In silico predicted compound targeting the IQGAP1-GRD domain selectively inhibits growth of human acute myeloid leukemia.

Acute myeloid leukemia (AML) is fatal in the majority of adults. Identification of new therapeutic targets and their pharmacologic modulators are needed to improve outcomes. Previous studies had shown that immunization of rabbits with normal peripheral WBCs that had been incubated with fluorodinitrobenzene elicited high titer antibodies that bound to a spectrum of human leukemias. We report that proteomic analyses of immunoaffinity-purified lysates of primary AML cells showed enrichment of scaffolding protein IQGAP1. Immunohistochemistry and gene-expression analyses confirmed IQGAP1 mRNA overexpression in various cytogenetic subtypes of primary human AML compared to normal hematopoietic cells. shRNA knockdown of IQGAP1 blocked proliferation and clonogenicity of human leukemia cell-lines. To develop small molecules targeting IQGAP1 we performed in-silico screening of 212,966 compounds, selected 4 hits targeting the IQGAP1-GRD domain, and conducted SAR of the 'fittest hit' to identify UR778Br, a prototypical agent targeting IQGAP1. UR778Br inhibited proliferation, induced apoptosis, resulted in G2/M arrest, and inhibited colony formation by leukemia cell-lines and primary-AML while sparing normal marrow cells. UR778Br exhibited favorable ADME/T profiles and drug-likeness to treat AML. In summary, AML shows response to IQGAP1 inhibition, and UR778Br, identified through in-silico studies, selectively targeted AML cells while sparing normal marrow.

Lysosomal acid lipase A modulates leukemia stem cell response to venetoclax/tyrosine kinase inhibitor combination therapy in blast phase chronic myeloid leukemia.

The treatment of blast phase chronic myeloid leukemia (bpCML) remains a challenge due at least in part to drug resistance of leukemia stem cells (LSCs). Recent clinical evidence suggests that the BCL-2 inhibitor venetoclax in combination with ABL-targeting tyrosine kinase inhibitors (TKIs) can eradicate bpCML LSCs. In this report, we employed preclinical models of bpCML to investigate the efficacy and underlying mechanism of LSC-targeting with venetoclax/TKI combinations. Transcriptional analysis of LSCs exposed to venetoclax and dasatinib revealed upregulation of genes involved in lysosomal biology, in particular lysosomal acid lipase A (LIPA), a regulator of free fatty acids. Metabolomic analysis confirmed increased levels of free fatty acids in response to venetoclax/dasatinib. Pre-treatment of leukemia cells with bafilomycin, a specific lysosome inhibitor, or genetic perturbation of LIPA, resulted in increased sensitivity of leukemia cells toward venetoclax/dasatinib, implicating LIPA in treatment resistance. Importantly, venetoclax/dasatinib treatment does not affect normal stem cell function, suggestive of a leukemia-specific response. These results demonstrate that venetoclax/dasatinib is an LSCselective regimen in bpCML and that disrupting LIPA and fatty acid transport enhances venetoclax/dasatinib response in targeting LSCs, providing a rationale for exploring lysosomal disruption as an adjunct therapeutic strategy to prolong disease remission.

MYC Inhibition Potentiates CD8+ T Cells Against Multiple Myeloma and Overcomes Immunomodulatory Drug Resistance.

PURPOSE: Immunomodulatory drugs (IMiDs), such as lenalidomide and pomalidomide, are a cornerstone of multiple myeloma (MM) therapies, yet the disease inevitably becomes refractory. IMiDs exert cytotoxicity by inducing cereblon-dependent proteasomal degradation of IKZF1 and IKZF3, resulting in downregulation of the oncogenic transcription factors IRF4 and MYC. To date, clinical IMiD resistance independent of cereblon or IKZF1/3 has not been well explored. Here, we investigated the roles of IRF4 and MYC in this context. EXPERIMENTAL DESIGN: Using bone marrow aspirates from patients with IMiD-naïve or refractory MM, we examined IKZF1/3 protein levels and IRF4/MYC gene expression following ex vivo pomalidomide treatment via flow cytometry and qPCR. We also assessed exvivo sensitivity to the MYC inhibitor MYCi975 using flow cytometry. RESULTS: We discovered that although pomalidomide frequently led to IKZF1/3 degradation in MM cells, it did not affect MYC gene expression in most IMiD-refractory samples. We subsequently demonstrated that MYCi975 exerted strong anti-MM effects in both IMiD-naïve and -refractory samples. Unexpectedly, we identified a cluster of differentiation 8+ (CD8+ T) cells from patients with MM as crucial effectors of MYCi975-induced cytotoxicity in primary MM samples, and we discovered that MYCi975 enhanced the cytotoxic functions of memory CD8+ T cells. We lastly observed synergy between MYCi975 and pomalidomide in IMiD-refractory samples, suggesting that restoring MYC downregulation can re-sensitize refractory MM to IMiDs. CONCLUSIONS: Our study supports the concept that MYC represents an Achilles' heel in MM across disease states and that MYCi975 may be a promising therapeutic for patients with MM, particularly in combination with IMiDs.

