Cytotoxicity In K562 Cells Research Articles

Diorganotin(IV) N-methyl-N-phenethyldithiocarbamate Compounds Induce Cytotoxicity via Apoptosis in K562 Human Erythroleukaemia Cells

Imatinib mesylate (IM), a leading treatment for chronic myeloid leukaemia (CML), has sparked worries about the possibility of CML patients developing a resistance to it. As a result, researchers are becoming more interested in organotin(IV) compounds due to their strong potential to be developed as anticancer agents and employed as an option to address the issues regarding IM-resistance therapy. Generally, this study is to determine the cytotoxicity induced by diorganotin(IV) dithiocarbamate compounds in K562 human erythroleukaemia cells. The two novel diorganotin(IV) compounds namely diphenyltin(IV) N-methyl-N-phenethyldithiocarbamate (C1) and dibutyltin(IV) N-methyl-N-phenethyldithiocarbamate (C2) were assessed their cytotoxicity via MTT [3-(4-5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay and mode of cell death via Annexin V-FITC/PI assay with the duration treatment of 24 h. Both compounds displayed strong cytotoxicity in K562 cells. At concentration of 4.2 µM for C1 and 1.6 µM for C2, both compounds were able to induce 49.70% and 46.83% apoptotic events, respectively. The changes in cells' morphological can also be seen 24 h after being exposed to the compounds at their respective IC50 doses. The findings demonstrated that the morphology of the cells was similar to apoptotic features, including cell shrinkage and the production of apoptotic bodies, meanwhile, the low levels of necrotic cells (<1%) also can be seen via cell lysis. In conclusion, both compounds possess the potential as antileukaemia drugs nevertheless, further studies on their action mechanism are required to ratify their qualities and suitability in the research of anticancer drugs development.

Evi1 involved in benzene-induced haematotoxicity via modulation of PI3K/mTOR pathway and negative regulation Serpinb2

Benzene is a widely used chemical and an environmental pollutant. Exposure to benzene can cause blood diseases, but the mechanisms underlying benzene haematotoxicity have not been fully clarified. Ecotropic virus integration site-1 (Evi1), a transcription factor, plays important roles in normal haematopoiesis and haematological diseases. In this study, we investigated the role and mechanism of Evi1 in benzene-induced haematotoxicity. We found that benzene exposure significantly increased Evi1 level in white blood cells (WBCs) in occupational benzene workers as well as mouse bone marrow cells. Further in vitro results demonstrated that compared with control cells exposed to same 1,4-benzoquinone (1,4-BQ, an important active metabolite of benzene) concentration, Evi1 downregulation significantly reduced cell proliferation, and disrupted cell viability, apoptosis, erythroid and megakaryotic cell differentiation and cell cycle. Additionally, down-regulation of Evi1 suppressed phosphoinositide 3-kinase (PI3K)/mTOR signalling pathway and elevated its target gene Serpinb2 following 1,4-BQ exposure. Moreover, the PI3K activator could partially relieve the inhibitory effect of down-regulation of Evi1 on cell proliferation and increase cell arrest in in G2/M phase. What's more, downregulation of Serpinb2 could partially alleviate proliferation inhibition and reverse cell cycle changes in G0/G1 phase and S phase induced by Evi1 inhibition. In conclusion, our data revealed that Evi1 downregulation aggravated the inhibition of cell proliferation and arrested cells in the G0/G1 phase when exposed to 1,4-BQ, potentially by inactivating the PI3K/mTOR pathway and upregulating downstream target gene Serpinb2. Our study provides novel insights on mechanism by which Evi1 participates in benzene-induced haematotoxicity.

CREB/Sp1-mediated MCL1 expression and NFκB-mediated ABCB1 expression modulate the cytotoxicity of daunorubicin in chronic myeloid leukemia cells

