Biotinylated photoactive Pt(iv) anticancer complexes

Light-Controlled Anticancer Activity and Cellular Uptake of a Photoswitchable Cisplatin Analogue

A photoactive analogue of cisplatin was synthesized with two arylazopyrazole ligands, able to undergo trans-cis/cis-trans photoisomerizations. The cis photoisomer showed a dark half-life of 9 days. The cytotoxicities of both photoisomers of the complex were determined in several cancer and normal cell lines and compared to that of cisplatin. The trans photoisomer of the complex was much more cytotoxic than both the cis photoisomer and cisplatin, and was more toxic for cancer (4T1) than for normal (NMuMG) murine breast cells. 4T1 cell death occurred through necrosis. Photoisomerization of the trans and cis photoisomers internalized by the 4T1 cells increased and decreased their viability, respectively. The cellular uptake of the trans photoisomer was stronger than that of both the cis photoisomer and cisplatin. Both photoisomers interacted with DNA faster than cisplatin. The trans photoisomer was bound stronger by bovine serum albumin and induced a greater decrease in cellular glutathione levels than the cis photoisomer.

Pt(iv) derivatives of cisplatin and oxaliplatin bearing an EMT-related TMEM16A/COX-2-selective dual inhibitor against colorectal cancer cells HCT116

Colorectal cancer represents the over-expression of TMEM16A and COX-2, offering a promising therapeutic strategy. Two Pt(iv) conjugates derived from Pt(ii) drug (cisplatin or oxaliplatin) and niflumic acid, complexes 1 and 2, were designed and prepared to exert the positive impact of multiple biological targets of DNA/TMEM16A/COX-2 against colorectal cancer. Complex 2 afforded higher cytotoxicity than 1 and the combination of an intermediate of oxidized oxaliplatin and NFA against cancer cells A549, HeLa, MCF-7, and HCT116. Especially for colorectal cancer cells HCT116, 2 was significantly more toxic (22-fold) and selective to cancer cells against normal HUVEC cells (4-fold) than first-line oxaliplatin. The outstanding anticancer activity of 2 is partly attributed to its dramatic increase in cellular uptake, DNA damage, and apoptosis. Mechanistic studies indicated that 2 inhibited HCT116 cell metastasis by triggering TMEM16A, COX-2, and their downstream signaling pathways, including EGFR, STAT3, E-cadherin and N-cadherin.

A Photodynamic and Photochemotherapeutic Platinum-Iridium Charge-Transfer Conjugate for Anticancer Therapy

The novel hetero-dinuclear complex trans,trans,trans-[PtIV(py)2(N3)2(OH)(μ-OOCCH2CH2CONHCH2-bpyMe)IrIII(ppy)2]Cl (Pt-Ir), exhibits charge transfer between the acceptor photochemotherapeutic Pt(IV) (Pt-OH) and donor photodynamic Ir(III) (Ir-NH2) fragments. It is stable in the dark, but undergoes photodecomposition more rapidly than the Pt(IV) parent complex (Pt-OH) to generate Pt(II) species, an azidyl radical and 1O2. The Ir(III)* excited state, formed after irradiation, can oxidise NADH to NAD⋅ radicals and NAD+. Pt-Ir is highly photocytotoxic towards cancer cells with a high photocytotoxicity index upon irradiation with blue light (465 nm, 4.8 mW/cm2), even with short light-exposure times (10-60 min). In contrast, the mononuclear Pt-OH and Ir-NH2 subunits and their simple mixture are much less potent. Cellular Pt accumulation was higher for Pt-Ir compared to Pt-OH. Irradiation of Pt-Ir in cancer cells damages nuclei and releases chromosomes. Synchrotron-XRF revealed ca. 4× higher levels of intracellular platinum compared to iridium in Pt-Ir treated cells under dark conditions. Luminescent Pt-Ir distributes over the whole cell and generates ROS and 1O2 within 1 h of irradiation. Iridium localises strongly in small compartments, suggestive of complex cleavage and excretion via recycling vesicles (e.g. lysosomes). The combination of PDT and PACT motifs in one molecule, provides Pt-Ir with a novel strategy for multimodal phototherapy.

