Prescribed Versus Taken Polypharmacy and Drug-Drug Interactions in Older Cardiovascular Patients during the COVID-19 Pandemic: Observational Cross-Sectional Analytical Study.

The study aimed to assess clinical pharmacology patterns of prescribed and taken medications in older cardiovascular patients using electronic health records (EHRs) (n = 704) (2019-2022). Medscape Drug Interaction Checker was used to identify pairwise drug-drug interactions (DDIs). Prevalence rates of DDIs were 73.5% and 68.5% among taken and prescribed drugs, respectively. However, the total number of DDIs was significantly higher among the prescribed medications (p < 0.05). Serious DDIs comprised 16% and 7% of all DDIs among the prescribed and taken medications, respectively (p < 0.05). Median numbers of DDIs between the prescribed vs. taken medications were Me = 2, IQR 0-7 vs. Me = 3, IQR 0-7 per record, respectively. Prevalence of polypharmacy was significantly higher among the prescribed medications compared with that among the taken drugs (p < 0.05). Women were taking significantly more drugs and had higher prevalence of polypharmacy and DDIs (p < 0.05). No sex-related differences were observed in the list of prescribed medications. ICD code U07.1 (COVID-19, virus identified) was associated with the highest median DDI number per record. Further research is warranted to improve EHR structure, implement patient engagement in reporting adverse drug reactions, and provide genetic profiling of patients to avoid potentially serious DDIs.

Targeting telomerase reverse transcriptase with the covalent inhibitor NU-1 confers immunogenic radiation sensitization.

Beyond synthesizing telomere repeats, the telomerase reverse transcriptase (TERT) also serves multiple other roles supporting cancer growth. Blocking telomerase to drive telomere erosion appears impractical, but TERT's non-canonical activities have yet to be fully explored as cancer targets. Here, we used an irreversible TERT inhibitor, NU-1, to examine impacts on resistance to conventional cancer therapies. In vitro, inhibiting TERT sensitized cells to chemotherapy and radiation. NU-1 delayed repair of double-strand breaks, resulting in persistent DNA damage signaling and cellular senescence. Although NU-1 alone did not impact growth of syngeneic CT26 tumors in BALB/c mice, it dramatically enhanced the effects of radiation, leading to immune-dependent tumor elimination. Tumors displayed persistent DNA damage, suppressed proliferation, and increased activated immune infiltrate. Our studies confirm TERT's role in limiting genotoxic effects of conventional therapy but also implicate TERT as a determinant of immune evasion and therapy resistance.

Trends and concerns of potentially inappropriate medication use in patients with cardiovascular diseases.

Introduction: The use of potentially inappropriate medications (PIM) is an alarming social risk factor in cardiovascular patients. PIM administration may result in iatrogenic disorders and adverse consequences may be attenuated by limiting PIM intake.Areas covered: The goal of this review article is to discuss the trends, risks, and concerns regarding PIM administration with focus on cardiovascular patients. To find data, we searched literature using electronic databases (Pubmed/Medline 1966-2021 and Web of Science 1975-2021). The data search terms were cardiovascular diseases, potentially inappropriate medication, potentially harmful drug-drug combination, potentially harmful drug-disease combination, drug interaction, deprescribing, and electronic health record.Expert opinion: Drugs for heart diseases are the most commonly prescribed medications in older individuals. Despite the availability of explicit and implicit PIM criteria, the incidence of PIM use in cardiovascular patients remains high ranging from 7 to 85% in different patient categories. Physician-induced disorders often occur when PIM is administered and adverse effects may be reduced by limiting PIM intake. Main strategies promising for addressing PIM use include deprescribing, implementation of systematic electronic records, pharmacist medication review, and collaboration among cardiologists, internists, geriatricians, clinical pharmacologists, pharmacists, and other healthcare professionals as basis of multidisciplinary assessment teams.

Mevalonate pathway activity as a determinant of radiation sensitivity in head and neck cancer.

