History-dependent domain and skyrmion formation in 2D van der Waals magnet Fe3GeTe2.

The discovery of two-dimensional magnets has initiated a new field of research, exploring both fundamental low-dimensional magnetism, and prospective spintronic applications. Recently, observations of magnetic skyrmions in the 2D ferromagnet Fe3GeTe2 (FGT) have been reported, introducing further application possibilities. However, controlling the exhibited magnetic state requires systematic knowledge of the history-dependence of the spin textures, which remains largely unexplored in 2D magnets. In this work, we utilise real-space imaging, and complementary simulations, to determine and explain the thickness-dependent magnetic phase diagrams of an exfoliated FGT flake, revealing a complex, history-dependent emergence of the uniformly magnetised, stripe domain and skyrmion states. The results show that the interplay of the dominant dipolar interaction and strongly temperature dependent out-of-plane anisotropy energy terms enables the selective stabilisation of all three states at zero field, and at a single temperature, while the Dzyaloshinksii-Moriya interaction must be present to realise the observed Néel-type domain walls. The findings open perspectives for 2D devices incorporating topological spin textures.

Stochastic thermodynamics of nanoscale friction.

Developing the thermodynamics of nanoscale friction is needed in a wide range of tribological applications, where the key objective is to optimally control the energy dissipation. Here we show that modern stochastic thermodynamics allows us to interpret the measurements obtained by friction force microscopy, which is the standard tool for investigating the frictional properties of materials, in terms of basic thermodynamics concepts such as fluctuating work and entropy. We show that this allows the identification of the heat produced during the friction process as an unambiguous measure of thermodynamic irreversibility. We have applied this procedure to quantify the heat produced during the frictional sliding in a broad velocity range, and we observe velocity-dependent scaling behavior, which is useful for interpreting the experimental outcomes.

Real-space imaging of confined magnetic skyrmion tubes.

Magnetic skyrmions are topologically nontrivial particles with a potential application as information elements in future spintronic device architectures. While they are commonly portrayed as two dimensional objects, in reality magnetic skyrmions are thought to exist as elongated, tube-like objects extending through the thickness of the host material. The study of this skyrmion tube state (SkT) is vital for furthering the understanding of skyrmion formation and dynamics for future applications. However, direct experimental imaging of skyrmion tubes has yet to be reported. Here, we demonstrate the real-space observation of skyrmion tubes in a lamella of FeGe using resonant magnetic x-ray imaging and comparative micromagnetic simulations, confirming their extended structure. The formation of these structures at the edge of the sample highlights the importance of confinement and edge effects in the stabilisation of the SkT state, opening the door to further investigation into this unexplored dimension of the skyrmion spin texture.

Unified model of hyperthermia via hysteresis heating in systems of interacting magnetic nanoparticles.

We present a general study of the frequency and magnetic field dependence of the specific heat power produced during field-driven hysteresis cycles in magnetic nanoparticles with relevance to hyperthermia applications in biomedicine. Employing a kinetic Monte-Carlo method with natural time scales allows us to go beyond the assumptions of small driving field amplitudes and negligible inter-particle interactions, which are fundamental to the applicability of the standard approach based on linear response theory. The method captures the superparamagnetic and fully hysteretic regimes and the transition between them. Our results reveal unexpected dipolar interaction-induced enhancement or suppression of the specific heat power, dependent on the intrinsic statistical properties of particles, which cannot be accounted for by the standard theory. Although the actual heating power is difficult to predict because of the effects of interactions, optimum heating is in the transition region between the superparamagnetic and fully hysteretic regimes.

Two-magnon bound state causes ultrafast thermally induced magnetisation switching.

There has been much interest recently in the discovery of thermally induced magnetisation switching using femtosecond laser excitation, where a ferrimagnetic system can be switched deterministically without an applied magnetic field. Experimental results suggest that the reversal occurs due to intrinsic material properties, but so far the microscopic mechanism responsible for reversal has not been identified. Using computational and analytic methods we show that the switching is caused by the excitation of two-magnon bound states, the properties of which are dependent on material factors. This discovery allows us to accurately predict the onset of switching and the identification of this mechanism will allow new classes of materials to be identified or designed for memory devices in the THz regime.