Although some studies have hinted at the therapeutic potential of daunorubicin (DNR) in chronic myeloid leukemia (CML), the mechanism by which DNR induces CML cell death is unclear. Therefore, this study aimed to investigate DNR-induced cell death signaling pathways in CML cell lines K562 and KU812. DNR-triggered apoptosis in K562 cells was characterized by inhibition of MCL1 expression, while restoration of MCL1 expression protected K562 cells from DNR-mediated cytotoxicity. In addition, DNR induced NOX4-dependent ROS production, leading to the activation of p38 MAPK and inactivation of Akt and ERK. Activated p38 MAPK stimulated protein phosphatase 2A-dependent dephosphorylation of CREB. Since Akt-mediated activation of ERK reduced β-TrCP mRNA stability, the inactivation of Akt-ERK axis increased β-TrCP expression, which in turn promoted proteasomal degradation of Sp1. Inhibition of CREB phosphorylation and Sp1 expression simultaneously reduced MCL1 transcription and protein expression. DNR-induced MCL1 suppression was not reliant on its ability to induce DNA damage. In addition, DNR induced the expression of drug exporter ABCB1 in K562 cells through the p38 MAPK/NFκB-mediated pathway, while imatinib or ABT-199 inhibited the DNR-induced effect. The combination of imatinib or ABT-199 with DNR showed synergistic cytotoxicity in K562 cells by increasing intracellular DNR retention. Cumulatively, our data indicate that DNR induces MCL1 downregulation in K562 cells by promoting p38 MAPK-mediated dephosphorylation of CREB and inhibiting the Akt-ERK axis-mediated Sp1 protein stabilization. Furthermore, experimental evidence indicates that DNR-induced death of KU812 cells occurs through a similar pathway.

Cytotoxic Effects of Combined Walnut Shell-Extracted Copper Oxide: Nanoparticles and Hydroalcoholic Extracts of Aloe vera Against Human Leukemic Cell Line

Background: Anticancer effects of Aloe vera and copper oxide nanoparticles (CuO NPs) have been separately determined. Hence, we investigated whether combining the hydroalcoholic extract of Aloe vera and green CuO NPs produced by eco-friendly and walnut shells could provide synergistic cytotoxicity against K562 cell lines. Methods: The K562 cells and PBMCs (1 × 105 cells/100 μL/well) were treated with serial dilution of Aloe vera extract (0, 20, 40, 60, 80, 160 and 320 mg/ mL) and green CuO NPs (0, 50, 100, 200 and 400 μM). After incubation for 24h, the viability of cells was determined by MTT assay. Cells were exposed to a mixture of Aloe vera extract and Green CuO NPs at the half-maximal inhibitory concentration (IC50) to assess the inhibitory effects. Results: The extract of Aloe vera and green CuO NPs had cytotoxic effects against K562 (cell-line in a dose-dependent manner). Unlike Aloe vera, the marginal safety of green CuO NPs was low. There were no significant dissimilarities in the IC50 value of the green CuO NPs against K562 cells compared to the IC50 value of the Green CuO NPs against PBMCs (175 ± 9 μM vs. 186.89 ± 8.88 μM). Combined treatment with minimal cytotoxic doses provided synergistic benefits and caused more cytotoxicity in K562 cells toward their separated treatment. Meanwhile, this combined concentration enhanced the cell-survival, not the cytotoxicity in PBMC treated cells. Conclusions: The combinative concentration of Aloe vera and green CuO may be considered alternative medicine later.

Quantification of immune cell-mediated destruction of tumor cells in vitro using the RNA disruption assay.

e15017 Background: Immune checkpoint inhibitors (ICIs) are increasingly being used in the treatment of human cancers, often in combination with cytotoxic chemotherapy drugs. However, current ICIs are costly and are only effective against a fraction of patient tumours. Thus, a tool that could reliably quantify tumour response to ICIs and predict outcome post-treatment would be highly valuable. Patients with non-responding tumours could be spared the costs and toxic side-effects of the ineffective drugs and moved promptly to alternate treatments. We have observed that a variety of structurally and mechanistically distinct chemotherapy agents induce the degradation of ribosomal RNA (rRNA) into a large number of high molecular weight fragments (between the 28S and 18S rRNAs)---a phenomenon we have termed “RNA disruption”. High tumour RNA disruption during treatment, as quantified using the RNA disruption assay (RDA), has been shown to predict pathologic complete response and improved disease-free survival in breast cancer patients. Methods: To assess whether RDA could be used to monitor immune cell killing of tumour cells, we collected peripheral blood mononuclear cells (PBMCs) from consenting healthy human donors and enriched the cell population for natural killer (NK) cells to 90% using a negative selection approach. The cells, with or without IL-2 pre-treatment, were incubated with K562 cells, after which K562 cell killing was quantified over time using a standard immunocytotoxicity assay and K562 cell RNA disruption was measured using RDA. Results: Freshly isolated human NK cells when incubated with K562 chronic myeloid leukemia cells induced cell destruction and RNA disruption in K562 cells in a dose-dependent manner. Pre-incubation with IL-2 augmented both NK cell-mediated RNA disruption and NK-mediated cytotoxicity in K562 cells. Interestingly, the pattern of K562 RNA disruption fragments generated by NK cells was similar to that generated by chemotherapy drugs. Conclusions: RDA was successfully used to quantify immune cell-mediated destruction of tumour cells, raising the prospect of its possible use to monitor tumour destruction by immune cells in vivo and to predict response to ICIs (alone or in concert with cytotoxic chemotherapy drugs).

