Abstract 155: A comparison of DNA methylation in identical twins discordant for Hodgkin lymphoma

DNA methylation is an epigenetic change that may affect gene expression. Environmental determinants are largely unknown but strongly suspected. Because twins are matched on genome and to some extent, early life exposures, a comparison of DNA methylation between twins is of more interest than one between unrelated individuals.

To evaluate the possibility of an association between DNA methylation and young adult Hodgkin lymphoma (HL), DNA samples from blood or saliva were collected from both members of 25 identical twin pairs in whom one twin had developed HL prior to age 50 (discordant pairs). The median time since diagnosis was 16 years. DNA methylation status at 27,578 loci in 14,475 genes was measured in each sample using the Illumina Infinium methylation assay. We measured any difference (< or > 0) in the level of DNA methylation at each locus between the case and the unaffected co-twin and applied a paired t-test.

The overall pattern indicated that cases had higher levels of DNA methylation at loci with lower average DNA methylation levels, but the reverse was true at loci with higher overall levels of DNA methylation (e.g., here the cases had lower levels). With respect to specific loci, the HL case consistently had a higher level of DNA methylation compared to his/her unaffected co-twin at locus cg24693053 in the MFSD7 (major facilitator superfamily domain containing 7) gene in 22/25 pairs; this was also the locus with the most significant p-value (p= 0.0000332). Twenty-two out of 25 cases had a lower level of DNA methylation than their unaffected co-twin at loci cg17385448 in the AGMAT (Agmatine ureohydrolase [agmatinase]) gene (p= 0.0001587) and cg09809672 in the EDARADD (EDAR-associated death domain) gene (p= 0.003775846).

Seventeen out of 19 cases with the nodular sclerosis subtype had consistently higher DNA methylation levels at 9 loci and lower levels at 7 loci compared to their unaffected co-twin (binomial test p=0.0007). There was no overall effect on the pattern of methylation by time since diagnosis.

We observed suggestive differences in DNA methylation levels in normal peripheral blood mononuclear cells collected from young adult HL patients in remission relative to their unaffected identical co-twins. The differences may have resulted from HL disease or treatment, or could have pre-dated the diagnosis. The results are compatible with a role of the cumulative environment on DNA methylation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 155.

The effect of selenium supplementation on DTH skin responses in healthy North American men

The trace element selenium (Se) is essential for immune system development and function in animals. However, the exact functions of Se in the human immune system and the achievable health benefits from Se supplementation remain unclear. To test whether an increased intake of dietary Se affects immune function, we conducted a randomized, controlled trial of Se supplementation in healthy free-living men. Forty-two men were administered 300microg of Se a day as high-Se Baker's yeast, or low-Se yeast for 48 weeks. Serum immunoglobulins, differential complete blood counts and lymphocyte sub-populations were measured every 6 weeks. Tests of delayed-type hypersensitivity (DTH) skin responses to mumps, candida, trychophyton, tuberculin-purified protein, and tetanus were performed at baseline and at the end of 48 weeks of treatment. Supplementation increased blood Se concentration by 50%. Surprisingly, consumption of the low-Se yeast induced anergy in DTH skin responses and increased counts of natural killer (NK) cells and T lymphocytes expressing both subunits of the high affinity interleukin-2 receptor (IL2R). DTH skin responses and IL2R+ cells did not change in the high-Se group, suggesting Se supplementation blocked induction of DTH anergy. There were no differences between groups in quality of life indicators, number of days sick, other leukocyte phenotypes, serum immunoglobulins, or complement factors. These results suggest that Se plays a role in immunotolerization, a cell-mediated process involved in many aspects of immune function.

