Relaxation of the rigid backbone of an oligoamide-foldamer-based α-helix mimetic: Identification of potent Bcl-xL inhibitors

Article abstract of DOI:10.1039/c2ob07125h

By conducting a structure-activity relationship study of the backbone of a series of oligoamide-foldamer-based α-helix mimetics of the Bak BH3 helix, we have identified especially potent inhibitors of Bcl-x_L. The most potent compound has a K_i value of 94 nM in vitro, and single-digit micromolar IC₅₀ values against the proliferation of several Bcl-x_L-overexpressing cancer cell lines. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2ob07125h

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COMMUNICATION
Relaxation of the rigid backbone of an oligoamide-foldamer-based α-helix
mimetic: identification of potent Bcl-xL inhibitors†
Jeremy L. Yap,a Xiaobo Cao,b Kenno Vanommeslaeghe,a Kwan-Young Jung,a Chander Peddaboina,b
Paul T. Wilder,c Anjan Nan,a Alexander D. MacKerell, Jr,a,d W. Roy Smytheb and Steven Fletcher*a,d
Received 18th December 2011, Accepted 31st January 2012
DOI: 10.1039/c2ob07125h
Over the last 10 years, many research groups have devised
their own α-helix mimetic scaffolds that present key side chains
in spatially similar loci to those adopted by the corresponding
“parent” side chains on one face of the native α-helix.10–15 Struc-
ture–activity relationship (SAR) studies of such α-helix mimetics
focus on the variation of the appendages that project from the
scaffold. However, an SAR analysis of the scaffold itself is
lacking. In this manuscript, we investigate the significance of the
backbone identity of a series of oligoamide-foldamer-based
α-helix mimetics, as evaluated by molecular modeling and
dynamics simulations, disruption of the Bak–Bcl-xL complex
in vitro and proliferation inhibition of Bcl-xL-overexpressing
cancer cells.
Proteins in the B-cell lymphoma (Bcl-2) family are critical
regulators of programmed cell death, or apoptosis.16 Bcl-xL and
Bcl-2 are two such family members that inhibit apoptosis; con-
versely, Bak and Bax are pro-apoptotic members. Bcl-xL is over-
expressed in many types of cancer,17 including mesothelioma,18
non-small cell lung19 and colon cancers,20 contributing to
tumour initiation and progression as well as to resistance to
chemo- and radiotherapies.21,22 Bcl-xL is able to inhibit Bak-
and Bax-mediated apoptosis by sequestering the proteins
through their B-cell homology 3 (BH3) “death” domains.16 The
Bak BH3 domain is α-helical, and, by NMR solution studies and
alanine scanning, it has been demonstrated that four hydrophobic
residues, Val74 (i), Leu78 (i + 4), Ile81 (i + 7) and Ile85 (i +
11), all of which lie on one face of the helix, are involved in
binding.23 The NMR solution structure of the Bak–Bcl-xL
complex (PDB ID: 1BXL) is shown in Fig. 1A, as is that of the
Bak BH3 α-helix in Fig. 1B. Towards the development of novel,
anti-cancer therapeutics, the disruption of the Bak–Bcl-xL inter-
action by small-molecule mimicry of the Bak BH3 α-helix is an
area of active research.7,9,24–29 Hamilton has achieved low
micromolar disruption of the Bak–Bcl-xL complex in vitro with
a synthetic α-helix mimetic (1; Fig. 1C) of the Bak BH3 domain
based on an oligoamide-foldamer strategy.9 Composed of three
identical pyridine-based subunits, the structure projects three iso-
propyl groups such that their relative positions effectively mimic
the side chains of Val74, Leu78 and Ile81.
By conducting a structure–activity relationship study of the
backbone of a series of oligoamide-foldamer-based α-helix
mimetics of the Bak BH3 helix, we have identified especially
potent inhibitors of Bcl-xL. The most potent compound has a
Ki value of 94 nM in vitro, and single-digit micromolar IC50
values against the proliferation of several Bcl-xL-overexpres-
sing cancer cell lines.