Radioresistance is a major hurdle in the treatment of head and neck squamous cell carcinoma (HNSCC). Here, we report that concomitant treatment of HNSCCs with radiotherapy and mevalonate pathway inhibitors (statins) may overcome resistance. Proteomic profiling and comparison of radioresistant to radiosensitive HNSCCs revealed differential regulation of the mevalonate biosynthetic pathway. Consistent with this finding, inhibition of the mevalonate pathway by pitavastatin sensitized radioresistant SQ20B cells to ionizing radiation and reduced their clonogenic potential. Overall, this study reinforces the view that the mevalonate pathway is a promising therapeutic target in radioresistant HNSCCs.

Repair-independent functions of DNA-PKcs protect irradiated cells from mitotic slippage and accelerated senescence.

The binding of DNA-dependent protein kinase catalytic subunit (DNA-PKcs, also known as PRKDC) to Ku proteins at DNA double-strand breaks (DSBs) has long been considered essential for non-homologous end joining (NHEJ) repair, providing a rationale for use of DNA-PKcs inhibitors as cancer therapeutics. Given lagging clinical translation, we reexamined mechanisms and observed instead that DSB repair can proceed independently of DNA-PKcs. While repair of radiation-induced DSBs was blocked in cells expressing shRNAs targeting Ku proteins or other NHEJ core factors, DSBs were repaired on schedule despite targeting DNA-PKcs. Although we failed to observe a DSB repair defect, the γH2AX foci that formed at sites of DNA damage persisted indefinitely after irradiation, leading to cytokinesis failure and accumulation of binucleated cells. Following this mitotic slippage, cells with decreased DNA-PKcs underwent accelerated cellular senescence. We identified downregulation of ataxia-telangiectasia mutated kinase (ATM) as the critical role of DNA-PKcs in recovery from DNA damage, insofar as targeting ATM restored γH2AX foci resolution and cytokinesis. Considering the lack of direct impact on DSB repair and emerging links between senescence and resistance to cancer therapy, these results suggest reassessing DNA-PKcs as a target for cancer treatment.

O-GlcNAcylation Enhances Double-Strand Break Repair, Promotes Cancer Cell Proliferation, and Prevents Therapy-Induced Senescence in Irradiated Tumors.

The metabolic reprogramming associated with characteristic increases in glucose and glutamine metabolism in advanced cancer is often ascribed to answering a higher demand for metabolic intermediates required for rapid tumor cell growth. Instead, recent discoveries have pointed to an alternative role for glucose and glutamine metabolites as cofactors for chromatin modifiers and other protein posttranslational modification enzymes in cancer cells. Beyond epigenetic mechanisms regulating gene expression, many chromatin modifiers also modulate DNA repair, raising the question whether cancer metabolic reprogramming may mediate resistance to genotoxic therapy and genomic instability. Our prior work had implicated N-acetyl-glucosamine (GlcNAc) formation by the hexosamine biosynthetic pathway (HBP) and resulting protein O-GlcNAcylation as a common means by which increased glucose and glutamine metabolism can drive double-strand break (DSB) repair and resistance to therapy-induced senescence in cancer cells. We have examined the effects of modulating O-GlcNAcylation on the DNA damage response (DDR) in MCF7 human mammary carcinoma in vitro and in xenograft tumors. Proteomic profiling revealed deregulated DDR pathways in cells with altered O-GlcNAcylation. Promoting protein O-GlcNAc modification by targeting O-GlcNAcase or simply treating animals with GlcNAc protected tumor xenografts against radiation. In turn, suppressing protein O-GlcNAcylation by blocking O-GlcNAc transferase activity led to delayed DSB repair, reduced cell proliferation, and increased cell senescence in vivo. Taken together, these findings confirm critical connections between cancer metabolic reprogramming, DDR, and senescence and provide a rationale to evaluate agents targeting O-GlcNAcylation in patients as a means to restore tumor sensitivity to radiotherapy. IMPLICATIONS: The finding that the HBP, via its impact on protein O-GlcNAcylation, is a key determinant of the DDR in cancer provides a mechanistic link between metabolic reprogramming, genomic instability, and therapeutic response and suggests novel therapeutic approaches for tumor radiosensitization.

