Cisplatin damage: are DNA repair proteins saviors or traitors to the cell?

Modes of Interactions with DNA/HSA Biomolecules and Comparative Cytotoxic Studies of Newly Synthesized Mononuclear Zinc(II) and Heteronuclear Platinum(II)/Zinc(II) Complexes toward Colorectal Cancer Cells

A series of mono- and heteronuclear platinum(II) and zinc(II) complexes with 4,4',4″-tri-tert-butyl-2,2':6',2″-terpyridine ligand were synthesized and characterized. The DNA and protein binding properties of [ZnCl2(terpytBu)] (C1), [{cis-PtCl(NH3)2(μ-pyrazine)ZnCl(terpytBu)}](ClO4)2 (C2), [{trans-PtCl(NH3)2(μ-pyrazine)ZnCl(terpytBu)}](ClO4)2 (C3), [{cis-PtCl(NH3)2(μ-4,4'-bipyridyl)ZnCl(terpytBu)}](CIO4)2 (C4) and [{trans-PtCl(NH3)2(μ-4,4'-bipyridyl)ZnCl(terpytBu)}](CIO4)2 (C5) (where terpytBu = 4,4',4″-tri-tert-butyl-2,2':6',2″-terpyridine), were investigated by electronic absorption, fluorescence spectroscopic, and molecular docking methods. Complexes featuring transplatin exhibited lower Kb and Ksv constant values compared to cisplatin analogs. The lowest Ksv value belonged to complex C1, while C4 exhibited the highest. Molecular docking studies reveal that the binding of complex C1 to DNA is due to van der Waals forces, while that of C2-C5 is due to conventional hydrogen bonds and van der Waals forces. The tested complexes exhibited variable cytotoxicity toward mouse colorectal carcinoma (CT26), human colorectal carcinoma (HCT116 and SW480), and non-cancerous mouse mesenchymal stem cells (mMSC). Particularly, the mononuclear C1 complex showed pronounced selectivity toward cancer cells over non-cancerous mMSC. The C1 complex notably induced apoptosis in CT26 cells, effectively arrested the cell cycle in the G0/G1 phase, and selectively down-regulated Cyclin D.

Tumor Cells Transmit Drug Resistance via Cisplatin-Induced Extracellular Vesicles

Cisplatin is a first-line clinical agent used for treating solid tumors. Cisplatin damages the DNA of tumor cells and induces the production of high levels of reactive oxygen species to achieve tumor killing. Tumor cells have evolved several ways to tolerate this damage. Extracellular vesicles (EVs) are an important mode of information transfer in tumor cells. EVs can be substantially activated under cisplatin treatment and mediate different responses of tumor cells under cisplatin treatment depending on their different cargoes. However, the mechanism of action of tumor-cell-derived EVs under cisplatin treatment and their potential cargoes are still unclear. This review considers recent advances in cisplatin-induced release of EVs from tumor cells, with the expectation of providing a new understanding of the mechanisms of cisplatin treatment and drug resistance, as well as strategies for the combined use of cisplatin and other drugs.

Controlling the reactivity of [Pd(II)(N^N^N)Cl]+ complexes using 2,6-bis(pyrazol-2-yl)pyridine ligands for biological application: Substitution reactivity, CT-DNA interactions and in vitro cytotoxicity study

Four [(N^N^N)Pd^(II)Cl]⁺ complexes [chloride-(2,2':6',2''-terpyridine)Pd(II)]Cl (PdL1), [chlorido(2,6-bis(N-pyrazol-2-yl)pyridine)Pd(II)]Cl (PdL2), [chlorido(2,6-bis(3,5-dimethyl-N-pyrazol-2-yl)pyridine)Pd(II)]Cl (PdL3) and [chlorido(2,6-bis(3,5-dimethyl-N-pyrazol-2-ylmethyl)pyridine)Pd(II)]BF₄ (PdL4) were synthesized and characterized. The rates of substitution of these Pd(II) complexes with thiourea nucleophiles viz; thiourea (Tu), N,N'-dimethylthiourea (Dmtu) and N,N,N',N'-tetramethylthiourea (Tmtu) was investigated under pseudo first-order conditions as a function of nucleophile concentration [Nu] and temperature using the stopped-flow technique. The observed rate constants vary linearly with [Nu]; k_obs = k₂[Nu] and decreased in the order: PdL1 > PdL2 > PdL3 ≫ PdL4. The lower π-acceptability of the cis-coordinated N-pyrazol-2-yl groups (which coordinates via pyrazollic-N π-donor atoms) of the PdL2-4 significantly decelerates the reactivity relative to PdL1. Furthermore, the six-membered chelates having methylene bridge in PdL4 do not allow π-extension in the ligand and introduces steric hindrance further lowering the reactivity. Trends in DFT calculated data supported the observed reactivity trend. Spectrophotometric titration data of complexes with calf thymus DNA (CT-DNA) and viscosity measurements of the resultant mixtures suggested that associative interactions occur between the complexes and CT-DNA, likely through groove binding with high binding constants (K_b = 10⁴ M^-1). In vitro MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] cytotoxic activity data showed that PdL1 was the most potent complex against MCF7 breast cancer cells; its IC₅₀ value is lower than that of cisplatin. The results demonstrate how modification of a spectator ligand can be used to slow down the reactivity of Pd(II) complexes. This is of special importance in controlling drug toxicity in both pharmaceutical and biomedical applications.

