Comparative analysis of the mutagenic activity of oxaliplatin and cisplatin in the Hprt gene of CHO cells

Loss-of-function mutation of REV1 (p.R704Q) mediates cetuximab primary resistance by activating autophagy in RAS-wild type metastatic colorectal cancer

Cetuximab in combination with FOLFIRI/FOLFOX is the standard first-line treatment for patients with RAS wild-type metastatic colorectal cancer (mCRC). However, some patients experience rapid tumor progression after treatment with cetuximab (primary resistance). Our previous research identified a gene mutation, REV1 p.R704Q, which may be a key biomarker for primary cetuximab resistance. This study aimed to study the mechanism of cetuximab resistance caused by REV1 p.R704Q mutation and reveal a novel mechanism to induce cetuximab resistance. Sanger sequencing and multivariate clinical prognostic analysis of 208 patients with mCRC showed that REV1 p.R704Q mutation is an independent risk factor for tumor progression after treatment with cetuximab in patients with RAS wild-type mCRC (Hazard ratio = 2.481, 95 % Confidence interval: 1.389-4.431, P = 0.002). The sensitivity of REV1 p.R704Q mutant cell lines to cetuximab decreased in vitro Cell Counting Kit-8 assay and in vivo subcutaneous tumor model. In vitro, we observed that decreased stability and accelerated degradation of REV1 mutant protein results in REV1 dysfunction, which activated autophagy and mediated cetuximab resistance. These findings suggested that REV1 p.R704Q mutation could predict cetuximab primary resistance in mCRC. REV1 p.R704Q mutation caused decreased stability and degradation of REV1 protein, as well as dysfunction of p.R704Q protein. REV1 p.R704Q mutation activates autophagy and mediates cetuximab resistance; further, inhibition of autophagy could reverse cetuximab resistance.

The mechanism of antiproliferative activity of the oxaliplatin pyrophosphate derivative involves its binding to nuclear DNA in cancer cells

(1R,2R-diaminocyclohexane)(dihydropyrophosphato) platinum(II), also abbreviated as RRD2, belongs to a class of potent antitumor platinum cytostatics called phosphaplatins. Curiously, several published studies have suggested significant mechanistic differences between phosphaplatins and conventional platinum antitumor drugs. Controversial findings have been published regarding the role of RRD2 binding to DNA in the mechanism of its antiproliferative activity in cancer cells. This prompted us to perform detailed studies to confirm or rule out the role of RRD2 binding to DNA in its antiproliferative effect in cancer cells. Here, we show that RRD2 exhibits excellent antiproliferative activity in various cancer cell lines, with IC50 values in the low micromolar or submicromolar range. Moreover, the results of this study demonstrate that DNA lesions caused by RRD2 contribute to killing cancer cells treated with this phosphaplatin derivative. Additionally, our data indicate that RRD2 accumulates in cancer cells but to a lesser extent than cisplatin. On the other hand, the efficiency of cisplatin and RRD2, after they accumulate in cancer cells, in binding to nuclear DNA is similar. Our results also show that RRD2 in the medium, in which the cells were cultured before RRD2 accumulated inside the cells, remained intact. This result is consistent with the view that RRD2 is activated by releasing free pyrophosphate only in the environment of cancer cells, thereby allowing RRD2 to bind to nuclear DNA.

Induction of cancer neoantigens facilitates development of clinically relevant models for the study of pancreatic cancer immunobiology

Neoantigen burden and CD8 T cell infiltrate are associated with clinical outcome in pancreatic ductal adenocarcinoma (PDAC). A shortcoming of many genetic models of PDAC is the lack of neoantigen burden and limited T cell infiltrate. The goal of the present study was to develop clinically relevant models of PDAC by inducing cancer neoantigens in KP2, a cell line derived from the KPC model of PDAC. KP2 was treated with oxaliplatin and olaparib (OXPARPi), and a resistant cell line was subsequently cloned to generate multiple genetically distinct cell lines (KP2-OXPARPi clones). Clones A and E are sensitive to immune checkpoint inhibition (ICI), exhibit relatively high T cell infiltration, and have significant upregulation of genes involved in antigen presentation, T cell differentiation, and chemokine signaling pathways. Clone B is resistant to ICI and is similar to the parental KP2 cell line in terms of relatively low T cell infiltration and no upregulation of genes involved in the pathways noted above. Tumor/normal exome sequencing and in silico neoantigen prediction confirms successful generation of cancer neoantigens in the KP2-OXPARPi clones and the relative lack of cancer neoantigens in the parental KP2 cell line. Neoantigen vaccine experiments demonstrate that a subset of candidate neoantigens are immunogenic and neoantigen synthetic long peptide vaccines can restrain Clone E tumor growth. Compared to existing models, the KP2-OXPARPi clones better capture the diverse immunobiology of human PDAC and may serve as models for future investigations in cancer immunotherapies and strategies targeting cancer neoantigens in PDAC.

Evaluation of toxicity and mutagenicity of oxaliplatin on germ cells in an alternative in vivo model Caenorhabditis elegans

The platinum compound oxaliplatin is a widely used chemotherapeutic drug that shows a broad spectrum of activity in various human tumors. While the treatment-related side effects of oxaliplatin on directly treated individuals have been well-documented, little is known about the influence of oxaliplatin on germ cells and non-exposed progenies. Here we investigated the reproductive toxicity of oxaliplatin in a 3R-compliant in vivo model Caenorhabditis elegans, and evaluated the germ cell mutagenicity of oxaliplatin by using whole genome sequencing. Our results indicated that oxaliplatin treatment significantly disrupts development of spermatids and oocytes. By treating parental worms with oxaliplatin for three successive generations, sequencing data unveiled the clear mutagenic effects of oxaliplatin on germ cells. Analysis of genome-wide mutation spectra showed the preferentially induction of indels by oxaliplatin. In addition, we uncovered the involvement of translesion synthesis polymerase ζ in modulating mutagenic effects of oxaliplatin. These findings suggest that germ cell mutagenicity is worthy of consideration for the health risk assessment of chemotherapeutic drugs, while the combined use of alternative in vivo models and next generation sequencing technology appears to be a promising way for the preliminary safety assessment of various drugs.

