Characterization of anticancer properties of 2,6-diisopropylphenol-docosahexaenoate and analogues in breast cancer cells

Article abstract of DOI:10.1016/j.bmc.2010.01.045

The present study describes the characterization and evaluation of novel anticancer conjugates, 2,6-diisopropylphenol-docosahexaenoate (PP-DHA), and its analogues including 2,4-diisopropylphenol-docosahexaenoate (DIPP-DHA), 2-isopropylphenol-docosahexaenoate (IPP-DHA), 2-cyclohexanephenol-docosahexaenoate (CHP-DHA) and phenol-docosahexaenoate (P-DHA) on breast cancer cell lines. Representative breast cancer cell lines, based on estrogen α receptor (ER) and oncogene Her-2 expression, were used and include MDA-MB-231 (ER-negative, Her-2-negative), MCF-7 (ER-positive, Her-2-negative) AU565 (ER-negative, Her-2-positive) and MDA-MB-361 (ER-positive, Her-2-positive). The PP-DHA conjugate significantly inhibited cell growth and induced cell loss in the breast cancer cell lines similarly; however, this conjugate was not effective against normal mammary epithelial cells. The effect of various conjugates were in PP-DHA > IPP-DHA > DIPP-DHA > CHP-DHA >> P-DHA order. PP-DHA and IPP-DHA conjugates were stable in human and mouse serum. Furthermore, the non-hydrolyzable amide-linked conjugate analogues affected breast cancer cells in a manner similar to that of the ester-linked conjugates. This suggests that ester-linked PP-DHA and IPP-DHA conjugates were stable during treatment to breast cancer cells due to structural hindrance. PP-DHA did not affect PPARα or PPARγ activities but its anticancer effects appear to be mediated in part though the inhibition of histone deacetylase (HDAC) activity. Further experiments are needed to confirm their molecular target and to test the effectiveness of these compounds in an in vivo model for their anticancer properties. In conclusion, these results suggest that the novel PP-DHA and IPP-DHA conjugates and their amide derivatives may be useful for the treatment of breast cancer.

Full text of DOI:10.1016/j.bmc.2010.01.045

Bioorganic & Medicinal Chemistry 18 (2010) 1866–1874
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Characterization of anticancer properties of 2,6-diisopropylphenol–
docosahexaenoate and analogues in breast cancer cells
Kevin A. Harvey a, Zhidong Xu a,b, Phillip Whitley a, V. Jo Davisson b, Rafat A. Siddiqui a,c,
*
a Cellular Biochemistry Laboratory, Methodist Research Institute, Clarian Health Partners, Inc., 1800 N. Capital Ave., Indianapolis, IN 46202, USA
b Department of Medicinal Chemistry and Molecular Pharmacology, Bindley Bioscience Center at Purdue Discovery Park, 1203 W. State Street, West Lafayette, IN 47907, USA
c Department of Medicine, Indiana University School of Medicine, 545 Barnhill Dr., Indianapolis, IN 46202, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The present study describes the characterization and evaluation of novel anticancer conjugates,
2,6-diisopropylphenol–docosahexaenoate (PP–DHA), and its analogues including 2,4-diisopropylphe-
nol–docosahexaenoate (DIPP–DHA), 2-isopropylphenol–docosahexaenoate (IPP–DHA), 2-cyclohexan-
ephenol-docosahexaenoate (CHP–DHA) and phenol–docosahexaenoate (P–DHA) on breast cancer cell
Received 16 December 2009
Revised 15 January 2010
Accepted 16 January 2010
Available online 25 January 2010
lines. Representative breast cancer cell lines, based on estrogen
a receptor (ER) and oncogene Her-2
expression, were used and include MDA-MB-231 (ER-negative, Her-2-negative), MCF-7 (ER-positive,
Her-2-negative) AU565 (ER-negative, Her-2-positive) and MDA-MB-361 (ER-positive, Her-2-positive).
The PP–DHA conjugate significantly inhibited cell growth and induced cell loss in the breast cancer cell
lines similarly; however, this conjugate was not effective against normal mammary epithelial cells. The
effect of various conjugates were in PP–DHA > IPP–DHA > DIPP–DHA > CHP–DHA >> P–DHA order. PP–
DHA and IPP–DHA conjugates were stable in human and mouse serum. Furthermore, the non-hydrolyz-
able amide-linked conjugate analogues affected breast cancer cells in a manner similar to that of the
ester-linked conjugates. This suggests that ester-linked PP–DHA and IPP–DHA conjugates were stable
Keywords:
Docosahexaenoic acid
2,6-Diisopropylphenol
Lipid-drug conjugates
Breast cancer
Histone deacetylase
during treatment to breast cancer cells due to structural hindrance. PP–DHA did not affect PPAR
a or
PPAR activities but its anticancer effects appear to be mediated in part though the inhibition of histone
c
deacetylase (HDAC) activity. Further experiments are needed to confirm their molecular target and to test
the effectiveness of these compounds in an in vivo model for their anticancer properties. In conclusion,
these results suggest that the novel PP–DHA and IPP–DHA conjugates and their amide derivatives may
be useful for the treatment of breast cancer.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
Several investigations have pursued the synthesis and testing of
novel compounds by conjugating naturally occurring lipids with
One of the basic concerns for successful and effective use of
anticancer therapeutics, which act on intracellular targets, is the
propensity for uptake by tumors and cellular retention. While tar-
geting through receptor-mediated endocytosis has shown utility,
many drugs cross the plasma membrane through either existing
transport systems, pinocytosis and/or diffusion to elicit the cellular
actions. A common approach to enhancing the cellular uptake and
membrane transport is to link drugs to lipophilic carriers.1–3 Doco-
sahexaenoic acid (22:6, DHA), a long chain dietary polyunsaturated
fatty acid has recently been the subject of numerous studies used
as a fatty acid of choice for conjugating drugs. This compound also
possesses moderate anticancer activities against a variety of can-
cers and shows synergy in pre-clinical models when used in com-
bination with certain drugs.4–9
known cancer chemotherapeutics. For example, chlorambucil-fatty
acid conjugates (including DHA) were synthesized and tested on
human lymphoma cell lines.3 The conjugates selectively inhibited
the growth of neoplastic lymphocytes with minimal effects on qui-
escent lymphocytes.3 More extensive studies have been conducted
with a paclitaxel-DHA ester-conjugate (TaxoprexinÒ), which has
been shown to behave as a prodrug in vivo.10–12 Pre-clinical testing
of this agent demonstrated antitumor activity in a mouse lung can-
cer model. In addition, enhanced pharmacokinetic and tissue dis-
tribution properties were observed that appear to lead to
improved efficacy with respect to paclitaxel alone. Early stage clin-
ical results have warranted continued Phase II trials as a single
agent. Other exploratory studies have been done with DHA conju-
gates to enhance the bio-availability and activity of the anticancer
drug methotrexate (MTX).2 More recently, conjugates of camptote-
cin with unsaturated fatty acids were developed as anticancer
agents13 and Ojima and co-workers have conjugated taxoids with
* Corresponding author. Tel.: +1 317 962 6941.
