Antitumor carboplatin is more toxic in tumor cells when photoactivated: enhanced DNA binding

Carboplatin, an analogue of "classical" cis-diamminedichloridoplatinum(II) (cisplatin), is a widely used second-generation platinum anticancer drug. Cytotoxicity of cisplatin and carboplatin is mediated by platinum-DNA adducts. Markedly higher concentrations of carboplatin are required, and the rate of adduct formation is considerably slower. The reduced toxic effects in tumor cells and a more acceptable side-effect profile are attributable to the lower reactivity of carboplatin with nucleophiles, since the cyclobutanedicarboxylate ligand is a poorer leaving group than the chlorides in cisplatin. Recently, platinum complexes were shown to be particularly attractive as potential photochemotherapeutic anticancer agents. Selective photoactivation of platinum complexes by irradiation of cancer cells may avoid enhancement of toxic side-effects, but may increase toxicity selectively in cancer cells and extend the application of photoactivatable platinum complexes to resistant cells and to a wider range of cancer types. Therefore, it was of interest to examine whether carboplatin can be affected by irradiation with light to the extent that its DNA binding and cytotoxic properties are altered. We have found that carboplatin is converted to species capable of enhanced DNA binding by UVA irradiation and consequently its toxicity in cancer cells is markedly enhanced. Recent advances in laser and fiber-optic technologies make it possible to irradiate also internal organs with light of highly defined intensity and wavelength. Thus, carboplatin is a candidate for use in photoactivated cancer chemotherapy.     

Improving platinum(II)-based anticancer drug delivery using cucurbit[n]urils

Despite the synthesis of hundreds of new platinum(II) and platinum(IV)-based complexes each year as potential anticancer drugs, only three have received world-wide approval: cisplatin, carboplatin and oxaliplatin. The next big advance in platinum-based chemotherapy is not likely to come from the development of new drugs, but from the controlled and targeted delivery of already approved drugs or those in late stage clinical trials. Encapsulation of platinum drugs inside macromolecules has already demonstrated promise, and encapsulation within cucurbit[n]urils has shown particular potential. Partial or full encapsulation within cucurbit[n]urils provides steric hindrance to drug degradation by peptides and proteins, and the use of different sized cucurbit[n]urils allows for the tuning of drug release rates, cytotoxicity and toxicity.     

Mini-review: discovery and development of platinum complexes designed to circumvent cisplatin resistance

The discovery and development of new platinum-containing anticancer drugs have represented an integral part of anticancer drug development at the Institute of Cancer Research, Sutton, over almost 20 years. As part of a collaboration with chemists at Johnson Matthey, later AnorMED, four major new classes of platinum drug have been discovered, three of which have entered clinical trial. Earlier studies led to the clinical development of the less toxic analogue carboplatin and JM216, the first orally administerable platinum drug. In recent years, the focus has been on two lead complexes designed to overcome the major mechanisms of tumour resistance to cisplatin: JM335 (trans-ammine (cyclohexylaminedichlorodihydroxo) platinum(IV)), an active trans platinum complex; and ZD0473 (cis-amminedichloro(2-methylpyridine) platinum(II)), a sterically hindered complex shown to be less reactive towards thiol-containing molecules than cisplatin. JM335 shows some circumvention of acquired cisplatin resistance in vitro and exhibits unique cellular pharmacological properties in comparison to cisplatin or its cis-isomer in terms gene-specific repair of adducts on DNA and the rate of induction of apoptosis. ZD0473 is now in phase I clinical trial. Myelosuppression is the dose-limiting toxicity at a dose of 130 mg/m2 given i.v. every 3 weeks and there has been evidence of antitumour activity. ZD0473-resistant human ovarian carcinoma cell lines have been established in vitro. Some mechanisms of resistance common to those described for cisplatin (decreased drug uptake, increased glutathione) have been observed plus, in one cell line, increased BCL2 levels and loss of the DNA mismatch repair protein MLH1.     

