Picoplatin binding to proteins: X-ray structures and mass spectrometry data on the adducts with lysozyme and ribonuclease A

The reactivity of the anticancer drug picoplatin (cis-amminedichlorido(2-methylpyridine)platinum(II) complex) with the model proteins hen egg white lysozyme (HEWL) and bovine pancreatic ribonuclease (RNase A) was investigated by electrospray ionisation mass spectrometry (ESI MS) and X-ray crystallography. The data were compared with those previously obtained for the adducts of these proteins with cisplatin, carboplatin and oxaliplatin under the same experimental conditions. ESI-MS data show binding of Pt to both proteins, with fragments retaining the 2-methylpyridine ligand and, possibly, a chloride ion. X-ray crystallography identifies different binding sites on the two proteins, highlighting a different behaviour of picoplatin in the absence or presence of dimethyl sulfoxide (DMSO). Metal-containing fragments bind to HEWL close to the side chains of His15, Asp18, Asp119 and both Lys1 and Glu7, whereas they bind to RNase A on the side chain of His12, Met29, His48, Asp53, Met79, His105 and His119. The data suggest that the presence of DMSO favours the loss of 2-methylpyridine and alters the ability of the Pt compound to bind to the two proteins. With both proteins, picoplatin appears to behave similarly to cisplatin and carboplatin when dissolved in DMSO, whereas it behaves more like oxaliplatin in the absence of the coordinating solvent. This study provides important insights into the pharmacological profile of picoplatin and supports the conclusion that coordinating solvents should not be used to evaluate the biological activities of Pt-based drugs.

Thermoresponsive carboplatin-releasing prodrugs

Platinum-based anticancer drugs, while potent, are associated with numerous and severe side effects. Hyperthermia therapy is an effective adjuvant in anticancer treatment, however, clinically used platinum drugs have not been optimised for combination with hyperthermia. The derivatisation of existing anticancer drugs with appropriately chosen thermoresponsive moieties results in drugs being activated only at the heated site. Perfluorinated chains of varying lengths were installed on carboplatin, a clinically approved drug, leading to the successful synthesis of a series of mono- and di- substituted platinum(IV) carboplatin prodrugs. Some of these complexes display relevant thermosensitivity on ovarian cancer cell lines, i.e., being inactive at 37 °C while having comparable activity to carboplatin under mild hyperthermia (42 °C). Nuclear magnetic resonance spectroscopy and mass spectrometry indicated that carboplatin is likely the active platinum(II) anticancer agent upon reduction and cyclic voltammetry revealed that the length of the fluorinated alkyl chain has a strong influence on the rate of carboplatin formation, regulating the subsequent cytotoxicity.

Platinum(IV) Prodrugs Incorporating an Indole-Based Derivative, 5-Benzyloxyindole-3-Acetic Acid in the Axial Position Exhibit Prominent Anticancer Activity

Kinetically inert platinum(IV) complexes are a chemical strategy to overcome the impediments of standard platinum(II) antineoplastic drugs like cisplatin, oxaliplatin and carboplatin. In this study, we reported the syntheses and structural characterisation of three platinum(IV) complexes that incorporate 5-benzyloxyindole-3-acetic acid, a bioactive ligand that integrates an indole pharmacophore. The purity and chemical structures of the resultant complexes, P-5B3A, 5-5B3A and 56-5B3A were confirmed via spectroscopic means. The complexes were evaluated for anticancer activity against multiple human cell lines. All complexes proved to be considerably more active than cisplatin, oxaliplatin and carboplatin in most cell lines tested. Remarkably, 56-5B3A demonstrated the greatest anticancer activity, displaying GI50 values between 1.2 and 150 nM. Enhanced production of reactive oxygen species paired with the decline in mitochondrial activity as well as inhibition of histone deacetylase were also demonstrated by the complexes in HT29 colon cells.

Platinum measurements in Dulbecco's phosphate-buffered saline are lower than in plasma and can be sampled with ultrafiltration probes in vitro

OBJECTIVE

To compare the influence of fluid on carboplatin elution, and assess the feasibility of ultrafiltration (UF) probe sampling.

SAMPLE

20 samples of 5 mg carboplatin in 1.0 mL 30% poloxamer 407 eluting in Dulbecco's phosphate-buffered saline (DPBS) or canine plasma and 6 samples of UF probe sampling in 0.01 mg/mL carboplatin in DPBS or plasma.

METHODS

Carboplatin-gel specimens in dialysis tubing (12- to 14-kDa pores) were placed in 100 mL of DPBS or canine plasma (37 °C and 600 rpm stirring) in a nonlidded and lidded experiment. Samples were collected in decreasing frequency for 96 hours. The 0.01-mg/mL carboplatin solutions in DPBS and plasma were sampled 6 times by UF probe (30-kDa pores) or direct aspiration. Platinum was measured using inductively coupled plasma mass spectrometry.

RESULTS

High fluid evaporation was noted in the nonlidded but not the lidded experiment. A burst release was seen in plasma (first 2 hours) and DPBS (first 5 hours) with the highest hourly increase in the first hour in both DPBS (6,040 ppb/h) and plasma (2,612 ppb/h), with no further increase after the first 22 hours. Platinum content in the specimens was higher at 96 hours than the surrounding fluid. Higher platinum concentrations were measured by both direct and UF probe sampling in DPBS than in plasma.

CLINICAL RELEVANCE

Platinum concentrations measured in DPBS were higher than in plasma, but elution patterns were similar. Ultrafiltration probes can be used to sample platinum in vitro and could be used in vivo to measure local unbound Pt tissue concentrations in local chemotherapy delivery.

Will the Interactions of Some Platinum (II)-Based Drugs with B-Vitamins Reduce Their Therapeutic Effect in Cancer Patients? Comparison of Chemotherapeutic Agents such as Cisplatin, Carboplatin and Oxaliplatin-A Review

Pt (II) derivatives show anti-cancer activity by interacting with nucleobases of DNA, thus causing some spontaneous and non-spontaneous reactions. As a result, mono- and diaqua products are formed which further undergo complexation with guanine or adenine. Consequently, many processes are triggered, which lead to the death of the cancer cell. The theoretical and experimental studies confirm that such types of interactions can also occur with other chemical compounds. The vitamins from B group have a similar structure to the nucleobases of DNA and have aromatic rings with single-pair orbitals. Theoretical and experimental studies were performed to describe the interactions of B vitamins with Pt (II) derivatives such as cisplatin, oxaliplatin and carboplatin. The obtained results were compared with the values for guanine. Two levels of simulations were implemented at the theoretical level, namely, B3LYP/6-31G(d,p) with LANL2DZ bases set for platinum atoms and MN15/def2-TZVP. The polarizable continuum model (IEF-PCM preparation) and water as a solvent were used. UV-Vis spectroscopy was used to describe the drug-nucleobase and drug-B vitamin interactions. Values of the free energy (ΔG_r) show spontaneous reactions with mono- and diaqua derivatives of cisplatin and oxaliplatin; however, interactions with diaqua derivatives are more preferable. The strength of these interactions was also compared. Carboplatin products have the weakest interaction with the studied structures. The presence of non-covalent interactions was demonstrated in the tested complexes. A good agreement between theory and experiment was also demonstrated.

