The potential of PCNA inhibition as a therapeutic strategy in cervical cancer.

Cervical cancers are the fourth most common and most deadly cancer in women worldwide. Despite being a tremendous public health burden, few novel approaches to improve care for these malignancies have been introduced. We discuss the potential for proliferating cell nuclear antigen (PCNA) inhibition to address this need as well as the advantages and disadvantages for compounds that can therapeutically inhibit PCNA with a specific focus on cervical cancer.

Small molecule targeting of transcription-replication conflict for selective chemotherapy.

Targeting transcription replication conflicts, a major source of endogenous DNA double-stranded breaks and genomic instability could have important anticancer therapeutic implications. Proliferating cell nuclear antigen (PCNA) is critical to DNA replication and repair processes. Through a rational drug design approach, we identified a small molecule PCNA inhibitor, AOH1996, which selectively kills cancer cells. AOH1996 enhances the interaction between PCNA and the largest subunit of RNA polymerase II, RPB1, and dissociates PCNA from actively transcribed chromatin regions, while inducing DNA double-stranded breaks in a transcription-dependent manner. Attenuation of RPB1 interaction with PCNA, by a point mutation in RPB1's PCNA-binding region, confers resistance to AOH1996. Orally administrable and metabolically stable, AOH1996 suppresses tumor growth as a monotherapy or as a combination treatment but causes no discernable side effects. Inhibitors of transcription replication conflict resolution may provide a new and unique therapeutic avenue for exploiting this cancer-selective vulnerability.

Therapeutic Targeting of DNA Replication Stress in Cancer.

This article reviews the currently used therapeutic strategies to target DNA replication stress for cancer treatment in the clinic, highlighting their effectiveness and limitations due to toxicity and drug resistance. Cancer cells experience enhanced spontaneous DNA damage due to compromised DNA replication machinery, elevated levels of reactive oxygen species, loss of tumor suppressor genes, and/or constitutive activation of oncogenes. Consequently, these cells are addicted to DNA damage response signaling pathways and repair machinery to maintain genome stability and support survival and proliferation. Chemotherapeutic drugs exploit this genetic instability by inducing additional DNA damage to overwhelm the repair system in cancer cells. However, the clinical use of DNA-damaging agents is limited by their toxicity and drug resistance often arises. To address these issues, the article discusses a potential strategy to target the cancer-associated isoform of proliferating cell nuclear antigen (caPCNA), which plays a central role in the DNA replication and damage response network. Small molecule and peptide agents that specifically target caPCNA can selectively target cancer cells without significant toxicity to normal cells or experimental animals.

Arginine shortage induces replication stress and confers genotoxic resistance by inhibiting histone H4 translation and promoting PCNA ubiquitination.

The arginine dependency of cancer cells creates metabolic vulnerability. In this study, we examine the impact of arginine availability on DNA replication and genotoxicity resistance. Using DNA combing assays, we find that limiting extracellular arginine results in the arrest of cancer cells at S phase and a slowing or stalling of DNA replication. The translation of new histone H4 is arginine dependent and influences DNA replication. Increased proliferating cell nuclear antigen (PCNA) occupancy and helicase-like transcription factor (HLTF)-catalyzed PCNA K63-linked polyubiquitination protect arginine-starved cells from DNA damage. Arginine-deprived cancer cells display tolerance to genotoxicity in a PCNA K63-linked polyubiquitination-dependent manner. Our findings highlight the crucial role of extracellular arginine in nutrient-regulated DNA replication and provide potential avenues for the development of cancer treatments.

Arginine shortage induces replication stress and confers genotoxic resistance by inhibiting histone H4 translation and promoting PCNA polyubiquitination.

The unique arginine dependencies of cancer cell proliferation and survival creates metabolic vulnerability. Here, we investigate the impact of extracellular arginine availability on DNA replication and genotoxic resistance. Using DNA combing assays, we find that when extracellular arginine is limited, cancer cells are arrested at S-phase and DNA replication forks slow or stall instantly until arginine is re-supplied. The translation of new histone H4 is arginine-dependent and impacts DNA replication and the expression of newly synthesized histone H4 is reduced in the avascular nutrient-poor breast cancer xenograft tumor cores. Furthermore, we demonstrate that increased PCNA occupancy and HLTF-catalyzed PCNA K63-linked polyubiquitination protects arginine-starved cells from hydroxyurea-induced, DNA2-catalyzed nascent strand degradation. Finally, arginine-deprived cancer cells are tolerant to genotoxic insults in a PCNA K63-linked polyubiquitination-dependent manner. Together, these findings reveal that extracellular arginine is the "linchpin" for nutrient-regulated DNA replication. Such information could be leveraged to expand current modalities or design new drug targets against cancer.

