Unexpected photoactivation pathways in a folate-receptor-targetedtrans-diazido Pt(iv) anticancer pro-drug

Article abstract of DOI:10.1039/d0dt02577a

A conjugate between a photoactivetrans-diazido Pt(iv) pro-drug,trans,trans,trans-[Pt(N₃)₂(OH)₂(py)₂], and folic acid has been synthesized and fully characterized by high resolution ESI-MS, NMR and UV-vis spectroscopy. Photoactivation of the Pt-folate conjugate with visible light confirmed the generation of cytotoxic Pt(ii) species capable of binding to guanine nucleobases. Importantly, photoreduction of the Pt(iv) complex triggered the photodecomposition of the folate vector into ap-aminobenzoate-containing fragment and several pterin derivatives, including 6-formylpterin. Besides exhibiting high dark stability in physiological-like conditions, the Pt-folate conjugate wasca. 2× more photocytotoxic towards MCF-7 breast cancer cell line than its parent Pt(iv) complex with a high photoselectivity index (PI > 6.9). The higher photocytotoxicity of the conjugate may be a consequence of its higher cellular accumulation and of the generation of a set of different cytotoxic species, including Pt(ii) photoproducts and several pterin derivatives, which are known to generate ROS.

Full text of DOI:10.1039/d0dt02577a

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14 March 2017
Pages 3073-3412
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Unexpected photoactivation pathways in a folate-receptor-targeted trans-
DOI: 10.1039/D0DT02577A
diazido Pt(IV) anticancer pro-drug.
Albert Gandioso,a Anna Rovira,a Huayun Shi,b Peter J. Sadler,b and Vicente Marchán*a
aDepartament de Química Inorgànica i Orgànica, Secció de Química Orgànica, IBUB,
Universitat de Barcelona, Martí i Franquès 1-11, E-08028 Barcelona (Spain).
E-mail: vmarchan@ub.edu
bDepartment of Chemistry, University of Warwick, Coventry CV4 7AL, UK.
Abstract
A conjugate between a photoactive trans-diazido Pt(IV) pro-drug, trans,trans,trans-
[Pt(N3)2(OH)2(py)2], and folic acid has been synthesized and fully characterized by high
resolution ESI-MS, NMR and UV-vis spectroscopy. Photoactivation of the Pt-folate conjugate
with visible light confirmed the generation of cytotoxic Pt(II) species capable of binding to
guanine nucleobases. Importantly, photoreduction of the Pt(IV) complex triggered the
photodecomposition of the folate vector into a p-aminobenzoate-containing fragment and
several pterin derivatives, including 6-formylpterin. Besides exhibiting high dark stability in
physiological-like conditions, the Pt-folate conjugate was ca. 2x more photocytotoxic towards
MCF-7 breast cancer cell line than its parent Pt(IV) complex with a high photoselectivity
index (PI >6.9). The higher photocytotoxicity of the conjugate may be a consequence of its
higher cellular accumulation and of the generation of a set of different cytotoxic species,
including Pt(II) photoproducts and several pterin derivatives, which are known to generate
ROS.
1

Dalton Transactions
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Folate receptors (FRs), which are involved in the uptake of folic acid (vitamin B9), exist in
DOI: 10.1039/D0DT02577A
three different isoforms (α, β, and ). Among them, FRα is expressed at very low levels in
normal tissues, but it is highly up-regulated on the cell surface of a wide variety of cancers,
including ovarian, kidney, brain, triple-negative breast, colon, lung tumors and head and neck
carcinomas, making it a well-stablished target for anticancer drug development.1 Owing to
the frequent overexpression of FRα on human cancers ( 40%), the attachment of folate to
potent cytotoxic agents represents a promising approach in tumor-targeted chemotherapy.2
Indeed, folate-based small drug conjugates bind to FRα on cancer cells with high affinity
resulting in subsequent internalization through receptor-mediated endocytosis, in a the
process usually as effective as that displayed by folic acid in its free form.
In recent years, a large variety of chemotherapeutic agents have been conjugated to folic
acid for active targeted drug delivery, including small organic drugs such as chlorambucil,3
paclitaxel and derivatives,4 mitomycin C,5 and photosensitizers for application in
photodynamic therapy.6 One of the most successful folate-small drug conjugates is
Vintafolide, which delivers a microtubule-destabilizing drug to tumors that overexpress FRα.7
Vintafolide has shown promising results, both as a single agent, as well as in combination
with doxorubicin in different clinical trials, being Phase III trials completed in 2014 for the
treatment of platinum-resistant ovarian cancer.
