Abstract 2110: Platinum-inducedBRCA1 promoter DNA hypermethylation and altered metabolic profile promotes chemoresistance in ovarian cancer

High grade serous ovarian cancer (HGSOC) is the most common and aggressive type of ovarian cancer (OC). Platinum resistance is a common occurrence in HGSOC leading to tumor relapse and patient mortality. Multiple mechanisms contribute to platinum resistance in OC, including enrichment of ovarian cancer stem cells (OCSCs), which is observed in relapsed tumors. Platinum treatment activates the DNA damage response (DDR) and the DNA repair protein BRCA1 is an OC susceptibility factor. In our study, we demonstrate that platinum treatment induces a decrease in BRCA1 levels that leads to an increase in activity of ALDH, an OCSC marker. In a parallel pathway that is associated with G2/M arrest, platinum treatment also induces an increase in NAMPT expression and NAD+ levels, the cofactor required for ALDH activity. BRCA1 is repressed through platinum-induced promoter DNA hypermethylation. Importantly, combination of platinum with decitabine, a DNA methyltransferase (DNMT) inhibitor, prevents the platinum-induced increase in OCSCs. This study uniquely provides preclinical support for the use of DNMT inhibitors in the neoadjuvant setting in combination with platinum treatment for OC patients.

Citation Format: Riddhi Sood, Sikai Xiao, Shruthi Sriramkumar, Christiane Hassel, Kenneth Nephew, Heather O'Hagan. Platinum-inducedBRCA1 promoter DNA hypermethylation and altered metabolic profile promotes chemoresistance in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2110.

Characterization of the ^{163}Ho Electron Capture Spectrum: A Step Towards the Electron Neutrino Mass Determination

The isotope ^{163}Ho is in many ways the best candidate to perform experiments to investigate the value of the electron neutrino mass. It undergoes an electron capture process to ^{163}Dy with an energy available to the decay, Q_{EC}, of about 2.8 keV. According to the present knowledge, this is the lowest Q_{EC} value for such transitions. Here we discuss a newly obtained spectrum of ^{163}Ho, taken by cryogenic metallic magnetic calorimeters with ^{163}Ho implanted in the absorbers and operated in anticoincident mode for background reduction. For the first time, the atomic deexcitation of the ^{163}Dy daughter atom following the capture of electrons from the 5s shell in ^{163}Ho, the OI line, was observed with a calorimetric measurement. The peak energy is determined to be 48 eV. In addition, a precise determination of the energy available for the decay Q_{EC}=(2.858±0.010_{stat}±0.05_{syst})  keV was obtained by analyzing the intensities of the lines in the spectrum. This value is in good agreement with the measurement of the mass difference between ^{163}Ho and ^{163}Dy obtained by Penning-trap mass spectrometry, demonstrating the reliability of the calorimetric technique.

Induction of endocycles represses apoptosis independently of differentiation and predisposes cells to genome instability

The endocycle is a common developmental cell cycle variation wherein cells become polyploid through repeated genome duplication without mitosis. We previously showed that Drosophila endocycling cells repress the apoptotic cell death response to genotoxic stress. Here, we investigate whether it is differentiation or endocycle remodeling that promotes apoptotic repression. We find that when nurse and follicle cells switch into endocycles during oogenesis they repress the apoptotic response to DNA damage caused by ionizing radiation, and that this repression has been conserved in the genus Drosophila over 40 million years of evolution. Follicle cells defective for Notch signaling failed to switch into endocycles or differentiate and remained apoptotic competent. However, genetic ablation of mitosis by knockdown of Cyclin A or overexpression of fzr/Cdh1 induced follicle cell endocycles and repressed apoptosis independently of Notch signaling and differentiation. Cells recovering from these induced endocycles regained apoptotic competence, showing that repression is reversible. Recovery from fzr/Cdh1 overexpression also resulted in an error-prone mitosis with amplified centrosomes and high levels of chromosome loss and fragmentation. Our results reveal an unanticipated link between endocycles and the repression of apoptosis, with broader implications for how endocycles may contribute to genome instability and oncogenesis.

Subnuclear partitioning of rRNA genes between the nucleolus and nucleoplasm reflects alternative epiallelic states

Eukaryotes can have thousands of 45S ribosomal RNA (rRNA) genes, many of which are silenced during development. Using fluorescence-activated sorting techniques, we show that active rRNA genes in Arabidopsis thaliana are present within sorted nucleoli, whereas silenced rRNA genes are excluded. DNA methyltransferase (met1), histone deacetylase (hda6), or chromatin assembly (caf1) mutants that disrupt silencing abrogate this nucleoplasmic-nucleolar partitioning. Bisulfite sequencing data indicate that active nucleolar rRNA genes are nearly completely demethylated at promoter CGs, whereas silenced genes are nearly fully methylated. Collectively, the data reveal that rRNA genes occupy distinct but changeable nuclear territories according to their epigenetic state.

