Altered DNA Damage Repair Research Articles

Genomic Profiling of Lower-Grade Gliomas Subtype with Distinct Molecular and Clinicopathologic Characteristics via Altered DNA-Damage Repair Features.

Lower WHO grade II and III gliomas (LGGs) exhibit significant genetic and transcriptional heterogeneity, and the heterogeneity of DNA damage repair (DDR) and its relationship to tumor biology, transcriptome, and tumor microenvironment (TME) remains poorly understood. In this study, we conducted multi-omics data integration to investigate DDR alterations in LGG. Based on clinical parameters and molecular characteristics, LGG patients were categorized into distinct DDR subtypes, namely, DDR-activated and DDR-suppressed subtypes. We compared gene mutation, immune spectrum, and immune cell infiltration between the two subtypes. DDR scores were generated to classify LGG patients based on DDR subtype features, and the results were validated using a multi-layer data cohort. We found that DDR activation was associated with poorer overall survival and that clinicopathological features of advanced age and higher grade were more common in the DDR-activated subtype. DDR-suppressed subtypes exhibited more frequent mutations in IDH1. In addition, we observed significant upregulation of activated immune cells in the DDR-activated subgroup, which suggests that immune cell infiltration significantly influences tumor progression and immunotherapeutic responses. Furthermore, we constructed a DDR signature for LGG using six DDR genes, which allowed for the division of patients into low- and high-risk groups. Quantitative real-time PCR results showed that CDK1, CDK2, TYMS, SMC4, and WEE1 were significantly upregulated in LGG samples compared to normal brain tissue samples. Overall, our study sheds light on DDR heterogeneity in LGG and provides insight into the molecular pathways of DDR involved in LGG development.

The effects of altered DNA damage repair genes on mutational processes and immune cell infiltration in esophageal squamous cell carcinoma.

Defects in DNA damage repair (DDR) pathways lead to genomic instability and oncogenesis. DDR deficiency is prevalent in esophageal squamous cell carcinoma (ESCC), but the effects of DDR alterations on mutational processes and tumor immune microenvironment in ECSS remain unclear. Whole-exome and transcriptome sequencing data of 45 ESCC samples from Taizhou, China, were used to identify genomic variations, gene expression modulation in DDR pathways, and the abundance of tumor-infiltrating immune cells. Ninety-six ESCC cases from The Cancer Genome Atlas (TCGA) project were used for validation. A total of 57.8% (26/45) of the cases in the Taizhou data and 70.8% (68/96) of the cases in the TCGA data carried at least one functional impact DDR mutation. Mutations in the DDR pathways were associated with a high tumor mutation burden. Several DDR deficiency-related mutational signatures were discovered and were associated with immune cell infiltration, including T cells, monocytes, dendritic cells, and mast cells. The expression levels of two DDR genes, HFM1 and NEIL1, were downregulated in ESCC tumor tissues and had an independent effect on the infiltration of mast cells. In the Taizhou data, increased expression of HFM1 was associated with a poor prognosis, and the increased expression of NEIL1 was associated with a good outcome, but no reproducible correlation was observed in the TCGA data. This research demonstrated that DDR alterations could impact mutational processes and immune cell infiltration in ESCC. The suppression of HFM1 and NEIL1 could play a crucial role in ESCC progression and may also serve as prognostic markers.

Clonal Hematopoiesis Analyses in Clinical, Epidemiologic, and Genetic Aging Studies to Unravel Underlying Mechanisms of Age-Related Dysfunction in Humans.

