Acute Promyelocytic Leukemia Cells Research Articles

P415: TARGETED 3RD-GENERATION (NANOPORE) SEQUENCING REVEALS MANY NOVEL CIRCULAR RNAS OF THE APOPTOSIS-RELATED BCL2L12 GENE, EXPRESSED IN HUMAN CELLS FROM ACUTE MYELOID LEUKEMIA AND MYELODYSPLASTIC SYNDROMES

Background: Circular RNAs (circRNAs) are non-coding RNAs generated via back-splicing. They are indirect – yet pivotal – regulators of gene expression, as many of them bind microRNAs (miRNAs) and render them unavailable to exert their direct regulatory functions. They also interact with chromatin, altering its structure and affecting transcription of several genes. Lastly, though considered as non-coding, few of them have also been shown to encode short, functional polypeptides. Due to their multifaceted role and the deregulation of their expression in cancer, circRNAs are related to the development and progression of malignancies, including myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). BCL2L12 is a prominent member of the apoptosis-related BCL2 family, with an already established role in AML. Moreover, BCL2L12 mRNA expression has been associated with chemoresistance of malignant bone marrow blasts. However, the identity and role of the circRNAs produced by alternative back-splicing of BCL2L12 primary transcripts in MDS and AML has not been investigated, so far. Aims: We sought to determine the identity of BCL2L12 circRNAs expressed in MDS and AML cell lines and to explore their putative interactions with miRNAs having an established role in these disease entities. Methods: MDS-L cells [MDS with del(5q) and complex karyotype], NB-4 and HL-60 cells (acute promyelocytic leukemia with and without PML-RARA, respectively), U-937 and THP-1 cells (acute monocytic leukemia), KASUMI-1 cells (AML with t(8;21)(q22;q22.1); RUNX1-RUNX1T1) and MOLM-13 cells (AML with t(9;11)(p21.3;q23.3); KMT2A-MLLT3) were propagated. Total RNA was extracted from these seven cell lines; 2μg of each RNA extract were reverse-transcribed using random hexamers. Next, nested PCR with divergent primers was performed, starting from each exon of the BCL2L12 gene; thus, only cDNAs from BCL2L12 circRNAs were amplified. After having mixed and purified all nested-PCR products of each cell line cDNA, nanopore sequencing libraries were built. Following nanopore sequencing and basecalling in a MinION Mk1C 3rd-generation sequencer, sequencing reads were aligned and corrected using Minimap2 and TranscriptClean, respectively. circRNA identification was performed using an in-house–built, PERL-based algorithm; miRDB was used for prediction of their interactions with miRNAs. Results: We discovered 83 novel BCL2L12 circRNAs, 9 of which were common between MDS-L cells and at least one AML cell line. The exon structure of these novel circRNAs showed a remarkable diversity, comprising exons also encountered in messenger RNAs (mRNAs) of BCL2L12 as intronic regions. This phenomenon was mostly observed in MDS-L cells. Several BCL2L12 circRNAs in NB-4 and HL-60 cells exhibited complete intron retention; additionally, a novel exon was present at a remarkable frequency in NB-4 cells. Moreover, several BCL2L12 circRNAs are predicted to sponge miRNAs with a key role in AML (miR-7-5p, miR-125b-5p and miR-182-5p) and/or MDS (miR-150-5p). Summary/Conclusion: Numerous circRNAs are produced through alternative back-splicing of the primary BCL2L12 transcripts. The circRNA expression profile of this gene differs among the MDS and AML cell lines, as well as among the six AML cell lines. Intronic regions of this apoptosis-related gene are included in several circRNAs, augmenting the repertoire of miRNAs predicted to be bound by BCL2L12 transcripts. This phenomenon was more common in the MDS cell line, followed by both acute promyelocytic leukemia cell lines. Our data suggest an important regulatory role for this gene in MDS and AML subtypes.

Exploring novel nitrofuranyl sulfonohydrazides as anti-Leishmania and anti-cancer agents: Synthesis, in vitro efficacy and hit identification.