Although less deeply investigated, folate conjugates involving metal-based anticancer drugs8
represent a viable choice for developing novel targeted chemotherapeutic agents operating
with alternative mechanisms of action compared with organic drugs,9 which would facilitate
overcoming of inherent or acquired resistance in cancer cells. Among them, Pt(II) and Pt(IV)
complexes have received great attention owing to the success history of cisplatin and its two
FDA-approved analogues in the clinical treatment of cancer. One of the first examples of a
folate-platinum conjugate was reported by Gibson and co-workers who developed long-
circulating PEGylated carboplatin analogues with improved cell permeation abilities by
conjugating the platinum moiety to folate-targeted PEG carriers.10 Another interesting
approach to delivering platinum drugs to cancer cells overexpressing FRα was described by
Lippard and collaborators who took advantage of the two axial positions of Pt(IV) complexes
to attach them simultaneously to folate and to a delivery system based on a single-wall
carbon nanotube.11
Photoactivatable metallodrugs have also demonstrated great potential in photoactivated
chemotherapy (PACT).12 Diazidodihydroxido Pt(IV) pro-drugs, such as trans,trans,trans-
[Pt(N3)2(OH)2(py)2] (1, Fig. 1), are particularly interesting for improved treatment of cancer
due to their high stability, low toxicity in the dark, potent photocytotoxicity upon irradiation
with visible light, and novel mechanisms of action.13 In addition, derivatization of the two
detachable axial ligands in Pt(IV) complexes offers the possibility to modulate or improve
2

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their physicochemical and pharmacological properties such as aqueous solubDilOityI: ,10.c10e3l9lu/Dla0DrT02577A
uptake and target specificity.14 In this context, we have conjugated Pt(IV) pro-drug 1 to small
peptides targeting different integrin receptors (αvβ3/αvβ5 or α6) that are overexpressed in
various cancer cells.15 Complex 1 has also been attached to drug delivery upconversion-
luminescent nanoparticles,16 hydrogels,17 and block copolymer micelles18 for triggering
activation with longer wavelengths and improving selectivity.
O
O
C
H
H
N
N
O
OR
Pt
N3
N
N3
N
N
N
O
folate receptor 
targeting vector
PEG
spacer
Pt
N3
N3
OH
OH
1
R = H,
3
Pt-folate conjugate,
2
R = succinate,
Fig.
1
Structure
of
trans,trans,trans-[Pt(N3)2(OH)2(py)2]
(1),
trans,trans,trans-
[Pt(N3)2(OH)(succ)(py)2] (2), and the schematic representation of the Pt–folate conjugate (3).
Based on these antecedents, herein we report the conjugation of Pt(IV) pro-drug 1 to folic
acid via its monosuccinate derivative (2, Fig. 1), and investigation of the photoactivation,
photocytoxicity and cellular accumulation of the resulting Pt-folate conjugate (3). As
previously found with conjugates involving photoactivatable metallodrugs and targeting
vectors based on receptor-binding peptides,15,19 the selectivity of the Pt-folate conjugate
towards cancer cells is controlled at two levels. First, the conjugate will be internalized only in
cancer cells overexpressing FR, and second, the release of cytotoxic Pt(II) species from the
Pt(IV) pro-drug will take place only at the tumor irradiation site. As shown in Fig. 1, a
polyethylene glycol (PEG) spacer was introduced between the Pt(IV) complex and folate to
increase hydrophilicity and biocompatibility, as well as to separate both moieties in the
conjugate, the latter being an important issue to maintain recognition by FR. Besides
increasing water solubility, PEG spacers are known to minimize aggregation and non-specific
uptake of the resulting conjugates by cells.7 In addition, derivatization of folic acid through the
 carboxyl group is known not to alter significantly binding affinity for FR, whereas the
corresponding -carboxyl-linked conjugates are not readily recognized.2b,11
First, we synthesized a suitable folic acid derivative (4) incorporating a short PEG spacer and
a primary amino function to facilitate conjugation with complex 2 via the formation of an
amide bond (Scheme 1). Compound 4 was synthesized in two steps by reaction of the N-
hydroxysuccinimidyl ester of folic acid and N-Boc-4,7,10-trioxa-1,13-tridecanediamine
followed by acidic TFA treatment to remove the Boc group.11 Then, complex 2 was attached
to the amino-containing folate derivative by using a strong activator (HATU) in the presence
of DIPEA in dry DMF for 2 h at RT under an Ar atmosphere and protected from light. The
3

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expected Pt-folate conjugate (3) was obtained as a pale yellow solid (32 %DOyIi:e1l0d.1)03a9/fDte0DrT02577A
purification by reversed-phase HPLC and lyophilization (Fig. S1, ESI†).