Aging is characterized by increased mortality, functional decline, and exponential increases in the incidence of diseases such as cancer, stroke, cardiovascular disease, neurological disease, respiratory disease, etc. Though the role of aging in these diseases is widely accepted and considered to be a common denominator, the underlying mechanisms are largely unknown. A significant age-related feature observed in many population cohorts is somatic mosaicism, the detectable accumulation of somatic mutations in multiple cell types and tissues, particularly those with high rates of cell turnover (e.g., skin, liver, and hematopoietic cells). Somatic mosaicism can lead to the development of cellular clones that expand with age in otherwise normal tissues. In the hematopoietic system, this phenomenon has generally been referred to as “clonal hematopoiesis of indeterminate potential” (CHIP) when it applies to a subset of clones in which mutations in driver genes of hematologic malignancies are found. Other mechanisms of clonal hematopoiesis, including large chromosomal alterations, can also give rise to clonal expansion in the absence of conventional CHIP driver gene mutations. Both types of clonal hematopoiesis (CH) have been observed in studies of animal models and humans in association with altered immune responses, increased mortality, and disease risk. Studies in murine models have found that some of these clonal events are involved in abnormal inflammatory and metabolic changes, altered DNA damage repair and epigenetic changes. Studies in long-lived individuals also show the accumulation of somatic mutations, yet at this advanced age, carriership of somatic mutations is no longer associated with an increased risk of mortality. While it remains to be elucidated what factors modify this genotype-phenotype association, i.e., compensatory germline genetics, cellular context of the mutations, protective effects to diseases at exceptional age, it points out that the exceptionally long-lived are key to understand the phenotypic consequences of CHIP mutations. Assessment of the clinical significance of somatic mutations occurring in blood cell types for age-related outcomes in human populations of varied life and health span, environmental exposures, and germline genetic risk factors will be valuable in the development of personalized strategies tailored to specific somatic mutations for healthy aging.

Acceleration or Brakes: Which Is Rational for Cell Cycle-Targeting Neuroblastoma Therapy?

Unrestrained proliferation is a common feature of malignant neoplasms. Targeting the cell cycle is a therapeutic strategy to prevent unlimited cell division. Recently developed rationales for these selective inhibitors can be subdivided into two categories with antithetical functionality. One applies a “brake” to the cell cycle to halt cell proliferation, such as with inhibitors of cell cycle kinases. The other “accelerates” the cell cycle to initiate replication/mitotic catastrophe, such as with inhibitors of cell cycle checkpoint kinases. The fate of cell cycle progression or arrest is tightly regulated by the presence of tolerable or excessive DNA damage, respectively. This suggests that there is compatibility between inhibitors of DNA repair kinases, such as PARP inhibitors, and inhibitors of cell cycle checkpoint kinases. In the present review, we explore alterations to the cell cycle that are concomitant with altered DNA damage repair machinery in unfavorable neuroblastomas, with respect to their unique genomic and molecular features. We highlight the vulnerabilities of these alterations that are attributable to the features of each. Based on the assessment, we offer possible therapeutic approaches for personalized medicine, which are seemingly antithetical, but both are promising strategies for targeting the altered cell cycle in unfavorable neuroblastomas.

A Comprehensive Analysis of Alterations in DNA Damage Repair Pathways Reveals a Potential Way to Enhance the Radio-Sensitivity of Esophageal Squamous Cell Cancer.

Esophageal squamous cell cancer (ESCC) is a common malignancy with a poor 5-year overall survival in China. Altered DNA damage repair (DDR) pathways are associated with a predisposition to cancer and contribute to therapeutic response and resistance in cancers. However, alterations of DDR pathway genes in ESCC are still largely unknown. In this study, we employed genome sequencing data of 192 samples, comparative genomic hybridization data of 123 cases, and gene expression microarray data of 119 patients to firstly perform a comprehensive analysis of the gene alterations of 7 DDR pathways in ESCC. Gene mutations and copy number variations (CNVs) were observed in all 7 DDR pathways, and especially, CNVs were the dominant alteration types. Compared with other pathways, two DNA double-strand break (DSB) repair pathways homologous recombination (HR) and non-homologous end joining (NHEJ), carried significant gene mutations and CNVs especially gene amplifications. Most genes including RAD54B, NBS1, RAD51B, and PRKDC were significantly amplified and over-expressed in ESCC. Amplification and high expression of DSB repair pathway genes were associated with poorer overall survival. Gene set variation analysis further showed that DSB repair pathways were up-regulated in ESCC. Besides, we firstly demonstrated that combination of mirin and NU7441, two inhibitors for HR and NHEJ respectively, with ionizing radiation treatment significantly enhanced DSBs, reduced clonogenic cell survival, inhibited cell proliferation, and promoted cell apoptosis in ESCC cells with DSB pathway gene amplification. These findings suggest that DSB repair pathways were significantly altered in ESCC and inhibiting DSB repair pathways might enhance the radio-sensitivity of ESCC with DSB repair up-regulation.