Leishmaniasis and cancer are two deadly diseases that plague the human population. There are a limited number of drugs available for the treatment of these diseases; however, their overuse has resulted in pathogenic resistance. Recent studies have indicated the repurposing of nitro‐containing compounds to be a new avenue into finding new treatments. In this study, new nitrofuranyl sulfonohydrazide derivatives were synthesized and evaluated for their in vitro antileishmanial and anticancer activities. The analogue 2h, featuring biphenyl moiety exhibited selective (SI > 10) submicromolar activity (IC50 0.97 μM) against acute promyelocytic leukemia cells hence was identified anticancer hit. This study revealed no antileishmanial hit. However, several promising analogues were uncovered and are worthy of further structural modifications to improve their toxicity and bioactivity profiles.

Abstract 3982: Molecular mechanism of cisplatin-induced p53 activation, cell cycle regulation, and apoptosis in acute leukemia cells

Abstract Cisplatin (CDDP) is an anticancer drug successfully used in the treatment of various human malignancies. Although it has been shown to enhance the potency of arsenic trioxide in chronic myelogenous leukemia (CML) cells and to induce cytotoxicity in acute promyelocytic leukemia (APL) cell lines, its molecular mechanism of action is mostly unknown. We investigated a novel mode of action of CDDP through modulation of stress signals, disruption of MDM2-DAXX-HAUSP complex, and activation of p53 in APL cell lines. We found that CDDP-induced stress signals were transmitted and reduced expression of complex molecules and also effected their association leading to p53 activation. CDDP-activated p53 led to cell cycle arrest and induced both early and late apoptosis in APL cells. Our findings also showed that CDDP stimulated more promyelocytes formation with dense granules, activated p53 expression, and reduced expression of MDM2 in both APL mice bone marrow cells and liver tissues. This novel mechanism of action of CDDP in APL cells may help in the design of new anti-leukemic drugs for treatment of APL patients. Citation Format: Paul B. Tchounwou, Sanjay Kumar. Molecular mechanism of cisplatin-induced p53 activation, cell cycle regulation, and apoptosis in acute leukemia cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3982.

PRMT5-mediated RNF4 methylation promotes therapeutic resistance of APL cells to As2O3 by stabilizing oncoprotein PML-RARα.

Acute promyelocytic leukemia (APL) is a hematological malignancy driven by the oncoprotein PML-RARα, which can be treated with arsenic trioxide (As2O3) or/and all-trans retinoic acid. The protein arginine methyltransferase 5 (PRMT5) is involved in tumorigenesis. However, little is known about the biological function and therapeutic potential of PRMT5 in APL. Here, we show that PRMT5 is highly expressed in APL patients. PRMT5 promotes APL by interacting with PML-RARα and suppressing its ubiquitination and degradation. Mechanistically, PRMT5 attenuates the interaction between PML-RARα and its ubiquitin E3 ligase RNF4 by methylating RNF4 at Arg164. Notably, As2O3 treatment triggers the dissociation of PRMT5 from PML nuclear bodies, attenuating RNF4 methylation and promoting RNF4-mediated PML-RARα ubiquitination and degradation. Moreover, knockdown of PRMT5 and pharmacological inhibition of PRMT5 with the specific inhibitor EPZ015666 significantly inhibit APL cells growth. The combination of EPZ015666 with As2O3 shows synergistic effects on As2O3-induced differentiation of bone marrow cells from APL mice, as well as on apoptosis and differentiation of primary APL cells from APL patients. These findings provide mechanistic insight into the function of PRMT5 in APL pathogenesis and demonstrate that inhibition of PRMT5, alone or in combination with As2O3, might be a promising therapeutic strategy against APL.

Effects of arsenic on the topology and solubility of promyelocytic leukemia (PML)-nuclear bodies.

