DNA Damage Induces p53-dependent Down-regulation of hCHK1

Abstract The levels of the human checkpoint gene hCHK1 were measured in human cancer cells growing in vitro after treatment with the DNA damaging agent cis-dichlorodiammine platinum(II) (DDP). Treatment of human cancer cell lines with DDP induced a decrease in the hCHK1 protein levels starting 6 h after treatment, with a further decline at 24 and 48 h. A similar decrease in the levels of hCHK1 was found at the mRNA level by using Northern blot analysis. By using isogenic cell systems in which p53 was disrupted either by transfection with HPV-E6 or by targeted homologous recombination, we found that the DNA damage-induced down-regulation of hCHK1 was only observable in wild type p53-expressing cells, with only a minor decline in the hCHK1 levels observable 48 h after treatment in cells with disrupted p53. Similarly, treatment of mutant p53-expressing human cancer cell lines with DDP did not result in changes in the levels of hCHK1. The p53-dependent down-regulation of hCHK1 is likely to be at transcriptional levels, as suggested by the lack of down-regulation of the hCHK1 when transfected under the control of a heterologous viral promoter. In addition, p53 is able to down-regulate the luciferase activity under the control of the 5′ flanking region of the hCHK1 gene. The data suggest a strict link between p53 and hCHK1 governing the activation and repression of the G2 checkpoint in which both proteins participate

PO-473 Quantification of ERCC1-XPF complexes in ovarian cancer xenografts with different sensitivity to cisplatin

Introduction Epithelial ovarian cancer is the most lethal gynaecological cancer due to the development of resistance to a platinum based therapy. As DNA repair capacity is a key determinant for the cellular response to platinum (DDP) agents, DNA repair functional assays are required to study its relevance in DDP resistance. We set up a proximity ligation assay (PLA) to study the activity of nucleotide excision repair (NER) in patient derived ovarian carcinoma xenografts (PDXs) sensitive (S) and resistant (R) to DDP. Material and methods Patient derived xenografts from fresh ovarian carcinomas were recently established in our laboratory. DDP antitumour activity was evaluated in most of the PDXs. Mice were sacrificed when tumours reached 1,5–2 gr. Tumours were fixed in formalin and paraffin embedded (FFPE). PLA was performed on tumour slides, using DuolinkII reagents (Sigma-Aldrich) and following the manufacturer instructions. PLA detects the presence of the protein complexes ERCC1-XPF, that are quantified as foci per nucleus and represent a biomarker of NER activity. Images were acquired by Olympus Virtual Slider (Olympus) and analysed with ImageJ software. Statistical analysis was performed with GraphPad Prism7. Results and discussions Our xenobank comprises PDXs with different response to DDP: MNHOC266 and MNHOC230 are very sensitive to the drug, while MNHOC315 is resistant. We also obtained three sublines resistant to DDP (MNHOC124R, MNHOC124LPR and MNHOC239R) starting from sensitive PDXs (MNHOC124S, MNHOC124LPS and MNHOC239S), after several in vivo drug treatments. Statistically significant higher level of ERCC1-XPF foci could be observed in MNHOC124R and MNHOC124LPR as compared to their sensitive counterparts. No differences were observed between MNHOC239S and R PDXs, even if the number of ERCC1-XPF foci in MNHOC239S were statistically higher than the ones observed in MNHOC124S and in MNHOC124LPS. MNHOC266 and MNHOC230 showed levels of foci comparable to those of MNHOC124S and MNHOC124LPS. mRNA and protein levels of the different isoforms of ERCC1 and of XPF were not different among the PDXs studied. Conclusion PLA for the detection of ERCC1-XPF complexes was set up in FFPE xenograft tumour slides. These preliminary results highlight a possible link between DDP resistance and higher NER activity that need to be confirmed in a wider panel of PDXs. In addition, these data confirm the importance to develop functional assays to directly evaluate the activity of different DNA repair pathways to predict DDP activity

