The interaction of cisplatin and analogues with DNA in reconstituted chromatin

Expression of ER stress markers (GRP78 and PERK) in experimental nephrotoxicity induced by cisplatin and gentamicin: roles of inflammatory response and oxidative stress

This study aimed to establish the relationship between two endoplasmic reticulum (ER) stress proteins, glucose-regulated protein 78 (GRP78/BiP) and PKR-like endoplasmic reticulum kinase (PERK), and oxidative stress markers in cisplatin (CIS)-induced and gentamicin (GEN)-induced nephrotoxicity.The study consisted of five groups: control (saline solution only), CIS D2 (2.5 mg/kg for 2 days), CIS D7 (2.5 mg/kg for 7 days), GEN D2 (160 mg/kg for 2 days), and GEN D7 (160 mg/kg for 7 days). All rats were sacrificed 24 h after the last injection for standard clinical chemistry, and ultrastructural and histological evaluation of the kidney.CIS and GEN increased blood urea nitrogen (BUN) and serum creatinine (Cr) levels, as well as total oxidant status (TOS), while decreasing total antioxidant status (TAS) level in CIS D7 and GEN D7 groups. Histopathological and ultrastructural findings were also consistent with renal tubular damage. In addition, expression of markers of renal inflammation (tumor necrosis factor-α (TNF-α) and interleukin 1β (IL-1β)) and ER stress markers (GRP78 and PERK) was significantly increased in the kidney tissue of rats treated with CIS and GEN for 7 days.These findings suggest that CIS and GEN administration for 7 days aggravates nephrotoxicity through the enhancement of oxidative stress, inflammation, and ER stress-related markers. As a result, the recommended course of action is to utilize CIS and GEN as an immediate but brief induction therapy, stopping after 3 days and switching to other drugs instead.

Brain Protection by Methylene Blue and Its Derivative, Azur B, via Activation of the Nrf2/ARE Pathway in Cisplatin-Induced Cognitive Impairment

Cisplatin is a cytotoxic chemotherapeutic drug that leads to DNA damage and is used in the treatment of various types of tumors. However, cisplatin has several serious adverse effects, such as deterioration in cognitive ability. The aim of our work was to study neuroprotectors capable of preventing cisplatin-induced neurotoxicity. Methylene blue (MB) and AzurB (AzB) are able to neutralize the neurotoxicity caused by cisplatin by protecting nerve cells as a result of the activation of the Ntf2 signaling pathway. We have shown that cisplatin impairs learning in the Morris water maze. This is due to an increase in the amount of mtDNA damage, a decrease in the expression of most antioxidant genes, the main determinant of the induction of which is the Nrf2/ARE signaling pathway, and genes involved in mitophagy regulation in the cortex. The expression of genes involved in long-term potentiation was suppressed in the hippocampus of cisplatin-injected mice. MB in most cases prevented cisplatin-induced impairment of learning and decrease of gene expression in the cortex. AzB prevented the cisplatin-induced decrease of genes in the hippocampus. Also, cisplatin induced disbalance in the gut microbiome, decreased levels of Actinotalea and Prevotella, and increased levels of Streptococcus and Veillonella. MB and AzB also prevented cisplatin-induced changes in the bacterial composition of the gut microbiome.

Low-intensity low-frequency pulsed ultrasound ameliorates sciatic nerve dysfunction in a rat model of cisplatin-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy is a neurological complication that frequently occurs during chemotherapeutic intervention, resulting in damaged myelin sheath, motor weakness and/or sensory impairment. This study aims to investigate the therapeutic efficiency of low-intensity pulsed low-frequency ultrasound on cisplatin-induced peripheral neuropathy. Rats were randomly divided into five experimental groups as control, cisplatin administration, 10 mg/kg melatonin treatment after cisplatin administration, 1 MHz frequency 0.5 W/cm² pulsed ultrasound treatment after cisplatin administration and 1 MHz frequency 1.5 W/cm² pulsed ultrasound treatment after cisplatin administration. Chemical neuropathy was induced by the injection of 3 mg/kg/week of cisplatin (i.p.) for 5 weeks. Afterwards, melatonin and pulsed ultrasound treatments were applied for 15 consecutive days. Cisplatin administration resulted in a decrease in nociceptive pain perception and nerve conduction velocities together with a decrease in myelin thickness and diameters of axons and myelinated fibers, indicating a dysfunction and degeneration in sciatic nerves. In addition, cisplatin administration led to a decrease, in superoxide dismutase activity, and an increase in malondialdehyde and IL-1β levels together with an increase in caspase-3 protein expression levels and a decrease in Bcl-2 and Parkin levels. The ultrasound treatments resulted in an increase in nociceptive pain perception and sciatic nerve conduction; led to a decrease in oxidative stress and inflammation, restored nerve degeneration and regulated apoptosis and mitophagy. Taken together, low-intensity pulsed low-frequency ultrasound was efficient in restoring the alterations attributable to cisplatin-induced peripheral neuropathy, and warrants further investigations.

