DNA double-strand breaks repair inhibitors potentiates the combined effect of VP-16 and CDDP in human colorectal adenocarcinoma (LoVo) cells.

I. BACKGROUND: A combination of etoposide (VP-16) and cisplatin (CDDP) is the standard treatment for certain colon cancers. These drugs promote the death of cancer cells via direct and indirect induction of the most lethal DNA lesions - DNA double-stand breaks. However, cancer cells can reverse the DNA damaging effect of anticancer drugs by triggering DNA repair processes. In eukaryotic cells, the main DNA repair pathway responsible for DNA double-stand breaks repair is non-homologous end-joining (NHEJ). Inhibitors of DNA repair are of special interest in cancer research as they could break the cellular resistance to DNA-damaging agents and increase the efficiency of standard cancer treatments. In this study, we investigated the effect of two NHEJ inhibitors, SCR7 and NU7441, on the cytotoxic mechanism of VP-16/CDDP in a LoVo human colorectal adenocarcinoma cell line. SCR7 blocks Ligase IV-mediated joining by interfering with its DNA binding, whereas NU7441 is a highly potent and selective DNA-PK inhibitor.II. METHODS AND RESULTS: Both inhibitors synergistically increased the cytotoxicity of CDDP and VP-16 when combined, but the effect of SCR7 was more pronounced. SCR7 and NU7441 also significantly increased VP-16; CDDP induced DNA double-stand breaks level and delayed drug-induced DSB repair, as seen on the comet assay and measured using H2AX foci. We also observed changes in cell cycle distribution and enhanced apoptosis ratio in colorectal adenocarcinoma cells treated with DNA repair inhibitors and VP-16/CDDP.III. CONCLUSIONS: Our data support the hypothesis that NHEJ inhibitors could be used in conjunction with standard therapy to provide effective clinical improvement and allow reduction in drug doses.

Menthol additives to tobacco products. Reasons for withdrawing mentholated cigarettes in European Union on 20th may 2020 according to tobacco products directive (2014/40/EU).

Menthol, which is a natural cyclic monoterpene alcohol with a minty smell, is one of the main constituents of essential oils that naturally occur in some aromatic plants, such as Mentha × piperita L. This natural compound shows many biological properties, such as anesthetic, analgesic, antibacterial and antifungal, immunomodulating, and skin penetration-enhancing. It is added to a variety of goods, such as food, oral-care products, OTC products, cosmetics, and tobacco products. Menthol is not just a simple flavoring agent, especially when it comes to tobacco products. Its ability to 'mask' the negative effects of nicotine and its additional positive sensory effects makes it the most common additive in such products. For the customers, mentholated tobacco products may be mistakenly perceived as less harmful for health, which may increase their consumption. However, as the evidence shows, menthol cigarettes are no safer than conventional cigarettes and may lead to more frequent disease exacerbation during prolonged exposure to smoke from such products. In addition, because of its complex interactions with nicotine, menthol may affect smoking behavior and may increase addiction to nicotine. For those reasons, the European Union banned flavored cigarettes (whose sale size reached more than 3% of the total tobacco product market) by implementing the Tobacco Products Directive (2014/40/EU) on 20th May 2020. While the menthol ban was based on health concerns, the ultimate effect on consumers, regarding potential quitting, is yet to be determined.

IQOS - a heat-not-burn (HnB) tobacco product - chemical composition and possible impact on oxidative stress and inflammatory response. A systematic review.

Objectives: This work attempts to summarize current knowledge about IQOS, the heat-not-burn tobacco products, their chemical composition and possible impact on oxidative stress and inflammatory response.Materials and Methods: The literature search was performed between January and April 2019 by a combination of terms: 'IQOS smoking', 'IQOS cigarette', 'I quit original smoking cigarette', 'heat-not-burn products', 'HnB tobacco products'.Results: The aim of IQOS system is to minimalize the exposure of its smokers to dangerous substances present in cigarette smoke and to lower the probability of development of tobacco-related diseases. As current studies suggest, this new heat-not-burn tobacco product emits significantly lower concentrations of tar, carbonyls, VOCs, CO, free radicals or nitrosamines when compared to conventional cigarette, and thus it may reduce health risk for smokers. However, it does not eliminate this risk of development of tobacco-related diseases.Discussion: For conventional tobacco smokers the IQOS products may be an alternative option, which helps to reduce exposure to hazardous and potentially hazardous constituents. However, for never-smokers using the IQOS cigarettes may develop an addiction or increase exposition to some substances, which may increase probability of tobacco-related diseases. Moreover, emission of unexpected substances depends on device cleaning strategy and puff regiments.Conclusions: There is only limited data about IQOS effect on smokers' health. The future investigation, especially comparison with healthy never-smokers or study of chronic exposure to IQOS, is needed.

Inhibition of DNA-PK potentiates the synergistic effect of NK314 and etoposide combination on human glioblastoma cells.