The field of α-helix mimicry, in which small-molecule scaffolds
are fashioned and appropriately functionalized to replicate the
positioning of specific side chains on one face of an α-helix, has
developed into a rational approach to disrupt protein–protein
interactions in contemporary medicinal chemistry.1–4 Pioneered
largely by Hamilton,5,6 α-helix mimicry has afforded inhibitors
of several therapeutically significant protein–protein interactions
6,7
that are mediated by α-helices, including Bak–Bcl-xL and
p53–HDM2.8 A variety of scaffolds has been designed, in par-
ticular the teraryls, the original of which is the 1,1′ : 4′,1′′-terphe-
nyl scaffold,6 wherein the ortho positions are functionalized with
appropriate side chains. This causes staggering of the rings
through steric interactions, leading to effective mimicry of the
i, i + 3/4 and i + 7 positions on one face of the α-helix. In
addition, Hamilton introduced the oligoamide-foldamer approach
to α-helix mimicry in which the integrity of the mimetic is main-
tained by the “folding” of the structure into an α-helical confor-
mation through the assembly of a network of bifurcated
hydrogen bonds.9
aDepartment of Pharmaceutical Sciences, University of Maryland
School of Pharmacy, 20 N Pine St, Baltimore, MD 21201, USA. E-mail:
sfletche@rx.umaryland.edu; Fax: +1 410 706 5017; Tel: +1 410 706
6361
bScott & White Memorial Hospital, 702 SW HK Dodgen Loop Room
219, Temple, TX 76504, USA
cDepartment of Biochemistry and Molecular Biology, University of
Maryland School of Medicine, 108 N Greene St, Baltimore, MD 21201,
USA
dUniversity of Maryland Marlene and Stewart Greenebaum Cancer
Center, 22 S Greene St, Baltimore, MD 21201, USA
†Electronic supplementary information (ESI) available: All synthetic
1
procedures, characterization data and H and 13C NMR spectra of inter-
A crystal structure of an analogue of 1 revealed that the pyri-
dine nitrogen atoms are engaged in bifurcated hydrogen bonds,9
rigidifying the backbone of the mimetic, whilst also inducing a
mediates 7–20f and final compounds 1–6; molecular dynamics simu-
lation data; procedures for the in vitro fluorescence polarization assay
and the XTT whole cell toxicity assay. See DOI: 10.1039/c2ob07125h
2928 | Org. Biomol. Chem., 2012, 10, 2928–2933
This journal is © The Royal Society of Chemistry 2012

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Fig. 1 A. PyMOL34 representation of the NMR solution structure of the Bak–Bcl-xL complex (PDB ID: 1BXL);23 Bcl-xL: uncharged amino acids in
grey, acidic residues in red, basic residues in blue; Bak BH3 peptide in green (coloured by atom type). B. The Bak BH3 α-helix (PDB ID: 1BXL),
illustrating the staggered arrangement of the key hydrophobic amino acids (highlighted as stick representations) and their location on the same face of
the helix. C. The structures of the picolinamide α-helix mimetic 1 and its benzamide analogue 2; dashed lines indicate hydrogen bonds; arrows indi-
cate hydrogen bond lengths studied.
Fig. 2 Probability distribution for the C-terminal bifurcated hydrogen
Fig. 3 Probability distribution for the C-terminal virtual dihedral angle
bond lengths in 1 and the analogous distances in 2, indicated by the
defined by (1) the ether oxygen of residue i, (2) its N-substituted aro-
arrows in Fig. 1c.
matic carbon, (3) the same N-substituted aromatic carbon of residue i +
4, and (4) the ether oxygen of residue i + 4 in compounds 1 (continuous
curve) and 2 (broken curve).
degree of curvature.30 However, it is not clear if such a constrain-
ing network of hydrogen bonds would be present under physio-
logical conditions. To examine this possibility, 50 ns molecular
its ether O. As is evident, the NH⋯N hydrogen bond is more
stable than the NH⋯O interaction; on the time scale of our MD
simulation, the former has no probability density above 3.1 Å,
while the latter has a significant probability corresponding to
non-hydrogen bonded conformations. The same plot for the N-
terminal bifurcated hydrogen bond is nearly identical, and the
plots for the NH⋯O distances in compound 2 are similar, except
that they are slightly broadened, which is probably a result of the
greater conformational flexibility associated with the loss of the
amide NH to pyridine N hydrogen bond that is present in 1.