Cancer Cells Upregulate Tau to Gain Resistance to DNA Damaging Agents

Recent reports suggested a role for microtubules in double-strand-DNA break repair. We herein investigated the role of the microtubule-associated protein Tau in radio- and chemotherapy. Noticeably, a lowered expression of Tau in breast cancer cell lines resulted in a significant decrease in mouse-xenograft breast tumor volume after doxorubicin or X-ray treatments. Furthermore, the knockdown of Tau impaired the classical nonhomologous end-joining pathway and led to an improved cellular response to both bleomycin and X-rays. Investigating the mechanism of Tau's protective effect, we found that one of the main mediators of response to double-stranded breaks in DNA, the tumor suppressor p53-binding protein 1 (53BP1), is sequestered in the cytoplasm as a consequence of Tau downregulation. We demonstrated that Tau allows 53BP1 to translocate to the nucleus in response to DNA damage by chaperoning microtubule protein trafficking. Moreover, Tau knockdown chemo-sensitized cancer cells to drugs forming DNA adducts, such as cisplatin and oxaliplatin, and further suggested a general role of Tau in regulating the nuclear trafficking of DNA repair proteins. Altogether, these results suggest that Tau expression in cancer cells may be of interest as a molecular marker for response to DNA-damaging anti-cancer agents. Clinically targeting Tau could sensitize tumors to DNA-damaging treatments.

Antimutagenic Activity as a Criterion of Potential Probiotic Properties

The antimutagenic activity of probiotic strains has been reported over several decades of studying the effects of probiotics. However, this activity is rarely considered an important criterion when choosing strains to produce probiotic preparations and functional food. Meanwhile, the association of antimutagenic activity with the prevention of oncological diseases, as well as with a decrease in the spread of resistant forms in the microbiota, indicates its importance for the selection of probiotics. Besides, an antimutagenic activity can be associated with probiotics' broader systemic effects, such as geroprotective activity. The main mechanisms of such effects are considered to be the binding of mutagens, the transformation of mutagens, and inhibition of the transformation of promutagens into antimutagens. Besides, we should consider the possibility of interaction of the microbiota with regulatory processes in eukaryotic cells, in particular, through the effect on mitochondria. This work aims to systematize data on the antimutagenic activity of probiotics and emphasize antimutagenic activity as a significant criterion for the selection of probiotic strains.

A Toxic Friend: Genotoxic and Mutagenic Activity of the Probiotic Strain Escherichia coli Nissle 1917

The probiotic Escherichia coli strain Nissle 1917 (DSM 6601, Mutaflor), generally considered beneficial and safe, has been used for a century to treat various intestinal diseases. However, Nissle 1917 hosts in its genome the pks pathogenicity island that codes for the biosynthesis of the genotoxin colibactin. Colibactin is a potent DNA alkylator, suspected to play a role in colorectal cancer development. We show in this study that Nissle 1917 is functionally capable of producing colibactin and inducing interstrand cross-links in the genomic DNA of epithelial cells exposed to the probiotic. This toxicity was even exacerbated with lower doses of the probiotic, when the exposed cells started to divide again but exhibited aberrant anaphases and increased gene mutation frequency. DNA damage was confirmed in vivo in mouse models of intestinal colonization, demonstrating that Nissle 1917 produces the genotoxin in the gut lumen. Although it is possible that daily treatment of adult humans with their microbiota does not produce the same effects, administration of Nissle 1917 as a probiotic or as a chassis to deliver therapeutics might exert long-term adverse effects and thus should be considered in a risk-versus-benefit evaluation.

IMPORTANCE Nissle 1917 is sold as a probiotic and considered safe even though it has been known since 2006 that it harbors the genes for colibactin synthesis. Colibactin is a potent genotoxin that is now linked to causative mutations found in human colorectal cancer. Many papers concerning the use of this strain in clinical applications ignore or elude this fact or misleadingly suggest that Nissle 1917 does not induce DNA damage. Here, we demonstrate that Nissle 1917 produces colibactin in vitro and in vivo and induces mutagenic DNA damage. This is a serious safety concern that must not be ignored in the interests of patients, the general public, health care professionals, and ethical probiotic manufacturers.

Genetic Characterization of Cancer of Unknown Primary Using Liquid Biopsy Approaches