O
OH
O
OH
O
O
H
OH
2 steps
N
O
O
N
H
OH
N
H
O
NH2
5
2
3
4
6
N
O
N
N
O
HN
N
N
N
4
H
H
7
2
H2N
N
N
H2N
N
O
2
, HATU, DIPEA
1
8
DMF, Ar, 2 h, RT
O
OH
N
N3
Pt OH
O
H
O
N
O
OH
N
N
H
O
N
2
H
O
N3
N
N
N
O
N
N
H
3
Pt-folate conjugate ( )
H2N
Scheme 1. Synthesis of Pt-folate conjugate (3).
1
13
Conjugate 3 was characterized by high-resolution ESI mass spectrometry, H and C NMR
and UV-vis spectroscopy. An m/z value consistent with the calculated value of the charged
species ([MH] and ([M2H]2) and with the expected isotopic mass distribution pattern of Pt
1
was obtained (Fig. S2, ESI†). In addition, the assignment of the H NMR spectra of 3 in
DMSO-d6 confirmed the covalent attachment of the Pt(IV) complex to folic acid. As shown in
Fig. 2, the three expected signals of the pyridine ligands in the platinum complex were
observed at 8.80, 8.27 and 7.82 ppm. In addition, all the diagnostic signals from the three
1
components of folate backbone were clearly identified in the aromatic region of the H NMR
spectra (Fig. 2): pterin (a singlet at 8.64 ppm corresponding to proton 7 of the heterocycle),
p-aminobenzoate (two doublets at 7.64 and 6.63 ppm with J = 8.6 Hz) and glutamate (the
free -carboxyl group at 11.46 ppm as a broad singlet), together with three signals
attributable to amide bonds in the Pt-folate conjugate. The UV-vis spectrum of conjugate 3 in
PBS buffer was essentially the sum of those of the two fragments. On the one hand, both the
N3 → Pt(IV) LMCT transition of the metal complex and the π-π* electronic transitions of the
pterin and p-aminobenzoate moieties of folic acid contribute to the broad absorption band
around 290 nm (Fig. 2). On the other hand, the absorption band in the spectral range 300–
1
400 nm can be assigned to n-π* electronic transitions in folic acid.20 As expected, H NMR
analysis indicated that Pt-folate conjugate 3 was obtained as mixture of two constitutional
isomers resulting from the attachment of the PEG linker in compound 4 to both the  and 
carboxyl groups of folic acid, with the -carboxyl-linked derivative drawn in Scheme 1 being
the major one (ca. 90%). These results are in good agreement with literature reports of other
folate derivatives since the less hindered  carboxyl group of folic acid reacts typically faster
to give the  regioisomer.6 The mixture of  and  regioisomers of Pt-folate conjugate 3,
without further separation, was used in photoactivation and biological studies. In addition, it is
4

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important to note that conjugate 3 was found to be completely stable after incubaDtiOoIn: 10f.o10r392/4D0hDT02577A
at 310 K in the dark in physiological-like conditions (Fig. S5, ESI†).
1
Fig. 2 Characterization of Pt-folate conjugate 3. H NMR spectra in DMSO-d6 showing the
region between 6 and 12 ppm (top) and comparison of the UV-vis spectra of complex 1, folic
acid and conjugate 3 in PBS buffer at 298 K (bottom). *This doublet corresponds to the p-
aminobenzoate moiety of folic acid in the  regioisomer of the conjugate.