Cytotoxic Effects of Plant Sap-Derived Extracellular Vesicles on Various Tumor Cell Types

Edible plants have been widely used in traditional therapeutics because of the biological activities of their natural ingredients, including anticancer, antioxidant, and anti-inflammatory properties. Plant sap contains such medicinal substances and their secondary metabolites provide unique chemical structures that contribute to their therapeutic efficacy. Plant extracts are known to contain a variety of extracellular vesicles (EVs) but the effects of such EVs on various cancers have not been investigated. Here, we extracted EVs from four plants-Dendropanax morbifera, Pinus densiflora, Thuja occidentalis, and Chamaecyparis obtusa-that are known to have cytotoxic effects. We evaluated the cytotoxic effects of these EVs by assessing their ability to selectively reduce the viability of various tumor cell types compared with normal cells and low metastatic cells. EVs from D. morbifera and P. densiflora sap showed strong cytotoxic effects on tumor cells, whereas those from T. occidentalis and C. obtusa had no significant effect on any tumor cell types. We also identified synergistic effect of EVs from D. morbifera and P. densiflora saps on breast and skin tumor cells and established optimized treatment concentrations. Our findings suggest these EVs from plant sap as new candidates for cancer treatment.

Comparison of responsiveness to cancer development and anti-cancer drug in three different C57BL/6N stocks

In our efforts to understand the systemic features of tumors, the importance of animal models is increasing due to the recent growth in the development of immunotherapy and targeted therapies. This has resulted in increased attention towards tumor animal models using C57BL/6N, which are mainly used in immunological studies. In this study, the C57BL/6NKorl stock and two other commercial stocks (C57BL/6NA and C57BL/N6B) are evaluated by comparing the occurrence of tumors using the syngeneic model; furthermore, we compare the response to anti-cancer drugs in the syngeneic model by evaluating survival, growth of tumors, proliferation and molecular biology analysis. In the syngeneic model using LLC (Lewis lung carcinoma) cells, the survival of mice and growth of the tumor showed a better response in the C57BL/6NKorl stock, and was dependent on the cell concentration of the dosing tumor, as compared to the other C57BL/6N stocks. However, the Ki-67 staining showed only little difference in cell proliferation within the tumor tissue each mouse stocks. Comparing the sensitivity to anti-cancer drug by examining changes in growth, volume and weight revealed that cisplatin treatment for tumor-bearing C57BL/6NKorl was more dependent on concentration. The Ki-67 staining, however, showed no difference among the C57BL/6N stocks after cisplatin treatment. The expressions of p27 and p53 tumor suppressor proteins, caspase-3 and Bax showed dose-dependent increase after exposure to cisplatin, whereas the expression of Bcl-2 was reduced in a dose-dependent manner. Furthermore, the expressions of MMP-2 and VEGF involved in metastasis, as well as inflammatory genes IL-1β, IL-6 and IL-10, showed dose-dependent decrease in tumor tissue after cisplatin exposure. Differences observed among the C57BL/6N stocks were not significant. Taken together, our studies reveal that C57BL/6NKorl has the potential of being a useful biological resource established in Korea, as it does not differ from the two commercially available C57BL/6N stocks when considering response to tumor generation and sensitivity to anti-cancer drugs using the syngeneic tumor model.

Hsa_circ_0001946 Inhibits Lung Cancer Progression and Mediates Cisplatin Sensitivity in Non-small Cell Lung Cancer via the Nucleotide Excision Repair Signaling Pathway

Background: Despite great advances in the diagnosis and treatment of non-small cell lung cancer (NSCLC), early diagnosis remains a challenge because patients usually have advanced lung cancer at the time they are diagnosed. The limited efficacy of conventional chemotherapy is another major problem in the treatment of NSCLC. Based on a published set of sequencing data, we find that hsa_circ_0001946 is a circRNA molecule with a significantly different expression level in three cell lines (human normal lung fibroblasts cell line MRC-5, human NSCLC cell line A549, cisplatin-resistant cell line A549/DDP), NSCLC tissues and paired adjacent normal tissues. We believe that hsa_circ_0001946 may have an effect on the progression of NSCLC and its sensitivity to cisplatin.