Targeting Acute Myeloid Leukemia Stem Cells Through Perturbation of Mitochondrial Calcium.

Acute myeloid leukemia stem cells (LSCs) are uniquely reliant on oxidative phosphorylation (OXPHOS) for survival. Moreover, maintenance of OXPHOS is dependent on BCL-2, creating a therapeutic opportunity to target LSCs using the BCL-2 inhibitor venetoclax. While venetoclax-based regimens have shown promising clinical activity, the emergence of drug resistance is prevalent. Thus, in the present study, we investigated how mitochondrial properties may influence venetoclax responsiveness. Our data show that utilization of mitochondrial calcium is fundamentally different between drug-responsive and non-responsive LSCs. By comparison, venetoclax-resistant LSCs demonstrate a more active metabolic (i.e. OXPHOS) status with relatively high levels of calcium. Consequently, we tested genetic and pharmacological approaches to target the mitochondrial calcium uniporter, MCU. We demonstrate that inhibition of calcium uptake reduces OXPHOS and leads to eradication of venetoclax-resistant LSCs. These findings demonstrate a central role for calcium signaling in LSCs and provide an avenue for clinical management of venetoclax resistance.

Temporal Single Cell Analysis of Leukemia Microenvironment Identifies Taurine-Taurine Transporter Axis as a Key Regulator of Myeloid Leukemia.

Signals from the microenvironment are known to be critical for development, sustaining adult stem cells, and for oncogenic progression. While candidate niche-driven signals that can promote cancer progression have been identified1-6, concerted efforts to comprehensively map microenvironmental ligands for cancer stem cell specific surface receptors have been lacking. Here, we use temporal single cell RNA-sequencing to identify molecular cues from the bone marrow stromal niche that engage leukemia stem cells (LSC) during oncogenic progression. We integrate these data with our RNA-seq analysis of human LSCs from distinct aggressive myeloid cancer subtypes and our CRISPR based in vivo LSC dependency map7 to develop a temporal receptor-ligand interactome essential for disease progression. These analyses identify the taurine transporter (TauT)-taurine axis as a critical dependency of myeloid malignancies. We show that taurine production is restricted to the osteolineage population during cancer initiation and expansion. Inhibiting taurine synthesis in osteolineage cells impairs LSC growth and survival. Our experiments with the TauT genetic loss of function murine model indicate that its loss significantly impairs the progression of aggressive myeloid leukemias in vivo by downregulating glycolysis. Further, TauT inhibition using a small molecule strongly impairs the growth and survival of patient derived myeloid leukemia cells. Finally, we show that TauT inhibition can synergize with the clinically approved oxidative phosphorylation inhibitor venetoclax8, 9 to block the growth of primary human leukemia cells. Given that aggressive myeloid leukemias continue to be refractory to current therapies and have poor prognosis, our work indicates targeting the taurine transporter may be of therapeutic significance. Collectively, our data establishes a temporal landscape of stromal signals during cancer progression and identifies taurine-taurine transporter signaling as an important new regulator of myeloid malignancies.

An immunophenotype-coupled transcriptomic atlas of human hematopoietic progenitors.

