An evaluation of Minor Groove Binders as anti-lung cancer therapeutics

Article abstract of DOI:10.1016/j.bmcl.2016.06.040

A series of 47 structurally diverse MGBs, derived from the natural product distamycin, was evaluated for anti-lung cancer activity by screening against the melanoma cancer cell line B16-F10. Five compounds have been found to possess significant activity, more so than a standard therapy, Gemcitabine. Moreover, one compound has been found to have an activity around 70-fold that of Gemcitabine and has a favourable selectivity index of greater than 125. Furthermore, initial studies have revealed this compound to be metabolically stable and thus it represents a lead for further optimisation towards a novel treatment for lung cancer.

Full text of DOI:10.1016/j.bmcl.2016.06.040

Bioorganic & Medicinal Chemistry Letters 26 (2016) 3478–3486
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
An evaluation of Minor Groove Binders as anti-lung cancer
therapeutics
b
a
c
b
Fraser J. Scott a, , Mireia Puig-Sellart , Abedawn I. Khalaf , Catherine J. Henderson , Gareth Westrop ,
⇑
David G. Watson b, Katharine Carter b, M. Helen Grant c, Colin J. Suckling a
a WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, United Kingdom
b Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, United Kingdom
c Department of Biomedical Engineering, University of Strathclyde, Wolfson Centre, Glasgow G1 0NW, United Kingdom
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 47 structurally diverse MGBs, derived from the natural product distamycin, was evaluated for
anti-lung cancer activity by screening against the melanoma cancer cell line B16-F10. Five compounds
have been found to possess significant activity, more so than a standard therapy, Gemcitabine.
Moreover, one compound has been found to have an activity around 70-fold that of Gemcitabine and
has a favourable selectivity index of greater than 125. Furthermore, initial studies have revealed this
compound to be metabolically stable and thus it represents a lead for further optimisation towards a
novel treatment for lung cancer.
Received 28 May 2016
Revised 14 June 2016
Accepted 15 June 2016
Available online 16 June 2016
Keywords:
Minor Groove Binders
Anti-cancer
Ó 2016 Elsevier Ltd. All rights reserved.
Lung cancer
Cancer is a major health problem responsible for approximately
13% of the deaths worldwide. The incidence is estimated to be
around 13 million cases a year, according to WHO.1 In particular,
lung cancer is one of the most frequent cancers causing around
1.4 million deaths per annum. The treatment of lung cancer is
based on chemotherapy and/or surgery. However, surgery is
limited to those tumours with peripheral location. Other types of
tumours with a more difficult access, such as small-cell lung
cancer, are generally treated with chemotherapeutic agents. A
first-line chemotherapy treatment is a platinum based combina-
tion of cisplatin or carboplatin with etoposide or irinotecan.2 The
mechanism of action of platinum based compounds is localised
at the major groove of the DNA where the drug interferes with
the genetic transcription. These modifications result in variations
in the product from crucial genes involved in cell-cycle replications
and finally induce cell apoptosis. Nonetheless, treatment with
many traditional anticancer drugs, such as cisplatin, is related to
drug resistances and unsuccessful therapeutic outcome. Therefore,
the need of new anticancer compounds that could overcome those
resistances by binding to the smaller groove of the DNA.3
Our approach at the University of Strathclyde has been to
diversify the structure of the first discovered MGB, distamycin,
and to generate a portfolio of significantly active Strathclyde Minor
Groove Binders (S-MGBs). We can now design novel S-MGBs with
tailored activities through
a detailed understanding of DNA
binding, sequence selectivity, and physicochemical characteristics
(Fig. 1).
Deviations from the distamycin structure have included tuning
the basicity (pKa) of the tail group amidine at the C-terminus, the
addition of larger alkyl side chains and the introduction of thiazole
rings. Aromatic rings replaced the distamycin formyl group and,
importantly, the N-terminal amide was replaced by its isosteric
alkene.5 These structural changes systematically modified the
physicochemical properties to increase hydrophobic contacts with
the target DNA resulting in a library of highly potent compounds
displaying distinct biological activities. The physicochemical
aspects of this design hypothesis were investigated in detail and
shown to lead to strong DNA binding driven largely by enthalpic
interactions.6 Furthermore, studies suggest that the physicochemi-
cal properties of MGBs substantially determine their net uptake into
target cells. Our knowledge in this area has led to the discovery of a
family of compounds with significant anti-Gram-positive bacterial
activity, the most active of which, MGB-BP-3, has successfully
completed Phase I clinical trials for the treatment of Clostridium
difficile infections. Furthermore, other S-MGBs have been shown to
be active against Trypanosoma both in cell-based studies and in
mouse models of disease and leishmaniasis.7
Minor Groove Binders (MGBs) are a class of compound that
specifically, and reversibly, bind to the minor groove of DNA. They
recognise specific base sequences of DNA with high selectivity and
achieve efficacy by interfering with transcription factors and
altering gene expression.4
⇑
Corresponding author.
http://dx.doi.org/10.1016/j.bmcl.2016.06.040
0960-894X/Ó 2016 Elsevier Ltd. All rights reserved.

