Communications
Tase, REP, and biotin-GPP (a GGPP analogue), and then the
inhibitor, is also the most potent inhibitor of cancer cell
proliferation. The inhibition of cancer cell proliferation (both
Ras-transformed and non-Ras-transformed) by the highly
selective RabGGTase inhibitors 14 and 15 is in accordance
with the finding that RabGGTase siRNA, but not FTase
siRNA, induces increased apoptosis in C. elegans and A549
cells.[4] Therefore, these results emphasize that RabGGTase
should be considered an anticancer target.
In conclusion, by applying protein/inhibitor cocrystal
structure analysis, VHS, individual docking, and synthesis
we have identified potent and selective RabGGTase inhib-
itors that inhibit proliferation of several cancer cell lines
without displaying cytotoxicity in PBMC cells. Guided by the
well-defined binding mode and conformation of BMS3 in
RabGGTase and FTase in the cocrystal structures, we have
shown that it is possible to make BMS3 analogues that are
selective for RabGGTase. This has been achieved by exploit-
ing recently identified structural features of the RabGGTase
active site such as a combination of the TAG tunnel and lipid
binding site. These results also indicate that RabGGTase-
THB cocrystal structures might be a valuable starting point
for more extensive structure-based design of selective
RabGGTase inhibitors, for example by using computational
methods based on fragment docking and growing/linking
approaches.
Rab-biotin-GPP conjugates were detected by Western blot-
ting (see the Supporting Information).[9] Compounds 4–7, 9–
11, 14, and 15 all caused increased labeling of endogenous
Rab proteins with biotin-GPP, thus indicating inhibition of
cellular prenylation, with IC50 values in the nanomolar range
(Table 2).[15] Furthermore, the cellular IC50 values roughly
follow the in vitro data, thus indicating that the modifications
did not significantly affect the bioavailability. As expected,
compound 8, which was inactive in vitro, did not inhibit
cellular Rab prenylation.
Table 2: Reprenylation assay results of THB library compounds.
Cmpd Reprenylation rel. IC50
Cmpd Reprenylation rel. IC50
[nm][a]
[nm][a]
BMS3 74Æ34
9
201Æ78
93Æ42
11Æ5
4
5
6
7
8
81Æ32
343Æ29
307Æ40
43Æ12
>30000
10
11
14
15
311Æ193
49Æ32
[a] For the calculation of relative IC50 values, the signal obtained from the
positive control (1 mm BMS3, which gives a saturated reprenylation
signal) was set as 100% RabGGTase inhibition.
Received: February 17, 2011
Published online: April 21, 2011
Next, we studied the effect of several inhibitors on the
viability of mammalian cancer cell lines and peripheral blood
mononuclear cells (PBMC; Table 3). In these experiments,
cultured cells were incubated with a THB for 72 h, followed
by incubation with resazurin. Viable cells reduce resazurin to
the fluorescent resorufin. Therefore, fluorescence intensity is
a measure of cell viability.[15]
Keywords: antitumor agents · drug design · inhibitors ·
.
protein modification · transferases
[2] a) K. F. Leung, R. Baron, M. C. Seabra, J. Lipid Res. 2006, 47,
Table 3: Cellular viability assay data (IC50, [nm]).[a]
Cmpd
HCT116
A2780
HeLa
PBMC
BMS3
4
5
7
11
14
15
63Æ8
43Æ0
101Æ2
151Æ21
745Æ303
59Æ2
>10000
>10000
>10000
>10000
>10000
>10000
>10000
[3] a) K. W. Cheng, J. P. Lahad, W. L. Kuo, A. Lapuk, K. Yamada, N.
Auersperg, J. S. Liu, K. Smith-McCune, K. H. Lu, D. Fishman,
Croizet-Berger, C. Daumerie, M. Couvreur, P. J. Courtoy, M. F.
[4] M. R. Lackner, R. M. Kindt, P. M. Carroll, K. Brown, M. R.
Cancilla, C. Y. Chen, H. de Silva, Y. Franke, B. Guan, T. Heuer,
T. Hung, K. Keegan, J. M. Lee, V. Manne, C. OꢀBrien, D. Parry,
J. J. Perez-Villar, R. K. Reddy, H. J. Xiao, H. J. Zhan, M.
Cockett, G. Plowman, K. Fitzgerald, M. Costa, P. Ross-Mac-
230Æ59
75Æ10
112Æ2
2Æ1
130Æ9
43Æ9
111Æ1
18Æ1
21Æ4
443Æ173
589Æ199
797Æ330
35Æ1
115Æ3
101Æ11
[a] The IC50 values for individual compounds reflect the inhibition of cell
proliferation. The compounds were evaluated against a DMSO control.
For further details, see the Supporting Information.
b) R. A. Gibbs, T. J. Zahn, J. S. Sebolt-Leopold, Curr. Med.
Chem. 2001, 8, 1437 – 1465.
[6] F. El Oualid, L. H. Cohen, G. A. van der Marel, M. Overhand,
Curr. Med. Chem. 2006, 13, 2385 – 2427.
[7] a) A. D. Basso, P. Kirschmeier, W. R. Bishop, J. Lipid Res. 2006,
47, 15 – 31; b) P. A. Konstantinopoulos, M. V. Karamouzis, A. G.
Kazi, A. Carie, M. A. Blaskovich, C. Bucher, V. Thai, S.
Moulder, H. Peng, D. Carrico, E. Pusateri, W. J. Pledger, N.
As can been seen in Table 3, the tested THBs were not
generally toxic to blood cells, but proved to be potent
inhibitors of the proliferation of three cancer cell lines. The
IC50 values in this assay generally follow the trends of the
cellular Rab prenylation assay. Most importantly, highly
selective RabGGTase inhibitor 15 inhibits cancer cell pro-
liferation as potently as the dual RabGGTase/FTase inhibitor
BMS3, whereas the somewhat lower potency of THB 14
corresponds well with its decreased potency as a cellular Rab
prenylation inhibitor. The most potent inhibitor of cellular
Rab prenylation, THB 11, which is also a highly potent FTase
[8] a) M. Watanabe, H. D. G. Fiji, L. Guo, L. Chan, S. S. Kinderman,
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 4957 –4961