Pt-DNA Adduct Formation Research Articles

NIR-Light-Triggered Mild-Temperature Hyperthermia to Overcome the Cascade Cisplatin Resistance for Improved Resistant Tumor Therapy.

Currently, cisplatin resistance has been recognized as a multistep cascade process for its clinical chemotherapy failure. Hitherto, it remains challenging to develop a feasible and promising strategy to overcome the cascade drug resistance (CDR) issue for achieving fundamentally improved chemotherapeutic efficacy. Herein, a novel self-assembled nanoagent is proposed, which is constructed by Pt(IV) prodrug, cyanine dye (cypate), and gadolinium ion (Gd3+), for systematically conquering the cisplatin resistance by employing near-infrared (NIR) light activated mild-temperature hyperthermia in tumor targets. The proposed nanoagents exhibit high photostability, GSH/H+-responsive dissociation, preferable photothermal conversion, and enhanced cellular uptake performance. In particular, upon 785-nm NIR light irradiation, the generated mild temperature of ≈ 43 °C overtly improves the cell membrane permeability and drug uptake, accelerates the disruption of intracellular redox balance, and apparently enhances the formation of Pt-DNA adducts, thereby effectively overcoming the CDR issue and achieves highly improved therapeutic efficacy for cisplatin-resistant tumor ablation.

Nuclear-Targeting Lipid PtIV Prodrug Amphiphile Cooperates with siRNA for Enhanced Cancer Immunochemotherapy by Amplifying Pt-DNA Adducts and Reducing Phosphatidylserine Exposure.

Patients treated with Pt-based anticancer drugs (PtII) often experience severe side effects and are susceptible to cancer recurrence due to the limited bioavailability of PtII and tumor-induced immunosuppression. The exposure of phosphatidylserine on the cell's outer surface induced by PtII results in profound immunosuppression through the binding of phosphatidylserine to its receptors on immune cells. Here, we report a novel approach for enhanced cancer chemoimmunotherapy, where a novel nuclear-targeting lipid PtIV prodrug amphiphile was used to deliver a small interfering RNA (siXkr8) to simultaneously amplify Pt-DNA adducts and reduce the level of exposure of phosphatidylserine. This drug delivery vehicle is engineered by integrating the PtIV prodrug with self-assembly performance and siXkr8 into a lipid nanoparticle, which shows tumor accumulation, cancer cell nucleus targeting, and activatable in a reduced microenvironment. It is demonstrated that nuclear-targeting lipid PtIV prodrug increases the DNA cross-linking, resulting in increased Pt-DNA adduct formation. The synergistic effects of the PtIV prodrug and siXkr8 contribute to the improvement of the tumor immune microenvironment. Consequently, the increased Pt-DNA adducts and immunogenicity effectively inhibit primary tumor growth and prevent tumor recurrence. These results underscore the potential of utilizing the nuclear-targeting lipid PtIV prodrug amphiphile to enhance Pt-DNA adduct formation and employing siXkr8 to alleviate immunosuppression during chemotherapy.

Effective monitoring of Platinum-DNA adducts formation under simulated physiological conditions by CE-ICP-MS/MS

The leading Pt(II)-based anticancer drugs have been used for decades; however, chemotherapy with their application is burdened with severe side effects. The administration of compounds capable of DNA platination in the form of prodrugs has the potential to overcome the drawbacks associated with their use. Progress toward their clinical application depends on establishing proper methodologies that would allow assessing their ability to bind to DNA in the biological environment. Herein, we propose implementing the approach based on the hyphenation of capillary electrophoresis with inductively coupled plasma tandem mass spectrometry (CE-ICP-MS/MS) for studying Pt-DNA adduct formation. The presented methodology opens the possibility to employ the multielement monitoring for studying the differences in the behavior of Pt(II) and Pt(IV) complexes and, interestingly, revealed the formation of various adducts with DNA and cytosol components for the latter one.

Cellular Toxicity Mechanisms and the Role of Autophagy in Pt(IV) Prodrug-Loaded Ultrasmall Iron Oxide Nanoparticles Used for Enhanced Drug Delivery.