Impact of the interplay between stemness features, p53 and pol iota on replication pathway choices

Using human embryonic, adult and cancer stem cells/stem cell-like cells (SCs), we demonstrate that DNA replication speed differs in SCs and their differentiated counterparts. While SCs decelerate DNA replication, differentiated cells synthesize DNA faster and accumulate DNA damage. Notably, both replication phenotypes depend on p53 and polymerase iota (POL$_{ι}$). By exploring protein interactions and newly synthesized DNA, we show that SCs promote complex formation of p53 and POL$_{ι}$ at replication sites. Intriguingly, in SCs the translocase ZRANB3 is recruited to POL$_{ι}$ and required for slow-down of DNA replication. The known role of ZRANB3 in fork reversal suggests that the p53–POL$_{ι}$ complex mediates slow but safe bypass of replication barriers in SCs. In differentiated cells, POL$_{ι}$ localizes more transiently to sites of DNA synthesis and no longer interacts with p53 facilitating fast POL$_{ι}$-dependent DNA replication. In this alternative scenario, POL$_{ι}$ associates with the p53 target p21, which antagonizes PCNA poly-ubiquitination and, thereby potentially disfavors the recruitment of translocases. Altogether, we provide evidence for diametrically opposed DNA replication phenotypes in SCs and their differentiated counterparts putting DNA replication-based strategies in the spotlight for the creation of therapeutic opportunities targeting SCs

Epithelioid Mesothelioma Patients with Very Long Survival Display Defects in DNA Repair

Aim: DNA repair has an important role in malignant pleural mesothelioma (MPM) tumorigenesis and progression. Prognostic/predictive biomarkers for better management of MPM patients are needed. In the present manuscript, we analyzed the expression of more than 700 genes in a cohort of MPM patients to possibly find biomarkers correlated with survival. Methods: A total of 54 MPM patients, all with epithelioid histology, whose survival follow-up and formalin-fixed paraffin-embedded tumors were available, were included in the study. Gene expression profiles were evaluated using a Nanostring platform analyzing 760 genes involved in different cellular pathways. The percentages of proliferating tumor cells positive for RAD51 and BRCA1 foci were evaluated using an immunofluorescence assay, as a readout of homologous recombination repair status. Results: Patient median survival time was 16.9 months, and based on this value, they were classified as long and short survivors (LS/SS) with, respectively, an overall survival ≥ and <16.9 months as well as very long and very short survivors (VLS/VSS) with an overall survival ≥ than 33.8 and < than 8.45 months. A down-regulation in the DNA damage/repair expression score was observed in LS and VLS as compared to SS and VSS. These findings were validated by the lower number of both RAD51 and BRCA1-positive tumor cells in VLS as compared to VSS. Conclusions: The down-regulation of DNA repair signature in VLS was functionally validated by a lower % of RAD51 and BRCA1-positive tumor cells. If these data can be corroborated in a prospective trial, an easy, cost-effective test could be routinely used to better manage treatment in MPM patients

The disruption of the CCDC6 - PP4 axis induces a BRCAness like phenotype and sensitivity to PARP inhibitors in high-grade serous ovarian carcinoma

Treatment with PARP inhibitors (PARPi) is primarily effective against high-grade serous ovarian cancers (HGSOC) with BRCA1/2 mutations or other deficiencies in homologous recombination (HR) repair mechanisms. However, resistance to PARPi frequently develops, mostly as a result of BRCA1/2 reversion mutations. The tumour suppressor CCDC6 is involved in HR repair by regulating the PP4c phosphatase activity on γH2AX. In this work, we reported that in ovarian cancer cells, a physical or functional loss of CCDC6 results synthetic lethal with the PARP-inhibitors drugs, by affecting the HR repair. We also unravelled a role for CCDC6 as predictive marker of PARPi sensitivity in ovarian cancer, and the impact of CCDC6 downregulation in overcoming PARPi resistance in these tumours

Platinum sensitivity and DNA repair in a recently established panel of patient-derived ovarian carcinoma xenografts