E-mail addresses: rsiddiqu@clarian.org, rasiddiq@iupui.edu (R.A. Siddiqui).
0968-0896/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2010.01.045

K. A. Harvey et al. / Bioorg. Med. Chem. 18 (2010) 1866–1874
1867
DHA to induce antitumor effects in drug resistant human colon tu-
mor xenografts in DLD-1 mice.14 A final example shows a DHA-
doxorubicin conjugate with improved anticancer efficacy over free
doxorubicin in an experimental animal model of L1210 leukemia
and B16 melanoma.15
in the presence of 2-(1H-7-azabenzotriazol-1-yl)-1,1,3,3-tetra-
methyl uronium hexafluorophosphate methanaminium (HATU)
and diisopropyl ethyl amine (DIEA) in the presence of inert condi-
tion at room temperature. The amide conjugates were purified by
flash chromatography on a silica gel column with a yield of 66–
90%. The structure of the phenolic-fatty acids conjugates are de-
picted in Scheme 2.
While these studies demonstrate the utility of a polyunsatu-
rated fatty acid ester for prodrugs to enhance efficacy of cancer
chemotherapy, there is a lack of examples of chemicals that utilize
an enhanced DHA effect on cancer cells. This is despite the epidemi-
ological evidence for dietary DHA leading to reduced risks of certain
cancers. In addition, the mechanism of cancer cell inhibition by
DHA remains unclear. One strategy that recently employed the con-
jugation of DHA with 2,6-diisopropylphenol (propofol)-DHA and
2,6-diisopropylphenol–EPA conjugates resulted in enhanced anti-
cancer activities against breast tumor cell lines.16 The selection of
propofol was based upon the fact that it is known to be a well tol-
erated and non-toxic anesthetic that has shown some elements of
being an anti-metastatic agent in pre-clinical models.17 Both conju-
gates exhibited anticancer effects that include the inhibition of cell
migration and adhesion and the induction of apoptosis within
MDA-MB-231 breast cancer cells. The present study focuses on
establishing the chemical features responsible for the enhanced
anticancer activity of DHA. In addition, the chemosensitivity of a
panel of breast cancer cell lines to a series of conjugates as well bio-
chemical studies have been investigated in an effort to understand
the mode of action of the conjugates. Our studies suggest that
2,6-diisopropylphenol–DHA is the most effective compound in
comparison to other analogues and that cleavage of the ester link-
age is not required for the cellular activity. The conjugates are also
stable in both human and mouse serum. The overall effects of these
compounds are not attributed to a major re-distribution of the lipid
components of the plasma membrane. The anticancer effects of the
conjugates appear to be mediated in part through the inhibition of
histone deacetylase (HDAC) activity.
2.2. Characterization of 2,6-diisopropylphenol–docosahexano-
ate and its analogues
The formation of the 2,6-diisopropylphenol–docosahexanoate
and its analogues were confirmed with 1H, 13C NMR and HR MS.
2.2.1. Compound 1: 2,6-diisopropylphenyl-docosahexaenoate
(PP–DHA)
The PP–DHA conjugate was purified by chromatography on a
preparative thin layer silica gel. The compound was eluted with
95:5 hexane/ethyl acetate as a colorless oil. The yield was 80.5%.
1H NMR (CDCl3)
d 1.02 (tri, 3H, J = 7.5 Hz), 1.24 (d, 12H,
J = 6.9 Hz), 2.12 (m, 2H), 2.62 (m, 2H), 2.74 (m, 2H), 2.84–3.00
(m, 12H), 5.38–5.44 (m, 10H), 5.53 (tri, 2H, J = 4.7 Hz), 7.18–7.25
(m, 3H); 13C NMR (CDCl3) d 14.2, 20.5, 22.8, 25.5, 25.6, 27.5, 34.0,
123.8, 126.4, 127.0, 127.7, 127.8, 127.9, 128.0, 128.2, 128.3,
128.5, 129.7, 132.0, 140.2, 145.5, 171; Mass spectrum (ESI), m/z
489.3738 (M+H)+ (C34H48O2 + H+ requires 489.3733).
2.2.2. Compound 2: 2,4-diisopropylphenyl-docosahexaenoate
(DIPP–DHA)
The DIPP–DHA conjugate was purified by chromatography on a
preparative thin layer silica gel. The compound was eluted with
95:5 hexane/ethyl acetate as a colorless oil. The yield was 94%.
1H NMR (CDCl3) d 1.00 (tri, 3H, J = 7.5 Hz), 1.23 (d, 6H, J = 6.9 Hz),
1.27 (d, 6H, J = 6.9 Hz), 2.11 (m, 2H), 2.57 (m, 2H), 2.67 (m, 2H),
2.82–2.94 (m, 10H), 3.02 (m, 2H), 5.36–5.45 (m, 10H), 5.50 (m,
2H,), 6.92 (d, 1H, J = 8.3 Hz), 7.24 (tetr, 2H, J = 8.3, J = 2.1 Hz), 7.16
(d, 1H, J = 2.1 Hz); 13C NMR (CDCl3) d 14.2, 20.5, 22.8, 22.9, 25.5,
25.6, 27.4, 33.8, 34.2, 121.8, 124.3, 124.6, 127.0, 127.6, 127.8,
128.0, 128.2, 128.5, 128.0, 129.6, 131.9, 139.4, 145.9, 146.5,
171.8; Mass spectrum (ESI), m/z 489.3731 (M+H)+ (C34H48O2 + H+
requires 489.3733).
2. Chemistry
2.1. Synthesis of 2,6-diisopropylphenol–docosahexanoate and
its analogues
2,6-Diisopropylphenol–docosahexanoate and its analogues
were synthesized with a one step reaction procedure as described
previously16 and outlined in Scheme 1.