Breakdown of chemo-immune resistance by a TDO2-targeted Pt(IV) prodrug via attenuating endogenous Kyn-AhR-AQP4 metabolic circuity and TLS-promoted genomic instability

A tryptophan-2,3-dioxygenase 2 (TDO2)-targeted Pt(IV) prodrug, DN604-TDOi, was designed to prove that the multi-action compound could overcome drug resistance and relieve immunosuppression via introducing a TDO2 inhibitor to the axial position of a six-coordinate Pt(IV) hybrid. Several in vitro biological studies on cisplatin-resistant NSCLC cancer cells suggested that TDO2-targeted Pt(IV) prodrug could combat cisplatin resistance via influencing TDO2-kynurenine (Kyn)-aryl hydrocarbon receptor (AhR)-Aquaporin-4 (AQP4) metabolic circuity and AhR-human DNA polymerase (hpol) κ-induced translesion DNA synthesis (TLS) genomic instability, which are positive in drug-resistant human tumors associated with malignant progression and poor survival. Remarkably, we observed that DN604-TDOi could inhibit TDO2-mediated constitutive Kyn-AhR-AQP4 signaling pathway and suppress hpol κ expression, leading to potential decrease of cell motility and genomic instability in A549/cDDP cells. It was confirmed that TDO2-targeted Pt(IV) prodrug could harness Kyn-AhR-AQP4 metabolic circuitry and TLS genomic instability, exerting antitumor effects in C57BL6 but not TDO2^-/- mice. Moreover, the Pt(IV) prodrug improved the intratumoral infiltration of T_eff cells and reduced the recruitment of T_reg cells. The results provided compelling preclinical evidence that TDO2-targeted Pt(IV) prodrug could abrogate immune chemotherapeutic resistance via decaying TDO2-mediated Kyn-AhR-AQP4 immunosuppression and AhR-hpol κ-induced TLS genomic instability, underscoring the development of a novel Pt(IV)-based candidate as a potent immunotherapeutic agent for chemo-immune resistance prevention.

Crystallization of carboplatin-loaded onto microporous calcium phosphate using high-vacuum method: Characterization and release study

Drug delivery systems are a new approach to increase therapeutic efficacy and to reduce the side effects of traditional treatments. Calcium phosphates (CaPs) have been studied as drug delivery systems, especially in bone diseases. However, each system has some particularities that depend on the physical and chemical characteristics of the biomaterials and drug interaction. In this work, granulated CaPs were used as a matrix for loading the anticancer drug carboplatin using the high-vacuum method. Five compositions were applied: hydroxyapatite (HA), β-tricalcium phosphate (β-TCP), biphasic HAp 60%/β-TCP 40% (BCP), β-TCP/MgO nanocomposite, and β-TCP/SiO2 nanocomposite. Carboplatin drug in 50, 60, and 70 mg/g was precipitated on the surface of CaPs. Morphological, chemical and surface modifications in the carboplatin-CaPs were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), backscattered electron microscopy (BSE), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), Fourier transform infrared (FT-IR), and Raman spectroscopy. The characterization of the CaP-carboplatin biomaterials showed heterogeneous crystalline precipitation of the drug, and no morphological modifications of the CaPs biomaterials. The in vitro release profile of carboplatin from CaPs was evaluated by the ultraviolet-visible (UV-Vis) method. The curves showed a burst release of upon 60% of carboplatin loaded followed by a slow-release of the drug for the time of the study. The results were typical of a low-interaction system and physisorption mechanism. The high-vacuum method permitted to load the high amount of carboplatin drug on the surface of the biomaterials despite the low interaction between carboplatin and CaPs.

Anti-tumor effects and cell motility inhibition of the DN604-gemcitabine combined treatment in human bladder cancer models

Bladder cancer is one of the major tumors for men in the world, in which therapy the combination of cisplatin and gemcitabine is still fist-line applied to treat with advanced or metastatic bladder cancer. In our early study, we developed a potential Pt(II) agent, DN604, which has anti-tumor effect as potent as cisplatin toward bladder cancers. Herein, we aim at investigating the combinatory application of DN604 with gemcitabine for bladder cancer treatment. In vitro studies proved that the combined treatment of DN604 and gemcitabine could limit cell proliferation by elevating the incidence of DNA damage induced apoptosis. Notably, further researches showed that the DN604-gemcitabine treatment suppressed cell autophagy to inhibit cell motility upon the ROS dependent p38 MAPK signaling pathway, explicating its better anti-tumor activity than single drug treatment or the cisplatin-gemcitabine treatment. In vivo tests confirmed that the DN604-gemcitabine treatment has superior anti-tumor activity with low toxicity to cisplatin or its combination with gemcitabine treatments. DN604 plus gemcitabine, is of great significance for the treatment with human bladder cancer. Our study has provided a potential combination treatment option.

Evaluation of bioabsorbable calcium sulfate hemihydrate beads for local delivery of carboplatin

The objectives of this study were to evaluate a novel kit of resorbable calcium sulfate beads marketed specifically for use in veterinary medicine and generally used for local delivery of antimicrobials as carboplatin-delivery system. The study characterized the elution of carboplatin in vitro, and investigated whether the initial dose and formulation of carboplatin, or the bead size significantly influences carboplatin elution in vitro. Calcium sulfate hemihydrate beads of 3- and 5-mm diameter were prepared. Five doses and two formulations of carboplatin (20, 50, 100, and 500 mg carboplatin per kit in powder formulation; 20 mg in liquid formulation) were tested in triplicates for each diameter beads. Beads were placed in 37°C phosphate buffered saline for 72 hours. Carboplatin concentrations in the eluent were measured by high-performance liquid chromatography at 11 time points with a modified United States Pharmacopeia assay. Concentrations of carboplatin in the eluent proportionally increased with the initial dose and peaked between 13 and 52 hours, ranging from 42.1% to 79.3% of the incorporated load. Higher peak concentrations, percentages released, and elution rates were observed with the liquid formulation and with higher carboplatin doses. There was no significant difference in maximum carboplatin concentrations between 3- and 5-mm diameter beads, but 5-mm diameter beads had slower elution rates. The novel kit can be used for preparation of carboplatin-impregnated resorbable calcium sulfate beads at variable doses, sizes and formulations. Further study is warranted to define the in vivo requirements and effective carboplatin dose, spatial diffusion and desired duration of elution.

In Vitro MCF-7 Cells Apoptosis Analysis of Carboplatin Loaded Silk Fibroin Particles

Breast cancer ranks as the fifth leading cause of death worldwide. Chemotherapy is commonly used directly or as neo-adjuvant therapy for the management of breast cancer with its attendant adverse effects, underscoring the need to develop biocompatible bioactive compounds for pharmacological applications. The aim of this study is to encapsulate carboplatin (CP) with silk fibroin protein (SF) by using an ionic gelation method as a drug carrier system and assess the apoptotic effect on MCF-7 breast cancer cells during in vitro studies. The characterization of silk fibroin encapsulated carboplatin (SFCP) microparticles was analyzed by FTIR spectrophotometer, SEM, Mastersizer, and biodegradation methods. The encapsulation efficiency and release profile of SFCP microparticles were analyzed by an indirect UV-Vis spectrophotometric method. An apoptotic screening of MCF-7 cells was carried out with 10-200 µg/mL CP loaded SFCP, which were cultured for 24, 48, and 72 h. Data were analyzed using the Student's t test and analysis of variance. FTIR and drug release studies confirmed an interaction of silk fibroin with the carboplatin moiety. SFCP showed successful encapsulation of the carboplatin moiety. Apoptotic screening showed a dose dependent increase in absorbance, indicating significant cell death (p < 0.05). Thus, the direct apoptotic effect of SFCP microparticles on MCF-7 was confirmed.

Heterogeneous drug penetrance of veliparib and carboplatin measured in triple negative breast tumors

BACKGROUND

Poly(ADP-ribose) polymerase inhibitors (PARPi), coupled to a DNA damaging agent is a promising approach to treating triple negative breast cancer (TNBC). However, not all patients respond; we hypothesize that non-response in some patients may be due to insufficient drug penetration. As a first step to testing this hypothesis, we quantified and visualized veliparib and carboplatin penetration in mouse xenograft TNBCs and patient blood samples.