Giant and reversible extrinsic magnetocaloric effects in La0.7Ca0.3MnO3 films due to strain.

Large thermal changes driven by a magnetic field have been proposed for environmentally friendly energy-efficient refrigeration, but only a few materials that suffer hysteresis show these giant magnetocaloric effects. Here we create giant and reversible extrinsic magnetocaloric effects in epitaxial films of the ferromagnetic manganite La(0.7)Ca(0.3)MnO(3) using strain-mediated feedback from BaTiO(3) substrates near a first-order structural phase transition. Our findings should inspire the discovery of giant magnetocaloric effects in a wide range of magnetic materials, and the parallel development of nanostructured bulk samples for practical applications.

Synergistic action of doxorubicin bound to the polymeric carrier based on N-(2-hydroxypropyl)methacrylamide copolymers through an amide or hydrazone bond.

The cytostatic effects of polymeric conjugates based on N-(2-hydroxypropyl)methacrylamide copolymers (PHPMA) and containing doxorubicin bound through amide and hydrazone bonds (mixed conjugates) were compared with the cytostatic effects of monoconjugates containing drug bound through an amide or hydrazone bond. One group of mixed conjugates was formed from two comonomers containing doxorubicin bound to the methacryloyl group through a spacer and an amide (DOX(AM)) or hydrazone (DOX(HYD)) bond via copolymerization with HPMA. A second group of mixed conjugates was formed from two different interconnected HPMA copolymers, one containing DOX(AM) and the other DOX(HYD), forming a high-molecular-weight branched structure. The third mixed polymeric system was a simple mixture of monoconjugates DOX(AM)-PHPMA and DOX(HYD)-PHPMA. Simultaneous treatment with all mixed forms of the polymeric derivatives of doxorubicin significantly increased antitumor efficacy after application of monoconjugates, suggesting a synergizing effect that could be used in designing new doxorubicin-containing therapeutic systems.

Visualization of symbiotic tissue in intact root nodules of Vicia tetrasperma using GFP-marked Rhizobium leguminosarum bv. viciae.

In rhizobial symbiosis with legume plant hosts, the symbiotic tissue in the root nodules of indeterminate type is localized to the basal part of the nodule where the symbiotic zones contain infected cells (IC) interspersed with uninfected cells (UC) that are devoid of rhizobia. Although IC are easily distinguished in nodule sections using standard histochemical techniques, their observation in intact nodules is hampered by nodule tissue characteristics. Tagging of Rhizobium leguminosarum bv. viciae strain 128C30 with a constitutively expressed gene for green fluorescent protein (nonshifted mutant form cycle3) in combination with the advantages of the tiny nodules formed by Vicia tetrasperma (L.) SCHREB . allowed for vital observation of symbiotic tissue using fluorescence microscopy. Separation of a red-shifted background channel and digital image stacking along z-axis enabled us to construct a nodule image in a classical fluorescence microscopy of nodules exceeding 1 mm in diameter. In parallel, visualization of nodule bacteria inside the symbiotic tissue by confocal microscopy at the excitation wavelength 488 nm clearly distinguished IC/UC pattern in the nodule virtual sections and revealed red-shifted fluorescence of nonrhizobial origin. This signal was located on the periphery of IC and increased with their degradation, thus suggesting accumulation of secondary metabolites, presumably flavonoids. The simultaneous detection of bacteria and secondary metabolites can be used for monitoring changes to intact nodule physiology in the model legumes. The advantage of V. tetrasperma as a suggested laboratory model for pea cross-inoculation group has been demonstrated.

Nonconverging hysteresis cycles in random spin networks.