Characterization and cellular uptake of platinum anticancer drugs encapsulated in apoferritin

Clinical application of platinum-based anticancer drugs is largely limited by severe general toxicity and drug resistance. Drug delivery systems with tumor-targeting potential are highly desired for improving the efficacy and applicability of these drugs. This study describes an alternative strategy for the delivery of platinum drugs (cisplatin, carboplatin and oxaliplatin) by encapsulating each of them in the cavity of apoferritin (AFt). The encapsulation was achieved through manipulating the pH-dependent unfolding-refolding process of AFt at pH 2.0 and 7.4, respectively, in saturated drug solution. UV-vis spectrometry, circular dichroism spectrometry, dynamic light scattering, and inductively coupled plasma mass spectrometry were used to characterize the AFt-drug complexes. The loading capacity of AFt varies with respective drugs and the structural integrity of the protein shell remains intact after encapsulation. In vitro assays on the rat pheochromocytoma cell line (PC12) show that AFt-cisplatin inhibits the cells in a slow but sustaining mode and the cellular uptake of platinum is enhanced by AFt. AFt-carboplatin and AFt-oxaliplatin complexes only exhibit a marginal cytotoxicity towards this cell line under similar concentrations.     

Tumour-inhibiting platinum complexes—state of the art and future perspectives

Thirty years after the onset of the first clinical studies with cisplatin, the development of antineoplastic platinum drugs continues to be a productive field of research. This article reviews the current preclinical and clinical status, including a discussion of the molecular basis for the activity of the parent drug cisplatin and platinum drugs of the second and third generation, in particular their interaction with DNA. Further emphasis is laid on the development of third generation platinum drugs with activity in cisplatin-resistant tumours, particularly on chelates containing 1,2-diaminocyclohexane (DACH) and on the promising and more recently evolving field of non-classic (trans- and multinuclear) platinum complexes. The development of oral platinum drugs and drug targeting strategies using liposomes, polymers or low-molecular-weight carriers in order to improve the therapeutic index of platinum chemotherapy are also covered. Electronic Publication     

Platinum cytotoxic drugs in the municipal wastewater and drinking water,a validation method and health risk assessment

Three cancerostatic platinum compounds (CPCs) including cisplatin, carboplatin and oxaliplatin are complexes of Pt and classified as probable carcinogenic compounds to humans. This study aimed to perform health risk assessment of platinum cytotoxic drugs for drinking water by developing a sensitive analytical method in the water resource of Qom Province in the central part of Iran. Concentrations of the platinum drugs were determined, including 052 ± 0.2 µg/L for cisplatin, 0.94 ± 0.36 µg/L for carboplatin and 0.27 ± 0.16 µg/L for oxaliplatin in influent samples, and 0.24 ± 0.07 µg/L for cisplatin, 0.28 ± 0.05 µg/L for carboplatin and 0.11 ± 0.01 µg/L for oxaliplatin in effluent samples. The results indicated that in all the well water samples related to the groundwater, the concentration of the platinum-based compounds was lower than the calculated limits of quantification (LOQ); the concentration of cisplatin, carboplatin and oxaliplatin across the samples in the station of drinking water distribution was also below the limits of detection (LOD). The resulting margin of exposure (MOE) is lower than one (MOE < 1) for the three groups including children, pregnant women and lactation women related to cisplatin and carboplatin was determined through exposure to raw and untreated drinking water. Further research is recommended to be conducted in this area, particularly environmental fate of metabolites and transformation products.     

