286
P. Zhao et al. / Bioorganic Chemistry 36 (2008) 278–287
Form II
Form I
0
1
2
3
4
5
6
7
Fig. 11. Photocleavage of pBR322 plasmid DNA in the presence of [AQPTMPyP]I3
and different inhibitors after irradiation by visible light (k > 470 nm) for 15 min.
Ten-microliters reaction mixtures contained 1.0
lg of plasmid DNA in buffer C.
[Por] = 2 M. Lane 0: DNA control; lane 1: in the presence of porphyrin, no
l
Fig. 13. The binding modes of cationic Por–AQ hybrids to CT DNA: (a) for
[AQPTMPyP]I3, [AQOTMPyP]I3 and [AQUTMPyP]I3; (b) for [AQATMPyP]I3.
inhibitor; lanes 2–6: in the presence of porphyrin and inhibitor: (2) ethanol (5 mM),
(3) methanol (5 mM), (4) DMSO (5 mM); (5) NaN3 (5 mM), (6) under an Ar
atmosphere, (7) 70% D2O.
and serve as wavelength-dependent photonucleases under irradia-
tion with visible and ultraviolet light. The order of efficiency for
DNA binding and photocleavage is [AQPTMPyP]I3 > [AQOTMPyP]I3 >
[AQUTMPyP]I3 > [AQATMPyP]I3. Proper length of flexible linkage
seems very significant in designing such kind of drugs with multi-
ple interactive sides. These results may facilitate the design of
highly-efficient yet noncardiotoxic anthracycline antitumor
antibiotics.
a
Form II
Form I
0
0
1
1
2
2
3
4
4
5
b
Form II
Form I
Acknowledgments
3
5
We are grateful to the supports of Guangzhou Municipality Sci-
ence and Technology Bureau of China, the National Natural Science
Foundation of China and National Key Foundation Research Devel-
opment Project (973) Item of China (No. 2007 CB815306).
Fig. 12. Photocleavage of pBR322 plasmid DNA after irradiated by visible light
(k > 470 nm) in air (a) or ultraviolet light (k < 350 nm) under an Ar atmosphere (b).
Ten-microliters reaction mixtures contained 1.0
lg of plasmid DNA in buffer C.
[Por] = 2 M. Lane 0: untreated DNA, no irradiation; Lanes 1, 2, 3, 4, 5: in the
l
presence of [HTMPyP]I3, [AQATMPyP]I3, [AQPTMPyP]I3, [AQOTMPyP]I3 and
[AQUTMPyP]I3, respectively, irradiation for 20 min.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
3.2.2. Wavelength-dependent DNA photocleavage
To investigate the photocleavage ability of Por and AQ moiety of
the hybrid, respectively, wavelength-dependent experiments were
carried out by irradiating with visible light (at porphyrin’s excited
wavelength) or UV light (at anthraquinone’s excited wavelength).
The results are given in Fig. 12. Without irradiation, no substantial
cleavage of DNA was observed for all the compounds (data not
shown). Under irradiation with visible light, the DNA-photoclea-
vage activities of the cationic Por–AQ hybrids follow an order
of [AQPTMPyP]I3 > [AQOTMPyP]I3 > [AQUTMPyP]I3 (>[HTMPyP]I3) >
[AQATMPyP]I3) which is in parallel with the magnitude of their
DNA-binding constants (Kb). It seems that large Kb and intercala-
tive binding mode are advantageous to effective DNA photoclea-
vage. These results are in high consistent with previous reports
on the relationship between DNA-binding and photocleavage of
cationic porphyrins [50,52].
The UV light irradiation experiment was carried out in Ar atmo-
sphere to get rid of the possible effect of Por moiety. The results
shows that the DNA-photocleavage abilities of [AQPTMPyP]I3,
[AQOTMPyP]I3 and [AQUTMPyP]I3 are similar and higher than that
of [AQATMPyP]I3. This may also result from the more effective DNA
binding of AQ moieties in the long-linked hybrids than that in
[AQATMPyP]I3.
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4. Conclusion
This paper and its predecessor [20] introduced a series of cat-
ionic Por–AQ hybrids with various bridging links and their binding
behaviors with CT DNA as well as their photocleavage activities to
plasmid DNA. Through spectral, thermodynamic and hydrody-
namic methods, it is found that the Por and AQ units in [AQPTMPy-
P]I3, [AQOTMPyP]I3 and [AQUTMPyP]I3 are sterically appropriate to
bis-intercalation while those of [AQATMPyP]I3 suffer from severe
steric strains in binding with DNA (see Fig. 13). All the cationic
water-soluble Por–AQ derivatives give rise to DNA photocleavage