2,2’-Bipyridine-Modified Tamoxifen: A Versatile Vector for Molybdacarboranes

Article abstract of DOI:10.1002/cmdc.201900554

Investigations on the antitumor activity of metallacarboranes are sparse in the literature and limited to a handful of ruthena- and molybdacarboranes. In this study, the molybdacarborane fragment [3-(CO)₂-closo-3,1,2-MoC₂B₉H₁₁] was combined with a vector molecule, inspired by the well-known drug tamoxifen or 4,4’-dihydroxytamoxifen (TAM-diOH). The molybdacarborane derivative [3,3-{4-[1,1-bis(4-hydroxyphenyl)but-1-en-2-yl]-2,2‘-bipyridine-κ²N,N’}-3-(CO)₂-closo-3,1,2-MoC₂B₉H₁₁] (10), as well as the ligand itself 4-[1,1-bis(4-hydroxyphenyl)but-1-en-2-yl]-2,2‘-bipyridine (6) showed cytotoxic activities in the low micromolar range against breast adenocarcinoma (MDA-MB-231, MDA-MB-361 and MCF-7), human glioblastoma (LN-229) and human glioma (U-251) cell lines. In addition, compounds 6 and 10 were found to induce senescence and cytodestructive autophagy, lower ROS/RNS levels, but only the molybdacarborane 10 induced a strong increase of nitric oxide (NO) concentration in the MCF-7 cells.

Full text of DOI:10.1002/cmdc.201900554

Accepted Article
Title: 2,2’-Bipyridine-modified Tamoxifen: A Versatile Vector for
Molybdacarboranes
Authors: Benedikt Schwarze, Sanja Jelača, Linda Welcke, Danijela
Maksimović-Ivanić, Sanja Mijatovic, and Evamarie Hey-
Hawkins
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ChemMedChem
FULL PAPER
2,2’-Bipyridine-modified Tamoxifen: A Versatile Vector for
Molybdacarboranes
Benedikt Schwarze,[a] Sanja Jelača,[b] Linda Welcke,[a] Danijela Maksimović-Ivanić,[b] Sanja Mijatović[b]
and Evamarie Hey-Hawkins*[a]
structures can be employed as bulky phenyl or cyclopentadienyl
Abstract: Investigations on the antitumour activity of
analogues.[4] Thus, a deboronation (i.e. formal loss of a B+ unit) of
the closo-C2B10H12 cluster and deprotonation, the so-called
dicarbollide, [C2B9H11]2−, is obtained and can be employed in the
metallacarboranes are sparse in the literature and limited to a handful
of ruthena- and molybdacarboranes. In this study, the
molybdacarborane fragment [3-(CO)2-closo-3,1,2-MoC2B9H11] was
preparation of a large variety of transition metal complexes
combined with a vector molecule, inspired by the well-known drug
resulting in full-, mixed- or half-sandwich structures.[5] Potential
tamoxifen
or
4,4’-dihydroxytamoxifen
(TAM-diOH).
The
applications of the full-sandwich cobalt bis(dicarbollide) ([3,3′-
Co(1,2-C2B9H11)2]−, COSAN) derivatives in medicine are well
molybdacarborane derivative [3,3-{4-[1,1-bis(4-hydroxyphenyl)but-1-
en-2-yl]-2,2‘-bipyridine-κ2N,N’}-3-(CO)2-closo-3,1,2-MoC2B9H11] (10),
as well as the ligand itself 4-[1,1-bis(4-hydroxyphenyl)but-1-en-2-yl]-
2,2‘-bipyridine (6) showed cytotoxic activities in the low micromolar
range against breast adenocarcinoma (MDA-MB-231, MDA-MB-361
and MCF-7), human glioblastoma (LN-229) and human glioma (U-
251) cell lines. In addition, compounds 6 and 10 were found to induce
senescence and cytodestructive autophagy, lower ROS/RNS levels,
but only the molybdacarborane 10 induced a strong increase of nitric
oxide (NO) concentration in the MCF-7 cells.
investigated,[6,7] but not as
cytotoxic/cytostatic icosahedral
a
pharmacophore.
Also
mixed-sandwich
metallacarboranes [3-(η6-arene)-3,1,2-RuC2B9H9] have been
reported.[8,9] Other half- and mixed-sandwich complexes with
potential application in medicine have been summarised in the
literature.[4] One advantage of half-sandwich metallacarboranes is
the incorporation of biologically relevant ligands in the
coordination sphere of the metals, as in the present study, where
[3-(2,2’-bipyridine-κ2N,N’)-3-(CO)2-closo-3,1,2-MoC2B9H11]
(i)
was equipped with a vector molecule which was inspired by the
well-known tamoxifen. Further examples were reported by
Causey et al.,[10] Hawkins et al.,[11] Pruitt et al.[12] and Louie et al.[13]
who used stable and hydrophobic rhenacarboranes including the
[Re(L)(CO)2] fragment (L = 2,2’-bipyridine derivative or [NO]+) as
imaging agents.
Nuclear receptor ligands using highly hydrophobic
icosahedral carborane clusters in structures like estradiol,[14]
testosterone[15] or selective estrogen receptor modulators
(SERMs)[16] were already reported. Also, a carborane-containing
tamoxifen derivative, namely boroxifen, was synthesised, which
showed, however, limited benefits.[17] Employing tamoxifen as
Introduction
Medicinal chemistry is still dominated by purely organic
molecules, but bioinorganic chemistry is becoming more and
more important and several successful examples of metal-based
drugs have already been reported (see special issue on Metals in
Medicine in ACS Chemical Reviews).[1] However, the available
biological data for molybdenum(II) complexes of the type
[Mo(R)(L)X] (where R = (η3-C3H5)−, (η5-C5H5)−, (η5-C9H7)−; L =
1,10-phenanthroline, 2,2’-bipyridine, (CO)2, (MeCN)2; X = Cl−,
−
BF4 ) are very limited, and only a few studies were reported until
now.[2] On the other hand, commercially available boron-based
drugs are still rare, and mainly employed in boron neutron capture
therapy (BNCT).[3] Unlike hydrocarbons, boranes and carboranes
readily form clusters in a large variety of 3D geometric shapes.