Methods: We focused on investigating the circular RNA, hsa_circ_0001946. RNA interference of hsa_circ_0001946 was carried out in A549 cell lines to determine the effect of reduced hsa_circ_0001946 expression on lung cancer progression and was analyzed by Cell Counting Kit-8 (CCK-8), 5-ethynyl-20-deoxyuridine, clone formation, Hoechst, wound healing, and transwell assays. The nucleotide excision repair (NER) signaling pathway was identified by Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. Moreover, cellular responses to cisplatin were assessed through CCK-8 and flow cytometry assays. Western blot analysis and host-cell reactivation assay were used to determine the effect of hsa_circ_0001946 on NER signaling.

Results: In this study, we found that the reduced expression of hsa_circ_0001946 promoted the viability, proliferation, migration, and invasion of NSCLC cells, as well as inhibition of cell apoptosis. Our findings suggest that hsa_circ_0001946 can affect the sensitivity of NSCLC cells to the chemotherapeutic drug cisplatin via modulation of the NER signaling pathway.

Conclusions: Our study demonstrated the role of hsa_circ_0001946 in NSCLC pathogenesis, development, and chemosensitivity, and suggests that hsa_circ_0001946 may serve as a novel biomarker for the diagnosis and prediction of platinum-based chemosensitivity in patients with NSCLC.

Cisplatin: The first metal based anticancer drug

Cisplatin or (SP-4-2)-diamminedichloridoplatinum(II) is one of the most potential and widely used drugs for the treatment of various solid cancers such as testicular, ovarian, head and neck, bladder, lung, cervical cancer, melanoma, lymphomas and several others. Cisplatin exerts anticancer activity via multiple mechanisms but its most acceptable mechanism involves generation of DNA lesions by interacting with purine bases on DNA followed by activation of several signal transduction pathways which finally lead to apoptosis. However, side effects and drug resistance are the two inherent challenges of cisplatin which limit its application and effectiveness. Reduction of drug accumulation inside cancer cells, inactivation of drug by reacting with glutathione and metallothioneins and faster repairing of DNA lesions are responsible for cisplatin resistance. To minimize cisplatin side effects and resistance, combination therapies are used and have proven more effective to defect cancers. This article highlights a systematic description on cisplatin which includes a brief history, synthesis, action mechanism, resistance, uses, side effects and modulation of side effects. It also briefly describes development of platinum drugs from very small cisplatin complex to very large next generation nanocarriers conjugated platinum complexes.

The anticancer effects and mechanisms of fucoxanthin combined with other drugs

PURPOSE

Fucoxanthin (Fx) is a characteristic carotenoid present in brown seaweed that has been shown to have various benefits, including anticancer effects. In vitro studies demonstrated these various effects, including the suppression of cell viability, the promotion of apoptosis, and antiangiogenic, antiproliferative, and antimetastatic activity. Interestingly, combinations of Fx with other drugs have better effects than either Fx or other drugs alone. Although the antiproliferative and cancer prevention activities of the combination of Fx and other drugs are still unclear, several effects have been discovered, including the induction of apoptosis, cell cycle arrest at G1/G0, enhanced gap junctional intercellular communication, and the induction of autophagy via various mechanisms, such as decreasing P-gp, activating the CYP3A4 promoter, increasing reactive oxygen species and cellular uptake and suppressing the PI3K/Akt/NFκB pathway. In this review, we address the anticancer effects and mechanisms of the combination of Fx and other drugs in different types of cancer.

METHODS

The relevant literature from PubMed and Web of Science databases is reviewed in this article.

RESULTS

Fx combined with other drugs could enhance the effect of both Fx and the other drug or reduce the dose without reducing the effect, which may create more effective and less harmful therapeutic strategies.

CONCLUSION

Fx combined with other drugs has significant anticancer effects by various mechanisms and could be a potential therapeutic strategy for different types of cancer.

Investigating the Frequency of the ERCC1 Gene C8092A Polymorphism in Iranian Patients with Advanced Gastric Cancer Receiving Platinum-based Chemotherapy

BACKGROUND

Platinum compounds are the main drugs for treatment of advanced gastric cancer. Previous studies have shown that clinical outcome with platinum-based compounds depends on ERCC1 polymorphisms. The aim of this study was to investigate the frequency of a common polymorphism of ERCC1 gene (C8092A) in Iranian patients with advanced gastric cancer receiving platinum chemotherapy.

MATERIALS AND METHODS

Genetic analysis of the ERCC1 C8092A polymorphism was performed by the PCR - RFLP method using 50 paraffin-embedded tissue specimens.

RESULTS

Of the 50 cases, 32% of individuals showed CC genotype, 24% of them had CA genotype and 44% of patients had AA genotype.

