Platinum-DNA adducts in leukocyte DNA correlate with disease response in ovarian cancer patients receiving platinum-based chemotherapy

Quantifying Intracellular Platinum Accumulation Using Inductively Coupled Mass Spectrometry

The platinum-based anticancer drug cisplatin and its analog carboplatin are the most used chemotherapeutic agents worldwide. It is estimated that approximately half of all cancer patients are treated with platinum drugs at some point during the therapy regimen. Cisplatin covalently binds to purine nucleobases to form DNA adducts. Cisplatin therapy is faced with two key challenges. First, despite the initial response, many patients develop cisplatin resistance. Reduced cellular accumulation of cisplatin is one common cause of therapy resistance. Second, cisplatin treatment causes general cytotoxicity, leading to severe side effects. Monitoring the subcellular concentration of platinum chemotherapeutics will help yield clinical efficacy with the minimum possible dose. Inductively coupled plasma-mass spectrometry (ICP-MS) is an analytical technique to quantify the elemental composition of various types of liquified bulk samples with high sensitivity. This article describes quantifying cisplatin accumulation in chromatin and total cell lysate using ICP-MS. The method involves treating cells with cisplatin, isolating RNA-free DNA, digesting samples, ICP-MS instrumentation, and data analysis. Although we describe these steps in one cancer cell line, the protocol can be adapted to any cell line or tissue. The protocol should be a valuable resource for investigators interested in accurate measurement of subcellular concentration of platinum and other metallo-drugs. © 2024 Wiley Periodicals LLC. Basic Protocol 1: Cell culture conditions for A2780 cells and cisplatin treatment Basic Protocol 2: Isolating cellular fractions and sample quantitation Basic Protocol 3: Sample digestion, ICP-MS data collection, and analysis.

The potential value of cancer-testis antigens in ovarian cancer: Prognostic markers and targets for immunotherapy

BACKGROUND

Tumor immunotherapy has become an important adjuvant therapy after surgery, radiotherapy, and chemotherapy. In recent years, the role of tumor-associated antigen (TAA) in tumor immunotherapy has become increasingly prominent. Cancer-testis antigen (CTA) is a kind of TAA that is highly restricted in a variety of tumors and can induce an immune response.

AIMS

This review article aimed to evaluate the role of CTA on the progression of ovarian cancer, its diagnostic efficacy, and the potential for immunotherapy.

METHODS

We analyzed publications and outlined a comprehensive of overview the regulatory mechanism, immunogenicity, clinical expression significance, tumorigenesis, and application prospects of CTA in ovarian cancer, with a particular focus on recent progress in CTA-based immunotherapy.

RESULTS

The expression of CTA affects the occurrence, development, and prognosis of ovarian cancer and is closely related to tumor immunity.

CONCLUSION

CTA can be used as a biomarker for the diagnosis and prognosis evaluation of ovarian cancer and is an ideal target for antitumor immunotherapy. These findings provide novel insights on CTA in the improvement of diagnosis and treatment for ovarian cancer. The successes, current challenges and future prospects were also discussed to portray its significant potential.

DNA Adducts in Cancer Chemotherapy

DNA adducting drugs, including alkylating agents and platinum-containing drugs, are prominent in cancer chemotherapy. Their mechanisms of action involve direct interaction with DNA, resulting in the formation of DNA addition products known as DNA adducts. While these adducts are well-accepted to induce cancer cell death, understanding of their specific chemotypes and their role in drug therapy response remain limited. This perspective aims to address this gap by investigating the metabolic activation and chemical characterization of DNA adducts formed by the U.S. FDA-approved drugs. Moreover, clinical studies on DNA adducts as potential biomarkers for predicting patient responses to drug efficacy are examined. The overarching goal is to engage the interest of medicinal chemists and stimulate further research into the use of DNA adducts as biomarkers for guiding personalized cancer treatment.

Relevance of Comet Assay and Phosphorylated-Hsp90α in Cancer Patients' Peripheral Blood Leukocytes as Tools to Assess Cisplatin-based Chemotherapy Clinical Response and Disease Outcome

Cisplatin (cPt) is a commonly used treatment for solid tumors. The main target of its cytotoxicity is the DNA molecule, which makes the DNA damage response (DDR) crucial for cPt-based chemotherapy. Therefore, it is essential to identify biomarkers that can accurately predict the individual clinical response and prognosis. Our goal was to assess the usefulness of alkaline comet assay and immunocytochemical staining of phosphorylated Hsp90α (p-Hsp90α), γH2AX, and 53BP1 as predictive/prognostic markers. Pre-chemotherapy peripheral blood leukocytes were exposed to cPt in vitro and collected at 0, 24 (T24), and 48 (T48) hr post-drug removal. Healthy subjects were also included. Baseline DNA damage was elevated in cancer patients (variability between individuals was observed). After cPt, patients showed increased γH2AX foci/nucleus (T24 and T48). Both in healthy persons and patients, the nuclear p-Hsp90α and N/C (nuclear/cytoplasmic) ratio augmented (T24), decreasing at T48. Favorable clinical response was associated with high DNA damage and p-Hsp90α N/C ratio following cPt. For the first time, p-Hsp90α significance as a predictive marker is highlighted. Post-cPt-DNA damage was associated with longer disease-free survival and overall survival. Our findings indicate that comet assay and p-Hsp90α (a marker of DDR) would be promising prognostic/predictive tools in cP-treated cancer patients.

Emerging and established therapies for chemotherapy-induced ototoxicity

PURPOSE

Ototoxicity is considered a dose-limiting side effect of some chemotherapies. Hearing loss, in particular, can have significant implications for the quality of life for cancer survivors. Here, we review therapeutic approaches to mitigating ototoxicity related to chemotherapy.

METHODS

Literature review.

CONCLUSIONS

Numerous otoprotection strategies are undergoing active investigation. However, numerous challenges exist to confer adequate protection while retaining the anti-cancer efficacy of the chemotherapy.

IMPLICATIONS FOR CANCER SURVIVORS

Ototoxicity can have significant implications for cancer survivors, notably those receiving cisplatin. Clinical translation of multiple otoprotection approaches will aid in limiting these consequences.

Comprehensive Network Analysis of Dysregulated Genes Revealed MNX1‐AS1/ hsa‐miR‐4697‐3p/ HOXB13 Axis in OC Chemotherapy Response

Poor chemotherapy response is the main obstacle of ovarian cancer (OC) treatment. Platinum‐refractory and ‐resistant patients are associated with a worse outcome than platinum‐sensitive and partially sensitive patients, but the comprehensive similarities and differences among them are not yet clear. In this study, we analyzed the data of patients with different chemotherapy response in The Cancer Genome Atlas. We found a minority of altered genes were overlapped in refractory and resistant groups, as did the enriched pathways and Gene Ontology terms. We noticed that the neural signaling and drug metabolism enzymes were more significantly enriched and the protein–protein interaction supported these results. The transcription analysis highlighted PDX1 as the common and central transcription factor in both refractory and resistant groups. The competing endogenous RNA (ceRNA) network shared no common ceRNA pairs, indicating a major difference in noncoding RNA post‐transcriptional regulation. In the end, we validated the expression, regulation, binding, and effect on chemotherapy response for selected MNX1‐AS1/hsa‐miR‐4697‐3p/HOXB13 in OC cell lines. Our study offered a novel and comprehensive insight into chemotherapy response, and potential targets for improving chemotherapy response in OC.

Identification of new candidate biomarkers to support doxorubicin treatments in canine cancer patients

Background

Both human and veterinary cancer chemotherapy are undergoing a paradigm shift from a “one size fits all” approach to more personalized, patient-oriented treatment strategies. Personalized chemotherapy is dependent on the identification and validation of biomarkers that can predict treatment outcome and/or risk of toxicity. Many cytotoxic chemotherapy agents, including doxorubicin, base their mechanism of action by interaction with DNA and disruption of normal cellular processes. We developed a high-resolution/accurate-mass liquid chromatography-mass spectrometry DNA screening approach for monitoring doxorubicin-induced DNA modifications (adducts) in vitro and in vivo. We used, for the first time, a new strategy involving the use of isotope-labeled DNA, which greatly facilitates adduct discovery. The overall goal of this work was to identify doxorubicin-DNA adducts to be used as biomarkers to predict drug efficacy for use in veterinary oncology.