Photoactivation of Pt-folate conjugate 3 was investigated in the presence of guanosine 5’-
monophosphate (5’-GMP), since guanine nucleobases in DNA are known to be one of the
main targets for Pt(II) photoproducts. Irradiation was performed with blue (420 nm) and green
light (505 nm) in H2O at 37 oC, and the course of the photoactivation process was monitored
by reversed-phase HPLC-MS. As shown in Fig. 3, irradiation with blue light led to the
complete disappearance of conjugate 3 and to the formation of the expected photolysis
products (Scheme 2, pathway A) according to ESI-MS characterization: succinate-folate (5),
photoreleased Pt(II) complex (6) and the Pt(II)-GMP adduct, trans-[Pt(N3)(5’-GMP)(py)2]+ (7)
(GMP is considered neutral in all the formulae), which parallels the behavior previously
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observed for the parent complex 1 and its peptide conjugates.15 In additionD,OHI: 1P0.L10C39-/MD0SDT02577A
analysis revealed the presence of compound 8 and several pterin derivatives, including 6-
formylpterin (9), whose formation can be explained through the cleavage of the bond
between the p-aminobenzoate-containing fragment and the pterin ring system in folate
(Scheme 2, pathway B). To our surprise, cleavage of this bond also occurred at the level of
the parent conjugate (Scheme 2, pathway C), which led to the formation of a Pt-folate
conjugate lacking the pterin fragment (10), which was subsequently transformed into the
expected photoproducts (6-8) due to photoreduction of the intact Pt(IV) complex. A minor
non-photoactivatable Pt-folate conjugate lacking the pterin ring (11) was also identified in the
crude mixture of photolysis products. Similar results were obtained upon irradiation with
green light (Fig. S6, ESI†).
View Article Online
Fig. 3 Reversed-phase HPLC-MS analysis of the photoactivation of Pt-folate conjugate 3 in
the presence of 5’-GMP (2 mol equiv.) in H2O with blue light.
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O
OH
O
OH
DOI: 10.1039/D0DT02577A
Pathway C
O
O
O
N
N3
O
N3
N
H
N
H
H
H
h
N
N
N
N
H
OH
N
N
H
9
O
+
Pt OH
R
O
Pt OH
N3
O
N
N
O
O
O
H2N
N
N
N
N
3
5
10
6
(R = N3)
H
H2N
Pathway A
h
11
+
(R = OH)
O
OH
O
7
8
+
+
O
N3
H
N
H
N
N
+
Pt
OH
N
N
OH
N
NCCH3
5'GMP
H
N
O
O
6
N
N
N3
N
H
N
H2N
N
Pathway B h
Pt
O
N
NH
O
OH
OH
O
P
O
O
N
H
N
H
N
NH2
N
N
CHO
+
O
O
N
N
O
N
H
OH
O
O
O
7
H2N
N
OH
H2N
OH
8
9
Scheme 2. Photoactivation pathways for Pt-folate conjugate 3.
Since photodecomposition of folic acid into p-aminobenzoyl-L-glutamic acid and 6-
formylpterin or 6-carboxypterin derivatives has been reported to occur upon irradiation with
UV light,21 we investigated the photostability of folate derivative 4 under the irradiation
conditions. As shown in Fig S7 (ESI†), 4 was stable both after irradiation with blue (2 h, 37
o
oC) or green (1 h, 37 C) light, which suggested the involvement of the Pt(IV) complex or its
photoproducts in the photodegradation of folic acid. In order to confirm this hypothesis, we
irradiated an equimolar mixture of 4 and complex 1. Very interestingly, HPLC-MS analysis
(Fig. S8, ESI†) revealed the presence of the p-aminobenzoate derivative 12 and 6-
formylpterin 9 together with several Pt(II) photoproducts, with 6 and 13 being the main
platinum species (Scheme 3). Further evidence of the photodecomposition of folic acid
mediated by complex 1 was obtained by 1H NMR spectroscopy. As shown in Fig. S9 (ESI†),
green light irradiation of an equimolar mixture of folic acid and Pt(IV) complex 1 in DMSO-
o
1
d6/D2O 8:2 (v/v) for 2 h at 37 C led to the disappearance of the H NMR peaks for the CH2
group linking p-aminobenzoate and pterin moieties. In addition, the appearance of peaks
around 9.9 ppm together with a shift of proton 7 of the pterin heterocycle to lower field (9.02
ppm vs. 8.61 ppm in free folic acid) confirmed the photodecomposition of folic acid in 6-
formylpterin derivatives and in the p-aminobenzoyl-L-glutamic acid.