Promyelocytic leukemia (PML) proteins are involved in the pathogenesis of acute promyelocytic leukemia (APL). Trivalent arsenic (As3+) is known to cure APL by binding to cysteine residues of PML and enhance the degradation of PML-retinoic acid receptor α (RARα), a t(15;17) gene translocation product in APL cells, and restore PML-nuclear bodies (NBs). The size, number, and shape of PML-NBs vary among cell types and during cell division. However, topological changes of PML-NBs in As3+-exposed cells have not been well-documented. We report that As3+-induced solubility shift underlies rapid SUMOylation of PML and late agglomeration of PML-NBs. Most PML-NBs were toroidal and granular dot-like in GFPPML-transduced CHO-K1 and HEK293 cells, respectively. Exposure to As3+ and antimony (Sb3+) greatly reduced the solubility of PML and enhanced SUMOylation within 2 h in the absence of changes in the number and size of PML-NBs. However, the prolonged exposure to As3+ and Sb3+ resulted in agglomeration of PML-NBs. Exposure to bismuth (Bi3+), another Group 15 element, did not induce any of these changes. ML792, a SUMO activation inhibitor, reduced the number of PML-NBs and increased the size of the NBs, but had little effect on the As3+-induced solubility change of PML. These results warrant the importance of As3+- or Sb3+-induced solubility shift of PML for the regulation intranuclear dynamics of PML-NBs.

G-CSF upregulates the expression of aquaporin-9 through CEBPB to enhance the cytotoxic activity of arsenic trioxide to acute myeloid leukemia cells

BackgroundArsenic trioxide (ATO) is highly effective in acute promyelocytic leukemia (APL) patients, but it fails to show satisfactory efficacy in other acute myeloid leukemia (AML) patients with non-APL subtypes. Different from the APL cells, most non-APL AML cells express low levels of the ATO transporter Aquaporin-9 (AQP9) protein, making them less sensitive to ATO treatment. Recently, we found that granulocyte colony stimulating factor (G-CSF) can upregulate the expression of AQP9. We hypothesized that the pretreatment with G-CSF may enhance the antitumor effect of ATO in non-APL AML cells. In addition, we aimed to elucidate the underlying mechanisms by which G-CSF upregulates the expression of AQP9.MethodsNon-APL AML cell lines including THP-1 and HL-60 were pretreated with or without G-CSF (100 ng/ml) for 24 h, followed by the treatment with ATO (2 μM) for 48 h. Cell morphology was observed under the microscope after Wright-Giemsa staining. Flow cytometry was performed to evaluate the cell apoptosis levels. The intracellular concentrations of ATO were determined by atomic fluorescence spectrometry. The mRNA and protein expression were respectively measured by quantitative reverse transcription PCR (RT-qPCR) and western blotting. Target genes were knocked down by transfection with small interfering RNA (siRNA), or overexpressed by transfection with overexpression plasmids. The cell line derived xenograft mouse model was established to confirm the results of the in vitro experiments.ResultsCompared with using ATO alone, the combination of G-CSF with ATO induced the cell apoptosis more dramatically. G-CSF upregulated the expression of AQP9 and enhanced the intracellular concentrations of ATO in AML cells. When AQP9 was overexpressed, it markedly enhanced the cytotoxic activity of ATO. On the other hand, when AQP9 was knocked down, it profoundly attenuated the combinational effect. Moreover, we found that the upregulation of AQP9 by G-CSF depends on the transcription factor CCAAT enhancer binding protein beta (CEBPB). We also demonstrated that the combination of G-CSF and ATO significantly inhibited tumor growth in the xenograft mouse model.ConclusionsThe combination of G-CSF and ATO may be a potential therapeutic strategy for AML patients.

Interplay between hypertriglyceridemia and acute promyelocytic leukemia mediated by the cooperation of peroxisome proliferator-activated receptor-α with the PML/RAR α fusion protein on super-enhancers.