Abstract C078: Substituted oxindoles as AMP-activated protein kinase (AMPK) inhibitors and their evaluation in models of leukemia

Abstract AMP-Activated protein kinase (AMPK) acts as a central metabolic sensor at the interface of metabolic and signaling networks. Activated AMPK promotes multiple catabolic processes to generate ATP, such as glucose uptake, glycolysis, fatty acid uptake and oxidation, and mitochondrial biogenesis. In addition, AMPK activation suppresses the cell cycle, and anabolic processes such as the mammalian Target of Rapamycin Complex 1 (mTORC1)-dependent protein synthesis and fatty acid biosynthesis via inactivating phosphorylation of cytosolic acetyl-CoA carboxylase 1 (ACC1) and mitochondrial ACC2. The activation of AMPK under conditions of energetic stress is modulated by an allosteric mechanism where the depletion of ATP promotes AMP binding at the γ subunit of AMPK with a subsequent conformational change in the catalytic α subunit. In the context of cancer AMPK has been reported to promote tumor survival and progression under hypoxia and the maintenance of cancer stem cells (CSCs). A major challenge to interrogating the therapeutic potential of targeting AMPK in cancer is the lack of potent and selective small molecule inhibitors. Compound C has been widely used as an AMPK inhibitor, but it lacks potency and has a poor selectivity profile. The multi-kinase inhibitor, sunitinib, has demonstrated potent nanomolar inhibition of AMPK activity, but has broad-spectrum activity across the kinome. Although sunitinib targets multiple kinases, its nanomolar potency for AMPK inhibition and large scope for chemical substitution on the core oxindole ring make it an attractive lead for AMPK inhibitor development. We have used a computational model of sunitinib docked into the ATP-binding site of the α subunit of AMPK to design and synthesize several series of oxindoles to examine structural modifications to improve AMPK inhibition and selectivity. These candidate inhibitors were evaluated against the activity of the α1 and α2 isoforms of AMPK using the TR-FRET assay and cell engagement was determined by ELISA, measuring p-ACC(Ser79), in the chronic myeloid leukemia K562 cell line. Our assays identified two novel, potent oxindole-based AMPK inhibitors that hadsignificantly reduced binding affinity when compared with sunitinib against members of the receptor tyrosine kinase (RTK) family, including VEGFR1, VEGFR2 and CSF1R, as well as BTK, a member of the B cell receptor (BCR) signaling pathway. Interestingly, cellular AMPK inhibition did not impact cell viability or result in cytotoxicity in K562 cells and may only sensitize these cells to chemotherapy. AMPK inhibition may be a more effective strategy to eliminate cancer cells in hypoxic microenvironments or against certain cell types, such as CSCs, that may be more reliant on AMPK for survival. Our current studies are designed to examine our AMPK inhibitors as single agents and in combination therapy in cancer cells grown under hypoxia and in CSC populations in order to eliminate these drug-resistant cancer cell populations with an aim to prevent cancer recurrence. In summary, we have developed two novel, potent AMPK inhibitors that were designed to interact with the DFG motif in the ATP-binding site of the α subunit of AMPK that are undergoing evaluation in advanced models of leukemia. Citation Format: Christopher J Matheson, Kimberly A Casalvieri, Donald S Backos, Craig T Jordan, Philip Reigan. Substituted oxindoles as AMP-activated protein kinase (AMPK) inhibitors and their evaluation in models of leukemia [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C078. doi:10.1158/1535-7163.TARG-19-C078

Design and synthesis of PEGylated amphiphilic block oligomers as membrane anchors for stable binding to lipid bilayer membranes