CONCLUSIONS

Based on the results, using of platinum-based chemotherapy would be expected to be specifically beneficial in only 32% of patients.

Role of Protein Linked DNA Breaks in Cancer

Topoisomerases are a group of specialized enzymes that function to maintain DNA topology by introducing transient DNA breaks during transcription and replication. As a result of abortive topoisomerases activity, topoisomerases catalytic intermediates may be trapped on the DNA forming topoisomerase cleavage complexes (Topcc). Topoisomerases trapping on the DNA is the mode of action of several anticancer drugs, it lead to formation of protein linked DAN breaks (PDBs). PDBs are now considered as one of the most dangerous forms of endogenous DNA damage and a major threat to genomic stability. The repair of PDBs involves both the sensing and repair pathways. Unsuccessful repair of PDBs leads to different signs of genomic instabilities such as chromosomal rearrangements and cancer predisposition. In this chapter we will summarize the role of topoisomerases induced PDBs, identification and signaling, repair, role in transcription. We will also discuss the role of PDBs in cancer with a special focus on prostate cancer.

Quercetin induces endoplasmic reticulum stress to enhance cDDP cytotoxicity in ovarian cancer: involvement of STAT3 signaling

There is an urgent need to make cisplatin (cDDP) more effective and less toxic in the treatment of ovarian cancer for its systemic side effects and high resistance rate. In this study, we investigated the effect of quercetin (Qu) pretreatment on the potentiation of cDDP in ovarian cancer. We found that Qu pretreatment significantly enhanced cDDP cytotoxicity in an ovarian cancer cell line and primary cancer cells. In addition, we demonstrated that Qu elicited obvious endoplasmic reticulum stress (ERS) and activated all three branches of ERS in ovarian cancer. Specific inhibitors of each ERS pathway, as well as the general ERS stabilizer tauroursodeoxycholic acid, notably diminished such enhancing effects. Furthermore, Qu notably suppressed STAT3 phosphorylation, leading to downregulation of the BCL-2 gene downstream of STAT3. Moreover, blocking ERS restored the protein levels of phosphorylated STAT3 as well as BCL-2 expression, thus abolishing the chemosensitization potency of Qu; these results revealed that Qu affected the STAT3 pathway to enhance cDDP cytotoxicity, and this effect involved ERS signaling. In a xenograft mouse model of ovarian cancer, Qu enhanced the antitumor effect of cDDP. Tumors from mice treated with cDDP in combination with Qu pretreatment had repressed STAT3 phosphorylation, lower BCL-2 and higher apoptosis levels compared with those from the other groups. Meanwhile, Qu markedly reduced the elevation of blood creatinine during cDDP intervention. These data indicate that Qu pretreatment potentiates the antitumor effects of cDDP in ovarian cancer while protecting the kidneys against damage. Therefore the strategy of Qu pretreatment may be beneficial in enhancing the therapeutic efficacy of cDDP against ovarian cancer.

Palladium(ii) complexes with highly basic imidazolin-2-imines and their reactivity toward small bio-molecules

Pd(ii) complexes with chelating imidazolin-2-imine ligands were synthesized, and the pK_a values and reactivity of these complexes were investigated.

A versatile methodology for the regioselective C⁸-metalation of purine bases

Purine nucleobases are excellent ligands for metal ions, forming normally coordinative Werner-type bonds by utilizing the N donor atoms of the nucleobase skeleton. Here we show that purines such as 8-chlorocaffeine and 8-bromo-9-methyladenine react with [Pt(PPh3)4] under oxidative addition of the C(8)-halogen bond to the metal center. The resulting Pt(II) complexes feature a C(8)-bound ylidene ligand. Protonation of the ylidene at the N(7/9)-atom yields complexes bearing a protic N-heterocyclic carbene ligand derived from the purine base with an NMe,NH-substitution pattern.

The use of X-ray absorption and synchrotron based micro-X-ray fluorescence spectroscopy to investigate anti-cancer metal compounds in vivo and in vitro

X-ray absorption spectroscopy (XAS) and micro-synchrotron based X-ray fluorescence (micro-SXRF) are element specific spectroscopic techniques and have been proven to be valuable tools for the investigation of changes in the chemical environment of metal centres. XAS allows the determination of the oxidation state, the coordination motif of the probed element, the identity and the number of adjacent atoms and the absorber-ligand distances. It is further applicable to nearly all types of samples independent of their actual physical state (solid, liquid, gaseous) down to μM concentrations. Micro-SXRF can provide information on the distribution and concentration of multiple elements within a sample simultaneously, allowing for the chemical state of several elements within subcellular compartments to be probed. Modern third generation synchrotrons offer the possibility to investigate the majority of the biologically relevant elements. The biological mode of action of metal-based compounds often involves interactions with target and/or transport molecules. The presence of reducing agents may also give rise to changes in the coordination sphere and/or the oxidation state. XAS and micro-SXRF are ideal techniques for investigating these issues. This tutorial review introduces the use of XAS and micro-SXRF techniques into the field of inorganic medicinal chemistry. The results obtained for platinum, ruthenium, gallium, gold and cobalt compounds within the last few years are presented.