Ultrasmall iron oxide nanoparticles (<10 nm) were loaded with cis-diamminetetrachloroplatinum (IV), a cisplatin (II) prodrug, and used as an efficient nanodelivery system in cell models. To gain further insight into their behavior in ovarian cancer cells, the level of cellular incorporation as well as the platination of mitochondrial and nuclear DNA were measured using inductively coupled plasma mass spectrometry (ICP-MS) strategies. Quantitative Pt results revealed that after 24 h exposure to 20 µM Pt in the form of the Pt(IV)-loaded nanoparticles, approximately 10% of the incorporated Pt was associated with nuclear DNA. This concentration increased up to 60% when cells were left to stand in drug-free media for 3 h. These results indicated that the intracellular reducing conditions permitted the slow release of cisplatin (II) from the cisplatin (IV)-loaded nanoparticles. Similar results were obtained for the platination of mitochondrial DNA, which reached levels up to 17,400 ± 75 ng Pt/ mg DNA when cells were left in drug-free media for 3 h, proving that this organelle was also a target for the action of the released cisplatin (II). The time-dependent formation of Pt-DNA adducts could be correlated with the time-dependent decrease in cell viability. Such a decrease in cell viability was correlated with the induction of apoptosis as the main route of cell death. The formation of autophagosomes, although observed upon exposure in treated cells, does not seem to have played an important role as a means for cells to overcome nanoparticles’ toxicity. Thus, the designed nanosystem demonstrated high cellular penetration and the “in situ” production of the intracellularly active cisplatin (II), which is able to induce cell death, in a sustained manner.

Abstract 1385: In vitro evaluation of platinum chemotherapy combinations with the ATR inhibitor, ceralasertib (AZD6738)

Abstract Introduction: The combination of platinum-based chemotherapy with inhibitors of the DNA damage response (DDR) is therapeutically challenging due to overlapping toxicities, such as myelosuppression. The optimal sequence and schedule of drug delivery to mitigate toxicity and maximise efficacy has not been determined for many combinations. Ceralasertib is an oral inhibitor of ATR, a key constituent of the DDR. Ceralasertib has entered early phase clinical trials in combination with carboplatin (NCT02264678). The aim of the current study was to investigate the mechanism of interaction of ceralasertib with platinum (Pt) chemotherapy, characterising the formation and removal of Pt-induced DNA adducts, in order to provide insight into the repair and recovery of DNA following combination treatment. Methods: The growth inhibitory effects of ceralasertib alone and in combination with cisplatin were tested using sulphorhodamine B (SRB) colorimetric assays in a panel of non-small cell lung (H460 and H23) and breast (MCF7, T47D, HCC1806, MDA-MB-436 and MDA-MB-468) cancer cell lines. Median effect analysis using CalcuSyn software (Biosoft, Cambridge, UK) was used to evaluate synergistic combinations. Time- and schedule-dependent analyses of Pt-DNA adduct formation in cells treated with the combination were carried out using inductively-coupled mass spectrometry (ICP-MS). Cell cycle analysis and DNA replication combing assays were performed to explore alternative mechanisms of synergy between ceralasertib and cisplatin. Results: Ceralasertib was synergistic with cisplatin, inhibiting growth across the cell line panel. However, neither pre-exposure with either agent or co-exposure of cisplatin treated cells to ceralasertib affected the total number, nor longevity, of Pt-DNA adducts compared with cisplatin treatment alone. Continued exposure to ceralasertib for up to 48 hours following wash out of cisplatin (after 4, 8 or 24 hours treatment) did not maintain Pt-induced adducts within the DNA. Peak Pt-DNA adduct formation did not consistently correlate with cell line sensitivity to either drug, combination synergy score, or the effects of ceralasertib or cisplatin on cell cycle progression. Combination treatment did result in a reduction in replication fork speed, but this effect was no greater than that seen with ceralasertib monotherapy. Conclusion: Synergy was observed between cisplatin and ceralasertib in the cell lines tested. However, our in vitro data suggests that this is not associated with an interaction at the level of Pt-DNA adduct formation. Citation Format: Sally E. Hall, Alan Lau, Emma Dean, Elizabeth Martin, Christopher Ottley, Yvette Drew, Gareth Veal. In vitro evaluation of platinum chemotherapy combinations with the ATR inhibitor, ceralasertib (AZD6738) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1385.