Drug-Induced Acute Kidney Injury

Medications are a common cause of AKI especially for patients admitted to hospital wards and the intensive care unit. Although drug-related kidney injury occurs through different mechanisms, this review will focus on three specific types of tubulointerstitial injury. Direct acute tubular injury develops from several medications, which are toxic to various cellular functions. Their excretory pathways through the proximal tubules contribute further to AKI. Drug-induced AKI may also develop through induction of inflammation within the tubulointerstitium. Medications can elicit a T cell-mediated immune response that promotes the development of acute interstitial nephritis leading to AKI. Although less common, a third pathway to kidney injury results from the insolubility of drugs in the urine leading to their precipitation as crystals within distal tubular lumens, causing a crystalline-related AKI. Intratubular obstruction, direct tubular injury, and localized inflammation lead to AKI. Clinicians should be familiar with the pathogenesis and clinical-pathologic manifestations of these forms of kidney injury. Prevention and treatment of AKI relies on understanding the pathogenesis and judiciously using these agents in settings where AKI risk is high.

The DNA binding properties of 9-aminoacridine carboxamide Pt complexes

Cisplatin analogues with an attached DNA-binding moiety represent a potentially effective class of DNA-damaging anti-tumour agents because they possess higher affinities for DNA and different DNA damage profiles compared with cisplatin. In this study, the interaction of four 9-aminoacridine carboxamide Pt complexes with purified DNA was investigated: firstly, using a fluorescent intercalator displacement (FID) assay with ethidium bromide; and secondly, with a DNA unwinding assay. The relative capacity of these compounds to perturb the fluorescence induced by DNA-bound ethidium bromide at clinically relevant drug concentrations was assessed over a 24-h period using an FID assay. All analogues were found to reduce the level of ethidium bromide-induced fluorescence in a concentration-dependent manner from the earliest time point of 10 min onwards. Cisplatin, however, showed a markedly slower reduction in ethidium bromide-induced fluorescence from 2 h onwards, producing a similar level of fluorescence reduction as that produced by the analogues from 6 h onwards. These results suggest that the altered DNA-binding modes of the DNA-targeted analogues confer a more efficient mechanism for DNA binding compared with cisplatin. Relative DNA binding coefficients were also determined for each of the compounds studied. With the DNA unwinding assay, an unwinding angle can be calculated from the coalescence point of plasmids in an agarose gel. It was found that all 9-aminoacridine carboxamide analogues had a greater unwinding angle compared with cisplatin. The knowledge obtained from these two assays has helped to further characterise the cisplatin analogues and could facilitate the development of more effective anti-tumour agents.

The influence of DNA methylation on the sequence specificity of UVB- and UVC-induced DNA damage

Ultraviolet light (UV) is one of the most common DNA damaging agents in the human environment. This paper examined the influence of DNA methylation on the level of UVB- and UVC-induced DNA damage. A purified DNA sequence containing CpG dinucleotides was methylated with a CpG methylase. We employed the linear amplification technique and the end-labelling approach followed by capillary electrophoresis with laser-induced fluorescence to investigate the sequence specificity of UV-induced DNA damage. The linear amplification technique mainly detects cyclobutane pyrimidine dimer (CPD) adducts, while the end-labelling approach mainly detects 6-4 photoproduct (6-4PP) lesions. The levels of CPD and 6-4PP adducts detected in methylated/unmethylated labelled sequences were analysed. The comparison showed that 5-methyl-cytosine significantly reduced the level of both CPD and 6-4PP adducts after UVB (308 nm) and UVC (254 nm) irradiation compared with the non-methylated counterpart.

Cisplatin-Mediated Upregulation of APE2 Binding to MYH9 Provokes Mitochondrial Fragmentation and Acute Kidney Injury

