A Platinum(IV) Anticancer Prodrug Targeting Nucleotide Excision Repair To Overcome Cisplatin Resistance

Article abstract of DOI:10.1002/anie.201608936

DNA damage response plays a key role not only in maintaining genome integrity but also in mediating the antitumor efficacy of DNA-damaging antineoplastic drugs. Herein, we report the rational design and evaluation of a Pt^IVanticancer prodrug inhibiting nucleotide excision repair (NER), one of the most pivotal processes after the formation of cisplatin-induced DNA damage that deactivates the drug and leads to drug resistance in the clinic. This dual-action prodrug enters cells efficiently and causes DNA damage while simultaneously inhibiting NER to promote apoptotic response. The prodrug is strongly active against the proliferation of cisplatin-resistant human cancer cells with an up to 88-fold increase in growth inhibition compared with cisplatin, and the prodrug is much more active than a mixture of cisplatin and an NER inhibitor. Our study highlights the importance of targeting downstream pathways after the formation of Pt-induced DNA damage as a novel strategy to conquer cisplatin resistance.

Full text of DOI:10.1002/anie.201608936

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201608936
German Edition: DOI: 10.1002/ange.201608936
Platinum Prodrugs Very Important Paper
A Platinum(IV) Anticancer Prodrug Targeting Nucleotide Excision
Repair To Overcome Cisplatin Resistance
Zhigang Wang, Zoufeng Xu, and Guangyu Zhu*
Abstract: DNA damage response plays a key role not only in
maintaining genome integrity but also in mediating the
antitumor efficacy of DNA-damaging antineoplastic drugs.
Herein, we report the rational design and evaluation of a PtIV
anticancer prodrug inhibiting nucleotide excision repair
(NER), one of the most pivotal processes after the formation
of cisplatin-induced DNA damage that deactivates the drug
and leads to drug resistance in the clinic. This dual-action
prodrug enters cells efficiently and causes DNA damage while
simultaneously inhibiting NER to promote apoptotic response.
The prodrug is strongly active against the proliferation of
cisplatin-resistant human cancer cells with an up to 88-fold
increase in growth inhibition compared with cisplatin, and the
prodrug is much more active than a mixture of cisplatin and an
NER inhibitor. Our study highlights the importance of
targeting downstream pathways after the formation of Pt-
induced DNA damage as a novel strategy to conquer cisplatin
resistance.
cancer drugs that are widely applied in the clinic,[7] and this
connection is evidenced by the fact that NER-deficient cells
are highly sensitive to platinum agents.[8] Extensive studies
support the notion that NER is greatly associated with
cisplatin resistance in different tumor types, including ovarian
and non-small-cell lung cancer (NSCLC).[9] Overexpression
of NER components such as XPA, ERCC1, or ERCC1–XPF
complex has been noted in cisplatin-resistant tumors and
contributes to enhanced repair.[10] In addition, ERCC1 is the
most useful resistance marker in cisplatin-based adjuvant
therapy in NSCLC patients,[11] and low levels of ERCC1 have
been correlated with overall prolonged survival in cisplatin-
treated NSCLC patients.[12] Thereby, inhibition of intrinsic
NER function, especially in cisplatin-refractory tumors, is
able to potentiate platinum drugs. Indeed, siRNAs or small
molecules targeting NER increase the cytotoxicity of cisplatin
in cisplatin-resistant cell lines.[13]
Based on the key role of NER in mediating the antitumor
efficacy of cisplatin, we rationally designed a dual-action
cisplatin prodrug targeting NER, aiming to improve the
anticancer activity of cisplatin and to conquer cisplatin
resistance. An NER inhibitor (NERi) was incorporated into
a PtIV prodrug in the axial position to obtain NERi-PtIV. This
prodrug strategy has been widely used for multifunctional
PtIV complexes bearing bioactive axial ligands.[14] We
