathways leads to the development of drug resistance and limits current therapeutic efficacy. Therefore, a multi-targeting inhibitor may overcome drug resistance observed in AML treatment. Recently, groups of flavonoids, such as flavones and flavonols, have been shown to inhibit a variety of kinase activities, which provides potential opportunities for further anticancer applications.

PURPOSE

In this study, we evaluated the anticancer effects of flavonoid compounds collected from our in-house library and investigated their potential anticancer mechanisms by targeting multiple kinases for inhibition in AML cells.

METHODS

The cytotoxic effect of the compounds was detected by cell viability assays. The kinase inhibitory activity of the selected compound was detected by kinase-based and cell-based assays. The binding conformation and interactions were investigated by molecular docking analysis. Flow cytometry was used to evaluate the cell cycle distribution and cell apoptosis. The protein and gene expression were estimated by western blotting and qPCR, respectively.

RESULTS

In this study, an O-methylated flavonol (compound 11) was found to possess remarkable cytotoxic activity against AML cells compared to treatment in other cancer cell lines. The compound was demonstrated to act against multiple kinases, which play critical roles in survival signaling in AML, including FLT3, MNK2, RSK, DYRK2 and JAK2 with IC₅₀ values of 1 - 2 μM. Compared to our previous flavonoid compounds, which only showed inhibitions against MNKs or FLT3, compound 11 exhibited multiple kinase inhibitory abilities. Moreover, compound 11 showed effectiveness in inhibiting internal tandem duplications of FLT3 (FLT3-ITDs), which accounts for 25% of AML cases. The interactions between compound 11 and targeted kinases were investigated by molecular docking analysis. Mechanically, compound 11 caused dose-dependent accumulation of leukemic cells at the G₀/G₁ phase and followed by the cells undergoing apoptosis.

CONCLUSION

O-methylated flavonol, compound 11, can target multiple kinases, which may provide potential opportunities for the development of novel therapeutics for drug-resistant AMLs. This work provides a good starting point for further compound optimization.

Investigation of Selected Flavonoid Derivatives as Potent FLT3 Inhibitors for the Potential Treatment of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is an aggressive disease with a poor prognosis and a high degree of relapse seen in patients. Overexpression of FMS-like tyrosine kinase 3 (FLT3) is associated with up to 70% of AML patients. Wild-type FLT3 induces proliferation and inhibits apoptosis in AML cells, while uncontrolled proliferation of FLT3 kinase activity is also associated with FLT3 mutations. Therefore, inhibiting FLT3 activity is a promising AML therapy. Flavonoids are a group of phytochemicals that can target protein kinases, suggesting their potential antitumor activities. In this study, several plant-derived flavonoids have been identified with FLT3 inhibitory activity. Among these compounds, compound 40 (5,7,4'-trihydroxy-6-methoxyflavone) exhibited the most potent inhibition against not only FLT3 (IC₅₀ = 0.44 μM) but also FLT3-D835Y and FLT3-ITD mutants (IC₅₀ = 0.23 and 0.39 μM, respectively). The critical interactions between the FLT3 binding site and the compounds were identified by performing a structure-activity relationship analysis. Furthermore, the results of cellular assays revealed that compounds 28, 31, 32, and 40 exhibited significant cytotoxicity against two human AML cell lines (MOLM-13 and MV-4-11), and compounds 31, 32, and 40 resulted in cell apoptosis and G0/G1 cell cycle arrest. Collectively, these flavonoids have the potential to be further optimized as FLT3 inhibitors and provide valuable chemical information for the development of new AML drugs.

Patients with FLT3-mutant AML needed to enroll on FLT3-targeted therapeutic clinical trials

We sought to identify the total number of therapeutic trials targeting FLT3-mutant acute myeloid leukemia (AML) to estimate the number of patients needed to satisfy recruitment when compared with the incidence of this mutation in the US AML population. A systematic review of all therapeutic clinical trials focusing on adult FLT3-mutated AML was conducted from 2000 to 2017. An updated search was performed using ClinicalTrials.gov for trials added between October 2017 and December 2018. Analysis was performed for ClinicalTrials.gov search results from 2000 to 2017 to provide descriptive estimates of discrepancies between anticipated clinical trial enrollment using consistently cited rates of adult participation of 1%, 3%, and 5%, as well as 10% participation identified by the American Society of Clinical Oncology in 2008. Twenty-five pharmaceutical or biological agents aimed at treating FLT3-mutant AML were identified. Pharmaceutical vs cooperative group/nonprofit support was 2.3:1, with 30 different pharmaceutical collaborators and 13 cooperative group/nonprofit collaborators. The number of patients needed to satisfy study enrollment begins to surpass the upper bound of estimated participation in 2010, noticeably surpassing projected participation rates between 2015 and 2016. The number of patients needed to satisfy study enrollment surpasses 3% and 5% rates of historical participation for US-only trials in 2017. We estimate that 15% of all US patients with FLT3-mutant AML would have to enroll in US and internationally accruing trials to satisfy requirements in 2017, or approximately 3 times the upper level of historical participation rates in the United States. The current clinical trial agenda in this space requires high percentage enrollment for sustainability.

