1
Department of Chemistry, University of Alaska-Anchorage, Anchorage, United States
2
Department of Medicine, Division of Hematology and Oncology, Penn State Hershey Cancer Institute, Penn
State College of Medicine, Hershey, United States
4
Department of Chemistry and Biochemistry, University of Alaska-Fairbanks, Fairbanks, United States
5
Drug Discovery, Development, and Delivery Core, Penn State College of Medicine, Hershey, United States
6
Department of Molecular, Cellular and Biomedical Sciences, University of New Hampshire, Durham, United States
Corresponding author details:
Brian M Barth, Ph.D
Department of Molecular
Cellular and Biomedical Sciences University of New Hampshire 46 College Road
Durham,United States
Copyright:
© 2018 Barth BM, et al. This is
an open-access article distributed under the
terms of the Creative Commons Attribution 4.0
international License, which permits unrestricted
use, distribution and reproduction in any
medium, provided the original author and source
are credited
Acute Myeloid Leukemia (AML) is an aggressive hematological malignancy
with limited treatment options. Inflammation is often a contributing factor to the
development and progression of AML, and related diseases and can potentiate therapy
failure. Previously, we had identified anti- inflammatory roles and anti-AML efficacy for
blueberry extracts. The present study extended these observations to determine that
the polyphenols Quercitin inhibited neutral Sphingomyelinase (N-SMase) activity and
exerted anti-AML efficacy. Moreover, Quercitin was shown to exert combinatorial antiAML efficacy with Nanoliposomal ceramide. Overall, this demonstrated that Quercitin
could block the pro-inflammatory actions of N-SMase and augment the efficacy of antiAML therapeutics, including ceramide-based therapeutics.
Acute myeloid leukemia; Blueberry; Quercitin; Neutral Sphingomyelinase;
Nanoliposomal ceramide
Inflammation has been linked to the development and progression of Myelodysplastic Syndrome (MDS) and AML [1-5], including the emergence of drug resistance [6]. Shin et al. demonstrated that AML1-ETO leukemogenesis could be mediated in part by loss of TLE4, which results in an up regulation of a Wnt-mediated pro-inflammatory phenotype [7]. In their study, inhibition of pro-inflammatory cyclooxygenase activity reversed the pro-leukemogenic phenotype triggered by TLE4 knockdown. This highlighted a key role for inflammation in the development of AML arising from the t (8:21) chromosomal translocation. Moreover, the Shanghai Health Study recently indicated that immunemediated inflammation was linked to the development of a plastic anemia, MDS and AML following exposure to benzene [8]. In another study, Ye H. et al. showed that adipose tissueresident chronic myeloid leukemia stem cells exhibited a pro-inflammatory phenotype and could evade chemotherapy [9]. Likewise, it was recently shown that a deregulated pro-inflammatory cytokine environment exists in patients with MDS and that this can be augmented upon treatment with hypomethylating therapies [10]. Altogether, these studies highlight the importance of inflammation in the pathogenesis of malignant myeloid hematological diseases and further indicate that inflammation may contribute to therapy failure.
Recently, we demonstrated that blueberry extracts could exert anti-AML therapeutic efficacy utilizing cell lines, primary patient samples, and multiple in vivo models [11]. Blueberries are rich sources for polyphenols, and both blueberries and polyphenols have been well- recognized for their health benefits [12,13]. Earlier, we had used models of neuroinflammation to show that blueberry extracts could inhibit neutral Sphingomyelinase (N-SMase) and NADPH Oxidase (NOX) activity [14,15]. N-SMase is an enzyme that liberates ceramide from sphingomyelin at the plasma membrane [14,16]. Its activity can be triggered by inflammatory mediators, growth factors, as well as chemotherapeutics. Ceramide is a bioactive Sphingolipid that is widely recognized to induce cellular stress and apoptosis and its generation has long been noted in response to chemotherapy [17-19]. Importantly, ceramide can play a role in growth factor signaling as an integral part of lipid micro domains, also known as rafts, which are necessary to bring together components of these signaling pathways [17,18]. The ability for N-SMase- generated ceramide to promote inflammation presents a therapeutic conundrum as there is a growing interest in the use of ceramide-based therapeutics for the treatment of cancer and leukemia [17]. However, ceramide may exert differential effects depending on its sub cellular localization and its metabolism to the profoundly pro-inflammatory bioactive Sphingolipid ceramide-1- phosphate [20].
In the present study, we identified the polyphenols Quercitin as
a component of blueberry extracts that inhibits N-SMase activity. We
then evaluated anti-AML efficacy for the combination of Quercitin
and Nanoliposomal ceramide (Lip-C6). Altogether, this reveals that
the anti-AML therapeutic efficacy of ceramide-based therapeutics
such as Lip-C6 can be augmented by co- treatment with an antiinflammatory/N-SMase compound.