2.2.3. Compound 3: 2-isopropylphenyl-docosahexaenoate
(IPP–DHA)
The fatty acid anhydride was formed through a 1,3-dicyclohex-
ylcarbodiimide (DCC) dehydration under an anhydrous condition,
which is then reacted with the hydroxyl group of 2,6-diisopropyl-
phenol or its analogues through a catalyzed esterification in the
present of N,N-dimethylpyridin-4-amine (DMAP). These ester-con-
jugates were isolated and purified through normal phase silica gel
chromatography with a yield of 74–94%.16 The amides of 2,6-diiso-
propylphenol its analogues were prepared similarly by amidation
The IPP–DHA conjugate was purified by chromatography on a
preparative thin layer silica gel. The compound was eluted with
95:5 hexane/ethyl acetate as a colorless oil. The yield was 91%.
1H NMR (CDCl3) d 1.02 (tri, 3H, J = 7.5 Hz), 1.25 (d, 6H, J = 7.0 Hz),
2.13 (m, 2H), 2.59 (m, 2H), 2.69 (m, 2H), 2.87–3.00 (m, 10H),
3.08 (m, 1H), 5.36–5.45 (m, 10H), 5.53 (m, 2H,), 7.04 (m, 1H),
7.24 (m, 2H), 7.34 (m, 1H); 13C NMR (CDCl3) d 14.3, 20.5, 22.8,
2
2
2
2
Scheme 1. Chemical reactions for synthesis of 2,6-diisopropylphenol–docosahexaenoate and its analogues.

1868
K. A. Harvey et al. / Bioorg. Med. Chem. 18 (2010) 1866–1874
O
O
O
O
O
O
O
O
Compound 1
Compound 2
Compound 3
2-Isopropylphenyl-
docosahexaenoate
(IPP-DHA)
Compound 4
2-Cyclohexylphenyl-
docosahexaenoate
(CHP-DHA)
2,6-Diisopropylphenyl- 2,4-Diisopropylphenyl-
docosahexaenoate
(PP-DHA)
docosahexaenoate
(DIPP-DHA)
H
N
H
N
H
N
O
O
O
O
O
Compound 8
Phenyl-
Compound 5
Phenyl-
Compound 7
2-Isopropylphenyl-
docosahexaenoamide
(IPA-DHA)
Compound 6
2,6-Diisopropylphenyl-
docosahexaenoamide
(DIPA-DHA)
docosahexaenoamide
(A-DHA)
docosahexaenoate
(P-DHA)
Scheme 2. Structure of 2,6-diisopropylphenol (analogues)–fatty acid conjugates.
22.9, 25.5, 25.6, 27.3, 34.2, 122.2, 126.2, 126.6, 127.0, 127.6, 127.8,
127.9, 128.0, 128.2, 128.3, 128.5, 129.7, 131.9, 140.0, 148.1, 171.6;
Mass spectrum (ESI), m/z 447.3267 (M+H)+ (C31H42O2 + H+ requires
447.3263).
23.5, 23.6, 25.6, 25.4, 25.5, 25.6, 28.3, 28.6, 36.3, 123.3, 123.8,
126.9, 127.8, 127.9, 128.0, 128.1, 128.2, 128.5, 128.8, 129.0,
129.5, 131.1, 131.9, 146.2, 171.7; Mass spectrum (HR ESI), m/z
488.3888 (M+H)+ (C34H49O2 requires 488.3892).
2.2.4. Compound 4: 2-cyclohexylphenyl-docosahexaenoate
(CHP–DHA)
2.2.7. Compound 7: 2-isopropylphenyl–docosahexaenoamide
(IPA–DHA)
The CHP–DHA conjugate was purified by chromatography on a
preparative thin layer silica gel. The compound was eluted with
95:5 hexane/ethyl acetate as a colorless oil. The yield was 81%.
1H NMR (CDCl3) d 0.99 (tri, 3H, J = 7.4 Hz), 1.31 (m, 2H), 1.39 (m,
4H), 1.80 (m, 5H), 2.09 (m, 2H), 2.58 (m, 2H), 2.67 (m, 2H), 2.83–
2.91 (m, 10H), 5.32–5.45 (m, 10H), 5.50 (m, 2H,), 6.99 (m, 1H),
7.20 (m, 2H), 7.31 (m, 1H); 13C NMR (CDCl3) d 14.2, 20.5, 22.8,
25.5, 25.6, 26.1, 26.9, 29.6, 30.2, 33.2, 34.2, 37.7, 122.2, 126.1,
126.5, 126.9, 127.1, 127.5, 127.8, 127.9, 128.0, 128.2, 128.3,
128.5, 129.7, 132.0, 139.2, 148.1, 171.7; Mass spectrum (ESI), m/z
487.3758(M+H)+ (C34H46O2 requires 487.3751).
The IPA–DHA conjugate was purified by chromatography on a
preparative thin layer silica gel. The compound was eluted with
92:8 hexane/ethyl acetate as a colorless oil. The yield was 66%.
1H NMR (CDCl3) d 0.98 (tri, 3H, J = 7.5 Hz), 1.23 (d, 6H, J = 6.9 Hz),
2.08 (m, 2H), 2.45 (m, 2H), 2.51 (m, 2H), 2.81–2.87 (br., m, 10H),
3.01 (m, 1H), 5.31–5.41 (br, m, 10H), 5.46 (m, 2H), 7.18 (m, 3H),
7.28 (m, 1H), 7.61 (m, 1H); 13C NMR (CDCl3) d 14.2, 20.5, 23.0,
23.4, 25.4, 25.5, 27.8, 37.1, 125.1, 125.5, 126.1, 126.2, 126.9,
127.8, 127.9, 128.0, 128.2, 128.3, 128.5, 128.7, 129.6, 131.9,
133.9, 140.7, 171.0; Mass spectrum (HR ESI), m/z 446.3428
(M+H)+ (C31H43O2 requires 446.3423).
2.2.5. Compound 5: phenyl–docosahexaenoate (P–DHA)
The P–DHA conjugate was purified by chromatography on a
preparative thin layer silica gel. The compound was eluted with
95:5 hexane/ethyl acetate as a colorless oil. The yield was 92%.
1H NMR (CDCl3) d 0.98 (tri, 3H, J = 7.5 Hz), 2.08 (m, 2H), 2.55 (m,
2H), 2.64 (m, 2H), 2.82–2.86 (br., m, 10H), 5.30–5.40 (br, m,
10H), 5.48 (m, 2H,), 7.09 (m, 2H), 7.25 (m, 1H), 7.38 (m, 2H); 13C
NMR (CDCl3) d 14.2, 20.5, 22.7, 25.5, 25.6, 34.2, 121.5, 124.8,
125.7, 126.9, 127.5, 127.8, 127.9, 128.0, 128.2, 128.3, 128.5,
129.3, 129.6, 132.0, 150.6, 171.5; Mass spectrum (ESI), m/z
404.2718 (M+H)+ (C28H36O2 + H+ requires 404.2715).