Overall, these experiments demonstrated the participation of the trans-diazido Pt(IV)
complex on the photodegradation of folic acid, even when both compounds were not
covalently attached. Oxidative attack of azidyl radicals produced by photodecomposition of
complex 1 on the pterin heterocycle might trigger the cleavage of folic acid in a similar
fashion as occurs with tryptophan amino acid and tryptophan-containing peptides.22 Such
unexpected results might be biologically relevant since pterin photoproducts generate
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reactive oxygen species (ROS)21c and, consequently, the mechanism of actionDoOfI: 1P0.t1-0f3o9l/aD0teDT02577A
View Article Online
conjugate 3 could involve photodynamic therapy (PDT) besides PACT.
O
OH
O
N3
N
H
N
NH2
+
OH
N
N
H
HO
Pt OH
N
N
O
N
N
H
N3
N
1
4
H2N
h
O
OH
OH
N
O
H
N
N3
N
HO
N
N
CHO
+
N
N
NH2
N
Pt
N
H
+
Pt
+
NCCH3
N
OH
O
H2N
H2N
12
6
13
9
Scheme 3. Photoactivation of an equimolar mixture of complex 1 and folate derivative 4.
Having established the photoactivation properties of the Pt-folate conjugate 3, we focused on
investigating photocytotoxicity towards MCF-7 breast cancer cell line. Since conventional cell
culture media contains a folic acid concentration much higher (ca. 2.2 M) than that typically
found in blood plasma (ca 4.5-50 nM),23 photocytotoxicity studies were carried out in folic
acid-free DMEM to assess the effect of the folate vector on delivery of the metallodrug into
MCF-7 cancer cells. The photocytotoxicity of conjugate 3 and of the parent Pt(IV) pro-drug
(1) was determined upon irradiation with blue visible LED light (irr = 465 nm, 4.8 mW cm-2).
The dose-dependent inhibition of cell viability for the compounds towards MCF-7 cells, which
was determined by the sulforhodamine B (SRB) colorimetric assay, and their phototoxic
indices are summarized in Table 1. First, it is worth noting that both compounds are found
non-toxic towards the MCF-7 cancer cell line in the dark with IC50 values >100 μM. However,
irradiation with blue light led to a significant enhancement of the cytotoxicity in both cases,
with the photocytotoxicity of Pt-folate conjugate (IC50 = 14.4 μM) being greater than that of
the parent Pt(IV) complex (IC50 = 32.4 μM) with photocytotoxicity indices (PI) of >6.9 and
>3.0, respectively. Overall, these results indicate that the photocytotoxicity of the trans-
diazido Pt(IV) pro-drug towards MCF-7 breast cancer cells can be significantly enhanced
through conjugation with folic acid without compromising its dark toxicity.
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Table 1. IC50 values and photocytotoxicity indices (PI) for Pt-folate conjugate 3 and the
DOI: 10.1039/D0DT02577A
parent Pt(IV) complex 1 in MCF-7 breast cancer cells after 1 h incubation, 1 h irradiation
(blue 465 nm, 4.8 mW cm-2) and 24 h recovery.
IC50 (µM)a
Dark
Irrad.
PI
> 100
14.4 ± 1.0
> 6.9
Pt-folate conjugate 3
Pt(IV) Complex 1
Dark
Irrad.
PI
> 100
32.4 ± 3.3
> 3.0
a Data are from three independent experiments
Cellular accumulation of metal-based anticancer drugs usually plays an important role in their
antiproliferative activity, especially when conjugated to targeting ligands whose receptors are
overexpressed on the cell surface.24 For this reason, we investigated platinum accumulation
by MCF-7 cancer cells after exposure to 10 μM solutions of Pt-folate conjugate 3 and
complex 1 for 1 h in the dark at 37 oC. Inductively-coupled plasma mass spectrometry (ICP-
MS) was used to quantify the intracellular level of Pt in both cases (Table 2). Very
interestingly, the cellular accumulation of Pt from conjugate 3 (5.8 ng per 106 cells) in MCF-7
cell line was about 9x higher than that of the parent complex 1 (0.67 ng per 106 cells), which
is in good agreement with the higher photocytotoxicity of the conjugate. In order to obtain
more insight into the participation of folate receptor in the cellular uptake of the conjugate, Pt
accumulation studies were repeated at low temperature. As shown in Table 2, the incubation
of MCF-7 cells with conjugate 3 at 4 oC led to a reduction in the Pt accumulation (ca. 33 %).