HMG-CoA Reductase Inhibition Delays DNA Repair and Promotes Senescence After Tumor Irradiation.

Despite significant advances in combinations of radiotherapy and chemotherapy, altered fractionation schedules and image-guided radiotherapy, many cancer patients fail to benefit from radiation. A prevailing hypothesis is that targeting repair of DNA double strand breaks (DSB) can enhance radiation effects in the tumor and overcome therapeutic resistance without incurring off-target toxicities. Unrepaired DSBs can block cancer cell proliferation, promote cancer cell death, and induce cellular senescence. Given the slow progress to date translating novel DSB repair inhibitors as radiosensitizers, we have explored drug repurposing, a proven route to improving speed, costs, and success rates of drug development. In a prior screen where we tracked resolution of ionizing radiation-induced foci (IRIF) as a proxy for DSB repair, we had identified pitavastatin (Livalo), an HMG-CoA reductase inhibitor commonly used for lipid lowering, as a candidate radiosensitizer. Here, we report that pitavastatin and other lipophilic statins are potent inhibitors of DSB repair in breast and melanoma models both in vitro and in vivo When combined with ionizing radiation, pitavastatin increased persistent DSBs, induced senescence, and enhanced acute effects of radiation on radioresistant melanoma tumors. shRNA knockdown implicated HMG-CoA reductase, farnesyl diphosphate synthase, and protein farnesyl transferase in IRIF resolution, DSB repair, and senescence. These data confirm on-target activity of statins, although via inhibition of protein prenylation rather than cholesterol biosynthesis. In light of prior studies demonstrating enhanced efficacy of radiotherapy in patients taking statins, this work argues for clinical evaluation of lipophilic statins as nontoxic radiosensitizers to enhance the benefits of image-guided radiotherapy. Mol Cancer Ther; 17(2); 407-18. ©2017 AACRSee all articles in this MCT Focus section, "Developmental Therapeutics in Radiation Oncology."

Efficacy of the Combination of a PARP Inhibitor and UVC on Cancer Cells as Imaged by Focus Formation by the DNA Repair-related Protein 53BP1 Linked to Green Fluorescent Protein.

BACKGROUND: The ability to image DNA repair in cancer cells after irradiation, as well as its inhibition by potential therapeutic agents, is important for the further development of effective cancer therapy. 53BP1 is a DNA repair protein that is overexpressed and forms foci when double-stranded DNA breaks occur in DNA. MATERIALS AND METHODS: The re-localization of green fluorescent protein (GFP) fused to the chromatin-binding domain of 53BP1 to form foci was imaged after UVC irradiation of breast and pancreatic cancer cells expressing 53BP1-GFP using confocal microscopy. RESULTS: During live-cell imaging, 53BP1-GFP focus formation was observed within 10 minutes after UVC irradiation. Most 53BP1 foci resolved by 100 minutes. To block UVC-induced double-strand break repair in cancer cells, poly(ADP-ribose) polymerase (PARP) was targeted with ABT-888 (veliparib). PARP inhibition markedly enhanced UVC-irradiation-induced persistence of 53BP1-foci, even beyond 100 minutes after UVC irradiation, and reduced proliferation of breast and pancreatic cancer cells. CONCLUSION: Confocal microscopy of 53BP1-GFP is a powerful method for imaging UVC-induced DNA damage and repair, as well as inhibition of repair.

Repurposing cephalosporin antibiotics as pro-senescent radiosensitizers.

Radiation therapy remains a significant therapeutic modality in the treatment of cancer. An attractive strategy would be to enhance the benefits of ionizing radiation (IR)with radiosensitizers. A high-content drug repurposing screen of approved and investigational agents, natural products and other small molecules has identified multiple candidates that blocked repair of IR damage in vitro. Here, we validated a subset of these hits in vitro and then examined effects on tumor growth after IR in a murine tumor model. Based on robust radiosensitization in vivo and other favorable properties of cephalexin, we conducted additional studies with other beta-lactam antibiotics. When combined with IR, each cephalosporin tested increased DNA damage and slowed tumor growth without affecting normal tissue toxicity. Our data implicate reactive oxygen species in the mechanism by which cephalosporins augment the effects of IR. This work provides a rationale for using commonly prescribed beta-lactam antibiotics as non-toxic radiosensitizers to enhance the therapeutic ratio of radiotherapy.