2.2.8. Compound 8: characterization of phenyl–docosahexae-
noamide (A–DHA)
The A–DHA conjugate was purified by chromatography on a
preparative thin layer silica gel. The compound was eluted with
90:10 hexane/ethyl acetate as a colorless oil. The yield was 90%.
1H NMR (CDCl3) d 0.98 (tri, 3H, J = 7.5 Hz), 2.08 (m, 2H), 2.41 (m,
2H), 2.49 (m, 2H), 2.81–2.86 (br., m, 10H), 5.33–5.44 (br, m,
12H), 7.08 (m, 1H), 7.27 (m, 2H), 7.51 (m, 2H), 7.74 (s, 1H); 13C
NMR (CDCl3) d 14.2, 20.5, 23.3, 25.5, 25.6, 37.3, 119.9, 124.1,
126.9, 127.8, 127.9, 128.0, 128.2, 128.3, 128.5, 128.8, 129.5,
131.9, 137.9, 170.9; Mass spectrum (HR ESI), m/z 404.2955
(M+H)+ (C28H37O2 requires 404.2953).
2.2.6. Compound 6: 2,6-diisopropylphenyl–docosahexaenoa-
mide (DIPA–DHA)
3. Results
The DIPA–DHA conjugate was purified by chromatography on a
preparative thin layer silica gel. The compound was eluted with
92:8 hexane/ethyl acetate as a colorless oil. The yield was 67%.
1H NMR (CDCl3) d 0.98 (tri, 3H, J = 7.6 Hz), 1.19 (m, 12H), 2.09
(m, 2H), 2.48 (m, 2H), 2.52 (m, 2H), 2.82–2.89 (m, 10H), 3.05–
3.08 (m, 2), 5.37–5.46 (m, 12H), 6.91(s, 1H), 7.18 (d, 2H,
J = 7.7 Hz), 7.29 (m, 1H); 13C NMR (CDCl3) d 14.2, 20.5, 22.3, 22.5,
3.1. Characterization of 2,6-diisopropylphenol–docosahexae-
noate and its analogues
All the proton and carbon signals from both moiety of fatty acid
and aromatic ring in the conjugate come up in the 1H and 13C NMR
spectrum, and all the HR MS spectrum data show the target

K. A. Harvey et al. / Bioorg. Med. Chem. 18 (2010) 1866–1874
1869
conjugates were formed. Furthermore, when NMR signal in 2,6-
a
125
100
75
diisopropylphenol–docosahexaenoate was compared with the par-
ent compounds, the hydroxyl proton signal in 2,6-diisopropylphe-
nol at about 4.82 ppm was disappeared, and the 13C signal of the C-
1 was shifted upfield from 149.9 ppm to 145.5 ppm, while its 13C
signal of the C-2 and C-6 were shifted downfield from 133.6 ppm
to 140.2 ppm, indicating that the ester bond was formed at the
C-1 hydroxyl group of the propofol.
50
25
0
-25
-50
-75
-100
3.2. Conjugation of 2,6-diisopropylphenol and its derivatives
with DHA induce cellular toxicity to MDA-MB-231 breast cancer
cells
DHA
Consistent with previous reports, MDA-MB-231 cell growth was
inhibited by DHA in a dose-dependent manner (Fig. 1a), while sig-
nificant cell loss was not observed at concentrations less than
0
5
5
5
10
15
20
20
20
25
25
25
30
Concentration [µM]
25
on growth inhibition and cell loss. Only one compound, CHP, had
limited reduction in growth at the highest concentration
screened (25 M), which showed no indication of any cell loss.
lM. Figure 1b depicts the effect of the individual compounds
b
125
100
75
a
l
The effect of the DHA conjugates varied dramatically as shown in
Figure 1c. Data points near ‘‘0” indicate overall viable cell activity
neither increased nor decreased from treatment initiation; how-
ever, data points falling below 0 denote a loss of cell viability prior
to treatment initiation. P–DHA conjugate demonstrated no signifi-
cant deviation from the vehicle-treated cell population. In stark
contrast, PP–DHA conjugate invoked remarkable growth inhibition
and cell loss in a dose-dependent manner. IPP–DHA, DIPP–DHA
and CHP–DHA conjugates were effective in inhibiting MDA-MB-
231 cell growth and inducing cell loss in a dose-dependent man-
ner; nonetheless, the effectiveness of these three conjugates was
intermediate.
In order to determine if the conjugate effectiveness was simply
a result of their hydrophobicity to permit more efficient cellular
incorporation, we assessed the conjugates’ ability to inhibit growth
(IC50 and total growth inhibition) in relationship to their hydro-
phobicity values. A summary of these findings can be found in
Table 1. If hydrophobicity alone was responsible for the dramatic
effect on MDA-MB-231 cells, then the DIPP–DHA and CHP–DHA
conjugates should mirror the observations produced upon PP–
DHA conjugate-treated cells. Clearly, these findings are not consis-
tent with this hypothesis.
50
25
0
PP
-25
-50
-75
-100
IPP
DIPP
CHP
P
0
10
15
30
Concentration [µM]
c
125
100
75
50
25
0
We utilized this growth assay to determine if the decrease in
MDA-MB-231 cell growth and the increase in cell cytotoxicity were
a result of an additive effect of DHA in combination with either PP
or IPA (Fig. 2). DHA, PP, IPP, and the combination of these com-
-25
-50
-75
-100
PP-DHA
IPP-DHA
DIPP-DHA
CHP-DHA
P-DHA
pounds (5
characteristics compared to vehicle treatment, while both PP–DHA
and IPP–DHA conjugates (10 M) displayed significant cell toxicity.
lM each) resulted in no significant alterations in growth
0
10
15
30
l
Concentration [µM]
This observation excludes the possibility of an enhanced DHA com-
binatorial effect on growth inhibition and cell cytotoxicity; further-
more, the DHA conjugates exert a novel mechanism thereby
inhibiting MDA-MB-231 cell growth and inducing cytotoxicity.