hypothesized that this PtIV prodrug enters cells efficiently
and is reduced by cytoplasmic reductants in the cancer cells to
release cisplatin and NERi. The latter is subsequently able to
inhibit NER to sensitize cancer cells to cisplatin, and the
metabolite cisplatin is able to kill cancer cells more effec-
tively. Furthermore, the conjugation may facilitate the
cellular accumulation of both platinum and NERi. We
envisioned that this synergistic cell-killing mode would lead
to significantly improved anticancer activity in cisplatin-
resistant cells, some of which have a higher NER capacity.[15]
First, the NERi component, (E)-2-(((8a,9a-dihydro-9H-
fluoren-9-ylidene)hydrazono)methyl)benzoic acid, was syn-
thesized.[16] In the NER process, the XPF–ERCC1 heterodi-
mer, a 5’-3’ structure-specific endonuclease, is responsible for
the cleavage of the damaged DNA segment from 5’ to 3’,
which is a rate-limiting step in NER.[13a] NERi is able to bind
to the XPF-binding site of ERCC1 and block the interaction
between ERCC1 and XPF.[16] The N-hydroxysuccinimide
(NHS) ester of NERi was obtained by the reaction of NERi
with NHS in the presence of N,N’-dicyclohexylcarbodiimide,
and the ester was subsequently reacted with c,c,t-[Pt-
(NH3)2Cl2(OH)2] to obtain NERi-PtIV, a monocarboxylated
PtIV prodrug (Figure 1; see also the Supporting Information,
Scheme S1). The purity of the compound was determined to
be > 95% by reverse-phase HPLC (Figure S1). The as-
D
NA damage response (DDR) plays pivotal roles in
maintaining human genome integrity, which is threatened
by different types of exogenous and endogenous genotoxins
that cause DNA damage and genome instability.[1] Defects in
DDR are one of the most pervasive characteristics of human
cancer, allowing cancer cells to survive and proliferate.[2]
DDR also plays crucial roles in regulating the efficacy of
anticancer drugs that exert cytotoxicity through DNA
damage.[3] Very recently, small molecules targeting different
DDR pathways have been used alone or in combination with
radiation therapy and genotoxic chemotherapy for cancer
treatment.[4]
Among different DDR pathways, nucleotide excision
repair (NER) is majorly responsible for the repair of bulky
covalent DNA lesions.[5] The NER process involves different
structure-specific DNA repair endonucleases to remove
a short single-strand DNA segment containing the lesion
after damage recognition and to fill the gap with a newly
synthesized strand.[6] NER is the key pathway to remove the
intrastrand DNA crosslinks formed by platinum-based anti-
[*] Z. Wang, Z. Xu, Prof. Dr. G. Zhu
Department of Biology and Chemistry
City University of Hong Kong
83 Tat Chee Ave, Kowloon Tong, Hong Kong SAR (P.R. China)
E-mail: guangzhu@cityu.edu.hk
Z. Wang, Z. Xu, Prof. Dr. G. Zhu
City University of Hong Kong
Shenzhen Research Institute, Shenzhen (P.R. China)
Supporting information for this article can be found under:
http://dx.doi.org/10.1002/anie.201608936.
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

Angewandte
Communications
Chemie
Table 1: IC50 values (nm) of NERi and Pt compounds. Cells were treated
for 72 h, and the cell viability was determined by MTT assays.
Cell line
cDDP
NERi
>50000 360Æ30
NERi+cDDP[a] NERi-PtIV FI[b]
A2780
360Æ10
60Æ10 6.0
A2780cisR 10300Æ1300 >50000 8170Æ1400
300Æ20 34
5.0
RF[c]
29
–
–
–
A549
4520Æ280
>50000 4350Æ360
260Æ90 17
A549cisR 25500Æ3800 >50000 15400Æ4900
290Æ20 88
RF
5.6
–
–
1.1
–
[a] The molar NERi/cDDP ratio was 1:1 in the NERi/cDDP mixture.
[b] The FI (fold increase) is defined as IC50(cDDP)/IC50(NERi-PtIV).
[c] The RF (resistance factor) is defined as the IC50 value in A2780cisR
divided by the IC50 value in A2780 cells or as the IC50 value in A549cisR
cells divided by the IC50 value in A549 cells. cDDP=cisplatin.
Figure 1. Chemical structures of NERi and NERi-PtIV.
prepared NERi-PtIV prodrug was also characterized by H,
13C, and 195Pt NMR spectroscopy, ESI-MS, and elemental
analysis (Figures S6–S9).