F. J. Scott et al. / Bioorg. Med. Chem. Lett. 26 (2016) 3478–3486
3479
Tail
H2N
N
Head
H
O
NH2
NH
N
O
HN
HN
H
N
H
N
O
N
HN
O
H
N
N
O
O
O
N
N
N
O
DNA-binding region
Distamycin
MGB-BP-3
Figure 1. Distamycin and our lead Gram-positive antibacterial compound, MGB-BP-3.
As a class of compounds, S-MGBs are not inherently cytotoxic:
structural alterations away from that of distamycin led to
anti-infective compounds with favourable selectivity indices.14
Despite the lack of class specific toxicity, some S-MGBs inhibit
the growth of lung cancer cells. This paper describes the evaluation
of a panel S-MGBs as potential lung cancer therapeutics.
HN
Cl
NH2
Cl
N
HN
O
NH
N
HN
O
H
The compounds synthesised for this investigation are typical of
S-MGBs in general. They include compounds with amide, amidine,
or alkene linked head groups with a range of polar and non-polar
features, N-alkyl pyrroles, a standard feature of Minor Groove
Binders, C-alkyl thiazoles, a specific feature of S-MGBs, and tertiary
amine tail groups with a variety of basicities (Fig. 3). These struc-
tural variations give rise to a set of compounds with a wide range
of physicochemical properties and DNA-binding specificity.15
Synthesis of these MGBs was achieved in a modular fashion,
initially building from the C-terminus, tail group end, of the mole-
cule and ending with a coupling reaction to attach the head group.
The synthesis of many of the compounds under study in this letter
has been published previously7 and that of the novel compounds
can be found in the Electronic supplementary information as the
synthetic methods are similar.
All MGBs were purified by HPLC to give a final purity greater
than 98%. Table 1 shows the structures of the MGBs that were
investigated in this study.
In this study the melanoma cancer cell line B16-F10, which
quickly metastases to the lungs, was used for initial screening. This
cell line was derived from pulmonary metastatic cells isolated from
the lungs of mice after ten successive passages of B16 sub-lines.16
The original B16-F10 cell line was transfected with firefly lucifer-
ase gene to develop the B16-F10-luc murine melanoma cell line
(BiowareÒ B16-F10-luc-G5, Caliper Life Sciences; Hopkinton,
N
N
O
N
O
Figure 2. Tallimustine.
Distamycin itself does not possess significant cytotoxicity;
however, other classes of MGB have displayed significant potential
as anti-cancer agents, most notably those which are directly derived
from the distamycin framework. Tallimustine (Fig. 2) in which the
formyl head group of distamycin has been replaced with a benzoic
acid mustard (BAM) moiety displays high activity against various
murine tumors and human xenografts. Most other BAM compounds
alkylate and cross-link within DNA’s major groove; however, with
the minor groove binding affinity conferred by the distamycin
framework, tallimustine has been shown to preferentially
monoalkylate the 30-adenine-N3 atom of 50-TTTTGA-30 sequences
in the minor groove.8 In distamycin type molecules, increasing the
number of pyrroles is linked to an increase in DNA binding affinity
and this is true of tallimustine where an increase to four pyrroles
significantly increases the cytotoxicity.9,10 Development of
tallimustine was promising as phase I and II clinical trials demon-
strating significant antitumor, but notably myelotoxicity led to
the phase II clinical development being halted.11–13
MeO
MeO
NH
N
O
N
O
H
N
NH
NH2
H
NH
H
O
O
N
N
N
O
O
MeO
H
N
NH
NH
H
N
N
H
O
Me
NH
N
N
H
N
O
N
HN
Me
N
Me
O
H
N
N
O
S
N
N
Figure 3. Exemplars of the structural variations in the S-MGB set investigated in this study.