Acidity-triggered TAT-presenting nanocarriers augment tumor retention and nuclear translocation of drugs

Hierarchical targeting strategy can combat the sequential drug delivery barriers by changing their properties with response to tumor stimuli. Among these strategies, much less attention has been paid to address the issues of rapid tumor clearance and insufficient cellular translocation. In this work, we demonstrate that a transactivator of transcription (TAT)-presenting nanomedicine (DATAT-NP/Pt), apart from improving tumor accumulation and cellular uptake, can simultaneously enhance tumor retention and promote nuclear translocation of encapsulated platinum prodrugs, and thus improve therapeutic efficacy. Specifically, a protecting 2,3-dimethylmaleic anhydride (DA) corona on the nanomedicine prevented the TAT peptide from serum. DATAT-NP/Pt efficiently accumulated at the tumor site through the enhanced permeability and retention (EPR) effect, followed by acid-triggered TAT presenting within the tumor acidic microenvironment (pH ~ 6.8). The exposed TAT peptide augmented tumor retention and nuclear translocation of DATAT-NP/Pt. We used a tumor-on-a-chip microfluidic system to real-time mimic and analyze tumor accumulation and retention at physiological flow conditions and revealed that surface absorption of nanomedicines on tumors was critical in determining their tumor retention and clearance. Furthermore, the TAT peptide rapidly translocated the DATAT-NP/Pt into the perinuclear region, allowing for higher nuclear platinum concentrations and increased Pt-DNA adduct formation in nuclei, which consequently reversed cisplatin resistance. Our work presents a new strategy to overcome pathophysiological barriers of tumor clearance and insufficient cellular translocation and provides new insights for the design of cancer nanomedicines.

Monofunctional BODIPY-Appended Imidazoplatin for Cellular Imaging and Mitochondria-Targeted Photocytotoxicity.

Monofunctional platinum(II) complexes of formulation cis-[Pt(NH3)2(L)Cl](NO3), where L is an imidazole base conjugated to 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) with emissive (L1 in 1) and nonemissive (L2 in 2) moieties were prepared and characterized, and their singlet oxygen-mediated photoinduced cytotoxicity was studied. The 1-methylimidazole (1-MeIm) complex 3 was prepared as a control and for structural characterization by X-ray crystallography. Complexes 1 and 2 showed strong visible absorption bands at 500 nm (ε = 2.7 × 104 M-1 cm-1) and 540 nm (1.4 × 104 M-1 cm-1). Complex 1 is emissive with a band at 510 nm (ΦF = 0.09) in 1% dimethyl sulfoxide/Dulbecco's Modified Eagle's Medium (pH 7.2). Singlet oxygen generation upon photoirradiation with visible light (400-700 nm) was evidenced from 1,3-diphenylisobenzofuran titration experiments showing significant photosensitizing ability of the BODIPY complexes. Both 1 and 2 were remarkably photocytotoxic in visible light (400-700 nm, 10 J cm-2) in skin keratinocyte HaCaT and breast cancer MCF-7 cells giving IC50 values in nanomolar concentration. The complexes were, however, essentially nontoxic to the cells in the dark (IC50 > 80 μM). Complex 2 having a diiodo-BODIPY unit is nonemissive but an efficient photosensitizer with high singlet oxygen generation ability in visible light (400-700 nm). Confocal microscopy using the emissive complex 1 showed significant mitochondrial localization of the complex. Cell death via apoptotic pathway was observed from the Annexin-V-FITC/PI assay. The formation of Pt-DNA adducts was evidenced from the binding experiments of the complexes 1 and 2 with 9-ethylguanine as a model nucleobase from 1H NMR and mass spectral studies.

Hyaluronan-Lysine Cisplatin Drug Carrier for Treatment of Localized Cancers: Pharmacokinetics, Tolerability, and Efficacy in Rodents and Canines