The icosahedral closo-dicarbadodecaboranes or carboranes are
highly interesting, due to their hydrophobicity, which is beneficial
for transport across the blood-brain barrier (BBB), their inorganic
nature preventing enzymatic degradation, their inherent low
toxicity lowering side effects, their high boron content for BNCT,
the variety of possible substitution patterns employing the three
isomers (ortho-, meta-, para-carborane) and their 3D aromatic
lead
structure
is
promising,
because
it
exhibits
oestrogenic/antioestrogenic activity as well as cytotoxic
properties,[18] and is also active in prevention of osteoporosis in
postmenopausal women with early-stage breast cancer[19] and in
the protection of cardiovascular functions.[20] Furthermore, its
mode of action can easily be modified by small changes; e.g. an
“A” ring substitution (Scheme 1) or modification with a nitro group
in para position leads to aromatase inhibition (the enzyme
producing oestrogen).[21]
One further prominent example is the ferrocene-containing
derivative ferrocifen (Fc-diOH) (Scheme 1), which was reported
and extensively biologically tested by Jaouen et al.. Ferrocifen
showed redox chemistry useful for the generation of reactive
oxygen (ROS) and nitrogen species (RNS) via Fenton chemistry
induced by the ferrocene unit[22–24] and high activity towards
hormone-dependent (e.g. MCF-7) and “hormone-independent”
(e.g. MDA-MB-231) cell lines.[25] Also a few other metal complex-
based SERMs are known.[26] Even though oestrogenic activity
(agonist or antagonist) was proven for ferrocifen, this effect is only
dominant at nanomolar concentrations, whereby other modes of
[a]
Dr. B. Schwarze, M.Sc. L. Welcke, Prof. Dr. Dr. h.c. mult. E. Hey-
Hawkins
Leipzig University, Faculty of Chemistry and Mineralogy, Institute of
Inorganic Chemistry
Johannisallee 29, D-04103 Leipzig (Germany)
E-mail: hey@uni-leipzig.de
[b]
[+]
M.Sc. S. Jelača, Prof. Dr. D. Maksimović-Ivanić, Prof. Dr. S.
Mijatović
University of Belgrade, Department of Immunology, Institute for
Biological Research “Siniša Stanković”, Bul. Despota Stefana 142,
11060 Belgrade (Serbia)
action, like induction of senescence (ca. 10−7
10−6−10−5 ) or Fenton chemistry (ca. 10−5−10−4
predominant effects at higher concentrations of ferrocifen in
vitro.[27] However, so far, no metallacarborane was combined with
the tamoxifen lead structure. Therefore, the “A” ring in 1,1-bis(4-
M), apoptosis (ca.
M
M
) become the
Supporting information for this article is given via a link at the end of
the document.
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10.1002/cmdc.201900554
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FULL PAPER
hydroxyphenyl)-2-phenylbut-1-ene (TAM-diOH) was replaced
with a well-known chelating moiety (2,2’-bipyridine), being able to
coordinate a variety of potential biologically active transition
metals (be it a pharmacophore or a traceable element, etc.), with
the goal to obtain novel potential SERMs (Scheme 1).
methods (Figure S1, SI). After obtaining the new ligands,
coordination studies were performed with [NEt4][3-(η3-C3H5)-3-
(CO)2-closo-3,1,2-MoC2B9H11] (7).
Scheme 2. Synthetic route yielding the organic vector incorporating the
chelating 2,2‘-bipyridine unit. (a) EtMgBr (2.2 equiv.) in THF, −40 °C, 4 h; (b)
reflux conditions: 2-(tributylstannyl)pyridine (1.1 equiv.), [Pd(PPh3)4] (10 mol%),
CsF (2.2 equiv.), CuI (16 mol%) in DMF, 120 °C, 3 d; (c) microwave conditions:
2-(tributylstannyl)pyridine (1.1 equiv.), [Pd(PPh3)4] (10 mol%), CsF (2.2 equiv.),
CuI (16 mol%) in DMF, 140 °C, 16 h; (d) CBr4, P(OiPr)3 in DCM, 0 °C to 40 °C,
4 d; (e) CCl4, PPh3 in toluene, 110 °C, 3 d; (f) 4-methoxyphenylboronic acid
(5.0 equiv.), [Pd(PPh3)4] (10 mol%), Na2CO3 (5.0 equiv.) in 1,4-dioxane/H2O
(4:1), 100 °C, 4 d; (g) BBr3 in DCM, −60 °C to rt, 12 h.
Scheme 1. Bioisosteric replacement approach: from TAM-diOH to ferrocifen
(Fc-diOH), an aromatase inhibitor,[21] 2,2’-bpy-TAM-diOR (R = Me (5), H (6)),
[[3,3-{4-[1,1-bis(4-methoxyphenyl)but-1-en-2-yl]-2,2‘-bipyridine-κ2N,N’}-3-
(CO)2-closo-3,1,2-MoC2B9H11] (9) or [3,3-{4-[1,1-bis(4-hydroxyphenyl)but-1-en-
2-yl]-2,2‘-bipyridine-κ2N,N’}-3-(CO)2-closo-3,1,2-MoC2B9H11] (10).
We here report on the combination of this novel 2,2’-bpy-TAM-
diOH vector system with half-sandwich molybdacarboranes.[28]
For antitumour studies, a formulation strategy using bovine serum
albumin (BSA) that was developed by us was applied, which led
to a substantial increase in the biological activity against the MCF-
7 breast cancer cell line for the new pharmacophor [3-(2,2’-
bipyridine-κ2N,N’)-3-(CO)2-closo-3,1,2-MoC2B9H11] (i).[29]
In 7, the acid-labile allyl ligand at molybdenum(II) was released
upon protonation and then replaced with the respective N,N-
chelating ligand 3, 5 and 6 to give the molybdacarborane
complexes 8, 9 and 10, respectively, according to Schwarze et al.
(Scheme 3).[28] Unlike the molybdacarboranes bearing a simple
2,2’-bipyridine or 1,10-phenanthroline ligand,[28] complexes 8−10
could be purified by flash column chromatography on silica gel in
low to moderate yields (18−35%). These low yields are most likely
related to a side reaction which was not observed for the simple
Results and Discussion
N,N-chelating
ligands
(e.g.
2,2’-bipyridine
or
1,10-
Syntheses and Characterisation
phenanthroline).[28] During the purification process, more than one
violet band could be observed for every complexation reaction.