A xenobank of patient-derived (PDX) ovarian tumor samples has been established consisting of tumors with different sensitivity to cisplatin (DDP), from very responsive to resistant. As the DNA repair pathway is an important driver in tumor response to DDP, we analyzed the mRNA expression of 20 genes involved in the nucleotide excision repair, fanconi anemia, homologous recombination, base excision repair, mismatch repair and translesion repair pathways and the methylation patterns of some of these genes. We also investigated the correlation with the response to platinum-based therapy. The mRNA levels of the selected genes were evaluated by Real Time-PCR (RT-PCR) with ad hoc validated primers and gene promoter methylation by pyrosequencing. All the DNA repair genes were variably expressed in all 42 PDX samples analyzed, with no particular histotype-specific pattern of expression. In high-grade serous/endometrioid PDXs, the CDK12 mRNA expression levels positively correlated with the expression of TP53BP1, PALB2, XPF and POLB. High-grade serous/endometrioid PDXs with TP53 mutations had significantly higher levels of POLQ, FANCD2, RAD51 and POLB than high-grade TP53 wild type PDXs. The mRNA levels of CDK12, PALB2 and XPF inversely associated with the in vivo DDP antitumor activity; higher CDK12 mRNA levels were associated with a higher recurrence rate in ovarian patients with low residual tumor. These data support the important role of CDK12 in the response to a platinum based therapy in ovarian patients

Exploiting endocytosis for transfection of mRNA for cytoplasmatic delivery using cationic gold nanoparticles

Gene therapy holds promise to cure various diseases at the fundamental level. For that, efficient carriers are needed for successful gene delivery. Synthetic 'non-viral' vectors, as cationic polymers, are quickly gaining popularity as efficient vectors for transmitting genes. However, they suffer from high toxicity associated with the permeation and poration of the cell membrane. This toxic aspect can be eliminated by nanoconjugation. Still, results suggest that optimising the oligonucleotide complexation, ultimately determined by the size and charge of the nanovector, is not the only barrier to efficient gene delivery. We herein develop a comprehensive nanovector catalogue comprising different sizes of Au NPs functionalized with two different cationic molecules and further loaded with mRNA for its delivery inside the cell. Tested nanovectors showed safe and sustained transfection efficiencies over 7 days, where 50 nm Au NPs displayed the highest transfection rates. Remarkably, protein expression was increased when nanovector transfection was performed combined with chloroquine. Cytotoxicity and risk assessment demonstrated that nanovectors are safe, ascribed to lesser cellular damage due to their internalization and delivery via endocytosis. Obtained results may pave the way to design advanced and efficient gene therapies for safely transferring oligonucleotides

Genomic instability in human cancer: molecular insights and opportunities for therapeutic attack and prevention through diet and nutrition

Genomic instability can initiate cancer, augment progression, and influence the overall prognosis of the affected patient. Genomic instability arises from many different pathways, such as telomere damage, centrosome amplification, epigenetic modifications, and DNA damage from endogenous and exogenous sources, and can be perpetuating, or limiting, through the induction of mutations or aneuploidy, both enabling and catastrophic. Many cancer treatments induce DNA damage to impair cell division on a global scale but it is accepted that personalized treatments, those that are tailored to the particular patient and type of cancer, must also be developed. In this review, we detail the mechanisms from which genomic instability arises and can lead to cancer, as well as treatments and measures that prevent genomic instability or take advantage of the cellular defects caused by genomic instability. In particular, we identify and discuss five priority targets against genomic instability: (1) prevention of DNA damage; (2) enhancement of DNA repair; (3) targeting deficient DNA repair; (4) impairing centrosome clustering; and, (5) inhibition of telomerase activity. Moreover, we highlight vitamin D and B, selenium, carotenoids, PARP inhibitors, resveratrol, and isothiocyanates as priority approaches against genomic instability. The prioritized target sites and approaches were cross validated to identify potential synergistic effects on a number of important areas of cancer biology