Results

We used our novel mass spectrometry approach to screen for adducts in purified DNA exposed to doxorubicin. This initial in vitro screening identified nine potential doxorubicin-DNA adduct masses, as well as an intense signal corresponding to DNA-intercalated doxorubicin. Two of the adduct masses, together with doxorubicin and its metabolite doxorubicinol, were subsequently detected in vivo in liver DNA extracted from mice exposed to doxorubicin. Finally, the presence of these adducts and analytes was explored in the DNA isolated from dogs undergoing treatment with doxorubicin. The previously identified nine DOX-DNA adducts were not detected in these preliminary three samples collected seven days post-treatment, however intercalated doxorubicin and doxorubicinol were detected.

Conclusions

This work sets the stage for future evaluation of doxorubicin-DNA adducts and doxorubicin-related molecules as candidate biomarkers to personalize chemotherapy protocols for canine cancer patients. It demonstrates our ability to combine in one method the analysis of DNA adducts and DNA-intercalated doxorubicin and doxorubicinol. The last two analytes interestingly, were persistent in samples from canine patients undergoing doxorubicin chemotherapy seven days after treatment. The presence of doxorubicin in all samples suggests a role for it as a promising biomarker for use in veterinary chemotherapy. Future studies will involve the analysis of more samples from canine cancer patients to elucidate optimal timepoints for monitoring intercalated doxorubicin and doxorubicin-DNA adducts and the correlation of these markers with therapy outcome.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03062-x.

Applications of Adductomics in Chemically Induced Adverse Outcomes and Major Emphasis on DNA Adductomics: A Pathbreaking Tool in Biomedical Research

Adductomics novel and emerging discipline in the toxicological research emphasizes on adducts formed by reactive chemical agents with biological molecules in living organisms. Development in analytical methods propelled the application and utility of adductomics in interdisciplinary sciences. This review endeavors to add a new dimension where comprehensive insights into diverse applications of adductomics in addressing some of society's pressing challenges are provided. Also focuses on diverse applications of adductomics include: forecasting risk of chronic diseases triggered by reactive agents and predicting carcinogenesis induced by tobacco smoking; assessing chemical agents' toxicity and supplementing genotoxicity studies; designing personalized medication and precision treatment in cancer chemotherapy; appraising environmental quality or extent of pollution using biological systems; crafting tools and techniques for diagnosis of diseases and detecting food contaminants; furnishing exposure profile of the individual to electrophiles; and assisting regulatory agencies in risk assessment of reactive chemical agents. Characterizing adducts that are present in extremely low concentrations is an exigent task and more over absence of dedicated database to identify adducts is further exacerbating the problem of adduct diagnosis. In addition, there is scope of improvement in sample preparation methods and data processing software and algorithms for accurate assessment of adducts.

Uev1A promotes breast cancer cell migration by up-regulating CT45A expression via the AKT pathway

Background

UEV1A encodes a ubiquitin-E2 variant closely associated with tumorigenesis and metastasis, but its underlying mechanism in promoting metastasis remains to be investigated.

Methods

In this study, we experimentally manipulated UEV1A and CT45A gene expression and monitored their effects on cancer-related gene expression, cell migration and the signal transduction cascade.

Results

It was found that UEV1A overexpression induces CT45A family gene expression in breast cancer cells. Indeed, ectopic expression of UEV1A was sufficient to induce CT45A and its downstream genes involved in tumorigenesis, epithelial-mesenchymal transition (EMT), stemness and metastasis, and to promote cell migration and EMT signaling. Consistently, depletion of CT45A abolished the above effects, indicating that CT45A is a critical downstream effector of Uev1A. The Uev1A-induced cell migration and EMT signaling was dependent on AKT but independent of NF-κB, indicating that CT45A acts downstream of the AKT pathway.

Conclusions

Based on previous reports and observations in this study, we propose that the Ubc13-Uev1A complex activates AKT through K63-linked polyubiquitination, which leads to enhanced CT45A expression, stimulated cell migration and EMT signaling in breast cells. Since similar effects were also observed in a colorectal cancer cell line, the Ubc13/Uev1A-AKT-CT45A axis may also promote tumorigenesis and metastasis in other tissues.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08750-3.

Oxaliplatin-DNA Adducts as Predictive Biomarkers of FOLFOX Response in Colorectal Cancer: A Potential Treatment Optimization Strategy

FOLFOX is one of the most effective treatments for advanced colorectal cancer. However, cumulative oxaliplatin neurotoxicity often results in halting the therapy. Oxaliplatin functions predominantly via the formation of toxic covalent drug-DNA adducts. We hypothesize that oxaliplatin-DNA adduct levels formed in vivo in peripheral blood mononuclear cells (PBMC) are proportional to tumor shrinkage caused by FOLFOX therapy. We further hypothesize that adducts induced by subtherapeutic "diagnostic microdoses" are proportional to those induced by therapeutic doses and are also predictive of response to FOLFOX therapy. These hypotheses were tested in colorectal cancer cell lines and a pilot clinical study. Four colorectal cancer cell lines were cultured with therapeutically relevant (100 μmol/L) or diagnostic microdose (1 μmol/L) concentrations of [14C]oxaliplatin. The C-14 label enabled quantification of oxaliplatin-DNA adduct level with accelerator mass spectrometry (AMS). Oxaliplatin-DNA adduct formation was correlated with oxaliplatin cytotoxicity for each cell line as measured by the MTT viability assay. Six colorectal cancer patients received by intravenous route a diagnostic microdose containing [14C]oxaliplatin prior to treatment, as well as a second [14C]oxaliplatin dose during FOLFOX chemotherapy, termed a "therapeutic dose." Oxaliplatin-DNA adduct levels from PBMC correlated significantly to mean tumor volume change of evaluable target lesions (5 of the 6 patients had measurable disease). Oxaliplatin-DNA adduct levels were linearly proportional between microdose and therapeutically relevant concentrations in cell culture experiments and patient samples, as was plasma pharmacokinetics, indicating potential utility of diagnostic microdosing.

Pharmacogenomics for the efficacy of platinum-based chemotherapy: Old drugs, new integrated perspective

Platinum-based chemotherapy remains the cornerstone of treatment for many malignancies. However, although therapeutic efficiency varies greatly among individuals, there is a lack of pharmacogenomic biomarkers that can be used in clinical settings to identify chemosensitive patients and allow stratification. With the development of high-throughput screening techniques and systems biology approaches, a growing body of evidence has shown that platinum resistance is a multifactorial, multi-dimensional, dynamic process incorporating genetic background, tumor evolution and gut microbes. This review critically summarizes potential pharmacogenomic biomarkers for predicting the efficacy of platinum drugs and provides a comprehensive, time-varying perspective that integrates multiple markers.

Multi-level Proteomics Identifies CT45 as a Chemosensitivity Mediator and Immunotherapy Target in Ovarian Cancer

Most high-grade serous ovarian cancer (HGSOC) patients develop resistance to platinum-based chemotherapy and recur, but 15% remain disease free over a decade. To discover drivers of long-term survival, we quantitatively analyzed the proteomes of platinum-resistant and -sensitive HGSOC patients from minute amounts of formalin-fixed, paraffin-embedded tumors. This revealed cancer/testis antigen 45 (CT45) as an independent prognostic factor associated with a doubling of disease-free survival in advanced-stage HGSOC. Phospho- and interaction proteomics tied CT45 to DNA damage pathways through direct interaction with the PP4 phosphatase complex. In vitro, CT45 regulated PP4 activity, and its high expression led to increased DNA damage and platinum sensitivity. CT45-derived HLA class I peptides, identified by immunopeptidomics, activate patient-derived cytotoxic T cells and promote tumor cell killing. This study highlights the power of clinical cancer proteomics to identify targets for chemo- and immunotherapy and illuminate their biological roles.

OIP5 Promotes Growth, Metastasis and Chemoresistance to Cisplatin in Bladder Cancer Cells

Opa interacting protein 5 (OIP5) has previously been identified as a tumorigenesis gene. The purpose of this study is to explore the role of OIP5 in the progression of bladder cancer (BC). The OIP5 expression and clinical behaviors in bladder cancer were collected from lager database. Our study showed that OIP5 was highly expressed in bladder cancer tissues and cells. Overexpression of OIP5 in tumor patients predicted worse overall survival (OS) and higher histological grade. Vitro and vivo experiments demonstrated that knockdown of OIP5 significantly inhibited cell growth of BC. Scratch assay and transwell assay suggested that migration capacity of BC cells was decreased after knockdown of OIP5. Cisplatin sensitivity assay indicated that depletion of OIP5 increased the sensitivity of BC cells to cisplatin. Finally, we identified 38 overlapping differentially expressed genes (DEGs) between RNA-seq and TCGA analyses which were closely linked to OIP5. Bioinformatics analysis showed that these DEGs enriched in oocyte meiosis, fanconi anemia pathway, cell cycle, and microRNAs regulation. TOP2A, SPAG5, SKA1, EXO1, TK1 were confirmed to associated with bladder cancer development. Our study suggests that OIP5 may be a potential biomarker for growth, metastasis and drug-resistance in bladder cancer.