Molecular and cellular paradigms of multidrug resistance in cancer.

The acquisition of resistance to chemotherapy is a major hurdle in the successful application of cancer therapy. Several anticancer approaches, including chemotherapies, radiotherapy, surgery and targeted therapies are being employed for the treatment of cancer. However, cancer cells reprogram themselves in multiple ways to evade the effect of these therapies, and over a period of time, the drug becomes inactive due to the development of multi-drug resistance (MDR). MDR is a complex phenomenon where malignant cells become insensitive to anticancer drugs and attain the ability to survive even after several exposures of anticancer drugs. In this review, we have discussed the molecular and cellular paradigms of multidrug resistance in cancer. An Extensive research in cancer biology revealed that drug resistance in cancer is the result of perpetuated intracellular and extracellular mechanisms such as drug efflux, drug inactivation, drug target alteration, oncogenic mutations, altered DNA damage repair mechanism, inhibition of programmed cell death signaling, metabolic reprogramming, epithelial mesenchymal transition (EMT), inherent cell heterogeneity, epigenetic changes, redox imbalance, or any combination of these mechanisms. An inevitable cross-link between inflammation and drug resistance has been discussed. This review provided insight molecular mechanism to understand the vulnerabilities of cancer cells to develop drug resistance. MDR is an outcome of interplays between multiple intricate pathways responsible for the inactivation of drug and development of resistance. MDR is a major obstacle in regimens of successful application of anti-cancer therapy. An improved understanding of the molecular mechanism of multi drug resistance and cellular reprogramming can provide a promising opportunity to combat drug resistance in cancer and intensify anti-cancer therapy for the upcoming future.

Incidence of mutated DNA damage response pathway and clinically actionable alterations in Chinese patients with unknown primary tumor revealed by comprehensive genomic profiling.

e13523 Background: Carcinoma of unknown primary(CUP) is a clinically aggressive disorder with early tumor dissemination. Without drugs specifically approved for CUP, the outcome of standard chemotherapy is generally poor. Identifying molecular traits of CUP can be beneficial not only for better therapy approach but also potentially for all patients with metastatic dissemination. Methods: From January 2015 to July 2019, 36 unique cases were diagnosed as CUP. DNA was extracted with formalin-fixed paraffin-embedded specimens(FFPEs) or plasma samples and sequenced with 400+ gene panels. Results: In this cohort, identified sites of tumor dissemination included lymph node(36%), bone(19%), liver(8%), lung(5%), gut(5%). More than half of patients were male(65%) with a median age of 62 years old(range:42-82). 83% of CUP patients harboured at least one altered DNA damage repair(DDR) gene including TP53(74%), ATM(19%), ARID1A(11%), ATR(11%). Patients with altered homologous recombination repair (HRR) pathway(42%) showed significantly increased tumor mutational burden(TMB) compared to patients with intact HRR(p = 0.025). MYC gene displayed the most copy number variation (gain, 22%) followed by CDKN2A(loss, 15%) and ZNF217(gain, 15%). Clinically actionable mutations were identified in ten patients including KRAS G12C(3), PIK3CA E545K(2), PIK3CA E542K(1), BRAF V600L(1), EGFR L861Q(1), EML4- ALK(1), ALK L1196M(1). One SCC patient with lymph node metastasis had a PIK3CA mutation E545K and a resistant ALK mutation L1196M without prior ALK TKI treatment, suggesting this patient might benefit from PI3K inhibitors. Unfortunately, He progressed on paclitaxel and cisplatin and died in 2019. The other ADC patient with lymph node metastasis achieved SD on pemetrexed disodium and oxaliplatin. He harboured a KRAS G12C mutation (allele frequency 77.75%), indicating target therapy with KRAS inhibitor might be a better treatment option. Conclusions: Majority of CUP patients showed impaired DDR pathway. TMB of CUP patients with altered HRR pathway is significantly higher than ones with intact HRR. Comprehensive genomic profiling revealed the potentiality of target therapy in CUP patients with clinically actionable mutations.