Novel Peptide Therapeutic Approaches for Cancer Treatment.

Peptides are increasingly being developed for use as therapeutics to treat many ailments, including cancer. Therapeutic peptides have the advantages of target specificity and low toxicity. The anticancer effects of a peptide can be the direct result of the peptide binding its intended target, or the peptide may be conjugated to a chemotherapy drug or radionuclide and used to target the agent to cancer cells. Peptides can be targeted to proteins on the cell surface, where the peptide-protein interaction can initiate internalization of the complex, or the peptide can be designed to directly cross the cell membrane. Peptides can induce cell death by numerous mechanisms including membrane disruption and subsequent necrosis, apoptosis, tumor angiogenesis inhibition, immune regulation, disruption of cell signaling pathways, cell cycle regulation, DNA repair pathways, or cell death pathways. Although using peptides as therapeutics has many advantages, peptides have the disadvantage of being easily degraded by proteases once administered and, depending on the mode of administration, often have difficulty being adsorbed into the blood stream. In this review, we discuss strategies recently developed to overcome these obstacles of peptide delivery and bioavailability. In addition, we present many examples of peptides developed to fight cancer.

A Quantitative Analysis of Surgical Smoke Exposure as an Occupational Hazard.

OBJECTIVE: We hypothesized that OR airborne PM was different in quantity and mutagenic potential than office air and cigarette smoke. SUMMARY OF BACKGROUND DATA: Exposure to surgical smoke has been equated to cigarette smoking and thought to be hazardous to health care workers despite limited data. METHODS: PM was measured during 15 operations in ORs with 24.8 ±â€Š2.0 air changes/h, and in controls (cigarettes, office air with 1.9-2.9 air changes/h). Mutagenic potential was assessed by gamma Histone 2A family member X staining of DNA damage in small airway epithelial cells co-cultured with PM. RESULTS: Average PM concentration during surgery was 0.002 ±â€Š0.002 mg/m3 with maximum values at 1.08 ±â€Š1.30 mg/m3. Greater PM correlated with more diathermy (ρ = 0.69, P = 0.006). Values were most often near zero, resulting in OR average values similar to office air (0.002 ±â€Š0.001 mg/m3) (P = 0.32). Cigarette smoke average PM concentration was significantly higher, 4.8 ±â€Š5.6 mg/m3 (P < 0.001). PM collected from 14 days of OR air caused DNA damage to 1.6% ±â€Š2.7% of cultured cells, significantly less than that from office air (27.7% ±â€Š11.7%, P = 0.02), and cigarette smoke (61.3% ±â€Š14.3%, P < 0.001). CONCLUSIONS: The air we breathe during surgery has negligible quantities of PM and mutagenic potential, likely due to low frequency of diathermy use coupled with high airflow. This suggests that exposure to surgical smoke is associated with minimal occupational risk.

Molecular Targeting of Cancer-Associated PCNA Interactions in Pancreatic Ductal Adenocarcinoma Using a Cell-Penetrating Peptide.

Pancreatic ductal adenocarcinoma is a particularly difficult cancer to treat due to a lack of effective screening or treatment. Pancreatic cancer cells exhibit high proliferating cell nuclear antigen (PCNA) expression, which is associated with poor prognosis. PCNA, an important nuclear DNA replication and repair protein, regulates a myriad of proteins via the interdomain connector loop. Within this region, amino acids 126-133 are critical for PCNA interactions in cancer cells. Here, we investigate the ability of a decoy cell-penetrating peptide, R9-caPeptide, that mimics the interdomain connector loop region of PCNA to disrupt PCNA-protein interactions in pancreatic cancer cells. Our data suggest that R9-caPeptide causes dose-dependent toxicity in a panel of pancreatic cancer cell lines by inhibiting DNA replication fork progression and PCNA-regulated DNA repair, ultimately causing lethal DNA damage. Overall, these studies lay the foundation for novel therapeutic strategies that target PCNA in pancreatic cancer.