In addition to inhibiting MDA-MB-231 cell growth, cell viability
appeared to be significantly compromised in the DHA conjugate-
treated cells. We investigated whether or not these treatments in-
duced apoptosis by labeling the cells with Annexin V FLUOS in
combination with propidium iodide to ascertain the extent of
apoptosis and/or necrosis following 24 h of treatment. Healthy
cells do not stain positive for Annexin V or incorporate propidium
iodide into their nuclei. Apoptotic cells, which accumulate phos-
phatidylserine on the outer leaflet of the plasma membrane, do
bind Annexin V in the presence of excess calcium. Propidium io-
dide serves as a discriminate to differentiate between apoptotic
and necrotic cells. Table 2 summarizes the apoptotic classification
of MDA-MB-231 cells following a 24 h treatment with the DHA
Figure 1. Conjugation of 2,6-diisopropylphenol and its derivatives with DHA
induces cellular toxicity to MDA-MB-231 breast cancer cells. Breast cancer MDA-
MB-231 cells (5000 cells/well) were cultured for 18 h in DMEM complete medium
in 96 well flat bottom tissue culture plates to establish a linear growth rate. At this
stage a subset of established wells were used to determine cellular growth (X)
(baseline at day 0) by administering WST-1 reagent (10
in other wells was replaced with DMEM supplemented with 2% FBS and treatment
conditions (100 total volume/well) for growth inhibition assessment. Cell
lL/well), whereas medium
l
L
cultures were maintained for 48 h at 37 °C in a humidified atmosphere containing
5% CO2. WST-1 reagent was added and readings were used to calculate growth
inhibition or cell loss based on baseline readings. Vehicle controls (ethanol) served
as the non-treated control was used for total cell growth (Y). The cell growth (Z) was
normalized to 100% using formula [(Y À X/X) Ã 100]. Effects of conjugates were
determined in comparison to Z values. Values from 100 to 0 indicate cell growth
inhibition whereas
0
to À100 indicates cell death. Results are expressed as
mean SD for at least four experiments. Compounds tested included 2,6-diisopro-
pylphenol–docosahexaenoate (PP–DHA), 2,4-isopropylphenol–docosahexaenoate
(IPP–DHA), 2,4-diisopropylphenol–docosahexaenoate (DIPP–DHA), 2-cyclohexyl-
phenol-docosahexaenoate (CHP) and phenol–docosahexaenoate (P–DHA).

1870
K. A. Harvey et al. / Bioorg. Med. Chem. 18 (2010) 1866–1874
Table 1
Table 2
Relation of the hydrophobicity of the conjugates to growth inhibition of MDA-MB-231
cells
Analysis of apoptotic and necrotic effects of the compounds
Viable
Apoptotic
Necrotic
Conjugates Hydrophobicity
Growth inhibition
Growth inhibition
(total, lM)
Vehicle (1% EtOH)
89.0 1.0
90.3 2.2
87.6 1.0
1.8 0.3
2.1 0.3
1.8 0.4
9.2 0.8
7.6 1.9
10.7 0.8
(Log p)
(IC50
,
lM)
DHA
1 lM
PP–DHA
DIPP–DHA
CHP–DHA
IPP–DHA
P–DHA
11.3 0.6
11.3 0.6
11.1 0.6
10.0 0.6
8.6 0.6
2.9
7.3
8.4
8.2
>25
4.2
10
l
M
12.6
18.7
12.1
>25
PP
1
lM
90.9 1.6
88.2 3.4
2.0 0.4
2.4 0.6
7.1 1.3
9.4 2.9
10
lM
PP–DHA
IPP
1
10
lM
90.5 1.6
37.4 0.1
1.8 0.2
22.2 0.1
7.7 1.4
40.4 0.1
*
*
*
*
*
lM
Hydrophobicity values (Log p) of the compounds were calculated using ChemDraw
10.0 (CambridgeSoft, Cambridge, MA, USA). Values for growth inhibition were
derived from the data presented in Figure 1.
*
1
lM
93.7 1.1
88.8 1.1
1.5 0.7
2.2 0.3
4.9 0.8
9.0 0.9
10
lM
IPP–DHA
1
lM
89.6 1.5
36.2 0.6
1.8 0.3
26.4 1.1
8.6 1.8
37.5 0.5
10
lM
*
*
conjugates or the individual compounds. DHA, PP, and IPP demon-
strated very limited variation in the percentage of apoptotic and
necrotic cells in comparison to vehicle-treated cells. Both PP–
DHA and IPP–DHA conjugates (10 lM) significantly induced a pop-
ulation shift by a majority of the cells into apoptosis and necrosis
Cells (1.5 Â 105) were treated with DHA, PP, IPP, PP–DHA and IPP–DHA as described
in the legends of Figure 1. After treatment, cell pellets were resuspended in Annexin
V FLUOS/Propidium iodide labeling solution, which was prepared as described by
the manufacturer. Cell analysis was performed on a FACSCalibur flow cytometer
(Becton Dickinson, San Jose, CA) equipped with an air-cooled argon laser emitting at
a 488 nm wavelength. Fluorescence was detected through a 530 nm band pass filter
and quantified using CellQuest Software (Becton Dickinson, San Jose, CA).
within the 24 h treatment. This confirms not only are the MDA-
MB-231 cells growth inhibited by 10 lM DHA conjugate treatment,
cell loss is emanate within 24 h of treatment.
DIPA–DHA conjugate was the most effective amide conjugate,
which inhibited 50% of the cell growth at 3.7
inhibited cell growth at 5.5 M. IPA–DHA conjugate significantly
impaired cell growth of MDA-MB-231 cells as well (IC50—6.5
and total growth inhibition—8.5 M). Importantly, the A–DHA
conjugate did not induce a growth inhibitory effect. Clearly, these
non-hydrolyzable aniline-conjugates closely mimicked their phe-
nolic-ester counterparts, which further suggest a certain degree
of stability within the conjugates.
lM and completely
3.3. Propylphenolic–DHA conjugates are stable during treat-
ment to MDA-MB-231 cells
l
lM
l
In order to check the stability of the conjugates in blood, we
incubated the conjugates with human and mouse serum at 37 °C
for 2 h. Presence of DHA and 2,6-diisopropylphenol from the hydro-
lysis of conjugates were then determined in the lipid extract by
HPLC. When comparing the retention time of the DHA and the con-
jugates with the corresponding reference standard, there were no
detectable DHA or 2,6-diiospropylphenol peaks from PP–DHA or
IPP–DHA in both mouse and human serum (Supplementary data).
In order to further insure that the PP–DHA is not readily hydro-
lyzed, we synthesized DHA conjugates using aniline-derivatives of
PP, IPP and P. The aniline-conjugates 2,6-diisopropyl aniline–DHA
(DIPA–DHA), 2-isopropyl aniline–DHA (IPA–DHA) and aniline–
DHA (A–DHA) responded similarly to their phenolic-ester counter-
parts in MDA-MB-231 growth inhibition and cell loss (Fig. 3).