Cell surface engineering is a potentially powerful method for manipulating living cells by decorating the cell membrane with specific molecules. Possible applications include cell therapy, drug delivery systems, bio-imaging, and tissue engineering. The stable binding of synthetic molecules to serve as artificial membrane protein anchors is a promising approach for appending functional molecules to the cell surface. However, such synthetic molecules have previously shown limitations, including cytotoxicity and low cell surface affinity. We synthesized amphiphilic block oligomers, using ruthenium-catalyzed living radical polymerization, as novel membrane anchors for stable binding to lipid bilayer membranes. AB and ABA-type amphiphilic block oligomers were synthesized with poly(ethylene glycol) methacrylate (PEGMA) and varying butyl methacrylate (BMA) contents (PEGMA/BMA ratios of 25/5–25/50). These PEGylated oligomers showed high binding efficiencies (up to 92%) for liposomes, which served as model cell membranes, and low cytotoxicity in K562 cells. Both the BMA content and the block segment sequence in the copolymers strongly affected their binding efficiencies. Oligomers with an ABA-type block structure were much more effective than AB-type block oligomers, random oligomers, or PEGMA homo-oligomers for stable membrane binding. Thus, precise control of the primary structures of the amphiphilic oligomers enabled tuning of their binding efficiencies. These amphiphilic block oligomers hold promise as novel membrane anchors in many biomedical applications. A series of amphiphilic block oligomers were designed and synthesized using ruthenium-catalyzed living radical polymerization with poly(ethylene glycol) and butyl methacrylates (BMA). These PEGylated oligomers showed high binding efficiencies for liposomal preparations as model cell membranes, and also had low cytotoxicity. BMA contents and monomer sequences in the copolymers strongly affected their binding efficiencies. Current method enabled precise control of the primary structures of amphiphilic oligomers, allowing tuning of their binding efficiencies. These amphiphilic block oligomers have promise as novel membrane anchors for many biomedical applications.

The novel piperazine-containing compound LQFM018: Necroptosis cell death mechanisms, dopamine D4 receptor binding and toxicological assessment

Piperazine is a promising scaffold for drug development due to its broad spectrum of biological activities. Based on this, the new piperazine-containing compound LQFM018 (2) [ethyl 4-((1-(4-chlorophenyl)-1H-pyrazol-4-yl)methyl)piperazine-1-carboxylate] was synthetized and some biological activities investigated. In this work, we described its ability to bind aminergic receptors, antiproliferative effects as well as the LQFM018 (2)-triggered cell death mechanisms, in K562 leukemic cells, by flow cytometric analyses. Furthermore, acute oral systemic toxicity and potential myelotoxicity assessments of LQFM018 (2) were carried out. LQFM018 (2) was originally obtained by molecular simplification from LASSBio579 (1), an analogue compound of clozapine, with 33% of global yield. Binding profile assay to aminergic receptors showed that LQFM018 (2) has affinity for the dopamine D4 receptor (Ki = 0.26 μM). Moreover, it showed cytotoxicity in K562 cells, in a concentration and time-dependent manner; IC50 values obtained were 399, 242 and 119 μM for trypan blue assay and 427, 259 and 50 μM for MTT method at 24, 48 or 72 h, respectively. This compound (427 μM) also promoted increase in LDH release and cell cycle arrest in G2/M phase. Furthermore, it triggered necrotic morphologies in K562 cells associated with intense cell membrane rupture as confirmed by Annexin V/propidium iodide double-staining. LQFM018 (2) also triggered mitochondrial disturb through loss of ΔΨm associated with increase of ROS production. No significant accumulation of cytosolic cytochrome c was verified in treated cells. Furthermore, it was verified an increase of expression of TNF-R1 and mRNA levels of CYLD with no involviment in caspase-3 and -8 activation and NF-κB in K562 cells. LQFM018 (2) showed in vitro myelotoxicity potential, but it was orally well tolerated and classified as UN GHS category 5 (LD50 > 2000–5000 mg/Kg). Thus, LQFM018 (2) seems to have a non-selective action considering hematopoietic cells. In conclusion, it is suggested LQFM018 (2) promotes cell death in K562 cells via necroptotic signaling, probably with involvement of dopamine D4 receptor. These findings open new perspectives in cancer therapy by use of necroptosis inducing agents as a strategy of reverse cancer cell chemoresistance.

In Vitro and In Vivo Antitumor Activities of Tenacissoside C from Marsdenia tenacissima

Tenacissoside C, a natural bioactive compound of C21 steroidal saponins, was isolated and purified from air-dried stems of Marsdenia tenacissima. In the present study, the MTT assay showed that tenacissoside C exhibited obvious cytotoxicity in K562 cells with IC50 values of 31.4, 22.2, and 15.1 µM for 24, 48, and 72 h, respectively. Flow cytometry analysis indicated that the antiproliferative activity induced by tenacissoside C might be executed via G0/G1 cell cycle arrest and proapoptosis in K562 cells. Western blotting analysis elucidated that: A) Tenacissoside C induced K562 cell cycle (G0/G1) arrest via downregulating cycline D1 protein expression; and B) Tenacissoside C induced K562 cell apoptosis via the mitochondrial pathway by downregulating Bcl-2 and Bcl-xL protein expression, upregulating Bax and Bak protein expression, and activating caspase-9 and caspase-3. In vivo, significant tumor growth inhibition activity of tenacissoside C was observed in K562 cell-bearing nude mice, accompanied by a significant antiangiogenic effect in vivo against K562 cells (a marked decrease in MVD) and associated with enhanced apoptotic cell death (TUNEL staining assay in vivo), both in dose-dependent manners. The treatment with tenacissoside C did not significantly affect body mass and macroscopic examination of the organs in this mouse tumor model.