The Anticancer Activity of a First-in-class Small-molecule Targeting PCNA.

PURPOSE: Proliferating cell nuclear antigen (PCNA) plays an essential role in regulating DNA synthesis and repair and is indispensable to cancer cell growth and survival. We previously reported a novel cancer associated PCNA isoform (dubbed caPCNA), which was ubiquitously expressed in a broad range of cancer cells and tumor tissues, but not significantly in nonmalignant cells. We found the L126-Y133 region of caPCNA is structurally altered and more accessible to protein-protein interaction. A cell-permeable peptide harboring the L126-Y133 sequence blocked PCNA interaction in cancer cells and selectively kills cancer cells and xenograft tumors. On the basis of these findings, we sought small molecules targeting this peptide region as potential broad-spectrum anticancer agents. EXPERIMENTAL DESIGN: By computer modeling and medicinal chemistry targeting a surface pocket partly delineated by the L126-Y133 region of PCNA, we identified a potent PCNA inhibitor (AOH1160) and characterized its therapeutic properties and potential toxicity. RESULTS: AOH1160 selectively kills many types of cancer cells at below micromolar concentrations without causing significant toxicity to a broad range of nonmalignant cells. Mechanistically, AOH1160 interferes with DNA replication, blocks homologous recombination-mediated DNA repair, and causes cell-cycle arrest. It induces apoptosis in cancer cells and sensitizes them to cisplatin treatment. AOH1160 is orally available to animals and suppresses tumor growth in a dosage form compatible to clinical applications. Importantly, it does not cause significant toxicity at 2.5 times of an effective dose. CONCLUSIONS: These results demonstrated the favorable therapeutic properties and the potential of AOH1160 as a broad-spectrum therapeutic agent for cancer treatment.

How Does the Proliferating Cell Nuclear Antigen Modulate Binding Specificity to Multiple Partner Proteins?

Proliferating cell nuclear antigen (PCNA) is a member of the family of sliding clamp proteins that serves as a clamp during DNA repair, DNA replication, cell cycle control, and multiple forms of chromatin modification. PCNA functions as a homotrimer and complexes with multiple proteins in order to carry out each of these varied functions. PCNA binds to different partner proteins in the same region of its structure, called the " interdomain connecting loop", but with different affinities. This interdomain connecting loop is an intrinsically disordered region that takes different conformations when binding to different partner proteins. In this work, we performed all-atom molecular dynamics simulations on PCNA trimer unbound to any partner protein, PCNA bound to peptides from different partner proteins, and PCNA bound to the full Fen 1 protein in two different conformations. Using this massive amount of simulation results, we analyzed whether PCNA in its free trimeric form samples conformations that are similar to those when it is bound to different partner proteins. We observed that PCNA samples many of these peptide-bound conformations even when not bound to the peptides and selects specific conformations when binding to partner proteins. We also identified PCNA-peptide interactions formed in the peptide bound simulation that play a crucial role in complex formation. The calculated binding energies correlate well with the measured binding affinities of various peptides to PCNA. Lastly, we studied the internal dynamics of PCNA and propose a mechanism through which PCNA recruits binding partners. This work highlights the functional role of intrinsically disordered regions in multifunctional proteins such as PCNA.

Partial Purification of a Megadalton DNA Replication Complex by Free Flow Electrophoresis.

We describe a gentle and rapid method to purify the intact multiprotein DNA replication complex using free flow electrophoresis (FFE). In particular, we applied FFE to purify the human cell DNA synthesome, which is a multiprotein complex that is fully competent to carry-out all phases of the DNA replication process in vitro using a plasmid containing the simian virus 40 (SV40) origin of DNA replication and the viral large tumor antigen (T-antigen) protein. The isolated native DNA synthesome can be of use in studying the mechanism by which mammalian DNA replication is carried-out and how anti-cancer drugs disrupt the DNA replication or repair process. Partially purified extracts from HeLa cells were fractionated in a native, liquid based separation by FFE. Dot blot analysis showed co-elution of many proteins identified as part of the DNA synthesome, including proliferating cell nuclear antigen (PCNA), DNA topoisomerase I (topo I), DNA polymerase δ (Pol δ), DNA polymerase ɛ (Pol ɛ), replication protein A (RPA) and replication factor C (RFC). Previously identified DNA synthesome proteins co-eluted with T-antigen dependent and SV40 origin-specific DNA polymerase activity at the same FFE fractions. Native gels show a multiprotein PCNA containing complex migrating with an apparent relative mobility in the megadalton range. When PCNA containing bands were excised from the native gel, mass spectrometric sequencing analysis identified 23 known DNA synthesome associated proteins or protein subunits.

