The tidal remnant of an unusually metal-poor globular cluster.

Globular clusters are some of the oldest bound stellar structures observed in the Universe1. They are ubiquitous in large galaxies and are believed to trace intense star-formation events and the hierarchical build-up of structure2,3. Observations of globular clusters in the Milky Way, and a wide variety of other galaxies, have found evidence for a 'metallicity floor', whereby no globular clusters are found with chemical (metal) abundances below approximately 0.3 to 0.4 per cent of that of the Sun4-6. The existence of this metallicity floor may reflect a minimum mass and a maximum redshift for surviving globular clusters to form-both critical components for understanding the build-up of mass in the Universe7. Here we report measurements from the Southern Stellar Streams Spectroscopic Survey of the spatially thin, dynamically cold Phoenix stellar stream in the halo of the Milky Way. The properties of the Phoenix stream are consistent with it being the tidally disrupted remains of a globular cluster. However, its metal abundance ([Fe/H] = -2.7) is substantially below the empirical metallicity floor. The Phoenix stream thus represents the debris of the most metal-poor globular clusters discovered so far, and its progenitor is distinct from the present-day globular cluster population in the local Universe. Its existence implies that globular clusters below the metallicity floor have probably existed, but were destroyed during Galactic evolution.

Delivery of TLR7 agonist to monocytes and dendritic cells by DCIR targeted liposomes induces robust production of anti-cancer cytokines.

Tumor immune escape is today recognized as an important cancer hallmark and is therefore a major focus area in cancer therapy. Monocytes and dendritic cells (DCs), which are central to creating a robust anti-tumor immune response and establishing an anti-tumorigenic microenvironment, are directly targeted by the tumor escape mechanisms to develop immunosuppressive phenotypes. Providing activated monocytes and DCs to the tumor tissue is therefore an attractive way to break the tumor-derived immune suppression and reinstate cancer immune surveillance. To activate monocytes and DCs with high efficiency, we have investigated an immunotherapeutic Toll-like receptor (TLR) agonist delivery system comprising liposomes targeted to the dendritic cell immunoreceptor (DCIR). We formulated the immune stimulating TLR7 agonist TMX-202 in the liposomes and examined the targeting of the liposomes as well as their immune activating potential in blood-derived monocytes, myeloid DCs (mDCs), and plasmacytoid DCs (pDCs). Monocytes and mDCs were targeted with high specificity over lymphocytes, and exhibited potent TLR7-specific secretion of the anti-cancer cytokines IL-12p70, IFN-α 2a, and IFN-γ. This delivery system could be a way to improve cancer treatment either in the form of a vaccine with co-formulated antigen or as an immunotherapeutic vector to boost monocyte and DC activity in combination with other treatment protocols such as chemotherapy or radiotherapy. STATEMENT OF SIGNIFICANCE: Cancer immunotherapy is a powerful new tool in the oncologist's therapeutic arsenal, with our increased knowledge of anti-tumor immunity providing many new targets for intervention. Monocytes and dendritic cells (DCs) are attractive targets for enhancing the anti-tumor immune response, but systemic delivery of immunomodulators has proven to be associated with a high risk of fatal adverse events due to the systemic activation of the immune system. We address this important obstacle by targeting the delivery of an immunomodulator, a Toll-like receptor agonist, to DCs and monocytes in the bloodstream. We thus focus the activation, potentially avoiding the above-mentioned adverse effects, and demonstrate greatly increased ability of the agonist to induce secretion of anti-cancer cytokines.

Monocyte targeting and activation by cationic liposomes formulated with a TLR7 agonist.

OBJECTIVES: Monocytes are one of the major phagocytic cells that patrol for invading pathogens, and upon activation, differentiate into macrophages or antigen-presenting dendritic cells (DCs) capable of migrating to lymph nodes eliciting an adaptive immune response. The key role in regulating adaptive immune responses has drawn attention to modulate monocyte responses therapeutically within cancer, inflammation and infectious diseases. We present a technology for targeting of monocytes and delivery of a toll-like receptor (TLR) agonist in fresh blood using liposomes with a positively charged surface chemistry. METHODS: Liposomes were extruded at 100 nm, incubated with fresh blood, followed by leukocyte analyses by FACS. Liposomes with and without the TLR7 agonist TMX-202 were incubated with fresh blood, and monocyte activation measured by cytokine secretion by ELISA and CD14 and DC-SIGN expression. RESULTS: The liposomes target monocytes specifically over lymphocytes and granulocytes in human whole blood, and show association with 75 - 95% of the monocytes after 1 h incubation. Formulations of TMX-202 in cationic liposomes were potent in targeting and activation of monocytes, with strong induction of IL-6 and IL-12p40, and differentiation into CD14(+) and DC-SIGN+ DCs. CONCLUSION: Our present liposomes selectively target monocytes in fresh blood, enabling delivery of TLR7 agonists to the intracellular TLR7 receptor, with subsequent monocyte activation and boost in secretion of proinflammatory cytokines. We envision this technology as a promising tool in future cancer immunotherapy.