Exemplarily for 9, the second violet fraction was collected in
sufficient purity and identified by 1H, 13C{1H}, 11B{1H} and 11B NMR
spectroscopy, HR-ESI mass spectrometry and diffraction
methods as a chlorine B(8)-substituted derivative of 9 (see SI),
where the respective position in the carborane ligand was
activated for EINS-type (electrophile induced nucleophilic
substitution) reactions (9b, Figure S2, SI).[34] This one-pot two-step
reaction (proton-mediated ligand exchange and EINS-type
(electrophile-induced nucleophilic substitution) reaction at the
dicarbollide) was attempted before without success for complexes
with the 2,2’-bipyridine and 1,10-phenanthroline ligand, [3-(L-
κ2N,N’)-3-(CO)2-closo-3,1,2-MoC2B9H11], with L = 2,2’-bipyridine
or 1,10-phenanthroline, using different strong acids and
The synthesis of the 2,2’-bipyridine-substituted tamoxifen
derivative 6 (Scheme 2) via the facile McMurry coupling was not
successful, probably due to the electron-poor 2,2’-bipyridine unit,
which renders the ketone in compound 3 less reactive in this type
of olefination reaction, unlike the electron-rich ferrocene
derivative in the synthesis of ferrocifen.[30] Equally unsuccessful
was the use of 3 in a Wittig–Horner-type reaction. Therefore,
ligand 6 was constructed stepwise starting from the commercially
available 2-halo-isonicotinic acid (1a,b), which was reduced to 1-
(2-halopyridin-4-yl)propan-1-one (2a,b) with ethylmagnesium
bromide in tetrahydrofuran (THF) at −40 °C (Scheme 2).[31]
A
[Pd(PPh3)4]-catalysed Stille coupling reaction resulted in the
asymmetric 2,2’-bipyridine derivative (3) in moderate to good
yields (gram scale 56%, small scale 69%). A Horner–Wadsworth–
Emmons modification for the Ramirez gem-dibromoolefination
gave compound 4 in good yield (78%).[32] A [Pd(PPh3)4]-catalysed
Suzuki coupling afforded compound 5 in good yield (76%).
Demethylation of the aryl-methyl ether 5 with BBr3 resulted in the
final ligand 6.[33] The conditions for the optimisation of both Pd0-
catalysed coupling reactions are given in the Supporting
Information (Tables S1 and S2, SI). Compounds 3−6 were fully
characterised by NMR, infrared spectroscopy, mass
spectrometry, and elemental analysis; the solid-state molecular
structure of 6 was also confirmed by single crystal X-ray diffraction
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FULL PAPER
solvents.[28] Further studies for employing the chloride in
carborane substitution chemistry are in progress.
illustration, one typical high-resolution ESI mass spectrum in the
negative mode is depicted in the supporting information (Figure
S18, SI), showing an agglomerisation pattern, where the
unidentifiable agglomerate X (m/z = 1965.6786) loses five times
a fragment [M−2H]2−. This effect can be minimised through
dissolution of the sample immediately before injection into the
ESI-MS instrument. This is a nice demonstration of the potential
agglomerisation properties of metallacarboranes in solution.
Bioanalytical Measurements
For in vitro cell culture tests, the stock solutions of sparingly water-
soluble compounds are typically prepared in DMSO (ethanol or
methanol are good alternatives) and stored below +4 °C. For that
purpose, the chemical stability of 3, 5, 6 and 8−10 was tested in
a solution of water-containing DMSO-d6 in air for at least 36 days
(3, 5, 6, 8, 9) and for 14 days for complex 10. 1H and 11B{1H} NMR
spectra revealed that the ligands 3, 5 and 6 can be stored in a
DMSO stock solution for at least one month without
decomposition, and the molybdacarboranes for 14 days up to one
month with minor decomposition (where the decomposition
products are the free ligands 3, 5 or 6, the nido-carborane ([nido-
C2B9H12]−) and most likely a molybdenum species in higher
oxidation states) (see Fehler! Verweisquelle konnte nicht
gefunden werden.−S14). Recently, we introduced a formulation
procedure for sparingly water-soluble metallacarboranes, using
Scheme 3. Synthesis of the molybdacarboranes 8, 9 and 10 via protonation of
[NEt4][3-(η3-C3H5)-3-(CO)2-closo-3,1,2-MoC2B9H11] (7) and reaction with N,N-
chelating ligands 3, 5 or 6. Both coordination isomers are formed for 8, 9 and
10.
The colour of all the ligands ranges from colourless to pale yellow.
On coordination to molybdenum(II), a colour change to deep
purple is observed for complexes 8−10 (for UV-Vis spectra of 6
and 10 see Figure S17, SI) indicating metal-to-ligand (MLCT) and
ligand-to-metal charge transfer (LMCT) (with L = 3, 5 or 6).[28] In
the infrared spectra, typical vibrations of all functional groups are
observed, e.g. (BH) (2595–2480 cm−1) and (CO) (1955–
1874 cm−1) vibrations, which are unique in biological systems and
could, therefore, be used for label-free imaging (first attempts
have been reported for [3-(2,2’-bipyridine-κ2N,N’)-3-(CO)2-closo-
3,1,2-MoC2B9H11].[29] In the 1H NMR spectra of the complexes 8,
9 and 10, there is a clear coordination shift observed compared
to the chemical shifts of the ligands 3, 5 and 6 (Figure S3−Fehler!
Verweisquelle konnte nicht gefunden werden., SI). The
CHcluster signals split into two broad singlets due to the asymmetric
N,N-chelating ligand. Importantly, the coordination of 3, 5 and 6
at molybdenum(II) generates always two isomers, which cannot
be distinguished via NMR spectroscopy. The carbonyl groups are
observed as two slightly different signals at 255.3 and 254.5 ppm
(8, CD2Cl2), 256.3 and 255.5 ppm (9, CDCl3) or 260.3 and
260.0 ppm (10, CD3CN) in the 13C{1H} NMR spectra of the
respective complexes according to the C1 symmetry of the whole
molecule.
fatty acids- and magnesium-free bovine serum albumin (BSAnoMg
)
in a 1:10 molar ratio, which led to a significant improvement of the
reproducibility, but also the cytotoxicity against MCF-7 breast
cancer cells.[29] Here, the biological activity of molybdacarboranes
(8−10), as well as ligands 3, 5 and 6, and literature-known
reference compounds (TAM-diOH and Fc-diOH) was evaluated
employing this formulation procedure to ensure comparability.
To understand the self-assembling behaviour of
metallacarboranes/BSAnoMg co-assemblies, exemplarily ligand 6
and complex 10 were investigated in phosphate-buffered saline
(PBS)/DMSO mixtures at physiological pH (pH 7.4) by UV-Vis,
fluorescence and Rayleigh light scattering (RLS) spectroscopy,
as well as Nanoparticle Tracking Analysis (NTA).[9,29,35]
For the fluorescence spectra, three excitation wavelengths
were chosen (exc = 280, 295 and 320 nm) and the investigations
were performed with two site markers, namely warfarin and
ibuprofen, binding selectively to Sudlow’s site I or Sudlow’s site II,
respectively. The same systems were investigated by UV-Vis
spectroscopy in parallel. Our measurements revealed that 6 binds
to both, Sudlow’s site I and II (Figure S15, SI).