Coordination of platinum therapeutic agents to met-rich motifs of human copper transport protein1

Platinum therapeutic agents are widely used in the treatment of several forms of cancer. Various mechanisms for the transport of the drugs have been proposed including passive diffusion across the cellular membrane and active transport via proteins. The copper transport protein Ctr1 is responsible for high affinity copper uptake but has also been implicated in the transport of cisplatin into cells. Human hCtr1 contains two methionine-rich Mets motifs on its extracellular N-terminus that are potential platinum-binding sites: the first one encompasses residues 7-14 with amino acid sequence Met-Gly-Met-Ser-Tyr-Met-Asp-Ser and the second one spans residues 39-46 with sequence Met-Met-Met-Met-Pro-Met-Thr-Phe. In these studies, we use liquid chromatography and mass spectrometry to compare the binding interactions between cisplatin, carboplatin and oxaliplatin with synthetic peptides corresponding to hCtr1 Mets motifs. The interactions of cisplatin and carboplatin with Met-rich motifs that contain three or more methionines result in removal of the carrier ligands of both platinum complexes. In contrast, oxaliplatin retains its cyclohexyldiamine ligand upon platinum coordination to the peptide.     

DNA damage induced by novel demethylcantharidin-integrated platinum anticancer complexes

Oxaliplatin is a third generation platinum (Pt) drug with a diaminocyclohexane (DACH) entity, which has recently obtained worldwide approval for the clinical treatment of colon cancer, and apparently operates by a different mechanism of action to the classical cisplatin or carboplatin. Introducing a novel dual mechanism of action is one approach in designing a new platinum-based anticancer agent, whereby an appropriate ligand, such as demethylcantharidin (DMC), is released from the parent compound to exert a cytotoxic effect, in addition to that of the DNA-alkylating function of the platinum moiety. To investigate the likelihood of a novel dual mechanism of anticancer action, demethylcantharidin-integrated Pt complexes: Pt(R,R-DACH)(DMC) with the same Pt-DACH moiety as oxaliplatin, and Pt(NH(3))(2)(DMC) akin to carboplatin; were studied for their ability to induce DNA damage in HCT116 colorectal cancer cells by an alkaline comet assay. The results showed that the DMC ligand released from the novel complexes caused additional DNA lesions when compared with oxaliplatin and carboplatin. The comet assay also revealed that the DNA-damaging behavior of cisplatin is characteristically different; and this study is the first to demonstrate the ability of DMC to induce DNA lesions, thus providing sufficient evidence to explain the superior antiproliferative effect of the novel DMC-integrated complexes.     

Nanocapsules: a novel lipid formulation platform for platinum-based anti-cancer drugs

Platinum-based anti-cancer agents have been used for many years to treat many different types of cancer. However, the efficacy of these drugs is limited by serious side effects. One of the strategies to reduce the side effects is encapsulation of the drug in a lipid formulation. Recently, we discovered a novel method for the efficient encapsulation of cisplatin in a lipid formulation. The method is unique in that it does not generate conventional liposomes but nanocapsules: small aggregates of solid cisplatin covered by a lipid bilayer. Also carboplatin, a cisplatin-derived anti-cancer drug with different chemical properties, can be efficiently encapsulated by a similar method. The encapsulation in nanocapsules dramatically improves the in vitro cytotoxicity of the platinum drugs. Our results hold the promise that the nanocapsule technology could prove successful in the efficient encapsulation of many other (platinum-based) drugs, and thereby improve their therapeutic index and profile in vivo.     

Nanocapsules: A Novel Lipid Formulation Platform for Platinum-based Anti-cancer Drugs

Platinum-based anti-cancer agents have been used for many years to treat many different types of cancer. However, the efficacy of these drugs is limited by serious side effects. One of the strategies to reduce the side effects is encapsulation of the drug in a lipid formulation. Recently, we discovered a novel method for the efficient encapsulation of cisplatin in a lipid formulation. The method is unique in that it does not generate conventional liposomes but nanocapsules: small aggregates of solid cisplatin covered by a lipid bilayer. Also carboplatin, a cisplatin-derived anti-cancer drug with different chemical properties, can be efficiently encapsulated by a similar method. The encapsulation in nanocapsules dramatically improves the in vitro cytotoxicity of the platinum drugs. Our results hold the promise that the nanocapsule technology could prove successful in the efficient encapsulation of many other (platinum-based) drugs, and thereby improve their therapeutic index and profile in vivo.     