Fucoxanthin: a marine carotenoid exerting anti-cancer effects by affecting multiple mechanisms

Fucoxanthin is a marine carotenoid exhibiting several health benefits. The anti-cancer effect of fucoxanthin and its deacetylated metabolite, fucoxanthinol, is well documented. In view of its potent anti-carcinogenic activity, the need to understand the underlying mechanisms has gained prominence. Towards achieving this goal, several researchers have carried out studies in various cell lines and in vivo and have deciphered that fucoxanthin exerts its anti-proliferative and cancer preventing influence via different molecules and pathways including the Bcl-2 proteins, MAPK, NFκB, Caspases, GADD45, and several other molecules that are involved in either cell cycle arrest, apoptosis, or metastasis. Thus, in addition to decreasing the frequency of occurrence and growth of tumours, fucoxanthin has a cytotoxic effect on cancer cells. Some studies show that this effect is selective, i.e., fucoxanthin has the capability to target cancer cells only, leaving normal physiological cells unaffected/less affected. Hence, fucoxanthin and its metabolites show great promise as chemotherapeutic agents in cancer.

Biological evaluation of transdichloridoplatinum(II) complexes with 3- and 4-acetylpyridine in comparison to cisplatin

BACKGROUND

In our previous study we reported the synthesis and cytotoxicity of two trans-platinum(II) complexes: trans-[PtCl2(3-acetylpyridine)2] (1) and trans-[PtCl2(4-acetylpyridine)2] (2), revealing significant cytotoxic potential of 2. In order to evaluate the mechanism underlying biological activity of both trans-Pt(II) isomers, comparative studies versus cisplatin were performed in HeLa, MRC-5 and MS1 cells.

MATERIALS AND METHODS

The cytotoxic activity of the investigated complexes was determined using SRB assay. The colagenolytic activity was determined using gelatin zymography, while the effect of platinum complexes on matrix metalloproteinases 2 and 9 mRNA expression was evaluated by quantitative real-time PCR. Apoptotic potential and cell cycle alterations were determined by FACS analyses. Western blot analysis was used to evaluate the effect on expression of DNA-repair enzyme ERCC1, and quantitative real-time PCR was used for the ERCC1 mRNA expression analysis. In vitro antiangiogenic potential was determined by tube formation assay. Platinum content in intracellular DNA and proteins was determined by inductively coupled plasma-optical emission spectrometry.

RESULTS

Compound 2 displayed an apparent cytoselective profile, and flow cytometry analysis in HeLa cells indicated that 2 exerted antiproliferative effect through apoptosis induction, while 1 induced both apoptosis and necrosis. Action of 1 and 2, as analyzed by quantitative real-time PCR and Western blot, was associated with down-regulation of ERCC1. Both trans-complexes inhibited MMP-9 mRNA expression in HeLa, while 2 significantly abrogated in vitro tubulogenesis in MS1 cells.

CONCLUSIONS

The ability of 2 to induce multiple and selective in vitro cytotoxic effects encourages further investigations of trans-platinum(II) complexes with substituted pyridines.

Fucoxanthin enhances cisplatin-induced cytotoxicity via NFκB-mediated pathway and downregulates DNA repair gene expression in human hepatoma HepG2 cells

Cisplain, a platinum-containing anticancer drug, has been shown to enhance DNA repair and to inhibit cell apoptosis, leading to drug resistance. Thus, the combination of anticancer drugs with nutritional factors is a potential strategy for improving the efficacy of cisplatin chemotherapy. In this study, we investigated the anti-proliferative effects of a combination of fucoxanthin, the major non-provitamin A carotenoid found in Undaria Pinnatifida, and cisplatin in human hepatoma HepG2 cells. We found that fucoxanthin (1–10 μΜ) pretreatment for 24 h followed by cisplatin (10 μΜ) for 24 h significantly decreased cell proliferation, as compared with cisplatin treatment alone. Mechanistically, we showed that fucoxanthin attenuated cisplatin-induced NFκB expression and enhanced the NFκB-regulated Bax/Bcl-2 mRNA ratio. Cisplatin alone induced mRNA expression of excision repair cross complementation 1 (ERCC1) and thymidine phosphorylase (TP) through phosphorylation of ERK, p38 and PI3K/AKT pathways. However, fucoxanthin pretreatment significantly attenuated cisplatin-induced ERCC1 and TP mRNA expression, leading to improvement of chemotherapeutic efficacy of cisplatin. The results suggest that a combined treatment with fucoxanthin and cisplatin could lead to a potentially important new therapeutic strategy against human hepatoma cells.