Patients with newly diagnosed acute promyelocytic leukemia (APL) are often obese or overweight, accompanied by metabolic disorders, such as dyslipidemia. However, the link between dyslipidemia and leukemia is obscure. Here, we conducted a retrospective study containing 1,412 cases (319 newly diagnosed APL patients, 393 newly diagnosed non-APL acute myeloid leukemia patients, and 700 non-tumor controls) and found that APL patients had higher triglyceride levels than non- APL and control groups. Using clinical data, we revealed that hypertriglyceridemia served as a risk factor for early death in APL patients, and there was a positive correlation between triglyceride levels and leukocyte counts. RNA sequencing analysis of APL patients having high or normal triglyceride levels highlighted the contribution of peroxisome proliferatoractivated receptor-α (PPARα), a crucial regulator of cell metabolism and a transcription factor involved in cancer development. The genome-wide chromatin occupancy of PPARα revealed that PPARα co-existed with PML/RARα within the super-enhancer regions to promote cell proliferation. PPARα knockdown affected the expression of target genes responsible for APL proliferation, including FLT3, and functionally inhibited the proliferation of APL cells. Moreover, in vivo results in mice having high fat diet-induced high triglyceride levels supported the connection between high triglyceride levels and the leukemic burden, as well as the involvement of PPARα-mediated-FLT3 activation in the proliferation of APL cells. Our findings shed light on the association between APL proliferation and high triglyceride levels and provide a genetic link to PPARα-mediated hyperlipidemia in APL.

Extracellular Traps Increase Burden of Bleeding by Damaging Endothelial Cell in Acute Promyelocytic Leukaemia.

The rate of complete remission of acute promyelocytic leukemia (APL) is currently over 90% because of the use of all-trans retinoic acid (ATRA) with arsenic trioxide (ATO). However, hemorrhagic mortality has emerged as the most significant barrier to APL-induced remission. Neutrophils extracellular traps (NETs/ETs) cause vascular leakage by damaging the integrity of endothelial cells. We have previously demonstrated that APL cells treated with ATRA/ATO undergo a cell death process, releasing extracellular chromatin, termed ETosis/NETosis. However, the mechanism underlying the involvement of ETs in endothelial injury in APL remain largely unknown. Here, we analysed the ability of mature and immature neutrophils to release ETs, and their interaction with platelets (PLTs) in APL. Importantly, the effect of ETs on vascular endothelium in APL was discussed. Our results showed that the ability of immature neutrophils to release ETs was impaired in APL, whereas mature neutrophils produced ETs, which were associated with activated PLTs. Moreover, ATRA+ATO induced immature neutrophil differentiation, as well as increased the release of ETs from mature neutrophils. The excessive ETs damaged endothelial cells, causing blood cell leakage. Removing ETs using DNase 1 alleviated endothelial damage and improved blood cells leakage. Our results indicate that vascular endothelial injury is at least partially associated with ETs in APL, and that targeting ETs production may be an effective approach for relieving vascular leakage and reducing the burden of bleeding in APL.

HTERT DNA Methylation Analysis Identifies a Biomarker for Retinoic Acid-Induced hTERT Repression in Breast Cancer Cell Lines.

Telomerase reactivation is responsible for telomere preservation in about 90% of cancers, providing cancer cells an indefinite proliferating potential. Telomerase consists of at least two main subunits: a catalytic reverse transcriptase protein (hTERT) and an RNA template subunit. Strategies to inhibit hTERT expression seem promising for cancer treatment. Previous works showed that all-trans retinoic acid (ATRA) induces hTERT repression in acute promyelocytic leukemia cells, resulting in their death. Here, we investigated the effects of ATRA in a subset of breast cancer cell lines. The mutational status of hTERT promoter and the methylation patterns at a single CpG resolution were assessed. We observed an inverse relationship between hTERT expression after ATRA treatment and the methylation level of a specific CpG at chr5: 1,300,438 in a region of hTERT gene at −5 kb of the transcription initiation site. This observation highlighted the significance of this region, whose methylation profile could represent a promising biomarker to predict the sensitivity to ATRA-induced hTERT repression in specific breast cancer subtypes. As hTERT repression promotes drug-induced cell death, checking the methylation status of this unique region and the specific CpG included can help in decision-making to include ATRA in combination therapy and contributes to a better clinical outcome.

Co-targeting leukemia-initiating cells and leukemia bulk leads to disease eradication.