We subsequently examined the solution-phase propensity of
compounds 1 and 2 for presenting the isopropyl ether groups in
the orientation required to mimic the i, i + 4 and i + 7 positions
of the Bak BH3 α-helix. Specifically, the virtual dihedral angle
defined by (1) the ether oxygen of residue i, (2) its N-substituted
dynamics (MD) simulations in explicit water were performed on
picolinamide 1 and the benzamide analogue 231 (Fig. 1C) –
the latter of which is incapable of forming intramolecular bifur-
cated hydrogen bonds – using the program CHARMM32 with
the CHARMM General Force Field.33 Computational details can
be found in the ESI.† Fig. 2 shows the calculated probability dis-
tribution for the C-terminal bifurcated hydrogen bond lengths in
1 and 2 (indicated by the arrows in Fig. 1C); the thin, continuous
line represents the hydrogen bond between the amide NH of
the C-terminal subunit of 1 and the central pyridine N, whilst the
thick, continuous line represents the hydrogen bond between the
same amide NH and its ether O. Similarly, the thin, broken line
represents the distance between the amide NH of 2 and the ana-
logous C of the central benzene ring, while the thick, broken line
represents the hydrogen bond between the same amide NH and
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Table 1 Measurements of selected distances and angles in Sattler
et al.’s Bak–Bcl-xL NMR structure23 compared to corresponding
average and median values from 50 ns MD simulations on compounds
1 and 2
angle in the oligoamide-foldamers; the full probability distri-
butions can be found in Fig. A in the ESI.† O1, O2 and O3
respectively correspond to the C-terminal, middle and N-term-
inal ether oxygens. The geometry of the O1–O2–O3 angle in
compound 1 is in good agreement with the V74Cα–L78Cα–
I81Cα angle in Bak. As a result of the increased conformational
flexibility, the average and median distances are uniformly too
large in compound 2, and the angle is significantly smaller,
bringing the O1–O2–O3 angle in 2 in closer agreement with the
V74Cα–L78Cβ–I81Cα angle in Bak. These data demonstrate that
both the rigid picolinamide 1 and the more flexible benzamide 2
are good mimetics of the orientation of the side chains being
projected from the Bak BH3 α-helix in aqueous solution.
Whilst both 1 and 2 present their side chains in orientations
that adequately mimic those adopted by Val74, Leu78 and Ile81
in the Bak–Bcl-xL structure, in terms of relative affinities we pos-
tulated that oligoamides of reduced rigidities (i.e. of increased
benzene-to-pyridine ratios) would afford Bcl-xL inhibitors of
greater potencies than the rigid oligoamide 1 for the following
reasons. Fig. 1B shows the staggered arrangement of the side
chains of the hydrophobic amino acids Val74, Leu78, Ile81 (and
Ile85) that occur on one face of the Bak BH3 α-helix. The side
chains of oligoamide 1, as a direct consequence of intramolecu-
lar bifurcated hydrogen bonding, are eclipsed rather than stag-
gered. It was anticipated that there would be a more favourable
enthalpic term with oligoamides of greater flexibilities/reduced
rigidities as they may more readily assume a (staggered) confor-
mation that maximizes interactions with the binding surface, a
phenomenon that may not be accessible to compounds whose
conformations are “locked” by bifurcated hydrogen bonds. In
addition, since the hydrophilic pyridine nitrogens may be poorly
tolerated in the hydrophobic crevice, it was anticipated that the
more hydrophobic the oligoamide, the more thermodynamically
favourable would be its binding to Bcl-xL.
Oligoamide-foldamera
Bak BH3 α-helix
1
2
V74Cα–L78Cα/Å 6.2
V74Cα–L78Cβ/Å 5.7
Average O1–O2/Å
Median O1–O2/Å
Average O2–O3/Å
Median O2–O3/Å
6.1 0.6
5.9
6.1 0.7
5.9
11.8 0.8 13.3 0.7
11.8
7.6 1.0
8.0
7.7 0.9
8.1
L78Cα–I81Cα/Å
L78Cβ–I81Cα/Å
V74Cα–I81Cα/Å
5.8
7.2
11.5 Average O1–O3/Å
Median O1–O3/Å
144
13.4
127 21
V74Cα–L78Cα–
I81Cα/°
Average O1–O2–O3/° 156 11
V74Cα–L78Cβ–
I81Cα/°
124
Median O1–O2–O3/° 157
125
a O1, O2 and O3 respectively correspond to the C-terminal, middle and N-
terminal ether oxygens in the oligoamide-foldamers. Averages are given the
corresponding standard deviation.
aromatic carbon, (3) the same N-substituted aromatic carbon of
residue i + 4, and (4) the ether oxygen of residue i + 4 was
measured. Fig. 3 shows the probability distribution of the C-
terminal instance of this virtual dihedral in compounds 1 and 2.