Behavior of hysteretic trajectories for cyclical input is investigated as a function of the internal structure of a system modeled by the classical random network of binary spins. Different regimes of hysteretic behavior are discovered for different network connectivity and topology. Surprisingly, hysteretic trajectories which do not converge at all are observed. They are shown to be associated with the presence of specific topological elements in the network structure, particularly with the fully interconnected spin groups of size equal to or greater than 4.

Doxorubicin release is not a prerequisite for the in vitro cytotoxicity of HPMA-based pharmaceuticals: in vitro effect of extra drug-free GlyPheLeuGly sequences.

A systematic study was designed to elucidate differences in cytostatic activity in vitro between HPMA-based doxorubicin conjugates synthesized using different polymerization techniques and differing in peptidyl side chain. A polymer-drug conjugate containing doxorubicin (DOX) bound to HPMA copolymer backbone through the enzymaticaly non-cleavable sequence GlyGly shows low but significant cytotoxicity in vitro in seven cancer cell lines of mouse (EL4, 38C13, 3T3, BCL1) and human (SW620, Raji, Jurkat) origin. The low cytotoxicity can be considerably increased by the presence of additional drug-free GlyPheLeuGly side chains. P1 conjugate, i.e. non-targeted HPMA copolymer bearing doxorubicin bound via a biodegradable GlyPheLeuGly sequence, synthesized by direct copolymerization of HPMA with monomeric doxorubicin and thus without additional drug-free GlyPheLeuGly sequences is less effective compared to PK1 synthesized by polymer analogous reaction and thus containing extra drug-free GlyPheLeuGly sequences. Significant activity-enhancing effect was not seen with other amino acid/oligopeptide sequences (e.g., Gly or GlyGly). The activity-enhancing effect of GlyPheLeuGly sequences is more obvious in the conjugate containing doxorubicin bound to HPMA through GlyGly sequence. Derivatization of the terminal carboxyl group of the extra GlyPheLeuGly side chains (amide, N-substituted amide, free carboxyl) does not significantly influence the cytotoxicity of the conjugates. The presence of the GlyPheLeuGly sequence in the conjugate structure increases its rate of intracellular accumulation. Normal cells (Balb/c splenocytes) accumulate less polymer-doxorubicin conjugate compared to cancer cells (T cell lymphoma EL4, B cell lymphoma Raji and T cell leukemia JURKAT).

Expression of IGF-1R and iNOS in nasal polyps; epithelial cell homeostasis and innate immune mechanisms in pathogenesis of nasal polyposis.

Nasal polyps (NP), edematous projections of nasal mucosa (NM), are characterized by an inflammatory cellular infiltrate, however, little is known about etiopathogenesis of NP. Both innate immune mechanisms leading to activation of NF-kappaB and homeostasis of epithelial cells were implicated in the pathogenesis of NP. In this study we investigated the expression of insulin-like growth factor-1 receptor (IGF-1R) and inducible nitric-oxide synthase (iNOS) in NP compared to healthy NM in both the epithelial and stromal compartments. Using immunohistochemistry, frozen tissue sections of NP from 18 patients, and mucosal biopsy specimens of the inferior turbinate from 17 subjects were stained for IGF-1R and iNOS markers. Fluorescence microscopy and computerized image analysis revealed low numbers of IGF-1R-positive cells in all specimens. However, substantially increased numbers of IGF-1R-positive cells were found in NP compared to NM both within the epithelium (1.63 vs. 0.43) and stroma (3.27 vs. 1.03). Positivity for iNOS was detected within the epithelium of NP compared with NM. Numbers of iNOS-positive single cells were highly increased in NP vs. NM in both epithelial (3.83 vs. 1.08) and stromal (4.96 vs. 2.67) compartments. An increased iNOS expression within the epithelial layer as well as increased number of iNOS- and IGF-1R-positive cells in NP was observed. This suggests that innate immune mechanism, and to a lesser extent also growth and homeostasis of epithelial cells, may play a role in formation of NP.

Induction of systemic antitumour resistance with targeted polymers.