According to a hierarchical model, targeting leukemia-initiating cells (LICs) was speculated to achieve complete remission (CR) or cure. Nonetheless, increasing evidence emphasized the plasticity of differentiated blasts undergoing interconversion into LICs. We exploited murine models of acute promyelocytic leukemia (APL), a subtype of acute myeloid leukemia driven by the promyelocytic leukemia/retinoic acid receptor (PML-RARα) oncofusion protein, which recruits histone deacetylase (HDAC)-containing complexes. We studied APLs with different LIC frequencies and investigated the effect of two HDAC inhibitors: valproic acid (VPA), with relative selectivity towards class I HDAC enzymes and vorinostat/suberoylanilide hydroxamic acid (SAHA) (pan-HDAC inhibitor) in combination with all-trans retinoic acid (ATRA), on the bulk APL cells and APL LICs. Indeed, we found that while VPA differentiates the bulk APL cells, SAHA selectively targets LICs. ATRA + VPA + SAHA combination efficiently induced CR in an APL model with lower LIC frequency. Substituting ATRA with synthetic retinoids as etretinate which promotes APL differentiation without downregulating PML/RARα compromised the therapeutic benefit of ATRA + VPA + SAHA regimen. Altogether, our study emphasizes the therapeutic power of co-targeting the plasticity and heterogeneity of cancer -herein demonstrated by tackling LICs and bulk leukemic blasts - to achieve and maintain CR.

All-Trans-Retinoic Acid Combined With Valproic Acid Can Promote Differentiation in Myeloid Leukemia Cells by an Autophagy Dependent Mechanism.

Acute myeloid leukemia (AML) is an aggressive blood cancer with an overall survival of 30%. One form of AML, acute promyelocytic leukemia (APL) has become more than 90% curable with differentiation therapy, consisting of all-trans-retinoic acid (ATRA) and arsenic trioxide (ATO). Application of differentiation therapy to other AML subtypes would be a major treatment advance. Recent studies have indicated that autophagy plays a key role in the differentiation of ATRA-responsive APL cells. In this study, we have investigated whether differentiation could be enhanced in ATRA resistant cells by promoting autophagy induction with valproic acid (VPA). ATRA sensitive (NB4) and resistant leukemia cells (NB4R and THP-1) were co-treated with ATRA and valproic acid, followed by assessment of autophagy and differentiation. The combination of VPA and ATRA induced autophagic flux and promoted differentiation in ATRA-sensitive and -resistant cell lines. shRNA knockdown of ATG7 and TFEB autophagy regulators impaired both autophagy and differentiation, demonstrating the importance of autophagy in the combination treatment. These data suggest that ATRA combined with valproic acid can promote differentiation in myeloid leukemia cells by mechanism involving autophagy.

Deneddylation of PML/RARα reconstructs functional PML nuclear bodies via orchestrating phase separation to eradicate APL.

Acute promyelocytic leukemia (APL) is driven by the oncoprotein PML/RARα, which destroys the architecture of PML nuclear bodies (NBs). PML NBs are critical to tumor suppression, and their disruption mediated by PML/RARα accelerates APL pathogenesis. However, the mechanisms of PML NB disruption remain elusive. Here, we reveal that the failure of NB assembly in APL results from neddylation-induced aberrant phase separation of PML/RARα. Mechanistically, PML/RARα is neddylated in the RARα moiety, and this neddylation enhances its DNA-binding ability and further impedes the phase separation of the PML moiety, consequently disrupting PML NB construction. Accordingly, deneddylation of PML/RARα restores its phase separation process to reconstruct functional NBs and activates RARα signaling, thereby suppressing PML/RARα-driven leukemogenesis. Pharmacological inhibition of neddylation by MLN4924 eradicates APL cells both in vitro and in vivo. Our work elucidates the neddylation-destroyed phase separation mechanism for PML/RARα-driven NB disruption and highlights targeting neddylation for APL eradication.

Harringtonine Ester Derivatives with Enhanced Antiproliferative Activities against HL-60 and HeLa Cells.