Cell Culture
Murine C1498 and 32D-FLT3-ITD cells, and human U937 cells were maintained at 37°C, and 5% CO2 , in RPMI-1640 supplemented with 10% fetal bovine serum (FBS) and 1% penicillin/streptomycin. Human KG-1 cells were likewise maintained in IMDM supplemented with 20% FBS and 1% penicillin/streptomycin.
Nanoliposome formulation
Nano liposomes were prepared by the Penn State College of Medicine Drug Discovery Core following previously established methods. All lipids were obtained from Avanti Polar Lipids (Alabaster, AL, USA). Ghost nanoliposomes (Lip-Ghost) and Lip-C6 were prepared as previously described [19,21]. Briefly, lipids dissolved in chloroform, or other organic solvents, were combined in specific molar ratios, dried to a film under a stream of nitrogen and then hydrated by addition of 0.9% NaCl. Solutions were sealed, heated at 60°C (60 min), and subjected to vortex mixing and sonicated until light no longer diffracted through the suspension. The lipid vesiclecontaining solution was quickly extruded at 60°C by passing the solution 10 times through 100 nm polycarbonate filters in an Avanti Mini-Extruder. Nanoliposomal size and integrity was determined using a Malvern Zetasizer Nano ZS at 25°C. Nanoliposome formulations were stored at room temperature until use.
In Vitro assays
Cellular viability assays were performed as previously described using a Cell Titer 96 Aqueous Non-Radioactive Cell Proliferation Assay according to the manufacturer’s instructions (Promega, Madison, WI) [11,19,21]. N-SMase assays were performed as previously described using a Sphingomyelinase Inhibitor Screening kit from Cayman Chemical (Ann Arbor, MI) according to the manufacturer’s instructions [14]. An ELISA assay was performed using previously established methods adapted using a specific cysteine sulfenic acid monoclonal antibody from Millipore (Billerica, MA) [15].
Blueberry extraction and fractionation
Solvents and reagents were obtained from VWR (Radnor, PA) and Sigma (St. Louis, MO). Vaccinium uliginosum was harvested in the interior of Alaska for extraction as previously described [14,15]. Briefly, whole berries were lyophilized, crushed to powder, and a crude extract was prepared by extracting with aqueous acetone (70/30 acetone/water), and dried by rotary- evaporation and lyophilization. For fractionation, crude extracts were separated by silica gel chromatography. Fractions were collected by elution with 80/20 dichloromethane/methanol, assessed individually by Thin Layer Chromatography (TLC), and dried by rotary evaporation. Fraction 1 was further separated by silica gel flash column chromatography, eluted using 92/8 dichloromethane/ methanol followed by pure methanol, and TLC was used to assess fractions (Figure 1A-B). The N-SMase assay was used through the fractionation process to define inhibitory bioactive fractions using an inflammation-stimulated SH-SY5Y neuroblastoma cell model (unpublished). Fraction 1,28 underwent a final clean-up purification by silica gel flash column chromatography, where elution with 85/15 dichloromethane/methanol yielded a relatively pure compound that was characterized by LC-MS (ESI, Q-TOF, in positive ion mode) and 1 H-NMR and identified as quercetin-3-O-arabinoside (Figure 1C).
Data analysis
CalcuSyn Software (Biosoft, Cambridge, UK) was used to determine combinatorial effects of treatments [21]. Cellular viability data was used for this analysis, and a Combination Index (CI) less than or equal to 0.9 was considered synergistic. CI values greater than or equal to 1.1 were considered antagonistic, whereas CI values between 0.9 and 1.1 were considered additive.
This study sought to identify a specific blueberry component with anti-AML activity. Given a potential role for N-SMase in inflammatory responses [14,16], a bioassay-directed approach was used to fractionate crude blueberry extracts to identify quercetin-3-O-arabinoside as a specific N-SMase-inhibiting compound (Figure 1). Inhibition of N-SMase by the parental compound Quercitin was verified in AML cell lines (Figure 2A), and coincided with inhibition in cysteine oxidation (Figure 2B). Quercitin may reduce cysteine oxidation either through an anti- oxidant effect, or by limiting N-SMase-dependent oxidative effects such as those mediated by NOX [15,16,20]. Importantly, the combination of Quercitin with Lip-C6 did not alter its ability to inhibit N-SMase or block cysteine oxidation. The ability of Quercitin to inhibit N-SMase may prevent paradoxical pro-inflammatory/leukemogenic effects associated with ceramide generation. Therefore, therapies that stimulate or delivery ceramide to malignant cells may be more effective because that ceramide can more effectively exert its classical apoptotic program.