1
Prior to biological evaluation, the reduction potential,
stability, and lipophilicity of NERi-PtIV were measured
because these properties may influence the antitumor activity
of PtIV prodrugs.[17] We first measured the reduction potential
of NERi-PtIV by cyclic voltammetry, which determines how
easily a PtIV prodrug can be reduced to its PtII equivalent. The
reduction potential of NERi-PtIV is À1.16 V (vs. Fc+/Fc =
+ 0.05 V; Figure S10), showing that the prodrug is not easily
reduced. The stability of NERi-PtIV in aqueous solution was
examined by reverse-phase HPLC, and the data suggest that
the compound has maintained its integrity after 24 h at 378C
in a phosphate buffer at pH 7.4 (Figure S11). As the lip-
ophilicity of a compound is associated with the cellular
accumulation, the LogPo/w value of NERi-PtIV was measured
to be 0.87, indicating that the complex is rather lipophilic.
Cell-based assays were carried out to determine the
activity and mechanism of the PtIV prodrug. We first
examined the cytotoxicity of NERi-PtIV against cisplatin-
resistant A2780cisR (ovarian) and A549cisR (NSCLC)
cancer cells with increased NER capability as well as
cisplatin-sensitive A2780 and A549 cells for comparison.[10c,18]
Cisplatin, NERi, and a mixture of cisplatin and NERi at
a molar ratio of 1:1 were included as controls. Cisplatin
showed moderate cytotoxicity against A2780 and A549 cells
with IC50 values of 0.36 and 4.52 mm, respectively, and the drug
was not active against the proliferation of cisplatin-resistant
A2780cisR and A549cisR cells (Table 1). NERi itself was not
cytotoxic against the tested cancer cells, and the IC50 values
were larger than the highest concentration used, which is
consistent with other findings that this type of NER inhibitors
alone has low cytotoxicity in cancer cells.[13c] The cytotoxicity
of the mixture of NERi and cisplatin was measured to
corroborate whether NERi is able to potentiate cisplatin. The
IC50 values of the mixture were lower than those of cisplatin,
and this effect is consistent with previous reports that the
inhibition of NER improves the cytotoxicity of cis-
platin.[13a,c,16] Compared with all the controls mentioned
above, NERi-PtIV showed significantly improved cytotoxicity
in different types of cancer cells, with up to 88-fold higher
cytotoxicity than cisplatin. Remarkably, NERi-PtIV is very
active in cisplatin-resistant cells. The IC50 values of cisplatin in
A2780cisR and A549cisR cells are 10300 Æ 1300 and 25500 Æ
3800 nm, respectively, whereas those of NERi-PtIV are as low
as 300 Æ 20 and 290 Æ 20 nm, respectively (Table 1). The
resistance factor (RF) values of cisplatin are 28.6 and 5.6 in
A2780/A2780cisR and A549/A549cisR cells, and the values of
NERi-PtIV are as low as 5.0 and 1.1, respectively. These results
indicate that NERi-PtIV exhibits a superior inhibitory effect
against the proliferation of cancer cells, especially for
cisplatin-resistant ones.
The cytotoxicity study had confirmed the activity of
NERi-PtIV against cisplatin resistance but mechanistic studies
were still required to determine the contributions of both the
PtIV and the NERi moieties. A549 and A549cisR cells were
used in the following biological assays owing to the dramat-
ically increased cytotoxicity of NERi-PtIV in these cell lines.
To explain the high cytotoxicity of the prodrug, the cellular
accumulation of NERi-PtIV was measured. A549 and
A549cisR cells were treated with 10 mm Pt complexes for
10 h, and the Pt content in the cells was assessed by ICP-MS.
The results indicate that the accumulation of NERi-PtIV is
much higher than that of cisplatin in both A549 and A549cisR
cells, with increases by factors of 47 and 62, respectively
(Figure S12). We attributed this effect to the high lipophilicity
of NERi-PtIV. Furthermore, compared with cisplatin-sensitive
cells, reduced accumulation of Pt was observed for cisplatin-
resistant cells for cisplatin but not for NERi-PtIV.