Harringtonine (HT), produced from Cephalotaxus species, is known to exhibit potent antiproliferative activity against myeloid leukemia cells by inhibiting protein synthesis. A previous study using acute promyelocytic leukemia (HL-60) cells raised the possibility that the C-5' methyl group of HT plays an important role in regulating leukemia cell line antiproliferative activity. In order to investigate the effect of hydrocarbon chains at C-5' on the resultant activity, the C-5' methyl group was replaced with various straight- and branched-chain hydrocarbons using the corresponding alcohols, and their antiproliferative activity against HL-60 and HeLa cells was investigated. As a result, 4'-n-heptyl-4'-demethylharringtonine (1f, n-heptyl derivative) showed the most potent cytotoxicity among the HT ester derivatives produced, with IC50 values of 9.4 nM and 0.4 μM for HL-60 and HeLa cells, respectively. Interestingly, the cytotoxicity of derivative 1f against HL-60 and HeLa cells respectively was ∼5 (IC50 = 50.5 nM) and ∼10 times (IC50 = 4.0 μM) those of HT and ∼2 (IC50 = 21.8 nM) and ∼4 times (IC50 = 1.7 μM) more than homoharringtonine (HHT). These results demonstrate the potential of the derivative 1f as a lead compound against leukemia.

Effects of Monoammonium Glycyrrhizinate on Stem Cell-like Characteristics, Oxidative Stress and Mitochondrial Function of Acute Promyelocytic Leukemia NB4 Cells

To investigate the effect of monoammonium glycyrrhizinate on the stem cell-like characteristics, oxidative stress and mitochondrial function of acute promyelocytic leukemia cells NB4. CCK-8 method was used to detect the viability of acute promyelocytic leukemia cells NB4, and the appropriate dose was screened; Cloning method was used to detect the proliferation rate of NB4 cell; Western blot was used to detect the expression of cell cycle-related protein; flow cytometry was used to detect cell apoptosis and sort NB4 stem cells positive (CD133+); Stem cell markers (Oct4, ABCG2, Dclk1) were detected by RT-PCR; ROS was detected by fluorescence; The kit was used to detect the level of oxidative stress markers (MDA); The flow cytometry was used to detect the change of mitochondrial membrane potential; Western blot was used to detect the expression of mitochondrial damage index-related proteins (Bax/BCL-2). Compared with the control group, if the concentration of MAG was less than 5 μmol/L, the cell NB4 viability showed no significant difference; if the concentration was higher than 5 μmol/L, the inhibitory effect on the growth of cell NB4 increased and showed significant difference (P<0.05), according to the results of CCK-8 experiment, four groups were set based on the concentration of MAG 0 μmol/L, MAG 5 μmol/L, MAG 10 μmol/L, and MAG 20 μmol/L; compared with the control group (MAG 0 μmol/L), the cells in MAG 5 μmol/L group showed no significant difference, while the proliferation rate, cyclin expression, mitochondrial membrane potential, stem cell CD133+ ratio, and marker mRNA level ( Oct4, ABCG2, Dclk1) of NB4 cell were significantly reduced (P<0.05); the apoptosis rate, reactive oxygen species, MDA content and Bax/BCL-2 expression of NB4 cell significantly increased (P<0.05). Monoammonium glycyrrhizinate has a significant inhibitory effect on acute promyelocytic leukemia cells NB4, which may be related to the regulation of stem cell-like characteristics, oxidative stress and mitochondrial function.

Oncogene-induced alterations in nuclear functions and architecture investigated by superresolution microscopy

Oncogenes can induce genomic instability by interfering with fundamental processes such as DNA transcription and replication (Negrini, Nat Rev Mol Cell Biol 2010) and chromatin organization (Wolffe, Oncogene 2001). The observation of these molecular processes, in intact nuclei, may elucidate how oncogenes affect chromatin architecture leading to tumor formation. Here we use an engineered Acute Promyelocytic Leukemia (APL) cell line, U937-PR9, which allows us to selectively activate the expression of the PML-RARα oncoprotein and to analyze its effects on the spatiotemporal organization of functional nuclear processes.

A Proteomic Platform Enables to Test for AML Normalization In Vitro.