In the presence of the bifurcated hydrogen bond (Fig. 3: com-
pound 1, continuous curve), the conformation at 0° (i.e. with the
ether oxygen atoms pointing in the same direction) is strongly
favoured, and there is no sampling at 180°, although small
shoulders can be observed around 120° and 240°. Conversely,
without a bifurcated hydrogen bond (Fig. 3: compound 2,
broken curve), the dihedral between the two aromatic rings
essentially acts as a free rotor, with a relatively weak preference
towards 180°. Again, the same plot of the N-terminal virtual
dihedral is nearly identical (ESI†).
Finally, the propensity for the ether oxygen atoms in com-
pounds 1 and 2 to mimic the positions of the corresponding
atoms in Sattler et al.’s NMR structure of the Bak peptide in
complex with Bcl-xL (PDB ID: 1BXL)23 was studied by means
of measuring the distances and angles between these atoms.
Table 1 shows the average and median values for the O1–O2–O3
Design and synthesis
In order to investigate the SAR of the oligoamide scaffold, we
prepared the novel compounds 3, 4, 5 and 6, along with the pre-
viously synthesized compounds 1 9 and 2;31 their structures are
Fig. 4 Structures of the target molecules prepared in this study, along with their predicted log P values.35 Dashed lines indicate hydrogen bonds.
2930 | Org. Biomol. Chem., 2012, 10, 2928–2933 This journal is © The Royal Society of Chemistry 2012

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given in Fig. 4. The distribution of pyridine versus benzene
rings was selected to systematically control the extent of intra-
molecular hydrogen bonding in the proteomimetics, thereby con-
trolling the extent of conformational flexibility. The predicted
log P value of each compound, which is a measure of lipophili-
city/hydrophobicity, is also given.35 A simple retrosynthetic
analysis of the target molecules 1–6 reveals they can be accessed
from the conjugation of otherwise identical benzene and/or pyri-
dine monomers. The requisite benzene monomers 7 and 8 were
prepared as described previously (Scheme 1).31 Briefly, esterifi-
cation of the carboxylic acid of 3-hydroxy-4-nitrobenzoic acid
(9) gave methyl ester 10. Alkylation of the phenol with isopropyl
alcohol under Mitsunobu conditions furnished compound 11 in
excellent yield. Subsequently, saponification of the methyl ester
gave acid 7 quantitatively, whilst reduction of the nitro group
delivered aniline 8. The original route to prepare the pyridine
monomers 12 and 13 is lengthy9 and proceeds via a pyridone
functionality whose regioselective alkylation can be non-
trivial.36 Our alternative route (Scheme 2) is shorter, higher-
yielding and by-passes the potentially-problematic pyridone
stage. Furthermore, this chemistry works well with a wide range
of other alcohols,37 facilitating the development of future conge-
ners of the desired subunits. The key step in our approach is the
ortho-selective nucleophilic aromatic substitution (SNAr) of 2,6-
dichloropyridine (14) with sodium isopropoxide. We observed
excellent ortho-regiochemical control in non-polar solvents,
which we have ascribed to coordination of the sodium counter-
ion (which remains associated with the isopropoxide anion in
non-polar solvents) to the ortho nitro group as this would lead to
a cyclic, 6-membered transition state.37 A Stille coupling of 15
with (tri-n-butyl)vinyltin introduced a vinyl group para to the
nitro function (compound 16), which was then oxidatively
cleaved with KMnO4 to give acid 12. Esterification and
reduction as with the benzene subunit synthesis afforded the
final monomer 13.
Scheme 1 (a) SOCl2, MeOH, reflux, 12 h, 100%; (b) 1. isopropyl
alcohol, PPh3, THF, rt, 2 min; 2. DIAD, 16 h, 83%; (c) LiOH·H2O,
THF–MeOH–H2O, 3 : 1 : 1, rt, 1 h, 95%; (d) H2, 10% Pd/C, MeOH, rt,
16 h, 95%.
Scheme 2 (a) Isopropanol, NaH, toluene, 0 °C to rt, 16 h, 98%; (b) (n-
Bu)3SnCHvCH2, Pd(PPh3)4, DMF, 120 °C, 16 h, 91%; (c) KMnO4,
acetone–H2O, 1 : 1, rt, 12 h, 74%; (d) SOCl2, MeOH, reflux, 12 h,
100%; (e) SnCl2·2H2O, EtOAc, 50 °C, 12 h, 96%.
All target compounds, including the previously-reported mol-
ecules 1 and 2, were prepared through the assembly of either the
benzene subunits 7 and 8 and/or pyridine subunits 12 and 13 as
appropriate (Scheme 3). Couplings of carboxylic acids to ani-
lines were accomplished through the in situ-generated acid chlor-
ides with PPh3Cl2 to give the nitro dimers 17, which were
subsequently reduced to the corresponding anilines 18 in excel-
lent overall yields of more than 80%. The sequence of coupling-
reduction was repeated once more, followed by saponification of
the methyl esters to give the final molecules 1–6 in quantitative
yields.