Analysis of the human hematopoietic progenitor compartment is being transformed by single-cell multimodal approaches. Cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) enables coupled surface protein and transcriptome profiling, thereby revealing genomic programs underlying progenitor states. To perform CITE-seq systematically on primary human bone marrow cells, we used titrations with 266 CITE-seq antibodies (antibody-derived tags) and machine learning to optimize a panel of 132 antibodies. Multimodal analysis resolved >80 stem, progenitor, immune, stromal and transitional cells defined by distinctive surface markers and transcriptomes. This dataset enables flow cytometry solutions for in silico-predicted cell states and identifies dozens of cell surface markers consistently detected across donors spanning race and sex. Finally, aligning annotations from this atlas, we nominate normal marrow equivalents for acute myeloid leukemia stem cell populations that differ in clinical response. This atlas serves as an advanced digital resource for hematopoietic progenitor analyses in human health and disease.

Multi-gene measurable residual disease assessed by digital polymerase chain reaction has clinical and biological utility in acute myeloid leukemia patients receiving venetoclax/azacitidine.

Venetoclax with azacitidine (ven/aza) is a lower-intensity therapeutic regimen that has been shown to improve outcomes in elderly patients with acute myeloid leukemia (AML). Measurable residual disease (MRD) using flow cytometry is a valuable tool for the prediction of relapse in AML using conventional therapies and ven/aza; however, the prognostic value for broadscale molecular MRD after ven/aza treatment is less clear. We aimed to determine the utility of retrospective assessment using multi-gene molecular MRD by droplet digital polymerase chain reaction (ddPCR). We found this approach correlates with outcomes in a cohort of patients receiving frontline ven/aza for AML. The predictive value of ddPCR MRD persisted when NPM1 mutations were removed from analysis, as well as after adjustment for the impact of stem cell transplant on outcomes. Late achievement of MRD negativity, including after SCT, was still associated with superior outcomes compared to persistently detectable MRD. We further explored the impact of ven/aza on the burden of different classes of mutations, and identified the persistence of splicing factor mutations, commonly associated with MDS, as a consistent finding after ven/aza treatment. These data add to our understanding of the effects of ven/aza on AML disease biology and provide details on molecular depth of remission that can guide prospective trials in the future.

Parthenolide As a Therapeutic for Disseminated Canine Neoplasms.

This study provides a unique translational research opportunity to help both humans and dogs diagnosed with diseases that carry dismal prognoses in both species: histiocytic sarcoma (HS), hemangiosarcoma (HSA), and disseminated mastocytosis/mast cell tumor (MCT). Although exceedingly rare in humans, these so called "orphan diseases" are relatively more common in dogs. For these and other more commonplace cancers like lymphoma (Lym), dogs are an excellent translational model for human disease due to remarkably similar disease biology. In this study, assays were performed to assess the therapeutic potential of parthenolide (PTL), a known canonical nuclear factor kappa B (NF-κB) signaling inhibitor with additional mechanisms of antineoplastic activity, including alteration of cellular reduction-oxidation balance. Canine cell lines and primary cells are sensitive to PTL and undergo dose-dependent apoptosis after exposure to drug. PTL exposure also leads to glutathione depletion, reactive oxygen species generation, and NF-κB inhibition in canine cells. Standard-of-care therapeutics broadly synergize with PTL. In two canine HS cell lines, expression of NF-κB pathway signaling partners is downregulated with PTL therapy. Preliminary data suggest that PTL inhibits NF-κB activity of cells and extends survival time in a mouse model of disseminated canine HS. These data support further investigation of compounds that can antagonize canonical NF-κB pathway signaling in these cancers and pave the way for clinical trials of PTL in affected dogs. As dogs are an excellent natural disease model for these cancers, these data will ultimately improve our understanding of their human disease counterparts and hopefully improve care for both species. SIGNIFICANCE STATEMENT: Disseminated neoplasms in human and canine cancers are challenging to treat, and novel therapeutic approaches are needed to improve outcomes. Parthenolide is a promising treatment for histiocytic sarcoma, hemangiosarcoma, and mast cell neoplasia.

Targeting Acute Myeloid Leukemia Stem Cells Through Perturbation of Mitochondrial Calcium.

