Genomic Instability Changes Research Articles

Abstract 424: Genomic instability changes of circulating tumor DNA reflect the responses to chemotherapy or targeted therapy in advanced gastric cancer

Abstract Background: Gastric cancer was characterized by frequent somatic copy number alterations and high genomic instability, yet the significance of genomic instability and its changes implicated by drug treatment in advanced gastric cancer (AGC) remain unclear. In this study, we investigated genomic instability changes of circulating tumor DNA (ctDNA). Methods: A total of 101 plasmas and paired blood cells from 26 patients with AGC before (N=26) and after (N=75) treatment were prospectively collected. Plasma ctDNA was separated and assessed for copy number variations (CNV) by whole genome sequencing (WGS), and we assessed the correlation between genomic indexes and therapeutic response. Results: Genomic instability with diverse patterns was observed in 20 of 26 patients (77%) prior to drug treatment. For patients with high (N=20) level genomic instability prior to drug treatment, the response rate (55%, 11/20) was significantly higher than that (17%, 1/6) in patients with low level (N=6) genomic instability (P=0.17). Notably, genomic instability changed with the administration of drugs, which reflected its correlation with therapeutic response. All ctDNAs (94%, 14/15) collected at the time of partial response (PR) after treatment displayed low-genomic instability. However, 52% ctDNAs (13/25) collected at the time of progressive disease (PD) after treatment showed high-level genomic instability. Furthermore, several patterns of CNV were categorized in ctDNAs. CNV pattern after acquiring drug resistance were largely unchanged with respect to CNV baseline patterns. Conclusions: Genomic instability based on ctDNA can be used to predict and monitor therapeutic response in gastric cancer, although validation in larger cohort would be necessary. Citation Format: Zuhua Chen, Cheng Zhang, Beifang Li, Yunyun Niu, Limeng Chen, Mengqi Zhang, Jing Yang, Sijia Lu, Jing Gao, Lin Shen. Genomic instability changes of circulating tumor DNA reflect the responses to chemotherapy or targeted therapy in advanced gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 424.

Abstract 3789: Genomic instability changes acquired by HPV16 E6/E7 targeting multipolar mitoses aneuploidy: Cellular sequelae

Abstract Malignant progression of high-risk Papillomavirus (HPV), associated lesions is a slow and inefficient process. HPV a non-enveloped epitheliotropic double stranded DNA virus, is an etiological agent of oral cancer. Oral cancer is related to the persistent infection by high-risk HPV type 16, E6/E7 oncoproteins. The E6/E7 complex significantly contribute to the carcinogenic genetic instability effect of high-risk HPV through the degradation of two gatekeeper proteins, p53 and pRB, respectively. This process is associated with viral genome integration into a host cellular chromosome and accumulation of numerical and structural chromosome aberrations. Viral genome integration results in consistent, sustained and dysregulated expression of the E6 and E7 oncogenes, and continued E6/E7 expression is necessary for maintenance of the transformed phenotype of HPV positive cancer cell. Induction of genomic instability by high-risk HPV E6/E7 demonstrates that HPV also drive malignant progression through targeting the nuclear and mitotic apparatus protein-1 (NuMA), and through subversion of DNA double strand break repair by HPV E6/E7 induced centrosome abnormalities. This in turn may cause abnormal localization of the microtubule protein dynein. The NuMA provides a cohesive force that guarantees the integrity of the mitotic spindle poles. However, there are no studies addressing the relationship between HPV16 infection-oral cancer, NuMA expression, and genomic instability. The aim of this study determined if HPV16 E6/E7 subverts centrosome coalescence in oral cancer caused by HPV oncogenes targeting the NuMA protein. In our experimental procedures, we proposed a novel approach to study HPV-induced chromosomal changes with reconstructed human oral epithelium in SCID mouse. We used HPV16, which is the most common HPV type found in oral cancer. Two plasmids were used to produce HPV-16 E6/E7. The first plasmid p16sheLL expresses the two viral capsid proteins, L1 and L2. The second plasmid pBR322HPV16 contains the full length HPV-16 genome. This approach closely mimics the architecture of normal human oral epithelium. In our study, we first focused on analyzing selected cellular processes involving multipolar mitoses. We examined Dynein localization in mitotic cells by immunofluorescence. We also analyzed progressive morphological and cytopathic changes in HPV-infected oral epithelia by using molecular cytogenetic analysis. In summary these data indicate that NuMA expression is alternated, and HPV16 E6/E7 oncoproteins can promote increased upregulation of genomic instability by induction of centrosome abnormalities and inhibition of DNA double strand break repair. We also found High-risk HPV16 E6/E7 oncoproteins induced mitotic defects and genetic aneuploidies through induction of supernumerary anaphase bridges, supernumerary centrosomes, and DNA double strand breaks. Citation Format: Eva McGhee, Mengtao Li, Yi-Ling Lin, Khadijah Lang, Meidrah Tyler, Judith Okoro, Mai Do, Naomi Long, Jenna Cormier, Adin Handler, Julian Handler, Sameeran Das, Benjamin Liu, Anthonia Duru, Billy Ballard, Roland Pattillo, Jay Vadgama. Genomic instability changes acquired by HPV16 E6/E7 targeting multipolar mitoses aneuploidy: Cellular sequelae [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3789.