METHODS

MDA-MB-231, HCC70 or MDA-MB-436 human TNBC cells were implanted in 41 beige SCID mice. Low dose (20 mg/kg) or high dose (60 mg/kg) veliparib was given three times daily for three days, with carboplatin (60 mg/kg) administered twice. In addition, blood samples were analyzed from 19 patients from a phase 1 study of carboplatin + PARPi talazoparib. Veliparib and carboplatin was quantified using liquid chromatography-mass spectrometry (LC-MS). Veliparib tissue penetration was visualized using matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI-MSI) and platinum adducts (covalent nuclear DNA-binding) were quantified using inductively coupled plasma-mass spectrometry (ICP-MS). Pharmacokinetic modeling and Pearson's correlation were used to explore associations between concentrations in plasma, tumor cells and peripheral blood mononuclear cells (PBMCs).

RESULTS

Veliparib penetration in xenograft tumors was highly heterogeneous between and within tumors. Only 35% (CI 95% 26-44%), 74% (40-97%) and 46% (9-37%) of veliparib observed in plasma penetrated into MDA-MB-231, HCC70 and MDA-MB-436 cell-based xenografts, respectively. Within tumors, penetration heterogeneity was larger with the 60 mg/kg compared to the 20 mg/kg dose (RSD 155% versus 255%, P = 0.001). These tumor concentrations were predicted similar to clinical dosing levels, but predicted tumor concentrations were below half maximal concentration values as threshold of response. Xenograft veliparib concentrations correlated positively with platinum adduct formation (R 2 = 0.657), but no PARPi-platinum interaction was observed in patients' PBMCs. Platinum adduct formation was significantly higher in five gBRCA carriers (ratio of platinum in DNA in PBMCs/plasma 0.64% (IQR 0.60-1.16%) compared to nine non-carriers (ratio 0.29% (IQR 0.21-0.66%, P < 0.0001).

CONCLUSIONS

PARPi/platinum tumor penetration can be measured by MALDI-MSI and ICP-MS in PBMCs and fresh frozen, OCT embedded core needle biopsies. Large variability in platinum adduct formation and spatial heterogeneity in veliparib distribution may lead to insufficient drug exposure in select cell populations.

Anticancer activity and tissue distribution of platinum (II) complex with lignin-derived polymer of benzene-poly-carboxylic acids

Platinum-containing antineoplastic agents with physiologically active ligands seem to be a promising direction in anticancer drug design. PDBA is a novel promising antineoplastic agent, containing polymer ligand of natural origin (international patent WO2013/143549 A1). Polymer ligand of PDBA has a highly functionalised polyphenolic backbone, which exerts its own pharmacological effect via immune modulation and regulation of gene expression. PDBA is a cis-diammineplatinum(II) complex, containing mono-deprotonated benzene-poly-carboxylic acids, derived from lignin, and hydroxyl group as O-donor ligands (approximate bulk formula C₈₃H₇₀N₂O₂₇Pt). The agent is being evaluated in Phase II controlled clinical trials in metastatic breast cancer patients. In the present study, tissue distribution and tumour growth inhibition effects of PDBA, cisplatin and carboplatin were compared in SHR female mice, bearing inoculated solid Ehrlich carcinoma. The agents were administered subcutaneously every second day for the period of 10days (5 injections) at 62.5mg/kg, 3.0mg/kg and 18.5mg/kg for PDBA, cisplatin and carboplatin, respectively. Experimental animals were sacrificed on the Days 11, 16 and 23 after the inoculation of the tumour. The doses of all studied drugs were selected to obtain similar antitumour efficacy with ca. 50% growth inhibition of the Ehrlich tumour at the end of the study. The efficacy of a single platinum reactive moiety [cis-diammineplatinum(II)] was shown to be the highest for cisplatin, followed by PDBA and finally carboplatin. However, the toxicity of PDBA was considerably lower than that of carboplatin and especially cisplatin. The drugs were mainly distributed in lungs, kidneys, liver, spleen and tumour tissue. PDBA showed quite high accumulation in the tumour tissue, possibly, owing to the effect of the lignin-derived ligand.

[18F]-Fluorinated Carboplatin and [111In]-Liposome for Image-Guided Drug Delivery

Radiolabeled liposomes have been employed as diagnostic tools to monitor in vivo distribution of liposomes in real-time, which helps in optimizing the therapeutic efficacy of the liposomal drug delivery. This work utilizes the platform of [111In]-Liposome as a drug delivery vehicle, encapsulating a novel 18F-labeled carboplatin drug derivative ([18F]-FCP) as a dual-molecular imaging tool as both a radiolabeled drug and radiolabeled carrier. The approach has the potential for clinical translation in individual patients using a dual modal approach of clinically-relevant radionuclides of 18F positron emission tomography (PET) and 111In single photon emission computed tomography (SPECT). [111In]-Liposome was synthesized and evaluated in vivo by biodistribution and SPECT imaging. The [18F]-FCP encapsulated [111In]-Liposome nano-construct was investigated, in vivo, using an optimized dual-tracer PET and SPECT imaging in a nude mouse. The biodistribution data and SPECT imaging showed spleen and liver uptake of [111In]-Liposome and the subsequent clearance of activity with time. Dual-modality imaging of [18F]-FCP encapsulated [111In]-Liposome showed significant uptake in liver and spleen in both PET and SPECT images. Qualitative analysis of SPECT images and quantitative analysis of PET images showed the same pattern of activity during the imaging period and demonstrated the feasibility of dual-tracer imaging of a single dual-labeled nano-construct.

Platinum derivatives: a multidisciplinary approach

Cancer is one of the most difficult diseases to be treated. The particularities regarding the tumors' occurrence mechanism, their evolution under chemotherapy, disease-free interval, but also the increasing number of patients make cancer an intensively studied health domain. Although introduced in therapy since the early 80s, platinum derivatives play an essential role in anticancer therapy. Their use in therapy resulted in improving the patient quality of life and prolonging disease-free interval, which makes them still a benchmark for other anticancer compounds. However, adverse reactions and allergic reactions are a major impediment in therapy with platinum derivatives. This paper summarizes data about platinum derivatives through a multidisciplinary approach, starting from a chemical point of view and on to their mechanism of action, mechanism of cellular resistance, predictive factors for the outcome of chemotherapy such as micro RNAs (miRNAs), tumor suppressor protein p53, and the excision repair cross-complementing 1 protein (ERCC1).

Chemical Imaging of Platinum-Based Drugs and their Metabolites

Platinum-based drugs (cisplatin, carboplatin, and oxaliplatin) are widely used therapeutic agents for cancer treatment. Even though the platinum (Pt)-drugs are routinely used clinically, a clear picture of their distribution within tumor tissues is lacking. The current methods to image the distribution of Pt drugs are limited and do not enable the discrimination of the drug from its metabolites. In this manuscript, we demonstrate a methodology that enables chemical imaging of a Pt drug and its metabolites simultaneously and specifically. Matrix-Assisted Laser Desorption/Ionization (MALDI) Mass Spectrometry Imaging (MSI) is combined with an on-tissue chemical derivatization using diethyldithiocarbamate (DDTC). DDTC abstracts the Pt atom to generate ionizable complexes that can be imaged by MALDI MSI. We demonstrate that Pt drugs and their metabolites can be specifically imaged. This approach was successfully applied to map the penetration and metabolism of oxaliplatin in hyperthermic intraperitoneal chemotherapy (HIPEC)-like treated 3D colorectal tumor mimics. The distribution of cisplatin and carboplatin was mapped in additional 3D tumor mimics. We demonstrate that the approach can also be used to image the distribution of copper ions in cells. This method has the potential to be used to evaluate the penetration and distribution of a wide range of compounds.

