Acute promyelocytic leukemia cell line AP-1060 established as a cytokine-dependent culture from a patient clinically resistant to all-trans retinoic acid and arsenic trioxide

Choosing the Right Cell Line for Acute Myeloid Leukemia (AML) Research

Immortalized cell lines are widely used in vitro tools in oncology and hematology research. While these cell lines represent artificial systems and may accumulate genetic aberrations with each passage, they are still considered valuable models for pilot, preliminary, and screening studies. Despite their limitations, cell lines are cost-effective and provide repeatable and comparable results. Choosing the appropriate cell line for acute myeloid leukemia (AML) research is crucial for obtaining reliable and relevant results. Several factors should be considered when selecting a cell line for AML research, such as specific markers and genetic abnormalities associated with different subtypes of AML. It is also essential to evaluate the karyotype and mutational profile of the cell line, as these can influence the behavior and response to the treatment of the cells. In this review, we evaluate immortalized AML cell lines and discuss the issues surrounding them concerning the revised World Health Organization and the French-American-British classifications.

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

All-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.

Current status and future prospects of nanomedicine for arsenic trioxide delivery to solid tumors

Despite having a rich history as a poison, arsenic and its compounds have also gained a great reputation as promising anticancer drugs. As a pioneer, arsenic trioxide has been approved for the treatment of acute promyelocytic leukemia. Many in vitro studies suggested that arsenic trioxide could also be used in the treatment of solid tumors. However, the transition from bench to bedside turned out to be challenging, especially in terms of the drug bioavailability and concentration reaching tumor tissues. To address these issues, nanomedicine tools have been proposed. As nanocarriers of arsenic trioxide, various materials have been examined including liposomes, polymer, and inorganic nanoparticles, and many other materials. This review gives an overview of the existing strategies of delivery of arsenic trioxide in cancer treatment with a focus on the drug encapsulation approaches and medicinal impact in the treatment of solid tumors. It focuses on the progress in the last years and gives an outlook and suggestions for further improvements including theragnostic approaches and targeted delivery.

A new ETV6-NTRK3 cell line model reveals MALAT1 as a novel therapeutic target - a short report

BACKGROUND

Previously, the chromosomal translocation t(12;15)(p13;q25) has been found to recurrently occur in both solid tumors and leukemias. This translocation leads to ETV6-NTRK3 (EN) gene fusions resulting in ectopic expression of the NTRK3 neurotropic tyrosine receptor kinase moiety as well as oligomerization through the donated ETV6-sterile alpha motif domain. As yet, no in vitro cell line model carrying this anomaly is available. Here we genetically characterized the acute promyelocytic leukemia (APL) cell line AP-1060 and, by doing so, revealed the presence of a t(12;15)(p13;q25). Subsequently, we evaluated its suitability as a model for this important clinical entity.

METHODS

Spectral karyotyping, fluorescence in situ hybridization (FISH), and genomic and transcriptomic microarray-based profiling were used to screen for the presence of EN fusions. qRT-PCR was used for quantitative expression analyses. Responses to AZ-23 (NTRK) and wortmannin (PI3K) inhibitors, as well as to arsenic trioxide (ATO), were assessed using colorimetric assays. An AZ-23 microarray screen was used to define the EN targetome, which was parsed bioinformatically. MAPK1 and MALAT1 activation were assayed using Western blotting and RNA-FISH, respectively, whereas an AML patient cohort was used to assess the clinical occurrence of MALAT1 activation.

RESULTS

An EN fusion was detected in AP1060 cells which, accordingly, turned out to be hypersensitive to AZ-23. We also found that AZ-23 can potentiate the effect of ATO and inhibit the phosphorylation of its canonical target MAPK1. The AZ-23 microarray screen highlighted a novel EN target, MALAT1, which also proved sensitive to wortmannin. Finally, we found that MALAT1 was massively up-regulated in a subset of AML patients.