Radiometal-Labeled Photoactivatable Pt(IV) Anticancer Complex for Theranostic Phototherapy

A novel photoactivatable Pt(IV) diazido anticancer agent, Pt-succ-DFO, bearing a pendant deferoxamine (DFO) siderophore for radiometal chelation, has been synthesized for the study of its in vivo behavior with radionuclide imaging. Pt-succ-DFO complexation of Fe(III) and Ga(III) ions yielded new heterobimetallic complexes that maintain the photoactivation properties and photocytotoxicity of the parent Pt complex in human cancer cell lines. Radiolabeled Pt-succ-DFO-68Ga (t1/2 = 68 min, positron emitter) was readily prepared under mild conditions and was stable in the dark upon incubation with human serum. PET imaging of Pt-succ-DFO-68Ga in healthy mice revealed a promising biodistribution profile with rapid renal excretion and limited organ accumulation, implying that little off-target uptake is expected for this class of agents. Overall, this research provides the first in vivo imaging study of the whole-body distribution of a photoactivatable Pt(IV) azido anticancer complex and illustrates the potential of radionuclide imaging as a tool for the preclinical development of novel light-activated agents.

Mitochondria-targeted biotin-conjugated BODIPYs for cancer imaging and therapy

Two BODIPY-biotin conjugates KDP1 and KDP2 are designed and synthesized for targeted PDT applications. Both have good absorption with a high molar absorption coefficient and decent singlet oxygen generation quantum yields. The photosensitizers KDP1 and KDP2 were found to be localized in the mitochondria with excellent photocytotoxicity of up to 18.7 nM in MDA-MB-231 breast cancer cells. The cell death predominantly proceeded through the apoptosis pathway via ROS production.

Stimuli-responsive platinum and ruthenium complexes for lung cancer therapy

Lung cancer is the most common cause of cancer-related deaths worldwide. More efficient treatments are desperately needed. For decades, the success of platinum-based anticancer drugs has promoted the exploration of metal-based agents. Four ruthenium-based complexes have also entered clinical trials as candidates of anticancer metallodrugs. However, systemic toxicity, severe side effects and drug-resistance impeded their applications and efficacy. Stimuli-responsiveness of Pt- and Ru-based complexes provide a great chance to weaken the side effects and strengthen the clinical efficacy in drug design. This review provides an overview on the stimuli-responsive Pt- and Ru-based metallic anticancer drugs for lung cancer. They are categorized as endo-stimuli-responsive, exo-stimuli-responsive, and dual-stimuli-responsive prodrugs based on the nature of stimuli. We describe various representative examples of structure, response mechanism, and potential medical applications in lung cancer. In the end, we discuss the future opportunities and challenges in this field.

Ligand Evolution in the Photoactivatable Platinum(IV) Anticancer Prodrugs

Photoactivatable Pt(IV) anticancer prodrugs with the structure of [Pt^IV(N₁)(N₂)(L₁)(L₂)(A₁)(A₂)], where N₁ and N₂ are non-leaving nitrogen donor ligands, L₁ and L₂ are leaving ligands, and A₁ and A₂ are axial ligands, have attracted increasing attention due to their promising photo-cytotoxicity even to cisplatin-resistant cancer cells. These photochemotherapeutic prodrugs have high dark-stability under physiological conditions, while they can be activated by visible light restrained at the disease areas, as a consequence showing higher spatial and temporal controllability and much more safety than conventional chemotherapy. The coordinated ligands to the Pt center have been proved to be pivotal in determining the function and activity of the photoactivatable Pt(IV) prodrugs. In this review, we will focus on the development of the coordinated ligands in such Pt(IV) prodrugs and discuss the effects of diverse ligands on their photochemistry and photoactivity as well as the future evolution directions of the ligands. We hope this review can help to facilitate the design and development of novel photoactivatable Pt(IV) anticancer prodrugs.

A theoretical study on the on-off phosphorescence of novel Pt(ii)/Pt(iv)-bisphenylpyridinylmethane complexes

An in-depth theoretical study on the Pt(ii)/Pt(iv)-bisphenylpyridinylmethane complexes was carried out, which focused on the geometric/electronic structures, excitation procedures, on-off phosphorescence mechanisms, and structure-optical performance relationships. The key roles of the linkages (LK) connected in the middle of phenylpyridines were carefully investigated using multiple wavefunction analysis methods, such as non-covalent interaction (NCI) visualizations and natural bond orbital (NBO) studies. The phosphorescence-off phenomenon was considered by hole-electron analysis and visualizations, spin-orbit coupling (SOC) studies, and NBO analysis. Through these investigations, the relationship of the substituents in LK and the optical performances were revealed, as well as the fundamental principles of the phosphorescence-quenching mechanism in Pt(iv) complexes, which pave the way for further performance/structural renovation works. In addition, an intuitive visualization method was developed using a heatmap to quantitatively express the SOC matrix elementary (SOCME), which is helpful for big data simplification for phosphorescence analysis.