Cisplatin chemotherapy is standard care for many cancers but is toxic to the kidneys. How this toxicity occurs is uncertain. In this study, we identified apurinic/apyrimidinic endonuclease 2 (APE2) as a critical molecule upregulated in the proximal tubule cells (PTC) following cisplatin-induced nuclear DNA and mitochondrial DNA damage in cisplatin-treated C57B6J mice. The APE2 transgenic mouse phenotype recapitulated the pathophysiological features of C-AKI (acute kidney injury, AKI) in the absence of cisplatin treatment. APE2 pulldown-MS analysis revealed that APE2 binds myosin heavy-Chain 9 (MYH9) protein in mitochondria after cisplatin treatment. Human MYH9-related disorder is caused by mutations in MYH9 that eventually lead to nephritis, macrothrombocytopenia, and deafness, a constellation of symptoms similar to the toxicity profile of cisplatin. Moreover, cisplatin-induced C-AKI was attenuated in APE2-knockout mice. Taken together, these findings suggest that cisplatin promotes AKI development by upregulating APE2, which leads to subsequent MYH9 dysfunction in PTC mitochondria due to an unrelated role of APE2 in DNA damage repair. This postulated mechanism and the availability of an engineered transgenic mouse model based on the mechanism of C-AKI provides an opportunity to identify novel targets for prophylactic treatment of this serious disease. SIGNIFICANCE: These results reveal and highlight an unexpected role of APE2 via its interaction with MYH9 and suggest that APE2 has the potential to prevent acute kidney injury in patients with cisplatin-treated cancer. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/3/713/F1.large.jpg.

Interactions of Cisplatin and Daunorubicin at the Chromatin Level

Unexpectedly, the widely used anticancer agents Cisplatin (Cis-Pt) and Daunorubicin (Dauno) exhibited cell type- and concentration-dependent synergy or antagonism in vitro. We attempted to interpret these effects in terms of the changes elicited by the drugs in the chromatin, the target held primarily responsible for the cytotoxicity of both agents. We measured the effect of Cis-Pt on the levels of Dauno in different cell compartments, the effect of Cis-Pt on Dauno-induced nucleosome eviction, and assessed the influence of Dauno on DNA platination in flow- and laser scanning cytometry as well as in laser ablation-inductively coupled plasma-mass spectrometry assays. We show that the two drugs antagonize each other through a decrease of interstrand crosslinks upon co-treatment with Dauno, and also via the diminished Dauno uptake in the presence of Cis-Pt, and both effects are observed already at low Dauno concentrations. At high Dauno concentrations synergy becomes dominant because histone eviction by Dauno intercalation into the DNA is enhanced in the presence of co-treatment with Cis-Pt. These interactions may have an impact on the efficacy of combination treatment protocols, considering the long retention time of DNA adducts formed by both agents.

Long-term arterial complications of chemotherapy in patients with cancer

The number of cancer survivors has gradually increased in recent decades. However, the cancer survivors are at risk for conditions related to their initial disease and its treatment, i.e. surgery, systemic treatment or radiotherapy. Cardiovascular complications, such as myocardial infarction, are common side effects of these therapies. Cardiovascular damage can occur during treatment or month to years after the initial treatment, as late effect of the cancer treatment. The pathophysiology of these effects is not yet fully understood, but an important part of the cardiovascular complications are thought to be the result of effects of anticancer agents on the structural and functional properties of the endothelium. Because these conditions can result in a high degree of morbidity and mortality, understanding how to improve the prevention, recognition, and treatment of vascular disease is an important medical priority in the care for cancer survivors. This review will focus on the long-term arterial complications of chemotherapy in cancer survivors. It will summarize the epidemiology and pathophysiology of these complications. Furthermore, important long-term clinical conditions related to these effects will be outlined, including cardiovascular risk management in terms of prevention, evaluation and therapy.

Chemosensitizing and nephroprotective effect of resveratrol in cisplatin -treated animals

Background

Cisplatin (CIS) is one of the most effective anticancer drug used in the treatment of several solid tumors .Its use is limited by its nephrotoxicity. The present study was designed to assess the role of a natural product resveratrol (RSVL) on sensitization of mammary carcinoma (Ehrlich ascites carcinoma) to the action of CIS and the possible protective effect against CIS-induced nephrotoxicity in rats.

Methods

The percent survival of female tumor bearing mice was used for determination the cytotoxic activity of CIS in the presence or the absence of RSVL. Uptake and cell cycle effect, serum creatinine (CREA), blood urea nitrogen (BUN), Reduced Glutathione (GSH) and histopatholgical examination of kidney tissues after CIS and/or RSVL therapy were also investigated.

Results

RSVL increased the intracellular level of CIS in EAC cells and there was a strong correlation between the high cellular level of CIS and its cytotoxicity. CIS at a dose level of 5 mg/kg increased the mean survival time of female tumor bearing mice to 25 days compared with 17 days for tumor-bearing control mice. Administration of RSVL at a dose level of 25 mg/kg simultaneously with CIS increased the mean survival time to 48 days with 60% survival of the tumor-bearing animals. Cell cycle analysis of tumor cells showed that CIS treatment decreases the proliferation index of tumor cells while in presence of RSVL there was more significant inhibitions. Also, CIS treatment caused increase in level of creatinine and blood urea with significant decrease in the GSH level. While, in the presence of RSVL, level of creatinine and blood urea restored to control level.

