Anti-cancer characteristics and ototoxicity of platinum(II) amine complexes with only one leaving ligand

Cytotoxic Pt(II) complexes containing alizarin: a selective carrier for DNA metalation

Many efforts have been made in the last few decades to selectively transport antitumor agents to their potential target sites with the aim to improve efficacy and selectivity. Indeed, this aspect could greatly improve the beneficial effects of a specific anticancer agent especially in the case of orphan tumors like the triple negative breast cancer. A possible strategy relies on utilizing a protective leaving group like alizarin as the Pt(II) ligand to reduce the deactivation processes of the pharmacophore enacted by Pt resistant cancer cells. In this study a new series of neutral mixed-ligand Pt(II) complexes bearing alizarin and a variety of diamine ligands were synthesized and spectroscopically characterized by FT-IR, NMR and UV-Vis analyses. Three Pt(II) compounds, i.e., 2b, 6b and 7b, emerging as different both in terms of structural properties and cytotoxic effects (not effective, 10.49 ± 1.21 μM and 24.5 ± 1.5 μM, respectively), were chosen for a deeper investigation of the ability of alizarin to work as a selective carrier. The study comprises the in vitro cytotoxicity evaluation against triple negative breast cancer cell lines and ESI-MS interaction studies relative to the reaction of the selected Pt(II) complexes with model proteins and DNA fragments, mimicking potential biological targets. The results allow us to suggest the use of complex 6b as a prospective anticancer agent worthy of further investigations.

Wireframe DNA Origami for the Cellular Delivery of Platinum(II)-Based Drugs

The DNA origami method has revolutionized the field of DNA nanotechnology since its introduction. These nanostructures, with their customizable shape and size, addressability, nontoxicity, and capacity to carry bioactive molecules, are promising vehicles for therapeutic delivery. Different approaches have been developed for manipulating and folding DNA origami, resulting in compact lattice-based and wireframe designs. Platinum-based complexes, such as cisplatin and phenanthriplatin, have gained attention for their potential in cancer and antiviral treatments. Phenanthriplatin, in particular, has shown significant antitumor properties by binding to DNA at a single site and inhibiting transcription. The present work aims to study wireframe DNA origami nanostructures as possible carriers for platinum compounds in cancer therapy, employing both cisplatin and phenanthriplatin as model compounds. This research explores the assembly, platinum loading capacity, stability, and modulation of cytotoxicity in cancer cell lines. The findings indicate that nanomolar quantities of the ball-like origami nanostructure, obtained in the presence of phenanthriplatin and therefore loaded with that specific drug, reduced cell viability in MCF-7 (cisplatin-resistant breast adenocarcinoma cell line) to 33%, while being ineffective on the other tested cancer cell lines. The overall results provide valuable insights into using wireframe DNA origami as a highly stable possible carrier of Pt species for very long time-release purposes.

Novel Platinum(II) and Platinum(IV) Antitumor Agents that Exhibit Potent Cytotoxicity and Selectivity

A novel platinum(II) complex 47OMESS(II) and its platinum(IV) derivative 47OMESS(IV) were synthesized and characterized. Cytotoxicity studies against mesenchymal cells (MCs) and lung (A549), breast (MDA-MB-231), and melanoma (A375) cancer cells demonstrated 7-20-fold superior activity for both complexes relative to cisplatin. Remarkably, 47OMESS(IV) demonstrated 17-22-fold greater selectivity toward the cancerous cells compared to the non-cancerous MCs. Western blot analysis on A549 cells showed the involvement of the intrinsic apoptotic pathway. Cellular fractionation and uptake experiments in A549 cells using ICP-mass spectrometry (MS) indicated that 47OMESS(II) and 47OMESS(IV) cross the cellular membrane predominantly via active transport mechanisms. The significant improvement in selectivity that is exhibited by 47OMESS(IV) is reported for the first time for this class of complexes.

New Platinum (II) Ternary Complexes of Formamidine and Pyrophosphate: Synthesis, Characterization and DFT Calculations and In vitro Cytotoxicity

AIM AND OBJECTIVE

Platinum (II) and platinum (IV) of pyrophosphate complexes have been prepared and characterized to discover their potential as antitumor drugs. This study was conducted to prepare and characterize new ternary platinum (II) complexes with formamidine and pyrophosphate as an antitumor candidate.

