Therapeutic targeting of constitutive PARP activation compromises stem cell phenotype and survival of glioblastoma-initiating cells.

Glioblastoma-initiating cells (GICs) are self-renewing tumorigenic sub-populations, contributing to therapeutic resistance via decreased sensitivity to ionizing radiation (IR). GIC survival following IR is attributed to an augmented response to genotoxic stress. We now report that GICs are primed to handle additional stress due to basal activation of single-strand break repair (SSBR), the main DNA damage response pathway activated by reactive oxygen species (ROS), compared with non-GICs. ROS levels were higher in GICs and likely contributed to the oxidative base damage and single-strand DNA breaks found elevated in GICs. To tolerate constitutive DNA damage, GICs exhibited a reliance on the key SSBR mediator, poly-ADP-ribose polymerase (PARP), with decreased viability seen upon small molecule inhibition to PARP. PARP inhibition (PARPi) sensitized GICs to radiation and inhibited growth, self-renewal, and DNA damage repair. In vivo treatment with PARPi and radiotherapy attenuated radiation-induced enrichment of GICs and inhibited the central cancer stem cell phenotype of tumor initiation. These results indicate that elevated PARP activation within GICs permits exploitation of this dependence, potently augmenting therapeutic efficacy of IR against GICs. In addition, our results support further development of clinical trials with PARPi and radiation in glioblastoma.

Cell-related sequences in the DNA genome of human cytomegalovirus strain AD169.

Human cytomegalovirus (HCMV) cloned EcoRI fragments R and b hybridized strongly, under standard high-stringency conditions, to uninfected cellular DNA of human, murine, or sea urchin origin. Less hybridization was detected with fragments, A, C, E, WL(F), WN(H), I, M, O, P, Q, V, c, d, and e. Southern blot analysis of the HCMV-related human DNA localized the major sites of hybridization of HCMV EcoRI fragments R, b, and d to defined regions of the 28S rRNA gene.

Sequences in human cytomegalovirus which hybridize with the avian retrovirus oncogene v-myc are G + C rich and do not hybridize with the human c-myc gene.

The degree of relatedness between previously identified cross-hybridizing regions within human cytomegalovirus strain AD169 and the avian retrovirus oncogene v-myc were investigated by nucleotide sequence comparison. We found that the homologous regions between the human cytomegalovirus genome and v-myc are limited to short G + C-rich regions in each genome and that the human cytomegalovirus genome shares little or no homology with the human c-myc gene.

Changes in bilirubins in human prenatal development.

1. A densitometric method has been developed for the quantification of azodipyrroles derived from dog bile pigments treated with diazotized ethyl anthranilate. 2. This method was used to estimate the bilirubins in bile and meconium from foetuses of 14-36 weeks gestation. 3. The proportion of the bilirubins in foetal bile changed during gestation. (a) No bile pigments were found until 14 weeks. (b) Between 14 and 15 weeks bilirubin-IX beta was the only bile pigment detected. (c) At 16-17 weeks some unconjugated bilirubin-IX alpha was found in the bile, but up to 20 weeks bilirubin-IX beta was the predominant bilirubin in the bile. (d) At about 20 weeks glucose, xylose, and an unidentified bilirubin-IX alpha monoconjugate were found in the bile. (e) Between 20 and 23 weeks bilirubin-IX alpha glucuronide appeared in the bile. (f) At 30 weeks monoconjugates of bilirubin-IX alpha were the predominant bilirubins in the bile. (g) Only in full-term foetuses was bilirubin-IX alpha monoglucuronide the major bilirubin derivative.

Conjugated and unconjugated bilirubins in humans and rhesus monkeys. Structural identity of bilirubins from biles and meconiums of newborn humans and rhesus monkeys.

1. Bilirubin-IXalpha monoglucuronide was the predominant bilirubin in biles and meconiums of newborn humans and rhesus monkeys. Rhesus-monkey baby biles contained slightly more diglucuronide than did human baby biles. 2. Bilrubin-IXalpha glucoside, bilirubin-IXalpha xyloside and bilirubin-IXbeta were also constituents of human and rhesus-monkey baby biles and meconiums. Bilirubin-IXalpha glucuronide glucoside was present in human and rhesus-monkey baby biles but not in meconiums. The identity of the bilirubins was confirmed by u.v.-visible and mass spectroscopy of the azodipyrroles obtained by treating the bilirubins with diazotized ethyl anthranilate. The resulting azodipyrroles were identical with the corresponding azodipyrroles obtained from human adult biles and also from reduced isomers of biliverdin. 3. Bilirubin-IXbeta was present in much higher proportions in the extracts of meconiums than in the extracts of biles from the same babies. 4. Oxidation of bilirubins to biliverdins occurs in utero to a small but undetermined extent. The resulting green pigments were present in meconiums collected from the lower small and large intestines of newborn babies and rhesus monkeys. 5. Butanol extracted most of the bilirubins present in biles. This modified method proved to be quick and easy. Little hydrolysis of bilirubins took place during extraction or separation by t.l.c.