Table 1
S-MGBs evaluated in this study
S-MGB
Structure
S-MGB
Structure
S-MGB
O
O
N
F
NH
HN
N
O
N
HN
H
N
H
N
N
HN
H
N
HN
1
17
33
O
H
N
H
N
N
O
H
N
O
N
O
O
N
O
O
S
N
N
O
N
O
N
S
N
O
N
O
N
N
NH
N
HN
H
HN
N
HN
O
HN
2
18
34
H
N
H
N
N
O
H
N
O
O
HN
O
N
N
O
N
N
O
O
F
MeO
O
O
N
O
N
N
HN
H
NH
N
O
O
3
19
35
HN
N
N
O
HN
H
S
H
N
H
N
N
O
O
HN
O
N
O
N
N
O
N
O
N
N
N
O
O
N
H
N
HN
N
O
H
N
N
N
O
4
20
36
O
HN
N
NH
O
S
O
N
O
HN
H
N
N
O
N
O
O
N
Cl
N
O
N
S
N
N
H2N
N
HN
H
N
N
H
HN
O
N
H
NH
N
O
5
21
37
N
N
HN
H
N
N
O
N
O
O
O
H
N
O
S
HN
O
N
O
N
O
N

Table 1 (continued)
S-MGB
Structure
S-MGB
Structure
S-MGB
O
O
H2N
S
N
CF3
N
N
N
H
N
HN
N
N
HN
N
O
N
O
H
N
O
HN
O
NH
N
N
HN
6
22
38
O
O
N
H
N
O
HN
O
N
O
N
F3C
O
N
N
N
O
O
NH
O
N
HN
H
N
O
HN
N
HN
N
H
N
O
N
H
N
O
O
NH
7
23
39
O
N
N
H
N
HN
O
N
O
N
O
N
N
O
O
MeO
N
N
HN
H
N
NH
HN
N
HN
N
O
N
O
O
NH
S
H
8
24
40
O
HN
N
N
O
O
N
H
HN
S
N
O
O
N
O
N
O
O
O
N
NH
O
O
N
S
N
HN
H
N
HN
9
25
26
H
41
42
H
N
N
H
N
H
N
O
O
N
O
O
O
N
O
N
N
N
N
O
O
O
O
O
N
O
N
MeS
N
HN
N
N
N
10
H
N
O
HN
HN
HN
O
H
H
N
N
N
H
N
N
H
N
O
O
O
N
O
O
N
S
N
N
O
O
(continued on next page)

Table 1 (continued)
S-MGB
Structure
S-MGB
Structure
S-MGB
N
O
N
N
H
N
NH
N
HN
S
HN
HN
HN
O
11
27
43
HN
N
S
H
N
O
H
N
N
H
N
HN
O
MeO
O
H
N
HN
O
N
H
N
O
N
N
O
HN
O
N
N
O
N
O
O
O
O
N
N
O
N
N
N
N
12
28
44
HN
H
N
HN
HN
H
N
H
N
H
N
H
N
H
O
O
O
N
O
N
O
O
N
N
N
N
N
O
O
O
Cl
Cl
O
O
N
O
N
NH
NH2
N
N
N
NH
N
HN
HN
O
HN
H
N
13
29
45
H
H
N
N
H
H
O
O
O
N
N
HN
O
N
O
N
N
N
N
O
O
O
N
O
O
O
Cl
O
NH
NH2
O
N
N
N
Cl
HN
HN
NH
H
N
H
N
14
30
46
O
HN
H
N
H
N
O
O
O
O
N
N
H
O
N
N
N
N
HN
O
O
O
N
O
N
F3C
O
MeO
O
O
O
N
N
N
N
NH
HN
HN
H
HN
15
31
47
H
N
N
H
N
HN
O
H
N
H
O
N
O
N
N
N
O
N
O
O
N
HN
O
N
O
O
N
N
O
O
N
O
H
N
N
HN
HN
16
32
HN
H
NH
N
N
H
N
O
HN
H
N
HN
O
N
S
N
O
N
O
N
O