MATERIALS AND METHODS

The complexes have been characterized by mass, infrared, UV-Vis. spectroscopy, elemental analysis, magnetic susceptibility, thermal analyses, and theoretical calculations. They have been tested for their cytotoxicity, which was carried out using the fastcolorimetric assay for cellular growth and survival against MCF-7 (breast cancer cell line), HCT- 116 (colon carcinoma cell line), and HepG-2 (hepatocellular cancer cell line).

RESULTS

All complexes are diamagnetic, and the electronic spectral data displayed the bands due to square planar Pt(II) complexes. The optimized complexes structures (1-4) indicated a distorted square planar geometry where O-Pt-O and N-Pt-N bond angles were 82.04°-96.44°, respectively. Results also show that all complexes are neutral, stable and non-hygroscopic and have noticeable cytotoxicity with IC50 (μM): 0.035-0.144 MCF-7(breast cancer cell line), 0.042-0.187 HCT-116 (colon carcinoma cell line), and 0.063-0.168 HepG-2 (hepatocellular cancer cell line). Moreover, the results show that the complex (4) has the best IC50 value.

CONCLUSION

The complexes showed noticeable cytotoxicity and are considered as promising antitumor candidates for further applications.

Regulating Twisted Skeleton to Construct Organ-Specific Perylene for Intensive Cancer Chemotherapy

The systemic use of pharmaceutical drugs for cancer patients is a compromise between desirable therapy and side effects because of the intrinsic shortage of organ-specific pharmaceutical drug. Design and construction of pharmaceutical drug to achieve the organ-specific delivery is thus desperately desirable. We herein regulate perylene skeleton to effect organ-specificity and present an example of lung-specific distribution on the basis of bay-twisted PDIC-NC. We further demonstrate that PDIC-NC can target into mitochondria to act as cellular respiration inhibitor, inducing insufficient production of adenosine triphosphate, promoting endogenous H₂ O₂ and ^. OH burst, elevating calcium overload, efficiently triggering the synergistic apoptosis, autophagy and endoplasmic reticulum stress of lung cancer cells. The antitumor performance of PDIC-NC is verified on in vivo xenografted, metastasis and orthotopic lung cancer, presenting overwhelming evidences for potentially clinical application. This study contributes a proof-of-concept demonstration of twisted perylene to well attain lung-specific distribution, and meanwhile achieves intensive lung cancer chemotherapy.

Cisplatin and phenanthriplatin modulate long-noncoding RNA expression in A549 and IMR90 cells revealing regulation of microRNAs, Wnt/β-catenin and TGF-β signaling

The monofunctional platinum(II) complex, phenanthriplatin, acts by blocking transcription, but its regulatory effects on long-noncoding RNAs (lncRNAs) have not been elucidated relative to traditional platinum-based chemotherapeutics, e.g., cisplatin. Here, we treated A549 non-small cell lung cancer and IMR90 lung fibroblast cells for 24 h with either cisplatin, phenanthriplatin or a solvent control, and then performed microarray analysis to identify regulated lncRNAs. RNA22 v2 microRNA software was subsequently used to identify microRNAs (miRNAs) that might be suppressed by the most regulated lncRNAs. We found that miR-25-5p, -30a-3p, -138-5p, -149-3p, -185-5p, -378j, -608, -650, -708-5p, -1253, -1254, -4458, and -4516, were predicted to target the cisplatin upregulated lncRNAs, IMMP2L-1, CBR3-1 and ATAD2B-5, and the phenanthriplatin downregulated lncRNAs, AGO2-1, COX7A1-2 and SLC26A3-1. Then, we used qRT-PCR to measure the expression of miR-25-5p, -378j, -4516 (A549) and miR-149-3p, -608, and -4458 (IMR90) to identify distinct signaling effects associated with cisplatin and phenanthriplatin. The signaling pathways associated with these miRNAs suggests that phenanthriplatin may modulate Wnt/β-catenin and TGF-β signaling through the MAPK/ERK and PTEN/AKT pathways differently than cisplatin. Further, as some of these miRNAs may be subject to dissimilar lncRNA targeting in A549 and IMR90 cells, the monofunctional complex may not cause toxicity in normal lung compared to cancer cells by acting through distinct lncRNA and miRNA networks.