Synthesis and anticancer activity of two highly water-soluble and ionic Pt(iv) complexes as prodrugs for Pt(ii) anticancer drugs

Two new Pt(iv) complexes featuring mesylate as the outer sphere anion, cis,trans,cis-[PtCl2(OH2)2(NH3)2](CH3SO3)2 (SPt-1) and cis,trans,cis-[PtCl2(OH2)2(1R,2R-DACH)](CH3SO3)2 (SPt-2), were synthesized and characterized by elemental analysis, 1H and 13C NMR, IR, and ESI-MS. Both complexes have excellent water-solubility, high molar conductivity and good water stability. They exhibit an irreversible two-electron reduction event with the peak potentials (E p) for the processes being -0.40 V for SPt-1 and -0.52 V for SPt-2. The biological tests reveal that SPt-2 possesses high in vitro anticancer activity against three human cancer cell lines (HCT-116, A549 and MKN-1) and its overall anticancer activity is slightly greater than that of oxaliplatin, whereas SPt-1 is less active than cisplatin. Moreover, the antitumor efficacy of SPt-2 on human colon carcinoma HCT-116 xenografts in nude mice is also greater than that of oxaliplatin, suggesting that SPt-2 deserves further evaluation as a prodrug for oxaliplatin.

Synthesis and In Vitro Studies of Photoactivatable Semisquaraine-type Pt(II) Complexes

The synthesis, full characterization, photochemical properties, and cytotoxic activity toward cisplatin-resistant cancer cell lines of new semisquaraine-type Pt(II) complexes are presented. The synthesis of eight semisquaraine-type ligands has been carried out by means of an innovative, straightforward methodology. A thorough structural NMR and X-ray diffraction analysis of the new ligands and complexes has been done. Density functional theory calculations have allowed to assign the trans configuration of the platinum center. Through the structural modification of the ligands, it has been possible to synthesize some complexes, which have turned out to be photoactive at wavelengths that allow their activation in cell cultures and, importantly, two of them show remarkable solubility in biological media. Photodegradation processes have been studied in depth, including the structural identification of photoproducts, thus justifying the changes observed after irradiation. From biological assessment, complexes C7 and C8 have been demonstrated to behave as promising photoactivatable compounds in the assayed cancer cell lines. Upon photoactivation, both complexes are capable of inducing a higher cytotoxic effect on the tested cells compared with nonphotoactivated compounds. Among the observed results, it is remarkable to note that C7 showed a PI > 50 in HeLa cells, and C8 showed a PI > 40 in A2780 cells, being also effective over cisplatin-resistant A2780cis cells (PI = 7 and PI = 4, respectively). The mechanism of action of these complexes has been studied, revealing that these photoactivated platinum complexes would actually present a combined mode of action, a therapeutically potential advantage.

The synthesis, full characterization, photochemical properties, and cytotoxic activity toward cisplatin-resistant cancer cell lines of new semisquaraine-type Pt(II) complexes are presented. Eight semisquaraine-type ligands and their corresponding Pt(II) complexes have been studied. These complexes have turned out to be photoactive at wavelengths that allow their activation in cell cultures. Two of them display remarkable solubility in biological media showing a promising behavior as photoactivatable compounds against several cancer cell lines.

Ferroptosis promotes sonodynamic therapy: a platinum(ii)–indocyanine sonosensitizer

Sonodynamic therapy (SDT) has unique advantages in deep tumour ablation due to its deep penetration depth, showing great preclinical and clinical potential. Herein, a platinum(ii)–cyanine complex has been designed to investigate its potential as a SDT anticancer agent. It generates singlet oxygen (¹O₂) under ultrasound (US) irradiation or light irradiation, and exhibits US-cytotoxicity in breast cancer 4T1 cells but with negligible dark-cytotoxicity. Mechanistic investigations reveal that Pt-Cy reduces the cellular GSH and GPX4, and triggers cancer cell ferroptosis under US irradiation. The metabolomics analysis illustrates that Pt-Cy upon US treatment significantly dysregulates glutathione metabolism, and finally induces ferroptosis. In vivo studies further demonstrate that Pt-Cy inhibits tumor growth under US irradiation and its efficiency for SDT is better than that for PDT in vivo. This is the first example of platinum(ii) complexes for sonodynamic therapy. This work extends the biological applications of metal complexes from PDT to SDT.