OR16-06 Age-Associated Local GH Promotes Colon Neoplasia

Colon polyp and cancer frequency increase with age, yet little is known about age-related mechanisms underlying development of these neoplasms. Defective DNA damage response and accumulation of unrepaired DNA damage can trigger genomic instability and cellular transformation.Patients with acromegaly have a higher prevalence of colon polyps and, arguably, colon adenocarcinoma, while those with GH signaling deficiency do not develop cancer. We showed that APC+/- mice that all develop colon adenomas exhibit a significant decrease in the number and volume of colon tumors with deletion of the GH transcription factor Prop1. Further, DNA damage response triggered GH expression in colon cells, and GH, in turn, altered DNA damage repair, resulting in DNA damage accumulation and cell transformation both in vitro and in vivo. These findings prompted us to hypothesize that accumulated DNA damage in aging colon induces local GH, suppressing DNA damage repair and creating a milieu consistent with genomic instability favoring neoplastic development.In human colon tissue we now show increased expression of γH2AX, a marker of DNA breaks, associated with increased GH transcription (detected by RNA scope) and translation (assessed by immunohistochemistry) as well as GH induction in both human and murine colon after DNA damaging radiotherapy. In vitro studies support these results, showing GH induction in normal human colon epithelial cells, fibroblasts, and 3D human intestinal organoids after DNA damage. Of note, local GH was secreted in the medium, indicating a paracrine effect. Paracrine/autocrine GH expression in these cellular models resulted in suppression of p53, induction of EMT, and attenuation of DNA damage response, and accumulated unrepaired DNA damage in human colon cells and in human intestinal organoids. In vivo, colon cells infected with lentivirus expressing GH generated more metastases than did cells expressing control vector. Co-culturing of human normal colon fibroblasts expressing GH together with normal human colon cells led to increased motility and accumulation of DNA damage as well as increased proliferation of epithelial cells on a gut-on-a-chip microfluidic device, confirming paracrine GH effects. In an in vitro model of aging, culturing human intestinal organoids for up to 2 months resulted in decreased telomere length and increased GH mRNA and protein expression associated with suppressed DNA damage response evident by decreased phosphorylation of ATM and DNA-PKcs, both kinases involved in DNA repair, and DNA damage accumulation assessed by Comet assay. Suppression of GH in these aging organoids led to increased phospho-p53 and reduced DNA damage. Although somatotroph axis endocrine activity decreases with age, local GH induced in response to age-related DNA damage may trigger a “field change,” creating a milieu favorable for colon neoplastic development.

Abstract P2-05-06: Nuclear STING localization induces chemoresistance in breast cancer

Abstract Efficient DNA damage repair (DDR) is crucial for a cell as aberrant repair can create deleterious mutations and genomic instability while unrepaired damage leads to cell apoptosis. Cells with altered DDR are more inclined to develop a variety of diseases, including cancers Cancer therapies including radiotherapy and chemotherapy rely on double strand break (DBS) formation to drive the killing of rapidly cycling tumor cells. As efficient DNA repair pathways can enable tumor cells to survive treatment-induced DNA damage, the identification of new actors participating in efficient DDR will help design alternative therapeutic approaches. Here we report that the well-known DNA sensor of innate immunity Stimulator of Interferon Genes (STING) is directly involved in the modulation of DSB repair efficiency in breast cancer cells. STING partly resides at the inner membrane of the nucleus where it interacts with core proteins of DNA-damage complexes and promotes its assembly with chromatin. STING silencing decreases DNA repair and cell viability, while STING overexpression protects cancer cells from genotoxic treatment. STING involvement in DNA repair is independent of the canonical STING-triggered pro-inflammatory response. In line with this observation, while overall STING expression level is positively correlated with favorable outcome in breast cancer patients, high STING expression in breast and ovarian cancer patients treated with adjuvant chemotherapy is associated with poor prognosis. This newly-identified function of STING elucidates a cell autonomous tumor-promoting mechanism complementary and independent from its well-documented role in tumor immunosurveillance. Citation Format: Laura Cheradame, Chiara Guerrera, Jean-Gabriel Judde, Vincent Goffin, Stefano Cairo. Nuclear STING localization induces chemoresistance in breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-05-06.