Conclusion

This study suggests that RSVL could increase the cytotoxic activity of CIS and protect against its nephrotoxicity.

Ligand substitutions between ruthenium-cymene compounds can control protein versus DNA targeting and anticancer activity

Ruthenium compounds have become promising alternatives to platinum drugs by displaying specific activities against different cancers and favourable toxicity and clearance properties. Nonetheless, their molecular targeting and mechanism of action are poorly understood. Here we study two prototypical ruthenium-arene agents-the cytotoxic antiprimary tumour compound [(η(6)-p-cymene)Ru(ethylene-diamine)Cl]PF6 and the relatively non-cytotoxic antimetastasis compound [(η(6)-p-cymene)Ru(1,3,5-triaza-7-phosphaadamantane)Cl2]-and discover that the former targets the DNA of chromatin, while the latter preferentially forms adducts on the histone proteins. Using a novel 'atom-to-cell' approach, we establish the basis for the surprisingly site-selective adduct formation behaviour and distinct cellular impact of these two chemically similar anticancer agents, which suggests that the cytotoxic effects arise largely from DNA lesions, whereas the protein adducts may be linked to the other therapeutic activities. Our study shows promise for developing new ruthenium drugs, via ligand-based modulation of DNA versus protein binding and thus cytotoxic potential, to target distinguishing epigenetic features of cancer cells.

Protective effect of magnesium preloading on cisplatin-induced nephrotoxicity: a retrospective study

OBJECTIVE

Magnesium supplementation has been reported to have a nephroprotective effect on cisplatin-induced renal dysfunction, but little evidence exists regarding the effect of magnesium preloading before cisplatin administration. We started to include magnesium preloading (8 mEq) in cisplatin-containing treatment regimens in January 2011. The aim of the present study was to evaluate whether magnesium preloading reduces cisplatin-induced nephrotoxicity.

METHODS

We retrospectively reviewed 496 thoracic malignancy patients treated with cisplatin (≥60 mg/m²)-containing regimens as a first-time chemotherapy between January 2009 and December 2011. We compared the incidence of Grade ≥2 serum creatinine elevation according to the Common Terminology Criteria for Adverse Events, version 4.0, between magnesium preloading group (n = 161 [32%]) and non-magnesium preloading group (n = 335 [68%]) during the first cycle and all cycles.

RESULTS

The median number of administered cycles was four in both groups. The incidence of Grade ≥2 serum creatinine elevation in magnesium preloading group was significantly lower during both the first cycle and all cycles than in the non-magnesium preloading group (4.9 versus 19.1% during the first cycle, and 14.2 versus 39.7% during all the cycles). A multivariate analysis indicated that magnesium preloading significantly reduced cisplatin-induced nephrotoxicity throughout the entire period from after the first administration (odds ratio: 0.262, 95% confidence interval: 0.106-0.596 during the first cycle, and odds ratio: 0.234, 95% confidence interval: 0.129-0.414 during all cycles).

CONCLUSIONS

Magnesium preloading before cisplatin administration significantly reduced cisplatin-induced nephrotoxicity.

Comparative study of the possible protective effects of cinnamic acid and cinnamaldehyde on cisplatin-induced nephrotoxicity in rats

This study aimed to assess the protective effect of cinnamic acid (CA) and cinnamaldehyde (CD) against cisplatin-induced nephrotoxicity. A single dose of cisplatin (5 mg/kg), injected intraperitoneally to male rats, caused significant increases in serum urea, creatinine levels, and lipid peroxides measured as the malondialdehyde content of kidney, with significant decreases in serum albumin, reduced glutathione, and the activity of antioxidant enzymes (catalase, superoxide dismutase, and glutathione peroxidase) of kidney as compared with the control group. On the other hand, administration of CA (50 mg/kg, p.o.) or CD (40 mg/kg, p.o.) for 7 days before cisplatin ameliorated the cisplatin-induced nephrotoxicity as indicated by the restoration of kidney function and oxidative stress parameters. Furthermore, they reduced the histopathological changes induced by cisplatin. In conclusion, CA and CD showed protective effects against cisplatin-induced nephrotoxicity where CD was more effective than CA; affects that might be attributed to their antioxidant activities.