Obtaining HR-ESI mass spectra of molybdacarboranes is
challenging, since they cannot be ionised easily and are either
detectable in negative or positive mode. Additionally, a strong
clustering effect can be observed for complexes 8−10. For
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Figure 1. Size distribution of 6 (left) and 10 (right) in PBS/DMSO mixtures from NTA measurements. Ratio BSAnoMg:6 or 10 was 10:1. [6] = [10] = 20 μ
M,
[BSA] = 200 μ . The dilution factors are adjusted to 11x for each sample. Samples were measured 1.5–22.25 h after preparation. The respective blanks (BSAnoMg
M
in PBS/DMSO) are measured after 2.2 h (6) or 2.4 h (10); 6 in PBS/DMSO after 2 h, 10 in PBS/DMSO after 0.5 h. Standard deviation (SD) for particle concentration
is ± 1.30–3.68 x 106 (samples regarding 6) and ± 2.68 x 106–3.88 x 107 (samples regarding 10) particles mL–1, for particle size ± 4–18 nm.
1
bovine serum albumin (BSAnoMg) in a 10:1 ratio. A sharp increase
in particle concentration is observed when the formulation
protocol is applied for molybdacarborane 10 with bimodal
distribution (after deconvolution) and relatively low polydispersity
(Figure 1, right) being stable over 20 h, supporting the findings
from previous studies.[29] Interestingly, when the aggregation
behaviour of only the ligand 6 is investigated, no such effect is
observed. Indeed, the very broad size distribution of particles of 6
in PBS/DMSO is transformed into a size distribution that
resembles BSA in PBS/DMSO (Figure 1, left) implying that 6 is
bound to BSA (see also spectroscopic data: Figure S15−S16, SI),
but does not induce agglomerisation as metallacarboranes do.
Remarkably, the fluorescence intensity at exc = 280 nm is
quenched to the same extent when 6 only is mixed with BSAnoMg
or together with ibuprofen, indicating that the binding strength is
in the same order of magnitude as for the site marker. The
situation is slightly different for 10, which binds to Sudlow’s site II,
but the fluorescence is quenched more in the ternary system
together with BSAnoMg and ibuprofen. The fluorescence intensity
is quenched more when 10 is added first, and ibuprofen
afterwards, which might imply a weak cooperative effect upon
binding of both components (Figure S15, SI). Evidently, there is a
strong cooperative effect of both 6 and 10 with warfarin (at the
excitation wavelengths
exc = 295 and 320 nm), which is
Thus, these findings are
a
strong evidence that
independent from the order of addition. Also, tamoxifen acts
differently, having a negative allosteric effect on warfarin−HSA
binding.[36] These findings are in contrast with the ones for the
metallacarboranes form nano-sized aggregates with BSAnoMg
,
which cannot be observed for organic hormone-like structures,
even though binding to BSAnoMg was proven for 6 via UV-Vis and
fluorescence spectroscopy.
molybdacarborane
[3-(2,2’-bipyridine-κ2N,N’)-3-(CO)2-closo-
3,1,2-MoC2B9H11] (i), which seems to bind stronger to Sudlow’s
site I than to site II, without any interaction being detected
between warfarin and i.[29] The absorption spectra of the ternary
systems (BSA–site marker–drug, Figure S16, SI) show the same
overall trend concerning binding events as the fluorescence
spectra. Notably, the UV-Vis spectrum of 10 in PBS/DMSO
mixture is essentially the same as for i; therefore, similar
electronic structures can be assumed.[28] The absorption
spectrum suggests that the solubility of 6 is improved on binding
to BSAnoMg, because the baseline shift, due to scattering, is
suppressed. This was confirmed by measuring Rayleigh Light
Scattering (RLS), which showed a decrease of scattering
aggregates, in an analogous way as we recently reported (Figure
S17 left, SI).[29] For 10, the binding to BSA (1:1) seems to increase
the scattering according to RLS (Figure S17 right, SI).
In vitro Cell Colourimetric Assays
After we found evidence of cytotoxic activity of [3-(2,2’-bipyridine-
κ2N,N’)-3-(CO)2-closo-3,1,2-MoC2B9H11] (i) against MCF-7
cells,[29] we wanted to expand our studies to other
molybdacarboranes with N,N-chelating ligands and a larger panel
of cell lines, i.e. three breast cancer adenocarcinomas (MDA-MB-
231, MDA-MB-361 and MCF-7), human glioblastoma (LN-229)
and human glioma (U-251) cell lines, plus mouse macrophages
(Mf), as an example for non-malignant immune cells (Table 1 and
Figures S19 and S20, SI). Cells were exposed to 3, 6 and 8−10
for
72 h,
after
which
3-(4,5-dimethylthiazol-2-yl)-2,5-
diphenyltetrazolium bromide (MTT) and crystal violet (CV) cell
viability assays were performed.
Nanoparticle Tracking Analysis (NTA) measurements were
performed in a PBS/DMSO mixture exemplarily for 6 and 10, with
and without the addition of fatty acids- and magnesium-free
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Table 1. IC50 values for 3, 6, 8–10 from MTT and CV cell viability assays. Standard deviations for each IC50 value are given.
IC50 (µ
Cells
M)
Compound
Assay
MDA-MB-231
MDA-MB-361
MCF-7
U-251
LN-229
Mf
[a]
MTT
CV
MTT
CV
MTT
CV
MTT
CV
MTT
CV
MTT
CV
MTT
CV
42.0 ± 3.4
38.1 ± 3.5
2.2 ± 0.2
2.5 ± 0.2
>100
78.1 ± 3.8
70.5 ± 5.2
2.4 ± 0.2
2.8 ± 0.3
71.0 ± 4.4
75.7 ± 5.0
18.3 ± 1.4
18.1 ± 2.4
4.0 ± 0.4
4.5 ± 0.6
24.5 ± 3.6
33.9 ± 1.3
1.5 ± 0.3
2.3 ± 0.2
43.0 ± 2.9
41.3 ± 2.2
1.8 ± 0.4
2.1 ± 0.6
34.4 ± 1.7
27.9 ± 3.5
6.0 ± 0.6
6.6 ± 0.9
9.3 ± 0.5
5.0 ± 0.7
24.3 ± 1.6
25.3 ± 2.4
1.0 ± 0.1
1.0 ± 0.1
38.0 ± 3.0
44.1 ± 1.6
15.2 ± 0.6
21.0 ± 3.5
97.4 ± 3.7
55.8 ± 5.1
17.2 ± 0.6
17.4 ± 1.0
30.1 ± 2.8
32.7 ± 3.8
>100
47.2 ± 0.9
54.9 ± 4.1
15.8 ± 2.0
17.7 ± 1.0
>100
–
3
>100
[a]
–
6
>100
[a]
–
8
9
>100
>100
>100
[a]
38.2 ± 1.4
30.8 ± 2.8
17.8 ± 2.0
18.5 ± 1.1
15.4 ± 0.6
16.8 ± 1.3
1.0 ± 0.1
0.9 ± 0.1
21.9 ± 1.6
25.8 ± 1.7
38.0 ± 0.9
41.0 ± 3.8
>100
>100
3.1 ± 0.2
2.6 ± 0.3
–
>100
[a]
–
10
>100
[a]
–
TAM-diOH
Fc-diOH
>100
1.4 ± 0.2
1.7 ± 0.1
97.1 ± 4.2
[a]
–
20.6 ± 0.6
All experiments were done using BSAnoMg formulation strategy (BSA/small molecule (10:1)), before dilution with cell culture medium.
