Non-DSB clustered DNA lesions induced by ionizing radiation are largely responsible for the loss of plasmid DNA functionality in the presence of cisplatin

Opuntia ficus indica cladode extract inhibit DNA double-strand breaks and locally multiply damaged sites induced by gamma radiation

It is beyond doubt that radiotherapy is extremely effective in treating a wide variety of cancers. The sensitivity of the surrounding normal tissues limits the amount of radiation administered to the tumor. There is an urgent need to develop a treatment that combines pharmacological treatment with ionizing radiation (IR) specifically designed to specifically target cancer cells while protecting the surrounding normal tissue, resulting in an increase in the efficacy of the cancer treatment. IR could cause many types of DNA lesions. Double-strand breaks (DSBs) andlocally multiple damaged sites (LMDS)arethe main radiotoxic damages.Recently, the identification of new antioxidants from natural sources has attracted the attention of scientists. In this context, the present study aims to determine if the Opuntia ficus indica cladode extract (CE) can be used as a radioprotector.

MATERIALS AND METHODS

The DNA treated by 137Cs γ-radiation (25-700 Gy) in the absence or presence of cactus cladode extract (CCE) was added to theE. colibase excision repair. The amounts of both DNA damages were calculated using the electrophoretic method.

RESULTS

The irradiation of DNA in the presence of CCE induced a dramatic decrease of the yields of purine and pyrimidine-DSB. A decrease of65 % and 84 % of the purine and pyrimidine-DSB sensitive sites have been calculated, respectively, when the sample added CCE3 during the radiotreatment. Moreover, a reduction of 80 % in the amount of Nth + Fpg-DSB SSs (non-DSB cluster damage) after γ-irradiation in the presence of CCE3 was observed.

CONCLUSION

Through the present it was found that the CCE can play an important role as a radio protector, maybe by scavenging the ROS formed during radio treatment or by other unknown pathways. The most toxic DNA lesions (DSBs, and LMDS) decreased dramatically. Studies aimed at obtaining more documentation about CCE components with potential radio-preventive activity are desirable because of their protective properties.

Comparisons between the Direct and Indirect Effect of 1.5 keV X-rays and 0-30 eV Electrons on DNA: Base Lesions, Stand Breaks, Cross-Links, and Cluster Damages

The interaction of low energy electrons (LEEs; 1-30 eV) with genomic material can induce multiple types of damage that may cause the loss of genetic information, mutations, genome instability, and cell death. For all damages measurable by electrophoresis, we provide the first complete set of G-values (yield of a specific product per energy deposited) induced in plasmid DNA by the direct and indirect effects of LEEs (GLEE) and 1.5 keV X-rays (GX) under identical conditions. Low energy photoelectrons are produced via X-rays incident on a tantalum (Ta) substrate covered with DNA and placed in a chamber filled with nitrogen at atmospheric pressure, under four different humidity levels, ranging from dry conditions to full hydration (Γ = 2.5 to Γ = 33, where Γ is the number of water molecules/nucleotide). Damage yields are measured as a function of X-ray fluence and humidity. GLEE values are between 2 and 27 times larger than those for X-rays. At Γ = 2.5 and 33, GLEE values for double strand breaks are 27 and 16 times larger than GX, respectively. The indirect effect contributes ∼50% to the total damage. These G-values allow quantification of potentially lethal lesions composed of strand breaks and/or base damages in the presence of varying amounts of water, i.e., closer to cellular conditions.

Interaction of low-energy electrons with radiosensitizers

We provide an experimentalist's perspective on the present state-of-the-art in the studies of low-energy electron interactions with common radiosensitizers, including compounds used in combined chemo-radiation therapy and their model systems. Low-energy electrons are important secondary species formed during the interaction of ionizing radiation with matter. Their role in the radiation chemistry of living organisms has become an important topic for more than 20 years. With the increasing number of works and reviews in the field, we would like to focus here on a very narrow area of compounds that have been shown to have radio-sensitizing properties on the one hand, and high reactivity towards low-energy electrons on the other hand. Gas phase experiments studying electron attachment to isolated molecules and environmental effects on reaction dynamics are reviewed for modified DNA components, nitroimidazoles, and organometallics. In the end, we provide a perspective on the future directions that may be important for transferring the fundamental knowledge about the processes induced by low-energy electrons into practice in the field of rational design of agents for concomitant chemo-radiation therapy.