A novel platinum(ii)–cyanine complex showed a greater excellent sonodynamic therapeutic effect than photodynamic therapy in vivo. This work expands the biological applications of metal complexes from traditional photodynamic therapy to sonodynamic therapy.

Single-Cell Chemistry of Photoactivatable Platinum Anticancer Complexes

The Pt(IV) prodrug trans, trans, trans-[Pt(pyridine)2(N3)2(OH)2] (Pt1) and its coumarin derivative trans, trans, trans-[Pt(pyridine)2(N3)2(OH)(coumarin-3-carboxylate)] (Pt2) are promising agents for photoactivated chemotherapy. These complexes are inert in the dark but release Pt(II) species and radicals upon visible light irradiation, resulting in photocytotoxicity toward cancer cells. Here, we have used synchrotron techniques to investigate the in-cell behavior of these prodrugs and visualize, for the first time, changes in cellular morphology and Pt localization upon treatment with and without light irradiation. We show that photoactivation of Pt2 induces remarkable cellular damage with extreme alterations to multiple cellular components, including formation of vacuoles, while also significantly increasing the cellular accumulation of Pt species compared to dark conditions. X-ray absorption near-edge structure (XANES) measurements in cells treated with Pt2 indicate only partial reduction of the prodrug upon irradiation, highlighting that phototoxicity in cancer cells may involve not only Pt(II) photoproducts but also photoexcited Pt(IV) species.

An erythrocyte-delivered photoactivatable oxaliplatin nanoprodrug for enhanced antitumor efficacy and immune response

The outcome of conventional platinum (Pt)-based chemotherapy is limited by reduced circulation, failure to accumulate in the tumor, and dose-limiting toxicity arising from non-controllable activation. To address these limitations, we present an erythrocyte-delivered and near-infrared (NIR) photoactivatable Pt^IV nanoprodrug for advanced cancer treatment. Compared with small molecule Pt^IV prodrugs, this nanoprodrug exhibits significantly enhanced stability, prolonged circulation in the blood, and minimized side effects. The hitchhiking of the nanoprodrug on erythrocytes dramatically increases Pt accumulation in the tumor. Upon irradiation, the nanoprodrug releases oxaliplatin in a controllable manner, resulting in significant antitumor activity against breast tumors in vivo, as evidenced by the complete elimination of tumors from a single-dose injection. Additionally, this nanoprodrug is associated with remarkably enhanced immunopotentiation. Our study highlights an efficient strategy to overcome the shortcomings of traditional Pt-based chemotherapy via the erythrocyte-mediated delivery of an NIR-activatable nanoprodrug of oxaliplatin, a clinically used anticancer drug.

Strategic illustration of an erythrocyte-delivered and near-infrared photoactivatable oxaliplatin nanoprodrug for enhanced antitumor efficacy and immune response.

Research progress of azido-containing Pt(IV) antitumor compounds

Cancer is a long-known incurable disease, and the medical use of cisplatin has been a significant discovery. However, the side-effects of cisplatin necessitate the development of new and improved drug. Therefore, in this study, we focused on the photoactivatable Pt(IV) compounds Pt[(X₁)(X₂)(Y₁)(Y₂)(N₃)₂], which have a completely novel mechanism of action. Pt(IV) can efficiently overcome the side-effects of cisplatin and other drugs. Here, we have demonstrated, summarized and discussed the effects and mechanism of these compounds. Compared to the relevant articles in the literature, we have provided a more detailed introduction and a made comprehensive classification of these compounds. We believe that our results can effectively provide a reference for the development of these drugs.

Platinum(IV)-azido monocarboxylato complexes are photocytotoxic under irradiation with visible light

Complexes trans,trans,trans-[Pt(N3)2(OH)(OCOR)(py)2] where py = pyridine and where OCOR = succinate (1); 4-oxo-4-propoxybutanoate (2) and N-methylisatoate (3) have been synthesized by derivation of trans,trans,trans-[Pt(OH)2(N3)2(py)2] (4) and characterised by NMR and EPR spectroscopy, ESI-MS and X-ray crystallography. Irradiation of 1-3 with green (517 nm) light initiated photoreduction to Pt(ii) and release of the axial ligands at a 3-fold faster rate than for 4. TD-DFT calculations showed dissociative transitions at longer wavelengths for 1 compared to 4. Complexes 1 and 2 showed greater photocytotoxicity than 4 when irradiated with 420 nm light (A2780 cell line IC50 values: 2.7 and 3.7 μM) and complex 2 was particularly active towards the cisplatin-resistant cell line A2780cis (IC50 3.7 μM). Unlike 4, complexes 1-3 were phototoxic under green light irradiation (517 nm), with minimal toxicity in the dark. A pKa(H2O) of 5.13 for the free carboxylate group was determined for 1, corresponding to an overall negative charge during biological experiments, which crucially, did not appear to impede cellular accumulation and photocytotoxicity.