F. J. Scott et al. / Bioorg. Med. Chem. Lett. 26 (2016) 3478–3486
3483
Table 2
The effect of treatment with different MGBs compounds on the proliferation of B16-F10-luc cells
MGB
Inhibition (% SD)
LogD7.4
MGB
Inhibition (% SD)
LogD7.4
MGB
Inhibition (% SD)
LogD7.4
1
2
3
4
5
6
7
8
NA
NA
NA
53 7.3
NA
NA
NA
40 26
NA
19 47
57.12 11.48*
30.92 28.62
16.13 8.45
NA
0.18
ꢀ2.42
2.77
6.51
7.56
1.90
0.80
4.97
0.56
4.99
2.22
3.15
2.39
3.15
1.48
3.81
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
46 0.43
37 17
NA
NA
NA
4.11
4.11
4.11
2.59
1.08
3.86
4.85
2.29
3.81
2.83
3.41
3.51
4.04
4.04
3.51
2.12
33
34
35
36
37
38
39
40
41
42
43
44
45
46
88 3.1***
55 26
55 24
69 14**
57 2.5*
2.2 6.9
72 4.4**
59 13*
76 5.1**
74 12**
NA
4.50
3.92
4.06
4.56
0.93
1.27
4.37
3.26
4.24
2.95
ꢀ1.74
ꢀ1.13
ꢀ0.48
0.50
NA
77 5.7*
34 4.7
NA
9
10
11
12
13
14
15
16
44 10
34 5.4
83 3.5***
84 3.4***
NA
NA
67 12
***
84 3.8
85 2.9
***
NA
54.10 9.16
77 12**
Cells (3.7 ꢁ 105 cells/well) were incubated for 24 h in the presence of medium containing DMSO (solvent control, 2.44% v/v DMSO) or different MGBs compounds (15.36
lg/
ml with 2.44% v/v DMSO). The effect of treatment on cell proliferation is shown as the mean percentage inhibition of n = 3 experiments compared to the mean solvent control
where NA is not active (*p 6 0.05, **p 6 0.01 and ***p 6 0.001 comparing bioluminescence of the cells treated with MGBs with the cells with solvent control). LogD7.4 predicted
using the software MarvinSketch (Version 15.6.29.0, ChemAxon, http://www.chemaxon.com).
USA). The integration of this gene allows disease progression to be
monitored by luciferin-luciferase bioluminescence imaging.17 46
compounds from the S-MGB library were tested at a single
concentration of 15 lg/mL for their ability to inhibit the growth
of B16-F10-luc cells. The bioluminescence emitted from the cells
treated with MGBs was compared to the bioluminescence emitted
for the solvent control cells to establish a baseline (Table 2).
S-MGBs have been extensively investigated as anti-infective
agents, initially as antibacterial and more recently as antiparasitic
agents.7 Two key properties of S-MGBs characterise their biological
activity, namely DNA binding and access to cells. Most S-MGBs are
based on the distamycin structure and thus possess an affinity
towards DNA binding; however, it is access to cells that has been
found to be the most important factor explaining activity, and
selective toxicity. For example, S-MGBs possess very strong
anti-Gram-positive activity but little anti-Gram-negative activity
and this appears principally to be due to efflux from Gram-negative
cells. Since S-MGBs show anti-Gram-negative activity in the
presence of efflux pump inhibitors it is possible that efflux is the
chief cause of the lack of activity in this class of bacteria. The action
of efflux pumps on S-MGBs appears to be related to their
physicochemical properties and it is thus likely that these will be
important in explaining anti-lung cancer activity. To this end,
logD7.4 was predicted using the software MarvinSketch (Version
15.6.29.0, ChemAxon, http://www.chemaxon.com), in an attempt
to gain some insight into the differences in activity. These results,
alongside the activity data, are presented in Table 2.
Figure 4. LogD7.4 versus % inhibition of B16-F10-luc cells. LogD7.4 predicted using
the software MarvinSketch (Version 15.6.29.0, ChemAxon, http://www.chemax-
on.com). Dotted box shows clustering of active compound around logD7.4 range of
3–5.
this subset of compounds has been shown to in general to lack
antibacterial activity, further evidence of differential activity
profiles for S-MGBs (manuscript submitted).
In an effort to explain the observed activities by considering the
physicochemical properties of S-MGBs, logD7.4, as a measure of
lipophilicity, was plotted against the% inhibition of B16-F10-luc
cells (Fig. 4). It is clear that lipophilicity, measured by logD7.4, alone
cannot explain the activities of this set of S-MGBs; however, the
most active compounds are clustered within a logD7.4 range of
3–5. The importance of lipophilicity is neatly explained through
compounds 45, 44, 26 and 28–31, which all contain the same
4-methoxyphenyl-2-pyridylethenyl head group. 45 and 44 have
basic amidine and dimethylamino tail groups, giving them very
low logD7.4 values (ꢀ0.48 and ꢀ1.13, respectively) and no activity.
The morpholino tail group in 26, with a logD7.4 of 2.83, gives a
moderate activity of 44% inhibition and further increasing the
lipophilicity by inclusion of a branched alkyl side chain (28–31,
logD7.4 3.51 and 4.04) affords an excellent inhibition of around
84%.
The data shown in Table 2 indicate that this selection of S-MGBs
contains both significantly active and inactive compounds with
respect to B16-F10 cells. It is significant that in this set of S-MGBs
none of those bearing an amide linked head group has any appre-
ciable activity against the B16-F10 cell line. Many of the inactive
compounds in this set have shown appreciable activity against
other disease targets: many have moderate antibacterial properties
with MICs around 10 lM; and, 45 has been shown to be
significantly active in a mouse model of Trypanosoma congolense
(manuscript submitted). This illustrates that the structure and
physicochemical properties of S-MGBs influence their activity
profiles against different organisms and cells. Compounds 34–41
represent a subset of short length S-MGBs having one pyrrole ring
less than the others. A greater number of pyrrole rings usually
correlates to greater DNA binding affinity and in many contexts
greater activity; therefore, it is interesting to note that these
shorter compounds still are active against B16-F10 cells. Moreover,
The % inhibition data was used to select a number of active
compounds with a variety of structural features. For example,
compound 28 was chosen to represent compounds 28 to 33 as
these all possess the same core structure but differ in their alkyl
side chain. The mean IC50 was determined for compounds 23, 28,