Linking Cancer Metabolism to DNA Repair and Accelerated Senescence.

UNLABELLED: Conventional wisdom ascribes metabolic reprogramming in cancer to meeting increased demands for intermediates to support rapid proliferation. Prior models have proposed benefits toward cell survival, immortality, and stress resistance, although the recent discovery of oncometabolites has shifted attention to chromatin targets affecting gene expression. To explore further effects of cancer metabolism and epigenetic deregulation, DNA repair kinetics were examined in cells treated with metabolic intermediates, oncometabolites, and/or metabolic inhibitors by tracking resolution of double-strand breaks (DSB) in irradiated MCF7 breast cancer cells. Disrupting cancer metabolism revealed roles for both glycolysis and glutaminolysis in promoting DSB repair and preventing accelerated senescence after irradiation. Targeting pathways common to glycolysis and glutaminolysis uncovered opposing effects of the hexosamine biosynthetic pathway (HBP) and tricarboxylic acid (TCA) cycle. Treating cells with the HBP metabolite N-acetylglucosamine (GlcNAc) or augmenting protein O-GlcNAcylation with small molecules or RNAi targeting O-GlcNAcase each enhanced DSB repair, while targeting O-GlcNAc transferase reversed GlcNAc's effects. Opposing the HBP, TCA metabolites including α-ketoglutarate blocked DSB resolution. Strikingly, DNA repair could be restored by the oncometabolite 2-hydroxyglutarate (2-HG). Targeting downstream effectors of histone methylation and demethylation implicated the PRC1/2 polycomb complexes as the ultimate targets for metabolic regulation, reflecting known roles for Polycomb group proteins in nonhomologous end-joining DSB repair. Our findings that epigenetic effects of cancer metabolic reprogramming may promote DNA repair provide a molecular mechanism by which deregulation of metabolism may not only support cell growth but also maintain cell immortality, drive therapeutic resistance, and promote genomic instability. IMPLICATIONS: By defining a pathway from deregulated metabolism to enhanced DNA damage response in cancer, these data provide a rationale for targeting downstream epigenetic effects of metabolic reprogramming to block cancer cell immortality and overcome resistance to genotoxic stress.

Real-time fluorescence imaging of the DNA damage repair response during mitosis.

The response to DNA damage during mitosis was visualized using real-time fluorescence imaging of focus formation by the DNA-damage repair (DDR) response protein 53BP1 linked to green fluorescent protein (GFP) (53BP1-GFP) in the MiaPaCa-2(Tet-On) pancreatic cancer cell line. To observe 53BP1-GFP foci during mitosis, MiaPaCa-2(Tet-On) 53BP1-GFP cells were imaged every 30 min by confocal microscopy. Time-lapse imaging demonstrated that 11.4 ± 2.1% of the mitotic MiaPaCa-2(Tet-On) 53BP1-GFP cells had increased focus formation over time. Non-mitotic cells did not have an increase in 53BP1-GFP focus formation over time. Some of the mitotic MiaPaCa-2(Tet-On) 53BP1-GFP cells with focus formation became apoptotic. The results of the present report suggest that DNA strand breaks occur during mitosis and undergo repair, which may cause some of the mitotic cells to enter apoptosis in a phenomenon possibly related to mitotic catastrophe.

Imaging UVC-induced DNA damage response in models of minimal cancer.

