4-[3-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)phenyl]benzoi c acid and heterocyclic-bridged analogues are novel retinoic acid receptor subtype and retinoid X receptor α agonists

Article abstract of DOI:10.1016/S0960-894X(00)00244-4

Aromatic retinoids having a meta-substituted aromatic ring bridge, such as 4-[3-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)phenyl]benzoic acid and its 3,5-diaryl-substituted 4,5-dihydroisoxazole analogue, function as retinoid receptor panagonists by activating both retinoic acid and retinoid X receptors to induce gene transcription, and thereby provide novel scaffolds for retinoid drug development. Both classes of these ligand-inducible transcription factors are involved in mediating the inhibitory effects of retinoids on cancer cell growth. (C) 2000 Elsevier Science Ltd. All rights reserved.

Full text of DOI:10.1016/S0960-894X(00)00244-4

Bioorganic & Medicinal Chemistry Letters 10 (2000) 1311±1313
4-[3-(5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-
naphthalenyl)phenyl]benzoic Acid and Heterocyclic-Bridged
Analogues are Novel Retinoic Acid Receptor Subtype and
Retinoid X Receptor ꢀ Agonists
Marcia I. Dawson,a,* Ling Jong,b Peter D. Hobbs,b Dongmei Xiao,c
Kai-Chia Feng,a Wan-ru Chao,b Chin Pan,a Joseph A. Fontanad
and Xiao-kun Zhangc
aMedicinal Chemistry Department, Molecular Medicine Research Institute, 325 East Middle®eld Road, Mountain View, CA 94043, USA
bRetinoid Program, SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025, USA
cThe Burnham Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
dJohn D. Dingell VA Medical Center and Kamaros Cancer Institute, Wayne State University, 4646 John R Street, Detroit,
MI 48201, USA
Received 14 January 2000; accepted 15 March 2000
AbstractÐAromatic retinoids having a meta-substituted aromatic ring bridge, such as 4-[3-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-
2-naphthalenyl)phenyl]benzoic acid and its 3,5-diaryl-substituted 4,5-dihydroisoxazole analogue, function as retinoid receptor
panagonists by activating both retinoic acid and retinoid X receptors to induce gene transcription, and thereby provide novel
sca€olds for retinoid drug development. Both classes of these ligand-inducible transcription factors are involved in mediating the
inhibitory e€ects of retinoids on cancer cell growth. # 2000 Elsevier Science Ltd. All rights reserved.
The aromatic retinoids (E)-4-[2-(5,6,7,8-tetrahydro-5,
5,8,8-tetramethyl-2-naphthalenyl)propenyl]benzoic acid
(TTNPB or Ro13-7410, 1 in Table 1)1 and 6-(5,6,7,8-
tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-2-naph-
thalenecarboxylic acid (TTNN, 2)2,3 were leads for the
development of the topical antipsoriatic drug tazarotene1
(ethyl 6-[2-(4,4-dimethyl-2,3-dihydro-6-thiochromanyl)-
ethynyl] nicotinate, AGN 190168)4 and the topical
antiacne drug adapalene1 (6-[3-(1-adamantyl)-4-meth-
oxyphenyl]-2-naphthalenecarboxylic acid, CD2715),
respectively. Here, we report another novel retinoid
sca€oldÐthe teraryl retinoid 4-[3-(5,6,7,8-tetrahydro-
5,5,8,8-tetramethyl-2-naphthalenyl)phenyl]benzoic acid
(TTNPB2, 3) and analogue structuresÐthat should be
useful for constructing new retinoid receptor panagonists,
which bind and activate both the retinoic acid receptor
(RAR) and retinoid X receptor (RXR) classes of ligand-
inducible transcription factors (reviewed in ref 6).