A diagnostic microdosing approach to investigate platinum sensitivity in non-small cell lung cancer

The platinum-based drugs cisplatin, carboplatin and oxaliplatin are often used for chemotherapy, but drug resistance is common. The prediction of resistance to these drugs via genomics is a challenging problem since hundreds of genes are involved. A possible alternative is to use mass spectrometry to determine the propensity for cells to form drug-DNA adducts-the pharmacodynamic drug-target complex for this class of drugs. The feasibility of predictive diagnostic microdosing was assessed in non-small cell lung cancer (NSCLC) cell culture and a pilot clinical trial. Accelerator mass spectrometry (AMS) was used to quantify [14 C]carboplatin-DNA monoadduct levels in the cell lines induced by microdoses and therapeutic doses of carboplatin, followed by correlation with carboplatin IC50 values for each cell line. The adduct levels in cell culture experiments were linearly proportional to dose (R2  = 0.95, p < 0.0001) and correlated with IC50 across all cell lines for microdose and therapeutically relevant carboplatin concentrations (p = 0.02 and p = 0.01, respectively). A pilot microdosing clinical trial was conducted to define protocols and gather preliminary data. Plasma pharmacokinetics (PK) and [14 C]carboplatin-DNA adducts in white blood cells and tumor tissues from six NSCLC patients were quantified via AMS. The blood plasma half-life of [14 C]carboplatin administered as a microdose was consistent with the known PK of therapeutic dosing. The optimal [14 C]carboplatin formulation for the microdose was 107 dpm/kg of body weight and 1% of the therapeutic dose for the total mass of carboplatin. No microdose-associated toxicity was observed in the patients. Additional accruals are required to significantly correlate adduct levels with response.

DNA Adducts from Anticancer Drugs as Candidate Predictive Markers for Precision Medicine

Biomarker-driven drug selection plays a central role in cancer drug discovery and development, and in diagnostic strategies to improve the use of traditional chemotherapeutic drugs. DNA-modifying anticancer drugs are still used as first line medication, but drawbacks such as resistance and side effects remain an issue. Monitoring the formation and level of DNA modifications induced by anticancer drugs is a potential strategy for stratifying patients and predicting drug efficacy. In this perspective, preclinical and clinical data concerning the relationship between drug-induced DNA adducts and biological response for platinum drugs and combination therapies, nitrogen mustards and half-mustards, hypoxia-activated drugs, reductase-activated drugs, and minor groove binding agents are presented and discussed. Aspects including measurement strategies, identification of adducts, and biological factors that influence the predictive relationship between DNA modification and biological response are addressed. A positive correlation between DNA adduct levels and response was observed for the majority of the studies, demonstrating the high potential of using DNA adducts from anticancer drugs as mechanism-based biomarkers of susceptibility, especially as bioanalysis approaches with higher sensitivity and throughput emerge.

HMGB1 Protein: A Therapeutic Target Inside and Outside the Cell

High-mobility group box 1 protein (HMGB1) is a nonhistone chromosomal protein discovered more than 30 years ago. It is an abundant nuclear protein that has a dual function-in the nucleus, it binds DNA and participates in practically all DNA-dependent processes serving as an architectural factor. Outside the cell, HMGB1 plays a different role-it acts as an alarmine that activates a large number of HMGB1-"competent" cells and mediates a broad range of physiological and pathological responses. This universality makes it an attractive target for innovative therapeutic strategies in the treatment of various diseases. Here we present an overview of the major nuclear and extracellular properties of HMGB1 and describe its interaction with different molecular partners as specific receptors or inhibitors, which are important for its role as a target in multiple diseases. We highlight its pivotal role as a target for cancer treatment at two aspects: first in terms of its substantial impact on the repair capacity of cancer cells, thus affecting the effectiveness of chemotherapy with the antitumor drug cis-platinum and, second, the possibility to be targeted by microRNAs influencing different pathways of human diseases, thus making it a promising candidate for a new strategy for therapeutic interventions against various pathological conditions but mainly cancer.

Markers of Exposure to Carcinogens: Methods for Human Biomonitoring

Methods have been developed for the detection of exposure to carcinogens and other DNA-damaging agents in experimental animals and humans, through the detection of carcinogens or metabolic derivatives of them in body fluids or adducts bound covalently to DNA or hemoglobin. These methods are being applied in studies of exposure to environmental carcinogens, the results of which demonstrate their adequacy for detecting ambient exposures. The successful use of urinary markers of genotoxic exposures has been reported with respect to nitrosoproline as an indicator of exposure to N-nitroso compounds. The same approach has been used to detect aflatoxin B1 (AFB1) metabolites and AFB1-N7-Gua as markers of exposure to aflatoxin B1. Detection of adducts formed between genotoxic agents and hemoglobin has been reported in studies of populations occupationally exposed to ethylene oxide, in which 3-hydroxyhistidine and 3-hydroxyva-line have been measured, and in smokers, whose hemoglobin has been found to contain levels of 4-aminobiphenyl and 3-hydroxyvaline that were correlated with the frequency of cigarette smoking. Albumin adducts of AFB1 have been identified in exposed people and their levels correlated with ingested amounts of the carcinogen.

DNA adducts of genotoxic agents have also been detected in the cells and tissues of exposed individuals. Several studies to date have focused on exposure to the ubiquitous polycyclic aromatic hydrocarbon benzo(a)pyrene. Immunoassays and physicochemical methods have been used to detect adducts formed through the major intermediate in the activation pathway, the benzpyrene-7,8-diol-9,10-epoxide (BPDE). BPDE adducts have been found in the DNA of peripheral leukocytes of workers in foundries, aluminum manufacturing plants, and coke oven plants, and also in roofers and cigarette smokers with the use of synchronous scanning fluorescence as well as by enzyme-linked immunosorbent assays (ELISA) or ultrasensitive enzyme radioimmunoassays (USERIA). DNA adducts of O6-methyl guanine have also been detected by immunoassay in the blood of populations at high risk for esophageal cancer. The method of 32P postlabeling has been used for the detection of DNA adducts in placentas, peripheral leukocytes, and oral mucosal cells of tobacco smokers as well as coke oven and foundry workers, and increased total levels of adducts were in general indicative of elevated levels of exposure.

Biological Monitoring of Exposure to Cisplatin in Rats Using SOS Chromotest

Cisplatin (CDDP) is a potent antitumor drug used in the treatment of a variety of solid tumors. The purpose of the present study was to establish screening biomarker of exposure to CDDP using SOS chromotest. The ultimate goal of this screen is to facilitate the choice of an effective drug and the prognosis of the therapy. In the current screening protocol, the SOS chromotests were performed on the urine of Sprague-Dawley rats administered intravenously with CDDP. Urine samples were collected individually in the metabolic cage at 6 (U0–6) and 12 hours (U6–12) after treatment and were tested their DNA damaging effects. The urine samples obtained from the rats administered with 1 mg/kg CDDP did not induce SOS response in our experimental conditions. At a dose of 5 mg/kg, two out of five rat showed more than 50% increase in the DNA damaging effect compared to that of the control. The genotoxic effect was observed only in the U0–6, whereas the U6–12 were not genotoxic but cytotoxic to the test strain. Similar results were obtained at a dose of 10 mg/kg: 5 out of 10 rats showed SOS response and the U6–12 were also proven to be cytotoxic. These results suggest that the method presented in this study could be used as a biomarker of exposure to CDDP.

Platinum anti-cancer drugs: Free radical mechanism of Pt-DNA adduct formation and anti-neoplastic effect

The literature on the anti-neoplastic effects of Pt drugs provides substantial evidence that free radical may be involved in the formation of Pt-DNA adducts and other cytotoxic effects. The conditions specific to cancerous tumours are more conducive to free radical mechanisms than the commonly accepted hydrolysis nucleophilic-electrophilic mechanism of Pt-DNA adduct formation. Molecular orbital studies of the adiabatic attachment of hydrated electrons to Pt drugs reveal that there is a significant lengthening of the Pt-X bond (where X is Cl, O in cisplatin, carboplatin and some pyrophosphate-Pt drugs but not oxaliplatin) in the anion radical species. This observation is consistent with a dissociative electron transfer (DET) mechanism for the formation of Pt-DNA adducts. A DET reaction mechanism is proposed for the reaction of Pt drugs with guanine which involves a quasi-inner sphere 2 electron transfer process involving a transient intermediate 5 co-ordinated activated anion radical species {R2Pt---Cl(G)(Cl)•}*(-) (where R is an ammine group, and G is guanine) and the complex has an elongated Pt---Cl (or Pt---O) bond. A DET mechanism is also proposed when Pt drugs are activated by reaction with free radicals such as HO•, CO3•(-), O2•(-) but do not react with DNA bases to form adducts, but form Pt-protein adducts with proteins such ezrin, FAS, DR5, TNFR1 etc. The DET mechanism may not occur with oxaliplatin.