Anti-Leukemic Activity Is Increased with Low Dose Busulfan and Irradiation: A Preclinical Model

Abstract 4696Combinations of busulfan (Bu) and low dose total body irradiation are commonly used in conditioning regimens for allogeneic stem cell transplant in acute myeloid leukemia (AML). In this study we tested the in vitro effect of physiologic doses of Bu and ionizing radiation (IR) to address the question whether additive or synergistic antileukemic activity can be demonstrated in two leukemic cell lines, one sensitive (HL60) and one resistant (K562) to radiation.Cells were treated for 24 hours with Bu at 0, 12.5, 25, 50, 100 or 200 μ g/ml, or IR at 1.5, 3 or 6 Gy, or a combination of both with 12.5 or 25 μ g/ml for 24 hours, followed by IR at 1.5 or 3Gy. Cells were then tested for proliferation by thymidine uptake, apoptosis by surface expression of annexin V and caspase 3, and in-vitro colony formation assays. Exposure to Bu or IR for 24, 48 and 72 hours induced a dose dependent inhibition of proliferation and colony formation in both cell lines. However, 3 or 6 Gy of IR were both very effective against HL60 cells whereas a significant increase in cytotoxicity in K562 cells was observed only by using 6Gy (p=0.008).In-vitro treatment with either Bu or IR caused apoptotic cell death mainly in HL60 cells, but in a very limited amount in K562 cells. To test the effect of the combination of Bu and IR we utilized a low dose of Bu for 24 hours with low doses of radiation. HL60 cells were strongly inhibited by both agents when separate or combined. In contrast, treatment of the relatively radio-resistant K562 cells with low dose IR (3Gy) alone inhibited colony formation by 28%. The inhibitory effect increased to 84% when combined with low dose Bu.In order to identify genes associated with a response to Bu, we formed a linear regression model controlled for cancer type and also leukemic cell lines using GI50 and Stanford cDNA array data from the NCI-60. Among 7 genes (p<0.001 and FDR ∼50%) that were identified for all cancers, CLK-2 was also shown to correlate with response to Bu in leukemic cell lines (p=0.047). We then tested how these significant genes performed in the Affymetric U133 plus 2.0 platform. Six other genes (ERC2, HCLS1, CD74, KCNH2, HLADQB2, CD53) were significantly associated with response to Bu (p<0.05).In conclusion, we demonstrated an additive effect of Bu and low dose IR even on radioresistant leukemic cells. These findings prompted the design of a clinical trial with IV Bu and marrow irradiation in the conditioning regimen prior to allogeneic stem cell transplant for acute leukemia. Expression of genes correlating with response to Bu may represent a novel biomarker to predict the outcome of leukemic patients undergoing stem cell transplant and could lead to a personalized anti-leukemic therapy with Bu. Disclosures:No relevant conflicts of interest to declare.

Coformulation of Doxorubicin and Curcumin in Poly(d,l-lactide-co-glycolide) Nanoparticles Suppresses the Development of Multidrug Resistance in K562 Cells

Doxorubicin (DOX) is a broad-spectrum anthracycline antibiotic used to treat a variety of cancers including leukemia. Chronic myeloid leukemia (CML) blasts like K562 cells are resistant to apoptosis induced by DOX due to several reasons, the primary being the sequestration of drug into cytoplasmic vesicles and induction of multidrug resistance (MDR) gene expression with DOX treatment resulting in intracellular resistance to this drug. Moreover, expression of antiapoptotic protein BCL-2 and the hybrid gene bcr/abl in K562 cells contributes resistance to DOX. Studies have shown that curcumin (CUR) has a pleiotropic therapeutic effect in cancer treatment, as it is an inhibitor of nuclear factor kappa B (NFκB) as well as a potent downregulator of MDR transporters. In this study, we investigated the potential benefit of using DOX and CUR in a single nanoparticle (NP) formulation to inhibit the development of drug resistance for the enhancement of antiproliferative activity of DOX in K562 cells. Results illustrate that the dual (DOX+CUR) drug loaded NPs were effectively delivered into K562 cells. CUR not only facilitates the retention of DOX in nucleus for a longer period of time but also inhibits the gradual expression of MDR1 and BCL-2 at the mRNA level in K562 cells. Moreover, Western blot results confirm that in combination both of the drugs were capable of inducing apoptosis even if in a lower concentration compared to either single drug in both solution or in formulation. Combinational therapy by using DOX and CUR, especially when administered in the NP formulation, has enhanced the cytotoxicity in K562 cells by promoting the apoptotic response. Overall, this combinational strategy has significant promise in the clinical management of intractable diseases, especially leukemia.

