A novel poly(ADP-ribose) polymerase inhibitor, ABT-888, radiosensitizes malignant human cell lines under hypoxia

The chemo- and radioresponse of tumor cells can be determined by genetic factors (e.g., those that modify cell cycle arrest, DNA damage repair or cell death) and microenvironmental factors, such as hypoxia. Poly(ADP-ribose) polymerase (PARP) is a nuclear enzyme that rapidly recognizes and binds to DNA breaks to facilitate DNA strand break repair. Pre-clinical data suggest that PARP inhibitors (PARPi) may potentiate the effects of radiotherapy and chemotherapy. However, it is unclear as to whether PARPi are effective against hypoxic cells. We therefore tested the role for a novel PARPi, ABT-888, as a radiosensitizing agent under hypoxic conditions. Using human prostate (DU-145, 22RV1) and non-small cell lung (H1299) cancer cell lines, we observed that ABT-888 inhibited both recombinant PARP activity and intracellular PARP activity (86% to 92% decrease in all 3 cells lines following 2.5muM treatment). ABT-888 was toxic to both oxic and hypoxic cells. When ABT-888 was combined with ionizing radiation (IR), clonogenic radiation survival was decreased by 40-50% under oxic conditions. Under acute hypoxia, ABT-888 radiosensitized malignant cells to a level similar to oxic radiosensitivity. To our knowledge, this is the first study to demonstrate that inhibition of PARP activity can sensitize hypoxic cancer cells and the combination of IR-PARPi has the potential to improve the therapeutic ratio of radiotherapy.     

Cardiovascular responses to hypoxemia in sinoaortic-denervated fetal sheep

Fetal cardiovascular response to acute hypoxemia is characterized by bradycardia, hypertension, and redistribution of cardiac output. The role of aortic and carotid chemoreceptors in mediating these responses was examined in eight sinoaortic-denervated and nine shamoperated fetal lambs. Blood gases, pH, heart rate, arterial pressure, and blood flow distribution were determined before and during hypoxemia. In intact fetuses, heart rate fell from 184 +/- 12 to 165 +/- 23 beats/min (p less than 0.01) but increased from 184 +/- 22 to 200 +/- 16 beats/min (p less than 0.05) in the sinoaortic-denervated fetuses. Intact fetuses showed an early hypertensive response to hypoxemia, whereas the sinoaortic-denervated fetuses developed a delayed, progressive rise in blood pressure. In both groups, fetal cardiac output and umbilical blood flow were maintained; cerebral, myocardial, and adrenal blood flow increased, and pulmonary blood flow decreased. Peripheral blood flow decreased 39% (p less than 0.001) in intact fetuses but was maintained in sinoaortic-denervated fetuses. Vascular responses to hypoxia in the brain, heart, adrenal, and lungs are regulated primarily by direct local effects. During hypoxemia, peripheral chemoreceptors mediate bradycardia and peripheral vasoconstriction but do not appear to be crucial for immediate fetal survival.     

Daily administration of the progesterone antagonist RU 486 prevents implantation in the cycling guinea pig.

Since progesterone is required to prepare the endometrium for implantation of an embryo, a progesterone antagonist may inhibit nidation and thus prevent pregnancy. We addressed this possibility in the guinea pig, the small laboratory animal whose reproductive physiology most resembles that of women. Daily administration of the antiprogestin RU 486 (0, 1, 2, or 3 mg/kg, subcutaneously) for 9 days after mating inhibited implantation in a dose-dependent fashion. When this compound was given daily throughout the estrous cycle, cyclic vaginal changes, ovulation, and mating were suppressed in up to 17%, 28%, and 55% of animals, respectively. Two of seven mated female animals receiving RU 486, 1 mg/kg/day, had implantation sites. Nidation was completely blocked at higher doses. Thus daily antiprogestin administration prevented pregnancy in sexually active, normally cycling guinea pigs. A similar strategy using a daily antinidatory dose of an antiprogestin may offer a novel approach to human fertility control.     

Loss of Brca2 and p53 synergistically promotes genomic instability and deregulation of T-cell apoptosis

BRCA2 is a breast cancer susceptibility gene of which the product is thought to be involved in monitoring genome integrity and cell cycle progression. Brca2-null mice have a defect in embryonic cellular proliferation and die in utero. Here we report the generation of T-cell lineage-specific Brca2-deficient (tBrca2(-/-)) mice using the Cre-loxP system. Mice with a flanked by loxP allele of Brca2 were crossed to transgenic mice bearing Cre recombinase driven by the T cell-specific promoter Lck. Thymic cellularity and distribution of subset populations were normal in tBrca2(-/-) mutants. Thymocytes from tBrca2(-/-) mice underwent normal apoptosis in response to a variety of stimuli, and activated tBrca2(-/-) T cells had normal proliferative capacity. tBrca2(-/-) T cells were more likely than wild-type cells to undergo spontaneous apoptosis, but apoptosed normally in response to restimulation or DNA-damaging stress signals. Examination of metaphase spreads of tBrca2(-/-) T cells revealed that the chromosomes often exhibited aberrations such as breaks and tri-radial structures. The level of chromosomal abnormalities was enhanced in T cells from tBrca2(-/-); p53(-/-) double-mutant mice. However, tBrca2(-/-); p53(-/-) T cells did not show the enhanced level of spontaneous apoptosis demonstrated by tBrca2(-/-) T cells, a difference that likely accounts for an increase in cell number and (3)[H]thymidine incorporation of double-mutant T cells in culture compared with either single mutant. Despite this increased T-cell number, the onset of T-cell lymphomas was only marginally accelerated in tBrca2(-/-); p53(-/-) mice compared with p53(-/-) mice. Our results support a role for Brca2 in repairing spontaneous DNA lesions, and suggest that loss of Brca2 enhances the susceptibility of mouse T-lineage cells to chromosomal aberrations and deregulation of apoptosis in the absence of p53.     

Mechanisms of embryonic coronary artery development

Coronary artery development is a complex vasculogenic process that begins shortly after heart looping. Coronary vasculogenesis is regulated by the myocardium, but is spatially and temporally dependent on the epicardium and its precursor, the proepicardial organ, for the provision of coronary vascular progenitor cells. Better understanding of the mechanisms of coronary artery development may clarify mechanisms of disease and suggest new potential therapies for disorders of the coronary vasculature.     

Practice MRI: Reducing the need for sedation and general anaesthesia in children undergoing MRI

The aim of this study was to evaluate the effectiveness of a practice magnetic resonance unit, in preparing children to undergo magnetic resonance procedures without general anaesthesia (GA) or sedation. The records of children who attended the practice MRI between February 2002 and April 2004 were retrospectively reviewed. Each record was assessed as to whether the child had passed or failed the practice MRI intervention. Those children who were considered to have passed and were proceeded to a clinical non‐GA MRI had the report of the clinical scan reviewed. If the scan had been reported as non‐diagnostic because of movement artefact it was classified as a failed scan, otherwise it was considered a pass. One hundred and thirty‐four children undertook a practice MRI (age range 4.1–16.1 years, median age 7.7 years, 47% boys) and 120/134 (90%) passed the practice session. In all, 117/120 (98%) subsequently had a clinical non‐GA MRI and 110/117 (94%) passed (median age 7.8 years, 47% boys). Preparation is a safe and effective method to reduce the need for sedation and GA in children undergoing a clinical MRI scan. It provides a positive medical experience for children, parents and staff, and results in cost savings for the hospital.