As it is widely agreed that platinum drugs exert their
cytotoxicity through DNA binding to block replication and
transcription, the levels of Pt–GG intrastrand crosslinks
formed by Pt complexes in genomic DNAwere also measured
by an immuno-slot blot (ISB) assay.[19] After 10 h treatment,
genomic DNA of A549 and A549cisR cells was extracted, an
equal amount of DNA was loaded onto a nylon membrane,
and cis-{Pt(NH3)2}2+ 1,2-d(GpG) (Pt–GG) intrastrand cross-
links were detected by an anti-Pt–GG antibody.[20] The result
shows that NERi-PtIV induces higher levels of Pt–GG intra-
strand crosslinks than cisplatin in both A549 and A549cisR
cells (Figure S13). For instance, the relative intensities of Pt–
GG intrastrand crosslinks in A549 and A549cisR cells treated
with 5 mm cisplatin are only 8.4 and 4.8, whereas those for
NERi-PtIV-treated cells are 34 and 47, showing four- and
tenfold enhancement, respectively. These results indicate that
NERi-PtIV is efficiently reduced in cells to release cisplatin for
DNA binding. The complexation of NERi with cisplatin
significantly enhances the levels of Pt accumulation and
2
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!

Angewandte
Communications
Chemie
platination of genomic DNA, which is one of the reasons for
induced apoptosis in both cisplatin-sensitive and -resistant
the remarkable cytotoxicity of NERi-PtIV.
cells. These data are consistent with a previous report that
cisplatin induces apoptosis in cells with inhibited NER
function.[23]
Next, we examined the cell cycle arrest ability of NERi-
PtIV and the cell death pathway upon treatment. Cells were
treated with different concentrations of cisplatin, NERi, or
NERi-PtIV for 24 h, and the cell cycle distribution was
determined by flow cytometry. As shown in Figure 2A,B,
To investigate whether NERi also contributes to the
elevated cytotoxicity of NERi-PtIV by inhibiting the repair of
cisplatin–DNA crosslinks, a time-dependent cell-based assay
was performed.[24] This assay was based on the assumption
that non-replicating cells treated with NERi-PtIV have a lower
DNA damage repair capability than those treated with
cisplatin, leaving more Pt–DNA crosslinks on the genomic
DNA at certain time points. A549cisR cells were treated with
2 mm hydroxyurea (HU) for 24 h prior to addition of the Pt
complexes to block DNA replication (Figure S15), followed
by treatment with 25 mm cisplatin or 1 mm NERi-PtIV for
2 h.[25] The concentrations were chosen to get an identical
level of platinated DNA as the starting points (Figure S16).
The cells were further incubated in a medium containing HU
only to allow for the DNA damage repair, and the levels of
Pt–GG intrastrand crosslinks in the genomic DNA were
determined by an ISB assay. As shown in Figure 3 and
Figure 2. Cell cycle arrest of A) A549 and B) A549cisR cells treated
with complexes for 24 h. C) Flow cytometry results for A549 and
A549cisR cells treated with cDDP and NERi-PtIV at their IC90 concen-
trations or with 50 mm NERi for 24 h. Bottom left: viable cells; bottom
right: early apoptotic cells; top right: dead cells; top left: early necrotic
cells.
Figure 3. NER efficiency of A549cisR cells treated with 1 mm NERi-PtIV
or 25 mm cDDP. Cells were pretreated with 2 mm hydroxyurea (HU) for
24 h, then treated with Pt complexes for 2 h, and released into HU-
containing medium for post-incubation to allow for repair of Pt-
induced DNA damage. A) Pt–GG intrastrand crosslink levels. B) Rela-
tive Pt–GG crosslink levels normalized to t=0 (*, p<0.05; ns=not
significant).