The purpose of this study was to develop a safe and efficacious drug delivery platform for sustained release of cisplatin after locoregional administration. We successfully synthesized hyaluronan-cisplatin nanoconjugates (HA-Lys-Pt) using an N-Ac-lysine linker, which formed a thermodynamically stable five-membered ring with the platinum. The conjugate was characterized for release kinetics, in vitro anti-proliferative activity, degradability, impurity content, formation of Pt-DNA adducts, pharmacokinetics, tolerability in rodents and canines, and for efficacy in rodents. The 75 kD HA-Lys-Pt (75HA-Lys-Pt) sustained release of platinum with a 69 h half-life in phosphate buffered saline without substantial burst release. Compared to intravenous cisplatin, subcutaneously injected 75HA-Lys-Pt formed 3.2-fold more Pt-DNA adducts in rat peripheral blood mononuclear cells compared to intravenous cisplatin over 96 h. Subcutaneous 75HA-Lys-Pt was tolerable in rats at 40 mg/kg (4 × LD50 of conventional cisplatin) and resulted in 62.5% partial response and 37.5% stable disease in murine xenografts of head and neck squamous cell cancer (20 mg/kg/wk × 3 weeks). 75HA-Lys-Pt demonstrated extended tmax and improved area-under-the-curve compared to cisplatin in rats and canines. Canine safety was demonstrated by liver enzyme and electrolyte levels, complete blood count, and urinalysis.

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.

DNA Condensing Effects and Sequence Selectivity of DNA Binding of Antitumor Noncovalent Polynuclear Platinum Complexes

The noncovalent analogues of antitumor polynuclear platinum complexes represent a structurally discrete class of platinum drugs. Their chemical and biological properties differ significantly from those of most platinum chemotherapeutics, which bind to DNA in a covalent manner by formation of Pt-DNA adducts. In spite of the fact that these noncovalent polynuclear platinum complexes contain no leaving groups, they have been shown to bind to DNA with high affinity. We report here on the DNA condensation properties of a series of noncovalent analogues of antitumor polynuclear platinum complexes described by biophysical and biochemical methods. The results demonstrate that these polynuclear platinum compounds are capable of inducing DNA condensation at more than 1 order of magnitude lower concentrations than conventional spermine. Atomic force microscopy studies of DNA condensation confined to a mica substrate have revealed that the DNA morphologies become more compact with increasing concentration of the platinum complexes. Moreover, we also found that the noncovalent polynuclear platinum complex [{Pt(NH3)3}2-μ-{trans-Pt(NH3)2(NH2(CH2)6NH2)2}](6+) (TriplatinNC-A) binds to DNA in a sequence-dependent manner, namely, to A/T-rich sequences and A-tract regions, and that noncovalent polynuclear platinum complexes protect DNA from enzymatic cleavage by DNase I. The results suggest that mechanisms of antitumor and cytotoxic activities of these complexes may be associated with their unique ability to condense DNA along with their sequence-specific DNA binding. Owing to their high cellular accumulation, it is also reasonable to suggest that their mechanism of action is based on the competition with naturally occurring DNA condensing agents, such as polyamines spermine, spermidine, and putrescine, for intracellular binding sites, resulting in the disturbance of the correct binding of regulatory proteins initiating the onset of apoptosis.

Glutathione modified CdTe quantum dots as a label for studying DNA interactions with platinum based cytostatics

Cisplatin, carboplatin, and oxaliplatin represent three generations of platinum based drugs applied successfully for cancer treatment. As a consequence of the employment of platinum based cytostatics in the cancer treatment, it became necessary to study the mechanism of their action. Current accepted opinion is the formation of Pt-DNA adducts, but the mechanism of their formation is still unclear. Nanomaterials, as a progressively developing branch, can offer a tool for studying the interactions of these drugs with DNA. In this study, fluorescent CdTe quantum dots (QDs, λem = 525 nm) were employed to investigate the interactions of platinum cytostatics (cisplatin, carboplatin, and oxaliplatin) with DNA fragment (500 bp, c = 25 μg/mL). Primarily, the fluorescent behavior of QDs in the presence of platinum cytostatics was monitored and major differences in the interaction of QDs with tested drugs were observed. It was found that the presence of carboplatin (c = 0.25 mg/mL) had no significant influence on QDs fluorescence; however cisplatin and oxaliplatin quenched the fluorescence significantly (average decrease of 20%) at the same concentration. Subsequently, the amount of platinum incorporated in DNA was determined by QDs fluorescence quenching. Best results were reached using oxaliplatin (9.4% quenching). Linear trend (R(2) = 0.9811) was observed for DNA platinated by three different concentrations of oxaliplatin (0.250, 0.125, and 0.063 mg/mL). Correlation with differential pulse voltammetric measurements provided linear trend (R(2) = 0.9511). As a conclusion, especially in the case of oxaliplatin-DNA adducts, the quenching was the most significant compared to cisplatin and nonquenching carboplatin.