Inhibition of ABC-transporter(s)' function in non-small cell lung cancer cells by platinum drugs]

With an account of the literature data that platinum drugs react with many cellular targets, including ATP and proteins, the authors suggested that disturbance of the function of energy-dependent ABC-transporters (markers of multidrug resistance, MDR) under the effect of platinum drugs could be a cause of increased efficacy of MDR agents (agents, MDR to which is developed by the classical mechanism) when used in combination with platinum drugs even in the treatment of multidrug resistant lung cancer. The cisplatin and carboplatin effect on accumulation of MDR doxorubicin in cells of non-small cell cancer was studied by flow cytometry with the use of biopsy specimens. The MDR phenotype of the tumors was determined by a change in doxorubicin intracellular accumulation under the action of the ABC-transporter(s)' inhibitors: verapamil and genistein (specific inhibitors of Pgp and MRP respectively) and sodium azide (an inhibitor of all energy-dependent ABC-transporters). The MDR phenotypes, i.e. Pgp-MRP+ or Pgp+MRP+, were detected in all the tumors investigated. Two types of changes in doxorubicin intracellular accumulation under the action of the inhibitors and the platinum drugs were shown: (a) an increase in doxorubicin cytoplasmic accumulation and (b) a change in subcellular distribution of the anthracycline (increased accumulation of doxorubicin in the cell nucleus and its higher binding to DNA). Cisplatin and carboplatin had an inhibitory effect on ABC-transporter(s) in all the tumors investigated but the effect of carboplatin was less pronounced. It was concluded that cisplatin and carboplatin stimulation of doxorubicin intracellular accumulation, as well as a change in subcellular distribution of the anthracycline under the action of the platinum drugs (increased doxorubicin accumulation in the cell nucleus) in multidrug resistant lung tumors could be at least partly explained by inhibition of the MDR transporter(s)' function. The results could provide a basis for the use of the sequential combination cisplatin (or carboplatin)-->doxorubicin in the treatment of multidrug resistant lung cancer.     

Reactivity of platinum-based antitumor drugs towards a Met- and His-rich 20mer peptide corresponding to the N-terminal domain of human copper transporter 1

Cellular uptake of platinum-based antitumor drugs is a critical step in the mechanism of the drug action and associated resistance, and deeper understanding of this step may inspire development of novel methods for new drugs with reduced resistance. Human copper transporter 1 (hCtr1), a copper influx protein, was recently found to facilitate the cellular entry of several platinum drugs. In the work reported here, we constructed a Met- and His-rich 20mer peptide (hCtr1-N20) corresponding to the N-terminal domain of hCtr1, which is the essential domain of hCtr1 for transporting platinum drugs. The interactions of the peptide with cisplatin and its analogues, including transplatin, carboplatin, oxaliplatin, and [Pt(l-Met)Cl₂], were explored at the molecular level. Electrospray ionization (ESI) mass spectrometry (MS) data revealed that all of the platinum(II) complexes used in present study can bind to hCtr1-N20 in 1:1 and 2:1 stoichiometry. Four Met residues should be involved in binding to cis-platinum complexes on the basis of the tandem MS spectrometry and previously reported data. Time-dependent 2D [¹H,¹⁵N] heteronuclear single quantum coherence NMR spectra indicate the reaction of cisplatin with hCtr1-N20 is a stepwise process. The intermediate, however, is transient, which is consistent with the ESI-MS results. Time-dependent ESI-MS data revealed that the geometry and the properties of both the leaving and the nonleaving groups of platinum(II) complexes play essential roles in controlling the reactivity and formation of the final products with hCtr1-N20.     