Aging in sexual and obligately asexual clones of Daphnia from temporary ponds

The freshwater crustacean Daphnia is an emerging model system in the biology of aging. Diversity in aging patterns is thought to be caused by ecological variation in selection on age-specific performance. Previous work in Daphnia has shown a strong correspondence between selective differences and genetic variation in aging in the Daphnia pulex species complex. However, recent evidence suggests obligate asexuality could account for the more rapid aging found in pond genotypes compared with lake genotypes without invoking differences in selection. Evolutionary biologists have to date assumed equivalent operation of neutral processes when comparing aging across populations, but a shift in the breeding system changes the basic dynamics of neutral evolution. To test the hypothesis that the breeding system could explain the short lifespans of pond-dwelling Daphnia, we compared aging of sexual and asexual Daphnia clones from temporary ponds. Our data contradict the breeding system hypothesis. Differences in aging between the breeding systems were slight, and trended in the opposite direction from that predicted: asexual clones had longer lifespans and appeared to age more slowly than sexual clones. We conclude that divergent selection between habitats remains the best explanation for differences in aging between Daphnia species.

Visualization of spin dynamics in single nanosized magnetic elements

The design of future spintronic devices requires a quantitative understanding of the microscopic linear and nonlinear spin relaxation processes governing the magnetization reversal in nanometer-scale ferromagnetic systems. Ferromagnetic resonance is the method of choice for a quantitative analysis of relaxation rates, magnetic anisotropy and susceptibility in a single experiment. The approach offers the possibility of coherent control and manipulation of nanoscaled structures by microwave irradiation. Here, we analyze the different excitation modes in a single nanometer-sized ferromagnetic stripe. Measurements are performed using a microresonator set-up which offers a sensitivity to quantitatively analyze the dynamic and static magnetic properties of single nanomagnets with volumes of (100 nm)(3). Uniform as well as non-uniform volume modes of the spin wave excitation spectrum are identified and found to be in excellent agreement with the results of micromagnetic simulations which allow the visualization of the spatial distribution of these modes in the nanostructures.

Magnetism of single-crystalline Fe nanostructures

The quantitative investigation of magnetic nanostructures by means of ferromagnetic resonance is demonstrated for single-crystalline iron nanostructures. It is shown that the single-crystalline nature leads to effects not being present in polycrystalline ones and helps to quantitatively interpret the results. First a method is presented that enables one to fabricate epitaxial Fe nanowires starting from a thin film of Fe grown under ultrahigh vacuum conditions on GaAs (110). The system allows, due to the combination of cubic and twofold magnetic anisotropy, to prepare wires whose easy axis in remanence is oriented perpendicular to the wires axis. This unique feature is only achievable in epitaxial systems. Furthermore, nearly perfect Fe nanocubes with 13.6 nm edge length prepared by wet-chemical methods are studied. While the shell of the particles is composed of either Fe3O4 or gamma-Fe2O3, the core consists of metallic Fe. Oxygen and hydrogen plasma are used to remove the ligand system and the oxide shell. The single-crystalline nature of the cubes enables one to quantitatively determine the magnetic properties of the individual particle by means of ferromagnetic resonance measurements on an ensemble together with a model based on the Landau-Lifshitz equation. The measurements reveal a magneto-crystalline anisotropy of K4 = 4.8. 10(4) J/m3 being equal to bulk value and a saturation magnetization which is reduced to M(5K) = (1.2 +/- 0.12). 10(6) A/m (70% of bulk value). The effective damping parameter alpha = 0.03 is increased by one order of magnitude with respect to bulk Fe, showing that magnetic damping in nanostructures differs from the bulk.

Regulation of heterochromatic DNA replication by histone H3 lysine 27 methyltransferases

Multiple pathways prevent DNA replication from occurring more than once per cell cycle. These pathways block re-replication by strictly controlling the activity of pre-replication complexes, which assemble at specific sites in the genome called origins. Here we show that mutations in the homologous histone 3 lysine 27 (H3K27) monomethyltransferases, ARABIDOPSIS TRITHORAX-RELATED PROTEIN5 (ATXR5) and ATXR6, lead to re-replication of specific genomic locations. Most of these locations correspond to transposons and other repetitive and silent elements of the Arabidopsis genome. These sites also correspond to high levels of H3K27 monomethylation, and mutation of the catalytic SET domain is sufficient to cause the re-replication defect. Mutation of ATXR5 and ATXR6 also causes upregulation of transposon expression and has pleiotropic effects on plant development. These results uncover a novel pathway that prevents over-replication of heterochromatin in Arabidopsis.