Oxaliplatin derived monofunctional triazole-containing platinum(II) complex counteracts oxaliplatin-induced drug resistance in colorectal cancer

Oxaliplatin-based chemotherapy is the current standard of care in adjuvant therapy for advanced colorectal cancer (CRC). But acquired resistance to oxaliplatin eventually occurs and becoming a major cause of treatment failure. Thus, there is an unmet need for developing new chemical entities (NCE) as new therapeutic candidates to target chemotherapy-resistant CRC. Novel Pt(II) complexes were designed and synthesized as cationic monofunctional oxaliplatin derivatives for DNA platination-mediated tumor targeting. The complex Ph-glu-Oxa sharing the same chelating ligand of diaminocyclohexane (DACH) with oxaliplatin but is equally potent in inhibiting the proliferation of HT29 colon cancer cells and its oxaliplatin-resistant phenotype of HT29/Oxa. The in vivo therapeutic potential of Ph-glu-Oxa was confirmed in oxaliplatin-resistant xenograft model demonstrating the reversibility of the drug resistance by the new complex and the efficacy was associated with the unimpaired high intracellular drug accumulation in HT29/Oxa. Guanosine-5'-monophosphate (5'-GMP) reactivity, double-strand plasmid DNA cleavage, DNA-intercalated ethidium bromide (EB) fluorescence quenching and atomic force microscopy (AFM)-mediated DNA denaturing studies revealed that Ph-glu-Oxa was intrinsically active as DNA-targeting agent. The diminished susceptibility of the complex to glutathione (GSH)-mediated detoxification, which confers high intracellular accumulation of the drug molecule may play a key role in maintaining cytotoxicity and counteracting oxaliplatin drug resistance.

RNA-Seq Analysis of Cisplatin and the Monofunctional Platinum(II) Complex, Phenanthriplatin, in A549 Non-Small Cell Lung Cancer and IMR90 Lung Fibroblast Cell Lines

Phenanthriplatin is a new monofunctional platinum(II) complex that binds only one strand of DNA and acts by blocking gene transcription, but its effect on gene regulation has not been characterized relative to the traditional platinum-based complex, cisplatin. A549 non-small cell lung cancer and IMR90 lung fibroblast cells were treated with cisplatin, phenanthriplatin, or a control and then their RNA transcripts were subjected to next generation sequencing analysis. DESeq2 and CuffDiff2 were used to identify up- and downregulated genes and Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases were used to identify pathways and functions. We found that phenanthriplatin may regulate the genes GPRC5a, TFF1, and TNFRSF10D, which act through p53 to control apoptosis, differently or to a greater extent than cisplatin, and that it, unlike cisplatin, could upregulate ATP5MD, a gene which signals through the Wnt/β catenin pathway. Furthermore, phenanthriplatin caused unique or enhanced effects compared to cisplatin on genes regulating the cytoskeleton, cell migration, and proliferation, e.g., AGAP1, DIAPH2, GDF15, and THSD1 (p < 0.05; q < 0.05). Phenanthriplatin may modulate some oncogenes differently than cisplatin potentially leading to improved clinical outcome, but this monofunctional complex should be carefully matched with cancer gene data to be successfully applied in chemotherapy.

Down-Regulation of the Mammalian Target of Rapamycin (mTOR) Pathway Mediates the Effects of the Paeonol-Platinum(II) Complex in Human Thyroid Carcinoma Cells and Mouse SW1736 Tumor Xenografts

Background

This study aimed to investigate the effects of the paeonol-platinum(II) (PL-Pt[II]) complex on SW1736 human anaplastic thyroid carcinoma cell line and the BHP7-13 human thyroid papillary carcinoma cell line in vitro and on mouse SW1736 tumor xenografts in vivo.

Material/Methods

The cytotoxic effects of the PL-Pt(II) complex on SW1736 cells and BHP7-13 cells was measured using the MTT assay. Western blot measured the expression levels of cyclins, cell apoptotic proteins, and signaling proteins. DNA content and apoptosis were detected by flow cytometry. SW1736 cell thyroid tumor xenografts were established in mice followed by treatment with the PL-Pt(II) complex.