We previously reported that acute myeloid leukemia stem cells (LSCs) are uniquely reliant on oxidative phosphorylation (OXPHOS) for survival. Moreover, maintenance of OXPHOS is dependent on BCL2, creating a therapeutic opportunity to target LSCs using the BCL2 inhibitor drug venetoclax. While venetoclax-based regimens have indeed shown promising clinical activity, the emergence of drug resistance is prevalent. Thus, in the present study, we investigated how mitochondrial properties may influence mechanisms that dictate venetoclax responsiveness. Our data show that utilization of mitochondrial calcium is fundamentally different between drug responsive and non-responsive LSCs. By comparison, venetoclax-resistant LSCs demonstrate a more active metabolic (i.e., OXPHOS) status with relatively high steady-state levels of calcium. Consequently, we tested genetic and pharmacological approaches to target the mitochondrial calcium uniporter, MCU. We demonstrate that inhibition of calcium uptake sharply reduces OXPHOS and leads to eradication of venetoclax-resistant LSCs. These findings demonstrate a central role for calcium signaling in the biology of LSCs and provide a therapeutic avenue for clinical management of venetoclax resistance.

A Novel Type of Monocytic Leukemia Stem Cell Revealed by the Clinical Use of Venetoclax-Based Therapy.

The BCL2 inhibitor venetoclax has recently emerged as an important component of acute myeloid leukemia (AML) therapy. Notably, use of this agent has revealed a previously unrecognized form of pathogenesis characterized by monocytic disease progression. We demonstrate that this form of disease arises from a fundamentally different type of leukemia stem cell (LSC), which we designate as monocytic LSC (m-LSC), that is developmentally and clinically distinct from the more well-described primitive LSC (p-LSC). The m-LSC is distinguished by a unique immunophenotype (CD34-, CD4+, CD11b-, CD14-, CD36-), unique transcriptional state, reliance on purine metabolism, and selective sensitivity to cladribine. Critically, in some instances, m-LSC and p-LSC subtypes can co-reside in the same patient with AML and simultaneously contribute to overall tumor biology. Thus, our findings demonstrate that LSC heterogeneity has direct clinical significance and highlight the need to distinguish and target m-LSCs as a means to improve clinical outcomes with venetoclax-based regimens. SIGNIFICANCE: These studies identify and characterize a new type of human acute myeloid LSC that is responsible for monocytic disease progression in patients with AML treated with venetoclax-based regimens. Our studies describe the phenotype, molecular properties, and drug sensitivities of this unique LSC subclass. This article is featured in Selected Articles from This Issue, p. 1949.

Therapy-Resistant Acute Myeloid Leukemia Stem Cells Are Resensitized to Venetoclax + Azacitidine by Targeting Fatty Acid Desaturases 1 and 2.

Recent advances in targeting leukemic stem cells (LSCs) using venetoclax with azacitidine (ven + aza) has significantly improved outcomes for de novo acute myeloid leukemia (AML) patients. However, patients who relapse after traditional chemotherapy are often venetoclax-resistant and exhibit poor clinical outcomes. We previously described that fatty acid metabolism drives oxidative phosphorylation (OXPHOS) and acts as a mechanism of LSC survival in relapsed/refractory AML. Here, we report that chemotherapy-relapsed primary AML displays aberrant fatty acid and lipid metabolism, as well as increased fatty acid desaturation through the activity of fatty acid desaturases 1 and 2, and that fatty acid desaturases function as a mechanism of recycling NAD+ to drive relapsed LSC survival. When combined with ven + aza, the genetic and pharmacologic inhibition of fatty acid desaturation results in decreased primary AML viability in relapsed AML. This study includes the largest lipidomic profile of LSC-enriched primary AML patient cells to date and indicates that inhibition of fatty acid desaturation is a promising therapeutic target for relapsed AML.

Higher-dose venetoclax with measurable residual disease-guided azacitidine discontinuation in newly diagnosed acute myeloid leukemia.