3484
F. J. Scott et al. / Bioorg. Med. Chem. Lett. 26 (2016) 3478–3486
Table 3
Given the significant activity of compound 23, which contains an
unusual trifluoromethyl substituent, the initial screening data were
scrutinised for information that could prompt the design of a
compound with greater activity. Compound 25 had no activity in
the initial screen; however, compound 33, with an isopropyl instead
The mean half maximal inhibitory concentration (IC50) values for different MGBs
compounds tested against B16-F10-luc cells
MGB
IC50
(
l
M
SD)
LogD7.4
Gemcitabine
11.0 1.7
0.16 0.01
0.81 0.08
1.1 0.51
10.4 0.50
2.2 0.22
ND
23
28
33
42
47
4.85
3.51
4.50
2.95
5.45
of a methyl side chain, had an IC50 of 1.1
importance of this simple alteration. The isopropyl side chain also
appears in compound 35, (IC50 of 0.81 M), and although its methyl
lM, highlighting the
l
side chain analogue, 26, was active (44% growth inhibition), there is
still a substantial increase associated with the presence of the iso-
propyl group. This prompted the design of compound 47 which is
an analogue of the most active compound, 23, but with the inclusion
The values shown are from three experiments and three replicates were used for
each concentration tested in each experiment.
of the isopropyl side chain. However, 47 (IC50 of 2.16 lM) was
13-fold less active than 23. With the inclusion of the isopropyl
group, the lipophilicity of compound 47 (logD7.4 = 5.45) is notably
higher than that of 23 (logD7.4 = 4.85), suggesting that a logD7.4 less
than 5 is required for optimal cellular activity. Nonetheless, with an
activity approximately 70-fold greater than Gemcitabine, com-
pound 23 is a significant find. Compound 23 has also been shown
to have no appreciable activity in any of our routine screens against
fungi, bacteria or parasites. Moreover, we have previously reported
compound 23 to have no measureable toxicity against HEK cells at
N
O
N
N
HN
H
N
O
HN
O
N
N
O
20 l
M thus giving a satisfactory selectivity index of >125.7 This
Figure 5. Compound 48, a fluorescent probe S-MGB.
discovery encouraged the further investigation of the biological
action of S-MGBs in the context of anti-lung cancer therapeutics,
in particular compound 23’s potential for further development.
Minor Groove Binders that have seen use previously as anti-
cancer agents are often modified with an DNA-alkylating moiety,
such as in tallimustine. DNA binding is thus a plausible mechanism
33 and 42 (Table 3). In these studies, Gemcitabine, a drug com-
monly used to treat cancer, was used as the positive control. 23,
28, and 33 had a smaller IC50 than Gemcitabine (p 6 0.05; Table 3)
whereas 42 had similar activity to Gemcitabine.
Figure 6. Fluorescence microscopy of B16/FO/Luc cells treated with S-MGB compound 48. Cells were exposed to various concentrations of the S-MGB for 1 hr and examined
under an inverted fluorescent microscope using the X20 objective with brightfield and UV or DAPI filter sets. Row (a), 3 g/ml compound 48; (b), 30 g/ml compound 48; (c)
DMSO only; (d), 250 M Hoechst 33342. Similar results were obtained in two experiments with separately prepared cells.
l
l
l