Results

Treatment of the SW1736 and BHP7-13 cells with the PL-Pt(II) complex reduced cell proliferation in a dose-dependent manner, with an IC50 of 1.25 μM and 1.0 μM, respectively, and increased the cell fraction in G0/G1phase, inhibited p53, cyclin D1, promoted p27 and p21 expression, and significantly increased the sub-G1 fraction. Treatment with the PL-Pt(II) complex increased caspase-3 degradation, reduced the expression of p-4EBP1, p-4E-BP1 and p-S6, and reduced the expression of p-ERK1/2 and p-AKT. Treatment with the PL-Pt(II) complex reduced the volume of the SW1736 mouse tumor xenografts on day 14 and day 21, and reduced AKT phosphorylation and S6 protein expression and increased degradation of caspase-3.

Conclusions

The cytotoxic effects of the PL-Pt(II) complex in human thyroid carcinoma cells, including activation of apoptosis and an increased sub-G1 cell fraction of the cell cycle, were mediated by down-regulation of the mTOR pathway.

Ginkgolide-Platinum(II) Complex GPt(II) Exhibits Therapeutic Effect on Depression in Mice via Upregulation of DA and 5-HT Neurotransmitters

Background

Depression is the 5^th most prevalent disorder adversely affecting the health of humans worldwide. The present study evaluated the antidepressant effect of ginkgolide-platinum(II) complex in vivo in a mice model of CMS-induced depression.

Material/Methods

Depression was induced in mice by social isolation followed by chronic mild stress. After stress, the mice were assigned randomly to a model group, a 3 mg/kg group, a 6 mg/kg group, and a 12 mg/kg group. The mice in the 3 treatment groups were intraperitoneally injected with a single dose of 3.0, 6.0, or 12.0 mg/kg GPt(II) on day 11 of stress. The behavioral changes in mice were analyzed on day 21 of GPt(II) treatment by suspension and open field tests.

Results

The GPt(II) treatment significantly increased the numbers of crossings and rearings in CMS mice. Treatment of mice with GPt(II) significantly elevated dopamine, BDNF, and serotonin levels in hippocampus tissues. The CMS-mediated reduction of neuropeptide production in the hippocampus tissues was significantly alleviated by GPt(II) treatment (P<0.05). The GPt(II) treatment suppressed the effect on CMS-induced elevated level of MAO-A in hippocampus tissues. Treatment with GPt(II) significantly repressed caspase-3 activation induced by CMS in the hippocampus tissues of mice. The GPt(II) treatment significantly (P<0.05) upregulated Hsp70 mRNA level in depression model mice. The levels of dopamine, serotonin, and BDNF were increased from 187.83±8.53, 289.65±10.76, and 7.98±1.87 ng/g, respectively, in the model group to 657.63±24.47, 720.54±28.09, and 22.56±3.11 ng/g, respectively, in the 12 mg/kg GPt(II) treatment group.

Conclusions

GPt(II) treatment significantly relieved characteristics of depression in the mice through upregulation of neurotransmitter, neuropeptide, and Hsp70 expression. Moreover, GPt(II) downregulated monoamine oxidase-A levels in the mouse hippocampus tissues. Therefore, further research is warranted on the possible therapeutic effect of GPt(II) in the treatment of depression.

The monofunctional platinum(II) compounds, phenanthriplatin and pyriplatin, modulate apoptosis signaling pathways in HEI-OC1 auditory hybridoma cells

Cisplatin is a platinum(II) chemotherapy drug that can cause the side-effect of ototoxicity and hearing loss. The monofunctional platinum(II) complexes, phenanthriplatin and pyriplatin, have recently been investigated as anti-cancer agents but their side-effects are largely unknown. Here, we used the auditory hybridoma cell line, HEI-OC1, to investigate the ototoxicity of cisplatin, phenanthriplatin and pyriplatin. The effect of these compounds against cellular viability, on reactive oxygen species (ROS) production, mitochondrial membrane polarization, caspase-3/7 activity, DNA integrity and caspase-12 expression were measured using spectrophotometric, flow cytometric and blot analyses. We found that the monofunctional complexes and cisplatin decreased cellular viability. All three compounds increased ROS yield at 24 h, but at 48 h, ROS levels returned to normal. Also, the compounds did not depolarize the mitochondrial membrane. All three compounds reduced caspase-3/7 activity at 24 h; cisplatin increased caspase-3/7 activity and caused apoptosis at 48 h. Caspase-12 expression was associated with all three compounds. In summary, the monofunctional complexes may cause ototoxicity like cisplatin. Phenanthriplatin and pyriplatin may cause ototoxicity initially by inducing ROS production, but they may also signal through distinct apoptotic pathways that do not integrate caspases-3/7, or may act at different time-points in the same pathways.