Cell viability is expressed as percentage (%) relative to control and presented as mean ± SD of three independent experiments performed in triplicate.
[a] “–“ means not tested.
Only minor discrepancies in the calculated IC50 values obtained from the two assays (MTT or CV) were found for most of the tested compounds.
As we found an improvement of the cytotoxicity for i upon
formulation with BSAnoMg in a 1:10 ratio (compound:BSAnoMg) in
previous studies, we performed all studies presented here with
the mentioned formulation protocol, also for the non-
metallacarborane compounds 3 and 6, as well as the two
reference compounds 1,1-bis(4-hydroxyphenyl)-2-phenylbut-1-
ene (TAM-diOH) and ferrocifen (Fc-diOH). Under the applied
conditions of the biological evaluation, 5 was not suitable for
testing due to precipitation from the solution, and 9b could not be
obtained in sufficient purity. The results revealed that ligand 3 and
the corresponding metallcarborane 8 have moderate to low
cytotoxic activity on the studied cell lines. In all cases, except for
the MCF-7 cells, the IC50 values for molybdacarborane complexes
are slightly higher than for the respective ligands alone. Complex
9, bearing a vector which is closer to the lead structure of TAM-
diOH, performs expectedly better, especially against the MCF-7
cell line (Table 1). Remarkably, also the human glioblastoma cells
(LN-229) and human glioma cells (U-251) were sensitive towards
treatment with 9 in the low/moderate micromolar range. The
couple 6 and 10 showed activity against all tested cell lines in the
low micromolar range (Table 1). Worth highlighting is that the
substitution of the phenyl ring “A” in TAM-diOH by a chelating 2,2’-
bipyridine unit does not only improve the anticancer activity for all
tested breast cancer cell lines, but also provides cytotoxic activity
against the very aggressive primary malignant glioblastoma cells
(LN-229) and the invasive, malignant human glioma cells (U-251).
The anticancer activity for Fc-diOH could be reproduced also with
the BSAnoMg formulation protocol.[37] In general, the IC50 values for
Fc-diOH against all malignant cell lines are lower than for the
other tested compounds; however, 6, 9 and 10 come close to the
same activity range, depending on the cell line. Remarkably, the
absolute toxicity of Fc-diOH against healthy immune cells (mouse
the preferential selectivity towards tumour cells is generally higher
for Fc-diOH (considering the experimental cut-off at 100 µ ). This,
however, does not extend to 6 regarding all breast cancer cell
lines and for 10 in the cases of the MDA-MB-361 and MCF-7 cell
lines.
Western blot analysis was performed to assess the oestrogen
receptor status (see Figure S21, SI), However, it seems that the
anticancer potential of our newly designed compounds is not in
correlation with ER receptor expression, under the applied
concentrations, indicating the existence of other targets for these
molecules.
M
Flow Cytometry
To evaluate a possible mode of action of the new compounds, 6
and 10 were selected for further analysis on the MCF-7 cell line
by flow cytometry. Fc-diOH was also tested, as reference, for
comparison. All following investigations were performed applying
the BSAnoMg formulation protocol.
Both 6 and 10 showed the same moderate inhibitory
properties on cell proliferation (carboxyfluorescein succinimidyl
ester (CFSE) staining, Figure 2A), whereas Fc-diOH featured
stronger inhibition of the proliferation, in line with the literature for
all ferrocifen-type anticancer drugs.[27] Senescence-associated
(SA) β-galactosidase staining revealed that
6
induces
senescence to a minor extent compared to the transition metal-
containing 10 and ferrocifen (Figure 2B).[39]
Cellular senescence is an important mechanism to prevent
tumour cell proliferation and might result in cellular death.[40]
However, the detailed role of senescence in general was found to
be way more complicated, because this process not only arrests
the cell cycle, but it also stimulates the cells to produce numerous
growth factors and other proteins (also called senescence-
associated secretory phenotype, SASP), which can, in turn,
provoke again tumour promotion but also tissue repair.[41]
Annexin-V/PI double staining indicates that apoptosis is not the
main mode of action for either 6 or 10 (Figure 2C), which is the
macrophages, Mf) is considerably high (20.6 ± 0.6 µ
to 3, 6 and 8−10 (>100 µ ) (Table 1 and Figure S20, SI). This
issue has already been reported for ferrocifen-type anticancer
drugs, showing an analogous high absolute toxicity (10 µ
against healthy brain tissue in vivo.[38] However, relatively seen
M) compared
M
M)
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case
for
the
reference
compounds
and
for
Additionally, autophagy processes were triggered by all three
tested compounds (Figure 3A); however, different modes of
action could be detected after treatment with the autophagy
inhibitor 3-methyladenine (3-MA). Since Fc-diOH further lowers
the cell viability when applied in combination with 3-MA, the
autophagy process can be considered as cytoprotective (pro-
survival) (Figure 3A, bottom right panel), while the addition of 6 as
well as 10 together with 3-MA resulted in restored viability
compared to 6 (or 10) alone, and it can therefore be regarded as
cytodestructive (cell death mediating, Figure 3A, upper right and
bottom left panel).
ruthenacarboranes.[8,27,42]
These results could be supported by 4’,6-diamidino-2-
phenylindole (DAPI) staining, highlighting shrunken nuclei with
condensed chromatin as sign of apoptosis (Figure 2D, red
arrows), in the case of 10 to a lesser extent than for Fc-diOH.
However, for 6 a prevalent observation is the presence of
irregular-shaped shrunken nuclei (Figure 2D, yellow arrows)
indicating sporadic cells with apoptotic morphology. In
concordance with the data above, the activation of caspases was
only detected upon treatment of MCF-7 cells with Fc-diOH (Figure
2E).
Figure 2. Flow cytometry analysis of MCF-7 cells exposed (72 h) to an IC50 dose of 6, 10 or Fc-diOH, respectively, applying the BSAnoMg formulation procedure. (A)
CFSE staining, fluorescence intensity from the FL1 channel; (B) senescence-associated (SA) β-galactosidase staining, fluorescence intensity from the FL1 channel;
(C) AnnV/PI double staining, fluorescence intensity from FL2 (y axis) vs. FL1 (x axis) channel; (D) DAPI-stained cells observed under a fluorescence microscope
(magnification x200), red arrows indicate shrunken nuclei with condensed chromatin, yellow arrows indicate irregular shape of nuclei as morphologic signs of
apoptosis; (E) ApoStat staining for caspase-dependent apoptosis, fluorescence intensity from the FL1 channel. Experiments were run in triplicate. The
representations are based exemplarily on one experiment. For each staining protocol, the respective control (cells treated with BSAnoMg) is also shown. (FL1: green
emission; FL2: orange emission).