Phase I pharmacokinetic (PK) and pharmacodynamic (PD) study of LBH589, a novel deacetylase (DAC) inhibitor given intravenously on a new once weekly schedule

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Background: LBH589 is a novel deacetylase inhibitor that inhibits proliferation of tumor cells at nanomolar levels. This phase I study tested the safety and tolerability of IV LBH589 once each week for 3 of 4 wks in pts with advanced solid tumors or lymphoma. Methods: LBH589 was administered IV over 30 min. on days 1, 8 and 15 of a 28-day cycle. Western blots on peripheral blood lymphocytes were used to study histone acetylation (HA). Plasma PK profiles were analyzed on Days 1 and 8. Results: Thirty five pts (median age: 70 yrs; 23M, 12F) have been treated on 3 dose levels [10 mg/m2 (8pts), 15 mg/m2 (8 pts), 20 mg/m2 (19 pts)] with the following tumor types: Cutaneous and peripheral T cell lymphoma (7 pts), prostate (6 pts), mesothelioma (4 pts), colon (3 pts) and other (15 pts). There was one dose-limiting toxicity (transient grade 4 thrombocytopenia) at 20 mg/m2, none at the lower doses. Other G3/G4 toxicities (all cycles) include: transient thrombocytopenia (G4–5 pts, G3–5 pts), neutropenia (G3–2 pts), anemia (G3–5 pts), G3 hypophosphatemia (1 pt), G3 hypokalemia (1 pt), G3 nausea (1 pt) and G3 pruritus (1 pt). Thrombocytopenia was transient. Of 2,042 ECGs, 1 pt had an increase in QTcF from baseline of > 60 msec another with a QTcF >500 msec, both at 20 mg/m2. There was a dose-dependent increase in HA 7 days after one dose with 43% (10 mg/m2), 50% (15 mg/m2) and 60% (20 mg/m2) of pts with increased acetylation. The LBH589 plasma conc. peaked at the end of the 0.5 hr infusion with a mean terminal half-life of 16 hr. Median Cmax achieved with 20 mg/m2 was 1,000 ng/mL (2.86 μM). The AUC0-inf increased linearly with IV doses of 10–20 mg/m2. One pt with CTCL achieved a complete response (CR) on cycle 3, Day 1; this pt had previously received oral LBH589 at 20 mg MWF, achieving a CR on cycle 6, Day 28 that lasted for 7 months. One peripheral T-Cell lymphoma pt achieved a partial response that has persisted for >7 months. One pt with prostate cancer has had a 26% reduction in nodal disease and > 50% drop in PSA in the first 2 cycles. Conclusions: The maximum tolerated dose of LBH589 given IV wkly on a 3 of 4 wk schedule is 20 mg/m2. This dose produced sustained PD effects and higher systemic exposure compared to oral LBH589. Preliminary evidence of antitumor activity has been observed.

No significant financial relationships to disclose.

Cell cycle-dependent usage of transcriptional start sites. A novel mechanism for regulation of cyclin B1

Cyclin B1 mRNA is expressed temporally throughout the cell cycle with peak expression in G2 and M phase. Both transcriptional and posttranscriptional controls are important for this cell cycle-dependent regulation of cyclin B1 mRNA. In this study, we observed that cyclin B1 has two major transcripts: (a) a constitutively expressed transcript, and (b) a cell cycle-regulated transcript expressed predominantly during G2-M phase. These different transcripts are due to alternative start sites. The constitutively expressed transcript starts 65 bases upstream from the cell cycle-regulated message. Changes in mRNA stability did not appear to control the expression of the cell cycle-specific transcript, but we were able to identify a 24-base pair region of the cyclin B1 promoter spanning the start site of the cell cycle-regulated transcript that was critical for its cell cycle-regulated promoter activity. This suggests that transcriptional regulation is responsible for controlling the presence of each message. The 24-base pair sequence required for cell cycle regulation was notable for containing the nucleotides GGCT repeated three times. The possibility that these two transcripts might be physiologically distinct was raised when the cell cycle-specific transcript was found to be translated more efficiently in vitro than the constitutively expressed transcript. These results characterize a novel mechanism for the regulation of cyclin B1 throughout the cell cycle that is dependent upon the use of different transcriptional start sites.