Venetoclax+azacitidine is the standard of care for newly-diagnosed patients with acute myeloid leukemia (AML) for whom intensive chemotherapy is inappropriate. Efforts to optimize this regimen are necessary. We designed a clinical trial to investigate two hypotheses: i) higher doses of venetoclax are tolerable and more effective, and ii) azacitidine can be discontinued after deep remissions. Forty-two newly diagnosed AML patients were enrolled in the investigator-initiated High Dose Discontinuation Azacitidine+Venetoclax (HiDDAV) Study (clinicaltrials gov. Identifier: NCT03466294). Patients received one to three "induction" cycles of venetoclax 600 mg daily with azacitidine. Responders received MRD-positive or MRDnegative "maintenance" arms: azacitidine with 400 mg venetoclax or 400 mg venetoclax alone, respectively. The toxicity profile of HiDDAV was similar to 400 mg venetoclax. The overall response rate was 66.7%; the duration of response (DOR), event-free survival (EFS) and overall survival were 12.9, 7.8 and 9.8 months, respectively. The MRD negativity rate was 64.3% by flow cytometry and 25.0% when also measured by droplet digital polymerase chain recation. MRD-negative patients by flow cytometry had improved DOR and EFS; more stringent measures of MRD negativity were not associated with improved OS, DOR or EFS. Using MRD to guide azacitidine discontinuation did not lead to improved DOR, EFS or OS compared to patients who discontinued azacitidine without MRD guidance. Within the context of this study design, venetoclax doses >400 mg with azacitidine were well tolerated but not associated with discernible clinical improvement, and MRD may not assist in recommendations to discontinue azacitidine. Other strategies to optimize, and for some patients, de-intensify, venetoclax+azacitidine regimens are needed.

Therapeutic resistance in acute myeloid leukemia cells is mediated by a novel ATM/mTOR pathway regulating oxidative phosphorylation.

While leukemic cells are susceptible to various therapeutic insults, residence in the bone marrow microenvironment typically confers protection from a wide range of drugs. Thus, understanding the unique molecular changes elicited by the marrow is of critical importance toward improving therapeutic outcomes. In this study, we demonstrate that aberrant activation of oxidative phosphorylation serves to induce therapeutic resistance in FLT3 mutant human AML cells challenged with FLT3 inhibitor drugs. Importantly, our findings show that AML cells are protected from apoptosis following FLT3 inhibition due to marrow-mediated activation of ATM, which in turn upregulates oxidative phosphorylation via mTOR signaling. mTOR is required for the bone marrow stroma-dependent maintenance of protein translation, with selective polysome enrichment of oxidative phosphorylation transcripts, despite FLT3 inhibition. To investigate the therapeutic significance of this finding, we tested the mTOR inhibitor everolimus in combination with the FLT3 inhibitor quizartinib in primary human AML xenograft models. While marrow resident AML cells were highly resistant to quizartinib alone, the addition of everolimus induced profound reduction in tumor burden and prevented relapse. Taken together, these data provide a novel mechanistic understanding of marrow-based therapeutic resistance and a promising strategy for improved treatment of FLT3 mutant AML patients.

Venetoclax and azacitidine followed by allogeneic transplant results in excellent outcomes and may improve outcomes versus maintenance therapy among newly diagnosed AML patients older than 60.

The combination of venetoclax (ven) and azacitidine (aza) has resulted in high response rates in the upfront treatment of AML in patients age > 75 and patients unfit for intensive chemotherapy. Given the poor historical outcomes in patients age ≥ 60 treated with induction chemotherapy, ven/aza has become our institutional preference for the initial treatment of non-core binding factor (CBF) AML patients age ≥ 60. The benefit of allogeneic stem cell transplant (SCT) in patients who achieve response to ven/aza is uncertain. We report outcomes of SCT-eligible patients treated at our center. Between 1/2015 and 1/2020, 119 newly diagnosed non-CBF AML patients age ≥ 60 received ven/aza as initial therapy. 21 patients underwent SCT; 31 additional patients were potentially SCT eligible but deferred SCT. Overall survival (OS) was significantly greater among SCT patients (median survival not reached) versus potentially SCT eligible patients not undergoing SCT (median 518 days) (p = 0.01). Our data suggest that ven/aza followed by SCT in newly diagnosed AML patients older than ≥ 60 results in excellent outcomes and likely improves outcomes over maintenance therapy. Ongoing investigation will further refine the optimal timing of and selection of patients for SCT based on prognostic disease features and response assessments.

The STAT3-MYC axis promotes survival of leukemia stem cells by regulating SLC1A5 and oxidative phosphorylation.