Cancers of unknown primary (CUPs) comprise a heterogeneous group of rare metastatic tumors whose primary site cannot be identified after extensive clinical-pathological investigations. CUP patients are generally treated with empirical chemotherapy and have dismal prognosis. As recently reported, CUP genome presents potentially druggable alterations for which targeted therapies could be proposed. The paucity of tumor tissue, as well as the difficult DNA testing and the lack of dedicated panels for target gene sequencing are further relevant limitations. Here, we propose that circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) could be used to identify actionable mutations in CUP patients. Blood was longitudinally collected from two CUP patients. CTCs were isolated with CELLSEARCH® and DEPArrayTM NxT and Parsortix systems, immunophenotypically characterized and used for single-cell genomic characterization with Ampli1TM kits. Circulating cell-free DNA (ccfDNA), purified from plasma at different time points, was tested for tumor mutations with a CUP-dedicated, 92-gene custom panel using SureSelect Target Enrichment technology. In parallel, FFPE tumor tissue was analyzed with three different assays: FoundationOne CDx assay, DEPArray LibPrep and OncoSeek Panel, and the SureSelect custom panel. These approaches identified the same mutations, when the gene was covered by the panel, with the exception of an insertion in APC gene. which was detected by OncoSeek and SureSelect panels but not FoundationOne. FGFR2 and CCNE1 gene amplifications were detected in single CTCs, tumor tissue, and ccfDNAs in one patient. A somatic variant in ARID1A gene (p.R1276∗) was detected in the tumor tissue and ccfDNAs. The alterations were validated by Droplet Digital PCR in all ccfDNA samples collected during tumor evolution. CTCs from a second patient presented a pattern of recurrent amplifications in ASPM and SEPT9 genes and loss of FANCC. The 92-gene custom panel identified 16 non-synonymous somatic alterations in ccfDNA, including a deletion (I1485Rfs∗19) and a somatic mutation (p. A1487V) in ARID1A gene and a point mutation in FGFR2 gene (p.G384R). Our results support the feasibility of non-invasive liquid biopsy testing in CUP cases, either using ctDNA or CTCs, to identify CUP genetic alterations with broad NGS panels covering the most frequently mutated genes.

A comparative analysis of the mutagenicity of platinum-containing chemotherapeutic agents reveals direct and indirect mutagenic mechanisms

Platinum-based drugs are a mainstay of cancer chemotherapy. However, their mutagenic effect can increase tumour heterogeneity, contribute to the evolution of treatment resistance and also induce secondary malignancies. We coupled whole genome sequencing with phenotypic investigations on two cell line models to compare the magnitude and examine the mechanism of mutagenicity of cisplatin, carboplatin and oxaliplatin. Cisplatin induced significantly more base substitution mutations than carboplatin or oxaliplatin when used at equitoxic concentrations on human TK6 or chicken DT40 cells, and also induced the highest number of short insertions and deletions. The analysis of base substitution spectra revealed that all three tested platinum drugs elicit both a direct mutagenic effect at purine dinucleotides, and an indirect effect of accelerating endogenous mutagenic processes, whereas the direct mutagenic effect appeared to correlate with the level of DNA damage caused as assessed through histone H2AX phosphorylation and single-cell agarose gel electrophoresis, the indirect mutagenic effects were equal. The different mutagenicity and DNA-damaging effect of equitoxic platinum drug treatments suggest that DNA damage independent mechanisms significantly contribute to their cytotoxicity. Thus, the comparatively high mutagenicity of cisplatin should be taken into account in the design of chemotherapeutic regimens.

A stapled POL κ peptide targets REV1 to inhibit mutagenic translesion synthesis

Stapled α-helical RIR (Rev1-interacting region) peptides of DNA POL κ bind more effectively to the RIR-interface of the C-terminal recruitment domain of the translesion synthesis DNA polymerase Rev1 than unstapled peptide. The tightest-binding stapled peptide translocates into cells and enhances the cytotoxicity of DNA damaging agents while reducing mutagenesis. Drugs with these characteristics could potentially serve as adjuvants to improve chemotherapy and reduce acquired resistance by inhibiting Rev1-dependent mutagenic translesion synthesis.

Evaluation of mutagenic activity of platinum complexes in somatic cells of Drosophila melanogaster

Cisplatin, carboplatin, and oxaliplatin are some of the most often used alkylating chemotherapeutic agents. In view of the paucity of data on the genotoxicity of oxaliplatin, this study compares the mutagenic activity of cisplatin (0.006, 0.012, 0.025, 0.05 mM), carboplatin (0.1, 0.2, 0,5, 1.0 mM), and oxaliplatin (0.1, 0.2, 0,5, 1.0 mM) using the somatic mutation and recombination test (SMART) in Drosophila melanogaster. Standard and high-bioactivation crosses of the drosophilid were used, which present basal and high levels of cytochrome P450 (CYP450) metabolization enzymes, respectively. All concentrations of cisplatin and carboplatin induced lesions in genetic material in both crosses, while oxaliplatin was mutagenic only to high bioactivation flies treated with 0.1, 0.5 and 1 mM of the compound. No significant differences were observed between genotoxicity values of cisplatin and carboplatin. However, CYP450 enzymes may have affected the mutagenic action of oxaliplatin. Carboplatin induced mainly mutation events, while cisplatin triggered mostly mutation and recombination events when low and high doses were used. Most events induced by oxaliplatin were generated by somatic recombination. Important differences were observed in genotoxic potential of platinum chemotherapeutic compounds, possibly due to the origin and type of the lesions induced in DNA and the repair mechanisms involved.

A Small Molecule Targeting Mutagenic Translesion Synthesis Improves Chemotherapy

Intrinsic and acquired drug resistance and induction of secondary malignancies limit successful chemotherapy. Because mutagenic translesion synthesis (TLS) contributes to chemoresistance as well as treatment-induced mutations, targeting TLS is an attractive avenue for improving chemotherapeutics. However, development of small molecules with high specificity and in vivo efficacy for mutagenic TLS has been challenging. Here, we report the discovery of a small-molecule inhibitor, JH-RE-06, that disrupts mutagenic TLS by preventing recruitment of mutagenic POL ζ. Remarkably, JH-RE-06 targets a nearly featureless surface of REV1 that interacts with the REV7 subunit of POL ζ. Binding of JH-RE-06 induces REV1 dimerization, which blocks the REV1-REV7 interaction and POL ζ recruitment. JH-RE-06 inhibits mutagenic TLS and enhances cisplatin-induced toxicity in cultured human and mouse cell lines. Co-administration of JH-RE-06 with cisplatin suppresses the growth of xenograft human melanomas in mice, establishing a framework for developing TLS inhibitors as a novel class of chemotherapy adjuvants.