Zhang et al. have previously described a fluorescence polariz-
ation (FP) competition assay using an FITC (fluorescein isothio-
cyanate)-N-terminus-labeled 16-mer Bak-BH3 peptide to
determine the Ki values of inhibitors of the Bcl-xL protein.38 We
conducted the assay as previously described, although a 6-ami-
nohexanoic acid (Ahx) spacer was added in between the N-
terminus of the Bak peptide and the FITC fluorophore so that the
fluorescent peptide used was FITC-Ahx-GQVGRQLAIIGD-
DINR-NH2. Titration of the fluorescent peptide with Bcl-xL
revealed its binding affinity (Kd) to be 12.5 nM, which is in
good agreement with the peptide lacking the Ahx linker.38
Results for the present compounds 1–6 in the competition assay
are reported in Table 2; Ki values were determined by entering
the appropriate IC50 value into the Cheng–Prusoff equation.39
The principal trend is that the stepwise replacement of the pyri-
dine subunits with benzene subunits led to an increase in Bcl-xL
inhibition, with the least potent compound picolinamide 1 (Ki =
970 nM) and the most potent compound benzamide 2 (Ki = 94
nM). Presumably, this is a consequence of the increased confor-
mational flexibility of 2, allowing it to better undergo more
favourable interactions with the Bcl-xL hydrophobic crevice, in
combination with its increased hydrophobicity. More particu-
larly, comparing the data for compounds 1 and 4, whose struc-
tures exhibit identical bifurcated hydrogen bonding, reveals a
three-fold improvement in Bcl-xL inhibition that must be attribu-
ted to the greater hydrophobicity of 4. Consistent with this are
the relative affinities of 5 and 6. Collectively, these data indicate
that the ability of an oligoamide-foldamer to form bifurcated
hydrogen bonds reduces its inhibitory activity against Bcl-xL,
and that the inclusion of hydrophilic nitrogen atoms on the
hydrophobic face is not tolerated.
We also evaluated the effects of our compounds in cancer
cells that harbour high expression levels of Bcl-xL. Since the
binding of our small-molecules to the hydrophobic BH3-binding
domain of Bcl-xL would disable its anti-apoptotic function, it is
This journal is © The Royal Society of Chemistry 2012
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Scheme 3 (a) PPh3Cl2, CHCl3, reflux, 2–12 h, 90–100%; (b) SnCl2·2H2O, EtOAc, 50 °C, 12 h, 83–100%; (c) NaOH, THF–MeOH–H2O, 3 : 1 : 1,
rt, 95–100%.
Table 2 Thermodynamic parameters for the disruption of the Bak–
Bcl-xL interaction by α-helix mimetics 1–6, as determined by an in vitro
fluorescence polarization (FP) assay
Table 3 Cell proliferation inhibition of several Bcl-xL-overexpressing
cell lines by α-helix mimetics 1–6, as determined by an XTT assay;
ND = not determined
Fluorescence polarization (FP, nM)
Cell line (IC50, μM)
Compound
IC50
Ki
Compound
DLD-1
I45
H1299
A549
1
2
3
4
5
6
2139 387
207 11
297 217
738 326
394 54
970 176 (23009)
94.0 5.0
135 98
335 148
179 24
1
2
3
4
5
6
2.0 0.1
9.2 0.8
4.3 0.1
4.1 0.3
2.2 0.1
3.9 0.7
1.1 0.1
4.4 0.9
ND
28
2
22
53
5
1
7
0.1
17
48
2
5
64 10
4.2 0.1
ND
ND
11
6.3 0.7
5.2 0.8
1
584 163
265 74
ND
ND
anticipated that these small-molecules would induce apoptosis in
these cell lines. The cancer cell lines investigated were DLD-1
(colon cancer),40 I45 (mesothelioma),41 H1299 (non-small cell
lung cancer)19 and A549 (adenocarcinoma).19 Briefly, cells were
incubated with various concentrations of the compounds for
72 h, then cell viability was determined by conducting an XTT
assay (ESI†). The data in Table 3 clearly demonstrate that most
oligoamides were potent inhibitors of the proliferation of Bcl-xL-
overexpressing cell lines, particularly compounds 1, 2 and 5,
with minimal toxicity towards untransformed human lung micro-
20 μM inhibitor, compound 1 was twice as cytotoxic as 2 and 5.