Resistance of a single domain wall in (Co/Pt)7 multilayer nanowires

Single (Co/Pt)_{7} multilayer nanowires prepared by electron beam lithography with perpendicular magnetic anisotropy are locally modified by means of Ga-ion implantation generating 180 degrees domain walls which are pinned at the edges of underlying thin Pt wires. Since we can exclude contributions from the anisotropic and the Lorentz magnetoresistance this allows us to determine the resistance of a single domain wall at room temperature. We find a positive relative resistance increase of DeltaR/R=1.8% inside the domain wall which agrees well with the model of Levy and Zhang [Phys. Rev. Lett. 79, 5110 (1997)10.1103/PhysRevLett.79.5110].

[Monitoring of heart function in the treatment with cardiotoxic cytostatic drugs]

It is the purpose of this paper to show the concept of noninvasive assessment of cardiomyopathy (CM) in cytostatic treatment, esp. with daunorubicin A (A). Our follow-up study during therapy with A shows 255 patients, examined by ECG, by systolic time intervals (STI)-PEP/LVET (normal value less than or equal to 0.44) and PEPI (normal value less than or equal to 148 ms) by echocardiography (UCG) with measurement of shortening fraction (SF), normal value less than or equal to 30% and in 6 cases by microcatheter with exercise test.

RESULTS

(1) ECG does not predict CM. (2) 23 patients (8%) had abnormal SF in UCG, 6 patients of these having no symptoms of cardiac failure. These patients were examined by microcatheter, all 6 having abnormal values during exercise. So all patients with abnormal SF had objective signs of latent or over CM. (3) PEP/LVET was abnormal in all patients with CM, but false positive in 22% of all investigations, mostly by shortening of LVET. PEPI, abnormal in all patients with CM, was false positive only in 8.8. UCG is the most specific noninvasive method for assessment of CM in cytostatic treatment. STI are less specific, but highly sensitive to CM and therefore a useful screening method. PEPI gives the highest specificity, allowing a better selection than PEP/LVET. STI in contrast to UCG can easily be obtained outside cardiologic centers, ie., in the oncologic department itself. UCG by cardiologic units are needed only about 10-15% of investigations. If all values are abnormal, cardiotoxic treatment should be stopped, even when patients are asymptomatic.

[Monitoring of Myocardial function during therapy with cardiotoxic cytostatics. Studies with the example of anthracycline-containing chemotherapy]

It is the purpose of this paper to show a concept of non-invasive assessment of cardiomyopathy (CM) in cytostatic treatment, especially with Docorubicin (A). In a follow-up study during therapy with A 150 patients were examined by ECG (QRS-amplitude), by systolic time intervals (STI), preejection period versus left ventricular ejection time (PEP/LVET), normal value greater than or equal to 0.45, and PEP corrected to 0-frequency (PEPc), normal value greater than or equal to 147 ms, by echocardiography (UCG), shortening fractions (SF), normal value greater than 30%, and in 6 cases by micro-catheter with exercise test.

RESULTS

(1) ECG does not predict CM (2) 11 patients (7%) had abnormal SF in UCG, 5 having symptoms of CM. 6 patients without clinical signs of CM were examined by microcatheter, 5 having abnormal pressure or HbO2 in the pulmonary artery at exercise. So nearly all patients with abnormal SF had objective signs of latent or overt CM (3) PEP/LVET was abnormal in all patients with CM but false positive in 44% of all investigations, mostly by shortening of LVET. PEPc, also abnormal in all patients with CM, was false positive only in 12%.

CONCLUSION

UCG is the most specific non-invasive method for assessment of CM in cytostatic treatment. STI are less specific but highly sensitive to CM and therefore a useful screening method. PEPc allows better selection than PEP/LVET because of its higher specificity. STI- contrary to UCG- can easily be obtained outside cardiologic centers, i.e. in the oncologic department itself, so that UCG is needed only in about 15-20% in treatment of patients. Cardiotoxic treatment should be stopped, when all values are abnormal, even when patients are asymptomatic. Since we adopted this policy we did not loose any of our last 100 patients from CM.