Comparative sequence analysis of patient-matched primary colorectal cancer, metastatic, and recurrent metastatic tumors after adjuvant FOLFOX chemotherapy

Background

In the era of genome-guided personalized cancer treatment, we must understand chemotherapy-induced genomic changes in tumors. This study evaluated whether adjuvant FOLFOX chemotherapy modifies the mutational profile of recurrent colorectal cancer (CRC).

Methods

Whole exome sequencing was performed on samples from primary CRC tumors, untreated metastatic tumors, and recurrent tumors following adjuvant FOLFOX chemotherapy. The samples were resected from four patients.

Results

The number of mutations or the mutation spectrum in individual patients was nearly identical. Copy number variants persisted regardless of FOLFOX therapy administration. The genomic signature of oxaliplatin exposure (G > T/C > A, T > A/A > T) was not enriched after FOLFOX chemotherapy. Overlapping single nucleotide variants (SNVs) and indels remained in 26–65% of the patient-matched tumor samples. One patient harbored an AKT1 E17K mutation in the recurrent tumor, whereas PIK3CA E542K and E88Q mutations were detected in the primary and untreated metastatic tumor samples. Genes related to intracellular Ca²⁺ homeostasis were enriched among the genes uniquely mutated after FOLFOX chemotherapy.

Conclusions

We found that the mutation rates, mutation spectrum, and copy number variants were nearly identical regardless of the administration of FOLFOX therapy in the four CRC cases. The mutational discordance between the patient-matched tumor samples is likely caused by tumor heterogeneity and chemotherapy-induced clonal selection. These findings might be useful as pilot data for larger studies to clarify the changes in the mutational landscape induced by adjuvant FOLFOX chemotherapy.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5479-6) contains supplementary material, which is available to authorized users.

Half-sandwich Os(ii) and Ru(ii) bathophenanthroline complexes: anticancer drug candidates with unusual potency and a cellular activity profile in highly invasive triple-negative breast cancer cells

There is an urgent need to discover new, selective compounds to add to the limited arsenal of chemotherapeutics displaying selective toxicity for aggressive triple-negative breast cancer (TNBC) cells. The effect of two, recently developed metal-based half-sandwich complexes [Os(η6-pcym)(bphen)(dca)]PF6 (Os-dca) and [Ru(η6-pcym)(bphen)(dca)]PF6 (Ru-dca) [pcym = 1-methyl-4-(propan-2-yl)benzene (p-cymene); bphen = 4,7-diphenyl-1,10-phenanthroline (bathophenanthroline); dca = dichloroacetate] on triple-negative breast cancer cells MDA-MB-231 is reported. The complexes display selective toxicity in several tumor cells (at submicromolar concentrations), and a prominent effect is observed against highly progressive triple negative breast cancer MDA-MB-231 cells for Os-dca. The lower potency of Ru-dca in comparison with Os-dca is apparently connected with a relatively quick release of the dca ligand due to the hydrolysis of Ru-dca before this complex enters the cells. Remarkably, both Os-dca and Ru-dca reduce successfully metastasis-related properties of the triple-negative breast cancer cells such as migration, invasion, and re-adhesion. The anti-metastatic effects of Os-dca and Ru-dca are associated with their ability to suppress matrix metalloproteinase activity and/or production and reduce the expression of aquaporins. Further detailed mechanistic studies reveal that Os-dca reverses Warburg's effect and oncosis seems to be a prominent mode of cell death that predominates over apoptosis. As such, Os-dca can efficiently overcome the resistance of cancer cells to clinically-used apoptotic inducers cisplatin and carboplatin. The cytostatic and anti-metastatic properties of Os-dca in MDA-MB-231 provide a strong impetus for the development of new metal-based compounds to target hardly treatable human TNBC cells and displaying different modes of action compared to the antitumor metallodrugs in clinical use.

Anticancer kiteplatin pyrophosphate derivatives show unexpected target selectivity for DNA

One of the promising new antitumor platinum complexes is a large-ring chelate complex [PtCl₂(cis-1,4-DACH)] (DACH = diaminocyclohexane) (kiteplatin). Recently, new platinum(ii) derivatives of kiteplatin with pyrophosphate as a carrier ligand have been synthesized and tested on a panel of human cancer cell lines. These derivatives of kiteplatin were found to be more effective than clinically used anticancer platinum drugs. The design of kiteplatin pyrophosphate derivatives was based on the concept of pyrophosphate coordinated platinum complexes, phosphaplatins. Phosphaplatins have been shown to function without binding to DNA and hence DNA has been excluded as the target of phosphaplatins in contrast to conventional antitumor platinum drugs. Cytotoxicity, major cellular targets and DNA interactions of the new anticancer platinum drug were characterized by standard biochemical methods and methods of molecular and cellular biology. We demonstrate that, in contrast to what has been reported on closely related phosphaplatins, the derivatives of kiteplatin with the pyrophosphate carrier ligand are activated in the cellular environment. This activation, which yields species capable of platination of DNA, very likely comprises the hydrolytic release of the pyrophosphate ligand that could be enzymatically catalyzed. Collectively, these data provide convincing evidence that unexpectedly DNA is an important target for the biological activity of the kiteplatin pyrophosphate derivatives, although the overall mechanism of action might be different from those of conventional platinum drugs.