Cadmium is a catalytic inhibitor of DNA topoisomerase II

Cadmium (Cd 2+) is a highly toxic and carcinogenic metal that is an environmental and occupational hazard. DNA topoisomerase II is an essential nuclear enzyme and its inhibition can result in the formation of genotoxic and recombinogenic DNA double strand breaks. In this study we showed that cadmium chloride strongly inhibited the DNA decatenation activity of human topoisomerase IIα in the low micromolar concentration range and that its inhibitory effects were reduced by glutathione. Because the activity of topoisomerase II is strongly inhibited by thiol-reactive compounds this result suggested that cadmium may be binding to critical topoisomerase II cysteine thiols. Cadmium, however, did not stabilize DNA-topoisomerase II covalent complexes, as measured by the lack of formation of DNA double strand breaks. Hence, it is not likely to be a topoisomerase II poison. Consistent with the idea that cadmium cytotoxicity may be modulated by glutathione levels, buthionine sulfoximine pretreatment to decrease glutathione levels resulted in a greatly increased cadmium-induced cytotoxicity in K562 cells. The results of this study suggest that cadmium may exert some of its cell growth inhibitory, and possibly its toxicity and carcinogenicity, by inhibiting topoisomerase IIα through reaction with critical cysteine thiols.

Reduction of doxorubicin resistance in P-glycoprotein overexpressing cells by hybrid cell-penetrating and drug-binding peptide

Drug efflux by the membrane transporter P-glycoprotein (P-gp) plays a key role in multidrug resistance (MDR). In order to bypass P-gp, thus overcoming MDR, a hybrid peptide comprising a cell penetrating peptide (Tat) and a drug binding motif (DBM) has been developed to noncovalently bind and deliver doxorubicin (Dox) into MDR cells. The uptake of Dox into the leukemia cell line K562 and its P-gp overexpressing subline KD30 increased in the presence of DBM-Tat peptide. Confocal microscopy indicated that DBM-Tat associated Dox was directed to a perinuclear area of KD30 cells, while this was not observed in parent K562 cells. When KD30 cells were pretreated with the endosomotropic agent chloroquine (CLQ), peptide associated Dox redistributed into the cytosol, indicating that endocytosis was the predominant uptake route. Altered drug uptake kinetics observed by cellular accumulation assay also supported an endocytic uptake. In the presence of CLQ, DBM-Tat was able to enhance the cytotoxicity of Dox by 68.4% at 5 µM peptide concentration in KD30 cells but there were only minor effects on Dox cytotoxicity in K562 cells even in the presence of CLQ. Thus, combining Dox with DBM-Tat reduces P-gp mediated drug efflux, without a requirement for drug modification or inhibiting P-gp function.

Antioxidant activity of mangostin in cell-free system and its effect on K562 leukemia cell line in photodynamic therapy

Mangostin (MAG), a kind of xanthone widely used in diet and medicine, has antioxidant, anti-inflammatory, antimicrobial, and anticancer activities. On account of its antioxidant activity, MAG might protect cancer cells from free radical damage in photodynamic therapy (PDT) during which reactive oxygen species production was stimulated leading to irreversible tumor cell injury. In this study, the antioxidant activity of MAG was investigated and the influence of MAG on K562 cells in 5-aminolevulinic acid (ALA)-based PDT is demonstrated. The results showed that MAG could scavenge hydroxyl radical, superoxide anion, and hydrogen peroxide and inhibit the formation of malondialdehyde (MDA), but increase the amounts of singlet oxygen in cell-free systems. MAG inhibits cell proliferation and enhances cell apoptosis, lipid peroxidation, and DNA damage in ALA-PDT on K562 cells. NaN3, a singlet oxygen quencher, suppresses the MAG-induced cell apoptosis, lipid peroxidation, and DNA damage. In conclusion, MAG enhances the PDT-induced cytotoxicity in K562 cells and singlet oxygen was involved in this process. These results implied that the effect of antioxidants on PDT might be determined by its sensitization ability to singlet oxygen.