Assessment of Listerine Cool Mint mouthwash influence on possible DNA damage measured by buccal micronucleus cytome assay-preliminary results

Listerine is a brand of mouthwash most used worldwide in oral hygene maintainance. With its antimicrobic and antifungal characteristics, it can stop/diminish plaque and gingivitis development. Among different types of this mouthwash, all 5 ingredients of Listerine Cool Mint, 21.6% ethanol and 4 herbal extracts-thymol, menthol, eucalyptol and methyl salicylate, have shown capacity to cause cell damage and buccal epithelial cells are in direct contact. Buccal micronucleus cytome assay (BMN) measures changes in differentiation as the frequency of basal/differentiated, binuclear, and cells in different phases of cell death-apoptosis/necrosis (cells with condensed chromatin, karriorhectic, pycnotic and karyolitic cells) and changes in genomic instability measured as micronucleus or nuclear buds/broken eggs frequency. Samples from 10 healthy individuals using Listerine Cool Mint mouthwash twice/day during two-week treatment were analyzed before and after the treatment. There was no significant influence on cell differentiation and genomic instability on the group level, although micronucleus frequency (MN) of entire group was higher after the treatment (1 vs. 1.5). We found interindividual differences and showed that strong alcoholic drinks consumers had higher MN. Future studies should include more individuals, especially with regular alcohol consummation for analysis of possible synergistic influence and therefore higher risk of genomic instability, together with genetic polymorphisms in enzymes responsible for metabolism of ethanol, since they can drastically influence the time duration of ethanol exposure and its metabolite acetaldehyde and also have an impact on genomic instability and possible development of oral squamous cell cancer.

Genomic Instability Changes of Circulating Tumor DNA Reflect the Responses to Chemotherapy or Targeted Therapy in Advanced Gastric Cancer

Background: Gastric cancer is characterized by frequent somatic copy number alterations (SCNV) and a high level of genomic instability. In this study, we investigated the genomic instability changes of circulating tumor DNA (ctDNA). Methods: A total of 101 plasmas and paired blood cells from 26 patients with AGC before (n = 26) and after (n = 75) drug treatment were collected. Plasma ctDNA was separated and assessed for SCNV by whole-genome sequencing (WGS), and the whole genome abnormality score (WGAS) was calculated. We next assessed the correlations between WGAS and therapeutic response. Findings: Genomic instability was observed in 20 of 26 patients (77%) prior to drug treatment. For patients with genomic instability prior to treatment, the response rate (55%, 11/20) was higher than that (17%, 1/6) of patients with stable genomes. Notably, genomic instability fluctuated during therapy, with 93% (14/15) of post-therapeutic ctDNAs showing low-genomic instability when sensitive to drug therapy and 52% (13/25) of ctDNAs with developed resistance to therapy showing high genomic instability. For ctDNAs with developed resistance, the genomic instability patterns were identical to those before treatment, but the instability level was lower than the pretherapeutic level. Interpretation: We found that genomic instability based on ctDNA could be used to predict and monitor therapeutic response in gastric cancer, although validation in a larger cohort will be necessary. Funding Statement: This work was supported by the National Key Research and Development Program of China (No. 2017YFC1308900, 2017YFC0908400) and the Beijing Municipal Science & Technology Commission Program (No. Z161100002616036). Declaration of Interests: The authors declare no conflict of competing interest. Ethics Approval Statement: This study was approved by the Medical Ethics Committee of Peking University Cancer Hospital, and written informed consent was obtained from all of the patients for their samples to be used in the future.