Identification of Small Molecule Translesion Synthesis Inhibitors That Target the Rev1-CT/RIR Protein-Protein Interaction

Translesion synthesis (TLS) is an important mechanism through which proliferating cells tolerate DNA damage during replication. The mutagenic Rev1/Polζ-dependent branch of TLS helps cancer cells survive first-line genotoxic chemotherapy and introduces mutations that can contribute to the acquired resistance so often observed with standard anticancer regimens. As such, inhibition of Rev1/Polζ-dependent TLS has recently emerged as a strategy to enhance the efficacy of first-line chemotherapy and reduce the acquisition of chemoresistance by decreasing tumor mutation rate. The TLS DNA polymerase Rev1 serves as an integral scaffolding protein that mediates the assembly of the active multiprotein TLS complexes. Protein-protein interactions (PPIs) between the C-terminal domain of Rev1 (Rev1-CT) and the Rev1-interacting region (RIR) of other TLS DNA polymerases play an essential role in regulating TLS activity. To probe whether disrupting the Rev1-CT/RIR PPI is a valid approach for developing a new class of targeted anticancer agents, we designed a fluorescence polarization-based assay that was utilized in a pilot screen for small molecule inhibitors of this PPI. Two small molecule scaffolds that disrupt this interaction were identified, and secondary validation assays confirmed that compound 5 binds to Rev1-CT at the RIR interface. Finally, survival and mutagenesis assays in mouse embryonic fibroblasts and human fibrosarcoma HT1080 cells treated with cisplatin and ultraviolet light indicate that these compounds inhibit mutagenic Rev1/Polζ-dependent TLS in cells, validating the Rev1-CT/RIR PPI for future anticancer drug discovery and identifying the first small molecule inhibitors of TLS that target Rev1-CT.

A comprehensive survey of the mutagenic impact of common cancer cytotoxics

BACKGROUND

Genomic mutations caused by cytotoxic agents used in cancer chemotherapy may cause secondary malignancies as well as contribute to the evolution of treatment-resistant tumour cells. The stable diploid genome of the chicken DT40 lymphoblast cell line, an established DNA repair model system, is well suited to accurately assay genomic mutations.

RESULTS

We use whole genome sequencing of multiple DT40 clones to determine the mutagenic effect of eight common cytotoxics used for the treatment of millions of patients worldwide. We determine the spontaneous mutagenesis rate at 2.3 × 10(-10) per base per cell division and find that cisplatin, cyclophosphamide and etoposide induce extra base substitutions with distinct spectra. After four cycles of exposure, cisplatin induces 0.8 mutations per Mb, equivalent to the median mutational burden in common leukaemias. Cisplatin-induced mutations, including short insertions and deletions, are mainly located at sites of putative intrastrand crosslinks. We find two of the newly defined cisplatin-specific mutation types as causes of the reversion of BRCA2 mutations in emerging cisplatin-resistant tumours or cell clones. Gemcitabine, 5-fluorouracil, hydroxyurea, doxorubicin and paclitaxel have no measurable mutagenic effect. The cisplatin-induced mutation spectrum shows good correlation with cancer mutation signatures attributed to smoking and other sources of guanine-directed base damage.

CONCLUSION

This study provides support for the use of cell line mutagenesis assays to validate or predict the mutagenic effect of environmental and iatrogenic exposures. Our results suggest genetic reversion due to cisplatin-induced mutations as a distinct mechanism for developing resistance.

Molecular Dissection of Induced Platinum Resistance through Functional and Gene Expression Analysis in a Cell Culture Model of Bladder Cancer

We report herein the development, functional and molecular characterization of an isogenic, paired bladder cancer cell culture model system for studying platinum drug resistance. The 5637 human bladder cancer cell line was cultured over ten months with stepwise increases in oxaliplatin concentration to generate a drug resistant 5637R sub cell line. The MTT assay was used to measure the cytotoxicity of several bladder cancer drugs. Liquid scintillation counting allowed quantification of cellular drug uptake and efflux of radiolabeled oxaliplatin and carboplatin. The impact of intracellular drug inactivation was assessed by chemical modulation of glutathione levels. Oxaliplatin- and carboplatin-DNA adduct formation and repair was measured using accelerator mass spectrometry. Resistance factors including apoptosis, growth factor signaling and others were assessed with RNAseq of both cell lines and included confirmation of selected transcripts by RT-PCR. Oxaliplatin, carboplatin, cisplatin and gemcitabine were significantly less cytotoxic to 5637R cells compared to the 5637 cells. In contrast, doxorubicin, methotrexate and vinblastine had no cell line dependent difference in cytotoxicity. Upon exposure to therapeutically relevant doses of oxaliplatin, 5637R cells had lower drug-DNA adduct levels than 5637 cells. This difference was partially accounted for by pre-DNA damage mechanisms such as drug uptake and intracellular inactivation by glutathione, as well as faster oxaliplatin-DNA adduct repair. In contrast, both cell lines had no significant differences in carboplatin cell uptake, efflux and drug-DNA adduct formation and repair, suggesting distinct resistance mechanisms for these two closely related drugs. The functional studies were augmented by RNAseq analysis, which demonstrated a significant change in expression of 83 transcripts, including 50 known genes and 22 novel transcripts. Most of the transcripts were not previously associated with bladder cancer chemoresistance. This model system and the associated phenotypic and genotypic data has the potential to identify some novel details of resistance mechanisms of clinical importance to bladder cancer.