Conjugates based on N-(2-hydroxypropyl)methacrylamide (HPMA) represent a new generation of antibody-targeted polymeric anticancer drugs with both cytotoxic and immunoprotecting/immunomobilizing activity. 20-90% of mice that are cured of EL4 mouse T-cell lymphoma, BCL1 mouse B-cell leukaemia and 38C13 mouse B-cell lymphoma by injection of doxorubicin-HPMA conjugate develop a long-lasting memory and systemic antitumour resistance. It is suggested that the main activity of the polymeric drug, directly after application is - due to the high level of the drug - of cytotoxic and cytostatic nature. Thereafter, long-term conjugates persist at low concentration in the circulation, which are capable of mobilizing the defence mechanisms of the host. Until now, seven patients with generalized carcinoma were treated with doxorubicin-HPMA-human-Ig conjugate. Disease stabilization, lasting from 6 to more than 18 months, was recorded.

Sex pheromone of horse-chestnut leafminer Camneraria ohridella and its use in a pheromone-based monitoring system.

Gas chromatography combined with electroantennographic detection (GC-EAD), electroantennography (EAG), and wind-tunnel and field experiments were used to reinvestigate the composition of Cameraria ohridella (Lepidoptera, Gracillariidae, Lithocolletinae) sex pheromone. The GC-EAD experiments showed one EAD-active area corresponding to the major pheromone component. (8E,10Z)-tetradeca-8,10-dienal. The EAG experiments proved that (9E)-tetracedecenal and stereoisomers of (8E,10Z)-tetradeca-8,10-dienal exhibited significant electrophysiological activity and could, therefore, be considered as possible minor pheromone components. However, wind-tunnel and field experiments demonstrated that none of these compounds affect the efficacy of the main pheromone component. A monitoring system based on (8E,10Z)tetradeca-8,10-dienal was developed and used to study the flight activity of C. ohridella.

Acquired and specific immunological mechanisms co-responsible for efficacy of polymer-bound drugs.

We present data providing new evidence that poly[N-(2-hydroxypropyl)methacrylamide] (PHPMA)-bound drugs, unlike free drugs, have both cytostatic and immunomobilizing activity (CIA). Immediately after injection, due to the high level of the drug, the main activity of the polymeric conjugate is cytotoxic and cytostatic. Later on, long-term circulating PHPMA-bound drug, at concentrations lower than its minimal inhibitory levels, mobilizes the defense mechanisms of the host. Cytotoxic and cytostatic effects of drug-PHPMA were repeatedly confirmed. The following data support the concept of the immunomobilizing activity of the N-(2-hydroxypropyl)methacrylamide (HPMA) conjugates: (a) pre-treatment with free drugs (doxorubicin, cyclosporin A) accelerates the appearance of EL4 mouse T-cell lymphoma while a similar pre-treatment with doxorubicin-PHPMA induces limited but definitive mobilization of the host's defense mechanisms; (b) mice cured of EL4 mouse T-cell lymphoma, BCL1 mouse B-cell leukemia and 38C13 mouse B-cell lymphoma by injection of doxorubicin-PHPMA conjugate targeted with monoclonal antibodies (anti-Thy 1.2 for EL4, anti-B1 for BCL1 and anti-CD71 for 38C13) and re-transplanted with a lethal dose of the same cancer cells survive without any treatment considerably longer than control mice; (c) increased NK activity and anti-cancer antibody was detected only in animals treated with doxorubicin-PHPMA conjugate; and (d) considerably increased NK and LAK activity was seen in a human patient treated for generalized breast carcinoma with doxorubicin-PHPMA-IgG.

Doxorubicin bound to a HPMA copolymer carrier through hydrazone bond is effective also in a cancer cell line with a limited content of lysosomes.