3.4. Effect of propylphenolic–DHA conjugates on different
breast cancer cell lines
As an extension of the findings with the MDA-MB-231 (ER-neg-
ative, Her-2 negative) cell line, representative breast cancer cell
lines, based on estrogen
a receptor (ER) and oncogene Her-2
expression, were chosen to determine the efficacy of the DHA con-
jugates, PP–DHA and IPP–DHA, in comparison to the individual
Vehicle
DHA (5 µM)
PP (5 µM)
PP + DHA
PP-DHA (10 µM)
*
IPP (5 µM)
IPP + DHA
IPP-DHA (10 µM)
*
-100
-50
0
50
100
Growth inhibition
(% total)
Figure 2. Propylphenolic and DHA compounds alone or combined are less potent then conjugated propylphenolic–DHA derivatives. Effect of DHA, PP, IPP alone and in
combination along with PP–DHA and IPP–DHA conjugate were determined on breast cancer MDA-MB-231 cells are as described in the legend of Figure 1. Results are
*
expressed as the mean SD four experiments and analyzed using Student t tests. An ‘ ’ represents significance at p <0.05.

K. A. Harvey et al. / Bioorg. Med. Chem. 18 (2010) 1866–1874
1871
150
125
100
75
DHA conjugate cancer cell inhibition. Figure 4 is a compilation of
the growth inhibition and cytotoxicity assay results for (a) MCF-7
(ER-positive, Her-2 negative); (b) MDA-MB-361 (ER-positive,
Her-2 positive); (c) AU565 (ER-negative, Her-2 positive); (d)
HMEC. The individual compounds, PP and IPP, did not dramatically
effect the growth of any cell line or provide any evidence of cyto-
50
toxicity at concentrations up to 25 lM. Conversely, the DHA conju-
25
gates, PP–DHA and IPP–DHA, significantly inhibited the growth of
MCF-7, MDA-MB-361 and AU565 cell lines and demonstrated signs
of cytotoxicity within each cell line. While both DHA conjugates
were effective, the PP–DHA conjugate was more efficient in all
breast cancer cell lines tested. Notably, the normal epithelial cells
were virtually unaffected by the individual compounds or the
0
-25
-50
-75
-100
DIPA-DHA
IPA-DHA
A-DHA
DHA conjugates at concentrations up to 25 lM.
0
5
10
15
20
25
30
Concentration [µM]
3.5. Fatty acid analysis of cells-treated with DHA conjugates
Figure 3. Non-hydrolyzable propylphenolic–DHA conjugates induce similar effects
on MDA-MB-231cells. The amide derivatives of PP, IPP and were used to
synthesize 2,6-diisopropyl aniline–DHA (DIPA–DHA), 2-isopropyl aniline–DHA
(IPA–DHA) and aniline–DHA (A–DHA). Growth inhibition effect on MDA-MB-231
cells was determined as described in the legends of Figure 1. Results are expressed
as the mean SD of four experiments.
In order to further evaluate if DHA is hydrolyzed from conju-
gates, we determined the concentration of DHA in MDA-MB-231
cells after treating them with DHA, PP–DHA or DIPA–DHA conju-
gates alone or DHA with PP–DHA or DIPA–DHA conjugates. The re-
sults shown in Figure 5a,b indicate that the similar concentration
of DHA was found in cell on either DHA alone or DHA + PP–DHA
or DIPA–DHA treatments. Furthermore, the concentration of DHA
in cell does not increase over controls when cells were treated with
conjugates alone.
P
compounds in terms of inhibiting growth and/or invoking cell loss.
Importantly, primary normal human mammary epithelial cells
(HMEC) were utilized as a control to insure specificity of the
A
B
150
150
125
100
75
50
25
0
125
100
75
50
25
0
-25
-25
DHA
PP
PP-DHA
IPP
DHA
PP
-50
-50
-75
PP-DHA
-75
IPP
IPP-DHA
IPP-DHA
-100
-100
-125
-125
0
5
10
15
20
25
30
0
5
10
15
20
25
30
Concentration [µM]
Concentration [µM]
C
D
150
125
100
75
175
150
125
100
75
50
50
25
25
0
0
-25
-50
-75
-100
-125
DHA
PP
PP-DHA
IPP
IPP-DHA
-25
-50
-75
-100
-125
DHA
PP
PP-DHA
IPP
IPP-DHA
0
5
10
15
20
25
30
0
5
10
15
20
25
30
Concentration [µM]
Concentration [µM]
Figure 4. Effect of propylphenolic–DHA conjugates on different breast cancer cell lines. PP–DHA and IPP–DHA conjugates along with free DHA, PP and IPP were tested on (A)
MCF-7, (B) MDA-MB-361, (C) AU565, and (D) normal mammary epithelial cells as described in the Figure 1 legend. Results are expressed as the mean SD of four
experiments.

1872
K. A. Harvey et al. / Bioorg. Med. Chem. 18 (2010) 1866–1874
60
50
40
30
20
10
0
a
110
100
90
80
70
DHA
PP
60
50
PP-DHA conjugate
0
5
10
15
20
25
30
DHA (10µM)
+
PP-DHA (5µM)
Vehicle
DHA (10µM)
PP-DHA (5µM)
Concentration [µM]
Figure 6. 2,6-Diisopropylphenol–DHA target histone deacetylase activity. MDA-
MB-231 breast cancer cells were treated for 2 h at 37 °C with varying concentra-
tions of the PP–DHA conjugate, DHA alone or PP alone in DMEM supplemented with
2% FBS. The histone deacetylase (HDAC) activity in the cell lysates was performed as
described by the manufacturer. An inhibitor of HDAC activity, trichostatin A, was
utilized to determine maximum inhibition in order to adjust for non-specific assay
readings. Data was expressed as the percentage of total HDAC activity.
60
50
40
30
20
10
0
b
times diarrhea. Previous attempts have been made to increase
bio-efficacy of n-3 PUFAs by making their ethyl esters. These fatty
acid esters are effective against cardiovascular diseases18 and have
been commercially marketed under various brand names. We de-
signed n-3 PUFAs-esters with phenolic derivatives. Our previous
study indicates that phenolic esters are far more efficacious than
free n-3 PUFAs against breast cancer. The present study is an elab-
oration of our previous work to demonstrate stabilities and cellular
effects of various analogues of phenolic–DHA conjugates.