Stem cell factor-activated bone marrow ameliorates amyotrophic lateral sclerosis by promoting protective microglial migration

Amyotrophic lateral sclerosis (ALS) is a progressive disease associated with motor neuron death. Several experimental treatments, including cell therapy using hematopoietic or neuronal stem cells, have been tested in ALS animal models, but therapeutic benefits have been modest. Here we used a new therapeutic strategy, bone marrow transplantation (BMT) with stem cell factor (SCF)- or FMS-like tyrosine kinase 3 (flt3)-activated bone marrow (BM) cells for the treatment of hSOD1(G93A) transgenic mice. Motor function and survival showed greater improvement in the SCF group than in the group receiving BM cells that had not been activated (BMT alone group), although no improvement was shown in the flt3 group. In addition, larger numbers of BM-derived cells that expressed the microglia marker Iba1 migrated to the spinal cords of recipient mice compared with the BMT alone group. Moreover, after SCF activation, but not flt3 activation or no activation, the migrating microglia expressed glutamate transporter-1 (GLT-1). In spinal cords in the SCF group, inflammatory cytokines tumor necrosis factor-α and interleukin-1β were suppressed and the neuroprotective molecule insulin-like growth factor-1 increased relative to nontreatment hSOD1(G93A) transgenic mice. Therefore, SCF activation changed the character of the migrating donor BM cells, which resulted in neuroprotective effects. These studies have identified SCF-activated BM cells as a potential new therapeutic agent for the treatment of ALS.

A novel bicistronic high-capacity gutless adenovirus vector that drives constitutive expression of herpes simplex virus type 1 thymidine kinase and tet-inducible expression of Flt3L for glioma therapeutics

Glioblastoma multiforme (GBM) is a deadly primary brain tumor. Conditional cytotoxic/immune-stimulatory gene therapy (Ad-TK and Ad-Flt3L) elicits tumor regression and immunological memory in rodent GBM models. Since the majority of patients enrolled in clinical trials would exhibit adenovirus immunity, which could curtail transgene expression and therapeutic efficacy, we used high-capacity adenovirus vectors (HC-Ads) as a gene delivery platform. Herein, we describe for the first time a novel bicistronic HC-Ad driving constitutive expression of herpes simplex virus type 1 thymidine kinase (HSV1-TK) and inducible Tet-mediated expression of Flt3L within a single-vector platform. We achieved anti-GBM therapeutic efficacy with no overt toxicities using this bicistronic HC-Ad even in the presence of systemic Ad immunity. The bicistronic HC-Ad-TK/TetOn-Flt3L was delivered into intracranial gliomas in rats. Survival, vector biodistribution, neuropathology, systemic toxicity, and neurobehavioral deficits were assessed for up to 1 year posttreatment. Therapeutic efficacy was also assessed in animals preimmunized against Ads. We demonstrate therapeutic efficacy, with vector genomes being restricted to the brain injection site and an absence of overt toxicities. Importantly, antiadenoviral immunity did not inhibit therapeutic efficacy. These data represent the first report of a bicistronic vector platform driving the expression of two therapeutic transgenes, i.e., constitutive HSV1-TK and inducible Flt3L genes. Further, our data demonstrate no promoter interference and optimum gene delivery and expression from within this single-vector platform. Analysis of the efficacy, safety, and toxicity of this bicistronic HC-Ad vector in an animal model of GBM strongly supports further preclinical testing and downstream process development of HC-Ad-TK/TetOn-Flt3L for a future phase I clinical trial for GBM.

FLT3 and Acute Myelogenous Leukemia: Biology, Clinical Significance and Therapeutic Applications

Acute myelogenous leukemia (AML) is a difficult disease to treat, and better treatments are needed. Molecular targeted therapy represents a novel therapeutic approach. The FLT3 tyrosine kinase receptor is mutated in approximately one-fourth to one-third of patients with AML. Normally, binding of FLT3 ligand to the FLT3 receptor leads to phosphorylation of tyrosine residues and activation of the receptor. This in turn leads to induction of intracellular signaling pathways essential to regulation of cell proliferation and apoptosis. Two classes of FLT3 activating mutations have been identified in AML patients: internal tandem duplications (ITDS) and point mutations in the activating loop of the kinase domain. Both mutations result in constitutive FLT3 tyrosine kinase activity and lead to transformation of hematopoietic cell lines in vivo and in vitro. FLT3 ITDs are also an independent poor prognostic factor for overall survival and disease free survival in patients with AML. Therefore, targeting FLT3 mutations represents a potential therapeutic target for AML. This review will discuss the biology and clinical significance of FLT3 and FLT3 mutations in cell growth and signaling. In addition, I will discuss some of the novel FLT3 inhibitors which are entering clinical trials for AML.