F. J. Scott et al. / Bioorg. Med. Chem. Lett. 26 (2016) 3478–3486
3485
Aliqots of the medium of the hepatocyte incubations were
extracted at 15 min, 60 min and 24 h and analysed by LC–MS in
order to further assess the stability of these compounds and to
identify any metabolites. Figure 8 shows the extracted ion trace
for the 15 min aliqot.
Compound 23 showed only around 1% metabolism, estimated
from the peak heights of the metabolites relative to the parent
compound, over the 24-hour monitoring period of the experiment,
the vast majority of this occurring within the first 15 min. The m/z
of the metabolites are 665.2703 and 681.2653 and thus likely
correspond to a mono and di-hydroxylated analogue of compound
23, which has a m/z of 649.2749. From these data, compound 23
can be concluded to be particularly stable over a sufficiently long
time period to be deemed appropriate for further development.
This study has indicated the importance of the activity profile of
S-MGBs and serves to provide further evidence that subtle struc-
tural variations can influence the activity profiles of compounds
within this class. A sub-set of S-MGBs has been identified which
have significant activity against a lung cancer cell line, more so
than a current treatment option, Gemcitabine. As a class, we have
also demonstrated that a plausible mechanism of action for
S-MGBs on mammalian cells is through DNA binding.
Figure 7. Phase contrast images of hepatocyte monolayers exposed to DMSO
control (left) and 7.5 compound 23 for 60 min (right). Zeiss Axiovision
l
M
Fluorescence microscope, ꢁ20 wet lens (N/A 0.5). There was no evidence of drug
uptake during 24 h exposure using either green, red or blue filter settings.
These general findings have allowed us to select one compound,
which is around 70-fold more active than Gemcitabine in our
in vitro assay, and possesses a favourable selectivity index of
>125 against the HEK cell line. Moreover, we have demonstrated
its stability in a hepatocyte model and thus identified this
compound as worthy for further development as an anti-lung
cancer therapeutic.
Figure 8. Extracted ion traces for compound 23 and its hydroxy and dihydroxy
metabolites (mets).
of action for this class of minor groove binder. In the case of other
classes of Minor Groove Binders, principally anti-infective agents
including S-MGBs, an alternative mechanism of action has been
suggested that involves cell membrane permeabilisation.18
S-MGBS that have strong affinities for DNA tend to also have strong
antibacterial properties and more recently, we have found that
significantly active S-MGBs gain access to both bacterial cells and
parasites, where nuclear localisation is observed.7 However, pene-
tration into mammalian cells has not yet been observed for any
significantly active and non-toxic S-MGB that has undergone
extensive investigation as anti-infective agents.19,20 To understand
better the behaviour of S-MGBs in mammalian cells the strongly
fluorescent probe S-MGB (48) was used in fluorescence microscopy
studies (Fig. 5).
Acknowledgements
The authors wish to thank Gavin Bain, Patricia Keating and
Craig Irving for their assistance during this study and also MGB
Biopharma for helpful discussions in the development of MGBs.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2016.06.
040.
To assess intracellular localisation in mammalian cells, B16-FO
References and notes
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l
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