Carbon nanotubes-liposomes conjugate as a platform for drug delivery into cells.

Carbon nanotubes (CNT) are widely explored as carriers for drug delivery due to their facile transport through cellular membranes. However, the amount of loaded drug on a CNT is rather small. Liposomes, on the other hand, are employed as a carrier of a large amount of drug. The aim of this research is to develop a new drug delivery system, in which drug-loaded liposomes are covalently attached to CNT to form a CNT-liposomes conjugate (CLC). The advantage of this novel approach is the large amount of drug that can be delivered into cells by the CLC system, thus preventing potential adverse systemic effects of CNT when administered at high doses. This system is expected to provide versatile and controlled means for enhanced delivery of one or more agents stably associated with the liposomes.

Characterization of PEGylated nanoliposomes co-remotely loaded with topotecan and vincristine: relating structure and pharmacokinetics to therapeutic efficacy.

Recently, developing drug delivery systems exhibiting controlled drug release at the tumor sites emerged as an attractive option for enhancing anticancer therapeutic efficacy. It seems, however, unlikely that single agent therapies will prove effective enough against the myriad cells present within the malignancy. Therefore, next generation nanotherapeutics must not only find their way to the solid tumor but also must effectively destroy the diverse populations of cells promoting tumor growth. Nanoliposomes offer an important advantage in the delivery of a combination of drugs acting synergistically in cancer treatment. They allow controlling the pharmacokinetics and biodistribution of the drugs by uniform time and spatial co-delivery of the agents. However, successful translation of such complex formulations into the clinic relies on understanding critical physicochemical characteristics. These include: liposomes' membrane phase and dynamics, size distribution, state of encapsulated drug, internal environment of liposome, state of grafted polyethylene glycol at the liposome surface, and in-vivo drug release rate. They determine the pharmacokinetics of the formulation and the bioavailability of the drugs. We encapsulated the combination of vincristine (VCR) and topotecan (TPT) in the same nanoliposome (LipoViTo). Our in-vitro and in-vivo characterization of LipoViTo provides an explanation for the good therapeutic efficacy that was previously reported by us. Moreover, we have described how to study these critical features for a two-drug in one nanoliposome formulation. This characterization is an important step for a rational clinical development and for how to ensure liposome product quality of LipoViTo and other liposomal formulations alike.

Optimization of vincristine-topotecan combination--paving the way for improved chemotherapy regimens by nanoliposomes.

There is an opportunity to improve the therapeutic potential of a combination of two drugs using nanoliposomes. The combination of topotecan (TPT) and vincristine (VCR) was selected. The ratio-dependent synergy between these two drugs was evaluated, in an attempt to improve the therapeutic efficacy of this combination in vivo. The interaction between the drugs was evaluated in tissue culture by the median-effect analysis. Certain ratios of combined drugs were synergistic, whereas, others were antagonistic, implying that the most efficacious combinations should be at a specific fixed drug ratio. For in vivo evaluation, nanoliposomes co-remotely loaded simultaneously with both drugs by transmembrane ammonium sulfate gradient were developed. VCR and TPT were successfully co-encapsulated at therapeutically relevant levels in the same nanoliposome (LipoViTo). The nanoliposomes controlled the drugs' "biofate" and maintained a fixed drug ratio in vivo, allowing one to compare the therapeutic efficacy of various predefined drug ratios. Pharmacokinetics and biodistribution studies showed that LipoViTo delivers the two drugs simultaneously to the tumors, where they are released at a predefined ratio. LipoViTo was more efficacious than the free drugs and liposomes with one agent, singly or in combination, in two tumor models in mice. LipoViTo co-loaded with both drugs corresponding to their maximal tolerated dose (MTD) ratio resulted in the best therapeutic efficacy. To summarize: liposomal co-encapsulation of anticancer drug combinations can profoundly influence therapeutic outcomes. Drug combinations can be optimized preclinically through pharmacokinetic control by remote loading into nanoliposomes.

Liposome drugs' loading efficiency: a working model based on loading conditions and drug's physicochemical properties.

Remote loading of liposomes by transmembrane gradients is one of the best approaches for achieving the high enough drug level per liposome required for the liposomal drug to be therapeutically efficacious. This breakthrough, which enabled the approval and clinical use of nanoliposomal drugs such as Doxil, has not been paralleled by an in-depth understanding that allows predicting loading efficiency of drugs. Here we describe how applying data-mining algorithms on a data bank based on Barenholz's laboratory's 15 years of liposome research experience on remote loading of 9 different drugs enabled us to build a model that relates drug physicochemical properties and loading conditions to loading efficiency. This model enables choosing candidate molecules for remote loading and optimizing loading conditions according to logical considerations. The model should also help in designing pro-drugs suitable for remote loading. Our approach is expected to improve and accelerate development of liposomal formulations for clinical applications.