Renal tissue injury and proliferative response after successive treatments with anticancer platinum derivatives and tobramycin

The administration of anticancer platinum derivatives such as cisplatin, or aminoglycoside antibiotics is frequently associated with tubular necrosis which can eventually lead to acute renal failure. Previously, we have shown that renal tissue injury induced by these drugs elicits a process of tissue repair involving the stimulation of cell proliferation. The present study was undertaken to examine the morphological alterations and the proliferative response resulting from tobramycin administration to animals previously challenged with the platinum derivatives cisplatin and carboplatin. Female Sprague-Dawley rats were treated i.p. with cisplatin (8 mg/kg delivered in four daily injections) or carboplatin (40 mg/kg given in one injection) and sacrificed 21 or 60 days after drug administration. Tobramycin was administered i.p. twice a day at a daily dose of 10 mg/kg over the ten days preceding sacrifice. At 1 h before sacrifice, each animal received i.p. 200 microCi of [3H] thymidine for the measurement of DNA synthesis and cell proliferation (determined by histoautoradiography). Successive treatments with cisplatin and tobramycin appeared to produce an increase in the severity of histopathological alterations such as tubular necrosis and cystic degeneration. Moreover, cisplatin pretreatment dramatically increased the severity of tobramycin-induced lysosomal phospholipidosis. Histopathological alterations were followed by an important proliferative response partly associated with tubular regeneration but also due to fibroblastic proliferation which led to peritubular fibrosis. Surprisingly, the additive effect of cisplatin and tobramycin on renal injury became particularly striking with increasing time intervals between treatments. In contrast, successive treatments with carboplatin and tobramycin did not cause significative changes of the degree of renal injury, compared with either drug given alone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of the DNA Base Excision Repair Protein,APE1 in Cisplatin,Oxaliplatin, or Carboplatin Induced Sensory Neuropathy

Although chemotherapy-induced peripheral neuropathy (CIPN) is a dose-limiting side effect of platinum drugs, the mechanisms of this toxicity remain unknown. Previous work in our laboratory suggests that cisplatin-induced CIPN is secondary to DNA damage which is susceptible to base excision repair (BER). To further examine this hypothesis, we studied the effects of cisplatin, oxaliplatin, and carboplatin on cell survival, DNA damage, ROS production, and functional endpoints in rat sensory neurons in culture in the absence or presence of reduced expression of the BER protein AP endonuclease/redox factor-1 (APE1). Using an in situ model of peptidergic sensory neuron function, we examined the effects of the platinum drugs on hind limb capsaicin-evoked vasodilatation. Exposing sensory neurons in culture to the three platinum drugs caused a concentration-dependent increase in apoptosis and cell death, although the concentrations of carboplatin were 10 fold higher than cisplatin. As previously observed with cisplatin, oxaliplatin and carboplatin also increased DNA damage as indicated by an increase in phospho-H2AX and reduced the capsaicin-evoked release of CGRP from neuronal cultures. Both cisplatin and oxaliplatin increased the production of ROS as well as 8-oxoguanine DNA adduct levels, whereas carboplatin did not. Reducing levels of APE1 in neuronal cultures augmented the cisplatin and oxaliplatin induced toxicity, but did not alter the effects of carboplatin. Using an in vivo model, systemic injection of cisplatin (3 mg/kg), oxaliplatin (3 mg/kg), or carboplatin (30 mg/kg) once a week for three weeks caused a decrease in capsaicin-evoked vasodilatation, which was delayed in onset. The effects of cisplatin on capsaicin-evoked vasodilatation were attenuated by chronic administration of E3330, a redox inhibitor of APE1 that serendipitously enhances APE1 DNA repair activity in sensory neurons. These outcomes support the importance of the BER pathway, and particularly APE1, in sensory neuropathy caused by cisplatin and oxaliplatin, but not carboplatin and suggest that augmenting DNA repair could be a therapeutic target for CIPN.     