Aberrant DNA damage response pathways may predict the outcome of platinum chemotherapy in ovarian cancer

Ovarian carcinoma (OC) is the most lethal gynecological malignancy. Despite the advances in the treatment of OC with combinatorial regimens, including surgery and platinum-based chemotherapy, patients generally exhibit poor prognosis due to high chemotherapy resistance. Herein, we tested the hypothesis that DNA damage response (DDR) pathways are involved in resistance of OC patients to platinum chemotherapy. Selected DDR signals were evaluated in two human ovarian carcinoma cell lines, one sensitive (A2780) and one resistant (A2780/C30) to platinum treatment as well as in peripheral blood mononuclear cells (PBMCs) from OC patients, sensitive (n = 7) or resistant (n = 4) to subsequent chemotherapy. PBMCs from healthy volunteers (n = 9) were studied in parallel. DNA damage was evaluated by immunofluorescence γH2AX staining and comet assay. Higher levels of intrinsic DNA damage were found in A2780 than in A2780/C30 cells. Moreover, the intrinsic DNA damage levels were significantly higher in OC patients relative to healthy volunteers, as well as in platinum-sensitive patients relative to platinum-resistant ones (all P<0.05). Following carboplatin treatment, A2780 cells showed lower DNA repair efficiency than A2780/C30 cells. Also, following carboplatin treatment of PBMCs ex vivo, the DNA repair efficiency was significantly higher in healthy volunteers than in platinum-resistant patients and lowest in platinum-sensitive ones (t_1/2 for loss of γH2AX foci: 2.7±0.5h, 8.8±1.9h and 15.4±3.2h, respectively; using comet assay, t_1/2 of platinum-induced damage repair: 4.8±1.4h, 12.9±1.9h and 21.4±2.6h, respectively; all P<0.03). Additionally, the carboplatin-induced apoptosis rate was higher in A2780 than in A2780/C30 cells. In PBMCs, apoptosis rates were inversely correlated with DNA repair efficiencies of these cells, being significantly higher in platinum-sensitive than in platinum-resistant patients and lowest in healthy volunteers (all P<0.05). We conclude that perturbations of DNA repair pathways as measured in PBMCs from OC patients correlate with the drug sensitivity of these cells and reflect the individualized response to platinum-based chemotherapy.

Prediction of individual response to anticancer therapy: historical and future perspectives

Since the introduction of chemotherapy for cancer treatment in the early 20th century considerable efforts have been made to maximize drug efficiency and at the same time minimize side effects. As there is a great interpatient variability in response to chemotherapy, the development of predictive biomarkers is an ambitious aim for the rapidly growing research area of personalized molecular medicine. The individual prediction of response will improve treatment and thus increase survival and life quality of patients. In the past, cell cultures were used as in vitro models to predict in vivo response to chemotherapy. Several in vitro chemosensitivity assays served as tools to measure miscellaneous endpoints such as DNA damage, apoptosis and cytotoxicity or growth inhibition. Twenty years ago, the development of high-throughput technologies, e.g. cDNA microarrays enabled a more detailed analysis of drug responses. Thousands of genes were screened and expression levels were correlated to drug responses. In addition, mutation analysis became more and more important for the prediction of therapeutic success. Today, as research enters the area of -omics technologies, identification of signaling pathways is a tool to understand molecular mechanism underlying drug resistance. Combining new tissue models, e.g. 3D organoid cultures with modern technologies for biomarker discovery will offer new opportunities to identify new drug targets and in parallel predict individual responses to anticancer therapy. In this review, we present different currently used chemosensitivity assays including 2D and 3D cell culture models and several -omics approaches for the discovery of predictive biomarkers. Furthermore, we discuss the potential of these assays and biomarkers to predict the clinical outcome of individual patients and future perspectives.

Human monocytes in the presence of interferons alpha2a and gamma are potent killers of serous ovarian cancer cell lines in combination with paclitaxel and carboplatin

Interferons (IFNs) play an important role in immune surveillance of tumors; however, their efficacy in the treatment of malignancies has been limited. Monocytes are mononuclear phagocytes that are critical to the generation of an innate immune response to tumors. The authors and others have shown that treatment of tumor cell lines in vitro and in vivo with human monocytes primed with type I and type II IFNs results in killing. We now expand on this work, in an extended panel of ovarian cancer cell lines. In this study, we hypothesized that there would be variable sensitivity amongst cell lines to the killing properties of monocytes and IFNs. To this end, we explored the interactions of IFN primed monocytes in conjunction with the standard of therapy for ovarian cancer, taxane, and platinum-based chemotherapeutics. Using 6 ovarian cancer cell lines, we demonstrated that there is variation from cell line to cell line in the ability of IFN-α2a and IFN-γ primed monocytes to synergistically kill target tumor cells, and further, there is an additive killing effect when target cells are treated with both IFN primed monocytes and chemotherapy.

Predictive effect of XPA and XPD polymorphisms on survival of advanced NSCLC patients treated with platinum-based chemotherapy: a three-dimensional (3-D), polyacrylamide gel-based DNA microarray method

Platinum-based chemotherapy is a primary treatment for patients with advanced non-small cell lung cancer (NSCLC). Considering individual differences, an effective and convenient method is urgently needed to identify the sensitivity of individual patient to platinum based regimen. Genetic variants in DNA repair genes are presumed to represent important determinants of drug efficacy. Our previous studies have demonstrated the involvement of xeroderma pigmentosum group A (XPA) codon23 and xeroderma pigmentosum group D (XPD) codon751 single-nucleotide polymorphisms (SNPs) in clinical response to platinum based chemotherapy in advanced NSCLC patients. Thus, a follow-up study was carried out to investigate the relevance of these genotypes and survival of the cohort (n = 115). The three-dimensional (3-D), polyacrylamide gel-based DNA microarray method was used to assess the genotypes of XPA and XPD in peripheral lymphocytes. Log-rank test revealed that the variant genotypes of XPA23 (A/G+G/G) were associated with significantly longer progression- free survival (PFS) (6.0 m vs. 10.6 m, log-rank P = 0.001) and overall survival (OS) (11.2 m vs. 20.8 m, log-rank P = 0.001). In Cox proportional hazards model, the hazard ratio (HR) for death in patients with G allele was 0.65 (P = 0.049). While no significant differences were observed in PFS or OS according to XPD Lys751Gln genotypes (log-rank P > 0.05). In combination with our previous short-term clinical results, this study further confirmed that by detecting the SNPs in blood cells, XPA A23G polymorphic variants might be a promising biomarker in predicting a favor prognosis of NSCLC patients and be helpful towards designing individualized treatments.

Development and validation of a PCR-based assay for the selection of patients more likely to benefit from therapeutic treatment with alkylating drugs

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Previous studies have indicated that the levels of DNA damage induced in peripheral blood mononuclear cells by the alkylating drugs melphalan, cisplatin and carboplatin can serve as useful biomarkers predictive of the therapeutic response of cancer patients to these drugs.

WHAT THIS STUDY ADDS

In the present study we developed a quantitative PCR-based assay, for the measurement of DNA damage. The advantages of this methodology are based on: its far greater sensitivity (about 250 times) than the traditional Southern blot-based method (the detection limit is ~10-20 lesions/10(6) nucleotides from the equivalent DNA of ~8000 cells); its simplicity and speed (results obtained within ~8h); its excellent reproducibility, with a coefficient of variance of 10-15% for different DNA preparations from similarly treated cells; its requirement for only minute amounts of material, and; the avoidance of radioisotope labeling. Moreover, emphasis was given to translate basic research findings into clinical practice through the validation of this assay for prediction of clinical outcome in multiple myeloma patients.

AIM

In order to develop and validate a simple, sensitive and rapid method for the quantitation of alkylating drug-induced DNA damage.

METHODS

HepG2 cells and blood samples were treated with alkylating drugs (melphalan, cisplatin, carboplatin). Gene-specific damage was examined using Southern blot and a multiplex long quantitative PCR (QPCR) carried out in a 7 kb fragment (part of the p53 gene) and a 0.5 kb fragment (part of the IFN-β1 sequence; internal standard).