We have previously demonstrated that the ultraviolet (UV) light is effective against a variety of cancer cells in vivo as well as in vitro. In the present report, we imaged the DNA damage repair response of minimal cancer after UVC irradiation. DNA-damage repair response to UV irradiation was imaged on tumors growing in 3D culture and in superficial tumors grown in vivo. UV-induced DNA damage repair was imaged with GFP fused to the DNA damage response (DDR)-related chromatin-binding protein 53BP1 in MiaPaCa-2 human pancreatic cancer cells. Three-dimensional Gelfoam® histocultures and confocal imaging enabled 53BP1-GFP nuclear foci to be observed within 1 h after UVC irradiation, indicating the onset of DNA damage repair response. A clonogenic assay showed that UVC inhibited MiaPaCa-2 cell proliferation in a dose-dependent manner, while UVA and UVB showed little effect on cell proliferation. Induction of UV-induced 53BP1-GFP focus formation was limited up to a depth of 40 µm in 3D-culture of MiaPaCa-2 cells. The MiaPaCa-2 cells irradiated by UVC light in a skin-flap mouse model had a significant decrease of tumor growth compared to untreated controls. Our results also demonstrate that 53BP1-GFP is an imageable marker of UV-induced DNA damage repair response of minimal cancer and that UVC is a useful tool for the treatment of residual cancer since UVC can kill superficial cancer cells without damage to deep tissue.

Dynamic color-coded fluorescence imaging of the cell-cycle phase, mitosis, and apoptosis demonstrates how caffeine modulates cisplatinum efficacy.

Caffeine enhances the effect of certain anticancer drugs, but the mechanism of modulation is poorly understood. In this study, modulation of cisplatinum efficacy induced by caffeine was visualized at the subcellular level by real-time fluorescent-protein imaging. Mitotic and apoptotic changes were observed by imaging 143B human osteosarcoma dual-color cells, in which GFP is expressed in the nucleus and RFP is expressed in the cytoplasm. Modulation of the cell cycle was imaged using time-lapse imaging of HeLa cells expressing a fluorescent ubiquitination-based cell cycle indicator (FUCCI) in the nucleus. Clonogenic assays showed that caffeine increased the inhibition by cisplatinum on cell proliferation. Subcellular imaging demonstrated that cisplatinum decreased mitosis and induced apoptosis in 143B cells. The combination of cisplatinum and caffeine enhanced mitosis and subsequently increased apoptosis. Time-lapse imaging showed that cisplatinum strongly induced cell-cycle arrest in the S/G2 phase in HeLa-FUCCI cells. Caffeine overcame the cell-cycle arrest induced by cisplatinum, thereby increasing its efficacy, since cisplatinum is ineffective against quiescent cells. The data in this report indicate that caffeine modulates the cell cycle in cancer cells, thereby enhancing efficacy of cell-cycle-dependent anticancer drugs such as cisplatinum.

Single cell time-lapse imaging of focus formation by the DNA damage-response protein 53BP1 after UVC irradiation of human pancreatic cancer cells.

We have previously demonstrated that ultraviolet (UV) light treatment is effective against various types of cancer cells expressing fluorescent proteins. In order to further understand the efficacy of UV treatment of cancer cells, we determined the kinetics of focus formation by imaging of a DNA damage-response (DDR) protein after UVC irradiation of human pancreatic cancer cells. A fusion protein consisting of the DDR protein 53BP1 and green fluorescent protein (GFP) (GFP-53BP1) was used as a live-cell imaging marker for cellular response after UVC irradiation. GFP-53BP1 foci were observed after UVC irradiation of MiaPaCa-2 human pancreatic cancer cells. During live-cell imaging, GFP-53BP1 foci were observed in the cells within 15 min after UVC irradiation, and some of the foci remained stable for at least three hours. GFP-53BP1 focus formation was observed in the pancreatic-cancer cells irradiated by 25-200 J/m(2) UVC. Our results indicate that an early response to DNA damage caused by UVC irradiation can be visualized by increased GFP-53BP1 focus formation by pancreatic cancer cells.

Radiation-inducible immunotherapy for cancer: senescent tumor cells as a cancer vaccine.