Acute promyelocytic leukaemia (APL) can be cured by the co-administration of arsenic trioxide (ATO) and all-trans retinoic acid (ATRA). These small molecules relieve the differentiation blockade of the transformed promyelocytes and trigger their maturation into functional neutrophils, which are physiologically primed for apoptosis. This normalization therapy represents a compelling alternative to cytotoxic anticancer chemotherapy, but lacks an in vitro model system for testing the efficiency of novel combination treatments consisting of inducers of differentiation and metallopharmaceuticals. Here, using proteome profiling we present an experimental framework that enables characterising the differentiation– and metal-specific effects of the combination treatment in a panel of acute myeloid leukaemia (AML) cell lines (HL-60 and U937), including APL (NB4). Differentiation had a substantial impact on the proteome on the order of 10% of the identified proteins and featured classical markers and transcription factors of myeloid differentiation. Additionally, ATO provoked specific cytoprotective effects in the AML cell lines HL-60 and U937. In HL-60, these effects included an integrated stress response (ISR) in conjunction with redox defence, while proteasomal responses and a metabolic rewiring were observed in U937 cells. In contrast, the APL cell line NB4 did not display such adaptions indicating a lack of plasticity to cope with the metal-induced stress, which may explain the clinical success of this combination treatment. Based on the induction of these cytoprotective effects, we proposed a novel metal-based compound to be used for the combination treatment instead of ATO. The organoruthenium drug candidate plecstatin-1 was previously shown to induce reactive oxygen species and an ISR. Indeed, the plecstatin-1 combination was found to affect similar pathways compared to the ATO combination in HL-60 cells and did not lead to cytoprotective response signatures in NB4. Moreover, the monocytic cell line U937 showed a low plasticity to cope with the plecstatin-1 combination, which suggests that this combination might achieve therapeutic benefit beyond APL. We propose that the cytoprotective plasticity of cancer cells might serve as a general proxy to discover novel combination treatments in vitro.

Mechanical phenotyping reveals unique biomechanical responses in retinoic acid-resistant acute promyelocytic leukemia

SummaryAll-trans retinoic acid (ATRA) is an essential therapy in the treatment of acute promyelocytic leukemia (APL), but nearly 20% of patients with APL are resistant to ATRA. As there are no biomarkers for ATRA resistance that yet exist, we investigated whether cell mechanics could be associated with this pathological phenotype. Using mechano-node-pore sensing, a single-cell mechanical phenotyping platform, and patient-derived APL cell lines, we discovered that ATRA-resistant APL cells are less mechanically pliable. By investigating how different subcellular components of APL cells contribute to whole-cell mechanical phenotype, we determined that nuclear mechanics strongly influence an APL cell’s mechanical response. Moreover, decondensing chromatin with trichostatin A is especially effective in softening ATRA-resistant APL cells. RNA-seq allowed us to compare the transcriptomic differences between ATRA-resistant and ATRA-responsive APL cells and highlighted gene expression changes that could be associated with mechanical changes. Overall, we have demonstrated the potential of “physical” biomarkers in identifying APL resistance.

Effect of Kaempferol and Its Glycoside Derivatives on Antioxidant Status of HL-60 Cells Treated with Etoposide.

Kaempferol is a well-known antioxidant found in many plants and plant-based foods. In plants, kaempferol is present mainly in the form of glycoside derivatives. In this work, we focused on determining the effect of kaempferol and its glycoside derivatives on the expression level of genes related to the reduction of oxidative stress—NFE2L2, NQO1, SOD1, SOD2, and HO-1; the enzymatic activity of superoxide dismutases; and the level of glutathione. We used HL-60 acute promyelocytic leukemia cells, which were incubated with the anticancer drug etoposide and kaempferol or one of its three glycoside derivatives isolated from the aerial parts of Lens culinaris Medik.—kaempferol 3-O-[(6-O-E-caffeoyl)-β-d-glucopyranosyl-(1→2)]-β-d-galactopyranoside-7-O-β-d-glucuropyranoside (P2), kaempferol 3-O-[(6-O-E-p-coumaroyl)-β-d-glucopyranosyl-(1→2)]-β-d-galactopyranoside-7-O-β-d-glucuropyranoside (P5), and kaempferol 3-O-[(6-O-E-feruloyl)-β-d-glucopyranosyl-(1→2)]-β-d-galactopyranoside-7-O-β-d-glucuropyranoside (P7). We showed that none of the tested compounds affected NFE2L2 gene expression. Co-incubation with etoposide (1 µM) and kaempferol (10 and 50 µg/mL) leads to an increase in the expression of the HO-1 (9.49 and 9.33-fold at 10 µg/mL and 50 µg/mL, respectively), SOD1 (1.68-fold at 10 µg/mL), SOD2 (1.72-fold at 10–50 µg/mL), and NQO1 (1.84-fold at 50 µg/mL) genes in comparison to cells treated only with etoposide. The effect of kaempferol derivatives on gene expression differs depending on the derivative. All tested polyphenols increased the SOD activity in cells co-incubated with etoposide. We observed that the co-incubation of HL-60 cells with etoposide and kaempferol or derivative P7 increases the level of total glutathione in these cells. Taken together, our observations suggest that the antioxidant activity of kaempferol is related to the activation of antioxidant genes and proteins. Moreover, we observed that glycoside derivatives can have a different effect on the antioxidant cellular systems than kaempferol.