CONCLUSIONS

From our data we conclude that AP-1060 may serve as a first publicly available preclinical model for EN. In addition, we conclude that these EN-positive cells are sensitive to the NTRK inhibitor AZ-23 and that this inhibitor may potentiate the therapeutic efficacy of ATO. Our data also highlight a novel AML EN target, MALAT1, which was so far only conspicuous in solid tumors.

Node-pore sensing enables label-free surface-marker profiling of single cells

Flow cytometry is a ubiquitous, multiparametric method for characterizing cellular populations. However, this method can grow increasingly complex with the number of proteins that need to be screened simultaneously: spectral emission overlap of fluorophores and the subsequent need for compensation, lengthy sample preparation, and multiple control tests that need to be performed separately must all be considered. These factors lead to increased costs, and consequently, flow cytometry is performed in core facilities with a dedicated technician operating the instrument. Here, we describe a low-cost, label-free microfluidic method that can determine the phenotypic profiles of single cells. Our method employs Node-Pore Sensing to measure the transit times of cells as they interact with a series of different antibodies, each corresponding to a specific cell-surface antigen, that have been functionalized in a single microfluidic channel. We demonstrate the capabilities of our method not only by screening two acute promyelocytic leukemia human cells lines (NB4 and AP-1060) for myeloid antigens, CD13, CD14, CD15, and CD33, simultaneously, but also by distinguishing a mixture of cells of similar size—AP-1060 and NALM-1—based on surface markers CD13 and HLA-DR. Furthermore, we show that our method can screen complex subpopulations in clinical samples: we successfully identified the blast population in primary human bone marrow samples from patients with acute myeloid leukemia and screened these cells for CD13, CD34, and HLA-DR. We show that our label-free method is an affordable, highly sensitive, and user-friendly technology that has the potential to transform cellular screening at the benchside.

Host b7x promotes pulmonary metastasis of breast cancer

B7x (B7-H4 or B7S1) is an inhibitory member of the B7 family of T cell costimulation. It is expressed in low levels in healthy peripheral tissues, such as the lung epithelium, but is overexpressed in a variety of human cancers with negative clinical associations, including metastasis. However, the function of B7x in the context of cancer, whether expressed on cancer cells or on surrounding "host" tissues, has not been elucidated in vivo. We used the 4T1 metastatic breast cancer model and B7x knockout (B7x (-/-)) mice to investigate the effect of host tissue-expressed B7x on cancer. We found that 4T1 cells were B7x negative in vitro and in vivo, and B7x(-/-) mice had significantly fewer lung 4T1 tumor nodules than did wild-type mice. Furthermore, B7x(-/-) mice showed significantly enhanced survival and a memory response to tumor rechallenge. Mechanistic studies revealed that the presence of B7x correlated with reduced general and tumor-specific T cell cytokine responses, as well as with an increased infiltration of immunosuppressive cells, including tumor-associated neutrophils, macrophages, and regulatory T cells, into tumor-bearing lungs. Importantly, tumor-associated neutrophils strongly bound B7x protein and inhibited the proliferation of both CD4 and CD8 T cells. These results suggest that host B7x may enable metastasizing cancer cells to escape local antitumor immune responses through interactions with the innate and adaptive immune systems. Thus, targeting the B7x pathway holds much promise for improving the efficacy of immunotherapy for metastatic cancer.

Missense mutations in PML-RARA are critical for the lack of responsiveness to arsenic trioxide treatment

Arsenic trioxide (As2O3) is a highly effective treatment for patients with refractory/relapsed acute promyelocytic leukemia (APL), but resistance to As2O3 has recently been seen. In the present study, we report the findings that 2 of 15 patients with refractory/relapsed APL treated with As2O3 were clinically As2O3 resistant. Leukemia cells from these 2 patients harbored missense mutations in promyelocytic leukemia gene–retinoic acid receptor-α gene (PML-RARA) transcripts, resulting in amino acid substitutions of A216V and L218P in the PML B2 domain. When wild-type or mutated PML-RARA (PR-WT and PR-B/L-mut, respectively) were overexpressed in HeLa cells, immunoblotting showed SUMOylated and/or oligomerized protein bands in PR-WT but not in PR-B/L-mut after As2O3 treatment. Protein-localization analysis indicated that PR-WT in the soluble fraction was transferred to the insoluble fraction after treatment with As2O3, but PR-B/L-mut was stably detected in fractions both with and without As2O3. Immunofluorescent microscopy analysis showed PR-WT localization as a microgranular pattern in the cytoplasm without As2O3 and as a macrogranular pattern with As2O3. PR-B/L-mut was diffusely observed in the cytoplasm with and without As2O3. Nearly identical localization patterns were observed in patients' primary cells. Therefore, B2 domain mutations may play an important role in aberrant molecular responses to As2O3 and may be critical for As2O3 resistance in APL.

