R. W. Heidebrecht et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2053–2058
2057
compound 11n (AUC = 50
tained with methoxy example 11o (AUC = 115 lM h).
l
M h). The most dramatic result was ob-
S
Minor improvements in AUC were observed when smaller
phosphorus-linked alkyl groups were installed. This is exemplified
O
by
a
comparison of ethyl-substituted phosphinate 11m
N
H
(AUC = 17
(AUC = 50
lM h) with the closely related methyl derivative 11n
NH2
R
l
M h). The same trend was observed for phosphine oxi-
des: 4-diisopropyl-phosphinomethyl (AUC = 1.3
much reduced exposure compared to 4-diethylphosphinomethyl
11j (AUC = 17 M h).
Promising compounds were tested in the PK/PD model for his-
tone acetylation (HCT116 tumor-bearing nude CD-1 mice,
150 mg/kg, po, qd, 3 days), and three examples are depicted below
(Fig. 4). Phosphinate 11n did not demonstrate changes to the ratio
of acetylated to deacetylated H2B histones relative to control;
however, a statistically significant response was demonstrated by
both phosphinate 11o and aminophosphonate 13.
Leads 11o and 13 were further tested in a mouse xenograft
model (HCT116 colon) at various daily oral doses for 21 days
(Fig. 5), and dose-dependent inhibition of tumor growth was ob-
served. Unfortunately, mice treated with 11o also experienced sig-
nificant and dose proportionate weight loss (22% loss in the
100 mg/kg cohort after 21 days), affording a very small therapeutic
window. On the other hand, compound 13 was very well tolerated
at all doses, illustrating the potential utility of phosphorus based
HDAC inhibitors for the treatment of cancer.
lM h) 11p gave
Compound
11n
R
Data Summary
l
HDAC1 IC50: 16 nM
O
P
Me
HCT116 GI50: 0.330 µM
PD(mouse): negative
EtO
Time Post Dose (h): 24
HDAC1 IC50: 54 nM
HCT116 GI50: 0.160 µM
PD(mouse): positive
O
P
Me
11o
13
MeO
Time Post Dose (h): 24
HDAC1 IC50: 7.7 nM
HCT116 GI50: 0.300 µM
PD(mouse): positive
O
P
EtO
H
N
EtO
Time Post Dose (h): 8
Figure 4. Summary of data for compounds 11n, 11o, and 13.
410
360
310
260
210
160
110
60
The phosphorus-containing biphenyl inhibitors disclosed in this
work possess the excellent selectivity for HDACs 1 and 2 that was
previously observed.7b Full data for compound 13 is provided as an
example (Fig. 6).20 A minimum of three logs of selectivity separates
the in vitro HDAC1 (IC50 = 7.7 nM) and HDAC2 (IC50 = 14 nM) po-
tency of 13 from other class I isoforms, i.e., the closely related
HDAC3 (IC50 = 12,000 nM) as well as HDAC8 (IC50 = 37,000 nM).
Excellent selectivity was observed over class II and III enzymes
(HDACs 4–7, 11, IC50 = >50,000 nM).
In summary, we observed a disconnect between rat and mouse
pharmacokinetics of phosphorus-containing SHI-1:2 analogs. A
survey of mouse PK parameters showed a strong correlation be-
tween smaller alkyl phosphorus-based groups and superior oral
exposure. Sample compound (13) showed promising and signifi-
cant tumor growth inhibition in a xenograft model without signif-
icant weight loss.21
Vehicle
11o, 50 mg/kg
11o, 100 mg/kg
2-way ANOVA
*** : P < 0.0001
1
4
7
10
13
16
19
22
Days after beginning treatment
350
300
250
200
150
100
50
Vehicle, Qd
13, 150 mg/kg
13, 300 mg/kg
2-way ANOVA analysis
*** : P < 0.001
Acknowledgements
We would like to express our appreciation to Sujal Deshmukh
and Dapeng Chen for assistance with pharmacokinetic studies.
References and notes
1
4
7
10
13
16
19
22
1. (a) Feinberg, A. P.; Vogelstein, B. Nature 1983, 301, 89; (b) Holliday, R. Science
1987, 238, 163; (c) Jones, P. A.; Baylin, S. B. Nat. Rev. Genet. 2002, 3, 415.
2. Grozinger, C. M.; Schreiber, S. L. Chem. Biol. 2002, 9, 3.
Days after beginning treatment
Figure 5. Xenograft results for compounds 11o and 13.
3. (a) Richon, V. M. Br. J. Cancer 2006, 95, S2; (b) O’Connor, O. A. Br. J. Cancer 2006,
95, S7; (c) Duvic, M.; Zhang, C. Br. J. Cancer 2006, 95, S13; (d) Marks, P. A.;
Breslow, R. Nat. Biotechnol. 2007, 25, 84.
4. (a) Suzuki, T.; Ando, T.; Tsuchiya, K.; Fukazawa, N.; Saito, A.; Mariko, Y.;
Yamashita, T.; Nakanishi, O. J. Med. Chem. 1999, 42, 3001; (b) Kell, J. Curr. Opin.
Invest. Drugs 2007, 8, 485.
5. Siliphaivahn, P.; Harrington, P.; Witter, D. J.; Otte, K.; Tempest, P.; Katter, S.;
Kral, A.; Fleming, J. C.; Deshmukh, S. V.; Harsch, A.; Secrist, P. J.; Miller, T. A.
Bioog. Med. Chem. Lett. 2007, 17, 4619.
6. Moradei, O. M.; Mallais, T. C.; Frechette, S.; Paquin, I.; Tessier, P. E.; Leit, S. M.;
Fournel, M.; Bonfils, C.; Trachy-Bourget, M.-C.; Liu, J.; Yan, T. P.; Lu, A.-H.; Rahil,
J.; Wang, J.; Lefebvre, S.; Li, Z.; Vaisburg, A. F.; Besterman, J. M. J. Med. Chem.
2007, 50, 5543.
7. (a) Weerasinghe, S. V. W.; Estiu, G.; Wiest, O.; Pflum, M. K. J. Med. Chem. 2008,
51, 5542; (b) Witter, D. J.; Harrington, P.; Wilson, K. J.; Chenard, M.; Cruz, J. C.;
Fleming, J. C.; Harsch, A.; Kral, A. M.; Secrist, J. P.; Miller, T. A. Bioorg. Med. Chem.
Lett. 2008, 18, 726; (c) Methot, J. L.; Chenard, M. C.; Close, J.; Cruz, J. C.;
Dahlberg, W. K.; Fleming, J.; Hamblett, C. L.; Hamill, J. E.; Harrington, O.;
HDAC1 IC50
HDAC2 IC50
HDAC3 IC50
HDAC4 IC50
HDAC5 IC50
HDAC6 IC50
HDAC7 IC50
HDAC8 IC50
:
:
:
:
:
:
:
:
7.7 nM
S
14 nM
12000 nM
>50000 nM
>50000 nM
>50000 nM
>50000 nM
37000 nM
>50000 nM
O
N
H
O
EtO P
EtO
H
N
NH2
HDAC11 IC50
:
13
Figure 6. Full HDAC selectivity data for 13.