Dual-modal SERS/fluorescence AuNP probe for mitochondrial imaging

A novel SERS/fluorescent multimodal imaging probe for mitochondria has been synthesised using 12 nm diameter gold nanoparticles (AuNP) surface functionalised with a rhodamine thiol derivative ligand. The normal pH dependant acidic fluorescence of the rhodamine based ligand is inversed when conjugated with the AuNP and higher emission intensity is observed at basic pH. This switch correlates to a pKa at pH 6.62, which makes it an ideal candidate for a pH sensitive imaging probe in the biological range (6.5-7.4). The observed pH sensitivity when attached to the AuNP is thought to be due to the formation of a spirolactam ring on the ligand, going from positively charged (+18 mV) to negatively charged (-60 mV) as the pH is changed from acidic to basic. Additionally, conjugation of the ligand to the AuNP serves to enhance the Raman signal of the rhodamine ligand through Surface Enhanced Raman Scattering (SERS). Confocal microscopy has shown that the probe enters HEK293 (kidney), A2780 (ovarian cancer) and Min6 (pancreatic beta) cells within an hour and a half incubation time. The probe was shown to localise in the mitochondria, thus providing a novel pH dependent SERS/fluorescent multimodal imaging probe for mitochondria

Cancer targeting with biomolecules: a comparative study of photodynamic therapy efficacy using antibody or lectin conjugated phthalocyanine-PEG gold nanoparticles

The functionalisation of therapeutic nanoparticle constructs with cancer-specific biomolecules can enable selective tumour accumulation and targeted treatment. Water soluble gold nanoparticles (ca. 4 nm) stabilised by a mixed monolayer of a hydrophobic zinc phthalocyanine photosensitiser (C11Pc) and hydrophilic polyethylene glycol (PEG) have been prepared. The C11Pc-PEG gold nanoparticle constructs were further functionalised with jacalin, a lectin specific for the cancer-associated Thomsen–Friedenreich (T) carbohydrate antigen, or with monoclonal antibodies specific for the human epidermal growth factor receptor-2 (HER-2). The two biofunctionalised nanoparticle conjugates produced similar levels of singlet oxygen upon irradiation at 633 nm. Importantly, both nanoparticle conjugates demonstrated extensive, yet comparable, phototoxicity in HT-29 colorectal adenocarcinoma cells (80–90%) and in SK-BR-3 breast adenocarcinoma cells (>99%). Non-conjugated C11Pc-PEG gold nanoparticles were only minimally phototoxic. Lysosomal colocalisation studies performed with the HT-29 colon cancer cells and the SK-BR-3 breast cancer cells revealed that both nanoparticle conjugates were partially localised within acidic organelles, which is typical of receptor-mediated endocytosis. The similarity of the targeted PDT efficacy of the two biofunctionalised C11Pc-PEG gold nanoparticles is discussed with respect to targeting ligand binding affinity and cell surface antigen density as key determinants of targeting efficiency. This study highlights how targeting small cell-surface molecules, such as the T antigen, can mediate a selective photodynamic treatment response which is similar to that achieved when targeting overexpressed protein receptors, such as HER-2. The high prevalence of the T antigen present on the cellular surface of primary tumours emphasises the broad potential applications for lectin-targeted therapies

Theoretical models of DNA topology simplification by type IIA DNA topoisomerases

It was discovered 12 years ago that type IIA topoisomerases can simplify DNA topology—the steady-state fractions of knots and links created by the enzymes are many times lower than the corresponding equilibrium fractions. Though this property of the enzymes made clear biological sense, it was not clear how small enzymes could selectively change the topology of very large DNA molecules, since topology is a global property and cannot be determined by a local DNA–protein interaction. A few models, suggested to explain the phenomenon, are analyzed in this review. We also consider experimental data that both support and contravene these models

“Breaking up is hard to do”: the formation and resolution of sister chromatid intertwines