The selective synthesis of metallanucleosides and metallanucleotides: a new tool for the functionalization of nucleic acids

Nucleobases team up: the efficient and selective preparation of purine-derived metallanucleosides, metallanucleotides, and metalladinucleotides having M-C bonds (M=Ir(III), Rh(III)) is reported for the first time. The results presented may be applied to the synthesis of functionalized nucleic acids, or DNA/RNA-modified segments.

Substitution behaviour of novel dinuclear Pt(II) complexes with bio-relevant nucleophiles

The novel dinuclear Pt(II) complexes [{trans-Pt(NH(3))(2)Cl}(2)(μ-pyrazine)](ClO(4))(2) (Pt1), [{trans-Pt(NH(3))(2)Cl}(2)(μ-4,4'-bipyridyl)](ClO(4))(2)·DMF (Pt2), and [{trans-Pt(NH(3))(2)Cl}(2)(μ-1,2-bis(4-pyridyl)ethane)](ClO(4))(2) (Pt3), were synthesized. Acid-base titrations, and temperature and concentration dependent kinetic measurements of the reactions with biologically relevant ligands such as thiourea (Tu), glutathione (GSH) and guanosine-5'-monophosphate (5'-GMP) were studied at pH 2.5 and 7.2. The reactions were followed under pseudo-first-order conditions by stopped-flow and UV-vis spectrophotometry. (1)H NMR spectroscopy was used to follow the substitution of chloride in the complex [{trans-Pt(NH(3))(2)Cl}(2)(μ-4,4'-bipyridyl)](ClO(4))(2)·DMF by guanosine-5'-monophosphate (5'-GMP) under second-order conditions. The results indicate that the bridging ligand has an influence on the reactivity of the complexes towards nucleophiles. The order of reactivity of the investigated complexes is Pt1 > Pt2 > Pt3.

Concordant and opposite roles of DNA-PK and the "facilitator of chromatin transcription" (FACT) in DNA repair, apoptosis and necrosis after cisplatin

Background

Platinum-containing chemotherapy produces specific DNA damage and is used to treat several human solid tumors. Tumors initially sensitive to platinum-based drugs frequently become resistant. Inhibition of DNA repair is a potential strategy to enhance cisplatin effectiveness. After cisplatin treatment, a balance between repair and apoptosis determines whether cancer cells proliferate or die. DNA-dependent protein kinase (DNA-PK) binds to DNA double strand breaks (DSBs) through its Ku subunits and initiates non-homologous end joining. Inhibition of DNA-PK sensitizes cancer cells to cisplatin killing. The goal of this study is to elucidate the mechanism underlying the effects of DNA-PK on cisplatin sensitivity.

Results

Silencing the expression of the catalytic subunit of DNA-PK (DNA-PKcs) increased sensitivity to cisplatin and decreased the appearance of γH2AX after cisplatin treatment. We purified DNA-PK by its Ku86 subunit and identified interactors by tandem mass spectrometry before and after cisplatin treatment. The structure specific recognition protein 1 (SSRP1), Spt16 and γH2AX appeared in the Ku86 complex 5 hours after cisplatin treatment. SSRP1 and Spt16 form the facilitator of chromatin transcription (FACT). The cisplatin-induced association of FACT with Ku86 and γH2AX was abrogated by DNase treatment. In living cells, SSRP1 and Ku86 were recruited at sites of DSBs induced by laser beams. Silencing SSRP1 expression increased sensitivity to cisplatin and decreased γH2AX appearance. However, while silencing SSRP1 in cisplatin-treated cells increased both apoptosis and necrosis, DNA-PKcs silencing, in contrast, favored necrosis over apoptosis.

Conclusions

DNA-PK and FACT both play roles in DNA repair. Therefore both are putative targets for therapeutic inhibition. Since DNA-PK regulates apoptosis, silencing DNA-PKcs redirects cells treated with cisplatin toward necrosis. Silencing FACT however, allows both apoptosis and necrosis. Targeting DNA repair in cancer patients may have different therapeutic effects depending upon the roles played by factors targeted.

Role of endonucleases XPF and XPG in nucleotide excision repair of platinated DNA and cisplatin/oxaliplatin cytotoxicity

Resistance of tumor cells to platinum anticancer agents poses a major problem in cancer chemotherapy. One of the mechanisms associated with platinum-based drug resistance is the enhanced capacity of the cell to carry out nucleotide excision repair (NER) on platinum-damaged DNA. Endonucleases XPF and XPG are critical components of NER, responsible for excising the damaged DNA strand to remove the DNA lesion. Here, we investigated possible consequences of down-regulation of XPF and XPG gene expression in osteosarcoma cancer cells (U2OS) and the impact on cellular transcription and DNA repair. We further evaluated the sensitivity of such cells toward the platinum anticancer drugs cisplatin and oxaliplatin.