The evaluation of cisplatin effect on tubular function in children on chemotherapy

The dose limiting side effect of cisplatin is nephrotoxicity. The aim of this study was to investigate tubular function in children who have received cisplatin and forced diuresis. We performed a cohort study on 20 children under 15 years of age with various type of malignancy on cisplatin-based chemotherapy. Twenty-four-hour urine was collected in three periods: before the first, third, and fifth doses of cisplatin administration to check urine for sodium (Na), magnesium (Mg), uric acid, creatinine (Cr), phosphorus (P), calcium (Ca), beta-2 microglobulin, and N-acetyl-beta-D-glucosaminidase (NAG) levels. At the same time, blood samples were taken to check serum Cr, Na, Mg, Ca, P, and uric acid levels. Then, we compared the mean of glomerular filtration rate (GFR); fraction excretions (FE,%) of Na, Mg, and uric acid; tubular phosphorous reabsorption (TPR,%), 24-hour urine Ca (mg); urine beta-2 microglobulin (mcg/mL); and NAG (IU/L) in three periods of cisplatin administration. The FE of Na, Mg, and urine beta-2 microglobulin increased after administration of cisplatin but TPR, FE, uric acid, and NAG decreased in the 2nd and 3rd period compared to 1st period. GFR revealed a little change that was not significant. Urine calcium was decreased significantly in the second and third periods of cisplatin administration. Since the patients were hydrated for forced diuresis and received magnesium sulfate to prevent nephrotoxicity, we did not see significant tubular dysfunction. But we saw that urine calcium excretion decreased after cisplatin injection without any change in serum calcium in spite of preventive measures.

Bleomycin DNA damage: Anomalous mobility of 3'-phosphoglycolate termini in an automated capillary DNA sequencer

An automated capillary DNA sequencer with laser-induced fluorescence detection can be utilised for DNA fragment analysis. The precise mobilities of DNA fragments with different chemical termini are especially important in the determination of the sequence specificity of DNA damaging agents. The aim of this study was to examine the electrophoretic mobility profile of DNA fragments with different 3'-termini. The nature of the 3'-teminal residue was found to have a major effect on the electrophoretic mobility of the DNA fragment, especially for 3'-phosphoglycolate termini that migrated anomalously by 3-6 nucleotides. Using the automated capillary sequencer, the electrophoretic mobilities of DNA fragments with different 3'-termini including 3'-hydrogen, 3'-hydroxyl, 3'-phosphate, and 3'-phosphoglycolate were extensively quantified and compared relative to each other. The 3'-hydrogen termini were generated by dideoxy sequencing; 3'-hydroxyl ends by minus sequencing; 3'-phosphate by Maxam-Gilbert chemical sequencing; and 3'-phosphoglycolate by bleomycin cleavage. The mobilities of these DNA fragments with different 3'-termini were found to be: (slowest) 3'-hydroxyl<3'-hydrogen<3'-phosphate<3'-phosphoglycolate (fastest); with average relative mobilities of 0.00<0.12<0.63<4.42 nucleotides, respectively. The possible causes of the unusual electrophoretic mobility of the 3'-phosphoglycolate termini were discussed.

DNA methylation in cancer development, diagnosis and therapy--multiple opportunities for genotoxic agents to act as methylome disruptors or remediators

The role of DNA methylation and recently discovered hydroxymethylation in the function of the human epigenome is currently one of the hottest topics in the life sciences. Progress in this field of research has been further accelerated by the discovery that alterations in the methylome are not only associated with key functions of cells and organisms, such as development, differentiation and gene expression, but may underlie a number of human diseases, including cancer. This review describes both well established and more recent observations concerning alterations in the methylome, i.e. the global and local distribution of 5-methylcytosines, involved in its normal functions. Then, the changes in DNA methylation pattern seen in cancer cells are discussed in the context of their utilisation in cancer diagnostics and treatment. On this basis, comparisons are made between natural covalent DNA modification and that induced by genotoxic agents, chemical carcinogens and antitumour drugs as regards their impact on epigenetic mechanisms. The available data suggest that DNA damage by genotoxins can mimic epigenetic markers and in consequence disrupt the proper function of the epigenome. On the other hand, the same processes in cancer cells, e.g. DNA demethylation as a result of DNA methyltransferase blocking or the induction of DNA repair by DNA adducts, may restore the activity of hypermethylated anticancer genes. The observed multiple mechanisms by which genotoxic agents directly affect methylome function suggest that chemical carcinogens act primarily as epigenome disruptors, whereas mutations are secondary events that occur at later stages of cancer development when genome-protecting mechanisms have already been deregulated.