Increasing evidence indicates that both RARs and
RXRs are involved in regulating the inhibitory e€ects of
retinoids on cancer cell growth and hyperproliferation.7 11
In the micromolar range TTNPB2 activates both recep-
tor classes in CV-1 cells cotransfected with an expres-
sion vector for one of the receptors and the (TREpal)2-
tk-CAT reporter construct (Table 1). Transcriptional
activation activities (as measured by AC50 values) for
RARb, RARg, and particularly RXRa are enhanced by
a methyl group at the 4-position of the 1,3-disubstituted
benzene bridge between the 4-substituted benzoic acid and
2-substituted tetrahydronaphthalene rings (MM11387);
whereas the AC50 value for RARa activation decreases
by almost two-logs. Activation levels at 1 mM MM11387
resemble those at 1 mM trans-retinoic acid (trans-RA) for
the RAR subtypes and at 1 mM 9-cis-RA for RXRa. A
second methyl group at the 3-position of the tetra-
hydronaphthalene ring (MM11388) further reduces
AC50 values for RARa and RXRa, although activation
of all four receptors at 1 mM MM11388 is 45% to 96%
of that at 1 mM trans-RA for the RARs and 70% of that
at 1 mM 9-cis-RA for RXRa. Use of a 2,6-disubstituted
pyridine bridge (MM11395) causes at least a one-log
*Corresponding author. Tel.: +1-650-237-7456; fax: +1-650-237-
7455; e-mail: mdawson@mmrx.org
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00244-4

1312
M. I. Dawson et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1311±1313
Table 1. Retinoic acid receptor (RAR) subtype and retinoid X receptor (RXR) a transcriptional activation (AC50) on the (TREpal)2-tk-CAT in
transfected CV-1 cells by retinoids 1 to 9 compared to 1 mM trans-RA for the RARs and 1 mM 9-cis-RA for RXRa
AC50 values (nM) (% activation at 1 mM)b
Retinoid structurea
Name or code number
TTNPB (Ro13-7410)c
RARa
RARb
RARg
RXRa
1
2
200 (85)
22 (86)
26 (75)
>1000 (0)
TTNNd
>1000 (23)
52 (82)
68 (95)
>1000 (0)
R1
H
Me
Me
H
R2
H
H
Me
H
Me
X
CH
CH
CH
N
3
4
5
6
7
TTNBP2 (MM11256)
MM11387
MM11388
1.0 (127)
4.3 (109)
<1 (113)
10 (96)
2.3 (99)
<1 (93)
1.0 (87)
>1000 (27)
135 (85)
430 (70)
>1000 (17)
>1000 (0)
79 (87)
>1000 (43)
370 (61)
MM11395
MM11396
140 (68)
>1000 (42)
>1000 (20)
1000 (5)
H
N
>1000 (26)
8
9
MM11176
MM11391
>1000 (6)
14 (86)
740 (36)
<1 (94)
220 (69)
<1 (88)
>1000 (8)
100 (65)
aNew compounds were fully characterized (IR, 1H NMR, mp) and passed analysis (elemental or HRMS).
bActivation (50%) for RARa, b, g, and RXRa on the (TREpal)2-tk-CAT by retinoids in monkey kidney CV-1 cells transfected with expression
vectors for each of these receptors, compared to that of 1 mM trans-RA for the RARs and 1 mM 9-cis-RA for RXRa as 100%. Two copies of the
TREpal response element, which is activated by RARs and RXRs, were linked to the chloramphenicol acetyl transferase (CAT) reporter containing
the thymidine kinase promotor (tk) (ref 11). The b-galactosidase expression vector was used to normalize for transfection ecacy. Data points are
the means of triplicate experiments. AC50 values were calculated by interpolation of concentration±response curves. Assays were conducted at the
Burnham Institute under license from Ligand Pharmaceuticals for use of this patented technology.
cRef 13.
dRef 12.
increase in the AC50 values for RARa and b, more than
a two-log increase for RARg, and a decrease in RXRa
activation. The MM11395 analogue having a methyl
group at the 3-position of the tetrahydronaphthalene
ring (MM11396) is almost devoid of activity. The 2,5-
disubstituted 1,3-thiazole bridge (MM11176) also pro-
duces low activity, with only RARg being moderately
activated at 1 mM MM11176. Potent activity is regained
by using a 3,5-disubstituted 4,5-dihydroisoxazole bridge
(MM11391) with activations for the RAR subtypes
comparable to those by TTNPB2 and RXRa activation
enhanced. MM11391 may behave as a panagonist
because of its structural similarities to the RAR-selective
Z-oxime of 6-(4,5,6,7-tetrahydro-5,5,8,8-tetramethyl-2-
naphthalenylcarbonyl)-2-naphthalenecarboxylic acid11
and the RXR-selective methyloxime of 4-(4,5,6,7-tetra-
hydro-5,5,8,8-tetramethyl-2-naphthalenylcarbonyl)ben-
zoic acid.13
Moreover, the 10.6 A 8-tetrahydronaphthalenyl carbon
and carboxylic acid carbon distance for the low-energy
conformer of MM11391 is between the 11.3 A and 9.6 A
C±C distances found for the low-energy conformers of
these RAR- and RXR-selective analogues using CAChe
software (Oxford Molecular Ltd) and the MM3 force
®eld.
TTNPB2 gave IC50 values of 2.7 mM for inhibiting the
growth of retinoid-sensitive NIH:OVCAR-3 ovarian can-
cer cells and 3.0 mM for inhibiting the growth of retinoid-
resistant MDA-MB-231 breast cancer cells compared to
IC50 values of 2.3 mM and greater than 12.5 mM,

M. I. Dawson et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1311±1313
1313
Acknowledgements
Support by the USPHS NCI Program Project Grant
CA51993 (to M.I.D., J.A.F., and X.Z.) is gratefully
acknowledged.