Thermodynamic and mechanistic insights into translesion DNA synthesis catalyzed by Y-family DNA polymerase across a bulky double-base lesion of an antitumor platinum drug

To determine how the Y-family translesion DNA polymerase η (Polη) processes lesions remains fundamental to understanding the molecular origins of the mutagenic translesion bypass. We utilized model systems employing a DNA double-base lesion derived from 1,2-GG intrastrand cross-links of a new antitumor Pt(II) complex containing a bulky carrier ligand, namely [PtCl(2)(cis-1,4-dach)] (DACH=diaminocyclohexane). The catalytic efficiency of Polη for the insertion of correct dCTP, with respect to the other incorrect nucleotides, opposite the 1,2-GG cross-link was markedly reduced by the DACH carrier ligand. This reduced efficiency of Polη to incorporate the correct dCTP could be due to a more extensive DNA unstacking and deformation of the minor groove induced in the DNA by the cross-link of bulky [PtCl(2)(cis-1,4-dach)]. The major products of the bypass of this double-base lesion produced by [PtCl(2)(cis-1,4-dach)] by Polη resulted from misincorporation of dATP opposite the platinated G residues. The results of the present work support the thesis that this misincorporation could be due to sterical effects of the bulkier 1,4-DACH ligand hindering the formation of the Polη-DNA-incoming nucleotide complex. Calorimetric analysis suggested that thermodynamic factors may contribute to the forces that governed enhanced incorporation of the incorrect dATP by Polη as well.

Structures of oxaliplatin-oligonucleotide adducts from DNA

Oxaliplatin, [(1R,2R)-cyclohexane-1,2-diamine](ethanedioato-O,O')platinum(II) shows a great efficiency against colorectal cancer. Although the mode of action of oxaliplatin is not yet understood, it is commonly accepted that binding of oxaliplatin to DNA prevents DNA synthesis and alters protein to DNA binding. In order to elucidate the modified DNA-protein interaction and thus to understand the mechanisms leading to cellular misinterpretation of DNA information and apoptosis, we have identified the preferential binding sites and the dynamics of the oxaliplatin-DNA intrastrand and interstrand adducts at the oligomer level using high-performance liquid chromatography/electrospray ionization-tandem mass spectrometry (HPLC/ESI-MS/MS) and HPLC/inductively coupled plasma-MS for quantitative studies. We used a combination of benzonase, alkaline phosphatase and Nuclease S1 for digestion. This digestion procedure allows the study of platinated oligomeric nucleotides and more complex interstrand adducts. The digestion products were mostly chromatographically separated and characterized using HPLC/ESI-ion trap MS/MS experiments. We could show that the adducts to guanine and adenine are quite dynamic; that is, the ratios are changing for several days. In addition, the resulting adducts provide evidence for the action of the digesting enzymes and indicate that the adduct spectrum at the oligomeric level is different to that at the commonly studies dinucleotide level.

Genotoxicity testing of combined treatment with cisplatin, bleomycin, and 5-fluorouracil in somatic cells of Drosophila melanogaster

The simultaneous treatment with the cross-linking agent cisplatin, the radiomimetic antitumoral drug bleomycin, and the anti-metabolite drug 5-fluorouracil has been used as a regimen to treat patients with squamous cell carcinoma of the head and neck. Considering that these drugs interact directly with DNA, one of the important late-occurring complications from treatment of primary malignancies is the therapy-related secondary cancers as a result of the genotoxic activity of the drugs on normal cells. In this sense, the genotoxicity of this combination was evaluated using the wing somatic mutation and recombination test in Drosophila melanogaster. The mutant spots observed in marker-heterozygous and balancer-heterozygous flies were compared in order to quantitatively and qualitatively estimate the genotoxic effect of these drugs. Cisplatin (0.003 and 0.006mM), bleomycin (0.005 and 0.01mM), and both combinations preferentially induced recombinational events, while mutation is the major event regarding the genetic toxicity of 5-fluorouracil (0.025 and 0.05mM). The combination of these drugs produced synergistic and antagonistic genotoxic effects, depending on the concentrations used, which could impose a higher risk of secondary effects associated with their genotoxic effects, emphasizing the importance of long-term monitoring in patients being treated with these drugs.

KRAS mutations in primary tumours and post-FOLFOX metastatic lesions in cases of colorectal cancer

BACKGROUND

KRAS mutations are predictive markers for the efficacy of anti-EGFR antibody therapies in patients with metastatic colorectal cancer. Although the mutational status of KRAS is reportedly highly concordant between primary and metastatic lesions, it is not yet clear whether genotoxic chemotherapies might induce additional mutations.

METHODS

A total of 63 lesions (23 baseline primary, 18 metastatic and 24 post-treatment metastatic) from 21 patients who were treated with FOLFOX as adjuvant therapy for stage III/IV colorectal cancer following curative resection were examined. The DNA samples were obtained from formalin-fixed paraffin-embedded specimens, and KRAS, NRAS, BRAF and PIK3CA mutations were evaluated.

RESULTS

The numbers of primary lesions with wild-type and mutant KRAS codons 12 and 13 were 8 and 13, respectively. The mutational status of KRAS remained concordant between the primary tumours and the post-FOLFOX metastatic lesions, irrespective of patient background, treatment duration and disease-free survival. Furthermore, the mutational statuses of the other genes evaluated were also concordant between the primary and metastatic lesions.

CONCLUSION

Because the mutational statuses of predictive biomarker genes were not altered by FOLFOX therapy, specimens from both primary tumours and post-FOLFOX tumour metastases might serve as valid sources of DNA for known genomic biomarker testing.