Cytoprotective Effects of 5 Benzophenones and a Xanthone from Hypericum annulatum in Models of Epirubicin-Induced Cytotoxicity: SARAnalysis and Mechanistic Investigations

A new benzophenone O-glucoside neoannulatophenonoside (1) together with the known pinocembrin-7-O-glucoside were isolated from the aerial parts of Hyperium annulatum Moris (Guttiferae). The former was identified as 3',5',6-trihydroxy-4-methoxybenzophenone-2-O-beta-D-glucopyranoside by means of chemical and physical evidence. The cytoprotective effects of the new compound together with the previously isolated from this species hypericophenonoside (2), annulatophenone (3), annulatophenonoside (4), acetylannulatophenonoside (5) and 1,3,7-trihydroxyxanthone (6) were evaluated in a model of epirubicin-induced cellular toxicity in K-562 cells. While the benzophenone O-glycosides 1, 2, 4 and 5 exerted substantial cytoprotective effects against the epirubicin cytotoxicity in K-562 cells the aglycones 3 and 6 lacked any significant cytoprotective activity. Biochemical investigations aimed at evaluating the free-radical scavenging activity of the tested compounds as well as their effects on the cellular glutathione stores were carried out as well, aiming at unravelling the mechanisms of cytoprotection. Finally, the ability of 1, 4 and 5 to ameliorate epirubicin-induced anticlonogenic effects on bone marrow cells colony forming units, in vitro were also evaluated. Taken together, the experimental data indicate that the benzophenone glycosides isolated from H. annulatum have a substantial cytoprotective potential against the toxic effects induced by epirubicin and necessitates further detailed pharmacological evaluation of these compounds as possible chemoprotective/radioprotective agents.

DNA targeted UVA photosensitization: Characterization of an extremely photopotent iodinated minor groove binding DNA ligand

Previous studies have described UVA-induced DNA strand breakage at the binding sites of iodinated DNA minor groove binding bisbenzimidazoles. The DNA breakage, presumably mediated by the carbon-centred ligand radical produced by photodehalogenation, was also shown to be cytotoxic. The earlier studies included a comparison of three ligand isomers, designated ortho-, meta- and para-iodoHoechst, and the efficiency of photo-induction of strand breaks in plasmid DNA proved to be much higher for the ortho-isomer. We have now extended the comparison of the three isomers with respect to photo-induced cytotoxicity in K562 cells. Although the relationship between the extent of nuclear uptake and the concentration of the ligand in the medium was similar for the three isomers, assay of in situ dehalogenation in drug-treated cells indicated that the apparent cross-section for dehalogenation of the ortho-isomer was greater than 5-fold higher than that for the meta- and para-isomers. Also, analysis of clonogenic survival data showed that the dehalogenation event associated with ortho-iodoHoechst was a more efficient mediator of UVA-induced cytotoxicity in K562 cells than that for meta- or para-iodoHoechst. The number of dehalogenation events associated with 50% cell-kill for ortho-iodoHoechst (1.23 ± 0.04 × 10 4) was less than that for the para- (3.92 ± 0.29 × 10 4) and meta- (11.6 ± 0.90 × 10 4) isomers. Thus it is concluded that the photopotency of ortho-iodoHoechst, which is an important feature in the context of its potential use in clinical phototherapy, is due not only to more efficient UVA-mediated dehalogenation of the ligand, but also to greater cytotoxic potency per dehalogenation event.

A differential assay of NK-cell-mediated cytotoxicity in K562 cells revealing three sequential membrane impairment steps using three-color flow-cytometry

Annexin V and propidium iodide (PI) staining is a general technique for detecting apoptosis by flow-cytometry (FCM). The release of 2′,7′-bis-(2-carboxyethyl)-5- (and-6)-carboxyfluorescein (BCECF), a non-lipophilic membrane-impermeable labeling dye, from the cytoplasm of target cells is an indicator of increased membrane permeability. This study aimed to devise a three-color FCM technique involving the BCECF-release parameter in addition to conventional Annexin V and PI staining for the analysis of target K562 cells undergoing cytotoxic/apoptotic processes mediated by natural killer (NK) cells. The results demonstrated the following step-wise process of membrane impairment: (1) initiation of Annexin V staining accompanied by increasing forward scatter (FSC) before BCECF-release, indicating membrane impairment without permeabilization by necrosis; (2) BCECF-release with decreasing FSC before PI influx; and (3) PI staining with the lowest FSC state. Therefore, the early stage of cytotoxicity/apoptosis conventionally defined by the flow-cytometric criteria of Annexin V staining before PI staining could be sub-divided into two stages before and after BCECF-release. Annexin-V staining in tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis was also initiated without BCECF-release. Although the underlying mechanism of the transition process from stage 1 to stage 2 is still unknown, this FCM technique should be a useful tool for differential assays of target cells regarding the sequential processes of NK-induced cytotoxicity.