Nanoscale Coordination Polymers Codeliver Carboplatin and Gemcitabine for Highly Effective Treatment of Platinum-Resistant Ovarian Cancer

Due to the ability of ovarian cancer (OCa) to acquire drug resistance, it has been difficult to develop efficient and safe chemotherapy for OCa. Here, we examined the therapeutic use of a new self-assembled core-shell nanoscale coordination polymer nanoparticle (NCP-Carbo/GMP) that delivers high loadings of carboplatin (28.0 ± 2.6 wt %) and gemcitabine monophosphate (8.6 ± 1.5 wt %). A strong synergistic effect was observed between carboplatin and gemcitabine against platinum-resistant OCa cells, SKOV-3 and A2780/CDPP, in vitro. The coadministration of carboplatin and gemcitabine in the NCP led to prolonged blood circulation half-life (11.8 ± 4.8 h) and improved tumor uptake of the drugs (10.2 ± 4.4% ID/g at 24 h), resulting in 71% regression and 80% growth inhibition of SKOV-3 and A2780/CDDP tumors, respectively. Our findings demonstrate that NCP particles provide great potential for the codelivery of multiple chemotherapeutics for treating drug-resistant cancer.

Platinum based radiochemotherapies: Free radical mechanisms and radiotherapy sensitizers

The radiosensitizing ability of Pt drugs can in the first instance be predicted based on the ease that they undergo activation by electron attachment accompanied by structural modification prior to forming Pt-DNA adducts. Unlike cisplatin, carboplatin and nedaplatin, oxaliplatin does not undergo a facile dissociative electron transfer reaction when an electron is attached. However, oxaliplatin undergoes a facile nucleophilic assisted proton coupled electron transfer (NAPCET), which may be key element of the success of FOLFOX radiochemotherapy against certain cancers. Under acidic conditions, oxaliplatin is a superior radiosensitizer to cisplatin or carboplatin, in the presence of nucleophiles such as water, chloride ions or thiols. Oxaliplatin may also be activated as a platinating agent and radiosensitizer by a minor hydrogen radical free radical mechanism as well as the more dominant NAPCET mechanism. The radiosensitizing synergism that is shown when oxaliplatin is combined with 5-fluorouracil can be due to the formation of a π complex between the two drugs, which is more potent under acidic conditions. These factors have a bearing on Pt based chemotherapy clinical regimes as well as clinical radiochemotherapy regimes, and could be a basis for optimizing how such drug schedules are administered.

The role of the equatorial ligands for the redox behavior, mode of cellular accumulation and cytotoxicity of platinum(IV) prodrugs

The current study aims to elucidate the possible reasons for the significantly different pharmacological behavior of platinum(IV) complexes with cisplatin-, carboplatin- or nedaplatin-like cores and how this difference can be related to their main physicochemical properties. Chlorido-containing complexes are reduced fast (within hours) by ascorbate and are able to unwind plasmid DNA in the presence of ascorbate, while their tri- and tetracarboxylato analogs are generally inert under the same conditions. Comparison of the lipophilicity, cellular accumulation and cytotoxicity of the investigated platinum compounds revealed the necessity to define new structure-property/activity relationships (SPRs and SARs). The higher activity and improved accumulation of platinum(IV) complexes bearing Cl(-) in equatorial position cannot only be attributed to passive diffusion facilitated by their lipophilicity. Therefore, further platinum accumulation experiments under conditions where active/facilitated transport mechanisms are suppressed were performed. Under hypothermic conditions (4°C), accumulation of dichloridoplatinum(IV) complexes is reduced down to 10% of the amount determined at 37°C. These findings suggest the involvement of active and/or facilitated transport in cellular uptake of platinum(IV) complexes with a cisplatin-like core. Studies with ATP depletion mediated by oligomycin and low glucose partially confirmed these observations, but their feasibility was severely limited in the adherent cell culture setting.

A sequential temperature cycling study for the investigation of carboplatin infusion stability to facilitate `dose-banding'

Study objective. To determine the physical and chemical stability of carboplatin infusion for dosebanding, with cycling between refrigerated storage and room temperature in-use conditions.

Design. A sequential study design was selected to closely simulate the temperatures and conditions experienced by drug infusions in pharmaceutical storage and in clinical use. Carboplatin infusions, 0.70 and 2.15 mg/mL, were stored refrigerated for up to 84 days, followed by incubation at 258C for 24 h. The infusions were also returned to refrigerated storage for 3 and 7 days, to replicate a situation in which returned, unused infusions are kept for re-issuing. On pre-determined time-points, infusion chemical and physical stability were determined by HLPC, sub-visual particulatecounts, pH-measurement, and weighing of infusions.

Results. Light protected carboplatin infusions at both study concentrations were chemically and physically stable following refrigerated storage for 84 days, followed by a further 24 h under ‘in-use’ conditions at 258C. Additionally, the infusions were stable following return to refrigerated storage again for at least 7 days.

Conclusion. This study has demonstrated extended stability of carboplatin infusions which enables batch-scale preparation of standard infusions for dose- J Oncol Pharm Practice (2007) 13: 119–126.

Crystallography and chemistry should always go together: a cautionary tale of protein complexes with cisplatin and carboplatin

The anticancer activity of platinum-containing drugs such as cisplatin and carboplatin is considered to primarily arise from their interactions with nucleic acids; nevertheless, these drugs, or the products of their hydrolysis, also bind to proteins, potentially leading to the known side effects of the treatments. Here, over 40 crystal structures deposited in the Protein Data Bank (PDB) of cisplatin and carboplatin complexes of several proteins were analysed. Significant problems of either a crystallographic or a chemical nature were found in most of the presented atomic models and they could be traced to less or more serious deficiencies in the data-collection and refinement procedures. The re-evaluation of these data and models was possible thanks to their mandatory or voluntary deposition in publicly available databases, emphasizing the point that the availability of such data is critical for making structural science reproducible. Based on this analysis of a selected group of macromolecular structures, the importance of deposition of raw diffraction data is stressed and a procedure for depositing, tracking and using re-refined crystallographic models is suggested.

Raman spectroscopic evaluation of DNA adducts of a platinum containing anticancer drug

Mechanistic understanding of the interaction of drugs with their target molecules is important for better understanding of their mode of action and to improve their efficacy. Carboplatin is a platinum containing anticancer drug, used to treat different type of tumors. In the present work, we applied Raman spectroscopy to study the interaction of carboplatin with DNA at molecular level using different carboplatin-DNA molar ratios. These Raman spectroscopic results provide comprehensive understanding on the carboplatin-DNA interactions and indicate that DNA cross-linked adducts formed by carboplatin are similar to cisplatin adducts. The results indicate that guanine N7 and adenine N7 are the putative sites for carboplatin interaction. It is observed that carboplatin has some affinity toward cytosine in DNA. Phosphate sugar backbone of DNA showed conformation perturbation in DNA which were easily sensible at higher concentrations of carboplatin. Most importantly, carboplatin interaction induces intermediate A- and B-DNA conformations at the cross-linking sites.

Carboplatin binding to histidine

Carboplatin is a second-generation platinum anticancer agent used for the treatment of a variety of cancers. Previous X-ray crystallographic studies of carboplatin binding to histidine (in hen egg-white lysozyme; HEWL) showed the partial conversion of carboplatin to cisplatin owing to the high NaCl concentration used in the crystallization conditions. HEWL co-crystallizations with carboplatin in NaBr conditions have now been carried out to confirm whether carboplatin converts to the bromine form and whether this takes place in a similar way to the partial conversion of carboplatin to cisplatin observed previously in NaCl conditions. Here, it is reported that a partial chemical transformation takes place but to a transplatin form. Thus, to attempt to resolve purely carboplatin binding at histidine, this study utilized co-crystallization of HEWL with carboplatin without NaCl to eliminate the partial chemical conversion of carboplatin. Tetragonal HEWL crystals co-crystallized with carboplatin were successfully obtained in four different conditions, each at a different pH value. The structural results obtained show carboplatin bound to either one or both of the N atoms of His15 of HEWL, and this particular variation was dependent on the concentration of anions in the crystallization mixture and the elapsed time, as well as the pH used. The structural details of the bound carboplatin molecule also differed between them. Overall, the most detailed crystal structure showed the majority of the carboplatin atoms bound to the platinum centre; however, the four-carbon ring structure of the cyclobutanedicarboxylate moiety (CBDC) remained elusive. The potential impact of the results for the administration of carboplatin as an anticancer agent are described.