Validating the disruption of proliferating cell nuclear antigen interactions in the development of targeted cancer therapeutics.

Human DNA replication and repair is a highly coordinated process involving the specifically timed actions of numerous proteins and enzymes. Many of these proteins require interaction with proliferating cell nuclear antigen (PCNA) for activation within the process. The interdomain connector loop (IDCL) of PCNA provides a docking site for many of those proteins, suggesting that this region is critically important in the regulation of cellular function. Previous work in this laboratory has demonstrated that a peptide mimicking a specific region of the IDCL (caPeptide) has the ability to disrupt key protein-protein interactions between PCNA and its binding partners, thereby inhibiting DNA replication within the cells. In this study, we confirm the ability of the caPeptide to disrupt DNA replication function using both intact cell and in vitro DNA replication assays. Further, we were able to demonstrate that treatment with caPeptide results in a decrease of polymerase δ activity that correlates with the observed decrease in DNA replication. We have also successfully developed a surface plasmon resonance (SPR) assay to validate the disruption of the PCNA-pol δ interaction with caPeptide.

The Novel Ribonucleotide Reductase Inhibitor COH29 Inhibits DNA Repair In Vitro.

COH29 [N-(4-(3,4-dihydroxyphenyl)-5-phenylthiazol-2-yl)-3,4-dihydroxybenzamide], a novel antimetabolite drug developed at City of Hope Cancer Center, has anticancer activity that stems primarily from the inhibition of human ribonucleotide reductase (RNR). This key enzyme in deoxyribonucleotide biosynthesis is the target of established clinical agents such as hydroxyurea and gemcitabine because of its critical role in DNA replication and repair. Herein we report that BRCA-1-defective human breast cancer cells are more sensitive than wild-type BRCA-1 counterparts to COH29 in vitro and in vivo. Microarray gene expression profiling showed that COH29 reduces the expression of DNA repair pathway genes, suggesting that COH29 interferes with these pathways. It is well established that BRCA1 plays a role in DNA damage repair, especially homologous recombination (HR) repair, to maintain genome integrity. In BRCA1-defective HCC1937 breast cancer cells, COH29 induced more double-strand breaks (DSBs) and DNA-damage response than in HCC1937 + BRCA1 cells. By EJ5- and DR-green fluorescent protein (GFP) reporter assay, we found that COH29 could inhibit nonhomologous end joining (NHEJ) efficiency and that no HR activity was detected in HCC1937 cells, suggesting that repression of the NHEJ repair pathway may be involved in COH29-induced DSBs in BRCA1-deficient HCC1937 cells. Furthermore, we observed an accumulation of nuclear Rad51 foci in COH29-treated HCC1937 + BRCA1 cells, suggesting that BRCA1 plays a crucial role in repairing and recovering drug-induced DNA damage by recruiting Rad51 to damage sites. In summary, we describe here additional biologic effects of the RNR inhibitor COH29 that potentially strengthen its use as an anticancer agent.

Human C6orf211 encodes Armt1, a protein carboxyl methyltransferase that targets PCNA and is linked to the DNA damage response.

Recent evidence supports the presence of an L-glutamyl methyltransferase(s) in eukaryotic cells, but this enzyme class has been defined only in certain prokaryotic species. Here, we characterize the human C6orf211 gene product as "acidic residue methyltransferase-1" (Armt1), an enzyme that specifically targets proliferating cell nuclear antigen (PCNA) in breast cancer cells, predominately methylating glutamate side chains. Armt1 homologs share structural similarities with the SAM-dependent methyltransferases, and negative regulation of activity by automethylation indicates a means for cellular control. Notably, shRNA-based knockdown of Armt1 expression in two breast cancer cell lines altered survival in response to genotoxic stress. Increased sensitivity to UV, adriamycin, and MMS was observed in SK-Br-3 cells, while in contrast, increased resistance to these agents was observed in MCF7 cells. Together, these results lay the foundation for defining the mechanism by which this post-translational modification operates in the DNA damage response (DDR).