RESULTS

The extent of PCR amplification of a p53 fragment was inversely proportional to the treatment concentrations of all anticancer drugs examined, indicating a dose-related inhibition by the DNA adducts formed. Parallel analysis of the same samples using both Southern blot and QPCR showed that the DNA adducts measured by QPCR corresponded to the interstrand cross-links in the case of melphalan, and to total drug-induced lesions in the case of the platinum drugs. The detection limit was ~10-20 lesions/10(6) nucleotides using DNA from ~8000 cells. The method is about 250 times more sensitive than the Southern blot-based method and the reproducibility is excellent, with an intraday coefficient of variance (CV) of 5-9% and an interday CV of 4-12%. Application of the QPCR assay to ex vivo melphalan-treated peripheral blood mononuclear cells from multiple myeloma patients, showed that the positive predictive value of this assay for clinical response to melphalan therapy was 92.9%.

CONCLUSION

The PCR-based assay developed in this study can be used for the selection of cancer patients more likely to benefit from therapeutic treatment with alkylating drugs.

Personalized medicine for targeted and platinum-based chemotherapy of lung and bladder cancer

The personalized medicine revolution is occurring for cancer chemotherapy. Biomarkers are increasingly capable of distinguishing genotypic or phenotypic traits of individual tumors, and are being linked to the selection of treatment protocols. This review covers the molecular basis for biomarkers of response to targeted and cytotoxic lung and bladder cancer treatment with an emphasis on platinum-based chemotherapy. Platinum derivatives are a class of drugs commonly employed against solid tumors that kill cells by covalent attachment to DNA. Platinum-DNA adduct levels in patient tissues have been correlated to response and survival. The sensitivity and precision of adduct detection has increased to the point of enabling subtherapeutic dosing for diagnostics applications, termed diagnostic microdosing, prior to the initiation of full-dose therapy. The clinical status of this unique phenotypic marker for lung and bladder cancer applications is detailed along with discussion of future applications.

Nucleotide excision repair and anti-cancer chemotherapy

DNA repair is an important effector of anti-cancer drug resistance. In recent years, it has become apparent that DNA repair is an extremely complex process. Processes within DNA repair that may contribute to one or more drug resistance phenotypes include; O-6-alkyltransferase activity, base excision repair, mismatch repair, nucleotide excision repair, and gene specific repair. Clearly, several of these processes may show increased activity within any single cell, or tumor, at any one time. This review attempts to touch briefly upon the question of the distinctions between each of these specific pathways; and then seeks to expand on nucleotide excision repair as a possible effector of cellular and clinical resistance to platinum-based anticancer therapy.

Molecular mechanisms of cisplatin resistance in bladder cancer

Metastatic disease is the most common mechanism of death in patients with advanced bladder cancer. As for most solid tumors, chemotherapy remains the only realistic option for palliating or curing metastatic disease. However, bladder cancer is characterized by chemoresistance. Only modest response rates are obtained using multiagent regimens including cisplatin. These low response rates and the toxicity of these regimens limit their use to patients at highest risk. Here, we review the molecular mechanisms of cisplatin resistance. These include methods to reduce cisplatin bioavailability within a cell, and defects in the machinery that produces cell death following cisplatin-induced DNA damage. While overcoming these mechanisms is a potential therapeutic approach that can increase response rates, in the short term this knowledge could be used to predict response in individual tumors.

Cisplatin GG-crosslinks within single-stranded DNA: origin of the preference for left-handed helicity

Molecular dynamics (MD) simulations of the single-stranded DNA trinucleotide TG*G*, with the G* guanines crosslinked by the antitumor drug cisplatin, were performed with explicit representation of the water as solvent. The purpose of the simulations was to explain previous NMR observations indicating that in single-stranded cisplatin-DNA adducts, the crosslinked guanines adopt a left-handed helical orientation, whereas in duplexes, the orientation is right-handed. The analysis of the MD trajectory of TG*G* has ascribed a crucial role to hydrogen-bonding (direct or through-water) interactions of the 5'-oriented NH(3) ligand of platinum with acceptor groups at the 5'-side of the crosslink, namely the TpG* phosphate and the terminal 5'-OH group. These interactions bring about some strain into the trinucleotide which is slightly but significantly (1-1.5 kcal.mol(-1)) higher for the right-handed orientation than for the left-handed one. During the unconstrained, 3 ns long MD simulation, left-handed conformations were ~15 times more abundant than the right-handed ones. This sampling difference agrees roughly with the calculated energy difference in strain energy. Overall, these results show that the Pt-GG crosslink within single-stranded DNA is malleable and can access different conformations at a moderate energy cost. This malleability could be of importance in interactions between the platinated DNA and cellular proteins, in which the DNA is locally unwound.

Progress in personalizing chemotherapy for bladder cancer

Platinum-based chemotherapy is commonly used for the treatment of locally advanced and metastatic bladder cancer. However, there are currently no methods to predict chemotherapy response in this disease setting. A better understanding of the biology of bladder cancer has led to developments of molecular biomarkers that may help guide clinical decision making. These biomarkers, while promising, have not yet been validated in prospective trials and are not ready for clinical applications. As alkylating agents, platinum drugs kill cancer cells mainly through induction of DNA damage. A microdosing approach is currently being tested to determine if chemoresistance can be identified by measuring platinum-induced DNA damage using highly sensitive accelerator mass spectrometry technology. The hope is that these emerging strategies will help pave the road towards personalized therapy in advanced bladder cancer.

Modulatory effects of gentisic acid against genotoxicity and hepatotoxicity induced by cyclophosphamide in Swiss albino mice

Objectives

This study evaluated the protective effects of gentisic acid (GA) against genotoxicity and hepatotoxicity induced by cyclophosphamide (CP) in Swiss albino mice.

Methods

Mice were pretreated with GA orally at doses of 50 and 100 mg/kg for 14 consecutive days before the administration of a single intraperitoneal dose of 50 mg/kg CP. The ameliorative effect of GA on genotoxicity was studied using the in-vivo bone marrow micronuclei induction test, DNA integrity and alkaline unwinding assay. The activity of various oxidative stress enzymes were estimated in hepatic tissue.

Key findings

A single intraperitoneal administration of CP in mice increased the malondialdehyde level, depleted the glutathione content and antioxidant enzyme activity (glutathione peroxidase, glutathione reductase, catalase and quinone reductase), and induced DNA strand breaks and micronuclei induction. Oral pretreatment with GA at both doses caused a significant reduction in malondialdehyde and glutathione levels, restoration of antioxidant enzyme activity, reduction in micronuclei formation and DNA fragmentation. Serum toxicity marker enzymes such as aspartate aminotransferase, alanine aminotransferase and lactate dehydrogenase were increased after CP treatment but restored in GA pretreated groups.

Conclusion

The results support the protective effect of GA against CP induced genotoxicity and hepatotoxicity.

Platinum-DNA interstrand crosslinks: molecular determinants of bending and unwinding of the double helix

Platinum diamine complexes are able to crosslink the guanines of d(GC)(2) dinucleotides within double-stranded DNA. The interstrand crosslink thus formed causes a bend of the double helix toward the minor groove and the helical sense changes locally to left-handed, resulting in a considerable unwinding. The bend and unwinding angles have been shown to depend on the platinum ligands. Here, we have used molecular dynamics simulations to investigate the DNA 20-mer d(C(1)T(2)C(3)T(4)C(5)C(6)T(7)T(8)G*(9)C(10)T(11)C(12)T(13)C(14)C(15)T(16)T(17)C(18)T(19)C(20))-d(G(21)A(22)G(23)A(24)A(25)G(26)G(27)A(28)G(29)A(30)G*(31)C(32)A(33)A(34)G(35)G(36)A(37)G(38)A(39)G(40)) with the G* guanines crosslinked by cis-Pt(NH(3))(2)(2+), Pt(R,R-DACH)(2+), or Pt(S,S-DACH)(2+). Previous investigations on cisplatin interstrand adducts indicated that the structure is similar in solid state and in solution; thus, we used the reported X-ray structure of a cisplatin adduct as a starting model. Replacing in the MD-relaxed model for the DNA duplex crosslinked with cis-Pt(NH(3))(2)(2+) the two NH(3) platinum ligands by R,R-DACH or S,S-DACH led to clashes between the DACH residue and the deoxyribose of C(12). Confrontation of MD-derived models with gel shift measurements suggested that these clashes are avoided differently in the adducts of Pt(R,R-DACH)(2+)versus Pt(S,S-DACH)(2+). The R,R-isomer avoids the clash by untwisting the T(11)/A(30)-C(12)/G(29) step, thus increasing the global unwinding. In contrast, the S,S-isomer modifies the shift and slide parameters of this step, which dislocates the helical axis and enhances the bend angle. The clash that leads to the differentiation of the structures as a function of the diamine ligand is related to a hydrogen bond between the platinum complex and the T(11) base and could be characteristic of interstrand crosslinks at d(pyG*Cpy)-d(puG*Cpu) sequences.

