Laura E. Taggart

Cell type-dependent uptake, localization, and cytotoxicity of 1.9 nm gold nanoparticles

Background This follow-up study aims to determine the physical parameters which govern the differential radiosensitization capacity of two tumor cell lines and one immortalized normal cell line to 1.9 nm gold nanoparticles. In addition to comparing the uptake potential, localization, and cytotoxicity of 1.9 nm gold nanoparticles, the current study also draws on comparisons between nanoparticle size and total nanoparticle uptake based on previously published data. Methods We quantified gold nanoparticle uptake using atomic emission spectroscopy and imaged intracellular localization by transmission electron microscopy. Cell growth delay and clonogenic assays were used to determine cytotoxicity and radiosensitization potential, respectively. Mechanistic data were obtained by Western blot, flow cytometry, and assays for reactive oxygen species. Results Gold nanoparticle uptake was preferentially observed in tumor cells, resulting in an increased expression of cleaved caspase proteins and an accumulation of cells in sub G1 phase. Despite this, gold nanoparticle cytotoxicity remained low, with immortalized normal cells exhibiting an LD50 concentration approximately 14 times higher than tumor cells. The surviving fraction for gold nanoparticle-treated cells at 3 Gy compared with that of untreated control cells indicated a strong dependence on cell type in respect to radiosensitization potential. Conclusion Gold nanoparticles were most avidly endocytosed and localized within cytoplasmic vesicles during the first 6 hours of exposure. The lack of significant cytotoxicity in the absence of radiation, and the generation of gold nanoparticle-induced reactive oxygen species provide a potential mechanism for previously reported radiosensitization at megavoltage energies.

Imaging and radiation effects of gold nanoparticles in tumour cells

Gold nanoparticle radiosensitization represents a novel technique in enhancement of ionising radiation dose and its effect on biological systems. Variation between theoretical predictions and experimental measurement is significant enough that the mechanism leading to an increase in cell killing and DNA damage is still not clear. We present the first experimental results that take into account both the measured biodistribution of gold nanoparticles at the cellular level and the range of the product electrons responsible for energy deposition. Combining synchrotron-generated monoenergetic X-rays, intracellular gold particle imaging and DNA damage assays, has enabled a DNA damage model to be generated that includes the production of intermediate electrons. We can therefore show for the first time good agreement between the prediction of biological outcomes from both the Local Effect Model and a DNA damage model with experimentally observed cell killing and DNA damage induction via the combination of X-rays and GNPs. However, the requirement of two distinct models as indicated by this mechanistic study, one for short-term DNA damage and another for cell survival, indicates that, at least for nanoparticle enhancement, it is not safe to equate the lethal lesions invoked in the local effect model with DNA damage events.

The role of mitochondrial function in gold nanoparticle mediated radiosensitisation

Gold nanoparticles (GNPs), have been demonstrated as effective preclinical radiosensitising agents in a range of cell models and radiation sources. These studies have also highlighted difficulty in predicted cellular radiobiological responses mediated by GNPs, based on physical assumptions alone, and therefore suggest a significant underlying biological component of response. This study aimed to determine the role of mitochondrial function in GNP radiosensitisation. Using assays of DNA damage and mitochondrial function through levels of oxidation and loss of membrane potential, we demonstrate a potential role of mitochondria as a central biological mechanism of GNP mediated radiosensitisation.

Activation of STING-Dependent Innate Immune Signaling By S-Phase-Specific DNA Damage in Breast Cancer.

Background: Previously we identified a DNA damage response–deficient (DDRD) molecular subtype within breast cancer. A 44-gene assay identifying this subtype was validated as predicting benefit from DNA-damaging chemotherapy. This subtype was defined by interferon signaling. In this study, we address the mechanism of this immune response and its possible clinical significance. Methods: We used immunohistochemistry (IHC) to characterize immune infiltration in 184 breast cancer samples, of which 65 were within the DDRD subtype. Isogenic cell lines, which represent DDRD-positive and -negative, were used to study the effects of chemokine release on peripheral blood mononuclear cell (PBMC) migration and the mechanism of immune signaling activation. Finally, we studied the association between the DDRD subtype and expression of the immune-checkpoint protein PD-L1 as detected by IHC. All statistical tests were two-sided. Results: We found that DDRD breast tumors were associated with CD4+ and CD8+ lymphocytic infiltration (Fisher’s exact test P < .001) and that DDRD cells expressed the chemokines CXCL10 and CCL5 3.5- to 11.9-fold more than DNA damage response–proficient cells (P < .01). Conditioned medium from DDRD cells statistically significantly attracted PBMCs when compared with medium from DNA damage response–proficient cells (P < .05), and this was dependent on CXCL10 and CCL5. DDRD cells demonstrated increased cytosolic DNA and constitutive activation of the viral response cGAS/STING/TBK1/IRF3 pathway. Importantly, this pathway was activated in a cell cycle–specific manner. Finally, we demonstrated that S-phase DNA damage activated expression of PD-L1 in a STING-dependent manner. Conclusions: We propose a novel mechanism of immune infiltration in DDRD tumors, independent of neoantigen production. Activation of this pathway and associated PD-L1 expression may explain the paradoxical lack of T-cell-mediated cytotoxicity observed in DDRD tumors. We provide a rationale for exploration of DDRD in the stratification of patients for immune checkpoint–based therapies.