References and Notes
1. Loeliger, P.; Bollag, W.; Mayer, H. Eur. J. Med. Chem.-
Chim. Ther. 1980, 15, 9.
2. Dawson, M. I.; Chan, R. L.-S.; Derdzinski, K.; Hobbs, P.
D.; Chao, W.; Schi€, L. J. J. Med. Chem. 1983, 26, 1653.
3. Lehmann, J. M.; Dawson, M. I.; Hobbs, P. D.; Husmann,
M.; Pfahl, M. Cancer Res. 1991, 51, 4804.
4. Nagpal, S.; Patel, S.; Jacobe, H.; DiSepio, D.; Ghosn, C.;
Malhotra, M.; Teng, M.; Duvic, M.; Chandraratna, R. A. J.
Invest. Dermatol. 1997, 109, 91.
5. Shroot, B.; Michel, S. J. Am. Acad. Dermatol. 1997, 36, S96.
6. Mangelsdorf, D. J.; Umesono, K.; Evans, R. M. In The
Retinoids. Biology, Chemistry, and Medicine; Sporn, M. B.;
Roberts, A. B.; Goodman, D. S., Eds.; Raven: New York,
1994; pp 319±350.
Scheme 1. Synthesis of TTNPB2 (3): (a) 2,5-dimethyl-2,5-dichlorohex-
ane (ref 12), Cl(CH2)2Cl, AlCl3, 0 ꢀC: 6-(3-bromophenyl)-1,2,3,4-tetra-
hydro-1,1,4,4-tetramethylnaphthalene (11) (97%); (b) [Pd[P(C6H5)3]4,
anhyd DME], 4-carbethoxyphenylboronic acid (ref 12), EtOH; aq
Na2CO3, re¯ux: ethyl 4-[3-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-
naphthalenyl)phenyl]benzoate (12) (79%); (c) KOH, 75% aq MeOH,
(70 ꢀC); (1 N HCl): 3 (99%). Synthesis of MM11391 (9); (d) 13 (ref 15),
NH2OHꢁ HCl, NaOAc, MeOH, 70ꢀC, 15 h; aq HCl (51%). (See ref 16
for mp and spectral data.).
7. Nagy, L.; Thomazy, V. A.; Shipley, G. L.; Fesus, L.;
Lamph, W.; Heyman, R. A.; Chandraratna, R. A. S.; Davies,
P. J. A. Mol. Cell. Biol. 1995, 15, 3540.
8. Bissonnette, R. P.; Brunner, T.; Lazarchik, S. B.; Yoo, N.
J.; Boehm, M. F.; Green, D. R.; Heyman, R. A. Mol. Cell.
Biol. 1995, 15, 5576.
9. Wu, Q.; Dawson, M. I.; Zheng, Y.; Hobbs, P. D.; Agadir,
A.; Jong, L.; Li, Y.; Liu, R.; Lin, B.; Zhang, X.-K. Mol. Cell.
Biol. 1997, 17, 6598.
Table 2. E€ects of 1 mM all-trans-retinoic acid (trans-RA), 9-cis-
RA, TTNBP2, MM11387, and MM11391 on the growth of retinoid-
sensitive T-47D and ZR-75-1 and retinoid-resistant MDA-MB-231
breast cancer cells after 10 daysa
Cell numbers (% relative to nontreated control)
10. Li, Y.; Dawson, M. I.; Agadir, A.; Li, M.-O.; Hobbs, P.
D.; Zhang, X. Int. J. Cancer 1998, 75, 88.
Retinoid
T-47D
ZR-75-1
MDA-MB-231
11. Chao, W.; Hobbs, P. D.; Jong, L.; Zhang, X.; Dawson,
M. I. Cancer Lett. 1997, 115, 1.
12. Jong, L.; Lehmann, J. M.; Hobbs, P. D.; Harlev, E.; Hu€-
man, J. C.; Pfahl, M.; Dawson, M. I. J. Med. Chem. 1993, 36,
2605.
13. Canan Koch, S. S.; Dardashti, L. J.; Cesario, R. M.;
Croston, G. E.; Boehm, M. F.; Heyman, R. A.; Nazdan, A.
M. J. Med. Chem. 1999, 42, 742.
14. Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
15. Kagechika, H.; Kawachi, E.; Hashimoto, Y.; Shudo, K. J.
Med. Chem. 1989, 32, 834.