Abstract P3-08-07: Distinct biological signatures describe differences in BRCA mutated subgroups

Abstract Background: BRCA mutated (BRCA+) breast cancers are expected to have increased activation of Homologous Recombination Deficiency (HRD) and altered DNA damage repair pathways when compared to BRCA wildtype (BRCA-). To better understand differences in these populations, biological patterns and immune responses to BRCA+ breast cancers were evaluated. The primary aim of our study was to use novel gene expression tools to assess early stage breast cancers with and without germline BRCA mutations, and within distinct BRCA+ subgroups. Methods: We identified 124 early stage untreated breast cancers with and without BRCA mutations (n = 62 and 62, respectively). Our BRCA- group was matched by hormone receptor (HR) status, age, and stage to the BRCA+ group. The NanoString Breast Cancer 360 panel was applied to RNA isolated from 80 breast tumors (BRCA+ = 39; BRCA- = 41). The BRCA+ group had a BRCA1+ subgroup (n=17) and a BRCA2+ subgroup (n=22). Results: There was a significant increase in two BC360 signatures in both the BRCA1+ and BRCA2+ tumors compared with the BRCA- population: Prosigna™Risk of Recurrence (ROR) score [BRCA1+: HR: 1.142 (95% CI 1.019, 1.279), p=0.02; BRCA2+: HR: 1.321 (95% CI 1.190, 1.466), p<0.001] and HRD [BRCA1+: HR: 3.576 (95% CI 2.174, 5.880), p=0.02; BRCA2+: HR: 1.801 (95% CI 1.142, 2.840), p<0.001]. BRCA1+ tumors had lower expression of ESR1 [p=0.03], PGR [p=0.02], ER signaling [p<0.001], and differentiation [p=0.005]; while BRCA2+ tumors had lower expression of stroma markers [p=0.02] and inflammatory chemokines [p=0.001]. The two BRCA+ subgroups had distinct molecular subtype correlation trends that were highly significant. BRCA1+ tumors were positively associated with a basal subtype [p<0.001], whereas this association was not significant for BRCA2+ tumors. BRCA2+ tumors were associated with an increase in luminal B subtype [p=0.05]. All BRCA+ tumors had a decrease in luminal A subtype correlation [BRCA1+: p<0.001; BRCA2+: p=0.002]. In addition to the BC360 signatures, a differential analysis of all genes in the BC360 panel revealed more single gene differences in BRCA2+ than BRCA1+ tumors when compared to BRCA- tumors. Conclusions: In early stage BRCA+ breast cancer, tumors have higher ROR and increased HRD signature scores compared to BRCA- tumors. Furthermore, BRCA1+ and BRCA2+ tumors have both signature and single gene expression differences when compared to BRCA- tumors, indicating distinct subgroup-related biology. The greater correlation of BRCA1+ tumors with basal-like biology and BRCA2+ tumors with aggressive hormonal biology confirms these trends. Distinctions in hormone receptor signaling, DNA-damage pathways, and microenvironment/inflammatory features between BRCA1 and BRCA2 associated cancers suggest a need for different prevention and therapeutic strategies for each of these breast cancer subtypes. The unique biological patterns identified here should be further evaluated as predictive or prognostic tools that could be translated into clinical care for early stage BRCA+ patients. Citation Format: Force J, Plichta J, Stashko I, Kimmick G, Westbrook K, Sammons S, Hwang S, Hyslop T, Kauff N, Castellar E, Nair S, Weinhold K, Davis S, Mashadi-Hossein A, Brauer HA, Marcom PK. Distinct biological signatures describe differences in BRCA mutated subgroups [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-08-07.