Acute myeloid leukemia (AML) is characterized by the presence of leukemia stem cells (LSCs), and failure to fully eradicate this population contributes to disease persistence/relapse. Prior studies have characterized metabolic vulnerabilities of LSCs, which demonstrate preferential reliance on oxidative phosphorylation (OXPHOS) for energy metabolism and survival. In the present study, using both genetic and pharmacologic strategies in primary human AML specimens, we show that signal transducer and activator of transcription 3 (STAT3) mediates OXPHOS in LSCs. STAT3 regulates AML-specific expression of MYC, which in turn controls transcription of the neutral amino acid transporter gene SLC1A5. We show that genetic inhibition of MYC or SLC1A5 acts to phenocopy the impairment of OXPHOS observed with STAT3 inhibition, thereby establishing this axis as a regulatory mechanism linking STAT3 to energy metabolism. Inhibition of SLC1A5 reduces intracellular levels of glutamine, glutathione, and multiple tricarboxylic acid (TCA) cycle metabolites, leading to reduced TCA cycle activity and inhibition of OXPHOS. Based on these findings, we used a novel small molecule STAT3 inhibitor, which binds STAT3 and disrupts STAT3-DNA, to evaluate the biological role of STAT3. We show that STAT3 inhibition selectively leads to cell death in AML stem and progenitor cells derived from newly diagnosed patients and patients who have experienced relapse while sparing normal hematopoietic cells. Together, these findings establish a STAT3-mediated mechanism that controls energy metabolism and survival in primitive AML cells.

Venetoclax and azacitidine compared with induction chemotherapy for newly diagnosed patients with acute myeloid leukemia.

Venetoclax (ven) plus azacitidine (aza) is the standard of care for patients with newly diagnosed acute myeloid leukemia (AML) who are not candidates for intensive chemotherapy (IC). Some patients who are IC candidates instead receive ven/aza. We retrospectively analyzed patients with newly diagnosed AML who received ven/aza (n = 143) or IC (n = 149) to compare outcomes, seek variables that could predict response to 1 therapy or the other, and ascertain whether treatment recommendations could be refined. The response rates were 76.9% for ven/aza and 70.5% for IC. The median overall survival (OS) was 884 days for IC compared with 483 days for ven/aza (P = .0020). A propensity-matched cohort was used to compare outcomes in the setting of equivalent baseline variables, and when matched for age, biological risk, and transplantation, the median OS was 705 days for IC compared with not reached for ven/aza (P = .0667). Variables that favored response to ven/aza over IC included older age, secondary AML, and RUNX1 mutations. AML M5 favored response to IC over ven/aza. In the propensity-matched cohort analyzing OS, older age, adverse risk, and RUNX1 mutations favored ven/aza over IC, whereas intermediate risk favored IC over ven/aza. In conclusion, patients receiving IC have improved OS compared with those receiving ven/aza. However, in a propensity-matched cohort of patients with equivalent baseline factors, there was a trend toward favorable OS for ven/aza. Specific variables, such as RUNX1 mutations, reported here for the first time, can be identified that favor ven/aza or IC, helping to guide treatment decisions for patients who may be eligible candidates for either therapy.

Antitumor properties of novel sesquiterpene lactone analogs as NFκB inhibitors that bind to the IKKß ubiquitin-like domain (ULD).

Melampomagnolide B (MMB, 3) is a parthenolide (PTL, 1) based sesquiterpene lactone that has been used as a template for the synthesis of a plethora of lead anticancer agents owing to its reactive C-10 primary hydroxyl group. Such compounds have been shown to inhibit the IKKß subunit, preventing phosphorylation of the cytoplasmic IκB inhibitory complex. The present study focuses on the synthesis and in vitro antitumor properties of novel benzyl and phenethyl carbamates of MMB (7a-7k). Screening of these MMB carbamates identified analogs with potent growth inhibition properties against a panel of 60 human cancer cell lines (71% of the molecules screened had GI50 values < 2 µM). Two analogs, the benzyl carbamate 7b and the phenethyl carbamate7k, were the most active compounds. Lead compound 7b inhibited cell proliferation in M9 ENL AML cells, and in TMD-231, OV-MD-231 and SUM149 breast cancer cell lines. Interestingly, mechanistic studies showed that 7b did not inhibit p65 phosphorylation in M9 ENL AML and OV-MD-231 cells, but did inhibit phophorylation of both p65 and IκBα in SUM149 cells. 7b also reduced NFκB binding to DNA in both OV-MD-231 and SUM149 cells. Molecular docking studies indicated that 7b and 7k are both predicted to interact with the ubiquitin-like domain (ULD) of the IKKß subunit. These data suggest that in SUM149 cells, 7b is likely acting as an allosteric inhibitor of IKKß, whereas in M9 ENL AML and OV-MD-231 cells 7b is able to inhibit an event after IκB/p65/p50 phosphorylation by IKKß that leads to inhibition of NFκB activation and reduction in NFκB-DNA binding. Analog 7b was by far the most potent compound in either carbamate series, and was considered an important lead compound for further optimization and development as an anticancer agent.