cisplatin arrests the cell cycle at the S phase in both A549 and
A549cisR cells, which is in accordance with other reports.[21]
NERi does not significantly alter the cell cycle, which was
attributed to the low cytotoxicity of the compound. Notably,
NERi-PtIV arrests the cell cycle at the S phase in a concen-
tration-dependent manner, which is similar to the action of
cisplatin. It is noteworthy that NERi-PtIV is able to arrest the
cell cycle at a lower concentration than cisplatin in both the
sensitive and resistant cells, confirming the higher cytotoxicity
of the prodrug especially in the latter case. Blocking the cell
cycle at the S phase suggests that NERi-PtIV may exert its
cytotoxicity through the inhibition of DNA replication and
that the Pt moiety in the prodrug strongly contributes to this
effect. To further evaluate the cell death pathways induced by
NERi-PtIV, an Annexin V-FITC/propidium iodide (PI)
double-staining assay was carried out.[22] A549 and
A549cisR cells were treated with different Pt compounds at
their IC90 concentrations or with NERi at 50 mm, and the
fractions of viable, early apoptotic, early necrotic, and dead
cells were quantified by flow cytometry (Figures 2C and S14).
Cisplatin mainly induced apoptosis in both cell lines whereas
NERi itself did not induce apoptosis or necrosis because of its
low cytotoxicity. The dual-targeting prodrug NERi-PtIV
Table S1, the intensities of the initial Pt–GG intrastrand
crosslinks in cisplatin- and NERi-PtIV-treated A549cisR cells
were 8.2 and 8.0, respectively, which are identical, and the
intensity decreased more slowly in cells treated with the
prodrug. For example, after 24 h, the intensities of the Pt–GG
intrastrand crosslinks in cisplatin- and NERi-PtIV-treated cells
had decreased to 1.9 and 3.5, respectively, and the percentages
of remaining Pt–GG intrastrand crosslinks were 23% and
43% for cisplatin and NERi-PtIV, respectively. As the removal
of Pt–GG intrastrand crosslinks mainly occurs through the
NER pathway, the higher levels of remaining Pt–GG intra-
strand crosslinks in A549cisR cells treated with NERi-PtIV
imply a lower NER efficiency, which is due to the inhibition of
NER achieved through blocking the interaction between XPF
and ERCC1. These results suggest that NERi-PtIV is able to
inhibit NER in A549cisR cells, resulting in high cytotoxicity.
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

Angewandte
Communications
Chemie
We further investigated the ability of NERi to inhibit the
transcription-coupled NER (TC-NER) of cisplatin–DNA
crosslinks. A transcription assay utilizing a Gaussia luciferase
plasmid (pGLuc) containing global cisplatin–DNA lesions
was carried out. The Pt damage results in decreased levels of
transcription, and transcription recovery indicates damage
removal. This assay has been utilized for the study of
transcription-coupled repair (TCR) of different types of Pt–
DNA lesions in a variety of mammalian cancer cells with
different repair deficiency statuses.[26] Cisplatin-damaged
pGLuc plasmids were transfected into A549cisR cells, and
the transcription level was normalized to that from intact
plasmids. As depicted in Figure S17, the transcription level
recovered for pGLuc plasmids containing 8.1 or 15.6 Pt/
plasmid, indicating the repair of Pt–DNA damage, and that
NER plays a major role in this case as Pt–DNA intrastrand
crosslinks are the major type of cisplatin-induced DNA
damage.[27] When the cells are treated with NERi, the
recovery rate is apparently lower than that of the untreated
control. For example, when the cells were treated with 20 mm
NERi and transfected with pGLuc plasmid containing 8.1 Pt/
plasmid, the transcription level increased from 30% at 0 h to
55% at 44 h, whereas it increased from 30% at 0 h to 76% at
44 h in the control group without NERi treatment. This result
clearly indicates that NERi is able to inhibit TCR of cisplatin-
induced DNA damage and additionally confirms the role of
NERi in NERi-PtIV, which elevates its anticancer activity by
inhibiting repair. Together with the data of the cellular
accumulation studies and the Pt levels on genomic DNA, it is
evident that the significantly elevated cytotoxicity of NERi-
PtIV over cisplatin results from a combination of improved
cellular accumulation and repair inhibition.
Keywords: cancer · cisplatin · DNA · platinum prodrugs ·
nucleotide excision repair
[1] P. A. Jeggo, L. H. Pearl, A. M. Carr, Nat. Rev. Cancer 2016, 16,
35 – 42.
[2] C. J. Lord, A. Ashworth, Nature 2012, 481, 287 – 294.