Xeroderma pigmentosum complementation group C single-nucleotide polymorphisms in the nucleotide excision repair pathway correlate with prolonged progression-free survival in advanced ovarian cancer

BACKGROUND

The nucleotide excision repair (NER) pathway is the principal DNA repair pathway for removing bulky platinum DNA adducts. Suboptimal DNA repair may lead to improved response to platinum agents. The objective of this study was to determine whether single-nucleotide polymorphisms (SNPs) in NER pathway genes could be markers of platinum response in ovarian cancer.

METHODS

The authors identified patients with advanced-stage, papillary serous ovarian cancer who underwent primary cytoreductive surgery followed by platinum-based chemotherapy. DNA was isolated from peripheral blood specimens. Twenty-two SNPs within NER genes (xeroderma pigmentosum [XP] complementation group A [XPA], XPB/excision repair cross-complementing rodent repair deficiency, complementation group 3 [ERCC3], XPC, XPD/ERCC2, XPF/ERCC4, XPG/ERCC5, Cockayne syndrome group B protein [CSB]/ERCC8, ERCC1) were genotyped using polymerase chain reaction analysis.

RESULTS

In total, 139 patients with stage III and IV papillary serous ovarian cancer were genotyped. The XPC (reference SNP 3731108 [rs3731108]) adenosine-guanine (AG)/AA genotype versus the GG genotype was associated with prolonged a progression-free survival (PFS) of 21.3 months versus 13.4 months (hazard ratio [HR], 0.63; 95% confidence interval [CI], 0.42-0.95; P = .03). The XPC (rs1124303) guanosine-thymidine (GT)/GG genotype versus the TT genotype was associated with a prolonged PFS of 22.8 months versus 14.9 months (HR, 0.47; 95% CI, 0.24-0.94; P = .03). The XPC poly(AT) (PAT) (-/+)/(-/-) genotype versus the (+/+) genotype was associated with a prolonged PFS of 17 months versus 11.6 months (HR, 0.56; 95% CI, 0.36-0.89; P = .01). The XPF/ERCC4 (rs12926685) cytidine-thymidine (CT)/CC genotype versus the TT genotype was associated with a prolonged PFS of 16.7 months versus 12.4 months (HR, 0.63; 95% CI, 0.41-0.95; P = .03). On multivariate analysis adjusting for breast cancer (BRCA) gene and cytoreductive surgery status, the XPC SNPs remained significantly associated with prolonged PFS.

CONCLUSIONS

The current results indicated that XPC is a key component of the NER pathway that participates in DNA damage repair. SNPs in the XPC gene may represent novel markers of ovarian cancer response to platinum-based chemotherapy.

Core cross-linked block ionomer micelles as pH-responsive carriers for cis-diamminedichloroplatinum(II)

Benefits of the frequently prescribed platinum (II) chemotherapy drugs are compromised by undesirable side effects, poor pharmacokinetics and development of drug resistance. Polymer micelles derived from amphiphilic block copolymers, offer a novel macromolecular platform for carrier based delivery of such compounds. Soft polymeric nanocarriers were synthesized by template-assisted method involving condensation of the poly(ethylene oxide)-b-polymethacrylate anions by metal ions into core-shell block ionomer complex micelles followed by chemical cross-linking of the polyion chains in the micelle cores. The resulting micelles can efficiently incorporate cisplatin with a high loading capacity (up to 42% w/w). Core cross-linking stabilized the micelles against structural disintegration and prevented premature drug release. The reversible cisplatin entrapment involved the carboxylate groups of the micellar core. The drug was released in a pH-responsive manner, without loss of its biological activity. The stable cross-linked polymer micelles can potentially improve platinum (II) drug disposition with improved therapeutic potential.

ERCC1 and ERCC2 polymorphisms predict clinical outcomes of oxaliplatin-based chemotherapies in gastric and colorectal cancer: a systemic review and meta-analysis

PURPOSE

Nucleotide excision repair (NER) modulates platinum-based chemotherapeutic efficacy by removing drug-produced DNA damage. To summarize published data on the association between polymorphisms of NER genes (ERCC1 and ERCC2) and responses to oxaliplatin-based chemotherapies, we carried out a meta-analysis of gastric and colorectal cancer for commonly studied polymorphisms ERCC1 rs11615C>T and ERCC2 rs13181T>G.

PATIENTS AND METHODS

In 17 previously published studies, 1,787 cancer patients were treated with the oxaliplatin-based regimen. Primary outcomes included therapeutic response (TR; i.e., complete response + partial response vs. stable disease + progressive disease), progression-free survival (PFS), and overall survival (OS). We calculated OR or HR with 95% CIs to estimate the risk or hazard.

RESULTS

We found consistent and clinically substantial risk or hazard for TR, PFS, and OS in the oxaliplatin-treated gastric and colorectal cancer patients with an ethnic discrepancy. For ERCC1 rs11615C>T, the T allele was associated with reduced response and poor PFS and OS in Asians (TR: OR = 0.53 and 95% CI = 0.35-0.81; PFS: HR = 1.69 and 95% CI = 1.05-2.70; and OS: HR = 2.03 and 95% CI = 1.60-2.59). For ERCC2 rs13181T>G, the G allele was associated with reduced response and poor PFS and OS in Caucasians (TR: OR = 0.56 and 95% CI = 0.35-0.88; PFS: HR = 1.41 and 95% CI = 1.02-1.95; and OS: HR = 1.42 and 95% CI = 1.11-1.81).

CONCLUSIONS

NER ERCC1 rs11615C>T and ERCC2 rs13181T>G polymorphisms are useful prognostic factors in oxaliplatin-based treatment of gastric and colorectal cancer. Larger studies and further clinical trials are warranted to confirm these findings.

A microdosing approach for characterizing formation and repair of carboplatin-DNA monoadducts and chemoresistance

Formation and repair of platinum (Pt)-induced DNA adducts is a critical step in Pt drug-mediated cytotoxicity. Measurement of Pt-DNA adduct kinetics in tumors may be useful for better understanding chemoresistance and therapeutic response. However, this concept has yet to be rigorously tested because of technical challenges in measuring the adducts at low concentrations and consistent access to sufficient tumor biopsy material. Ultrasensitive accelerator mass spectrometry was used to detect [(14)C]carboplatin-DNA monoadducts at the attomole level, which are the precursors to Pt-DNA crosslink formation, in six cancer cell lines as a proof-of-concept. The most resistant cells had the lowest monoadduct levels at all time points over 24 hr. [(14)C]Carboplatin "microdoses" (1/100th the pharmacologically effective concentration) had nearly identical adduct formation and repair kinetics compared to therapeutically relevant doses, suggesting that the microdosing approach can potentially be used to determine the pharmacological effects of therapeutic treatment. Some of the possible chemoresistance mechanisms were also studied, such as drug uptake/efflux, intracellular inactivation and DNA repair in selected cell lines. Intracellular inactivation and efficient DNA repair each contributed significantly to the suppression of DNA monoadduct formation in the most resistant cell line compared to the most sensitive cell line studied (p < 0.001). Nucleotide excision repair (NER)-deficient and -proficient cells showed substantial differences in carboplatin monoadduct concentrations over 24 hr that likely contributed to chemoresistance. The data support the utility of carboplatin microdosing as a translatable approach for defining carboplatin-DNA monoadduct formation and repair, possibly by NER, which may be useful for characterizing chemoresistance in vivo.

Gemcitabine causes minimal modulation of carboplatin-DNA monoadduct formation and repair in bladder cancer cells

We are developing a method to identify cellular resistance to carboplatin by using accelerator mass spectrometry to measure carboplatin-DNA adducts formed from drug microdoses (∼1/100th the therapeutic dose). Such an approach would be particularly useful if it is still valid in combination chemotherapy. We examined whether the addition of gemcitabine, another chemotherapeutic drug, could influence carboplatin-DNA adduct levels. There were no substantial differences in the levels of carboplatin-DNA adducts in cells upon exposure to the carboplatin/gemcitabine combination at various doses and schedules. These data demonstrate that microdosing is feasible for the characterization of carboplatin resistance when given in combination with gemcitabine.