We have synthesized conjugates containing doxorubicin (DOX) bound to oligopeptide side chains (GlyGly or GlyPheLeuGly) of a water-soluble copolymer carrier based on poly[N-(2-hydroxypropyl)methacrylamide] (PHPMA) either through proteolytically (PK1 conjugates) [Synthetic polymeric drugs. U.S. Patent 5,037,883 (1991)] or hydrolytically cleavable bond (HC conjugates). Pharmacological efficacy of PK1 and HC conjugates was compared in vitro on murine: T-cell lymphoma EL4, B-cell leukemia BCL1, B-cell lymphoma 38C13, leukemia P388 and Con A-stimulated A/Ph splenocytes and on human: primary (SW480) and metastatic (SW620) colorectal cancer cell lines parent and transfected with Thy 1.2 gene [2] and on erythromyeloid leukemia cell line K 562. Inhibition of proliferation determined by 3[H]-thymidine incorporation revealed that the cytostatic effect of HC conjugates is up to two orders of magnitude higher compared to PK1 conjugates. In some cancer cell lines (SW 620/T, SW 480) the pharmacological activity of HC conjugates is in vitro comparable with the activity of the free drug. Unlike PK1 conjugates, HC conjugates with a lysosomally degradable spacer (GlyPheLeuGly) are less effective compared to HC conjugates containing lysosomally non-degradable spacer (GlyGly). Moreover, HC conjugates exert pronounced anti-proliferative activity also in erythroblastoid leukemia cell line K 562 with a limited content of lysosomes.

Composition of the labial gland secretion of the bumblebee males Bombus pomorum.

Labial gland secretions of 22 males of the bumblebee Bombus pomorum, collected in the Czech Republic, were analysed separately for each individual. The secretions contained 70 compounds among which saturated and unsaturated hydrocarbons strongly dominated. The proportion of hydrocarbons in the secretion was unusually high (85-100%) compared to other bumblebee species studied so far (3-15%). Methyl and ethyl esters of fatty acids, known from many other bumblebee species, formed only minor components (less than 1% in sum) of the secretions of several B. pomorum individuals. No terpenic compounds, typical for males' marking secretion of many bumblebee species, were detected in B. pomorum. The absolute quantities of hydrocarbons present in the labial gland extracts were comparable with those usually present in other species. The composition of hydrocarbons found in the labial glands was different from the profile of the cuticular hydrocarbons. Despite our expectations in species exhibiting a regular patrolling and scent-marking behaviour, the labial gland extracts obtained from B. pomorum males were unusually low concentrated and their chemical composition was atypical with respect of the proportions of hydrocarbons when compared with other patrolling species. This is the first report on the analysis of the labial gland secretion of the B. pomorum males.

Antiproliferative effect of a lectin- and anti-Thy-1.2 antibody-targeted HPMA copolymer-bound doxorubicin on primary and metastatic human colorectal carcinoma and on human colorectal carcinoma transfected with the mouse Thy-1.2 gene.

The aim of this study was to compare the potential of two plant lectins [peanut agglutinin (PNA) and wheat germ agglutinin (WGA)], monoclonal antibody (anti-Thy-1.2), its F(ab')(2) fragments, and galactosamine as targeting moieties bound to the polymer drug carrier to deliver a xenobiotic, doxorubicin, to selected cancer cell lines. We have used primary (SW 480, HT 29) and metastatic (SW 620) human colorectal cancer cell lines and a transfectant, genetically engineered SW 620 cell line with mouse gene Thy-1.2 (SW 620/T) to test the possibility of marking human cancer with xenogeneic mouse gene and use it for effective site-specific targeting. The targeting moieties and doxorubicin were conjugated to a water-soluble copolymer based on N-(2-hydroxypropyl)methacrylamide (HPMA) acting as a carrier responsible for controlled intracellular release of the targeted drug. FACS analysis showed a strong binding of WGA-FITC to all tested cell lines. Binding of PNA-FITC was considerably weaker. The in vitro antiproliferative effect of lectin-targeted HPMA carrier-bound doxorubicin evaluated as [(3)H]TdR incorporation reflected both the intensity of the binding and the different sensitivity of the tested cancer cells lines to doxorubicin. The antiproliferative effect of conjugates targeted with WGA was comparable to that with the conjugates targeted with the anti-Thy-1.2 monoclonal antibody or their F(ab')(2) fragments. The magnitude of the cytotoxic effect of HPMA-doxorubicin targeted with PNA was lower in all tested cell lines. While the conjugates with WGA were more cytotoxic, the conjugates with PNA were more specific as their binding is limited to cancer cells and to the sites of inflammation. Noncytotoxic conjugates with a very low concentration of doxorubicin and targeted with PNA, anti-Thy-1.2, or their F(ab')(2) fragments exerted in some lines (SW 480, SW 620) low mitogenic activity. The Thy-1.2 gene-transfected SW 620 metastatic colorectal cancer cell line was sensitive to the antiproliferative effect of Thy-1.2-targeted doxorubicin as was shown for the Thy-1. 2(+) EL4 cell line and for Thy-1.2(+) concanavalin A-stimulated mouse T lymphocytes. These results represent the first indication of the suitability of transfection of human cancer cells with selected targeting genes for site-specific therapy of malignancies.