Copper transporter 2 regulates endocytosis and controls tumor growth and sensitivity to cisplatin in vivo

Copper transporter 2 (CTR2) is one of the four copper transporters in mammalian cells that influence the cellular pharmacology of cisplatin and carboplatin. CTR2 was knocked down using a short hairpin RNA interference. Robust expression of CTR2 was observed in parental tumors grown in vivo, whereas no staining was found in the tumors formed from cells in which CTR2 had been knocked down. Knockdown of CTR2 reduced growth rate by 5.8-fold, increased the frequency of apoptotic cells, and decreased the vascular density, but it did not change copper content. Knockdown of CTR2 increased the tumor accumulation of cis-diamminedichloroplatinum(II) [cisplatin (cDDP)] by 9.1-fold and greatly increased its therapeutic efficacy. Because altered endocytosis has been implicated in cDDP resistance, uptake of dextran was used to quantify the rate of macropinocytosis. Knockdown of CTR2 increased dextran uptake 2.5-fold without reducing exocytosis. Inhibition of macropinocytosis with either amiloride or wortmannin blocked the increase in macropinocytosis mediated by CTR2 knockdown. Stimulation of macropinocytosis by platelet-derived growth factor coordinately increased dextran and cDDP uptake. Knockdown of CTR2 was associated with activation of the Rac1 and cdc42 GTPases that control macropinocytosis but not activation of the phosphoinositide-3 kinase pathway. We conclude that CTR2 is required for optimal tumor growth and that it is an unusually strong regulator of cisplatin accumulation and cytotoxicity. CTR2 regulates the transport of cDDP in part through control of the rate of macropinocytosis via activation of Rac1 and cdc42. Selective knockdown of CTR2 in tumors offers a strategy for enhancing the efficacy of cDDP.

Recognition of platinum-DNA damage by poly(ADP-ribose) polymerase-1

Poly(ADP-ribose) polymerase-1 (PARP-1) was recently identified as a platinum-DNA damage response protein. To investigate the properties of binding of PARP-1 to different platinum-DNA adducts in greater detail, biotinylated DNA probes containing a site-specific cisplatin 1,2-d(GpG) or 1,3-d(GpTpG) intrastrand cross-link or a cisplatin 5'-GC/5'-GC interstrand cross-link (ICL) were utilized in binding assays with cell-free extracts (CFEs) in vitro. The activated state of PARP-1 was generated by treatment of cells with a DNA-damaging agent or by addition of NAD(+) to CFEs. PARP-1 binds with a higher affinity to cisplatin-damaged DNA than to undamaged DNA, and the amount of protein that binds to the most common cisplatin-DNA cross-link, 1,2-d(GpG), is greater than the amount that binds to other types of cisplatin-DNA cross-links. Both DNA damage-activated PARP-1 and unactivated PARP-1 bind to cisplatin-damaged DNA, and both automodified PARP-1 and cleaved PARP-1 bind to cisplatin-DNA lesions. The role of poly(ADP-ribose) (pADPr) in mediating binding of PARP-1 to platinum damage was further investigated. The extent of binding of PARP-1 to the cisplatin 1,2-d(GpG) cross-link decreases upon automodification, and overactivated PARP-1 loses its affinity for the cross-link. Elimination of pADPr facilitates binding of PARP-1 to the cisplatin 1,2-d(GpG) cross-link. PARP-1 also binds to DNA damaged by other platinum compounds, including oxaliplatin and pyriplatin, indicating protein affinity for the damage in an adduct-specific manner rather than recognition of distorted DNA. Our results reveal the unique binding properties for binding of PARP-1 to platinum-DNA damage, providing insights into, and a better understanding of, the cellular response to platinum-based anticancer drugs.

Cellular responses to Cisplatin-induced DNA damage

Cisplatin is one of the most effective anticancer agents widely used in the treatment of solid tumors. It is generally considered as a cytotoxic drug which kills cancer cells by damaging DNA and inhibiting DNA synthesis. How cells respond to cisplatin-induced DNA damage plays a critical role in deciding cisplatin sensitivity. Cisplatin-induced DNA damage activates various signaling pathways to prevent or promote cell death. This paper summarizes our current understandings regarding the mechanisms by which cisplatin induces cell death and the bases of cisplatin resistance. We have discussed various steps, including the entry of cisplatin inside cells, DNA repair, drug detoxification, DNA damage response, and regulation of cisplatin-induced apoptosis by protein kinases. An understanding of how various signaling pathways regulate cisplatin-induced cell death should aid in the development of more effective therapeutic strategies for the treatment of cancer.