Abstract 4463: Loss of APC mediates doxorubicin resistance in breast cancer cells

Abstract Resistance to chemotherapy is one of the leading causes of breast cancer related deaths. Understanding the molecular basis for chemoresistance is essential for the advancement of novel therapeutic approaches to ultimately improve patient outcomes. The Adenomatous Polyposis Coli (APC) tumor suppressor is either mutated or hypermethylated in up to 70% of sporadic breast cancer; however, little is known about how loss of APC contributes to chemoresistance. Using the ApcMin/+ mouse crossed to the Polyoma middle T antigen (PyMT) transgenic model, we demonstrated that APC loss decreased cisplatin and doxorubicin-induced apoptosis. We previously showed that loss of APC in MMTV-PyMT;ApcMin/+ cells induced STAT3-activation resulting in an enhanced tumor initiating cell (TIC) population and increased multidrug resistance protein 1 (MDR1) expression. Therefore, we hypothesized that APC loss increased MDR1 activity and decreased doxorubicin-mediated DNA damage, ultimately preventing cell death. Using calcein incorporation, we first demonstrated that APC loss increased MDR1 activity which was normalized to WT control levels by the MDR1 inhibitor, Valspodar. We next showed that MDR1 inhibition in MMTV-PyMT;ApcMin/+ cells could restore doxorubicin-mediated apoptosis to that of MMTV-PyMT;Apc+/+ treated cells. Due to STAT3 inducing MDR1 activity and TIC population, MDR1 inhibition in MMTV-PyMT;ApcMin/+ cells was also shown to reduce the TIC population. In addition, we are investigating the effect of APC loss on DNA damage repair pathways. Preliminary studies have shown decreased γH2AX in MMTV-PyMT;ApcMin/+ cells treated with doxorubicin, suggesting a decrease in DNA damage. Downstream signaling of γH2AX, measured by phosphorylation of ATM, also demonstrated decreased DNA damage with ongoing studies measuring phosphorylation of ATR. Due to APC binding to topoisomerase IIα (topo IIα), a target of doxorubicin, the activity of topo IIα was measured to address whether this decreased DNA damage was attributed to impaired topo IIα activity or decreased intracellular doxorubicin due to increased MDR1 efflux. Future studies will investigate whether MDR1 inhibition in combination with doxorubicin will reduce tumor burden in vivo. Taken together, APC loss mediates doxorubicin resistance via enhanced MDR1 activity and altered DNA damage repair pathways demonstrating the potential use of combination therapy to overcome resistance to chemotherapy. Citation Format: Casey D. Stefanski, Kaitlyn Keffler, Stephanie McClintock, Jenifer R. Prosperi. Loss of APC mediates doxorubicin resistance in breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4463.

Genetic variants of the DNA damage repair genes XRCC4 and RAD51 are associated with susceptibility to esophageal cancer

Altered DNA damage repair genes have been demonstrated to contribute to tumorigenesis. This study explored the relationship of genetic polymorphisms of the DNA repair genes XRCC4 and RAD51 to the risk of esophageal cancer. Genotyping of XRCC4 G-1394T (rs6869366) and RAD51-G135C by PCR-RFLP analysis was performed on 477participants, of whom 219 were patients with esophageal cancer; the remaining participants were healthy. Statistical analysis, including Chi(2) test and logistic regression, was used to assess genotypic distributions and their correlation with cancer risk. Carriers of the XRCC4 rs6869366 G allele (GT+GG) were at a significantly higher risk of esophageal cancer compared to individuals with the TT genotype [odds ratio (OR)=3.35, 95% confidence interval (CI): (1.16-10.24)]. Carriers of the C allele of RAD51 G135C (GC+CC) had a significantly increased risk of esophageal cancer compared to individuals with the GG genotype (OR=2.53, 95%CI: 1.15-6.70). Further, the variant genotypes of XRCC4 and RAD51 interacted to exacerbate the risk of esophageal cancer (OR=8.92, 95%CI: 2.47-38.20). Variants of the DNA damage repair genes XRCC4 and RAD51 increase the risk of esophageal cancer.