DHA (10µM)
+
DIPA-DHA (5µM)
Vehicle
DHA (10µM)
DIPA-DHA (5µM)
We conjugated phenolic analogues with DHA using both ester
and amide bonds. The esterified phenolic–DHA conjugate include
PP–DHA, DIPP–DHA, CHP–DHA, IPP–DHA and P–DHA, whereas
the amidified conjugates include DIPA–DHA, IPA–DHA and
A–DHA. These conjugates were positively identified and character-
ized using 1H and 13C NMR and HR MS spectrum. We assayed the
effect of these conjugates on growth inhibition and cell death. The
effect of phenolic–DHA conjugates was similar in different breast
cancer cell lines irrespective of their expression of ER and Her2;
however, the conjugate was not effective against normal
mammary epithelial cells. Our data demonstrate that the effect
of various phenolic–conjugates were in PP–DHA > IPP–DHA >
DIPP–DHA > CHP–DHA >> P–DHA order. This rank order of their ef-
fect was not correlated with their hydophobicity values suggesting
that PP–DHA simply did not have greater access to pass through
the cell membrane as compared to other analogues. PP–DHA con-
jugate remarkably affected growth inhibition and cell loss in a
dose-dependent manner, whereas the effectiveness of IPP–DHA,
DIPP–DHA and CHP–DHA conjugates was intermediate and P–
DHA was not effective. This implies that these conjugates are var-
iably stable in media and hydrolyzed by serum esterases. PP–DHA
was most stable because of the structural hindrance due to the
presence of two bulky propyl groups around the ester linkages.
IPP–DHA, DIPP–DHA, and CHP have only one bulky group around
the ester linkage and are therefore relatively less stable. P–DHA
has no protective group around the ester linkage and therefore
was quickly cleaved off and was not effective. Since we plan to
use these conjugates for in vivo studies in mice and eventually
for clinical trials, we tested the stability of these compounds in
mouse and human serum. Our data demonstrated that both PP–
DHA as well as IPP–DHA conjugates were stable in both serum as
evident by the absence of 2,6-diisopropylphenol and DHA peaks.
We further confirmed the effect of phenolic–DHA conjugates on
Figure 5. Concentration of DHA in cells on conjugate treatment. Effect on DHA
concentrations in cell after treatment with (a) PP–DHA or (b) DIPA–DHA conjugates
were determined by treating cells vehicle alone, DHA (10
(10 M) + PP–DHA (5 M), or DHA (10 M) + DIPA–DHA (5 M) along with PP–
DHA (5 M), and DIPA–DHA (5 M) as described in the legend of Figure 1. Lipids
lM) or DHA
l
l
l
l
l
l
were extracted and fatty acids concentrations were determined as methyl ester by
Gas Chromatography. Results are expressed as the mean SD of four experiments.
3.6. 2,6-Diisopropylphenol–DHA conjugate targets histone
deacetylase activity
To determine the effect of DHA, PP, and PP–DHA conjugate-trea-
ted MDA-MB-231 cell lysates on HDAC activity, we employed a
non-specific HDAC assay kit to measure the overall effect of these
compounds in respect to total HDAC activity. The PP–DHA
conjugate inhibited HDAC activity in a dose-dependent manner
(Fig. 6). Maximum HDAC inhibition was observed between 10–
25
lM, which depleted HDAC activity by approximately 30%
compared to vehicle-treated samples. Neither DHA nor PP alone
inhibited total HDAC activity at the highest 25
suggesting conjugate specificity.
lM concentration,
4. Discussion
The epidemiological studies, animal studies and cell culture
experiments strongly suggest that omega-3 polyunsaturated fatty
acids (n-3 PUFAs), namely docosahexaenoic acid and eicosapenta-
enoic acid, possess anticancer properties. A dose of 2–6 g of n-3 PU-
FAs/day is recommended using for their cancer effects. This
amount is achievable by taking 4–12 fish oil capsules/day.
Although this is achievable, taking high amounts of fish oil may
lead to some undesirable effects including fishy burps and some-

K. A. Harvey et al. / Bioorg. Med. Chem. 18 (2010) 1866–1874
1873
cellular growth by testing DIPA–DHA, IPA–DHA and A–DHA, which
are conjugated through amide linkages and represent non-hydro-
lyzable analogues of PP–DHA, IPP–DHA, and P–DHA, respectively.
The effect of non-hydrolyzable amide-linked conjugates is remark-
ably similar to the ester-linked conjugates. This data clearly sug-
gest that ester-linked phenolic–DHA conjugates are as stable as
non-hydrolyzable amide-linked aniline–DHA conjugates. Stability
of the conjugates was further tested by analyzing the concentra-
tion of DHA in cells. It is clear from data in Figure 5a,b that concen-
tration of DHA in cell does not increase over controls when cells
were treated with conjugates alone, as well as similar concentra-
tions of DHA was found in cell on either DHA alone or DHA + PP–
DHA or DIPA–DHA treatments. These observations suggest that
both ester and amide-linked conjugates were non-hydrolyable in
cells. Furthermore, this data suggest that the presence of side
chains around ester or amide linkage may have resulted in struc-
tural hindrance and played an important part in their cellular ef-
fects. Compounds are most effective when both side chains are
present. Removal of one side chain decreases their effectiveness
and the removal of both side chains results in loss of their activity.
It is possible that these side chains play an essential role in binding
of these conjugates to the target molecule.
proliferation reagent, WST-1, and the Annexin V FLUOS staining
kits were purchased from Roche Applied Science (Indianapolis,
IN). Histone deacetylation fluorometric cellular activity assay kits
were purchased from BioVision (Mountain View, CA). Additional
reagents were obtained from Sigma–Aldrich (St. Louis, MO), unless
otherwise noted.
5.2. Cell culture maintenance
Human mammary epithelial cells (HMEC) were maintained in
mammary epithelial basal media supplemented with bullet kit
materials as specified by the manufacturer. All breast cancer cell
lines were maintained in DMEM containing 5% fetal bovine serum
(FBS) and a 1% antibiotic-antimycotic solution. Cells were main-
tained at 37 °C in a humidified atmosphere containing 5% CO2.