Polymeric drugs based on conjugates of synthetic and natural macromolecules. II. Anti-cancer activity of antibody or (Fab')(2)-targeted conjugates and combined therapy with immunomodulators.

We provide data on in vivo targeting of the Thy 1.2 (CDw90) cell surface receptor expressed on neoplastic T cells, mouse EL4 T cell lymphoma. The targeting antibody and the anticancer drug, doxorubicin (DOX) were conjugated to a water-soluble copolymer based on N-(2-hydroxypropyl)methacrylamide (HPMA) acting as a carrier responsible for controlled intracellular release of the conjugated drug. The in vivo therapeutic efficacy of HPMA copolymer-bound DOX targeted with anti-EL4 antibody, polyclonal anti-thymocyte globulin (ATG), monoclonal anti-Thy 1.2 antibody or its F(ab')(2) fragment was compared with the efficacy of DOX conjugated to HPMA copolymer containing nonspecific IgG or bovine serum albumin (BSA). Anti-EL4 antibody-targeted conjugate caused a significant retardation of tumor growth and an extension of the life span of treated mice. The effect was comparable with that of HPMA copolymer-bound DOX targeted with ATG, anti-Thy 1.2 antibody or its F(ab')(2) fragment. However, considerable antitumor effect was seen also in conjugates targeted instead of specific antibodies with syngeneic nonspecific IgG or BSA. Patients with advanced cancer are often immunocompromised due to dysfunction of their immune system induced by cancer and cytotoxic drugs. A significant decrease of unwanted side-effects of targeted drugs against a number of vital organs was already documented. In this study we have compared immunotoxic effects of free DOX with those of its antibody-targeted form on NK cells and cytolytic T lymphocytes (CTLs) isolated from C57BL/10 mice bearing EL4 T cell lymphoma. In the same model we have tested the combination therapy with immunomodulators (beta-glucan or AM-2) injected together with targeted daunomycin. We have observed a significant protective effect of targeted DOX against NK cells and CTLs. Moreover, the data revealed that combination therapy considerably enhances antitumor efficacy of the targeted anticancer drug.

Biological activities of oligoketide pigments of Monascus purpureus.

Rubropunctatin (1), monascorubrin (2), monascin (3) and ankaflavin (4) were purified from the mycelium of Monascus purpureus by flash chromatography on silica gel or reversed phase. Their embryotoxicity towards chicken embryos decreased in the order 2 > 1 > 3 > 4. The lower homologues 1 and 3 exhibited teratogenic effects on these organisms. Significant antibiotic activities against Bacillus subtilis and Candida pseudotropicalis were found with compounds 1 and 2. Immunosuppressive activity on mouse T-splenocytes was most pronounced with compounds 3 and 4. None of the compounds showed significant cytotoxic activity towards rat hepatocytes in vitro. Incubation of resting cells of M. purpureus with glycine afforded the dark-red compounds 5 and 6 where the pyran moiety of 1 and 2 changed into the N-substituted dihydropyridine moiety by replacement of the O-atom by the amino group of glycine. Compounds 5 and 6 were less biologically active than the major pigments 1-4.