Protein disulphide isomerase as a target for nanoparticle-mediated sensitisation of cancer cells to radiation

Radiation resistance and toxicity in normal tissues are limiting factors in the efficacy of radiotherapy. Gold nanoparticles (GNPs) have been shown to be effective at enhancing radiation-induced cell death, and were initially proposed to physically enhance the radiation dose deposited. However, biological responses of GNP radiosensitization based on physical assumptions alone are not predictive of radiosensitisation and therefore there is a fundamental research need to determine biological mechanisms of response to GNPs alone and in combination with ionising radiation. This study aimed to identify novel mechanisms of cancer cell radiosensitisation through the use of GNPs, focusing on their ability to induce cellular oxidative stress and disrupt mitochondrial function. Using N-acetyl-cysteine, we found mitochondrial oxidation to be a key event prior to radiation for the radiosensitisation of cancer cells and suggests the overall cellular effects of GNP radiosensitisation are a result of their interaction with protein disulphide isomerase (PDI). This investigation identifies PDI and mitochondrial oxidation as novel targets for radiosensitisation.

A mechanistic study of gold nanoparticle radiosensitisation using targeted microbeam irradiation

Gold nanoparticles (GNPs) have been demonstrated as effective radiosensitizing agents in a range of preclinical models using broad field sources of various energies. This study aimed to distinguish between these mechanisms by applying subcellular targeting using a soft X-ray microbeam in combination with GNPs. DNA damage and repair kinetics were determined following nuclear and cytoplasmic irradiation using a soft X-ray (carbon K-shell, 278 eV) microbeam in MDA-MB-231 breast cancer and AG01522 fibroblast cells with and without GNPs. To investigate the mechanism of the GNP induced radiosensitization, GNP-induced mitochondrial depolarisation was quantified by TMRE staining, and levels of DNA damage were compared in cells with depolarised and functional mitochondria. Differential effects were observed following radiation exposure between the two cell lines. These findings were validated 24 hours after removal of GNPs by flow cytometry analysis of mitochondrial depolarisation. This study provides further evidence that GNP radiosensitisation is mediated by mitochondrial function and it is the first report applying a soft X-ray microbeam to study the radiobiological effects of GNPs to enable the separation of physical and biological effects.

Review of applications of high-throughput sequencing in personalized medicine: barriers and facilitators of future progress in research and clinical application

Abstract There has been an exponential growth in the performance and output of sequencing technologies (omics data) with full genome sequencing now producing gigabases of reads on a daily basis. These data may hold the promise of personalized medicine, leading to routinely available sequencing tests that can guide patient treatment decisions. In the era of high-throughput sequencing (HTS), computational considerations, data governance and clinical translation are the greatest rate-limiting steps. To ensure that the analysis, management and interpretation of such extensive omics data is exploited to its full potential, key factors, including sample sourcing, technology selection and computational expertise and resources, need to be considered, leading to an integrated set of high-performance tools and systems. This article provides an up-to-date overview of the evolution of HTS and the accompanying tools, infrastructure and data management approaches that are emerging in this space, which, if used within in a multidisciplinary context, may ultimately facilitate the development of personalized medicine.

Abstract 4000: A DNA damage response deficiency (DDRD) group in breast cancer is associated with activation of the STING innate immune pathway and PD-L1 expression