Impact of fractionated cisplatin and radiation treatment on cell growth and accumulation of DNA damage in two normal cell types differing in origin

Evidence on the impact of chemotherapy on radiotherapy-induced second malignant neoplasms is controversial. We estimated how cisplatin modulates the in vitro response of two normal cell types to fractionated radiation. AHH-1 lymphoblasts and VH10 fibroblasts were irradiated at 1 Gy/fraction 5 and 3 times per week during 12 and 19 days, respectively, and simultaneously treated with 0.1, 0.2, 0.4, 0.8, 1.7 and 3.3 µM of cisplatin twice a week. Cell growth during treatment was monitored. Cell growth/cell death and endpoints related to accumulation of DNA damage and, thus, carcinogenesis, were studied up to 21 days post treatment in cells exposed to radiation and the lowest cisplatin doses. Radiation alone significantly reduced cell growth. The impact of cisplatin alone below 3.3 µM was minimal. Except the lowest dose of cisplatin in VH10 cells, cisplatin reduced the inhibitory effect of radiation on cell growth. Delayed cell death was highest in the combination groups while the accumulation of DNA damage did not reveal a clear pattern. In conclusion, fractionated, concomitant exposure to radiation and cisplatin reduces the inhibitory effect of radiation on cell proliferation of normal cells and does not potentiate delayed effects resulting from accumulation of DNA damage.

Recognition and removal of clustered DNA lesions via nucleotide excision repair

Clustered damage of DNA consists of two or more lesions located within one or two turns of the DNA helix. Clusters consisting of lesions of various structures can arise under the influence of strong damaging factors, especially if the cells have a compromised repair status. In this work, we analyzed how the presence of an analog of the apurinic/apyrimidinic site - a non-nucleoside residue consisting of diethylene glycol phosphodiester (DEG) - affects the recognition and removal of a bulky lesion (a non-nucleoside site of the modified DNA strand containing a fluorescein residue, nFlu) from DNA by a mammalian nucleotide excision repair system. Here we demonstrated that the efficiency of nFlu removal decreases in the presence of DEG in the complementary strand and is completely suppressed when the DEG is located opposite the nFlu. By contrast, protein factor XPC-RAD23B, which initiates global genomic nucleotide excision repair, has higher affinity for DNA containing clustered damage as compared to DNA containing a single bulky lesion; the affinity of XPC strengthens as the positions of DEG and nFlu become closer. The changes in the double-stranded DNA's geometry caused by the presence of clustered damage were also assessed. The obtained experimental data together with the results of molecular dynamics simulations make it possible to get insight into the structural features of DNA containing clustered lesions that determine the efficiency of repair. Speaking more broadly, this study should help to understand the probable fate of bulky adduct-containing clusters of various topologies in the mammalian cell.

Short-Term Efficacy of Different First-Line Chemotherapy Regimens for Advanced Non-Small Cell Lung Cancer: A Network Meta-Analysis

This study intends to compare short-term efficacy of 12 chemotherapy regimens in treatment of advanced non-small cell lung cancer (NSCLC) by a network meta-analysis (NMA). PubMed, Cochrane Library, and Embase were searched from the inception of each database to June 2018. Randomized controlled trials (RCTs) of the 12 chemotherapy regimens for advanced NSCLC were included. Direct and indirect evidence were combined by NMA to evaluate the odds ratio and the surface under the cumulative ranking curves (SUCRA) of the 12 chemotherapy regimens. Nineteen RCTs that met our inclusion criteria were collected in this study. For partial response (PR), gemcitabine exhibited relatively poor efficacy compared with cisplatin + gemcitabine, carboplatin + gemcitabine, carboplatin + paclitaxel, paclitaxel + gemcitabine, and cisplatin + gemcitabine + vinorelbine. For overall response rate (ORR), gemcitabine had poorer efficacy than cisplatin + gemcitabine and paclitaxel + gemcitabine. For disease control rate (DCR), compared with carboplatin + gemcitabine and gemcitabine, paclitaxel + gemcitabine had a better efficacy. Gemcitabine had the lowest SUCRA values in terms of complete response, PR, ORR, stable disease, and DCR; whereas paclitaxel + gemcitabine ranked the highest in ORR, progressive disease, and DCR. The cluster analysis revealed that cisplatin + gemcitabine, paclitaxel + gemcitabine, and cisplatin + gemcitabine + vinorelbine had better short-term efficacy for advanced NSCLC. Collectively, short-term efficacy of multidrug combination chemotherapy regimens was superior to that of single-drug chemotherapy regimens for advanced NSCLC. Cisplatin + gemcitabine, paclitaxel + gemcitabine, and cisplatin + gemcitabine + vinorelbine may have particularly prominent short-term efficacy for advanced NSCLC.