16. Characterization data, 11: white solid, mp 78±80 ꢀC (hex-
Control
trans-RA
9-cis-RA
TTNPB2 (3)
MM11387 (4)
MM11391 (9)
100Æ4
39Æ2*
35Æ3*
32Æ4*
35Æ5*
23Æ4*
100Æ3
70Æ4*
59Æ5*
47Æ4*
49Æ1*
42Æ3*
100Æ4
94Æ2
69Æ2*
80Æ5*
75Æ5*
65Æ4*
aCells were cultured at 37 ꢀC in medium containing 10% fetal bovine
serum and either 1.0 mM retinoid or Me2SO vehicle alone, with med-
ium and retinoid solution replaced every 48 h. Cell numbers were
determined using the MTT assay.9 Results (% growth) represent the
average of three experiments Æ the standard error and are statistically
signi®cant (*) relative to the control (P< 0.001).
ane); Rf 0.45 (hexane); IR (KBr) 2956, 1591, 1551, 1469, 1386,
1
1361, 793 cm
;
1H NMR (300 MHz, CDCl3) d 1.32 (s, 6,
CMe2), 1.34 (s, 6, CMe2), 1.72 (s, 4, CH2CH2), 7.28 (dd, J=7.8,
7.8 Hz, 1, ArH), 7.31 (dd, J=2.0, 8.1 Hz, 1, ArH), 7.38 (d,
J=8.1 Hz, 1, ArH), 7.47 (m, 3, ArH), 7.70 (dd, J=1.7, 1.7 Hz,
1, ArH). 12: White solid, mp 148±149 ꢀC (CH2Cl2/hexane); Rf
0.35 (50% CH2Cl2/hexane); IR (KBr) 2956, 1712, 1272, 1102,
respectively, for trans-RA after treatment for seven days
at 37 ꢀC in medium containing 10% fetal bovine serum
with viable cell numbers determined spectro-
photometrically. After 10 days, growth inhibition by 1
mM TTNPB2, MM11387, or MM11391 on retinoid-
sensitive ZR-75-1 and T-47D breast cancer cells or on
retinoid-insensitive MDA-MB-231 breast cancer cells
was comparable to or greater than that of 1 mM trans-
RA or 9-cis-RA (see Table 2).
1
771 cm 1; H NMR (300 MHz, CDCl3) d 1.33 (s, 6, CMe2),
1.35 (s, 6, CMe2), 1.42 (t, J=7.1 Hz, 3, CO2CH2CH3), 1.73 (s,
4, CH2CH2), 4.41 (q, J=7.1 Hz, 2, CO2CH2CH3), 7.40 (br s, 2,
ArH), 7.56 (m, 4, ArH), 7.71 (d, J=8.5 Hz, 2, ArH), 7.79 (dd,
J=1.4, 1.4 Hz, 1, ArH), 8.13 (d, J=8.5 Hz, 2, ArH). 3: White
crystalline solid, mp 232±233 ꢀC (CH2Cl2/hexane); IR (KBr)
1
2955, 1685, 1609, 1422, 1298, 771 cm 1; H NMR (300 MHz,
CDCl3) d 1.34 (s, 6, CMe2), 1.36 (s, 6, CMe2), 1.74 (s, 4,
CH2CH2), 7.41 (br s, 2, ArH), 7.58 (m, 4, ArH), 7.75 (d,
J=8.6 Hz, 2, ArH), 7.81 (dd, J=1.4, 1.4 Hz, 1, ArH), 8.21 (d,
The teraryl sca€old of TTNPB2 is suitable for combi-
natorial analogue synthesis using Suzuki-type palladium-
catalyzed biaryl-couplings14 to introduce 1,3-disubstituted
aryl or heterocyclic ring bridging groups. The syntheses of
TTNPB2 and MM11391 are shown in Scheme 1 and
described in the accompanying legend. MM11387,
MM11388, MM11395, MM11396, and MM11176, the
structures of which are shown in Table 1, were readily
prepared using similar methodologies.
J=8.6 Hz, 2, ArH). 9: White solid; IR (KBr) 2900±3500, 1700,
1
1614, 1460, 1293, 1020, 829 cm
;
1H NMR (300 MHz,
DMSO-d6) d 1.16, 1.19, 1.21 (3s, 12, 2 CMe2), 1.61 (s, 4,
CH2CH2), 2.89 (dd, J=14, 9 Hz, 1, CH2CH anti to Ar), 3.18
(dd, J=14, 7 Hz, 1, CH2CH syn to Ar), 4.25 (m, 1, CH2CH),
7.2±7.3 (dd, 3, NapH), 7.35 (d, J=9 Hz, 2, ArH meta to
CO2H), 7.38 (d, J=9 Hz, 2, ArH ortho to CO2H).