Apoptosis Activation in Thyroid Cancer Cells by Jatrorrhizine-Platinum(II) Complex via Downregulation of PI3K/AKT/Mammalian Target of Rapamycin (mTOR) Pathway

Background

Thyroid cancer, which is the most common endocrine cancer, has shown a drastic increase in incidence globally over the past decade. The present study investigated the thyroid cancer-inhibitory potential of jatrorrhizine-platinum(II) complex (JR-P(II) in vitro and in vivo.

Material/Methods

The JR-P(II)-mediated cytotoxicity in thyroid carcinoma cells was determined by using MTT assay. Assessment of acetylated histones, tubulin, and DNA repair proteins was made by Western blot assays. Flow cytometry was used for apoptosis and ROS accumulation measurement.

Results

The JR-P(II) suppressed proliferative capacity of SW1736, BHP7-13, and 8305C cells. JR-P(II) treatment markedly promoted expression of acetylated histone H3, H4, and tubulin in a dose-dependent manner. Treatment with JR-P(II) significantly elevated the proportion of cells in sub-G1 and promoted cleaved caspase-3 and -9. In JR-P(II)-treated cells, DCFH-DA fluorescence was much higher relative to control cells. The JR-P(II) treatment consistently suppressed expression of pS6, p-ERK1/2, p-4E-BP1, and p-AKT, and increased p-H2AX expression and suppressed KU70 and KU80 protein levels. The level of RAD51 was repressed in JR-P(II)-treated cells. JR-P(II) administration in mice caused no significant change in body weight, and it inhibited SW1736 tumor growth in mice.

Conclusions

The JR-P(II) induced cytotoxicity in thyroid cancer cells by inhibiting the mechanism responsible for repair of double-stranded DNA. The in vivo data also revealed that JR-P(II) effectively inhibits thyroid tumor growth by inducing DNA damage. Thus, our results suggest that further evaluation of JR-P(II) as a therapeutic candidate for thyroid cancer is warranted.

Effects of L-Serine Against Cisplatin-Mediated Reactive Oxygen Species Generation in Zebrafish Vestibular Tissue Culture and HEI-OC1 Auditory Hybridoma Cells

Cisplatin is a platinum-based chemotherapy compound effective against a variety of cancers. However, it can cause increased reactive oxygen species (ROS) production in auditory and vestibular tissue leading to permanent hearing and balance loss. The amino acid, L-serine, has been shown to reduce ROS in some tissue types. In this project, we first investigated whether L-serine could reduce cisplatin-mediated ROS generation in zebrafish utricular tissue culture using spectrophotometry and the fluorescent ROS detector dye, H₂DCFDA. Then, we examined whether L-serine could prevent the effect of cisplatin against cellular viability in the mouse auditory hybridoma cell line, HEI-OC1, using the spectrophotometric (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (MTT) assay. As a final step, we used H₂DCFDA dye and flow cytometry analysis to determine if L-serine could counteract the effect of cisplatin on ROS production in this cell line. We found that cisplatin and L-serine treatment may influence ROS production in utricular tissue. Further, although L-serine did not counteract the effect of cisplatin against HEI-OC1 cellular viability, the amino acid did prevent the platinum compound's effect to increase ROS in these cells. These results suggest that L-serine may act in auditory and vestibular tissues as an effective protectant against cisplatin-mediated toxicity.

Use of zebrafish larvae lateral line to study protection against cisplatin-induced ototoxicity: A scoping review

AIM

The present review aimed to consolidate and analyze the recent information about the use of zebrafish in studies concerning cisplatin-induced ototoxicity and otoprotection.

MATERIAL AND METHODS

The PubMed, Web of Science, and Scopus databanks were searched using the following MESH terms: zebrafish, cisplatin, ototoxicity. The identified publications were screened according to inclusion and exclusion criteria and the 26 qualifying manuscripts were included in the full-text analysis. The experimental protocols, including cisplatin concentrations, the exposure duration and the outcome measurements used in zebrafish larvae studies, were evaluated and the reported knowledge was summarized.