Overcoming biochemical pharmacologic mechanisms of platinum resistance with a texaphyrin-platinum conjugate.

In our effort to investigate further texaphyrin conjugation as a means of increasing delivery and accumulation of known anticancer platinum agents in cancer cells, we have continued our studies on the mode of action of a texaphyrin-platinum conjugate, particularly in cisplatin-resistant tumor cells that are characterized by several mechanisms of resistance, including reduced drug accumulation. Our results provide support for the proposal that intracellular platinum and Pt-DNA adduct levels were significantly increased using our conjugate relative to corresponding Pt controls. Moreover, no differences were found in cellular accumulation and Pt-DNA adduct formation between Pt sensitive and Pt resistant ovarian cells. As a result, resistance to the conjugate was lower than cisplatin in resistant cells. Based on these results we conclude that texaphyrin conjugation provides a promising strategy for overcoming biochemical pharmacologic mechanisms of resistance.

Combination effects of platinum drugs and N 1, N 11 diethylnorspermine on spermidine/spermine N 1-acetyltransferase, polyamines and growth inhibition in A2780 human ovarian carcinoma cells and their oxaliplatin and cisplatin-resistant variants

PurposeTo understand the mechanisms behind platinum drug/DENSPM-induced inhibition of cancer cell growth, we compared the effects of oxaliplatin and cisplatin when combined with DENSPM on the induction of SSAT mRNA, activity, polyamines and cell growth in A2780 human ovarian carcinoma cells and their oxaliplatin- and cisplatin-resistant variants A2780/C10B and A2780/CP, respectively.MethodsParental and Pt-resistant cells were treated with platinum agent alone, DENSPM alone or combination (10 μM each, 20 h). QRT–PCR, radioactive product measurement and HPLC were used for mRNA, activity and polyamine pools, respectively; drug interaction on cell growth was by SRB and isobologram analysis.ResultsBoth platinum agents induced SSAT mRNA in parental A2780 cells, but not in resistant cells. Platinum drug/DENSPM combinations produced high levels of SSAT activity in parental cells with significant depletion of spermine and spermidine, but not in resistant cells. Co-treatment with platinum agents increased the levels of DENSPM in all cell lines. Oxaliplatin/DENSPM combination was superior to cisplatin/DENSPM in the inhibition of cell growth in parental cells. No synergy was observed in the resistant cells.ConclusionsIncreased DENSPM levels following co-treatment with Pt agents enhances the translation and stability of SSAT protein leading to polyamine pool depletion, facilitating more Pt–DNA adduct formation in parental cells. Oxaliplatin/DENSPM combination is superior to cisplatin/DENSPM in cell growth inhibition as DACH-Pt DNA adducts are cytotoxic even at relatively fewer numbers. Reduced platinum uptake in Pt-resistant cells contributes to reduced SSAT mRNA induction and absence of synergy when combined with DENSPM.

Platinum–DNA Interactions and Subsequent Cellular Processes Controlling Sensitivity to Anticancer Platinum Complexes

Platinum-based compounds are widely used as chemotherapeutics for the treatment of a variety of cancers. The anticancer activity of cisplatin and other platinum drugs is believed to arise from their interaction with DNA. Several cellular pathways are activated in response to this interaction, which include recognition by high-mobility group and repair proteins, translesion synthesis by polymerases, and induction of apoptosis. The apoptotic process is regulated by activation of caspases, p53 gene, and several proapoptotic and antiapoptotic proteins. Such cellular processing eventually leads to an inhibition of the replication or transcription machinery of the cell. Deactivation of platinum drugs by thiols, increased nucleotide excision repair of Pt-DNA adducts, decreased mismatch repair, and defective apoptosis result in resistance to platinum therapy. The differences in cytotoxicity of various platinum complexes are attributed to the differential recognition of their adducts by cellular proteins. Cisplatin and oxaliplatin both produce mainly 1,2-GG intrastrand cross-links as major adducts, but oxaliplatin is found to be more active particularly against cisplatin-resistant tumor cells. Mismatch repair and replicative bypass appear to be the processes most likely involved in differentiating the molecular responses to these two agents. This review describes the formation of Pt-DNA adducts, their interaction with cellular components, and biological effects of this interaction.