Facile protein conjugation of platinum for light-activated cytotoxic payload release

The novel Pt(iv) complex trans,trans-[Pt(N3)2(Py)2(OH)(OCO-(PEG)2-NHCSNH-Ph-NCS)] (Pt4) conjugates to the side chain of lysine amino acids in proteins under mild conditions. Reaction with myoglobin generated a bioconjugate that was stable in the dark, but released a Pt(iv) prodrug upon visible light irradiation. A similar procedure was used to conjugate Pt4 to the antibody trastuzumab, resulting in the first photoactivatable Pt(iv)-antibody conjugate, demonstrating potential for highly selective cancer phototherapy.

DNA-Intercalative Platinum Anticancer Complexes Photoactivated by Visible Light

Photoactivatable agents offer the prospect of highly selective cancer therapy with low side effects and novel mechanisms of action that can combat current drug resistance. 1,8-Naphthalimides with their extended π system can behave as light-harvesting groups, fluorescent probes and DNA intercalators. We conjugated N-(carboxymethyl)-1,8-naphthalimide (gly-R-Nap) with an R substituent on the naphthyl group to photoactive diazido PtIV complexes to form t,t,t-[Pt(py)2 (N3 )2 (OH)(gly-R-Nap)], R=H (1), 3-NO2 (2) or 4-NMe2 (3). They show enhanced photo-oxidation, cellular accumulation and promising photo-cytotoxicity in human A2780 ovarian, A549 lung and PC3 prostate cancer cells with visible light activation, and low dark cytotoxicity. Complexes 1 and 2 exhibit pre-intercalation into DNA, resulting in enhanced photo-induced DNA crosslinking. Complex 3 has a red-shifted absorption band at 450 nm, allowing photoactivation and photo-cytotoxicity with green light.

Oxoplatin-B, a cisplatin-based platinum(IV) complex with photoactive BODIPY for mitochondria specific "chemo-PDT" activity

Oxoplatin-B, a platinum(IV) complex [Pt(NH₃)₂Cl₂(L¹)(OH)] (1) of 4-methylbenzoic acid (HL¹) functionalized with 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) was prepared, characterized and its antitumor activity studied. [Pt(NH₃)₂Cl₂(L²)(OH)] (2) of 4-methylbenzoic acid (HL²) was studied as a control. Complex 1 showed an absorption band at 500 nm (ɛ = 4.34 × 10⁴ M^-1 cm^-1) and an emission band at 515 nm (λ_ex = 488 nm, Φ_F = 0.64) in 1% dimethyl sulfoxide/Dulbecco's Modified Eagle's Medium (pH = 7.2). Visible light-induced (400-700 nm) generation of singlet oxygen was evidenced from 1,3-diphenylisobenzofuran titration study. Complex 1 showed photo-induced cytotoxicity in visible light (400-700 nm, 10 J cm^-2) against human breast cancer (MCF-7), cervical cancer (HeLa) and lung cancer (A549) cells (IC₅₀: 1.1-3.8 μM) while being less toxic in normal cells. Confocal imaging showed mitochondrial localization with additional evidence from platinum content from isolated mitochondria and 5,5,6,6'-tetrachloro-1,1',3,3' tetraethylbenzimi-dazoylcarbocyanine iodide (JC-1) assay. Cellular apoptosis was observed from Annexin-V-FITC (fluorescein isothiocyanate)/propidium iodide assay.