Germline polymorphisms discovered via a cell-based, genome-wide approach predict platinum response in head and neck cancers

Identifying patients prior to treatment who are more likely to benefit from chemotherapeutic agents or more likely to experience adverse events is an aim of personalized medicine. Pharmacogenomics offers a potential means of achieving this goal through the discovery of predictive germline genetic biomarkers. When applied particularly to the treatment of head and neck cancers, such information could offer significant benefit to patients as a means of potentially reducing morbidity associated with platinum-based chemotherapy. We developed a genome-wide, cell-based approach to identify single nucleotide polymorphisms (SNPs) associated with platinum susceptibility and then evaluated these SNPs as predictors for response and toxicity in head and neck cancer patients treated with platinum-based therapy as part of a phase II clinical trial. Sixty head and neck cancer patients were evaluated. Of 45 genome-wide SNPs examined, we found that 2 SNPs, rs6870861 (P=0.004; false discovery rate [FDR] <0.05) and rs2551038 (P=0.005; FDR <0.05), were associated significantly with overall response to carboplatin-based induction chemotherapy when incorporated into a model along with total carboplatin exposure. Interestingly, these 2 SNPs are associated strongly with the baseline expression of >20 genes (all P ≤10(-4)), and that 2 genes (SLC22A5 and SLCO4C1) are important organic cation/anion transporters known to affect platinum uptake and clearance. Several other SNPs were associated nominally with carboplatin-related hematologic toxicities. These findings demonstrate importantly that a genome-wide, cell-based model can identify novel germline genetic biomarkers of platinum susceptibility, which are replicable in a clinical setting with treated cancer patients and seem clinically meaningful for potentially enabling future personalization of care in such patients.

Consequences of cisplatin binding on nucleosome structure and dynamics

The effects of cisplatin binding to DNA were explored at the nucleosome level to incorporate key features of the eukaryotic nuclear environment. An X-ray crystal structure of a site-specifically platinated nucleosome carrying a 1,3-cis-{Pt(NH₃)₂}²+-d(GpTpG) intrastrand cross-link reveals the details of how this adduct dictates the rotational positioning of DNA in the nucleosome. Results from in vitro nucleosome mobility assays indicate that a single platinum adduct interferes with ATP-independent sliding of DNA around the octamer core. Data from in vitro transcription experiments suggest that RNA polymerases can successfully navigate along cisplatin-damaged DNA templates that contain nucleosomes, but stall when the transcription elongation complex physically contacts a platinum cross-link located on the template strand. These results provide information about the effects of cisplatin binding to nuclear DNA and enhance our understanding of the mechanism of transcription inhibition by platinum anticancer compounds.

Nucleosomes and cisplatin

In order to form a covalent complex with DNA inside human cells, cisplatin has to overcome the protective environment of a nucleosome, where DNA is complexed with histone proteins. Todd and Lippard (2010) expand our understanding of this process by describing the structure of a nucleosome containing a Pt-DNA adduct, which has important implications for more effective chemotherapeutic drug development.

The influence of chromatin structure on DNA damage induced by nitrogen mustard and cisplatin analogues

The interaction of anti-tumour drugs with reconstituted chromatin has been investigated using defined nucleosomal complexes. This allowed the effect of nucleosome cores on drug-induced DNA damage to be assessed for four nitrogen mustard analogues, dimethylsulphate and three cisplatin analogues. A defined nucleosomal complex was employed that contained two precisely positioned nucleosome cores. The construct was then subjected to drug treatment, and the resulting DNA damage was quantitatively analysed using a Taq DNA polymerase stop assay. At the sites of damage, densitometric comparisons between purified and reconstituted DNA were used to evaluate the influence of nucleosomal core proteins on specific drug-DNA interactions. Results were combined with previous data obtained for other DNA-damaging drugs investigated using the same nucleosomal construct. For most of the DNA-damaging agents studied, this method revealed protection at the positioned nucleosome cores and indicated that the preferred site of DNA binding for these compounds was in the linker region of the construct. Statistical analyses confirmed the significant level of damage protection conferred by the nucleosome cores and revealed differences between the examined compounds. Larger compounds generally displayed a greater tendency to target the linker region of the nucleosomal DNA and were impeded from damaging nucleosomal core DNA. In contrast, smaller molecules had greater access to nucleosomal core DNA.

Population differences in platinum toxicity as a means to identify novel genetic susceptibility variants

OBJECTIVES

Clinical studies show that Asians (ASN) are more susceptible to toxicities associated with platinum-containing regimens. We hypothesized that studying ASN as an 'enriched phenotype' population could enable the discovery of novel genetic determinants of platinum susceptibility.

METHODS

Using well-genotyped lymphoblastoid cell lines from the HapMap, we determined cisplatin and carboplatin cytotoxicity phenotypes (IC50s) for ASN, Caucasians (CEU), and Africans (YRI). IC50s were used in genome-wide association studies.