Effects of reduced glutathione (GSH) on oxaliplatin pharmacokinetics (OXA pk) and on Pt-DNA adducts formation in advanced colorectal cancer patients treated by FOLFOX4 regimen

2559 Background: Neurotoxicity is a common OXA toxicity in FOLFOX4 regimen for patients with advanced colorectal cancer. Recently, Cascinu et al. (JCO 2002; 20: 3478–3483) provided evidence that GSH reduces the OXA-induced neurotoxicity, but GSH influence on the formation of Pt-DNA adducts still remains unknown. This study evaluated the effect of GSH addition on OXA pk and on Pt-DNA adducts formation Table of Contents Methods: 28 patients were given twelve FOLFOX4 courses and randomized to receive either GSH 1,500 mg/m2 or normal saline solution (placebo) before OXA iv infusion. OXA pk and Pt-DNA adducts formation were evaluated at courses 5, 9 and 12. Total and ultrafiltered platinum were analyzed by atomic adsorption, Pt-DNA adducts in leukocytes (as model for tumour tissue) by adsorptive stripping voltammetry. Pk analysis were done by non-compartmental analysis, statistical analysis by non-parametric Mann-Whitney test. Results: Median total and ultrafiltered platinum median Cmax and AUCtot values were comparable to previously reported ones, being higher in the placebo arm, due to a moderate reduction of platinum clearance. The formation of Pt-DNA adducts was more pronounced in GSH arm (median value 20.3 Pt atoms/106 nucleotides vs. 5.7 Pt atoms/106 nucleotides), even not statistically significant. Conclusions: The addition of GSH to FOLFOX4 regimen is able to reduce the OXA-induced neurotoxicity, without affecting either the OXA pk behaviour or the formation of Pt-DNA adducts, without modifying FOLFOX4 clinical efficacy. [Table: see text] No significant financial relationships to disclose.

Cisplatin-DNA damage in p21WAF1/Cip1 deficient mouse keratinocytes exposed to cisplatin

In response to DNA damage, cell cycle arrest, apoptosis, and DNA repair are mediated by a TP53 pathway that induces p21(WAF1/Cip1). The chemotherapeutic drug cis-diamminedichloroplatinum-II (cisplatin) damages cellular DNA by forming cis-diammineplatinum-N(7)-d[GpG] and cis-diammine-platinum-N(7)-d[ApG] adducts. To investigate the role of p21, skin keratinocytes from p21(WAF1/Cip1) wild-type (+/+), heterozygous (+/-), and null (-/-) mice, cultured in calcium levels designed to maintain a proliferating state, were exposed to 5 microM cisplatin continuously for 0, 8, 24, 48 and 72 h. At all time points the (+/-) cells had the fewest Pt-DNA adducts, and at 24 h mean Pt-DNA adduct levels were 541, 153 and 779 fmol adduct/mug DNA for p21(WAF1/Cip1) (+/+), (+/-) and (-/-) cells, respectively [P < 0.05 for (+/+) versus (+/-) and (-/-) versus (+/-)]. In order to understand underlying events, we examined p21(WAF1/Cip1) messenger RNA (mRNA), cell cycle arrest, and apoptosis in these cells. At 48 h of cisplatin exposure p21(WAF1/Cip1) mRNA expression was 2-fold higher in the (+/+) cells, compared to the (+/-) cells. At 24 h, the % of cells in S-phase in cisplatin-exposed cultures, compared to unexposed cultures, was decreased by 51, 40 and 11% in p21(WAF1/Cip1) (+/+), (+/-) and (-/-) cells, respectively (P = 0.04, ANOVA). At 24, 48 and 72 h the % of cisplatin-exposed (+/+) cells in apoptosis was 9.4-10.5%, while the cisplatin-exposed (+/-) and (-/-) cells had 1.2-3.7% of cells in apoptosis. The data support the interpretation that DNA replication arrest and apoptosis do not completely explain the low levels of Pt-DNA adducts in the (+/-) cells, and suggest that p21(WAF1/Cip1) controls activity resulting in either low Pt-DNA adduct formation or enhanced Pt-DNA adduct removal.