[3] P. Bouwman, J. Jonkers, Nat. Rev. Cancer 2012, 12, 587 – 598.
[4] a) T. Helleday, E. Petermann, C. Lundin, B. Hodgson, R. A.
Sharma, Nat. Rev. Cancer 2008, 8, 193 – 204; b) L. H. Pearl, A. C.
Schierz, S. E. Ward, B. Al-Lazikani, F. M. Pearl, Nat. Rev. Cancer
2015, 15, 166 – 180.
[5] S. P. Jackson, J. Bartek, Nature 2009, 461, 1071 – 1078.
[6] a) S. C. Shuck, E. A. Short, J. J. Turchi, Cell Res. 2008, 18, 64 – 72;
b) A. Sancar, Angew. Chem. Int. Ed. 2016, 55, 8502 – 8527;
Angew. Chem. 2016, 128, 8643 – 8670.
[7] D. Wang, S. J. Lippard, Nat. Rev. Drug Discovery 2005, 4, 307 –
320.
[8] a) G. Damia, L. Imperatori, M. Stefanini, M. DꢀIncalci, Int. J.
Cancer 1996, 66, 779 – 783; b) T. Furuta, T. Ueda, G. Aune, A.
Sarasin, K. H. Kraemer, Y. Pommier, Cancer Res. 2002, 62,
4899 – 4902.
[9] B. Kçberle, M. T. Tomicic, S. Usanova, B. Kaina, Biochim.
Biophys. Acta Rev. Cancer 2010, 1806, 172 – 182.
[10] a) M. Dabholkar, F. Bostick-Bruton, C. Weber, V. A. Bohr, C.
Egwuagu, E. Reed, J. Natl. Cancer Inst. 1992, 84, 1512 – 1517;
b) M. Dabholkar, J. Vionnet, F. Bostick-Bruton, J. J. Yu, E.
Reed, J. Clin. Invest. 1994, 94, 703 – 708; c) K. V. Ferry, T. C.
Hamilton, S. W. Johnson, Biochem. Pharmacol. 2000, 60, 1305 –
1313.
[11] K. A. Olaussen et al., N. Engl. J. Med. 2006, 355, 983 – 991.
[12] R. V. N. Lord et al., Clin. Cancer Res. 2002, 8, 2286 – 2291.
[13] a) M. Selvakumaran, D. A. Pisarcik, R. Bao, A. T. Yeung, T. C.
Hamilton, Cancer Res. 2003, 63, 1311 – 1316; b) I.-Y. Chang, M.-
H. Kim, H. B. Kim, D. Y. Lee, S.-H. Kim, H.-Y. Kim, H. J. You,
Biochem. Biophys. Res. Commun. 2005, 327, 225 – 233; c) E. M.
McNeil et al., DNA Repair 2015, 31, 19 – 28.
[14] a) R. K. Pathak, S. Marrache, J. H. Choi, T. B. Berding, S. Dhar,
Angew. Chem. Int. Ed. 2014, 53, 1963 – 1967; Angew. Chem. 2014,
126, 1994 – 1998; b) Q. Cheng, H. Shi, H. Wang, Y. Min, J. Wang,
Y. Liu, Chem. Commun. 2014, 50, 7427 – 7430; c) D. Y. Q. Wong,
C. H. F. Yeo, W. H. Ang, Angew. Chem. Int. Ed. 2014, 53, 6752 –
6756; Angew. Chem. 2014, 126, 6870 – 6874; d) S. G. Awuah, Y.-
R. Zheng, P. M. Bruno, M. T. Hemann, S. J. Lippard, J. Am.
Chem. Soc. 2015, 137, 14854 – 14857; e) R. Raveendran, J. P.
Braude, E. Wexselblatt, V. Novohradsky, O. Stuchlikova, V.
Brabec, V. Gandin, D. Gibson, Chem. Sci. 2016, 7, 2381 – 2391;
f) J. S. Butler, P. J. Sadler, Curr. Opin. Chem. Biol. 2013, 17, 175 –
188; g) X. Y. Wang, Z. J. Guo, Chem. Soc. Rev. 2013, 42, 202 –
224.