Structural insight into dynamic bypass of the major cisplatin-DNA adduct by Y-family polymerase Dpo4

Y-family DNA polymerases bypass Pt-GG, the cisplatin-DNA double-base lesion, contributing to the cisplatin resistance in tumour cells. To reveal the mechanism, we determined three structures of the Y-family DNA polymerase, Dpo4, in complex with Pt-GG DNA. The crystallographic snapshots show three stages of lesion bypass: the nucleotide insertions opposite the 3'G (first insertion) and 5'G (second insertion) of Pt-GG, and the primer extension beyond the lesion site. We observed a dynamic process, in which the lesion was converted from an open and angular conformation at the first insertion to a depressed and nearly parallel conformation at the subsequent reaction stages to fit into the active site of Dpo4. The DNA translocation-coupled conformational change may account for additional inhibition on the second insertion reaction. The structures illustrate that Pt-GG disturbs the replicating base pair in the active site, which reduces the catalytic efficiency and fidelity. The in vivo relevance of Dpo4-mediated Pt-GG bypass was addressed by a dpo-4 knockout strain of Sulfolobus solfataricus, which exhibits enhanced sensitivity to cisplatin and proteomic alterations consistent with genomic stress.

Tumour regression and ERCC1 nuclear protein expression predict clinical outcome in patients with gastro-oesophageal cancer treated with neoadjuvant chemotherapy

Aims:

Neoadjuvant chemotherapy followed by surgery is the standard of care for patients with gastro-oesophageal adenocarcinoma. Previously, we validated the utility of the tumour regression grade (TRG) as a histopathological marker of tumour downstaging in patients receiving platinum-based neoadjuvant chemotherapy. In this study we profiled key DNA repair and damage signalling factors and correlated them with clinicopathological outcomes, including TRG response.

Methods and results:

Formalin-fixed human gastro-oesophageal cancers were constructed into tissue microarrays (TMAs). The first set consisted of 142 gastric/gastro-oesophageal cancer cases not exposed to neoadjuvant chemotherapy and the second set consisted of 103 gastric/gastro-oesophageal cancer cases exposed to preoperative platinum-based chemotherapy. Expressions of ERCC1, XPF, FANCD2, APE1 and p53 were investigated using immunohistochemistry.

In patients who received neoadjuvant chemotherapy, favourable TRG response (TRG 1, 2 or 3) was associated with improvement in disease-specific survival (P=0.038). ERCC1 nuclear expression correlated with lack of histopathological response (TRG 4 or 5) to neoadjuvant chemotherapy (P=0.006) and was associated with poor disease-specific (P=0.020) and overall survival (P=0.040).

Conclusions:

We provide evidence that tumour regression and ERCC1 nuclear protein expression evaluated by immunohistochemistry are promising predictive markers in gastro-oesophageal cancer patients receiving neoadjuvant platinum-based chemotherapy.

Emodin enhances cisplatin-induced cytotoxicity via down-regulation of ERCC1 and inactivation of ERK1/2

Emodin, a tyrosine kinase inhibitor, is a natural anthraquinone derivative found in the roots and rhizomes of numerous plants; it exhibits an anticancer effect on many malignancies. The most important chemotherapeutic agent for patients with advanced non-small cell lung cancer (NSCLC) is a platinum-containing compound such as cisplatin or carboplatin. The molecular mechanism underlying decreased NSCLC cell viability after treatment with emodin and cisplatin is unclear. Therefore, the aim of this study was to assess the cytotoxic effect of combined emodin and cisplatin on NSCLC cell lines and to clarify underlying molecular mechanisms. Exposure of human NSCLC cells to emodin decreased cisplatin-elicited ERK1/2 activation and ERCC1 protein induction by increasing instability of ERCC1 protein. Cisplatin alone did not affect expression of ERCC1 mRNA. However, emodin alone or combined with cisplatin significantly decreased expression of ERCC1 mRNA levels. Enhancement of ERK1/2 activation by transfection with constitutively active MKK1/2 (MKK1/2-CA) vector increased ERCC1 protein levels and protein stability, as well as increasing viability of NSCLC cells treated with emodin and cisplatin. In contrast, blocking ERK1/2 activation by U0126 (an MKK1/2 inhibitor) decreased cisplatin-elicited ERCC1 expression and enhanced cisplatin-induced cytotoxicity. Depletion of endogenous ERCC1 expression by si-ERCC1 RNA transfection significantly enhanced cisplatin's cytotoxic effect. In conclusion, ERCC1 protein protects NSCLC cells from synergistic cytotoxicity induced by emodin and platinum agents. Further investigation of combined emodin and cisplatin may lead to novel therapy in the future for NSCLC through down-regulating expression of ERCC1.