Thermodynamics of translesion synthesis across a major DNA adduct of antitumor oxaliplatin: differential scanning calorimetric study

Differential scanning calorimetry (DSC) was used to measure the thermodynamic changes associated with translesion synthesis across major lesion induced in DNA by antitumor oxaliplatin [1,2-d(GG) intrastrand cross-link]. Insertion of matched nucleotides dC at the primer terminus (across unique 3'- or 5'-dG in the unplatinated template) and subsequent extensions resulted in an incremental increase in thermodynamic parameters. In contrast, incorporation of dC opposite either platinated dG in the intrastrand cross-link formed in the template strand and subsequent extensions by one nucleotide resulted only in little changes in thermodynamics. A similar thermodynamic delay was observed for a control template primer containing a dG:dT mismatch across 3'- or 5'-dG in the template and subsequent Watson-Crick primer extensions. The thermodynamic scarcity generated by either the lesion or mismatches was not localized but extended to the 5'-downstream sites, which may be connected with the phenomenon termed "short-term memory" of replication errors retained by some DNA polymerases responding to DNA damages or mismatches. Interestingly, formation of the 1,2-d(GG) intrastrand cross-link of oxaliplatin altered the overall DSC profiles of the dG:dT mismatch template/primers only in a very small extent. While addition of matched nucleotide dC across either dG in the template strand was thermodynamically favored over the presence of a mismatched dT (ΔΔG(0)(310) was 7.6 or 6.8 kJ mol(-1), ΔΔH was 14 or 49 kJ mol(-1)), no such thermodynamic advantage was observed with the 1,2-d(GG) intrastrand cross-link of oxaliplatin at these positions (ΔΔG(0)(310) was 2.8 or -0.3 kJ mol(-1), ΔΔH was 4 or 9 kJ mol(-1)). The equilibrium thermodynamic data also provide insight into the processes associated with misincorporation of incorrect nucleotides during replication bypass across major cross-links of antitumor oxaliplatin. On the other hand, besides thermodynamic effects also kinetic factors play an important role in the processing of the cross-links of antitumor platinum drugs. The impact of the two effects in overall processing DNA adducts by a particular DNA polymerase will depend on its nature.

DNA polymerase eta and chemotherapeutic agents

The discovery of human DNA polymerase eta (pol η) has a major impact on the fields of DNA replication/repair fields. Since the discovery of human pol η, a number of new DNA polymerases with the ability to bypass various DNA lesions have been discovered. Among these polymerases, pol η is the most extensively studied lesion bypass polymerase with a defined major biological function, that is, to replicate across the cyclobutane pyrimidine dimers introduced by UV irradiation. Cyclobutane pyrimidine dimer is a major DNA lesion that causes distortion of DNA structure and block the replicative DNA polymerases during DNA replication process. Genetic defects in the pol η gene, Rad30, results in a disease called xeroderma pigmentosum variant. This review focuses on the overall properties of pol η and the mechanism that involved in regulating its activity in cells. In addition, the role of pol η in the action of DNA-targeting anticancer compounds is also discussed.

Differences in the cellular response and signaling pathways between cisplatin and monodentate organometallic Ru(II) antitumor complexes containing a terphenyl ligand

The new monofunctional Ru(II)-arene complex [(η⁶-arene)Ru(II)(en)Cl]+, where en = 1,2-diaminoethane and the arene is para-terphenyl (complex 1) exhibits promising cytotoxic effects in human tumor cells including those resistant to conventional cisplatin (J. Med. Chem.2008, 51, 5310). The present study is focused on the cellular pharmacology of 1 to elucidate more deeply the mechanisms underlying its antitumor effects. We have identified several cellular mechanisms induced by 1 in human ovarian carcinoma cells, including inhibition of DNA synthesis, overexpression and activation of p53, expression of proapoptotic proteins p21(WAF1) and Bax, G₀/G₁ arrest, and nuclear fragmentation as a result of apoptotic, and, to a much lower extent, also necrotic processes. Thus, 1 inhibits growth of the cancer cells through induction of apoptotic cell death and G₀/G₁ cell cycle arrest. Further investigations have shown that 1 induces apoptosis by regulating the expression of Bcl-2 family proteins. There were significant differences in cellular responses to the treatment with 1 and with conventional cisplatin, particularly in the kinetics and the extent of these responses. In addition, the distinct p53 activation profile of 1 compared with cisplatin provides an explanation for the activity of this ruthenium drug against cisplatin-resistant cells. Hence complex 1 may provide an alternative therapy in patients with acquired cisplatin resistance, particularly with respect to its very low mutagenicity and different mode of action compared to platinum antitumor drugs in clinical use.

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

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.

Increased levels and defective glycosylation of MRPs in ovarian carcinoma cells resistant to oxaliplatin

Pt compounds still represent the mainstay of the treatment of ovarian carcinoma. The aim of the present study was to investigate the molecular bases of resistance to Pt drugs using an oxaliplatin-resistant ovarian carcinoma cell model IGROV-1/OHP. These cells exhibited high levels of resistance to oxaliplatin, cross-resistance to cisplatin and topotecan and displayed a marked accumulation defect of Pt drugs. This feature was associated with increased expression and altered N-linked glycosylation of ATP binding cassette transporters MRP1 and MRP4. Pre-treatment with tunicamycin, which inhibits the biosynthesis of N-linked oligosaccharides, decreased the accumulation of Pt in sensitive cells exposed to oxaliplatin or cisplatin and increased the electrophoretic mobility of MRP1 and MRP4, reproducing the association between decreased glycosylation of MRP1 and MRP4 and decreased Pt accumulation observed in the resistant IGROV-1/OHP cells. The observed N-glycosylation defect of oxaliplatin-resistant cells was linked to reduced levels of N-acetylglucosamine-1-phosphotransferase (GNPTG) and mannosyl (alpha-1,6-)-glycoprotein beta-1,6-N-acetyl-glucosaminyltransferase (MGAT5). This feature, observed in IGROV-1/OHP cells, was associated with decreased retention of Pt drugs. In addition, the overexpression of fully glycosylated MRP1 or MRP4 in tumor cell line of ovarian origin was associated with resistance to oxaliplatin and cisplatin. Our findings, showing that development of resistance to oxaliplatin results in up-regulation of MRPs, support that patients with oxaliplatin-refractory ovarian carcinomas may benefit from non-Pt-based regimens which do not contain MRP1 and MRP4 substrates.