RESULTS

ASN were most sensitive to platinums, corroborating clinical findings. ASN genome-wide association studies produced 479 single-nucleotide polymorphisms (SNPs) associating with cisplatin susceptibility and 199 with carboplatin susceptibility (P<10). Considering only the most significant variants (P<9.99x10), backwards elimination was then used to identify reduced-model SNPs, which robustly described the drug phenotypes within ASN. These SNPs comprised highly descriptive genetic signatures of susceptibility, with 12 SNPs explaining more than 95% of the susceptibility phenotype variation for cisplatin, and eight SNPs approximately 75% for carboplatin. To determine the possible function of these variants in ASN, the SNPs were tested for association with differential expression of target genes. SNPs were highly associated with the expression of multiple target genes, and notably, the histone H3 family was implicated for both drugs, suggesting a platinum-class mechanism. Histone H3 has repeatedly been described as regulating the formation of platinum-DNA adducts, but this is the first evidence that specific genetic variants might mediate these interactions in a pharmacogenetic manner. Finally, to determine whether any ASN-identified SNPs might also be important in other human populations, we interrogated all 479/199 SNPs for association with platinum susceptibility in an independent combined CEU/YRI population. Three unique SNPs for cisplatin and 10 for carboplatin replicated in CEU/YRI.

CONCLUSION

Enriched 'platinum susceptible' populations can be used to discover novel genetic determinants governing interindividual platinum chemotherapy susceptibility.

DNA cleavage and binding selectivity of a heterodinuclear Pt-Cu(3-Clip-Phen) complex

The synthesis and nuclease activity of a new bifunctional heterodinuclear platinum–copper complex are reported. The design of this ditopic coordination compound is based on the specific mode of action of each component, namely, cisplatin and Cu(3-Clip-Phen), where 3-Clip-Phen is 1-(1,10-phenanthrolin-3-yloxy)-3-(1,10-phenanthrolin-8-yloxy)propan-2-amine. Cisplatin is not only able to direct the Cu(3-Clip-Phen) part to the GG or AG site, but also acts as a kinetically inert DNA anchor. The nuclease activity of this complex has been investigated on supercoiled DNA. The dinuclear compound is not only more active than Cu(3-Clip-Phen), but is also capable of inducing direct double-strand breaks. The sequence selectivity of the mononuclear platinum complex has been investigated by primer extension experiments, which reveal that its interaction with DNA occurs at the same sites as for cisplatin. The Taq polymerase recognizes the resulting DNA damage as different from that for unmodified cisplatin. The sequence-selective cleavage has been investigated by high-resolution gel electrophoresis on a 36-bp DNA fragment. Sequence-selective cleavages are observed in the close proximity of the platinum sites for the strand exhibiting the preferential platinum binding sites. The platinum moiety also coordinates to the other DNA strand, most likely leading only to mono guanine or adenine adducts.

A 1,2-d(GpG) cisplatin intrastrand cross-link influences the rotational and translational setting of DNA in nucleosomes

The mechanism of action of platinum-based anticancer drugs such as cis-diamminedichloroplatinum(II), or cisplatin, involves three early steps: cell entry, drug activation, and target binding. A major target in the cell, responsible for the anticancer activity, is nuclear DNA, which is packaged in nucleosomes that comprise chromatin. It is important to understand the nature of platinum-DNA interactions at the level of the nucleosome. The cis-{Pt(NH3)2}2+ 1,2-d(GpG) intrastrand cross-link is the DNA lesion most commonly encountered following cisplatin treatment. We therefore assembled two site-specifically platinated nucleosomes using synthetic DNA containing defined cis-{Pt(NH3)2}2+ 1,2-d(GpG) cross-links and core histones from HeLa-S3 cancer cells. The structures of these complexes were investigated by hydroxyl radical footprinting and exonuclease III mapping. Our experiments demonstrate that the 1,2-d(GpG) cross-link alters the rotational setting of the DNA on the histone octamer core such that the lesion faces inward, with disposition angles of the major groove relative to the core of xi approximately -20 degrees and xi approximately 40 degrees . We observe increased solvent accessibility of the platinated DNA strand, which may be caused by a structural perturbation in proximity of the 1,2-d(GpG) cisplatin lesion. The effect of the 1,2-d(GpG) cisplatin adduct on the translational setting of the nucleosomal DNA depends strongly on the position of the adduct within the sequence. If the cross-link is located at a site that is in phase with the preferred rotational setting of the unplatinated nucleosomal DNA, the effect on the translational position is negligible. Minor exonuclease III digestion products in this substrate indicate that the cisplatin adduct permits only those translational settings that differ from one another by integral numbers of DNA helical turns. If the lesion is located out of phase with the preferred rotational setting, the translational position of the main conformation was shifted by 5 bp. Additionally, a fraction of platinated nucleosomes with widely distributed translational positions was observed, suggesting increased nucleosome sliding relative to platinated nucleosomes containing the 1,3-intrastrand d(GpTpG) cross-link investigated previously (Ober, M.; Lippard, S. J. J. Am. Chem. Soc. 2007, 129, 6278-6286).