Regulation of telomerase activity by apparently opposing elements

Telomeres, the ends of chromosomes, undergo frequent remodeling events that are important in cell development, proliferation and differentiation, and neoplastic immortalization. It is not known how the cellular environment influences telomere remodeling, stability, and lengthening or shortening. Telomerase is a ribonucleoprotein complex that maintains and lengthens telomeres in the majority of cancers. Recent studies indicate that a number of factors, including hormones, cytokines, ligands of nuclear receptor, vitamins and herbal extracts have significantly influence telomerase activity and, in some instances, the remodeling of telomeres. This review summarizes the advances in understanding of the positive and negative regulation by extracellular factors of telomerase activity in cancer, stem cells and other systems in mammals.

Immunotoxicity and biodistribution analysis of arsenic trioxide in C57Bl/6 mice following a 2-week inhalation exposure

In these studies the immunotoxicity of arsenic trioxide (ATO, As(2)O(3)) was evaluated in mice following 14 days of inhalation exposures (nose only, 3 h per day) at concentrations of 50 microg/m(3) and 1 mg/m(3). A biodistribution analysis performed immediately after inhalation exposures revealed highest levels of arsenic in the kidneys, bladder, liver, and lung. Spleen cell levels were comparable to those found in the blood, with the highest concentration of arsenic detected in the spleen being 150 microg/g tissue following the 1 mg/m(3) exposures. No spleen cell cytotoxicity was observed at either of the two exposure levels. There were no changes in spleen cell surface marker expression for B cells, T cells, macrophages, and natural killer (NK) cells. There were also no changes detected in the B cell (LPS-stimulated) and T cell (Con A-stimulated) proliferative responses of spleen cells, and no changes were found in the NK-mediated lysis of Yac-1 target cells. The primary T-dependent antibody response was, however, found to be highly susceptible to ATO suppression. Both the 50 microg/m(3) and 1 mg/m(3) exposures produced greater than 70% suppression of the humoral immune response to sheep red blood cells. Thus, the primary finding of this study is that the T-dependent humoral immune response is extremely sensitive to suppression by ATO and assessment of humoral immune responses should be considered in evaluating the health effects of arsenic containing agents.

Downregulation of topoisomerase IIbeta in myeloid leukemia cell lines leads to activation of apoptosis following all-trans retinoic acid-induced differentiation/growth arrest

Among the topoisomerase (topo) II isozymes (alpha and beta), topo IIbeta has been suggested to regulate differentiation. In this study, we examined the role of topo IIbeta in all-trans retinoic acid (ATRA)-induced differentiation of myeloid leukemia cell lines. Inhibition of topo IIbeta activity or downregulation of protein expression enhanced ATRA-induced differentiation/growth arrest and apoptosis. ATRA-induced apoptosis in topo IIbeta-deficient cells involved activation of the caspase cascade and was rescued by ectopic expression of topo IIbeta. Gene expression profiling led to the identification of peroxiredoxin 2 (PRDX2) as a candidate gene that was downregulated in topo IIbeta-deficient cells. Reduced expression of PRDX2 validated at the mRNA and protein level, in topo IIbeta-deficient cells correlated with increased accumulation of reactive oxygen species (ROS) following ATRA-induced differentiation. Overexpression of PRDX2 in topo IIbeta-deficient cells led to reduced accumulation of ROS and partially reversed ATRA-induced apoptosis. These results support a role for topo IIbeta in survival of ATRA-differentiated myeloid leukemia cells. Reduced expression of topo IIbeta induces apoptosis in part by impairing the anti-oxidant capacity of the cell owing to downregulation of PRDX2. Thus, suppression of topo IIbeta and/or PRDX2 levels in myeloid leukemia cells provides a novel approach for improving ATRA-based differentiation therapy.