Pt(II) and Ag(I) complexes with acesulfame: crystal structure and a study of their antitumoral, antimicrobial and antiviral activities

Two new complexes of platinum(II) and silver(I) with acesulfame were synthesized. Acesulfame is in the anionic form acesulfamate (ace). The structures of both complexes were determined by X-ray crystallography. For K(2)[PtCl(2)(ace)(2)] the platinum atom is coordinated to two Cl(-) and two N-acesulfamate atoms forming a trans-square planar geometry. Each K(+) ion interacts with two oxygen atoms of the S(O)(2) group of each acesulfamate. For the polymeric complex [Ag(ace)](n) the water molecule bridges between two crystallographic equivalent Ag1 atoms which are related each other by a twofold symmetry axis. Two Ag1 atoms, related to each other by a symmetry centre, make bond contact with two equivalent oxygen atoms. These bonds give rise to infinite chains along the unit cell diagonal in the ac plane. The in vitro cytotoxic analyses for the platinum complex using HeLa (human cervix cancer) cells show its low activity when compared to the vehicle-treated cells. The Ag(I) complex submitted to in vitro antimycobacterial tests, using the Microplate Alamar Blue (MABA) method, showed a good activity against Mycobacterium tuberculosis, responsible for tuberculosis, with a minimal inhibitory concentration (MIC) value of 11.6microM. The Ag(I) complex also presented a promising activity against Gram negative (Escherichia coli and Pseudomonas aeruginosa) and Gram positive (Enterococcus faecalis) microorganisms. The complex K(2)[PtCl(2)(ace)(2)] was also evaluated for antiviral properties against dengue virus type 2 (New Guinea C strain) in Vero cells and showed a good inhibition of dengue virus type 2 (New Guinea C strain) replication at 200microM, when compared to vehicle-treated cells.

DNA damage induced by cis- and carboplatin as indicator for in vitro sensitivity of ovarian carcinoma cells

Background

The DNA damage by platinum cytostatics is thought to be the main cause of their cytotoxicity. Therefore the measurement of the DNA damage induced by cis- and carboplatin should reflect the sensitivity of cancer cells toward the platinum chemotherapeutics.

Methods

DNA damage induced by cis- and carboplatin in primary cells of ovarian carcinomas was determined by the alkaline comet assay. In parallel, the reduction of cell viability was measured by the fluorescein diacetate (FDA) hydrolysis assay.

Results

While in the comet assay the isolated cells showed a high degree of DNA damage after a 24 h treatment, cell viability revealed no cytotoxicity after that incubation time. The individual sensitivities to DNA damage of 12 tumour biopsies differed up to a factor of about 3. DNA damage after a one day treatment with cis- or carboplatin correlated well with the cytotoxic effects after a 7 day treatment (r = 0,942 for cisplatin r = 0.971 for carboplatin). In contrast to the platinum compounds the correlation of DNA damage and cytotoxicity induced by adriamycin was low (r = 0,692), or did not exist for gemcitabine.

Conclusion

The measurement of DNA damage induced by cis- and carboplatin is an accurate method to determine the in vitro chemosensitivity of ovarian cancer cells towards these cytostatics, because of its quickness, sensitivity, and low cell number needed.

Development of an ultraperformance liquid chromatography/mass spectrometry method to quantify cisplatin 1,2 intrastrand guanine-guanine adducts

Platinum chemotherapeutic agents have been widely used in the treatment of cancer. Cisplatin was the first of the platinum-based chemotherapeutic agents and therefore has been extensively studied as an antitumor agent since the late 1960s. Because this agent forms several DNA adducts, a highly sensitive and specific quantitative assay is needed to correlate the molecular dose of individual adducts with the effects of treatment. An ultraperformance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) assay for quantification of 1,2 guanine-guanine intrastrand cisplatin adducts [CP-d(GpG)], using (15)N(10) CP-d(GpG) as an internal standard, was developed. The internal standard was characterized by MS/MS, and its concentration was validated by inductively coupled plasma mass spectrometry. Samples containing CP-d(GpG) in DNA were purified by enzyme hydrolysis, centrifugal filtration, and HPLC with fraction collection prior to quantification by UPLC-MS/MS in the selective reaction monitoring mode [m/z 412.5-->248.1 for CP-d(GpG); m/z 417.5-->253.1 for [(15)N(10)] CP-d(GpG)]. The recovery of standards was >90%, and quantification was unaffected by increasing concentrations of calf thymus DNA. This method utilizes 25 mug of DNA per injection. The limit of quantification was 3 fmol or 3.7 adducts per 10(8) nucleotides, which approaches the sensitivity of the (32)P postlabeling method for this adduct. These data suggested that this method is suitable for in vitro and in vivo assessment of CP-d(GpG) adducts formed by cisplatin and carboplatin. Subsequently, the method was applied to studies using ovarian carcinoma cell lines and C57/BL6 mice to illustrate that this method is capable of quantifying CP-d(GpG) adducts using biologically relevant systems and doses. The development of biomarkers to determine tissue-specific molecular dosimetry during treatment will lead to a more complete understanding of both therapeutic and adverse effects of cisplatin and carboplatin. This will support the refinement of therapeutic regimes and appropriate individualized treatment protocols.

Administration of reduced glutathione in FOLFOX4 adjuvant treatment for colorectal cancer: effect on oxaliplatin pharmacokinetics, Pt-DNA adduct formation, and neurotoxicity

Oxaliplatin is a promising drug for cancer therapy and the oxaliplatin/5-fluorouracil/leucovorin (FOLFOX) regimen has become the standard adjuvant treatment for colorectal cancer. However, the oxaliplatin-induced neurotoxicity still represents a clinical problem leading to a discontinuation of the therapy. Many strategies have been proposed in order to manage the neurotoxicity, but their effect on antitumoral efficacy is still unclear. In this study, we investigated the effect of reduced glutathione administration on neurotoxicity, oxaliplatin pharmacokinetics, and platinum-DNA (Pt-DNA) adduct formation in patients affected by colorectal cancer treated with FOLFOX4 adjuvant regimen. Twenty-seven patients were randomized to receive GSH 1500 mg/m or saline solution before oxaliplatin infusion. Evaluation of neurotoxicity, pharmacokinetics of plasmatic total and ultrafiltered Pt, and determination of Pt-DNA adduct formation on white blood cells was performed during the 5th, 9th, and 12th cycles. At the end of all cycles of therapy, the patients in the GSH arm showed a statistically significant reduction of neurotoxicity (P=0.0037) compared with the placebo arm. There were no significant differences in the main pharmacokinetic parameters between the two arms except a lower area under the plasma concentration-time curve and a smaller apparent steady-state volume of distribution (Vss) when GSH was coadministered. This difference can be explained by the natural function of GSH in the detoxification of oxaliplatin and by its ability to remove the Pt bound to plasma proteins. The determination of Pt-DNA adduct formation shows no statistically significant differences between the two arms. In conclusion, this study indicates that coadministration of GSH is an effective strategy to reduce the oxaliplatin-induced neurotoxicity without impairing neither the pharmacokinetics of oxaliplatin, nor the Pt-DNA adduct formation.

DNA repair proteins and telomerase reverse transcriptase in the cochlear lateral wall of cisplatin-treated rats

Cochlear lateral wall damage is a side effect of cisplatin chemotherapy. Recent studies have shown that cisplatin treatment precipitates platinated DNA adducts in the cochlear lateral wall which suggest that DNA damage may contribute to ototoxicity. Platinated adducts are high-affinity substrates for the global genomic nucleotide excision repair (GG-NeR) pathway which is facilitated by xeroderma pigmentosum (Xp) complementing proteins, such as XpC, XpD and XpA. tumor biology has shown that in addition to stimulating GG-NeR, cisplatin may deplete telomerase reverse transcriptase (teRt). in the current study Fischer344 rats were treated with cisplatin (2 mg/kg/4 days, i.p.) and their cochleae harvested for immunohistochemistry. XpC, XpD and XpA expression increased while teRt expression decreased among cisplatin treated animals compared to vehicle control. these findings suggest that in addition to forming platinated adducts, cisplatin chemotherapy may up-regulate DNA repair proteins and modify teRt expression in the cochlear lateral wall.