Experiences with archived raw diffraction images data: capturing cisplatin after chemical conversion of carboplatin in high salt conditions for a protein crystal

The archiving of raw diffraction images data is the focus of an IUCr Diffraction Data Deposition Working Group (see http://forums.iucr.org/). Experience in archiving and sharing of raw diffraction images data in collaboration between Manchester and Utrecht Universities, studying the binding of the important anti-cancer agents, cisplatin and carboplatin to histidine in a protein, has recently been published. Subsequently, these studies have been expanded due to further analyses of each data set of raw diffraction images using the diffraction data processing program XDS. The raw diffraction images, measured at Manchester University, are available for download at Utrecht University and now also mirrored at the Tardis Raw Diffraction Data Archive in Australia. Thus a direct comparison of processed diffraction and derived protein model data from XDS with the published results has been made. The issue of conversion of carboplatin to cisplatin under a high chloride salt concentration has been taken up and a detailed crystallographic assessment is provided. Overall, these new structural chemistry research results are presented followed by a short summary of developing raw data archiving policy and practicalities as well as documenting the challenge of making appropriate and detailed recording of the metadata for crystallography.

Design and evaluation of biological activity of diazenecarboxamide-extended cisplatin and carboplatin analogues

Construction of a library of structurally diverse diazenecarboxamide-extended cis-[Pt(2-picolyl-1,2,3-triazole)Cl2,] and cis-[Pt(propan-1,3-diamine)CBDCA] (CBDCA = 1,1 -cyclobutanedicarboxylate) complexes 1-4 is described. These compounds retain oxidative properties of parent diazenecarboxamides against glutathione as demonstrated by NMR spectroscopy and high resolution mass spectrometry experiments. Cytotoxic activity of 1-4 was investigated against human cervical carcinoma HeLa cells. Four library members were found to possess moderate cytotoxic activity. Some model compounds were also examined, returning [PtCl2L2] (L = 1-(2-picolyl)-4-phenyl-1H-1,2,3-triazole) as the most potent under this investigation with IC50 of 19.05 microM, comparable to that of cisplatin (IC50 = 16.3 microM).

Room-temperature X-ray diffraction studies of cisplatin and carboplatin binding to His15 of HEWL after prolonged chemical exposure

The anticancer complexes cisplatin and carboplatin are known to bind to both the Nδ and the Nℇ atoms of His15 of hen egg-white lysozyme (HEWL) in the presence of dimethyl sulfoxide (DMSO). However, neither binds in aqueous media after 4 d of crystallization and crystal growth, suggesting that DMSO facilitates cisplatin/carboplatin binding to the N atoms of His15 by an unknown mechanism. Crystals of HEWL cocrystallized with cisplatin in both aqueous and DMSO media, of HEWL cocrystallized with carboplatin in DMSO medium and of HEWL cocrystallized with cisplatin and N-acetylglucosamine (NAG) in DMSO medium were stored for between seven and 15 months. X-ray diffraction studies of these crystals were carried out on a Bruker APEX II home-source diffractometer at room temperature. Room-temperature X-ray diffraction data collection removed the need for cryoprotectants to be used, ruling out any effect that the cryoprotectants might have had on binding to the protein. Both cisplatin and carboplatin still bind to both the Nδ and Nℇ atoms of His15 in DMSO media as expected, but more detail for the cyclobutanedicarboxylate (CBDC) moiety of carboplatin was observed at the Nℇ binding site. However, two molecules of cisplatin were now observed to be bound to His15 in aqueous conditions. The platinum peak positions were identified using anomalous difference electron-density maps as a cross-check with Fo-Fc OMIT electron-density maps. The occupancies of each binding site were calculated using SHELXTL. These results show that over time cisplatin binds to both N atoms of His15 of HEWL in aqueous media, whereas this binding is speeded up in the presence of DMSO. The implication of cisplatin binding to proteins after a prolonged period of time is an important consideration for the length of treatment in patients who are given cisplatin.

Stability of carboplatin, paclitaxel, and docetaxel with acetyl-l-carnitine during simulated Y-site administration

The compatibility of acetyl-l-carnitine with three chemotherapy agents was studied during simulated Y-site administration. Acetyl-l-carnitine 30 mg/mL in 5% dextrose for injection (D5W) was combined with carboplatin 4 mg/mL, paclitaxel 2 mg/mL, and docetaxel 0.74 mg/mL in glass vials. Physical compatibility over the 4-hour storage at room temperature was assessed by visual examinations with unaided eye under fluorescent light and by measuring the percent transmittance at 600 nm. Chemical compatibility was measured by the percent of initial concentration remaining using stability-indicating high-performance liquid chromatographic-ultraviolet and high-performance liquid chromatographic-mass spectrometry methods. No visible particulate matter, haze, or color change was observed, and the percent transmittance was >95% for all admixtures. After a 4-hour incubation, 93.2% of the paclitaxel and 96.5% of docetaxel remained in separate mixtures with acetyl-l-carnitine. Carboplatin 4 mg/mL, paclitaxel 1.2 mg/mL, and docetaxel 0.74 mg/mL are physically and chemically compatible with acetyl-l-carnitine 30 mg/mLin D5W during a simulated 4-hour Y-site administration.

Theoretical studies of molecular structures and properties of platinum (II) antitumor drugs

The molecular structure and vibration spectra of carboplatin were investigated by the different density functional models (mPW1PW, BPV86, HCTH, PBEPBE, LSDA and PBE1PBE) using several basis sets including LANL2DZ, SDD, LANL2MB, CEP-4G, CEP-31G and CEP-121G. The results indicate that LSDA/SDD and LSDA/LANL2DZ levels are clearly superior to all the remaining density functional methods in predicting the structures of carboplatin. Mean absolute deviation between the calculated harmonic and observed fundamental vibration frequencies for each method indicates that PBE1PBE/CEP-121G and PBE1PBE/SDD methods are sufficient to predict vibration spectrum of carboplatin comparing with other DFT methods.

Delivery of carboplatin by carbon-based nanocontainers mediates increased cancer cell death

Since the activity of several conventional anticancer drugs is restricted by resistance mechanisms and dose-limiting side-effects, the design of nanocarriers seems to be an efficient and promising approach for drug delivery. Their chemical and mechanical stability and their possible multifunctionality render tubular nanomaterials, such as carbon nanotubes (CNTs) and carbon nanofibres (CNFs), promising delivery agents for anticancer drugs. The goal of the present study was to investigate CNTs and CNFs in order to deliver carboplatin in vitro. No significant intrinsic toxicity of unloaded materials was found, confirming their biocompatibility. Carboplatin was loaded onto CNTs and CNFs, revealing a loading yield of 0.20 mg (CNT-CP) and 0.13 mg (CNF-CP) platinum per milligram of material. The platinum release depended on the carrier material. Whereas CNF-CP marginally released the drug, CNT-CP functioned as a drug depot, constantly releasing up to 68% within 14 days. The cytotoxicity of CNT-CP and CNF-CP in urological tumour cell lines was dependent on the drug release. CNT-CP was identified to be more effective than CNF-CP concerning the impairment of proliferation and clonogenic survival of tumour cells. Moreover, carboplatin, which was delivered by CNT-CP, exhibited a higher anticancer activity than free carboplatin.

[Platinum salts hypersensitivity]

It become usually after 4 to 8 courses of treatment. A long platin free interval is an increased risk of reaction. Clinical manifestations are various and can be separate in light to mild or severe reactions. Diagnose is retrospective with results of skin test. Prick test and IDR (using sequentially diluted platin salt and delayed reading) are the most available, essentially in case of acute reaction (<2h after injection of platin salt). IDR realized 30 min before injection of platin salt can be a good predictive test of hypersensitivity reaction. Management of this adverse effect depends on clinical manifestation: light to mild: careful re-introduction with a desensitization protocol; severe: no re-introduction. If it's necessary, careful replacement by another platin salt can be possible, eventually in accordance with results of IDR to all platinum salt.