We have previously identified a DNA damage response deficient (DDRD) subgroup in breast cancer, associated with loss of the Fanconi Anemia/BRCA DNA repair pathway. The 44-gene DDRD signature developed to prospectively identify this subgroup has been validated as predictive of response to DNA damaging chemotherapy in the treatment of breast cancer. This subgroup is defined by immune signalling, with immune genes, such as the chemokines CXCL10 and CCL5, and immune checkpoints IDO1 and PD-L1 (CD274) overexpressed within the signature and subgroup. Here we report innate immune pathway activation in this subgroup, and association with PD-L1 expression. Methods: We used isogenic cell line models to identify and model pathways constitutively active in DDRD cancer cells. CD4+, CD8+ T-cell infiltration and PD-L1 expression was identified by immunohistochemistry (IHC) on a previously described breast TMA of 191 breast tumor samples, of which 65 were in the DDRD subgroup. DNA microarray data from FFPE samples was used to identify other immune checkpoints associated with this subgroup. Results: CD4+ and CD8+ T-cell infiltration, and PD-L1 expression were significantly associated with DDRD breast tumors on IHC analysis. In addition, expression of immune checkpoints such as IDO1, TIM-3 and LAG-3 were associated with the DDRD subgroup. Increased migration of peripheral blood mononuclear cells was identified into media conditioned by DDRD cells, this was dependent on chemokines secreted by DDRD cells. Endogenous activation of the innate immune pathway STING/TBK1/IRF3 was identified in DDRD cancer cells, and required for expression of chemokines CXCL10 and CCL5. This chemokine expression was associated with cytosolic DNA detected by cGAS and activation of the innate immune pathway STING/TBK1/IRF3. Importantly, this pathway was cell cycle related with upregulation of chemokine expression in S-phase of the cell cycle. Chemokine expression could be induced by S-phase DNA damaging chemotherapy but not by taxanes. Similarly, PD-L1 was induced by treatment with DNA damaging agents in cancer cells dependent on STING. Conclusions: We have identified constitutive activation of the innate immune STING pathway in a DNA damage response deficient subgroup of breast cancer, which is associated with CD4+, CD8+ infiltration and PD-L1 expression. We propose activation of the STING pathway as an important signal for lymphocytic infiltration, independent of tumor-associated neoantigens. The DDRD signature could identify patients with innate immune activation in response to endogenous DNA damage, which may allow stratification for immune checkpoint targeted treatments. Moreover, S-phase DNA damaging agents activate PD-L1 expression, and a combination approach of immune checkpoint inhibitors and S-phase specific chemotherapy may be synergistic in the clinic. Citation Format: Eileen E. Parkes, Steven M. Walker, Nuala McCabe, Laura E. Taggart, Laura Hill, Niamh E. Buckley, Kienan I. Savage, Manuel Salto-Tellez, Stephen McQuaid, Mary T. Harte, Paul B. Mullan, D Paul Harkin, Richard D. Kennedy. A DNA damage response deficiency (DDRD) group in breast cancer is associated with activation of the STING innate immune pathway and PD-L1 expression. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4000.

Abstract C105: DNA damage response deficiency (DDRD) in breast cancer is associated with a STING-dependent innate immune response

Background In breast cancer the presence of an immune infiltration has been recognised as a prognostic factor, however the mechanisms underpinning this response are not clearly defined. Previously we identified a gene expression signature that defines a DNA damage response defective (DDRD) molecular subgroup in breast cancer, that is enriched for BRCA1 and 2 mutations, and has a good outcome following DNA-damaging chemotherapy. Importantly, this DDRD subgroup is associated with up-regulation of type I Interferon-related genes. We therefore investigated the mechanism activating this immune response in the context of abnormal DNA repair. Results IHC analysis demonstrated that both intra-tumoral and stromal CD8+ and CD4+ T cell infiltration were associated with DDRD positive breast tumors. The CXCL10 and CCL5 cytokines were shown to be significantly up-regulated in DDRD positive breast tumours and in tissue culture models for the DDRD molecular subgroup. Furthermore, conditioned media from DDRD positive cell lines stimulated inward migration of peripheral blood mononuclear cells, when compared to media from DDRD negative cells, indicating the presence of active cytokines. We identified constitutive activation of the innate immune pathway STING/TBK1/IRF3 specifically in DDRD positive cells when compared to DDRD negative cells and found that binding of the DNA sensor cGAS to cytosolic Histone H3 was required for this immune response. Treatment of HeLa cells with DNA damaging chemotherapies but not taxanes resulted in STING-dependent expression of CXCL10 and CCL5 cytokines. Conclusion We have identified that the STING/TBK1/IRF3 immune pathway is activated by endogenous DNA damage in DDRD breast cancers and may explain lymphocytic infiltration observed in this subtype of breast tumours. These data suggest that the DDRD signature can identify an innate immune response to DNA damage in breast cancer, which may have therapeutic applications for immune targeted therapies. Citation Format: Eileen E. Parkes, Steven M. Walker, Nuala McCabe, Laura E. Taggart, Laura Hill, Karen D. McCloskey, Niamh E. Buckley, Manuel Salto-Tellez, Paul B. Mullan, D. P. Harkin, Richard D. Kennedy. DNA damage response deficiency (DDRD) in breast cancer is associated with a STING-dependent innate immune response. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C105.