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This non-apoptotic and autophagy-mediated cell death
mechanism could be the pathway of how 6 and 10 act on the
tested cancer cells. In the literature, also autophagy is discussed
as a double-edged sword, depending on healthy or cancer cell
type, microenvironment, and development status.[43]
While in the luminal breast cancer cell line MCF-7 autophagy
seems to be a reasonable cell death process, it was recently
shown for other common chemotherapeutics that autophagy in
e.g. MDA-MB-231 cells is dependent on other signalling
pathways.[44] Autophagy, as one of the main cellular processes,
can have a large spectrum of physiological functions affecting cell
fate in various ways. Its specific role, however, is determined by
the cell specificity, the intensity of triggered processes, as well as
the type of the chemotherapeutic that induced it.[45]
(DHR 123) staining was performed. It could be shown for Fc-diOH
that the ROS/RNS levels in the treated cells were increased, as it
is reported in the literature via the inhibition of cytoprotective
radical scavenger thioredoxin,[46] as well as the self-generation of
ROS/RNS species, which all together lead to apoptosis also in
hormone-independent cell lines.[22] Similarly, other ferrocene-
containing bioactive molecules induce apoptosis through the
generation of ROS.[23,47] In contrast, both 6 and 10 “scavenge” or
lower the cellular ROS/RNS levels (DHR 123, dihydrorhodamine
123 staining; Figure 3C), which corresponds well with the
absence of caspase-dependent apoptosis induction. Worth
mentioning is that the molybdacarborane 10 is way more efficient
in scavenging/reducing radical concentration compared to its
ligand (6) only. How exactly 6 and 10 lower the cellular ROS/RNS
levels remains unclear and will be addressed in future studies.
To investigate the capability of the drugs to generate reactive
oxygen/nitrogen species (ROS/RNS), dihydrorhodamine 123
Figure 3. Flow cytometry analysis of MCF-7 cells exposed (72 h) to an IC50 dose of 6, 10 or Fc-diOH, respectively, applying the BSAnoMg formulation procedure. (A)
AO staining (upper left panel), fluorescence intensity from the FL3 channel (dark red emission) for detection of acidic vacuoles; cell viability of MCF-7 cells was
determined via CV assays upon treatment with 3-MA, 6, 10 or Fc-diOH and 3-MA with 6, 10 or Fc-diOH. Experiments were run in triplicate. The respective control
(cells treated with BSAnoMg) is also shown. p<0.05 in comparison to * non-treated cells or # treated with the respective compounds alone (6, 10 or Fc-diOH). (B)
DAF-FM staining allows to detect the nitric oxide (NO) level, fluorescence intensity from the FL1 channel; (C) DHR 123 staining for determination of the ROS/RNS
species, fluorescence intensity from the FL1 channel (green emission). For flow cytometry, experiments were run in triplicate. The representations are based
exemplarily on one experiment. For each staining protocol, the respective control (cells treated with BSAnoMg) is also shown.
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Remarkably, compound 10 strongly upregulates the NO
production in MCF-7 cells (Figure 3B). Either it scavenges
ROS/RNS and thus generates NO, or it interacts with one or more
of the nitric oxide synthases (NOS), as known for other mixed-
sandwich ferracarborane or COSAN-type structures.[7] This effect
is in high contrast to the other two tested compounds (6 and Fc-
diOH) in flow cytometry analysis. Also, nitric oxide has an
ambivalent role in healthy and cancer cell correlation.[48] In low
Experimental Section
See Supporting Information.
Acknowledgements
Support from the Fonds der Chemischen Industrie (doctoral grant
for B. S.), the Graduate School Leipzig School of Natural
concentrations, i.e. 10−300 n
be induced via HIF-1α (hypoxia-induced factor 1α), whereas in
higher concentrations, i.e. > 300 n , the p53 tumour protein is
M, proliferation of MCF-7 cells could
Sciences
–
Building with Molecules and Nano-objects
M
(BuildMoNa) and the Serbian Ministry of Education, Science and
Technological Development (Grant No. 173013) is gratefully
acknowledged. We thank Dr. P. Coburger for X-ray data collection
on single crystals and Lysanne Thunich for synthetic support.
Special thanks to Dr. Marta Gozzi for a very professional and
effective collaboration in metallacarborane chemistry and help
with bioanalytical measurements.
further phosphorylated inducing an apoptotic cell death
mechanism.[49]
Conclusions
We could synthesise a 2,2’-bipyridine vector (6) in five synthetic
steps that can be employed as ligand for a large variety of
organometallic or inorganic transition metal complex fragments
giving distinct functions to the whole complex. The activity of the
prototypic molybdacarborane [3-(2,2’-bipyridine-κ2N,N’)-3-(CO)2-
closo-3,1,2-MoC2B9H11] (i), already active against MCF-7 breast
Keywords: breast cancer • molybdacarborane • tamoxifen • nitric
oxide (NO) • nanoparticles
References
cancer cell line (IC50 = ca. 40 µM
),[29] could be improved by
incorporating the 2,2’-bpy-TAM-diOH (6) ligand. Furthermore, the
ligands 3 and 6 were tested in cell viability studies (CV and MTT
assays) in comparison to the respective molybdacarborane
complexes (8−10) against breast adenocarcinoma (MDA-MB-
231, MDA-MB-361 and MCF-7), human glioblastoma (LN-229)
and human glioma (U-251) cell lines and showed IC50 values in
low to moderate micromolar range. Importantly, viability of mouse
macrophages (Mf) was not significantly affected by the new
[1] K. J. Franz, N. Metzler-Nolte, Chem. Rev. 2019, 119, 727.
[2] a) L. Šebestová, R. Havelek, M. Řezáčová, J. Honzíček, Z.
Kročová, J. Vinklárek, Chem. Biol. Interact. 2015, 242, 61;
b) O. Mrózek, L. Šebestová, J. Vinklárek, M. Řezáčová, A.
Eisner, Z. Růžičková, J. Honzíček, Eur. J. Inorg. Chem.
2016, 2016, 519; c) J. Honzíček, J. Vinklárek, M. Erben, Z.
Padělková, L. Šebestová, M. Řezáčová, J. Organomet.
Chem. 2014, 749, 387; d) J. Honzíček, J. Vinklárek, Z.
Padělková, L. Šebestová, K. Foltánová, M. Řezáčová, J.
Organomet. Chem. 2012, 716, 258; e) C. C. L. Pereira, C.