Role of DNA Damage and Epigenetic DNA Methylation Changes in Radiation-Induced Genomic Instability and Bystander Effects in Germline In Vivo

Ionizing radiation (IR) is a curative treatment for many human malignancies, an important diagnostic modality, and a pivotal preparative regimen for bone marrow transplantation. On the other hand, IR is a potent damaging agent that can affect a variety of processes in directly exposed cells, in their descendents, and in neighboring un-irradiated naïve 'bystander' cells. Accumulation of DNA damage caused by IR in conjunction with disrupted cellular regulation processes can lead to genome instability in the germline, and therefore to transgenerational genome instability in offspring of exposed males. The exact mechanisms of IR-induced genome instability in directly exposed and in naïve bystander germ cells remain obscure, yet accumulating evidence points to the role of DNA damage and DNA methylation changes in genome instability development. In the current study, we used a well-established murine model to define the role of DNA methylation, DNA damage, as well as two important germline regulators of DNA methylation, Brother of the Regulator of Imprinted Sites (BORIS) and CCCTC binding factor (CTCF), in IR and bystander responses of the male germline. Here we report that irradiation leads to a significant accumulation of DNA damage in the exposed and bystander testis tissue, and to altered DNA methylation and dysregulated BORIS expression in the exposed testis tissue. The possible molecular mechanisms and biological consequences of the observed changes are discussed.

Transgenerational changes in somatic and germ line genetic integrity of first-generation offspring derived from the DNA damaged sperm

To report a more quantitative approach to study the influence of varying levels of sperm DNA damage on transgenerational changes in genomic instability in a mouse model. Experimental prospective study. Embryology research laboratory. Swiss albino mice. The sperm DNA damage was induced by different doses of gamma-irradiation to male mice followed by mating with healthy female mice. Genomic integrity in embryos, fetus, and spermatozoa of F1 mice derived from the DNA-damaged sperm. The transgenerational changes in genetic integrity were attributed by a dose-dependent increase in the frequency of micronuclei in preimplantation embryos and a concomitant increase in genomic instability in fetal liver cells and sperm chromatin modifications in F1 males. A strong positive correlation was observed between the extent of sperm DNA damage and somatic and germ-line genomic instability. Sperm-mediated transgenerational genomic instability is dependent on the amount of DNA damage present in the sire's sperm at the time of fertilization.

A stochastic model of cancer initiation including a bystander effect

A stochastic model of cancer initiation is considered. The model is used to evaluate whether a bystander effect may be important in the pre-malignant and malignant stages of carcinogenesis, and furthermore, on the basis of epidemiological data, to estimate the mutation rates of genes involved in the development of oral leukoplakias. The bystander effect is defined here as the capability of oncogenic mutations to increase the mutation probability of neighbouring (bystander) cells, thus leading potentially to a cascade of neighbouring mutated and neoplastic cells as a pre-stage in the development to leukoplakias and cancer. We find that incidence data for oral cancer are indeed in accordance with a significant bystander effect, operating either alone or in combination with genomic instability in the early stages of carcinogenesis, i.e. the development of neoplasia. Simulations performed gave a picture of how mutations and neoplasia may spread in a tissue, to form characteristic leukoplakias with a core of neoplastic cells. The model also showed that the probability of finding at least one neoplastic cell in the tissue after a given number of years is more sensitive to changes in genomic instability within the cell itself than to changes in a bystander effect. Based on epidemiological data we also calculate the maximum number of oncogenic genes that may be involved in the bystander effect and development of genomic instability. Even if capable of explaining the initial development of oncogenic mutations towards neoplastic cells, the bystander model could not reproduce the observed incidence rates of leukoplakia without assuming a carcinogen mutation probability per cell per year of neoplastic cells practically equal to one. This means that the bystander effect, to be of substantial importance in the final development of neoplastic cells towards leukoplakias, requires a very significant increase in mutation probabilities for bystanders to neoplastic cells. Alternatively, additional mechanisms such as abnormal cell differentiation and uncontrolled proliferation and apoptotis in the neoplastic stage may be of major importance during the development to cancerization.