The absolute necessity to resolve every intertwine between the two strands of the DNA double helix provides a massive challenge to the cellular processes that duplicate and segregate chromosomes. Although the overwhelming majority of intertwines between the parental DNA strands are resolved during DNA replication, there are numerous chromosomal contexts where some intertwining is maintained into mitosis. These mitotic sister chromatid intertwines (SCIs) can be found as; short regions of unreplicated DNA, fully replicated and intertwined sister chromatids—commonly referred to as DNA catenation—and as sister chromatid linkages generated by homologous recombination-associated processes. Several overlapping mechanisms, including intra-chromosomal compaction, topoisomerase action and Holliday junction resolvases, ensure that all SCIs are removed before they can prevent normal chromosome segregation. Here, I discuss why some DNA intertwines persist into mitosis and review our current knowledge of the SCI resolution mechanisms that are employed in both prokaryotes and eukaryotes, including how deregulating SCI formation during DNA replication or disrupting the resolution processes may contribute to aneuploidy in cancer

Water soluble, multifunctional antibody-porphyrin gold nanoparticles for targeted photodynamic therapy

Photodynamic therapy (PDT) is a treatment of cancer by which tumour cells are destroyed using reactive oxygen species produced by photosensitizers following activation with visible or near infrared light. Successful PDT depends on the solubility and the targeting ability of the photosensitizers. In this work, the synthesis of a porphyrin-based water soluble nanoparticle conjugate containing a targeting agent that recognizes the erbB2 receptor overexpressed on the surface of particular cancer cells is reported. The nanoparticle conjugates were synthesized following two different protocols, viz. a biphasic and a monophasic method, with the aim to determine which method yielded the optimal nanosystem for potential PDT applications. The nanoparticles were characterized using UV–Vis absorption and fluorescence spectroscopies together with transmission electron microscopy and zeta potential measurements; and their ability to produce singlet oxygen following irradiation was investigated following the decay in absorption of a singlet oxygen probe. The nanoparticles synthesized using the monophasic method were shown to produce the highest amount of singlet oxygen and were further functionalized with anti-erbB2 antibody to target the erbB2 receptors expressed on the surface of SK-BR-3 human breast cancer cells. The water soluble, antibody-porphyrin nanoparticle conjugates were shown to elicit targeted PDT of the breast cancer cells

Helical Chirality: a Link between Local Interactions and Global Topology in DNA

DNA supercoiling plays a major role in many cellular functions. The global DNA conformation is however intimately linked to local DNA-DNA interactions influencing both the physical properties and the biological functions of the supercoiled molecule. Juxtaposition of DNA double helices in ubiquitous crossover arrangements participates in multiple functions such as recombination, gene regulation and DNA packaging. However, little is currently known about how the structure and stability of direct DNA-DNA interactions influence the topological state of DNA. Here, a crystallographic analysis shows that due to the intrinsic helical chirality of DNA, crossovers of opposite handedness exhibit markedly different geometries. While right-handed crossovers are self-fitted by sequence-specific groove-backbone interaction and bridging Mg2+ sites, left-handed crossovers are juxtaposed by groove-groove interaction. Our previous calculations have shown that the different geometries result in differential stabilisation in solution, in the presence of divalent cations. The present study reveals that the various topological states of the cell are associated with different inter-segmental interactions. While the unstable left-handed crossovers are exclusively formed in negatively supercoiled DNA, stable right-handed crossovers constitute the local signature of an unusual topological state in the cell, such as the positively supercoiled or relaxed DNA. These findings not only provide a simple mechanism for locally sensing the DNA topology but also lead to the prediction that, due to their different tertiary intra-molecular interactions, supercoiled molecules of opposite signs must display markedly different physical properties. Sticky inter-segmental interactions in positively supercoiled or relaxed DNA are expected to greatly slow down the slithering dynamics of DNA. We therefore suggest that the intrinsic helical chirality of DNA may have oriented the early evolutionary choices for DNA topology

Формирование метакомпетенций студентов вуза в процессе научно-исследовательской работы на иностранном языке