Electron impact ionisation cross sections of cis- and trans-diamminedichloridoplatinum(II) and its hydrolysis products

We report total electron-impact ionisation cross sections (EICSs) of cisplatin, its hydrolysis products and transplatin in the energy range from threshold to 10 keV using the binary-encounter-Bethe (BEB) and its relativistic variant (RBEB), and the Deutsch-Märk (DM) methods. We find reasonable agreement between all three methods, and we also note that the RBEB and the BEB methods yield very similar (almost identical) results in the considered energy range. For cisplatin, the resulting EICSs yield cross section maxima of 22.09 × 10-20 m2 at 55.4 eV for the DM method and 18.67 × 10-20 m2 at 79.2 eV for the (R)BEB method(s). The EICSs of monoaquated cisplatin yield maxima of 12.54 × 10-20 m2 at 82.8 eV for the DM method and of 9.74 × 10-20 m2 at 106 eV for the (R)BEB method(s), diaquated cisplatin yields maxima of 7.56 × 10-20 m2 at 118.5 eV for the DM method and of 5.77 × 10-20 m2 at 136 eV for the (R)BEB method(s). Molecular geometry does not affect the resulting EICS significantly, which is also reflected in very similar EICSs of the cis- and trans-isomer. Limitations of the work as well as desirable future directions in the research area are discussed.

Molecular efficacy of radio- and chemotherapy sequences from direct DNA damage measurements

PURPOSE

To investigate the molecular aspects of the synergy between ionizing radiation and platinum (Pt) chemotherapeutic agents in cancer treatment with chemoradiation therapy (CRT) by measuring damages induced by low-energy electrons (LEE) to DNA bound to cisplatin. LEE are produced abundantly by any type of ionizing radiation and cisplatin represents a typical Pt-chemotherapeutic agents.

MATERIALS AND METHODS

Our strategy involves two parallel administrations of cisplatin and irradiation with a 4.6 and 9.6 eV electron fluence of 1.1 × 10¹²: (1) LEE bombardment of supercoiled DNA and its subsequent reaction with cisplatin; (2) the reaction of DNA with cisplatin followed by LEE irradiation. The damage yields for the loss of supercoiled (LS), single-strand breaks (SSB) and double-strand breaks (DSB) were obtained from gel electrophoresis analysis. Base modifications were revealed by treating the samples with Escherichia coli base excision repair endonuclease (Nth and Fpg).

RESULTS

The yields were deduced from the respective time-response for the reaction of DNA with cisplatin. The results show that binding cisplatin to DNA followed by LEE irradiation, consistently yields more DNA damages than the reverse order. In comparison to non-treated DNA, administration (2) results in an increase of LS and SSB of 1.4-3.3 folds and of DSB by more than an order of magnitude. Furthermore, after enzyme treatment, the yields of DSB rise by factors of 5.3-15.4, indicating a large increase of clustered damages, which should at least partially translate into an increase of lethal damages in cancer cells during the CRT.

CONCLUSIONS

Our results demonstrate that a strong synergy between radiation and cisplatin can only be achieved at the molecular level, if the drug is present at the time of irradiation. Furthermore, this work confirms the LEE mechanism previously proposed to explain the synergy between radiation and Pt drugs in CRT. It involves chemical sensitization of DNA prior to irradiation, to facilitate strand breaks and clustered damages induced by the highly reactive LEE.

Radiation-induced clustered DNA lesions: Repair and mutagenesis

Clustered DNA lesions, also called Multiply Damaged Sites, is the hallmark of ionizing radiation. It is defined as the combination of two or more lesions, comprising strand breaks, oxidatively generated base damage, abasic sites within one or two DNA helix turns, created by the passage of a single radiation track. DSB clustered lesions associate DSB and several base damage and abasic sites in close vicinity, and are assimilated to complex DSB. Non-DSB clustered lesions comprise single strand break, base damage and abasic sites. At radiation with low Linear Energy Transfer (LET), such as X-rays or γ-rays clustered DNA lesions are 3-4 times more abundant than DSB. Their proportion and their complexity increase with increasing LET; they may represent a large part of the damage to DNA. Studies in vitro using engineered clustered DNA lesions of increasing complexity have greatly enhanced our understanding on how non-DSB clustered lesions are processed. Base excision repair is compromised, the observed hierarchy in the processing of the lesions within a cluster leads to the formation of SSB or DSB as repair intermediates and increases the lifetime of the lesions. As a consequence, the chances of mutation drastically increase. Complex DSB, either formed directly by irradiation or by the processing of non-DSB clustered lesions, are repaired by slow kinetics or left unrepaired and cause cell death or pass mitosis. In surviving cells, large deletions, translocations, and chromosomal aberrations are observed. This review details the most recent data on the processing of non-DSB clustered lesions and complex DSB and tends to demonstrate the high significance of these specific DNA damage in terms of genomic instability induction.