Since the pro-apoptotic protein Bak had been silenced, these
findings suggest that the increased cytotoxicity of 1 was due to
the antagonism of biological targets other than the Bak–Bcl-xL
complex. Furthermore, at lower doses, analogous experiments
with Bcl-xL siRNAs led to increased cytotoxic sensitivities to
the oligoamides 1, 2 and 5, relative to cells treated with control
siRNAs, indicating that these compounds have anti-apoptotic
protein targets in addition to Bcl-xL. Poor specificity should not
necessarily be considered as detrimental, however, since it is
anticipated that inhibiting several anti-apoptotic proteins should
potentiate a small-molecule’s anti-tumour activity.43
In conclusion, we have investigated the significance of the
backbone identity of a series of oligoamide-foldamer-based
α-helix mimetics in the context of disruption of the Bak–Bcl-xL
complex through effective mimicry of the Bak BH3 α-helix. The
present results indicate that oligoamides of greater benzene-to-
pyridine ratios are more potent Bcl-xL inhibitors. This appears to
be a consequence of both a greater capacity to assume more
favourable binding conformations, through a reduction of intra-
molecular bifurcated hydrogen bonding, as well as presenting
increased hydrophobic surfaces that better complement the Bcl-
xL hydrophobic crevice. Our compounds were also effective at
inhibiting the proliferation of cancer cells that overexpress Bcl-
xL. Other proteins of the Bcl-2 family, specifically Bcl-2 and
Mcl-1, are also up-regulated in various cancers.19,20 ABT-737 is
an especially potent Bcl-2/Bcl-xL inhibitor but demonstrates
vascular endothelial cells (HMVEC; 1: IC50 = 19 μM, 2: IC50
=
28 μM, 5: IC50 = 36 μM). However, the whole cell data do not
mirror the in vitro FP data. In particular, oligoamide 1, which
was the least potent in vitro, was consistently the most cytotoxic.
This may be a consequence of differences in cell uptake. More-
over, since our inhibitors are rather simple molecules whose
activities are presumably dominated by hydrophobic–hydro-
phobic interactions, it is likely that these compounds suffer from
a variety of off-target effects, which may further explain the dis-
parity between the in vitro and whole cell evaluations. For
example, analogous to Bcl-xL, the related Bcl-2 proteins Bcl-2
(e.g. PDB ID: 2XA0) and Mcl-1 (e.g. PDB ID: 3PK1),23 as well
as the non-Bcl-2 family member HDM2 (e.g. PDB ID:
1YCR),42 all possess a hydrophobic crevice that recognizes the
hydrophobic face of its α-helix protein partner. To investigate
this further, we transfected Bak siRNAs into A549 cells, and
evaluated the cytotoxic effects of compounds 1, 2 and 5. At
2932 | Org. Biomol. Chem., 2012, 10, 2928–2933
This journal is © The Royal Society of Chemistry 2012

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limited activity against Mcl-1.25,44 It is expected that small-mol-
ecule BH3 mimetics that bind only Bcl-2 and Bcl-xL but not
Mcl-1 might lead to resistant tumors through high expression
levels of Mcl-1, and this has, indeed, been observed with
ABT-737.44 Therefore, future work is aimed at developing pan-
Bcl-2 inhibitors using a structure-based design strategy that
includes modeling of protein–BH3 α-helix mimetic interactions.
Our results will be reported in due course.
19 H. Zhang, S. Guttikonda, L. Roberts, T. Uziel, D. Semizarov, S.
W. Elmore, J. D. Leverson and L. T. Lam, Oncogene, 2011, 30, 1963.
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21 J. M. Adams and S. Cory, Oncogene, 2007, 26, 1324.
22 J. M. Adams and S. Cory, Science, 1998, 281, 1322.
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Acknowledgements
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We are grateful to Prof. Jean-Marie Hardwick (Johns Hopkins
University) for the generous gift of Bcl-xL. We thank the Univer-
sity of Maryland School of Pharmacy (SF), the University of
Maryland Computer-Aided Drug Design Center (ADM), the
American Association of Colleges of Pharmacy (AACP) New
Pharmacy Faculty Research Award (SF) and NSF CHE-0823198
(ADM) for financial support of this work. Additionally, these
studies were supported by the Center for Biomolecular Thera-
peutics, the University of Maryland School of Medicine and the
Institute for Bioscience and Biotechnology Research.
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