A Peptide mimicking a region in proliferating cell nuclear antigen specific to key protein interactions is cytotoxic to breast cancer.

Proliferating cell nuclear antigen (PCNA) is a highly conserved protein necessary for proper component loading during the DNA replication and repair process. Proteins make a connection within the interdomain connector loop of PCNA, and much of the regulation is a result of the inherent competition for this docking site. If this target region of PCNA is modified, the DNA replication and repair process in cancer cells is potentially altered. Exploitation of this cancer-associated region has implications for targeted breast cancer therapy. In the present communication, we characterize a novel peptide (caPeptide) that has been synthesized to mimic the sequence identified as critical to the cancer-associated isoform of PCNA. This peptide is delivered into cells using a nine-arginine linking mechanism, and the resulting peptide (R9-cc-caPeptide) exhibits cytotoxicity in a triple-negative breast cancer cell line, MDA-MB-436, while having less of an effect on the normal counterparts (MCF10A and primary breast epithelial cells). The novel peptide was then evaluated for cytotoxicity using various in vivo techniques, including ATP activity assays, flow cytometry, and clonogenetic assays. This cytotoxicity has been observed in other breast cancer cell lines (MCF7 and HCC1937) and other forms of cancer (pancreatic and lymphoma). R9-cc-caPeptide has also been shown to block the association of PCNA with chromatin. Alanine scanning of the peptide sequence, combined with preliminary in silico modeling, gives insight to the disruptive ability and the molecular mechanism of action of the therapeutic peptide in vivo.

The Mechanism by Which MYCN Amplification Confers an Enhanced Sensitivity to a PCNA-Derived Cell Permeable Peptide in Neuroblastoma Cells.

Dysregulated expression of MYC family genes is a hallmark of many malignancies. Unfortunately, these proteins are not amenable to blockade by small molecules or protein-based therapeutic agents. Therefore, we must find alternative approaches to target MYC-driven cancers. Amplification of MYCN, a MYC family member, predicts high-risk neuroblastoma (NB) disease. We have shown that R9-caPep blocks the interaction of PCNA with its binding partners and selectively kills human NB cells, especially those with MYCN amplification, and we now show the mechanism. We found elevated levels of DNA replication stress in MYCN-amplified NB cells. R9-caPep exacerbated DNA replication stress in MYCN-amplified NB cells and NB cells with an augmented level of MYC by interfering with DNA replication fork extension, leading to Chk1 dependence and susceptibility to Chk1 inhibition. We describe how these effects may be exploited for treating NB.

Expression of a novel peptide derived from PCNA damages DNA and reverses cisplatin resistance.

BACKGROUND: An 8 amino acid peptide sequence derived from proliferating cell nuclear antigen (PCNA) has been shown to effectively kill several breast cancer and neuroblastoma cell lines when added exogenously to cell cultures. METHODS: In this study, the expression of the 8 amino acid peptide sequence (caPeptide) was placed under control of a tetracycline responsive promoter in MDA-MB-231 cells. RESULTS: Endogenous expression of the peptide resulted in an increase in genomic DNA damage. CaPeptide induction combined with treatment of sublethal doses of cisplatin resulted in a marked increase in death of the cisplatin-resistant MDA-MB-231 cell line. CaPeptide was found to interact with POLD3, one of the subunits of DNA polymerase delta necessary for binding to PCNA. CONCLUSION: These results suggest an important line of inquiry into the possible role that caPeptide might play in the reversal of cisplatin resistance in breast and other cancers. This is of particular interest in those cancers where cisplatin is the first line of chemotherapy and where the acquisition of resistance is a common malady.

A PCNA-derived cell permeable peptide selectively inhibits neuroblastoma cell growth.