Glutathione induces cellular resistance against cationic dinuclear platinum anticancer drugs

The sulfur-containing tripeptide glutathione (GSH) is one of the most abundant molecules in cells. Elevated levels of GSH render some types of cancer cells resistant against well-known platinum anti-cancer drugs such as cisplatin and carboplatin. Platinum complexes are often very reactive towards the cysteine residue of GSH, which detoxifies these compounds by a rapid binding mechanism. Clearly, this resistance mechanism poses a severe obstacle to any new platinum drugs designed to overcome cisplatin resistance. In the present study the cytotoxicity of dinuclear platinum compounds of the 1,1/t,t type, as developed by Farrell, is determined in human ovarium A2780 cells and in the cisplatin-resistant cell line A2780cisR, which possesses elevated levels of GSH. Further, the effect of depletion of GSH levels by L-buthionine-S,R-sulfoximine (L-BSO) in A2780cisR was investigated. The experiments show that detoxification by GSH is an effective resistance mechanism against dinuclear platinum compounds. However, the dinuclear complexes are less sensitive towards detoxification compared to cisplatin. This is probably because of the rapid binding of dinuclear cationic complexes to DNA. Compared to cisplatin, the rapid binding to DNA reduces the time during which the drug molecules are exposed to GSH in the cytosol. The reaction of a representative dinuclear compound with glutathione (pH 7, 37 degrees C) was studied in detail by 195Pt NMR. The dinuclear complex BBR3005 ([trans-PtCl(2)(NH(3))(2)(mu-H(2)N(CH(2))(6)NH(2))](2+), abbreviated as 1,1/t,t n=6), follows different pathways in the reaction with GSH, depending on the molar ratio of the reactants. When reacted in stoichiometric amounts (1:1), first a chloride on each platinum is replaced by a sulfur, forming a PtN(3)S product at -2977 ppm. After 2-3 h, this intermediate reacts further to form a sulfur-bridged N(3)Pt-S-PtN(3) species as the main product at -2811 ppm. When BBR3005 is reacted with GSH in a ratio of 1:4, the sulfur-bridged species is not observed. Instead, the final product is trans-Pt(GS)(2)(NH(3))(2) (at -3215 ppm); the same product appears if GSH is reacted with trans-PtCl(2)(NH(3))(2). Apparently, GSH first replaces the chlorides and subsequently degrades the dinuclear compound by replacement of the diaminealkyl linker.     

Quantitative measurement of the reduction of platinum(IV) complexes using X-ray absorption near-edge spectroscopy (XANES)

The platinum(II) drugs cisplatin, carboplatin and oxaliplatin are usefully employed against a range of malignancies, but toxicities and resistance have spurred the search for improved analogs. This has included investigation of the platinum(IV) oxidation state, which provides greater kinetic inertness. It is generally accepted that Pt(IV) complexes must be reduced to Pt(II) for activation. As such, the ability to monitor reduction of Pt(IV) complexes is critical to guiding the design of candidates, and providing mechanistic understanding. Here we report in full that the white line height of X-ray absorption near-edge spectra (XANES) of Pt complexes, normalized to the post-edge minima, can be used to quantitatively determine the proportion of each oxidation state in a mixture. A series of Pt(IV) complexes based on the Pt(II) complexes cisplatin and transplatin were prepared with chlorido, acetato or hydroxido axial ligands, and studies into their reduction potential and cytotoxicity against A2780 human ovarian cancer cells were performed, demonstrating the relationship between reduction potential and cytotoxicity. Analysis of white line height demonstrated a clear and consistent difference between Pt(II) (1.52 ± 0.05) and Pt(IV) (2.43 ± 0.19) complexes. Reduction of Pt(IV) complexes over time in cell growth media and A2780 cells was observed by XANES, and shown to correspond with their reduction potentials and cytotoxicities. We propose that this method is useful for monitoring reduction of metal-based drug candidates in complex biological systems.     