Identification by NMR spectroscopy of the two stereoisomers of the platinum complex [PtCl2(S-ahaz)] (S-ahaz = 3(S)-aminohexahydroazepine) bound to a DNA 14-mer oligonucleotide. NMR evidence of structural alteration of a platinated A x T-rich 14-mer DNA duplex

The enantiomers of the asymmetric, chiral platinum(II) complex [PtCl(2)(S-ahaz)] (S-ahaz = 3(S)-aminohexahydroazepine) each form two stereoisomers on binding to GpG sequences of DNA: one in which the primary amine is directed toward the 5' end of the DNA and one in which it is directed toward the 3' end. Previous binding studies have revealed that the S-enantiomer forms the two stereoisomers in a 7:1 ratio while the R-enantiomer forms them in close to a 1:1 ratio. In an attempt to elucidate the reasons behind the stereoselectivity displayed by the S-enantiomer and to establish which isomer is formed in the greater amount, we report here its reaction with a 14-mer oligodeoxyribonucleotide having a single GpG site. The two stereoisomers that formed were separated using HPLC methods, and their integrities were confirmed by electrospray ionization mass spectrometry. The DNA duplex was formed by combination of each of the purified reaction products with the complementary strand of DNA. Identification of both of the stereoisomers was achieved using 2D NMR spectroscopy, which is the first time this has been achieved for an unsymmetric platinum complex bound to DNA. The minor stereoisomer, with the bulk of the ahaz ring directed toward the 3' end of the platinated strand, induced considerable disruption to the 14-mer DNA duplex structure. The primary amine of the ahaz ligand was oriented toward the 3' side of the duplex in the major isomer, giving a DNA structure that was less disrupted and was more akin to the structure of the DNA on binding of cisplatin to the same sequence.

Characterization of an inhibitory dynamic pharmacophore for the ERCC1-XPA interaction using a combined molecular dynamics and virtual screening approach

Combination chemotherapy involving Cisplatin is a standard treatment for many cancers. However, following an initial positive response, patients will often relapse, presenting with Cisplatin-resistant disease. One possible mechanism for the acquired resistance to Cisplatin is an increase in DNA repair through the up-regulation of ERCC1, an essential component of the nucleotide excision repair complex. Recruitment of ERCC1 to the site of DNA damage is coordinated through its interaction with a protein known as XPA. As there are currently no effective inhibitors of this interaction, inhibition of the ERCC1/XPA interaction may provide an effective strategy for overcoming the development of Cisplatin-resistant cancers. To discover small molecule inhibitors of this interaction, we have screened both the NCI diversity set of ligands and DrugBank-small molecules against the XPA binding site in ERCC1. These compounds were screened using two different techniques in AUTODOCK to account for receptor flexibility. First, using a set of flexible residues, as determined from MD simulations of the XPA/ERCC1 complex and second, using the relaxed complex scheme implemented by performing independent docking experiments against an ensemble of target conformations that were generated from MD simulations. Lowest energy poses from the two different methods were then used to construct a pharmacophore model, which was then validated by comparison to UCN-01, a weak inhibitor of ERCC1 mediated nucleotide excision.

The influence of Cisplatin on the gas-phase dissociation of oligonucleotides studied by electrospray ionization tandem mass spectrometry

cis-Diamminedichloroplatinum(II) (cisplatin, DDP) is a cornerstone of anticancer therapy and has become one of the most widely used drugs for the treatment of various epithelial malignancies. The cytotoxicity of cisplatin is mainly based upon its affinity to adjacent guanines in nucleic acids, resulting in the formation of 1,2-intrastrand adducts. In this study the gas-phase dissociation of DNA- and RNA-cisplatin adducts is investigated by electrospray ionization (ESI) tandem mass spectrometry (MS/MS). The fundamental mechanistic aspects of fragmentation are elucidated to provide the basis for the tandem mass spectrometric determination of binding motifs and binding sites of this important anticancer drug. It is shown that the binding of cisplatin to vicinal guanines drastically alters the gas-phase fragmentation behavior of oligonucleotides. The 3'-C-O bond adjacent to the GG base pair is preferentially cleaved, leading to extensive formation of the corresponding w-ion. This observation was even made for oligoribonucleotides, which usually tend to form c- and y-ions under CID conditions. The absence of complementary ions of equal abundance indicates that oligonucleotide-cisplatin adducts are following more than one dissociation pathway in the gas-phase. Several mechanisms that explain the increased cleavage of the 3'-C-O bond and the lack of the complementary a-ion are proposed. Results of additional MS/MS experiments on methylphosphonate-oligodeoxynucleotides confirm the proposed mechanisms.

Oxaliplatin-DNA adduct formation in white blood cells of cancer patients

In this study, we investigated the kinetics of oxaliplatin-DNA adduct formation in white blood cells of cancer patients in relation to efficacy as well as oxaliplatin-associated neurotoxicity. Thirty-seven patients with various solid tumours received 130 mg m(-2) oxaliplatin as a 2-h infusion. Oxaliplatin-DNA adduct levels were measured in the first cycle using adsorptive stripping voltammetry. Platinum concentrations were measured in ultrafiltrate and plasma using a validated flameless atomic absorption spectrometry method. DNA adduct levels showed a characteristic time course, but were not correlated to platinum pharmacokinetics and varied considerably among individuals. In patients showing tumour response, adduct levels after 24 and 48 h were significantly higher than in nonresponders. Oxaliplatin-induced neurotoxicity was more pronounced but was not significantly different in patients with high adduct levels. The potential of oxaliplatin-DNA adduct measurements as pharmacodynamic end point should be further investigated in future trials.

Mechanism of double-base lesion bypass catalyzed by a Y-family DNA polymerase

As a widely used anticancer drug, cis-diamminedichloroplatinum(II) (cisplatin) reacts with adjacent purine bases in DNA to form predominantly cis-[Pt(NH₃)₂{d(GpG)-N7(1),-N7(2)}] intrastrand cross-links. Drug resistance, one of the major limitations of cisplatin therapy, is partially due to the inherent ability of human Y-family DNA polymerases to perform translesion synthesis in the presence of DNA-distorting damage such as cisplatin–DNA adducts. To better understand the mechanistic basis of translesion synthesis contributing to cisplatin resistance, this study investigated the bypass of a single, site-specifically placed cisplatin-d(GpG) adduct by a model Y-family DNA polymerase, Sulfolobus solfataricus DNA polymerase IV (Dpo4). Dpo4 was able to bypass this double-base lesion, although, the incorporation efficiency of dCTP opposite the first and second cross-linked guanine bases was decreased by 72- and 860-fold, respectively. Moreover, the fidelity at the lesion decreased up to two orders of magnitude. The cisplatin-d(GpG) adduct affected six downstream nucleotide incorporations, but interestingly the fidelity was essentially unaltered. Biphasic kinetic analysis supported a universal kinetic mechanism for the bypass of DNA lesions catalyzed by various translesion DNA polymerases. In conclusion, if human Y-family DNA polymerases adhere to this bypass mechanism, then translesion synthesis by these error-prone enzymes is likely accountable for cisplatin resistance observed in cancer patients.

Cisplatin induces cytoplasmic to nuclear translocation of nucleotide excision repair factors among spiral ganglion neurons

Genomic DNA is a high-affinity target for the antineoplastic molecule cisplatin. Cell survival from cisplatin DNA damage is dependent on removal of cisplatin-DNA adducts by nucleotide excision repair (NER) pathways. The rate-limiting steps in the NER pathways are DNA damage identification and verification. These steps are accomplished by xeroderma pigmentosum complementation group C and A (XPC and XPA) and RNA polymerase II. Unlike RNA polymerase II, XPC and XPA have no known cellular function beyond DNA repair. Cisplatin is known to damage spiral ganglion neurons at the basal coil of the cochlea therefore it was posited that cisplatin may target their DNA and mobilize XPC and XPA. Female Fisher344 rats were given two, four day cycles of cisplatin (2mg/kg) or saline, separated by a 10day rest period. A 2 x 3 x 2 factorial design, consisting of two treatment conditions (cisplatin and saline treatment), three survival times (5, 19 and 22 days) and two analysis methods (quantitative RT-PCR and immunohistochemistry) was employed to evaluate the expression and distribution of XPC and XPA. Quantitative RT-PCR revealed statistically significant differences in cochlear XPC and XPA mRNA levels after cisplatin treatment at all times except day 22 for XPA. Immunohistochemistry revealed that a proportion ( approximately 50%) of spiral ganglion neurons in control rats showed cytoplasmic expression of XPC and XPA. After cisplatin treatment, a similar proportion ( approximately 50%) of spiral ganglion neurons showed increased nuclear expression of XPC and XPA, which appears to represent translocation from the cytoplasm. Basal coil spiral ganglion neurons translocated XPC and XPA at later treatment cycles and with less magnitude than apical coil neurons after cisplatin treatment. Therefore, it is suggested that cisplatin treatment induces nuclear translocation of NER proteins among spiral ganglion neurons and that this nuclear translocation is less efficient at the base relative to the apex.