Hetero-Bis-Conjugation of Bioactive Molecules to Half-Sandwich Ruthenium(II) and Iridium(III) Complexes Provides Synergic Effects in Cancer Cell Cytotoxicity

Four bipyridine-type ligands variably derivatized with two bioactive groups (taken from ethacrynic acid, flurbiprofen, biotin, and benzylpenicillin) were prepared via sequential esterification steps from commercial 2,2'-bipyridine-4,4'-dicarboxylic acid and subsequently coordinated to ruthenium(II) p-cymene and iridium(III) pentamethylcyclopentadienyl scaffolds. The resulting complexes were isolated as nitrate salts in high yields and fully characterized by analytical and spectroscopic methods. NMR and MS studies in aqueous solution and in cell culture medium highlighted a substantial stability of ligand coordination and a slow release of the bioactive fragments in the latter case. The complexes were assessed for their antiproliferative activity on four cancer cell lines, showing cytotoxicity to the low micromolar level (equipotent with cisplatin). Additional biological experiments revealed a multimodal mechanism of action of the investigated compounds, involving DNA metalation and enzyme inhibition. Synergic effects provided by specific combinations of metal and bioactive fragments were identified, pointing toward an optimal ethacrynic acid/flurbiprofen combination for both Ru(II) and Ir(III) complexes.

Platinum(IV) anticancer agents; are we en route to the holy grail or to a dead end?

Pt(IV) complexes are designed as prodrugs that are intended to overcome resistance. Pt(IV) prodrugs are activated inside cancer cells releasing cytotoxic Pt(II) drugs as well as two axial ligands that can be used to confer favorable pharmacological properties to the prodrug. The ligands can be innocent spectators, cancer targeting agents or bioactive moieties. The choice of axial ligands determines the chemical and pharmacological properties of the prodrugs. Over the years, several approaches were employed in attempts to increase the selectivity of the prodrugs to cancer cells and to utilize multi-action prodrugs to overcome resistance. In this review, we critically examine several of these approaches in order to evaluate the validity of some of the working hypotheses that are driving the current research.

The Role of Norrish Type-I Chemistry in Photoactive Drugs: An ab initio Study of a Cyclopropenone-Enediyne Drug Precursor

We present a contemporary mechanistic description of the light-driven conversion of cyclopropenone containing enediyne (CPE) precusors to ring-opened species amenable to further Bergman cyclization and formation of stable biradical species that have been proposed for use in light-induced cancer treatment. The transformation is rationalized in terms of (purely singlet state) Norrish type-I chemistry, wherein photoinduced opening of one C-C bond in the cyclopropenone ring facilitates non-adiabatic coupling to high levels of the ground state, subsequent loss of CO and Bergman cyclization of the enediyne intermediate to the cytotoxic target biradical species. Limited investigations of substituent effects on the ensuing photochemistry serve to vindicate the experimental choices of Popik and coworkers (J. Org. Chem., 2005, 70, 1297-1305). Specifically, replacing the phenyl moiety in the chosen model CPE by a 1,4-benzoquinone unit leads to a stronger, red-shifted parent absorption, and increases the exoergicity of the parent → biradical conversion.

Axial functionalisation of photoactive diazido platinum(iv) anticancer complexes

Mono-axial functionalised octahedral diazido Pt(iv) complexes trans, trans, trans-[Pt(py)₂(N₃)₂(OR₁)(OR₂)] (OR₁ = OH and OR₂ = anticancer agent coumarin-3 carboxylate (cou, 2a), pyruvate dehydrogenase kinase (PDK) inhibitors 4-phenylbutyrate (PhB, 2b) or dichloroacetate (DCA, 2c)), and their di-axial functionalised analogues with OR₁ = DCA and OR₂ = cou (3a), PhB (3b), or DCA (3c) have been synthesised and characterised, including the X-ray crystal structures of complexes 2a, 3a, 3b and 3c. These complexes exhibit dark stability and have the potential to generate cytotoxic Pt(ii) species and free radicals selectively in cancer cells when irradiated. Mono-functionalised complexes 2a-2c showed higher aqueous solubility and more negative reduction potentials. Mono- and di-functionalised complexes displayed higher photocytotoxicity with blue light (1 h, 465 nm, 4.8 mW cm^-2) than the parent dihydroxido complex 1 (OR₁ = OR₂ = OH) in A2780 human ovarian (IC₅₀ 0.9-2.9 μM for 2a-2c; 0.11-0.39 μM for 3a-3c) and A549 human lung cancer cells (5.4-7.8 μM for 2a-2c; 1.2-2.6 μM for 3a-3c) with satisfactory dark stability. Notably, no apparent dark cytotoxicity was observed in healthy lung MRC-5 fibroblasts for all complexes (IC₅₀ > 20 μM). Significantly higher platinum cellular accumulation and photo-generated ROS levels were observed for the di-functionalised complexes compared with their mono-functionalised analogues when cancer cells were treated under the same concentrations.