On the Hydrolysis Mechanism of the Second-Generation Anticancer Drug Carboplatin

The hydrolysis reaction mechanisms of carboplatin, a second-generation anticancer drug, have been explored by combining density functional theory (DFT) with the conductor-like dielectric continuum model (CPCM) approach. The decomposition of carboplatin in water is expected to take place through a biphasic mechanism with a ring-opening process followed by the loss of the malonato ligand. We have investigated this reaction in water and acid conditions and established that the number of protons present in the malonato ligand has a direct effect on the energetics of this system. Close observation of the optimised structures revealed a necessary systematic water molecule in the vicinity of the amino groups of carboplatin. For this reason we have also investigated this reaction with an explicit water molecule. From the computed potential-energy surfaces it is established that the water hydrolysis takes place with an activation barrier of 30 kcal mol(-1), confirming the very slow reaction observed experimentally. The decomposition of carboplatin upon acidification was also investigated and we have computed a 21 kcal mol(-1) barrier to be overcome (experimental value 23 kcal mol(-1)). We have also established that the rate-limiting process is the first hydration, and ascertained the importance of a water molecule close to the two amine groups in lowering the activation barriers for the ring-opening reaction.

Free Radical-Induced Redox Chemistry of Platinum-Containing Anti-cancer Drugs

Arrhenius parameters for the reactions of oxidizing hydroxyl radicals and reducing hydrated electrons with cisplatin, transplatin and carboplatin in aqueous solution have been determined using pulsed electron radiolysis and absorption spectroscopy techniques. Under physiological pH and chloride concentration conditions, hydroxyl radical reaction rate constants of (9.99 +/- 0.20) x 10(9), (8.38 +/- 0.55) x 10(9), and (6.03 +/- 0.08) x 10(9) M(-1) s(-1) at 24.0, 20.7 and 24.0 degrees C, respectively, with corresponding activation energies of 12.79 +/- 0.57, 13.88 +/- 1.14, and 14.35 +/- 0.56 kJ mol(-1) for these three reactions, were determined. These oxidations of cisplatin and transplatin to form a Pt(III) transient are significantly faster than reported previously at room temperature. The lower rate constant for carboplatin is consistent with hydroxyl radical reaction partitioning between reaction at the platinum center and the cyclobutanedicarboxylate ligand. The equivalent reductive hydrated electron reaction rate constants measured were (1.99 +/- 0.04) x 10(10) (24.0 degrees C), (1.77 +/- 0.08) x 10(10) (22.0 degrees C), and (8.92 +/- 0.06) x 10(9) M(-1) s(-1) (24.0 degrees C), with corresponding activation energies of 15.75 +/- 1.00, 19.74 +/- 1.82, and 19.99 +/- 0.34 kJ mol(-1). Again, the values determined for cisplatin and transplatin are faster than reported; however, all three values are consistent with direct reduction of the platinum center to form a Pt(I) moiety.

Modification of carboplatin by Jurkat cells

Using [(1)H,(15)N] heteronuclear single quantum coherance (HSQC) NMR and (15)N-labeled carboplatin, 1, we show that Jurkat cells affect the rate of disappearance of the HSQC NMR peak in culture medium for this Pt(2+) anticancer drug. The decay or disappearance rate constant for 1 in culture medium containing cells is k(1)=k(c)[CO(3)(2-)]+k(m)+k(u)N, where k(c) is the rate constant for reaction of 1 with carbonate in the medium, k(m) is the rate constant for reaction of 1 with all other components of the medium, and k(u) is the rate constant for reaction of 1 with cells having a number density N in the medium. Since Jurkat cells only take up a small amount of the platinum present in the medium (<1%), the observed disappearance of the HSQC NMR peak for 1 cannot be due to uptake of carboplatin by the cells.

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.

Encapsulation of platinum anticancer drugs by apoferritin

Apoferritin derived from the native protein ferritin was employed to encapsulate anticancer drugs cisplatin and carboplatin.

Role of carbonate in the cytotoxicity of carboplatin

Carboplatin, [Pt(NH3)2(CBDCA-O,O')], 1, where CBDCA is cyclobutane-1,1-dicarboxylate, is used against ovarian, lung, and other types of cancer. We recently showed (Di Pasqua et al. (2006) Chem. Res. Toxicol. 19, 139-149) that carboplatin reacts with carbonate under conditions that simulate therapy to produce carbonato carboplatin, cis-[Pt(NH3)2(O-CBDCA)(CO3)]2-, 2. We use 13C and 1H NMR and UV-visible absorption spectroscopy to show that solutions containing carboplatin that have been aged in carbonate buffer under various conditions contain 1, 2, and other compounds. We then show that aging carboplatin in carbonate produces compounds that are more toxic to human neuroblastoma (SK-N-SH), proximal renal tubule (HK-2) and Namalwa-luc Burkitt's lymphoma (BL) cells than carboplatin alone. Moreover, increasing the aging time increases the cytotoxicity of the platinum solutions as measured by the increase in cell death. Although HK-2 cells experience a large loss in survival upon exposure to carbonato forms of the drug, they have the highest values of IC50 of the three cell lines studied, so that HK-2 cells remain the most resistant to the toxic effects of the carbonato forms in the culture medium. This is consistent with the well-known low renal toxicity observed for carboplatin in therapy. The uptake rates for normal Jurkat cells (NJ) and cisplatin-resistant Jurkat cells (RJ), measured by inductively coupled plasma mass spectrometry (ICP-MS), are 16.6 +/- 4.2 and 12.3 +/- 4.8 amol of Pt h-1 cell-1, respectively, when exposed to carboplatin alone. However, when these cells are exposed to carboplatin that has been aged in carbonate media, normal Jurkat cells strongly bind/take up Pt at a rate of 14.5 +/- 4.1 amol of Pt h-1 cell-1, while resistant cells strongly bind/take up 5.1 +/- 3.3 amol of Pt h-1 cell-1. Collectively, these studies show that carboplatin carbonato species may play a major role in the cytotoxicity and uptake of carboplatin by cells.

ESI mass spectrometry and X-ray diffraction studies of adducts between anticancer platinum drugs and hen egg white lysozyme

The interactions of cisplatin and its analogues, transplatin, carboplatin and oxaliplatin, with hen egg white lysozyme were analysed through ESI mass spectrometry, and the resulting metallodrug-protein adducts identified; the X-ray crystal structure of the cisplatin lysozyme derivative, solved at 1.9 A resolution, reveals selective platination of imidazole Nepsilon of His15.

Carboplatin nanocapsules: a highly cytotoxic, phospholipid-based formulation of carboplatin

Platinum-based drugs are widely used in cancer chemotherapy. However, their clinical use is limited by systemic toxicity, rapid blood clearance, and the occurrence of resistance. Our research is aimed at increasing the therapeutic index of these drugs by encapsulation in a lipid formulation. Previously, we developed a method for efficient encapsulation of cisplatin in a lipid formulation, yielding cisplatin nanocapsules. Here, we show that carboplatin, a cisplatin-derived anticancer drug with different chemical properties, can be efficiently encapsulated in a lipid formulation by a similar method. The carboplatin nanocapsules exhibit a very high cytotoxicity in vitro: the IC(50) value of carboplatin nanocapsules is up to a 1,000-fold lower than that of conventional carboplatin when tested on a panel of carcinoma cell lines. Cellular platinum content analysis and confocal fluorescent imaging of the interaction of the carboplatin nanocapsules with IGROV-1 cells indicate that the improved cytotoxicity is due to increased platinum accumulation in the cells, resulting from uptake of the formulation by endocytosis.