In conclusion, we have rationally designed a unique PtIV
prodrug by considering the mechanism of action of cisplatin.
This dual-action prodrug, NERi-PtIV, contains both a cisplatin
moiety and a NERi moiety. NERi-PtIV shows dramatically
enhanced cytotoxicity compared with cisplatin, especially in
cisplatin-resistant ovarian and lung cancer cells. NERi-PtIV
efficiently enters cells and is reduced to cisplatin with
concomitant liberation of NERi. DNA damage induced by
cisplatin and reduced DNA damage repair by NERi were
confirmed to occur inside cells, and these two processes result
in synergistic cell killing. We have provided the first example
of a PtIV prodrug targeting DNA damage repair, the key
process in mediating the antitumor activity of and resistance
to cisplatin. Our study encourages the development of more
distinct PtIV prodrugs by inhibiting DNA damage repair
pathways and highlights the importance of targeting down-
stream pathways after the formation of Pt-induced DNA
damage as a strategy to conquer cisplatin resistance.
[15] a) L. P. Martin, T. C. Hamilton, R. J. Schilder, Clin. Cancer Res.
2008, 14, 1291 – 1295; b) J. Y. Choi, J.-M. Park, J. M. Yi, S.-H.
Leem, T.-H. Kang, Oncotarget 2015, 6, 22575 – 22586; c) H.
Masuda, R. F. Ozols, G.-M. Lai, A. Fojo, M. Rothenberg, T. C.
Hamilton, Cancer Res. 1988, 48, 5713 – 5716.
[16] L. P. Jordheim et al., Mol. Pharmacol. 2013, 84, 12 – 24.
[17] M. D. Hall, H. R. Mellor, R. Callaghan, T. W. Hambley, J. Med.
Chem. 2007, 50, 3403 – 3411.
[18] N. Zeng-Rong, J. Paterson, L. Alpert, M.-S. Tsao, J. Viallet,
M. A. Alaoui-Jamali, Cancer Res. 1995, 55, 4760 – 4764.
[19] B. M. Barakat, Q.-E. Wang, C. Han, K. Milum, D.-T. Yin, Q.
Zhao, G. Wani, E.-S. A. Arafa, M. A. El-Mahdy, A. A. Wani, Int.
J. Cancer 2010, 127, 977 – 988.
Acknowledgements
We thank the National Natural Science Foundation of China
(21371145) and the City University of Hong Kong (9667114
and 9667131) for funding.
[20] B. Liedert, D. Pluim, J. Schellens, J. Thomale, Nucleic Acids Res.
2006, 34, 47 – 58.
4
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!

Angewandte
Communications
Chemie
[21] G. I. Shapiro, J. W. Harper, J. Clin. Invest. 1999, 104, 1645 – 1653.
[26] G. Zhu, M. Myint, W. H. Ang, L. Song, S. J. Lippard, Cancer Res.
[22] S. E. Logue, M. Elgendy, S. J. Martin, Nat. Protoc. 2009, 4, 1383 –
1395.
2012, 72, 790 – 800.
[27] Z. H. Siddik, Oncogene 2003, 22, 7265 – 7279.
[23] S. Lomonaco, PhD Thesis, Wayne State University, 2007.
[24] Q. E. Wang, K. Milum, C. Han, Y. W. Huang, G. Wani, J.
Thomale, A. A. Wani, Mol. Cancer 2011, 10, 24 – 35.
[25] A. Koc, L. J. Wheeler, C. K. Mathews, G. F. Merrill, J. Biol.
Chem. 2004, 279, 223 – 230.
Received: September 13, 2016
Published online: && &&, &&&&
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Platinum Prodrugs
No DNA damage repair: A platinum(IV)
anticancer prodrug targeting nucleotide
excision repair was developed that over-
comes cisplatin resistance. The cytotox-
icity of this prodrug was up to 88 times
higher than that of cisplatin in cisplatin-
resistant human cancer cells.
Z. Wang, Z. Xu, G. Zhu*
&&&& — &&&&
A Platinum(IV) Anticancer Prodrug
Targeting Nucleotide Excision Repair To
Overcome Cisplatin Resistance
6
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!