6104
H.-G. Häcker et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6102–6105
chosen. All four compounds showed similar effects in the MTT
assay (see Supplementary data). In agreement with the accumula-
tion assay, toxic effects of daunorubicin were reduced. However,
for vinblastine, a potentiation of the cytotoxicity was observed
(Fig. 3). The thienopyrimidines showed no effect on colchicine
transport. Therefore, we could demonstrate a modulation of P-gp
substrate specificity for 12 (QB13) and analogous thieno[2,3-
d]pyrimidines. With respect to the transport profile, this family
of substances corresponded to QB102.15 Moreover, the results
agree with the overlays of QB11, QB13 and QB102 in the pharma-
cophore pattern of the Hoechst 33342 binding site of P-gp.16
In summary, we evaluated a panel of thieno[2,3-d]pyrimidines
and quinazolines as activators of P-gp mediated daunorubicin
transport. Structural modifications in different positions of the
scaffolds were well tolerated by the transporter. Moreover, we
could demonstrate a bidirectional modulation of P-gp activity for
selected compounds in combination with different cytostatic
drugs.
Figure 2. Concentration–effect curve of 12 (QB13) in the daunorubicin accumula-
tion assay. The curve represents the average of three independent experiments.
In the second set (15–24), most phenethyl derivatives were
superior to analogous ethyl acetates. Only the dimethoxyquinazo-
lines 23, 24 had comparable EC50 values. The pyrano derivative 18
Acknowledgments
The authors are grateful to N. Karadag, S. Michels, A. Reiner, M.
Schneider and S. Terhart-Krabbe for assistance. This work has been
supported by the German Research Society (GRK 804).
(0.56 lM) and the N-benzyl-pyrido annelated ester 19 (0.64 lM)
were the most potent substances of this set. A bioisosteric ex-
change of thiophene for benzene gave three active quinazolines
(22–24) with EC50 values in the range of the lead structure 12.
Taken together, the somewhat higher activities of compounds with
aryl substituents in the sulfanyl side chain might be explained by a
further hydrophobic aromatic interaction, as suggested by the
pharmacophore model.16 However, structural modifications of
the lead compound 12 seemed to be well tolerated by P-gp. For
example, truncation of the phenethyl to an ethyl residue led to
the most potent compound 9. An additional carbonyl function in
the phenacyl residue of 13 also gained activity. Moreover, the
introduction of heteroatoms (18) and larger substituents (19)
within the annelated tetrahydrobenzothieno moiety resulted in ac-
tive representatives, too.
Supplementary data
Supplementary data associated with this article can be found, in
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Figure 3. Concentration–effect curves of vinblastine in P-gp-overexpressing cells
(closed circles), P-gp-overexpressing cells + compound 12 (open squares, 31.6
and wild-type cells (closed triangles). No shift was observed for wild-type cells
when compound 12 (31.6 M) was added (see Supplementary data). Curves show a
representative experiment with three replicates.
lM),
l