PARP inhibition sensitizes p53-deficient breast cancer cells to doxorubicin-induced apoptosis.

p53 deficiency confers resistance to doxo (doxorubicin), a clinically active and widely used antitumour anthracycline antibiotic. The purpose of the present study was to investigate the reversal mechanism of doxo resistance by the potent PARP [poly(ADP-ribose) polymerase] inhibitor ANI (4-amino-1,8-naphthalimide) in the p53-deficient breast cancer cell lines EVSA-T and MDA-MB-231. The effects of ANI, in comparison with doxo alone, on doxo-induced apoptosis, were investigated in matched pairs of EVSA-T or MDA-MB-231 with or without ANI co-treatment. Doxo elicited PARP activation as determined by Western blotting and immunofluorescence of poly(ADP-ribose), and ANI enhanced the cytotoxic activity of doxo 2.3 times and in a caspase-dependent manner. The long-term cytotoxic effect was studied by a colony-forming assay. Using this assay, ANI also significantly potentiates the long-term cytotoxic effect with respect to treatment with doxo alone. Decrease in mitochondrial potential together with an increase in cytochrome c release, association of Bax with the mitochondria and caspase 3 activation were also observed in the presence of ANI. Therefore PARP inhibition may represent a novel way of selectively targeting p53-deficient breast cancer cells. The underlying mechanism is probably a potentiation of unrepaired DNA damage, shifting from DNA repair to apoptosis due to the effective inhibition of PARP activity.

Crosstalk between PARP-1 and NF-kappaB modulates the promotion of skin neoplasia.

Poly (ADP-ribose) polymerase-1 (PARP-1)-deficient mice are protected against septic shock, type I diabetes, stroke and inflammation. It is now accepted that inflammation and related events, such as activation of NF-kappaB, are key components in the initiation and progression of epithelial cancer and in particular in the neoplastic transformation of keratinocytes and skin carcinogenesis. Here, we report that PARP-1-deficient mice display a strikingly reduced susceptibility to skin carcinogenesis. In parp-1(-/-) mice, development of papilloma-like premalignant lesions induced with DMBA and TPA, is strongly delayed and the final number of tumor-bearing mice and total tumor number were significantly reduced. In addition, epidermis of parp-1(-/-) mice did not show increased proliferation rates after treatment with carcinogen. Deregulated NF-kappaB is a hallmark for tumorigenesis together with the concomitant release of early inflammatory mediators. In the absence of PARP-1, NF-kappaB activation and induction kappaB-target genes did not take place during the promotion of tumor development. These results suggest that PARP-1 abolition impairs the promotion of skin carcinogenesis interfering with the activation of NF-kappaB and might have an important implication in targeting PARP-1 as a new antineoplastic therapeutic approach.

Attention capture by auditory significant stimuli: semantic analysis follows attention switching.

Event-related potentials (ERPs) were recorded from the scalp to investigate a long-standing controversy in auditory attention research, namely when the 'breakthrough of the unattended' takes place in the human brain. Nine subjects classified visual stimuli appearing 300 ms after task-irrelevant standard tones (80%, i.e. P = 0.8) or novel sounds (20%, i.e. P = 0.2) into odd/even categories. After the recording session, subjects scored the novel sounds as to whether they had any particular meaning (identifiable) or were perceived as a burst of noise (non-identifiable), and performance and ERPs were analysed according to this classification. A control condition, in which the visual stimuli were presented with no sounds, showed that subjects covertly monitored the task-irrelevant sounds during visual task-performance, and a further condition, in which the auditory and visual stimuli appeared regardless of each other, made it possible to trace the processing of the distracters during allocation of attention outside the auditory environment. Results yielded identical N1-enhancement for the two types of novel sounds, indicating similar attention switching triggered to these two types of unexpected sounds. However, there was a stronger orientating of attention towards identifiable novel sounds, as indicated both by behavioural distraction and by larger novelty-P3. Furthermore, this stronger orientating of attention was due to the sounds being contingent on the visual stimuli, as no increase in novelty-P3 to identifiable novel sounds was observed in the control condition, in which the sounds occurred outside the attentional set. Therefore, provided that the N1-enhancement reflects a call for focal attention, and novelty-P3 the effective orientating of attention towards the eliciting sounds, the present results suggest that semantic analysis of significant sounds occurs after a transitory switch of attention towards the eliciting stimuli. Moreover, as the novelty-P3 increase in amplitude was observed only when subjects covertly monitored the sounds, the present data suggest that semantic analysis of irrelevant sounds depends on the top-down cognitive influences of the attentional set.

Breast cancer acute radiotherapy morbidity evaluated by different scoring systems.

Reporting of the outcome of radiotherapy is not satisfactory without a description of the treatment-related side effects. The purposes of this paper were: (1) to evaluate the frequency and the severity of collateral skin reactions in a group of breast cancer patients; (2) to report the acute reactions using some current scoring systems and to compare the application of them, and (3) to investigate the variation between intra- and interobservers using these different scales. We studied 108 breast cancer patients who, after surgical treatment, received adjuvant radiotherapy. Clinical skin evaluation was always performed by the same radiotherapist the last day of treatment, and the collateral radiation effects were photographed at that moment to facilitate later evaluations by another two expert doctors. Normal tissue damage was scored according to the Radiation Therapy Oncology Group/The European Organisation for Research, and Treatment of Cancer/ (RTOG/EORTC), the Danish, the European, and the Biomed2 side-effect scales. The most frequent acute complications found were erythema (91.7%), dry desquamation (29.6%) and moist desquamation (35.2%). The reactions were classified as severe in 13.9, 23, 18.5 and 13% of the patients with each of the different systems used, respectively. The concordance between the scoring of radiation-induced side effects on the skin assessed by direct observation of the patients or by examination of the photographic document was sufficient. This is a warrant of accuracy in the evaluation of acute normal tissue lesions. Our results allow us to state the advantage of the RTOG system over the others in terms of evaluating the acute effects produced by radiotherapy of women with breast cancer.

PARP-1 modifies the effectiveness of p53-mediated DNA damage response.

The tumour suppressor protein p53 plays a key role in the cell's decision to arrest the cell cycle or undergo apoptosis following a genotoxic insult. p53 is stabilized and activated after DNA damage, however the cascade of events signalling from DNA lesions to p53 stabilization and activation is still controversial. Poly (ADP-ribosylation) of different nuclear acceptors by PARP-1 is an early event when a single strand DNA lesion is produced. We present here evidences that interplay between PARP-1 and p53 is dependent on the type of damage induced to DNA. Primary mouse embryonic fibroblasts derived from parp-1 -/- mice exhibited decreased p53 accumulation and activation following gamma-irradiation compared to parp-1 proficient cells. On the other hand, treatment with the single alkylating agent 2'-methyl-2'-nitrose-urea (MNU), resulted in the rapid and sustained accumulation and activation of p53 in parp-1-deficient cells, while very little accumulation was observed in parp-1 +/+ cells. After IR, the turnover of the p53 inhibitory protein MDM-2 is perturbed and the level of phosphorylation of p53 at serine-15 is blunted in parp-1 -/- cells. PARP-1 is determinant in the cytotoxic response to alkylating agents but only partially contributes to radiation-induced cell killing, as determined by colony forming assay. Altogether, these results suggest that PARP-1 participates in the p53 response following irradiation, resides upstream of p53 and indirectly modulates the level of phosphorylation of key substrates in this pathway while treatment with MNU results in an enhanced p53-mediated response in parp-1-null cells.