Radiation and the G2 phase of the cell cycle

Exposure of mammalian cells to X rays results in prolongation of the cell cycle, including delays or arrests in G1, S and G2 phase. While G1-phase arrest occurs only in cells with wild-type p53 function, a G2-phase delay occurs in all cells regardless of p53 status. In this review, we summarize what is known about cell cycle progression through G2 and M phase and discuss the experimental findings that implicate different mechanisms in the G2-phase delay. Finally, we consider the possibility that G2-phase arrest plays a role in cell survival after irradiation.

Delayed cyclin B1 expression during the G2 arrest following DNA damage

Exposure of cells to DNA damaging agents results in a G2 arrest. Exposure of HeLa cells to camptothecin, etoposide or nitrogen mustard for 1 h in S phase resulted in delayed expression of cyclin B1 mRNA during the G2 arrest. Initially the levels of cyclin B1 protein were low as well; however, with extended time the cells blocked in G2 regained higher levels of cyclin B1 protein. In the case of cells treated with nitrogen mustard the higher levels coincided with cells exiting the G2 block into G1. However, with camptothecin or etoposide treatment, while the accumulation of cyclin B1 protein was delayed, its levels eventually surpassed peak levels seen in control cells, in spite of the fact that cells were still blocked in G2. These cells did not continue to progress through the cell cycle indicating further complexity to the mechanisms underlying the G2 block. Decreased transcription and stability of cyclin B1 mRNA were shown to occur after treatment with these DNA damaging agents. These results indicate that suppression of cyclin B1 mRNA expression is one consequence of DNA damage in HeLa cells.

Cell cycle-dependent regulation of the cyclin B1 promoter

Cyclin B1 mRNA expression varies through the cell cycle with its peak in G2/M. In cycling mammalian cells, its lowest level is in G1 with a steady increase in S until a level 50-fold greater than that in G1 is reached. In order to characterize the transcriptional component to this variation in expression, we cloned the upstream region 872 base pairs upstream from the start site of the cyclin B1 gene and have demonstrated that it confers cell cycle-dependent regulation onto two reporter genes, both chloramphenicol acetyltransferase and luciferase. Its activity was 25-fold greater in G2/M than in G1 in HeLa cells with intermediate activity in S. This cyclical activity could be seen with sequences encompassing only 90 base pairs upstream from the start site. Protein binding to this region was demonstrated using electrophoretic mobility shift assays, and the binding profiles appeared to vary depending upon the phase of the cycle in which the extracts are made. Thus, transcriptional control plays an important role in determining cyclin B1 mRNA levels, and cell cycle-dependent activity is regulated through interactions with the region 90 bases upstream from the start site.

Endomyocardial gene expression during development of pacing tachycardia-induced heart failure in the dog

Selective and specific changes in gene expression characterize the end-stage failing heart. However, the pattern and relation of these changes to evolving systolic and diastolic dysfunction during development of heart failure remains undefined. In the present study, we assessed steady-state levels of mRNAs encoding a group of cardiac proteins during the early development of left ventricular dysfunction in dogs with pacing-induced cardiomyopathy. Corresponding hemodynamic assessments were made in the conscious state in the same animals and at the same time points at baseline, after 1 week of ventricular pacing, and at the onset of clinical heart failure. Systolic dysfunction dominated after 1 week of pacing, whereas diastolic dysfunction was far more pronounced with the onset of heart failure. Atrial natriuretic factor mRNA was undetectable in 7 of 12 hearts at baseline but was expressed in all hearts at 1 week (P < .01 by chi 2 test), and it increased markedly with progression to failure (P = .05). Creatine kinase-B mRNA also rose markedly with heart failure (P < .01). Levels of mRNA encoding beta-myosin heavy chain, mitochondrial creatine kinase, phospholamban, and sarcoplasmic reticulum Ca(2+)-ATPase did not significantly change from baseline, despite development of heart failure. Additional analysis to determine if these mRNA changes were related to the severity of diastolic or systolic dysfunction revealed that phospholamban mRNA decreased in hearts with larger net increases in end-diastolic pressure (+19.2 +/- 1.9 mm Hg) compared with those hearts in which it did not change (+4.0 +/- 4.9, P < .02).(ABSTRACT TRUNCATED AT 250 WORDS)