Radiotherapy offers an effective treatment for advanced cancer but local and distant failures remain a significant challenge. Here, we treated melanoma and pancreatic carcinoma in syngeneic mice with ionizing radiation (IR) combined with the poly(ADP-ribose) polymerase inhibitor (PARPi) veliparib to inhibit DNA repair and promote accelerated senescence. Based on prior work implicating cytotoxic T lymphocytes (CTLs) as key mediators of radiation effects, we discovered that senescent tumor cells induced by radiation and veliparib express immunostimulatory cytokines to activate CTLs that mediate an effective antitumor response. When these senescent tumor cells were injected into tumor-bearing mice, an antitumor CTL response was induced which potentiated the effects of radiation, resulting in elimination of established tumors. Applied to human cancers, radiation-inducible immunotherapy may enhance radiotherapy responses to prevent local recurrence and distant metastasis.

Progression of cancer from indolent to aggressive despite antigen retention and increased expression of interferon-gamma inducible genes.

Many cancers escape host immunity without losing tumor-specific rejection antigens or MHC class I expression. This study tracks the evolution of one such cancer that developed in a mouse following exposure to ultraviolet light. The primary autochthonous tumor was not highly malignant and was rejected when transplanted into naïve immunocompetent mice. Neoplastic cells isolated from the primary tumor were susceptible to the growth-inhibitory effects of IFNγ in vitro, but expressed very low levels of MHC I antigen and were resistant to tumor-specific T cells unless they were first exposed to IFNγ. Serial passage of the primary tumor cells in vivo led to a highly aggressive variant that caused fast-growing tumors in normal mice. In vitro, the variant tumor cells showed increased resistance to the growth-inhibitory effects of IFNγ but expressed high levels of immunoproteasomes and MHC I molecules and were susceptible to tumor-specific T cells even without prior exposure to IFNγ.

Response of human prostate cancer cells and tumors to combining PARP inhibition with ionizing radiation.

Radiation therapy remains a promising modality for curative treatment of localized prostate cancer, but dose-limiting toxicities significantly limit its effectiveness. Agents that enhance efficacy at lower radiation doses might have considerable value in increasing tumor control without compromising organ function. Here, we tested the hypothesis that the PARP inhibitor ABT-888 (veliparib) can enhance the response of prostate cancer cells and tumors to ionizing radiation (IR). Following exposure of DU-145 and PC-3 prostate cancer cell lines to the combination of 10 µmol/L ABT-888 and 6 Gy, we observed similar persistence between both cell lines of DNA damage foci and in vitro radiosensitization. We have previously observed that persistent DNA damage foci formed after ABT-888 plus IR efficiently promote accelerated cell senescence, but only PC-3 cells displayed the expected senescent response of G(2)-M arrest, induction of p21 and ß-galactosidase expression, and accumulation as large flat cells. In turn, combining ABT-888 with 6 Gy resulted in delayed tumor regrowth compared with either agent alone only in PC-3 xenograft tumors, whereas DU-145 tumors continued to grow. By 7 days after treatment with ABT-888 plus IR, PC-3 tumors contained abundant senescent cells displaying persistent DNA damage foci, but no evidence of senescence was noted in the DU-145 tumors. That equivalent radiosensitization by ABT-888 plus IR in vitro failed to predict comparable results with tumors in vivo suggests that the efficacy of PARP inhibitors may partially depend on a competent senescence response to accumulated DNA damage.

Ionizing radiation-induced foci persistence screen to discover enhancers of accelerated senescence.