V. Diogo, A. Burgeiro, P. J. Oliveira, M. P. M. Marques, S.
S. Braga, F. A. A. Paz, M. Pillinger, I. S. Gonçalves,
Organometallics 2008, 27, 4948; f) C. C. L. Pereira, S. S.
Braga, F. A. A. Paz, M. Pillinger, J. Klinowski, I. S.
Gonçalves, Eur. J. Inorg. Chem. 2006, 2006, 4278; g) H.
Pfeiffer, M. Dragoun, A. Prokop, U. Schatzschneider, Z.
Anorg. Allg. Chem. 2013, 639, 1568; h) D. Bandarra, M.
Lopes, T. Lopes, J. Almeida, M. S. Saraiva, M.
compounds up to a concentration of 100 µM, in contrast to Fc-
diOH. Modification of the “A” ring in 4,4’-dihydroxytamoxifen
(TAM-diOH) or ferrocifen (Fc-diOH) with 2,2’-bipyridine or [3-(2,2’-
bipyridine-κ2N,N’)-3-(CO)2-closo-3,1,2-MoC2B9H11]
modulates
the anticancer activity profile significantly. Compounds 6 and 10
were found to have distinctly diverse activities (compared to Fc-
diOH), e.g. induction of senescence, cytodestructive autophagy,
lowering of ROS/RNS levels, and, uniquely for 10, strong increase
of nitric oxide (NO) concentration. In perspective, it might be a
good chance that the tested compounds are active on different
routes rather than causing apoptosis, because most anticancer
drugs kill through apoptotic cell death, thus having only little effect
on cancer cell lines with defects in the classical apoptotic
signalling pathway.[50] Further details on the mode of action of 6
and 10 are under way.
Vasconcellos-Dias, C. D. Nunes, V. Félix, P. Brandão, P.
D. Vaz, M. Meireles, M. J. Calhorda, J. Inorg. Biochem.
2010, 104, 1171.
[3] a) R. F. Barth, J. A. Coderre, M. G. H. Vicente, T. E. Blue,
Clin. Cancer Res. 2005, 11, 3987; b) K. Yokoyama, S.-I.
Miyatake, Y. Kajimoto, S. Kawabata, A. Doi, T. Yoshida, T.
Asano, M. Kirihata, K. Ono, T. Kuroiwa, J. Neurooncol.
2006, 78, 227.
This study shows that half-sandwich molybdacarboranes are
highly interesting bioactive pharmacophores with distinct activity
profile, which can modulate the mode of action of established
organic and organometallic anticancer agents. Additionally, it
could be shown via Nanoparticle Tracking Analysis (NTA) that the
metallacarborane unit is essential for triggering the formation of
nanoparticles upon preparation with bovine serum albumin
(BSAnoMg), which might have a positive impact on in vivo studies.
Thus, both, 6 and 10, are promising drug candidates for
application in breast cancer, glioma and glioblastoma therapy.
[4] B. Schwarze, M. Gozzi, E. Hey-Hawkins in Boron-Based
Compounds (Eds.: E. Hey-Hawkins, C. V. Teixidor), John
Wiley & Sons, Ltd., Chichester, UK, 2018, pp. 60–108.
[5] M. F. Hawthorne, D. C. Young, T. D. Andrews, D. V. Howe,
R. L. Pilling, A. D. Pitts, M. Reintjes, L. F. Warren, P. A.
Wegner, J. Am. Chem. Soc. 1968, 90, 879.
[6] K. B. Gona, A. Zaulet, V. Gómez-Vallejo, F. Teixidor, J.
Llop, C. Viñas, Chem. Commun. 2014, 50, 11415.
[7] R. Kaplánek, P. Martásek, B. Grüner, S. Panda, J. Rak, B.
S. S. Masters, V. Král, L. J. Roman, J. Med. Chem. 2012,
55, 9541.
This article is protected by copyright. All rights reserved.

10.1002/cmdc.201900554
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FULL PAPER
[8] M. Gozzi, B. Schwarze, M.-B. Sárosi, P. Lönnecke, D.
Drača, D. Maksimović-Ivanić, S. Mijatović, E. Hey-Hawkins,
Dalton Trans. 2017, 46, 12067.
[9] M. Gozzi, B. Murganic, D. Drača, J. Popp, P. Coburger, D.
Maksimović-Ivanić, S. Mijatović, E. Hey-Hawkins,
ChemMedChem 2019, DOI: 10.1002/cmdc.201900349.
[10] P. W. Causey, T. R. Besanger, J. F. Valliant, J. Med.
Chem. 2008, 51, 2833.
[11] P. M. Hawkins, P. A. Jelliss, N. Nonaka, X. Shi, W. A.
Banks, J. Pharmacol. Exp. Ther. 2009, 329, 608.
[12] D. G. Pruitt, K. M. Bullock, W. A. Banks, P. A. Jelliss, Inorg.
Chim. Acta 2017, 466, 139.
[13] A. S. Louie, L. E. Harrington, J. F. Valliant, Inorg. Chim.
Acta 2012, 389, 159.
[14] Y. Endo, T. Iijima, Y. Yamakoshi, M. Yamaguchi, H.
Fukasawa, K. Shudo, J. Med. Chem. 1999, 42, 1501.
[15] a) S. Fujii, Y. Hashimoto, T. Suzuki, S. Ohta, Y. Endo,
Bioorg. Chem. Med. Lett. 2005, 15, 227; b) S. Fujii, T.
Goto, K. Ohta, Y. Hashimoto, T. Suzuki, S. Ohta, Y. Endo,
J. Med. Chem. 2005, 48, 4654.
[16] a) Y. Endo, T. Yoshimi, C. Miyaura, Pure Appl. Chem.
2003, 75, 1197; b) Y. Endo, T. Yoshimi, T. Iijima, Y.
Yamakoshi, Bioorg. Chem. Med. Lett. 1999, 9, 3387.
[17] a) J. F. Valliant, P. Schaffer, K. A. Stephenson, J. F.
Britten, J. Org. Chem. 2002, 67, 383; b) M. L. Beer, J.
Lemon, J. F. Valliant, J. Med. Chem. 2010, 53, 8012.
[18] V. Lubczyk, H. Bachmann, R. Gust, J. Med. Chem. 2002,
45, 5358.
[19] J. Zidan, Z. Keidar, W. Basher, O. Israel, Med. Oncol.
2004, 21, 117.
[20] S. Menazza, E. Murphy, Circ. Res. 2016, 118, 994.
[21] L.-M. Zhao, H.-S. Jin, J. Liu, T. C. Skaar, J. Ipe, W. Lv, D.
A. Flockhart, M. Cushman, Boorg. Med. Chem. 2016, 24,
5400.
[36] J. Chen, D. S. Hage, Anal. Chem. 2006, 78, 2672.