The Exploitation of Low-Energy Electrons in Cancer Treatment

Given the distinct characteristics of low-energy electrons (LEEs), particularly at energies less than 30 eV, they can be applied to a wide range of therapeutic modalities to improve cancer treatment. LEEs have been shown to efficiently produce complex molecular damage resulting in substantial cellular toxicities. Since LEEs are produced in copious amounts from high-energy radiation beam, including photons, protons and ions; the control of LEE distribution can potentially enhance the therapeutic radio of such beams. LEEs can play a substantial role in the synergistic effect between radiation and chemotherapy, particularly halogenated and platinum-based anticancer drugs. Radiosensitizing entities containing atoms of high atomic number such as gold nanoparticles can be a source of LEE production if high-energy radiation interacts with them. This can provide a high local density of LEEs in a cell and produce cellular toxicity. Auger-electron-emitting radionuclides also create a high number of LEEs in each decay, which can induce lethal damage in a cell. Exploitation of LEEs in cancer treatment, however, faces a few challenges, such as dosimetry of LEEs and selective delivery of radiosensitizing and chemotherapeutic molecules close to cellular targets. This review first discusses the rationale for utilizing LEEs in cancer treatment by explaining their mechanism of action, describes theoretical and experimental studies at the molecular and cellular levels, then discusses strategies for achieving modification of the distribution and effectiveness of LEEs in cancerous tissue and their associated clinical benefit.

DNA damage response (DDR) pathway engagement in cisplatin radiosensitization of non-small cell lung cancer

Non-small cell lung cancers (NSCLC) are commonly treated with a platinum-based chemotherapy such as cisplatin (CDDP) in combination with ionizing radiation (IR). Although clinical trials have demonstrated that the combination of CDDP and IR appear to be synergistic in terms of therapeutic efficacy, the mechanism of synergism remains largely uncharacterized. We investigated the role of the DNA damage response (DDR) in CDDP radiosensitization using two NSCLC cell lines. Using clonogenic survival assays, we determined that the cooperative cytotoxicity of CDDP and IR treatment is sequence dependent, requiring administration of CDDP prior to IR (CDDP-IR). We identified and interrogated the unique time and agent-dependent activation of the DDR in NSCLC cells treated with cisplatin-IR combination therapy. Compared to treatment with CDDP or IR alone, CDDP-IR combination treatment led to persistence of γH2Ax foci, a marker of DNA double-strand breaks (DSB), for up to 24h after treatment. Interestingly, pharmacologic inhibition of DDR sensor kinases revealed the persistence of γ-H2Ax foci in CDDP-IR treated cells is independent of kinase activation. Taken together, our data suggest that delayed repair of DSBs in NSCLC cells treated with CDDP-IR contributes to CDDP radiosensitization and that alterations of the DDR pathways by inhibition of specific DDR kinases can augment CDDP-IR cytotoxicity by a complementary mechanism.

Stress-induced DNA damage biomarkers: applications and limitations

A variety of environmental stresses like chemicals, UV and ionizing radiation and organism's endogenous processes such as replication stress and metabolism can lead to the generation of reactive oxygen and nitrogen species (ROS/RNS) that can attack cellular vital components like DNA, proteins and lipid membranes. Among them, much attention has been focused on DNA since DNA damage plays a role in several biological disorders and aging processes. Thus, DNA damage can be used as a biomarker in a reliable and accurate way to quantify for example radiation exposure and can indicate its possible long term effects and cancer risk. Based on the type of DNA lesions detected one can hypothesize on the most probable mechanisms involved in the formation of these lesions for example in the case of UV and ionizing radiation (e.g., X- or α-, γ-rays, energetic ions, neutrons). In this review we describe the most accepted chemical pathways for DNA damage induction and the different types of DNA lesions, i.e., single, complex DNA lesions etc. that can be used as DNA damage biomarkers. We critically compare DNA damage detection methods and their limitations. In addition, we suggest the use of DNA repair gene products as biomarkes for identification of different types of stresses i.e., radiation, oxidative, or replication stress, based on bioinformatic approaches and meta-analysis of literature data.