TRAIL Triggers CRAC-Dependent Calcium Influx and Apoptosis through the Recruitment of Autophagy Proteins to Death-Inducing Signaling Complex.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) selectively kills various cancer cell types, but also leads to the activation of signaling pathways that favor resistance to cell death. Here, we investigated the as yet unknown roles of calcium signaling and autophagy regulatory proteins during TRAIL-induced cell death in leukemia cells. Taking advantage of the Gene Expression Profiling Interactive Analysis (GEPIA) project, we first found that leukemia patients present a unique TRAIL receptor gene expression pattern that may reflect their resistance to TRAIL. The exposure of NB4 acute promyelocytic leukemia cells to TRAIL induces intracellular Ca2+ influx through a calcium release-activated channel (CRAC)-dependent mechanism, leading to an anti-apoptotic response. Mechanistically, we showed that upon TRAIL treatment, two autophagy proteins, ATG7 and p62/SQSTM1, are recruited to the death-inducing signaling complex (DISC) and are essential for TRAIL-induced Ca2+ influx and cell death. Importantly, the treatment of NB4 cells with all-trans retinoic acid (ATRA) led to the upregulation of p62/SQSTM1 and caspase-8 and, when added prior to TRAIL stimulation, significantly enhanced DISC formation and the apoptosis induced by TRAIL. In addition to uncovering new pleiotropic roles for autophagy proteins in controlling the calcium response and apoptosis triggered by TRAIL, our results point to novel therapeutic strategies for sensitizing leukemia cells to TRAIL.

In Vitro Anticancer Activity and Mechanism of Action of an Aziridinyl Galactopyranoside.

We recently screened a series of new aziridines β-D-galactopyranoside derivatives for selective anticancer activity and identified 2-methyl-2,3-[N-(4-methylbenzenesulfonyl)imino]propyl 2,3-di-O-benzyl-4,6-O-(S)-benzylidene-β-D-galactopyranoside (AzGalp) as the most promising compound. In this article, we explore the possible mechanisms involved in the cytotoxicity of this aziridine and evaluate its selective anticancer activity using cancer cells and normal cells from a variety of tissues. Our data show that AzGalp induces DNA damage (comet assay). Cells deficient in the nucleotide excision repair (NER) pathway were hypersensitive to the cytotoxicity of this compound. These results suggest that AzGalp induces bulky DNA adducts, and that cancer cells lacking a functional NER pathway may be particularly vulnerable to the anticancer effects of this aziridine. Several experiments revealed that neither the generation of oxidative stress nor the inhibition of glycolysis played a significant role in the cytotoxicity of AzGalp. Combinations of AzGalp with oxaliplatin or 5-fluorouracil slightly improved the ability of both anticancer drugs to selectively kill cancer cells. AzGalp also showed selective cytotoxicity against a panel of malignant cells versus normal cells; the highest selectivity was observed for two acute promyelocytic leukemia cell lines. Additional preclinical studies are necessary to evaluate the anticancer potential of AzGalp.