Comprehensive Structure-Activity Profiling of Micheliolide and its Targeted Proteome in Leukemia Cells via Probe-Guided Late-Stage C-H Functionalization.

The plant-derived sesquiterpene lactone micheliolide was recently found to possess promising antileukemic activity, including the ability to target and kill leukemia stem cells. Efforts toward improving the biological activity of micheliolide and investigating its mechanism of action have been hindered by the paucity of preexisting functional groups amenable for late-stage derivatization of this molecule. Here, we report the implementation of a probe-based P450 fingerprinting strategy to rapidly evolve engineered P450 catalysts useful for the regio- and stereoselective hydroxylation of micheliolide at two previously inaccessible aliphatic positions in this complex natural product. Via P450-mediated chemoenzymatic synthesis, a broad panel of novel micheliolide analogs could thus be obtained to gain structure-activity insights into the effect of C2, C4, and C14 substitutions on the antileukemic activity of micheliolide, ultimately leading to the discovery of "micheliologs" with improved potency against acute myelogenic leukemia cells. These late-stage C-H functionalization routes could be further leveraged to generate a panel of affinity probes for conducting a comprehensive analysis of the protein targeting profile of micheliolide in leukemia cells via chemical proteomics analyses. These studies introduce new micheliolide-based antileukemic agents and shed new light onto the biomolecular targets and mechanism of action of micheliolide in leukemia cells. More broadly, this work showcases the value of the present P450-mediated C-H functionalization strategy for streamlining the late-stage diversification and elucidation of the biomolecular targets of a complex bioactive molecule.

PU.1 enforces quiescence and limits hematopoietic stem cell expansion during inflammatory stress.

Hematopoietic stem cells (HSCs) are capable of entering the cell cycle to replenish the blood system in response to inflammatory cues; however, excessive proliferation in response to chronic inflammation can lead to either HSC attrition or expansion. The mechanism(s) that limit HSC proliferation and expansion triggered by inflammatory signals are poorly defined. Here, we show that long-term HSCs (HSCLT) rapidly repress protein synthesis and cell cycle genes following treatment with the proinflammatory cytokine interleukin (IL)-1. This gene program is associated with activation of the transcription factor PU.1 and direct PU.1 binding at repressed target genes. Notably, PU.1 is required to repress cell cycle and protein synthesis genes, and IL-1 exposure triggers aberrant protein synthesis and cell cycle activity in PU.1-deficient HSCs. These features are associated with expansion of phenotypic PU.1-deficient HSCs. Thus, we identify a PU.1-dependent mechanism triggered by innate immune stimulation that limits HSC proliferation and pool size. These findings provide insight into how HSCs maintain homeostasis during inflammatory stress.

Targeting Energy Metabolism in Cancer Stem Cells: Progress and Challenges in Leukemia and Solid Tumors.

Malignant stem cells have long been considered a key therapeutic target in leukemia. Therapeutic strategies designed to target the fundamental biology of leukemia stem cells while sparing normal hematopoietic cells may provide better outcomes for leukemia patients. One process in leukemia stem cell biology that has intriguing therapeutic potential is energy metabolism. In this article we discuss the metabolic properties of leukemia stem cells and how targeting energy metabolism may provide more effective therapeutic regimens for leukemia patients. In addition, we highlight the similarities and differences in energy metabolism between leukemia stem cells and malignant stem cells from solid tumors.