Altered spectrum of somatic hypermutation in common variable immunodeficiency disease characteristic of defective repair of mutations

Pathogenic common variable immunodeficiency diseases (CVID) are genetic, usually inherited diseases for which a limited number of genetic defects have been implicated. As CVID presents with a wide range of clinical characteristics, there are likely diverse and for the most part unidentified genetic causes. In some individuals, defects in somatic hypermutation (SHM) have been suggested as the underlying cause of CVID. To address the mechanisms of SHM defects in CVID, we conducted a comprehensive mutational analysis of immunoglobulin heavy chain sequences from CVID patients. We identified several remarkably specific alterations in the spectra of SHM in comparison to healthy individuals. We provide evidence that some CVID cases are associated with defective repair of AID-induced mutations by the DNA mismatch repair (MMR) machinery. Our findings together with reports of increased chromosomal radiosensitivity and associated lymphoproliferative disorders amongst CVID patients, suggest that altered DNA damage repair may be a cause of CVID.

Mechanisms Mediating the Effects of Prepubertal (n-3) Polyunsaturated Fatty Acid Diet on Breast Cancer Risk in Rats

Dietary exposures during childhood may influence later breast cancer risk. We tested in an animal model the hypothesis that prepubertal intake of (n-3) PUFAs, present mainly in fish, reduces susceptibility to breast cancer. Between postnatal days 5 to 25, rat pups were fed (n-3) PUFA-containing diets at a 2:1 ratio of (n-6):(n-3) PUFAs (typical of prehistoric societies) or a control (n-6) PUFA diet at a 17:1 ratio of (n-6):(n-3) PUFAs (comparable with current Western societies). These fatty acids were given in a low- or high-fat context (16 or 39% energy from fat). The low-(n-3) PUFA diet reduced while the high-(n-3) PUFA diet increased carcinogen-induced mammary tumorigenesis. The low-(n-3) PUFA diet reduced mammary cell proliferation and increased apoptosis, particularly in the terminal end buds (the mammary source of malignant breast tumors). The high-(n-3) PUFA diet had opposite effects on these 2 key biomarkers and increased phospho-Akt levels, a survival factor. Microarray analyses identified genes that were permanently upregulated in the low-(n-3) PUFA-exposed glands and function in oxidative damage repair. Serum levels of 8-hydroxy-2'deoxyguanosine, a marker of DNA damage, were significantly reduced in these low-(n-3) PUFA-fed rats, and increased in the high-(n-3) PUFA-exposed group. The latter group exhibited reduced expression of BRCA1, a DNA repair gene. Our results indicate that the opposing susceptibilities to mammary tumorigenesis between the low- versus high-fat (n-3) PUFA-exposed groups were associated with altered DNA damage repair and gene expression linked to proliferation, survival, and differentiation.

Radiosensitization and cell kinetics: clinical implications for S-phase-specific radiosensitizers.

Rapid repopulation of tumor cells during conventional radiation therapy has been recently recognized as a factor that might significantly impair tumor response in several different tumor sites. One clinical strategy to overcome rapid tumor proliferation is to use S-phase-specific radiosensitizers such as hydroxyurea and the halopyrimidines 5-iododeoxyuridine (IUDR), 5-bromo-2'-deoxyuridine (BUDR), 5-fluoro-2'-deoxy-beta-uridine (FUDR), and 5-fluorouracil (5-FU). Indeed, several recent clinical trials have shown the positive antiproliferative effects of these radiosensitizers in various human tumors. In spite of this resurgence of clinical interest, the basic mechanism(s) of radiosensitization is not clearly understood. Although the halopyrimidines have similar biochemical pathways involving two key regulatory enzymes, thymidine kinase and thymidylate synthase, it appears that DNA-incorporation is important for radiosensitization by BUDR and IUDR but not for FUDR or 5-FU. Recent laboratory data suggest that biochemical modulation of the key regulatory enzymes can result in selective tumor radiosensitization with halopyrimidines. Hydroxyurea, like 5-FU, sensitizes cells when present prior to and following irradiation; this interaction may be related to cell synchronization as well as altered DNA damage repair. Exploiting differences in cell proliferation and cellular metabolism of these S-phase-specific radiosensitizers in tumors and normal tissues will be a major focus of clinical research in human tumor radiosensitization over the next few years.