Effects of gemcitabine on cis-platinum-DNA adduct formation and repair in a panel of gemcitabine and cisplatin-sensitive or -resistant human ovarian cancer cell lines

Gemcitabine (dFdC) can increase the sensitivity of both cisplatin (CDDP)-sensitive and -resistant cell lines. It has been postulated that both formation and repair of platinum-(Pt)-DNA adducts are related to these effects. Therefore, we investigated the effects of dFdC on the formation and repair of Pt-DNA adducts in the human ovarian cancer cell line, A2780, and its CDDP- or dFdC-resistant variants, ADDP and AG6000, which have a different expression of various repair enzymes. Cells were exposed for 1 h to CDDP alone or combined with dFdC in IC50 concentrations, followed by a 1-h exposure to thiourea and, subsequently, by a drug-free period of 1, 3 or 23 h (i.e. 2, 4 or 24 h after CDPP +/- dFdC removal). Pt-DNA adducts were quantified with 32P-post-labeling. The gene expression of the repair enzymes, XPA and XRCC1, was the same in all 3 cell lines but ERCC1, ERCC3 and XPC were 2-6 times higher in AG6000 compared to A2780 cells. In contrast, both ERCC1 and ERCC3 were 10- and 1.5-fold lower in ADDP cells compared to A2780. The mismatch enzyme, MLH1, was lower in ADDP cells. At equally toxic CDDP concentrations, all cell lines formed comparable peak levels of total Pt-DNA adducts (36-48 fmol/microg DNA). However, the time at which peak levels were reached showed large variation. The repair of the adducts was very efficient in the resistant cell lines whereas, in A2780 cells, plateau levels were retained until 24 h after CDDP exposure. In A2780 cells, dFdC shifted the adduct peaks from 4 h to directly after CDDP exposure and increased peak levels by >3.9-fold. dFdC also enhanced the repair of adducts by >1.7-fold and increased the Pt-GG:Pt-AG ratio compared to CDDP alone by >1.4-fold. Overall, dFdC decreased the area under the Pt-DNA adduct-time curve (AUA0-25 h) in A2780 cells by 2.7-fold. In ADDP cells, dFdC shifted the adduct peaks from 2 to 4 h and increased them by >2.2-fold. dFdC also increased the Pt-GG:Pt-AG ratio during the repair process by 1.4-fold. Overall, dFdC increased the AUA0-25 h in ADDP cells by 1.7-fold. In AG6000 cells, dFdC increased the Pt-GG:Pt-AG ratio by 1.6-fold directly after exposure but did not clearly affect the AUA0-25 h. In conclusion, dFdC can affect both Pt-DNA adduct formation and repair, depending on the initial sensitivity of the cells.

One-milliliter wet-digestion for inductively coupled plasma mass spectrometry (ICP-MS): determination of platinum-DNA adducts in cells treated with platinum(II) complexes

Platinum (Pt)-DNA adducts formed by the anti-tumor agent cisplatin are recognized by the DNA mismatch repair (MMR) system. To investigate the involvement of MMR proteins including hMLH1 in the removal of these adducts, we developed a mL-scale wet-digestion method for inductively coupled plasma mass spectrometry (ICP-MS). The detection limit was 0.01 ng mL(-1) Pt, which corresponded to 2 pg Pt/microg DNA when 10 microg of DNA was used. The mean relative errors were 5.4% or better for a dynamic range of 0.01-10 ng mL(-1) Pt. DNA (approximately 500 microg) had no matrix effect. To improve the accuracy, DNA preparations were treated with ribonuclease and the apparent reduction in the concentration of Pt was corrected using cellular DNA levels, which were determined with Hoechst 33258. No significant differences were observed, in terms of the formation of Pt-DNA adducts or their removal over 6 h, between hMLH1-deficient HCT116 cells, a human colorectal cancer cell line, and hMLH1-complemented HCT116+ch3 cells (n=5; P>0.05), indicating that the hMLH1-dependent DNA repair systems contribute to neither the formation nor the removal of the adducts at detectable levels. In addition, approximately 19% of the adducts were removed within 6 h in both cell lines. A time course analysis (~24 h) suggested that the removal of cisplatin-generated Pt-DNA adducts follows first-order kinetics (t(1/2)=32 h). The amount of Pt-DNA adduct formed by oxaliplatin in 1 h was 56% (ratio of means) of that generated by an equimolar concentration of cisplatin in HCT116. The proposed procedure could be useful for determining Pt-DNA adducts formed by Pt(II) complexes.