This work is an attempt to generalize the theory and practice of the formation of metacompetencies of university students interpreted as the basis that remains in the sub subject position and determines the effectiveness of further self-realization of a university graduate in a certain professional field of activity. The necessity to analyze the theoretical and practical aspects of this activity has affected the purpose of the study. The authors use the systematic method as the main one. To understand and clarify the essence and prerequisites for the formation of metacompetencies of university students in the process of research work in foreign language at the present stage, the authors use general logical research methods and techniques. The current paper identifies and justifies the common and distinctive features and peculiarities of the content and organization of research work in foreign language applying the principles of structural-functional analysis. The results of a pedagogical experiment conducted at the Siberian Transport University aimed at studying the influence of research work in a foreign language on the formation of students» metacompetencies are presented. A model of organization of students» research work has been proposed, which includes the levels ofperception, analysis and synthesis of scientific information. The study reveals the content of each of the levels of organization of students» research work. The authors pay special attention to the formation of academic writing skills that are necessary for increasing of the publication activity of various groups of researches who take into account international rules and norms, as well as the skills ofpublic scientific presentation in a foreign language, allowing to present the results of the study at the international level. The authors conclude that modeling the process of students» research work has allowed to systematize and generalize the requirements for its organization, taking in consideration relevant international requirements for the content of report, the design of scientific articles in a foreign language, the specific features ofpeer-re-viewed papers, the ranking of scientific journals, and indicators of the publication activity of students and organizations.Работа представляет собой попытку обобщения теории и практики формирования метакомпетенций студентов вуза, которые трактуются авторами данного исследования как над-предметные базисы, определяющие результативность дальнейшей самореализации выпускника вуза в определенной профессиональной сфере деятельности. Необходимость анализа теоретических и практических аспектов этой деятельности обусловила цель данной статьи. В качестве основного авторами был использован системный метод. Для понимания и уточнения сущности и предпосылок формирования метакомпетенций студентов вуза в процессе научно-исследовательской работы на иностранном языке на современном этапе авторы обратились к общелогическим методам и приемам исследования. Для выявления и обоснования общих и отличительных признаков и свойств содержания и организации научно-исследовательской работы на иностранном языке, использовались принципы структурно-функционального анализа. Приводятся результаты педагогического эксперимента, проведенного в Сибирском государственном университете путей сообщения, направленного на изучение влияния научно-исследовательской работы на иностранном языке на формирование метакомпетенций студентов. Предложена модель организации научно-исследовательской работы студентов, включающая уровни восприятия, анализа и синтеза научной информации. Раскрывается содержание каждого из уровней организации научно-исследовательской работы студентов. Особое внимание авторами уделено формированию навыков академического письма, необходимых для повышения публикационной активности различных групп исследователей с учетом международных правил и норм, а также навыков публичного научного выступления на иностранном языке, позволяющих представлять результаты исследования на международном уровне. Авторы заключают, что моделирование процесса научно-исследовательской работы студентов позволило систематизировать и обобщить рекомендации к ее организации с учетом актуальных международных требований к содержанию доклада, оформлению научных статей на иностранном языке, специфики рецензирования работ и ранжирования научных журналов, показателей публикационной деятельности ученых, организаций

Photosensitiser-gold nanoparticle conjugates for photodynamic therapy of cancer

Gold nanoparticles (AuNPs) have been extensively studied within biomedicine due to their biocompatibil- ity and low toxicity. In particular, AuNPs have been widely used to deliver photosensitiser agents for photodynamic therapy (PDT) of cancer. Here we review the state-of-the-art for the functionalisation of the gold nanoparticle surface with both photosensitisers and targeting ligands for the active targeting of cancer cell surface receptors. From the initial use of the AuNPs as a simple carrier of the photosensitiser for PDT, the field has significantly advanced to include: the use of PEGylated modification to provide aqueous compatibility and stealth properties for in vivo use; gold metal-surface enhanced singlet oxygen generation; functionalisation of the AuNP surface with biological ligands to specifically target over- expressed receptors on the surface of cancer cells and; the creation of nanorods and nanostars to enable combined PDT and photothermal therapies. These versatile AuNPs have significantly enhanced the efficacy of traditional photosensitisers for both in vitro and in vivo cancer therapy. From this review it is apparent that AuNPs have an important future in the treatment of cancer

The why and how of DNA unlinking

The nucleotide sequence of DNA is the repository of hereditary information. Yet, it is now clear that the DNA itself plays an active role in regulating the ability of the cell to extract its information. Basic biological processes, including control of gene transcription, faithful DNA replication and segregation, maintenance of the genome and cellular differentiation are subject to the conformational and topological properties of DNA in addition to the regulation imparted by the sequence itself. How do these DNA features manifest such striking effects and how does the cell regulate them? In this review, we describe how misregulation of DNA topology can lead to cellular dysfunction. We then address how cells prevent these topological problems. We close with a discussion on recent theoretical advances indicating that the topological problems, themselves, can provide the cues necessary for their resolution by type-2 topoisomerases