Next, the anti-AML activity of Quercitin was confirmed using AML
cell lines (Figure 2C-D). Another polyphenols, cyanidin, was not as
effective as an anti-AML agent as Quercitin was. This may further
suggest that Quercitin is a polyphenols partially responsible for the
anti-AML efficacy of blueberry extracts [11]. Notably, the combination
of Quercitin and Lip-C6 exerted a more profound anti-AML effect than
either treatment alone or than the combination of Lip-C6 and cyanidin
(Figure 2C-D). Finally, we conducted a combinatorial index analysis
that showed the combination of Quercitin and Lip-C6 was synergistic in KG-1 cells, but that the combination of cyanidin and Lip-C6 was
not (Table 1). Overall, these results demonstrated anti-AML efficacy
for the polyphenols Quercitin, which may act synergistically with the
ceramide-based therapeutic Lip- C6.Our prior studies highlighted the
anti-AML, N-SMase-inhibiting, and NOX-inhibiting utility of blueberry
extracts [11,14,15]. These studies noted that identification of the
specific bioactive components from blueberry extracts responsible
for these effects may be of significant interest to the development
of minimally toxic therapies. This was thought to be due in part to
the non-toxic consumption of these fruits. Moreover, compounds
with specific anti-inflammatory bioactivity may be especially useful
due to the specific role of inflammation in the pathogenesis of AML
and related malignant hematological disorders [1-10]. Hence, the
anti-inflammatory compounds from blueberry extracts may be
useful because they can block inflammatory pathways that would
otherwise negate the effects of cytotoxic therapies. In the case of
quercetin, the blockade of N- SMase serves to diminish a potentially
pro-inflammatory axis further mediated by ceramide kinase and NOX
[15,20]. Consequently, therapies that stimulate ceramide generation,
or deliver exogenous ceramide, may trigger the classical ceramide mediated apoptotic pathways. Therefore, quercetin can augment
and focus the anti-AML efficacy of Lip-C6 and other ceramide- based
therapeutics.
Figure 1: Crude blueberry extract was separated by repeated silica column fractionation and a N-SMase assay was used to determine fractions that inhibited enzyme activity
(a)Representative thin layer chromatography of the initial fractionation using dichloromethane/methanol as the solvent (92/8) with fraction #1 selected for further separation.
(b)Representative thin layer chromatography of the second fractionation using dichloromethane/methanol as the solvent (85/15) with fraction #28 selected for further separation.
(c)Following a clean-up fractionation, quercetin-3-Oarabinoside was identified by LC-MS (ESI, Q-TOF, in positive
ion mode) and 1
H- NMR (inset) as the primary component of
fraction 1,28.
Figure 2: Quercitin inhibits N-SMase activity and exerts combinatorial anti-AML efficacy with Lip- C6
(a) N-SMase inhibition by Quercitin was confirmed by measuring N-SMase activity in AML cell lines (KG-1, 32D-FLT3-ITD) following 4-hour exposure to respective controls, 10 µM liposomal C6-ceramide (Lip-C6), 10 µM Quercitin, or the combination of both. Activity (fluorescence) per total protein content was normalized to the untreated controls, and a heat map was generated (pink: high activity, blue low activity).
(b) Cellular cysteine sulfenic acid content (oxidation) was determined by ELISA. Following 4-hour exposure of KG-1 and 32D-FLT3- ITD cells to respective controls (white bar: untreated, gray bar: empty/ghost liposomes), 10 µM Lip- C6 (blue bar), 10 µM Quercitin (green bar), or the combination of both (purple bar) (1-way ANOVA, *p < 0.05 compared with both controls, n=4)).
(c) Cellular viability was determined by MTS assay following 48-hour exposure of KG-1 cells to Quercitin (green line), Lip-C6 (blue line), or the combination of both (dashed green line). Cyanidin (purple line), or a combination of cyaniding and Lip-C6 (dashed purple line) was used to compare a distinct polyphenols also found in the blueberry.
(d) In a similar manner, cellular viability was assessed using the 32D-FLT3-ITD cell line.
Table 1: Combinatorial index analysis
The authors would like to thank Drs. Thomas P. Clauson and
Thomas B. Kuhn of the University of Alaska-Fairbanks for their helpful
insight during the blueberry extraction and fractionation process. We
would like to thank Dr. Hubert Serve of the University of Munster for
generously providing the 32D-FLT3-ITD cells. This study was funded
in part by the National Institute for General Medical Sciences of the
National Institutes for Health under award number P20- GM103395
(K.L.D.), the National Cancer Institute of the National Institutes for
Health under award number K22-CA190674 (B.M.B.) and P01-
CA171983 (M.K. and D.F.C.), as well as the Penn State University
Kiesendahl Family Endowed Leukemia Research Fund (D.F.C.), the
Kenneth Noel Memorial Fund (D.F.C.), and PA Tobacco Settlement
funds (M.K. and D.F.C.). The Penn State Research Foundation has
licensed ceramide-based delivery systems and nanotechnologies to
Keystone Nano Inc. (State College, PA). M.K. serves as the C.M.O. of
Keystone Nano, Inc.
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