Use of combination therapy with cisplatin and calcitriol in the treatment of Y-79 human retinoblastoma xenograft model

BACKGROUND

Retinoblastoma is the most common primary malignant intraocular neoplasm of childhood. The poor outcomes of patients with metastatic retinoblastoma have encouraged the search for new therapies. In the current study, the efficacy of combination therapy with calcitriol and cisplatin in athymic mice with subcutaneous Y-79 human retinoblastoma tumours was assessed.

METHODS

60 athymic mice were subcutaneously injected with human Y79 retinoblastoma cells. Animals were randomised into four groups: group 1, 50 microg of cisplatin; group 2, 0.05 microg of calcitriol; group 3, 0.05 microg of calcitriol and 50 microg of cisplatin; group 4, control. The cisplatin was administered once a week, and the calcitriol was given five times a week.

RESULTS

There was a significant inhibition of tumour growth in animals treated with the combination therapy of calcitriol and cisplatin as compared with controls and cisplatin alone (p = 0.0001 and p = 0.0041 respectively). In terms of toxicity, serum calcium levels were increased, but there was no mortality and minimal nephrotoxicity in any of the groups.

CONCLUSION

The present study shows that cisplatin given in combination with calcitriol may be a viable multidrug therapy option in the treatment of high-risk retinoblastoma.

Molecular dynamic simulations of cisplatin- and oxaliplatin-d(GG) intrastand cross-links reveal differences in their conformational dynamics

Mismatch repair proteins, DNA damage-recognition proteins and translesion DNA polymerases discriminate between Pt-GG adducts containing cis-diammine ligands (formed by cisplatin (CP) and carboplatin) and trans-RR-diaminocyclohexane ligands (formed by oxaliplatin (OX)) and this discrimination is thought to be important in determining differences in the efficacy, toxicity and mutagenicity of these platinum anticancer agents. We have postulated that these proteins recognize differences in conformation and/or conformational dynamics of the DNA containing the adducts. We have previously determined the NMR solution structure of OX-DNA, CP-DNA and undamaged duplex DNA in the 5'-d(CCTCAGGCCTCC)-3' sequence context and have shown the existence of several conformational differences in the vicinity of the Pt-GG adduct. Here we have used molecular dynamics simulations to explore differences in the conformational dynamics between OX-DNA, CP-DNA and undamaged DNA in the same sequence context. Twenty-five 10 ns unrestrained fully solvated molecular dynamics simulations were performed starting from two different DNA conformations using AMBER v8.0. All 25 simulations reached equilibrium within 4 ns, were independent of the starting structure and were in close agreement with previous crystal and NMR structures. Our data show that the cis-diammine (CP) ligand preferentially forms hydrogen bonds on the 5' side of the Pt-GG adduct, while the trans-RR-diaminocyclohexane (OX) ligand preferentially forms hydrogen bonds on the 3' side of the adduct. In addition, our data show that these differences in hydrogen bond formation are strongly correlated with differences in conformational dynamics, specifically the fraction of time spent in different DNA conformations in the vicinity of the adduct, for CP- and OX-DNA adducts. We postulate that differential recognition of CP- and OX-GG adducts by mismatch repair proteins, DNA damage-recognition proteins and DNA polymerases may be due, in part, to differences in the fraction of time that the adducts spend in a conformation favorable for protein binding.

Solution structures of a DNA dodecamer duplex with and without a cisplatin 1,2-d(GG) intrastrand cross-link: comparison with the same DNA duplex containing an oxaliplatin 1,2-d(GG) intrastrand cross-link

Proteins that discriminate between cisplatin-DNA adducts and oxaliplatin-DNA adducts are thought to be responsible for the differences in tumor range, toxicity, and mutagenicity of these two important chemotherapeutic agents. However, the structural basis for differential protein recognition of these adducts has not been determined and could be important for the design of more effective platinum anticancer agents. We have determined high-resolution NMR structures for cisplatin-GG and undamaged DNA dodecamers in the AGGC sequence context and have compared these structures with the oxaliplatin-GG structure in the same sequence context determined previously in our laboratory. This structural study allows the first direct comparison of cisplatin-GG DNA and oxaliplatin-GG DNA solution structures referenced to undamaged DNA in the same sequence context. Non-hydrogen atom rmsds of 0.81 and 1.21 were determined for the 15 lowest-energy structures for cisplatin-GG DNA and undamaged DNA, respectively, indicating good structural convergence. The theoretical NOESY spectra obtained by back-calculation from the final average structures showed excellent agreement with the experimental data, indicating that the final structures are consistent with the NMR data. Several significant conformational differences were observed between the cisplatin-GG adduct and the oxaliplatin-GG adduct, including buckle at the 5' G6.C19 base pair, opening at the 3' G7.C18 base pair, twist at the A5G6.T20C19 base pair step, slide, twist, and roll at the G6G7.C19C18 base pair step, slide at the G7C8.C18G17 base pair step, G6G7 dihedral angle, and overall bend angle. We hypothesize that these conformational differences may be related to the ability of various DNA repair proteins, DNA binding proteins, and DNA polymerases to discriminate between cisplatin-GG and oxaliplatin-GG adducts.