Etoposide (VP-16) is the topoisomerase 2 (Top2) inhibitor used for treating of glioma patients however at high dose with serious side effects. It induces DNA double-strand breaks (DSBs). These DNA lesions are repaired by non-homologous DNA end joining (NHEJ) mediated by DNA-dependent protein kinase (DNA-PK). One possible approach to decrease the toxicity of etoposide is to reduce the dose while maintaining the anticancer potential. It could be achieved through combined therapy with other anticancer drugs. We have assumed that this objective can be obtained by (1) a parallel topo2 α inhibition and (2) sensitization of cancer cells to DSBs. In this work we investigated the effect of two Top2 inhibitors NK314 and VP-16 in glioma cell lines (MO59 K and MO59 J) sensitized by DNA-PK inhibitor, NU7441. Cytotoxic effect of VP-16, NK314 alone and in combination on human glioblastoma cell lines, was assessed by a colorimetric assay. Genotoxic effect of anticancer drugs in combination with NU7441 was assessed by comet assay. Cell cycle distribution and apoptosis were analysed by flow cytometry. Compared with VP-16 or NK314 alone, the combined treatment significantly inhibited cell proliferation. Combination treatment was associated with a strong accumulation of DSBs, modulated cell cycle phases distribution and apoptotic cell death. NU7441 potentiated these effects and additionally postponed DNA repair. Our findings suggest that NK314 could overcome resistance of MO59 cells to VP-16 and NU7441 could serve as sensitizer to VP-16/NK314 combined treatment. The combined tripartite approach of chemotherapy could reduce the overall toxicity associated with each individual therapy, while concomitantly enhancing the anticancer effect to treat human glioma cells. Thus, the use of a tripartite combinatorial approach could be promising and more efficacious than mono therapy or dual therapy to treat and increase the survival of the glioblastoma patients.

Comparison of the effect of three different topoisomerase II inhibitors combined with cisplatin in human glioblastoma cells sensitized with double strand break repair inhibitors.

Topoisomerase II (Topo2) inhibitors in combination with cisplatin represent a common treatment modality used for glioma patients. The main mechanism of their action involves induction of DNA double-strand breaks (DSBs). DSBs are repaired via the homology-dependent DNA repair (HRR) and non-homologous end-joining (NHEJ). Inhibition of the NHEJ or HRR pathway sensitizes cancer cells to the treatment. In this work, we investigated the effect of three Topo2 inhibitors-etoposide, NK314, or HU-331 in combination with cisplatin in the U-87 human glioblastoma cell line. Etoposide as well as NK314 inhibited Topo2 activity by stabilizing Topo2-DNA cleavable complexes whereas HU-331 inhibited the ATPase activity of Topo2 using a noncompetitive mechanism. To increase the effectiveness of the treatment, we combined cisplatin and Topo2 inhibitor treatment with DSB repair inhibitors (DRIs). The cells were sensitized with NHEJ inhibitor, NU7441, or the novel HRR inhibitor, YU238259, prior to drug treatment. All of the investigated Topo2 inhibitors in combination with cisplatin efficiently killed the U-87 cells. The most cytotoxic effect was observed for the cisplatin + HU331 treatment scheme and this effect was significantly increased when a DRI pretreatment was used; however, we did not observed DSBs. Therefore, the molecular mechanism of cytotoxicity caused by the cisplatin + HU331 treatment scheme is yet to be evaluated. We observed a concentration-dependent change in DSB levels and accumulation at the G2/M checkpoint and S-phase in glioma cells incubated with NK314/cisplatin and etoposide/cisplatin. In conclusion, in combination with cisplatin, HU331 is the most potent Topo2 inhibitor of human glioblastoma cells.

DNA Double Strand Breaks Repair Inhibitors: Relevance as Potential New Anticancer Therapeutics.

DNA double-strand breaks are considered one of the most lethal forms of DNA damage. Many effective anticancer therapeutic approaches used chemical and physical methods to generate DNA double-strand breaks in the cancer cells. They include: IR and drugs which mimetic its action, topoisomerase poisons, some alkylating agents or drugs which affected DNA replication process. On the other hand, cancer cells are mostly characterized by highly effective systems of DNA damage repair. There are two main DNA repair pathways used to fix double-strand breaks: NHEJ and HRR. Their activity leads to a decreased effect of chemotherapy. Targeting directly or indirectly the DNA double-strand breaks response by inhibitors seems to be an exciting option for anticancer therapy and is a part of novel trends that arise after the clinical success of PARP inhibitors. These trends will provide great opportunities for the development of DNA repair inhibitors as new potential anticancer drugs. The main objective of this article is to address these new promising advances.

Effect of smoking on gene expression profile - overall mechanism, impact on respiratory system function, and reference to electronic cigarettes.

Cigarette smoke has a crucial impact on transcriptome alteration by its effect on chromatin remodeling and DNA methylation status. The first mechanism is associated with the histone acetylation/deacetylation balance damage as a result of increased activity of NFĸB and lipid peroxidation products, which lead to an increased activity of HATs and DNMTs and reduced HDACs. The second mechanism is connected with direct damaging of DNA by smoke components, activation of downstream repair mechanism and recruitment of DNMTs into the breakage site, 'nicotine effect' and carbon monoxide (CO) activity on gene transcription and DNA methylation reduction. Cigarette smoking activates oxidative and inflammatory response and leads to uncontrolled structural changes in airways and alters gene expression. Such changes have a characteristic similar to that for COPD patients. Therefore, smoking is determined as a key risk factor for chronic respiratory disease development. Furthermore, electronic cigarettes, an alternative of tobacco cigarettes, also affect gene expression profile, which suggests some similarities in action mechanisms for both conventional and electronic cigarettes. However, there is only a limited number of trials discussing this issue and future investigations are needed.