Identification of degradation products from aqueous carboplatin injection samples by electrospray mass spectrometry

Four different carboplatin injection samples in water ( approximately 10mg/ml) stored at room temperature were investigated for degradation products by electrospray liquid chromatography-mass spectrometry (ESI/LC-MS). A mass spectrometer compatible mobile phase system with 0.02% formic acid and methanol was used to resolve the impurities. Possible chemical structures of the unknown impurities and its degradation mechanism were proposed based on its experimental results and literature findings.

Activation of carboplatin by carbonate

Carboplatin, [Pt(NH3)2(CBDCA-O,O')], 1, where CBDCA is cyclobutane-1,1-dicarboxylate, is in wide clinical use for the treatment of ovarian, lung, and other types of cancer. Because carboplatin is relatively unreactive toward nucleophiles, an important question concerning the drug is the mechanism by which it is activated in vivo. Using [1H,15N] heteronuclear single quantum coherance spectroscopy (HSQC) NMR and 15N-labeled carboplatin, we show that carboplatin reacts with carbonate ion in carbonate buffer to produce ring-opened products, the nature of which depends on the pH of the medium. The assignment of HSQC NMR resonances was facilitated by studying the reaction of carboplatin in strong acid, which also produces a ring-opened product. The HSQC NMR spectra and UV-visible difference spectra show that reaction of carboplatin with carbonate at pH > 8.6 produces mainly cis-[Pt(NH3)2(CO3(-2))(CBDCA-O)]-2, 5, which contains the mono-dentate CBDCA ligand and mono-dentate carbonate. At pH 6.7, the primary product is the corresponding bicarbonato complex, which may be in equilibrium with its decarboxylated hydroxo analogue. The UV-visible absorption data indicate that the pKb for the protonation of 5 is approximately 8.6. Thus, the reaction of carboplatin with carbonate produces a mixture of ring-opened species that are anions at physiological pH. HSQC NMR studies on 15N-labeled carboplatin in RPMI culture media containing 10% fetal bovine serum with and without added carbonate suggest that carbonate is the attacking nucleophile in culture media. However, because the rate of reaction of carbonate with carboplatin at physiological pH is small, NMR peaks for ring-opened carboplatin were not detected with HSQC NMR. The rate of disappearance of carboplatin in culture medium containing 9 x 10(8) Jurkat cells is essentially the same as that in carbonate buffer, indicating that the ring-opening reaction is not affected by the presence of cells. This work shows that carbonate at concentrations found in culture media, blood, and the cytosol readily displaces one arm of the CBDCA ligand of carboplatin to give a ring-opened product, which at physiological pH is a mixture of anions. These ring-opened species may be important in the uptake, antitumor properties, and toxicity of carboplatin.

EXAFS and IR Structural Study of Platinum-Based Anticancer Drugs' Degradation by Diethyl Dithiocarbamate

Platinum compounds constitute a discrete class of DNA-damaging anticancer drug agents, including cisplatin, carboplatin, and oxaliplatin. The toxicity of such drugs raises the problem of waste detoxification. Diethyl dithiocarbamate (DDTC) is recommended by the World Heath Organization (WHO) for the destruction of cisplatin, but the degradation product has not been structurally characterized. This paper deals with the extended X-ray absorption fine structure (EXAFS) and IR structural study of the reaction products of DDTC with cisplatin, carboplatin, and oxaliplatin. Cisplatin and carboplatin give the same reaction product: Pt(DDTC)2. In the case of oxaliplatin, we observed the formation of [(diaminocyclohexane)(DDTC)Pt(II)]. In all cases, the replacement of labile ligands by strong ligands should lead to inactive compounds. Our results suggest that the WHO inactivation protocol might be extended to carboplatin and oxaliplatin. Nevertheless, this should be validated by toxicity tests of the degradation products.

High-performance Liquid Chromatographic Assay for Carboplatin in Ultrafiltered Plasma Combined with Hyperbaric Oxygenation

A specific, sensitive and reproducible high-performance liquid chromatographic procedure was developed for the quantitative analysis of carboplatin in human plasma. Plasma was ultrafiltered with an Amicon Centrifree system and then injected onto an analytical NH2 column. Carboplatin was monitored at 230 nm and eluted by 10 min using acetonitrile/methanol/5 mM sodium perchlorate buffer (pH 2.4) (75:15:10, v/v) as a mobile phase. The method yielded intra-day and inter-day precision and accuracy of <6% with a linearly from 0.1 to 80 microg/mL and a recovery of >98%. Plasma concentrations of intravenously administered carboplatin in three patients could be determined by this system. Slightly higher plasma concentrations of carboplatin were detected even 30 min after hyperbaric oxygenation therapy for 60 min than expected. The results suggest that this method could be applicable for measurement of carboplatin in plasma samples to evaluate carboplatin therapy together with hyperbaric oxygenation.

Study on the interaction between DNA and protein induced by anticancer drug carboplatin

The interaction of DNA and human serum albumin (HSA) in the presence of anticancer drug carboplatin was studied with piezoelectric quartz crystal impedance (PQCI) and electrochemistry techniques. In the PQCI analysis, the correlative parameters including the frequency (f0), the motional resistance (R(m)), and the static capacitance (C0) in the experiment were obtained and discussed in detail. Additionally, the kinetics parameters of the cross-linking process were investigated and a response kinetics model was deduced. The values of association rate constant k1, dissociation rate constant k(-1) and the reaction equilibrium constant K were estimated to be 1.895 mg/ml(-1) s(-1), 4.7 x 10(-5) s(-1) and 4.03 x 10(4) (mg/ml)-1, respectively. Furthermore, cyclic voltammetry (CV) and electrochemical AC impedance techniques were employed to testify the cross-linking process.

In vitro platination of human breast cancer suppressor gene1 (BRCA1) by the anticancer drug carboplatin

Carboplatin is an anticancer drug for the treatment of cancers affecting various organs including ovary and testes. It essentially exerts its cytotoxicity against cancerous cells via covalent attachment of platinum atom to DNA, generating various platinum-DNA adducts. Platinum-DNA adducts inhibit biological processes essential for cellular viability. However, carboplatin interacts nonspecifically with DNA, resulting in damaging of normal cell DNA. Potential in vitro interaction of carboplatin with genes encoding tumor suppressor proteins such as human breast cancer suppressor gene 1(BRCA1) was herein investigated. The 696--bp fragment of the 3'-region of BRCA1 gene (nucleotide 4897--5592) was amplified by RT-PCR using mRNA templates isolated from human white blood cells. Retardation of the electrophoretic migration on agarose gel of drug-treated DNA, in the dose-response manner, was observed. Analysis by restriction digestion with PvuII and Eco O 109I suggested that the platination favorably occurred at the dGpG sequence of Eco O 109I-cleaved site. The semi-quantitative PCR-based assay was used to determine the lesion frequencies produced by carboplatin in the 696-bp fragment of the 3'-region of BRCA1 gene and in the 3,426-bp fragment of the BRCA1 exon 11 of human breast adenocarcinoma MCF-7 cells. A significant decrease in DNA amplification was observed at 400 microM of carboplatin with approximately 1--2 platinum atoms per BRCA1 fragment. Carboplatin caused slightly less damage at equimolar concentrations in cells than in cell-free BRCA1 fragment.

Determination of binding sites in carboplatin-bound cytochrome c using electrospray ionization mass spectrometry and tandem mass spectrometry

Interaction of carboplatin with cytochrome c (Cyt. c) has been investigated by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). ESI-MS studies revealed that the ring-opened adducts of carboplatin with Cyt. c were formed in the stoichiometric ratio of 1:1 and 2:1 at pH 5.0 and 37 degrees C and in the stoichiometric ratio of 1:1 only at pH 7.0 and 37 degrees C. It was also found that Cyt. c could be cleaved by carboplatin at pH 2.5 and 50 degrees C. The cleaved fragments of Cyt. c were determined by ESI-MS and MS/MS analysis to be Glu66 approximately Met80, Ac-Gly01 approximately Met65, Glu66 approximately Glu104, Ac-Gly01 approximately Met80 and Ile81 approximately Glu104. The carboplatin prefers to anchor to Met65 first, then to Met80. To further confirm the binding site of Met, AcMet-Gly was used as the model molecule to investigate its interaction with carboplatin and its hydrolysis reaction. On the basis of species detected during the reaction monitored by ESI-MS, a possible pathway of the cleavage reaction was proposed.