Site selectivity of platinum anticancer therapeutics

X-ray crystallographic and biochemical investigation of the reaction of cisplatin and oxaliplatin with nucleosome core particle and naked DNA reveals that histone octamer association can modulate DNA platination. Adduct formation also occurs at specific histone methionine residues, which could serve as a nuclear platinum reservoir influencing adduct transfer to DNA. Our findings suggest that the nucleosome center may provide a favorable target for the design of improved platinum anticancer drugs.

Chromatin as a target for the DNA-binding anticancer drugs

Chemotherapy has been a major approach to treat cancer. Both constituents of chromatin, chromosomal DNA and the associated chromosomal histone proteins are the molecular targets of the anticancer drugs. Small DNA binding ligands, which inhibit enzymatic processes with DNA substrate, are well known in cancer chemotherapy. These drugs inhibit the polymerase and topoisomerase activity. With the advent in the knowledge of chromatin chemistry and biology, attempts have shifted from studies of the structural basis of the association of these drugs or small ligands (with the potential of drugs) with DNA to their association with chromatin and nucleosome. These drugs often inhibit the expression of specific genes leading to a series of biochemical events. An overview will be given about the latest understanding of the molecular basis of their action. We shall restrict to those drugs, synthetic or natural, whose prime cellular targets are so far known to be chromosomal DNA.

Cisplatin-induced apoptosis in cultures of human Schwann cells

To investigate the sensitivity of human Schwann cells to cisplatin (cis-DDP), different approaches to estimate DNA damage were used: the comet assay, morphological evaluation of the granular condensation of nuclear chromatin and the terminal transferase-mediated dUTP nick-end-labelling (TUNEL) method. The number of micronuclei (MNi), as a sign of cisplatin-induced genotoxicity, was counted. DNA damage assessed by the comet assay was already evident after 1.5 microM cisplatin treatment at all exposure times (24, 48, and 72 h). Initial morphological changes characterised by the granular condensation of nuclear chromatin were detectable after 24 h exposure to 25 microM cis-DDP, while an increased number of apoptotic cells, determined by the TUNEL method, was noted after 48 h exposure to the same concentration. The first significant increase in the number of MNi was observed in cells treated with 75 microM cis-DDP for 24 h. We demonstrate that the comet assay is a highly sensitive method for measuring cisplatin induced DNA damage. Morphological observation revealed advanced as well as less prominent alterations in the nuclear chromatin. In contrast, the TUNEL method detected only those cells with advanced DNA fragmentation.

Modifications of DNA by platinum complexes. Relation to resistance of tumors to platinum antitumor drugs

The importance of platinum drugs in cancer chemotherapy is underscored by the clinical success of cisplatin [cis-diamminedichloroplatinum(II)] and its analogues and by clinical trials of other, less toxic platinum complexes that are active against resistant tumors. The antitumor effect of platinum complexes is believed to result from their ability to form various types of adducts with DNA. Nevertheless, drug resistance can occur by several ways: increased drug efflux, drug inactivation, alterations in drug target, processing of drug-induced damage, and evasion of apoptosis. This review focuses on mechanisms of resistance and sensitivity of tumors to conventional cisplatin associated with DNA modifications. We also discuss molecular mechanisms underlying resistance and sensitivity of tumors to the new platinum compounds synthesized with the goal to overcome resistance of tumors to established platinum drugs. Importantly, a number of new platinum compounds were designed to test the hypothesis that there is a correlation between the extent of resistance of tumors to these agents and their ability to induce a certain kind of damage or conformational change in DNA. Hence, information on DNA-binding modes, as well as recognition and repair of DNA damage is discussed, since this information may be exploited for improved structure-activity relationships.

Cellular processing of platinum anticancer drugs

Cisplatin, carboplatin and oxaliplatin are platinum-based drugs that are widely used in cancer chemotherapy. Platinum-DNA adducts, which are formed following uptake of the drug into the nucleus of cells, activate several cellular processes that mediate the cytotoxicity of these platinum drugs. This review focuses on recently discovered cellular pathways that are activated in response to cisplatin, including those involved in regulating drug uptake, the signalling of DNA damage, cell-cycle checkpoints and arrest, DNA repair and cell death. Such knowledge of the cellular processing of cisplatin adducts with DNA provides valuable clues for the rational design of more efficient platinum-based drugs as well as the development of new therapeutic strategies.