Competitive studies with folic acid further confirmed the involvement of folate receptor in the
internalization of the Pt-folate conjugate in breast cancer cells, which have been reported to
exhibit medium folate receptor expression on their surface.25 Indeed, pre-treatment of MCF-7
cells with folic acid (100 mol equiv.) led to a slight reduction in Pt accumulation from 3.
Overall, these results suggest the participation of the folate receptor in the cellular uptake of
Pt-folate conjugate in MCF-7 cells and that it enters the cells through an energy-dependent
pathway and not only by passive diffusion.
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6
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Table 2. Cell accumulation of Pt (ng per 10 cells) in MCF-7 cancer cells after DeOxIp: 1o0.s10u3r9e/D0toDT02577A
Pt-folate conjugate 3 and the parent Pt(IV) complex 1 (10 μM, 1 h, in the dark).
Platinum accumulation
Compound
Temperature
(ng per 106 cells)a
3.9 ± 0.6
4°C
Pt-folate conjugate 3
37°C
5.8 ± 0.4 ***
5.5 ± 0.7 **
0.67 ± 0.12*
Pt-folate+100 eq folate
37°C
37°C
Complex 1
a All data were determined from triplicate samples and compared with values obtained for
*
**
untreated cells using a two-tail t-test with unequal variances. p < 0.05, p < 0.01, ***p <
0.005.
In summary, we have synthesized and characterized a novel conjugate between a
photoactivatable trans-diazido Pt(IV) pro-drug and folic acid with the aim of generating folate-
receptor targeted anticancer metallodrugs operating with a novel mechanism of action.
Photoactivation of the Pt-folate conjugate with visible light confirmed the generation of
cytotoxic Pt(II) species capable of binding to guanine nucleobases. In addition,
photoreduction of the Pt(IV) complex was accompanied by the photodecomposition of the
folate vector into a p-aminobenzoate-containing fragment and several pterin derivatives,
including 6-formylpterin, a process that might be triggered by azidyl radicals produced during
the photoactivation of the Pt(IV) pro-drug. Besides exhibiting high dark stability under
physiological-like relevant conditions, the Pt-folate conjugate was found ca. 2x photocytotoxic
towards MCF-7 breast cancer cell line than its parent Pt(IV) complex. The higher
photocytotoxicity of the conjugate (PI >6.9) compared with the parent Pt(IV) pro-drug (PI
>3.0) might be attributable both to a higher cellular accumulation and to the generation of
several cytotoxic species, including Pt(II) photoproducts and pterin derivatives which are
known to generate ROS. This work suggests for the first time that folic acid conjugation to
photoactivatable metallodrugs could be exploited to improve selectivity towards cancer cells
overexpressing folate receptor as well as to attack them by combining PACT and PDT. Work
is in progress to investigate the contribution of photoreleased pterin derivatives to the
photocytotoxicity of such Pt-folate conjugates.
Acknowledgements
This work was supported by funds from the Spanish Government (MCIU/AEI/FEDER, UE;
grants CTQ2017-84779-R) and the Generalitat de Catalunya (2017 DI 072), EPSRC (grant
no EP/P030572/1), a University of Warwick Chancellor’s Scholarship (for H.S.) and Anglo
American Platinum. We acknowledge helpful assistance of Dr. Francisco Cárdenas (NMR)
10

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and Dr. Irene Fernández and Laura Ortiz (MS) from CCiTUB, and technical assisDtaOnI: 1c0e.10a39t/tDh0eDT02577A
University of Warwick from Drs Lijiang Song and Ivan Prokes. A.G. and A.R. were recipient
fellows of the University of Barcelona.
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DOI: 10.1039/D0DT02577A
Table of Contents
Photoactivation of a conjugate between a photoactive trans-diazido Pt(IV) pro-drug and
folic acid generates different cytotoxic species, including Pt(II) photoproducts and pterin
derivatives.
Folate-targeted Pt photochemotherapy
O
OH
O
O
N3
N
H
H
N
N
OH
N
H
O
Pt OH
N3
N
N
O
O
Dark IC50 > 100 M
Photo IC50 = 14.4 M
N
N
N
H
N
Pt-folate conjugate
H2N
N
(465 nm)
PI >6.9
or
O
OH
OH
O
O
N3
H
H
N
N
N
CHO
+
N
N
Pt
+
N
H
OH
N
NCCH3
O
O
H2N
N
H2N
Pt(II) photoproducts
Pterin derivatives
PDT & PACT
ROS generators
DNA target