Evaluation of the Taguchi methods for the simultaneous assessment of the effects of multiple variables in the tumour microenvironment

BackgroundThe control of proliferation, differentiation and survival of normal and malignant cells in the tumour microenvironment is under the control of a wide range of different factors, including cell:cell interactions, cytokines, growth factors and hormonal influences. However, the ways in which these factors interact are poorly understood. In order to compare the effects of multiple variables, experimental design becomes complex and difficult to manage. We have therefore evaluated the use of a novel approach to multifactorial experimental design, the Taguchi methods, to approach this problem.MethodThe Taguchi methods are widely used by quality engineering scientists to compare the effects of multiple variables, together with their interactions, with a simple and manageable experimental design. In order to evaluate these methods, we have used a simple and robust system to compare a traditional experimental design with the Taguchi Methods. The effect of G-CSF, GM-CSF, IL3 and M-CSF on daunorubicin mediated cytotoxicity in K562 cells was measured using the MTT assay.ResultsBoth methods demonstrated that the same combination of growth factors at the same concentrations minimised daunorubicin cytotoxicity in this assay.ConclusionsThese findings demonstrate that Taguchi methods may be a valuable tool for the investigation of the interactions of multiple variables in the tumour microenvironment.

Effects of the Bcr/abl kinase inhibitors STI571 and adaphostin (NSC 680410) on chronic myelogenous leukemia cells in vitro

AbstractThe adenosine triphosphate binding-site–directed agent STI571 and the tyrphostin adaphostin are undergoing evaluation as bcr/abl kinase inhibitors. The current study compared the effects of these agents on the survival of K562 cells, bcr/abl-transduced FDC-P1 cells, and myeloid progenitors from patients with chronic myelogenous leukemia (CML) compared with healthy donors. Treatment of K562 cells with 10 µM adaphostin resulted in decreased p210bcr/ablpolypeptide levels in the first 6 hours, followed by caspase activation and accumulation of apoptotic cells in less than 12 hours. By 24 hours, 90% of the cells were apoptotic and unable to form colonies. In contrast, 20 µM STI571 caused rapid inhibition of bcr/abl autophosphorylation without p210bcr/abl degradation. Although this was followed by the inhibition of Stat5 phosphorylation and the down-regulation of Bcl-xL and Mcl-1, only 7% ± 3% and 25% ± 9% of cells were apoptotic at 16 and 24 hours, respectively. Instead, the cytotoxic effects of STI571 became more pronounced with prolonged exposure, with IC90values greater than 20 µM and 1.0 ± 0.6 µM after 24 and 48 hours, respectively. Consistent with these results, 24-hour adaphostin exposure inhibited CML granulocyte colony-forming units (CFU-G) (median IC50, 12 µM) but not normal CFU-G (median IC50, greater than 20 µM), whereas 24-hour STI571 treatment had no effect on CML or normal CFU-G. Additional experiments revealed that STI571-resistant K562 cells remained sensitive to adaphostin. Moreover, the combination of STI571 + adaphostin induced more cytotoxicity in K562 cells and in CML CFU-G than either agent alone did. Collectively, these results identify adaphostin as a mechanistically distinct CML-selective agent that retains activity in STI571-resistant cell lines.

Peptide-based analysis of amino acid sequences important to the biological activity of eosinophil granule major basic protein

Synthetic peptides corresponding to amino acid sequences in eosinophil granule major basic protein (MBP) were evaluated for cytotoxic activity toward K562 cells and for ability to stimulate basophil mediator release. Results obtained using 14 peptides spanning the 117-amino acid sequence of MBP in overlapping fashion indicated that the activities mapped to peptide sequences near the amino and carboxy termini of MBP. The activity of these regions was confirmed using two peptides corresponding to MBP residues 18–45 and 89–117. A 20-h incubation with 5 μM peptide 18–45 or peptide 89–117 caused approximately the same levels (>60%) of cytotoxicity in K562 cells as 5 μM MBP. Similarly, a 30-min incubation with peptides 18–44 and 89–117 stimulated basophil histamine release in a concentration-dependent manner over the range of 5–20 μM. The level of release stimulated by 20 μM peptide 89–117 approached that stimulated by 2 μM MBP. A 20 μM concentration of peptide 89–117 also stimulated leukotriene C4 (LTC4) production by the basophils. Neither peptide 18–45 nor peptide 89–117 was cytotoxic for basophils under the experimental conditions for histamine and LTC4 release, as determined by 51Cr release. These results indicate that two MBP peptide sequences, including one (89–117) that contains a unique carbohydrate-binding region, share the biologic activities of MBP.