5.3. Growth inhibition and toxicity assay
Epithelial cells (5000 cells/well) were cultured overnight in
DMEM complete medium in 96 well flat bottom tissue culture
plates to establish a linear growth rate. Spent medium was re-
placed with DMEM supplemented with 2% FBS and treatment con-
Next we looked for the possible target molecule for PP–DHA
conjugate cellular effects. DHA and other fatty acids binding to nu-
clear receptors such as peroxisome proliferator-activated receptor
(PPAR) and retinoid X receptors (RXRs) have been reported.19 DHA
is a general ligand of PPARs, but binds more selectively to RXR
transcription factors. RXRs form homo- or heterodimers with PPAR
and other nuclear hormone receptor super-families that include
receptors for steroids, thyroid hormones, retinoic acid and vitamin
D. In order to elucidate a role of PPARs effect in PP–DHA cellular
ditions (100 lL total volume/well) upon initiation of the growth
inhibition assessment. Vehicle controls (ethanol) served as the
non-treated total growth potential. To obtain baseline values and
an initial cell viability assessment, a subset of established wells
were used for monitoring cellular growth using WST-1 assay as
recommended by the manufacturer (Roche Applied Science, India-
napolis, IN). The cell cultures treated with different phenolic-fatty
acids conjugates were continued to maintain for 48 h at 37 °C in a
humidified atmosphere containing 5% CO2. At the end of the incu-
bation period, cellular growth (inhibition or cell loss) was deter-
mined using WST-1 assay reagent as described previously.21
effects, we used GW9662 as an inhibitor for PPAR
However, our results clearly demonstrated that PP–DHA activates
neither PPAR nor PPAR (data not shown). Furthermore, PP–DHA
a and PPARc.
a
c
appears to have structural resemblance to trichostatin A (TSA),
which selectively inhibits the class I and II mammalian histone
deacetylase (HDAC) families of enzymes.20 Our data demonstrated
5.4. Apoptosis detection
Cells (1.5 Â 105) were plated in complete DMEM in six well tis-
sue culture treated plates overnight to initiate a linear growth rate.
Spent media was replaced with 3 mL of DMEM supplemented with
2% FBS with varying doses of DHA, 2,6-diisopropylphenol (PP), and
the PP–DHA conjugate. An equal volume of ethanol served as the
vehicle control. At the conclusion of the treatments, the cells were
rinsed in phosphate buffered saline (PBS) and trypsinized from the
wells. All spent medium, PBS washes and trypsinized cells were
collected and combined to harvest both adherent and non-adher-
ent cells for analysis. Cell pellets were resuspended in Annexin V
FLUOS/Propidium iodide labeling solution, which was prepared
as described by the manufacturer. Cell suspensions were labeled
in the dark at room temperature for 20 min. Analysis was per-
formed on a FACSCalibur flow cytometer (Becton Dickinson, San
Jose, CA) equipped with an air-cooled argon laser emitting at a
that PP–DHA conjugate 10–25 lm concentration partially inhibited
HDAC activity (30%) whereas PP or DHA alone has no effect. This
observation suggests that inhibition of HDAC activity is perhaps
one possible contributory mechanism of action of these conjugates.
Further experimentation is needed to elucidate the mechanism of
action of these potent anticancer phenolic conjugates.
In conclusion, our results demonstrated that PP–DHA or DIPA–
DHA conjugates effectively inhibited breast cancer growth irre-
spective of their ER or Her-2 expression. The presence of both side
chains is essential for their maximum effects of these conjugates.
Removal of one side chain results in reduction in their effects;
whereas, complete removal of both side chains results in loss of
their effects. Inhibition of HDAC activity may be one possible
mechanism through which PP–DHA exerts its effects on breast
cancer cells.
488 nm wavelength. Fluorescence was detected through
a
530 nm band pass filter and quantified using CellQuest Software
(Becton Dickinson, San Jose, CA).
5. Experimental
5.1. Materials
5.5. Determination of phenolic conjugate stabilities in serum
All disposable tissue culture materials were obtained from Fish-
er Scientific (Pittsburgh, PA). Dulbecco’s Modified Eagle’s Medium
(DMEM) and tissue culture supplements were purchased from
Invitrogen Corporation (Carlsbad, CA). Normal human mammary
epithelial cells (HMEC) and mammary epithelial basal medium
bullet kits were acquired from Lonza Incorporation (Walkersville,
MD). Breast cancer cell lines were obtained from American Type
Culture Collection (Manassas, VA). Docosahexaenoic acid was
obtained from Nu-Chek Prep Incorporated (Elysian, MN). The cell
The phenolic–fatty acid conjugates (1 mM) suspended in ethanol
were mixed with human and mouse serum (1 ml) and incubated at
37 °C for 2 h. At the end of incubation period, the serum was ex-
tracted using Folch method22 and the dried lipid extracts were sus-
pended in 200lL ethanol for HPLC analysis. The HPLC analysis was
performed with reversed-phase high-performance liquid chroma-
tography (RP-HPLC) method by using a Agilent 1100 HPLC system
equipped with an Agilent 1100 Diode-Array detector, an Agilent
1100 Auto Sampler system and an Agilent ZORBAX SB-C18 column

1874
K. A. Harvey et al. / Bioorg. Med. Chem. 18 (2010) 1866–1874
(4.6 Â 250 mm, 5
lm particle size), with an injection volume of
20 lL and a flow rate of 1.5 mL/min. The mobile phase is a mixture
Acknowledgments
of water containing 0.01% trifluoroacetic acid (solvent A), acetoni-
trile containing 0.01% trifluoroacetic acid (solvent B). The elution
gradient was from 80% (B), to 100% (B) in 40 min, followed by
100% (B) for 10 min to clean the column. The chromatograms were
detected at 214 nm.
This work was supported by a grant from the Methodist
Research Institute, Clarian Health, Indianapolis, IN 46202.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmc.2010.01.045.
5.6. Histone deacetylase activity assay
MDA-MB-231 breast cancer cells were treated for 2 h at 37 °C
with varying concentrations of the PP–DHA conjugate, DHA alone
or PP alone in DMEM supplemented with 2% FBS. Spent media
was removed and the cells were rinsed in PBS and harvested by
trypsinization. Samples were normalized to 2 Â 106 cells/mL in
PBS containing 0.1% Triton X-100. Samples were kept on ice and
sonicated to insure cell lysis. The HDAC activity assay was per-
formed as described by the manufacturer. An inhibitor of HDAC
activity, trichostatin A, was utilized to determine maximum inhibi-
tion in order to adjust for non-specific assay readings. Data was ex-
pressed as the percentage of total HDAC activity.
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ron ZB-WAX plus column (100 m, 0.25 mm ID, 0.25 lm film thick-
ness). The oven temperature was programmed from 30 °C (2 min
hold) to 180 °C @ 20 °C/min (2 min hold), then to 207 °C @ 4 °C/
min (3 min hold), then to 220 °C @ 2 °C/min (2 min hold), and final-
ly to 240 °C @ 2 °C/min (2 min hold). Detection was performed
with a FID @ 250 °C to resolve fatty acids peaks, which were iden-
tified using authentic standards (Restek Corp., Bellefonte, PA). Data
was analyzed with Shimadzu’s GC solutions software.
5.8. Data analysis
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Results are expressed as the mean SD four experiments and
analyzed using Student t tests. An ‘*’ represents significance at
p <0.05.