The influence of temperature on antiproliferative effects, cellular uptake and DNA platination of the clinically employed Pt(II)-drugs

Cellular uptake of a drug is one of the most important factors influencing its pharmacodynamics and pharmacokinetics. Our laboratory has previously studied platinum uptake following cisplatin, carboplatin and oxaliplatin treatment at sub-lethal doses of selected tumour cell lines. Here we report on the influence of temperature on dose-dependent antiproliferative effects, cellular uptake and DNA platination of these platinum-based drugs tested on MCF-7 human mammary carcinoma cell line. Inductively coupled plasma-mass spectrometry (ICP-MS) technique has been chosen to perform Pt determinations on cells treated with drug concentrations similar with those usually found in vivo in human plasma. The high sensitivity and analytical rapidity of this technique made possible to carry out a very large amount of Pt determinations (about 300) necessary for this study. Hyperthermia (43 degrees C) proved a synergistic effect with cisplatin on cell growth inhibition, while only an additive effect was demonstrated for carboplatin and oxaliplatin. This behaviour might be explained by the higher DNA platination ratio between data at 43 and 37 degrees C of cisplatin with respect to those of carboplatin and oxaliplatin.     

The activation of platinum(II) antiproliferative drugs in carbonate medium evaluated by means of a DNA-biosensor

We report on the binding of cisplatin, carboplatin and oxaliplatin to double-stranded DNA in two different (phosphate and carbonate) buffers, using an electrochemical DNA-biosensor. The propensity of the electrophilic agent produced by hydrolysis to interact with DNA was measured as a function of the decrease of guanine oxidation signal of the metal-DNA adduct immobilized on a screen-printed electrode, by using square wave voltammetry. The results obtained confirm that carbonate reacts with platinum drugs to form activated carbonato complexes, which are able to react readily with DNA.     

Chloroxine overrides DNA damage tolerance to restore platinum sensitivity in high-grade serous ovarian cancer

High-grade serous cancer (HGSC) accounts for ~67% of all ovarian cancer deaths. Although initially sensitive to platinum chemotherapy, resistance is inevitable and there is an unmet clinical need for novel therapies that can circumvent this event. We performed a drug screen with 1177 FDA-approved drugs and identified the hydroxyquinoline drug, chloroxine. In extensive validation experiments, chloroxine restored sensitivity to both cisplatin and carboplatin, demonstrating broad synergy in our range of experimental models of platinum-resistant HGSC. Synergy was independent of chloroxine’s predicted ionophore activity and did not relate to platinum uptake as measured by atomic absorption spectroscopy. Further mechanistic investigation revealed that chloroxine overrides DNA damage tolerance in platinum-resistant HGSC. Co-treatment with carboplatin and chloroxine (but not either drug alone) caused an increase in γH2AX expression, followed by a reduction in platinum-induced RAD51 foci. Moreover, this unrepaired DNA damage was associated with p53 stabilisation, cell cycle re-entry and triggering of caspase 3/7-mediated cell death. Finally, in our platinum-resistant, intraperitoneal in vivo model, treatment with carboplatin alone resulted in a transient tumour response followed by tumour regrowth. In contrast, treatment with chloroxine and carboplatin combined, was able to maintain tumour volume at baseline for over 4 months. In conclusion, our novel results show that chloroxine facilitates platinum-induced DNA damage to restore platinum sensitivity in HGSC. Since chloroxine is already licensed, this exciting combination therapy could now be rapidly translated for patient benefit.Subject terms: Ovarian cancer, High-throughput screening     

Comparative study of the interactions of cisplatin and carboplatin with nucleotides using UV resonance raman spectroscopy

We have obtained the UV excited resonance Raman spectra of five mononucleotides bound to cisplatin and to carboplatin using excitation in resonance with the first electronic absorption bands of the nucleotide bases. Substantial changes in the spectra are observed following interaction with both platinum drugs, indicating modifications to nucleotide structure. Pt (II) binds to base portions of the nucleotide molecules, altering their normal modes of vibration significantly. We present comparative data of cisplatin and carboplatin, and discuss the implications of these results. The kinetics of the drug/nucleotide reactions differ, but final products are found to be similar. © 1993 John Wiley & Sons, Inc.