Proliferating cell nuclear antigen (PCNA), through its interaction with various proteins involved in DNA synthesis, cell cycle regulation, and DNA repair, plays a central role in maintaining genome stability. We previously reported a novel cancer associated PCNA isoform (dubbed caPCNA), which was significantly expressed in a broad range of cancer cells and tumor tissues, but not in non-malignant cells. We found that the caPCNA-specific antigenic site lies between L126 and Y133, a region within the interconnector domain of PCNA that is known to be a major binding site for many of PCNA's interacting proteins. We hypothesized that therapeutic agents targeting protein-protein interactions mediated through this region may confer differential toxicity to normal and malignant cells. To test this hypothesis, we designed a cell permeable peptide containing the PCNA L126-Y133 sequence. Here, we report that this peptide selectively kills human neuroblastoma cells, especially those with MYCN gene amplification, with much less toxicity to non-malignant human cells. Mechanistically, the peptide is able to block PCNA interactions in cancer cells. It interferes with DNA synthesis and homologous recombination-mediated double-stranded DNA break repair, resulting in S-phase arrest, accumulation of DNA damage, and enhanced sensitivity to cisplatin. These results demonstrate conceptually the utility of this peptide for treating neuroblastomas, particularly, the unfavorable MYCN-amplified tumors.

A novel berbamine derivative inhibits cell viability and induces apoptosis in cancer stem-like cells of human glioblastoma, via up-regulation of miRNA-4284 and JNK/AP-1 signaling.

Glioblastoma (GBM) is the most common primary brain tumor, accounting for approximately 40% of all central nervous system malignancies. Despite standard treatment consisting of surgical resection, radiotherapy and/or chemotherapy, the prognosis for GBM is poor; with a median survival of 14.6 months. The cancer stem cell or cancer-initiating cell model has provided a new paradigm for understanding development and recurrence of GBM following treatment. Berbamine (BBM) is a natural compound derived from the Berberis amurensis plant, and along with its derivatives, has been shown to exhibit antitumor activity in several cancers. Here, we reported that a novel synthetic Berbamine derivative, BBMD3, inhibits cell viability and induces apoptosis of cancer stem-like cells (CSCs) in a time- and dose-dependent manner when the CSCs from four GBM patients (PBT003, PBT008, PBT022, and PBT030) were cultured. These CSCs grew in neurospheres and expressed CD133 and nestin as markers. Treatment with BBMD3 destroyed the neurosphere morphology, and led to the induction of apoptosis in the CSCs. Induction of apoptosis in these CSCs is dependent upon activation of caspase-3 and cleavage of poly (ADP-ribose) polymerase (PARP). MicroRNA-4284 (miR-4284) was shown to be over-expressed about 4-fold in the CSCs following BBMD3 treatment. Furthermore, transfection of synthetic anti-sense oligonucleotide against human miR-4284 partially blocked the anticancer effects of BBMD3 on the GBM derived CSCs. BBMD3 also increased phosphorylation of the c-Jun N-terminal kinase (JNK)/stress-activated protein kinase (SAPK), resulting in an increase expression of phosphorylated c-Jun and total c-Fos; the major components of transcriptional factor AP-1. The JNK-c-Jun/AP-1 signaling pathway plays an important role in the induction of apoptosis in response to UV irradiation and some drug treatments. Targeting glioblastoma stem-like cells with BBMD3 is therefore novel, and may have promise as an effective therapeutic strategy for treating GBM patients.

Error-promoting DNA synthesis in ovarian cancer cells.

OBJECTIVE: The objective of this study is to determine whether an altered DNA replication process is responsible for some of genetic damage observed in ovarian cancer. METHODS: The replication fidelity of the DNA synthetic process was evaluated in both malignant and non-malignant human ovarian cells. The types of replication errors produced were identified. In addition, kinetic analyses of the efficiency of ovarian cancer DNA polymerases for misincorporating nucleotides were performed. RESULTS: We report for the first time that ovarian cancer cells harbor an error promoting DNA replication apparatus which contributes to the decrease in DNA synthetic fidelity exhibited by these cells. Our study also shows that the decrease in DNA replication fidelity was not a result of an increased DNA replication activity. In addition, it was observed that the higher rate of DNA replication errors does not result in significant differences in the type of DNA replication-errors made during the DNA replication process; just the relative abundance. A detailed kinetic analysis of the efficiency of misincorporating nucleotides demonstrated that the DNA polymerases within the ovarian cancer cells exhibited a significant propensity for creating purine-pyrimidine nucleotide mismatches relative to non-malignant ovarian cells, while being only slightly more efficient at incorrectly pairing a purine nucleotide with a purine nucleotide. CONCLUSIONS: All together, these data suggest that the systematic analysis of the DNA replication process in ovarian cancer could uncover information on some of the molecular mechanisms that drive the accumulation of genetic damage, and probably contribute to the pathogenesis of the disease.