Novel apoptosis-inducing trans-platinum piperidine derivatives: synthesis and biological characterization.

The synthesis, chemical characterization, and interaction with cells of new sterically hindered trans- and cis-diaminedichloroplatinum(II) complexes are described. The amine ligands include monofunctional piperidine (pip) and piperazine (pz). The poor solubility of trans-diaminedichloroplatinum complexes was overcome by introducing the positively charged pz ligand, which allows retaining of the classic platinum coordination sphere. In vitro evaluation in OV-1063 and C-26 tumor cells revealed that replacing one NH3 of the inactive transplatin by an aromatic planar ligand (4-picoline, 4-pic) or by an aliphatic nonplanar heterocyclic ligand (pip) or replacing both NH3 groups with a 4-pic ligand and a pip or pz ligand significantly increases the cytotoxic activity of these complexes. The unsymmetric complexes trans-[PtCl2(4-pic)(pip)] and trans-[PtCl2(4-pic)(pz)]HCl were the most cytotoxic compounds against the cisplatin-sensitive tumor cell line C-26 (IC50 = 4.5 and 5.5 microM, respectively) and the cisplatin-sensitive tumor cell line OV-1063 (IC50 = 6.5 and 7.4 microM, respectively). In contrast, replacing one NH3 of the cis isomer by an aromatic planar ligand (4-pic) or by an aliphatic amine lowered their cytotoxiciy in comparison to cisplatin. Cell penetration and Pt-DNA adduct formation were also evaluated, and it was clearly shown that both trans-[PtCl2(4-pic)(pip)] and trans-[PtCl2(4-pic)(pz)]HCl penetrate efficiently the cellular membrane of the tumor cells and platinate the cellular DNA. When comparing cellular DNA platination, positively charged trans-[PtCl2(4-pic)(pz)]HCl was 7-fold higher than both cisplatin and its neutral analogue trans-[PtCl2(4-pic)(pip)]. Moreover, in contrast to cisplatin, in the cell lines used, cell death caused by both complexes appeared to be apoptotic according to several criteria including early phosphatidylserine exposure, activation of caspases, and characteristic morphological changes. Our results suggest that these novel mixed nonclassical trans-Pt(II) complexes are biologically and mechanistically distinct from known Pt complexes and deserve evaluation of their efficacy in tumor-bearing animals.

JM216-, JM118-, and cisplatin-induced cytotoxicity in relation to platinum-DNA adduct formation, glutathione levels and p53 status in human tumour cell lines with different sensitivities to cisplatin

The aim of this study is to establish anti-tumour potency of the new oral platinum drug JM216 and its metabolite JM118 in relation to the platinum (Pt)-DNA adduct formation, glutathione (GSH)-levels, and p53 status in human cancer cell lines with different sensitivities to cisplatin (CDDP). These parameters were studied in the CDDP sensitive human germ cell cancer cell line Tera and the small-cell lung cancer cell line GLC 4 and their sublines with in vitro acquired CDDP resistance, Tera-CP and GLC 4-CDDP, in a human ovarian cancer cell line transfected with mutant p53 (A2780/mt273) and with an empty vector as control (A2780/cmv), and in the intrinsic CDDP resistant human non-small-cell lung cancer cell line SW1573/S1 and colon carcinoma cell line Caco-2. Cytotoxicity was tested with the microculture tetrazolium (MTT)-assay. Pt-DNA adduct levels were assessed immunocytochemically. Quantitative analysis was performed by double fluorescence video microscopy. Results were correlated with GSH levels and p53 status of the cell lines. This study showed that both JM216 and JM118 can partially circumvent intrinsic and acquired resistance to CDDP. Drug-induced cytotoxicity only correlated negatively with GSH levels for JM216 and CDDP in the tested unselected cell lines. At equimolar basis, JM216 induced lower levels of Pt-DNA adducts in the various cell lines than JM118 and CDDP, whereas the JM118-induced amount and pattern of Pt-DNA adducts was comparable to CDDP. No difference in initial Pt-DNA adducts levels was observed between cell lines sensitive, acquired or intrinsic resistant to CDDP suggesting a Pt-resistance mechanism based on tolerance or increased repair, rather than decreased initial Pt-DNA adduct formation.