Cell cycle arrest and apoptotic cell death in cultured human gastric carcinoma cells mediated by arsenic trioxide

AIM: To investigate the effect of arsenic trioxide on human gastric cancer cell line MKN45 with respect to both cytotoxicity and induction of apoptosis in vitro.

METHODS: MKN45 cells were treated with arsenic trioxide (As₂O₃) at the concentration of 1, 5, and 10 µmol/L, respectively, for three successive days. Cell growth and proliferation were observed by cell counting and trypan blue exclusion. Cytotoxicity of As₂O₃ was determined by MTT assay. Morphologic changes were studied with light microscopy. Flow cytometry was used to assay cell DNA distribution and apoptotic cells were confirmed with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and DNA electrophoresis.

RESULTS: The growth of MKN45 cells was significantly inhibited by As₂O₃ which was confirmed by colony-forming assay. After 7 d of culture with various concentrations of As₂O₃, colony-forming capacity of MKN45 cells decreased with As₂O₃ increment in comparison with that of control group. The inhibitory rate of colony-formation was 38.5%, 99.1%, and 99.5% when the concentration of As₂O₃ was 1, 5, and 10 μmol/L in culture medium, respectively. The cell number of a single colony in drug treatment groups was less than that of control group. The cell-killing rate of As₂O₃ to MKN45 cells was both dose- and time-dependent with an IC₅₀ of (11.05±0.25) µmol/L. After incubation in 10 μmol/L As₂O₃ for 24 h, the cell-killing rate was 27.1%, and it was close to 50% after 48 h. The results showed that As₂O₃ induced time- and dose-dependent apoptosis in MKN45 cells, blocked at G2/M phase. The apoptotic peak (sub-G1 phase) appeared and cell apoptotic rate in MKN45 cells was 18.3-32.5% after treatment by 10 μmol/L As₂O₃ for 48 h. The percentage of G2/M cell of the experimental groups was 2.0-5.0 times than that of the control group. Gel electrophoresis of DNA from cells treated with each concentration of As₂O₃ for 48 h revealed a “ladder” pattern, indicating preferential DNA degradation at the internucleosomal, linker DNA sections. TUNEL also demonstrated strand breaks in DNA of MKN45 cells treated with As₂O₃, while control cells showed negative labeling.

CONCLUSION: As₂O₃ can induce apoptosis of human gastric carcinoma cells MKN45, which is the basis of its effectiveness. It shows great potential in the treatment of gastric carcinoma.

Inhibition of apoptosis in acute promyelocytic leukemia cells leads to increases in levels of oxidized protein and LMP2 immunoproteasome

On reaching maturity, animal organs cease to increase in size because of inhibition of cell replication activities. It follows that maintenance of optimal organ function depends on the elimination of oxidatively damaged cells and their replacement with new cells. To examine the effects of oxidative stress and apoptosis on the accumulation of oxidized proteins, we exposed acute promyelocytic leukemia cells to arsenic trioxide (As(2)O(3)) in the presence and absence of a general caspase inhibitor (benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone), which is known to inhibit caspase-induced apoptosis. We confirm that treatment of cells with As(2)O(3) induces apoptosis and leads to the accumulation of oxidized proteins. Furthermore, inhibition of caspase activities prevented As(2)O(3)-induced apoptosis and led to a substantial increase in accumulation of oxidized proteins. Moreover, inhibition of caspase activity in the absence of As(2)O(3) led to elevated levels of the LMP2 immunoproteasome protein. We also show that caspase inhibition leads to increases in the levels of oxidized proteins obtained by treatments with hydrogen peroxide plus ferrous iron. Collectively, these results suggest the possibility that an age-related loss in capacity to carry out apoptosis might contribute to the observed accumulation of oxidized proteins during aging and in age-related diseases.