RESULTS

Twenty-six substances protecting from cisplatin-induced toxicity were identified with the use of zebrafish larvae. These substances include quinine, salvianolic acid B, berbamine 6, benzamil, quercetin, dexmedetomidine, dexamethsanone, quinoxaline, edaravone, apocynin, dimethyl sulfoxide, KR-22335, SRT1720, ORC-13661, 3-MA, D-methionine, mdivi-1, FUT-175, rapamycin, Z-LLF-CHO, ATX, NAC, CYM-5478, CHCP1, CHCP2 and leupeptin. The otoprotective effects of compounds were attributed to their anti-ROS, anti-apoptotic and cisplatin uptake-blocking properties. The broadest range of protection was achieved when the experimental flow used preconditioning with an otoprotective compound and later a co-incubation with cisplatin. Protection against a high concentration of cisplatin was observed only in protocols using short exposure times (4 and 6 h).

CONCLUSIONS

The data extracted from the selected papers confirm that despite the differences between the human and the zebra fish hearing thresholds (as affected by cisplatin), the sensory cells of zebrafish and larval zebrafish are a valuable tool which could be used: (i) for the discovery of novel otoprotective substances and compounds; (ii) to screen their side effects and (iii) to extend the knowledge on the mechanisms of cisplatin-induced inner ear damage. For future studies, the development of a consensus experimental protocol is highly recommended.

Anti-Cancer and Ototoxicity Characteristics of the Curcuminoids, CLEFMA and EF24, in Combination with Cisplatin

In this study, we investigated whether the curcuminoids, CLEFMA and EF24, improved cisplatin efficacy and reduced cisplatin ototoxicity. We used the lung cancer cell line, A549, to determine the effects of the curcuminoids and cisplatin on cell viability and several apoptotic signaling mechanisms. Cellular viability was measured using the MTT assay. A scratch assay was used to measure cell migration and fluorescent spectrophotometry to measure reactive oxygen species (ROS) production. Western blots and luminescence assays were used to measure the expression and activity of apoptosis-inducing factor (AIF), caspases-3/7, -8, -9, and -12, c-Jun N-terminal kinases (JNK), mitogen-activated protein kinase (MAPK), and proto-oncogene tyrosine-protein kinase (Src). A zebrafish model was used to evaluate auditory effects. Cisplatin, the curcuminoids, and their combinations had similar effects on cell viability (IC₅₀ values: 2-16 μM) and AIF, caspase-12, JNK, MAPK, and Src expression, while caspase-3/7, -8, and -9 activity was unchanged or decreased. Cisplatin increased ROS yield (1.2-fold), and curcuminoid and combination treatments reduced ROS (0.75-0.85-fold). Combination treatments reduced A549 migration (0.51-0.53-fold). Both curcuminoids reduced auditory threshold shifts induced by cisplatin. In summary, cisplatin and the curcuminoids might cause cell death through AIF and caspase-12. The curcuminoids may potentiate cisplatin's effect against A549 migration, but may counteract cisplatin's effect to increase ROS production. The curcuminoids might also prevent cisplatin ototoxicity.

Platinum(iv) dihydroxido diazido N-(heterocyclic)imine complexes are potently photocytotoxic when irradiated with visible light

A series of trans-di-(N-heterocyclic)imine dihydroxido diazido PtIV complexes of the form trans,trans,trans-[Pt(N3)2(OH)2(L1)(L2)] where L = pyridine, 2-picoline, 3-picoline, 4-picoline, thiazole and 1-methylimidazole have been synthesised and characterised, and their photochemical and photobiological activity evaluated. Notably, complexes 19 (L1 = py, L2 = 3-pic) and 26 (L1 = L2 = 4-pic) were potently phototoxic following irradiation with visible light (420 nm), with IC50 values of 4.0 μM and 2.1 μM respectively (A2780 cancer cell line), demonstrating greater potency than the previously reported complex 1 (L1 = L2 = py; 6.7 μM); whilst also being minimally toxic in the absence of irradiation. Complexes with mixed N-(heterocyclic)imine ligands 19 and 20 (L1 = py, L2 = 4-pic) were particularly photocytotoxic towards cisplatin resistant (A2780cis) cell lines. Complex 18 (L1 = py, L2 = 2-pic) was comparatively less photocytotoxic (IC50 value 14.5 μM) than the other complexes, despite demonstrating the greatest absorbance at the irradiation wavelength and the fastest half-life for loss of the N3 → Pt LMCT transition upon irradiation (λ irr = 463 nm) in aqueous solution. Complex 29 (X1 = X2 = thiazole) although potently phototoxic (2.4 μM), was also toxic towards cells in the absence of irradiation.