Much like replicative senescence, the irreversible cell-cycle arrest induced by eroded telomeres, accelerated senescence occurs when replicative cells suffer irreparable DNA double-strand breaks (DSBs). Along with apoptosis and necrosis, senescence is a desirable outcome in cancer treatment with ionizing radiation (IR) or chemotherapy. In both normal and cancer cells, DSBs promote the assembly of IR-induced foci (IRIF), domains of modified chromatin that serve a key role in DNA damage signaling. IRIF persistence is a critical determinant of accelerated senescence, making drugs that promote persistent IRIF an attractive strategy to sensitize cancer to genotoxic therapy. As an IRIF reporter, we have expressed an inducible green fluorescent protein (GFP) fusion to the IRIF-binding domain (IBD) of 53BP1 (GFP-IBD) in the breast cancer cell line MCF7. Within minutes of exposure to IR, the GFP-IBD relocalizes to form fluorescent nuclear foci, which disperse within several hours. A pair of high-content screening assays for IRIF formation and persistence were established in multiwell plates based on imaging and quantifying GFP-IBD foci per Hoechst-stained MCF7 nucleus at 2 hours and 24 hours. Using the ataxia telangiectasia-mutated inhibitor CGK733 to block IRIF formation and the topoisomerase II inhibitor etoposide to prevent IRIF resolution, we obtained a Z' >0.8 both for IRIF formation at 2 hours and IRIF persistence at 24 hours. Screening the diverse drugs and natural products in the National Cancer Institute Developmental Therapeutics Program Approved Oncology Drugs Set, the National Institutes of Health Clinical Collection, and the MicroSource Spectrum Collection yielded multiple hits that significantly delayed IRIF resolution. Secondary screening suggested some of these otherwise nontoxic drugs also enhance accelerated senescence, indicating strong potential for their repurposing as radiation sensitizers to improve the efficacy of cancer therapy.

Poly(ADP-ribose) polymerase inhibitor induces accelerated senescence in irradiated breast cancer cells and tumors.

Persistent DNA double-strand breaks (DSB) may determine the antitumor effects of ionizing radiation (IR) by inducing apoptosis, necrosis, mitotic catastrophe, or permanent growth arrest. IR induces rapid modification of megabase chromatin domains surrounding DSBs via poly-ADP-ribosylation, phosphorylation, acetylation, and protein assembly. The dynamics of these IR-induced foci (IRIF) have been implicated in DNA damage signaling and DNA repair. As an IRIF reporter, we tracked the relocalization of green fluorescent protein fused to a chromatin binding domain of the checkpoint adapter protein 53BP1 after IR of breast cancer cells and tumors. To block DSB repair in breast cancer cells and tumors, we targeted poly(ADP-ribose) polymerase (PARP) with ABT-888 (veliparib), one of several PARP inhibitors currently in clinical trials. PARP inhibition markedly enhanced IRIF persistence and increased breast cancer cell senescence both in vitro and in vivo, arguing for targeting IRIF resolution as a novel therapeutic strategy.

Radioresistance of Stat1 over-expressing tumour cells is associated with suppressed apoptotic response to cytotoxic agents and increased IL6-IL8 signalling.

PURPOSE: To determine the mechanisms of Signal Transducer and Activator of Transcription 1 (Stat1)-associated radioresistance developed by nu61 tumour selected in vivo by fractionated irradiation of the parental radiosensitive tumour SCC61. MATERIALS AND METHODS: Radioresistence of nu61 and SCC61 in vitro was measured by clonogenic assay. Apoptotic response of nu61 and SCC61 cells to genotoxic stress was examined using caspase-based apoptotic assays. Co-cultivation of carboxyfluorescein diacetate, succinimidyl ester (CFDE-SE)-labeled nu61 with un-labeled SCC61 was performed at 1:1 ratio. Production of interleukin-6, interleukin-8 and soluble receptor of interleukin 6 (IL6, IL8 and sIL6R) was measured using Enzyme-Linked Immunosorbent Assay (ELISA). RESULTS: Radioresistant nu61 was also resistant to interferon-gamma (IFNgamma) and the death ligands of tumour necrosis factor alpha receptor (TNFR) family when compared to SCC61. This combined resistance is due to an impaired apoptotic response in nu61. Relative to SCC61, nu61 produced more IL6, IL8 and sIL6R. Using Stat1 knock-downs we demonstrated that IL6 and IL8 production is Stat1-dependent. Treatment with neutralising antibodies to IL6 and IL8, but not to either cytokine alone sensitised nu61 to genotoxic stress induced apoptosis. CONCLUSION: Nu61, which over-expresses Stat1 pathway, is deficient in apoptotic response to ionising radiation and cytotoxic ligands. This resistance to apoptosis is associated with Stat1-dependent production of IL6 and IL8 and suppression of caspases 8, 9 and 3.