368
S. Price et al. / Bioorg. Med. Chem. Lett. 17 (2007) 363–369
Truncating the tether of compound 5e by a methylene
unit to provide the tethered compound 9 led to retention
of HDAC inhibitory activity, but resulted in significant-
ly reduced cell-based activity.
the HDAC enzyme assay is shown in Table 6. In addition,
these compounds demonstrated IC50 values of less than
200 nM in two cell proliferation assays. To expand the
variety of cancer cell lines that the compounds were rou-
tinely tested against, the MDA-MB-231 breast cancer cell
line was replaced by the HCT116 colon cancer cell line.
Moving the basic amine of compounds 5e and 5f further
away from the pyridyl ring provided the corresponding
isomeric compounds 13a and 13b, which possessed al-
most comparable activity in the HDAC and MCF-7
assays.
Generally, it was found that a very broad range of phenyl
substitutions was well tolerated, with the best substituents
including halogens, electron-donating groups, fused elec-
tron-rich ring systems and biaryl rings. Further profiling
of selected compounds will be reported in due course.
Table 2 includes three compounds with IC50 values be-
low 20 nM in the primary assay and below 100 nM in
the MCF-7 cell proliferation assay. On the basis of
structural simplicity, compound 5b was selected as a
prototype compound for further profiling (Table 3).
Compound 5b was over an order of magnitude more ac-
tive than SAHA in the HDAC enzyme and MCF-7,
MDA-MB231, and HCT-116 cell proliferation assays.
Compound 5b was 2-fold more active than
ADS102550 in the HDAC enzyme assay, and 3- to 6-
fold more potent in the cell-based assays. Compound
5b possessed a 10-fold reduction in CYP450 3A4 inhibi-
tion value compared to ADS102550, and also had a sig-
nificantly enhanced permeability. Modest stability for
both of the biaryl hydroxamic acids, 5b and
ADS102550, was observed in rat hepatocytes, with poor
stability being demonstrated in mouse microsomes.
In summary, we have expanded the initial series of
thienyl-based hydroxamic acids to include substituted
5-pyridin-2-yl-thiophene-2-hydroxamic acids as potent
HDAC inhibitors. One of the compounds identified,
compound 5b, has demonstrated improved potency,
cytochrome P450 3A4 inhibition, Caco-2 permeability
and increased oral bioavailability in rat, compared to
ADS102550. Substitution of the tethered phenyl group
of the 5-pyridin-2-yl-thiophene-2-hydroxamic acids 5b,
5e, and 13a was shown to be well tolerated, and further
expanded the SAR of substituted 5-pyridin-2-yl-thio-
phene-2-hydroxamic acids.
Acknowledgments
Compound 5b was evaluated in rat PK experiments (iv
and po, Table 4) for comparison with ADS102550 and
SAHA. Compound 5b possessed improved clearance
compared to ADS102550 and SAHA. Based on the re-
sults observed in rat hepatocyte stability assays, the high
clearance for SAHA was unpredicted. The good oral
bioavailability observed for compound 5b was consis-
tent with its high Caco-2 permeability.
We thank Mike Podmore and Russell Scammell from
the analytical department at Argenta Discovery for
NMR and LCMS analysis. We also thank Don Daley,
Rob Jenkins, Colin Bright and Gerry Buckley from
the DMPK department at Argenta Discovery for the
in vivo and in vitro studies completed on compounds
within this paper.
Encouraged by the in vivo rat PK data, we next pro-
ceeded with a series of mouse PK experiments (iv, ip,
and po, Table 5). Unfortunately, compound 5b dis-
played high clearance and had a very short half-life. This
high clearance for compound 5b compared to
ADS102550 was not predicted from the in vitro mouse
microsomal stability measurements. However, the in-
creased oral bioavailability observed was once again
consistent with the Caco-2 measurements.
References and notes
1. Butler, L. M.; Agus, D. B.; Scher, H. I.; Higgins, B.;
Rose, A.; Cordon-Cardo, C.; Thaler, H. T.; Rifkind, R.
A.; Marks, P. A.; Richon, V. M. Cancer Res. 2000, 60,
5165.
2. (a) Weinmann, E.; Ottow, E. Expert Opin. Ther. Patents
2005, 15, 1677; (b) Miller, T. A. Expert Opin. Ther. Patents
2004, 14, 791.
3. (a) Bolden, J. E.; Peart, M. J.; Johnstone, R. W. Nat.
Rev. Drug Disc. 2006, 5, 769; (b) Yoo, C. B.; Jones,
P. A. Nat. Rev. Drug Disc. 2006, 5, 37; (c) Inche, A.
G.; La Thangue, N. B. Drug Discovery Today 2006,
11, 97; (d) Vigushin, D. M.; Coombes, R. C.
Anticancer Drugs 2002, 13, 1.
Considering the promising potency, improved CYP450
3A4 profile and high permeability of compound 5b, we
elected to investigate the SAR of substituted 5-pyridin-
2-yl-thiophene-2-hydroxamic acids further in an attempt
to identify potent HDAC inhibitors and anti-prolifera-
tive agents possessing an improved PK profile, especially
lower clearance.
4. Rosato, R. R.; Grant, S. Expert Opin. Investig. Drugs 2004,
13, 1354.
5. See the preceding paper: Price, S.; Bordogna, W.; Bull, R.
J.; Clark, D. E.; Crackett, P. H.; Dyke, H. J.; Gill, M.;
Harris, N. V.; Gorski, J.; Lloyd, J.; Lockey, P. M.; Mullett,
J.; Roach, A. G.; Roussel, F.; White, A. B. Bioorg. Med.
Chem. Lett. 2006.
6. The HDAC inhibitory activity of compounds was
assessed using the commercially available HDAC
Fluorescent Activity Assay Kit (Biomol, #AK-500)
following the manufacturer instructions, but with
minor modifications: the reaction was carried out at
A series of over fifty compounds that had substituents
appended to the tethered phenyl ring of compounds
5b, 5e, and 13a was prepared using the synthetic routes
depicted in Schemes 2 and 3.
A selection of some of the most active compounds, 5h–u
and 13c, d, that possessed IC50 values below 20 nM in