[37] a) P. Pigeon, S. Top, O. Zekri, E. A. Hillard, A. Vessières,
M.-A. Plamont, O. Buriez, E. Labbé, M. Huché, S.
Boutamine, C. Amatore, G. Jaouen, J. Organomet. Chem.
2009, 694, 895; b) A. Nguyen, A. Vessières, E. A. Hillard,
S. Top, P. Pigeon, G. Jaouen, Chimia 2007, 61, 716.
[38] E. Allard, C. Passirani, E. Garcion, P. Pigeon, A.
Vessières, G. Jaouen, J.-P. Benoit, J. Control. Release
2008, 130, 146.
[39] C. Bruyère, V. Mathieu, A. Vessières, P. Pigeon, S. Top, G.
Jaouen, R. Kiss, J. Inorg. Biochem. 2014, 141, 144.
[40] D. E. Crews, J. Physiol. Anthropol. 2007, 26, 365.
[41] F. Rodier, J. Campisi, J. Cell Biol. 2011, 192, 547.
[42] C. Ferlini, G. Scambia, M. Marone, M. Distefano, C.
Gaggini, G. Ferrandina, A. Fattorossi, G. Isola, P.
Benedetti Panici, S. Mancuso, Br. J. Cancer. 1999, 79,
257.
[43] a) N. S. Katheder, R. Khezri, F. O'Farrell, S. W. Schultz, A.
Jain, M. M. Rahman, K. O. Schink, T. A. Theodossiou, T.
Johansen, G. Juhász, D. Bilder, A. Brech, H. Stenmark, T.
E. Rusten, Nature 2017, 541, 417; b) E. White, R. S.
DiPaola, Clin. Cancer Res. 2009, 15, 5308; c) A. Thorburn,
PLoS Biol. 2014, 12, e1001967.
[44] C. Garbar, C. Mascaux, J. Giustiniani, Y. Merrouche, A.
Bensussan, Sci. Rep. 2017, 7, 7201.
[45] T. Yonekawa, A. Thorburn, Essays Biochem. 2013, 55,
105.
[46] a) Masutani, H., & Yodoi, J., H. Masutani, J. Yodoi,
Methods Enzymol. 2002, 347, 279; b) A. Citta, A. Folda, A.
Bindoli, P. Pigeon, S. Top, A. Vessières, M. Salmain, G.
Jaouen, M. P. Rigobello, J. Med. Chem. 2014, 57, 8849.
[47] A. Mooney, R. Tiedt, T. Maghoub, N. O'Donovan, J. Crown,
B. White, P. T. M. Kenny, J. Med. Chem. 2012, 55, 5455.
[48] a) F. Vannini, K. Kashfi, N. Nath, Redox Biol. 2015, 6, 334;
b) J. Scicinski, B. Oronsky, S. Ning, S. Knox, D. Peehl, M.
M. Kim, P. Langecker, G. Fanger, Redox Biol. 2015, 6, 1;
c) Jason R. Hickok, Douglas D. Thomas, J. Hickok, D.
Thomas, Curr. Pharm. Des. 2010, 16, 381.
[22] C. Lu, J.-M. Heldt, M. Guille-Collignon, F. Lemaître, G.
Jaouen, A. Vessières, C. Amatore, ChemMedChem 2014,
9, 1286.
[23] H. Hagen, P. Marzenell, E. Jentzsch, F. Wenz, M. R.
Veldwijk, A. Mokhir, J. Med. Chem. 2012, 55, 924.
[24] Q. Michard, G. Jaouen, A. Vessieres, B. A. Bernard, J.
Inorg. Biochem. 2008, 102, 1980.
[49] D. D. Thomas, M. G. Espey, L. A. Ridnour, L. J. Hofseth,
D. Mancardi, C. C. Harris, D. A. Wink, Proc. Natl. Acad.
Sci. U S A 2004, 101, 8894.
[25] E. A. Hillard, A. Vessières, G. Jaouen in Topics in
Organometallic Chemistry (Eds.: G. Jaouen, N. Metzler-
Nolte), Springer Berlin Heidelberg, Berlin, Heidelberg,
2010, pp. 81–117.
[50] P. Kahlem, B. Dörken, C. A. Schmitt, J. Clin. Invest. 2004,
113, 169.
[26] a) K. Nikitin, Y. Ortin, H. Müller-Bunz, M.-A. Plamont, G.
Jaouen, A. Vessières, M. J. McGlinchey, J. Organomet.
Chem. 2010, 695, 595; b) A. Vessières, S. Top, W. Beck,
E. Hillard, G. Jaouen, Dalton Trans. 2006, 529.
[27] G. Jaouen, A. Vessières, S. Top, Chem. Soc. Rev. 2015,
44, 8802.
[28] B. Schwarze, S. Sobottka, R. Schiewe, B. Sarkar, E. Hey-
Hawkins, Chem. Eur. J. 2019, 25, 8550.
[29] B. Schwarze, M. Gozzi, C. Zilberfain, J. Rüdiger, C.
Birkemeyer, I. Estrela-Lopis, E. Hey-Hawkins 2019, under
revision.
[30] S. Top, B. Dauer, J. Vaissermann, G. Jaouen, J.
Organomet. Chem. 1997, 541, 355.
[31] K. E. Henegar, S. W. Ashford, T. A. Baughman, J. C. Sih,
R.-L. Gu, J. Org. Chem. 1997, 62, 6588.
[32] Y.-Q. Fang, O. Lifchits, M. Lautens, Synlett 2008, 2008,
413.
[33] E. H. Vickery, L. F. Pahler, E. J. Eisenbraun, J. Org. Chem.
1979, 44, 4444.
[34] R. Frank, A. K. Adhikari, H. Auer, E. Hey-Hawkins, Chem.
Eur. J. 2014, 20, 1440.
[35] M. Gozzi, B. Schwarze, P. Coburger, E. Hey-Hawkins,
Inorganics 2019, 7, 91.
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Table-of-Contents:
RESEARCH ARTICLE
Benedikt Schwarze, Sanja Jelača, Linda
Welcke, Danijela Maksimović-Ivanić,
Sanja Mijatović and Evamarie Hey-
Hawkins*
Page No. – Page No.
2,2’-Bipyridine-modified Tamoxifen: A
Versatile Vector for
Molybdacarboranes
Privileged structures. Applying this drug design concept on the well-known tamoxifen leads to its 2,2’-bipyridine-modified derivative, being a
vector for molybdacarboranes. The biological activity profile contrast with those of other organic or inorganic SERMs: while the ROS/RNS levels
are decreased, the NO level increase. The ability to form nanoparticles with bovine serum albumin opens the way to modern nanomedicine.
Keywords: breast cancer • molybdacarborane • tamoxifen • nitric oxide (NO) • nanoparticles
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