Convection-Enhanced Drug Delivery: Increased Efficacy and Magnetic Resonance Image Monitoring

Convection-enhanced drug delivery (CED) is a novel approach to directly deliver drugs into brain tissue and brain tumors. It is based on delivering a continuous infusion of drugs via intracranial catheters, enabling convective distribution of high drug concentrations over large volumes of the target tissue while avoiding systemic toxicity. Efficient formation of convection depends on various physical and physiologic variables. Previous convection-based clinical trials showed significant diversity in the extent of convection among patients and drugs. Monitoring convection has proven to be an essential, yet difficult task. The current study describes the application of magnetic resonance imaging for immediate assessment of convection efficiency and early assessment of cytotoxic tissue response in a rat brain model. Immediate assessment of infusate distribution was obtained by mixing Gd-diethylenetriaminepentaacetic acid in the infusate prior to infusion. Early assessment of cytotoxic tissue response was obtained by subsequent diffusion-weighted magnetic resonance imaging. In addition, the latter imaging methodologies were used to establish the correlation between CED extent and infusate's viscosity. It was found that low-viscosity infusates tend to backflow along the catheter track, whereas high-viscosity infusates tend to form efficient convection. These results suggest that CED formation and extent may be significantly improved by increasing the infusate's viscosities, thus increasing treatment effects.

Interactions of carboplatin with fibrin(ogen), implications for local slow release chemotherapy

The effect of carboplatin (CPt) on fibrin(ogen) clot formation and the possible use of this combination for local slow release chemotherapy were examined. CPt significantly reduced thrombin-induced fibrin clotting time (CT) and increased clot turbidity in a concentration-dependent manner. When CPt was mixed with physiological levels of fibrinogen (>1 mg/ml), electron-dense nanoparticles (3 nm) were formed, as demonstrated by both optical particle counter and transmission electron microscopy (TEM). Upon thrombin-induced coagulation, the CPt nanoparticles were trapped within the fibrin mesh. At higher fibrinogen levels (>5 mg/ml), the 3-nm CPt nanoparticles aggregated, so that approximately 2% and approximately 0.5% of the CPt on the fibrinogen appeared as larger particles of 10 and 50 nm, respectively. Dialysis experiments showed that 60-70% of the CPt was released from the fibrin clot within one hour as a non-particulate soluble form, while approximately 30% of particulate CPt were retained. Up to 5 mg/ml this portion of firmly attached CPt was dependent of the initial drug level. CPt released from the fibrin by either diffusion or by fibrinolysis exhibited cytotoxic activity towards retinoblastoma (RB) cell lines (Y-79 and Weri RB1) equivalent to free drug. Our study indicates that CPt enhances fibrin clot formation and suggests the use of fibrin with high dose CPt for slow release chemotherapy against localized tumors such as retinoblastoma.

Experimental study of renal disorder caused by oxaliplatin in rat renal cortical slices

BACKGROUND

Oxaliplatin is a newly developed antitumor platinum complex that is known to have low nephrotoxicity. The inhibitory effects of oxaliplatin on several tubular functions were compared with those of cisplatin and carboplatin, using a renal cortical slice system.

METHODS AND RESULTS

Rat renal cortical slices were incubated with 0.25 mM to 2.0 mM of oxaliplatin, cisplatin, on carboplatin at 37 degrees C for 120 min. Para-amino hippuric acid (PAH) accumulation, gluconeogenesis, and ATP content in the rat renal slices were determined. PAH accumulation was not inhibited by carboplatin, but it was significantly inhibited by oxaliplatin and cisplatin. Inhibition of PAH accumulation by cisplatin was greater than that by oxaliplatin. Gluconeogenesis was not decreased by carboplatin, but it was suppressed by oxaliplatin and cisplatin in a dose-dependent manner. The decrease in gluconeogenesis induced by oxaliplatin was significantly greater than that induced by cisplatin. ATP content in the renal slices was decreased by oxaliplatin, cisplatin, and carboplatin to almost the same extent. As an in vivo experiment, 21.6 mmole/kg of oxaliplatin, cisplatin, or carboplatin was injected into rats; then blood urea nitrogen (BUN) and serum creatinine were determined on day 4. Significantly elevated levels of BUN and serum creatinine were observed only in the rats injected with cisplatin.

CONCLUSIONS

Oxaliplatin did not cause nephrotoxicity in the in vivo study; however, the nephrotoxic pattern of oxaliplatin observed in the renal cortical-slice system resembled that of cisplatin. The reason why oxaliplatin is less nephrotoxic than cisplatin in vivo could not be fully elucidated in the present experiment using the renal cortical-slice system.

Interaction of Oxaliplatin, Cisplatin, and Carboplatin with Hemoglobin and the Resulting Release of a Heme Group

Oxaliplatin, carboplatin, and cisplatin are widely used to treat a number of cancers. While their DNA adducts are believed to cause cell death, the involvement of their protein adducts in the toxicity and action of these drugs is unclear. Here, we report the interactions of hemoglobin (Hb) with the three platinum (Pt) drugs, demonstrating the formation of Hb-Pt complexes and the release of a heme group from Hb. Oxaliplatin (0.05 microM) was able to form three major complexes with Hb (3-10 microM) after 1 h of incubation at room temperature, and these complexes accounted for approximately 60% of the total oxaliplatin. Cisplatin and carboplatin formed one major and two minor complexes only after 24 and 96 h of incubation, respectively. Incubation of these Pt drugs (0.05-10 microM) with whole blood of healthy volunteers and the analysis of red blood cells confirmed the relative ability of these Pt drugs binding to Hb. For the whole blood samples incubated with oxaliplatin and cisplatin for 24 h, only protein complexes were detected in red blood cells, indicating a complete binding of oxaliplatin and cisplatin to the protein. In contrast, carboplatin was partially bound; both the free and the protein-bound carboplatin species were detected in red blood cells. The binding of the Pt drugs to Hb was accompanied by the release of a heme group from Hb, which was monitored by size fractionation, chromatographic separation, and selective detection of both Pt- and iron (Fe)-containing molecular species. The released heme was further identified by size fractionation and nanospray mass spectrometry. The findings of the Pt drug interaction with Hb and the dissociation of heme from Hb are potentially useful for a better understanding of the toxicity and side effects of these chemotherapeutic drugs.

Nuclear Localization Signal-Targeted Poly(ethylene glycol) Conjugates as Potential Carriers and Nuclear Localizing Agents for Carboplatin Analogues

Carboplatin is a low-molecular-weight anticancer drug that acts by binding to the nuclear DNA of cells. Thus, efficient delivery of the platinum drugs to the nucleus of the cancer cells may enhance the cytotoxicity of the drug. Efficient drug delivery to the nucleus of cancer cells requires three levels of localization: targeting to the cancerous tissue, accumulation in the cancer cells, and intracellular localization in the nucleus. Nuclear localization signals (NLS) are short positively charged basic peptides that actively transport large proteins across the nuclear membrane. We have prepared conjugates in which the NLS is tethered to poly(ethyleneglycol)carboplatin conjugate (NLS-PEG-Pt) and compared their pharmacological properties to those of their untargeted analogues that do not possess the NLS (PEG-Pt). NLS-PEG-Pt conjugates are rapidly internalized into cancer cells and accumulate in the nucleus. Despite their rapid nuclear localization, they form less Pt-DNA adducts than the untargeted analogues, PEG-Pt, and are also less cytotoxic. These results support the hypothesis that carboplatin (unlike cisplatin) may require cytosolic activation prior to its binding to nuclear DNA.