Safety and efficacy of G2-S16 dendrimer as microbicide in healthy human vaginal tissue explants.

BACKGROUND: The absence of an effective treatment and vaccine in HIV-1 pandemic place preventive strategies such as safety and effective microbicide development as a central therapeutic approach to control HIV-1 pandemic nowadays. RESULTS: Studies of cytotoxicity, immune population status, inflammation or tissue damage and mainly prophylactic inhibition of HIV-1 infection in vaginal human explants demonstrate the biosafety and effectivity of G2-S16 dendrimer. Human explants treated with G2-S16 dendrimer or treated and HIV-1 infected do not presented signs of irritation, inflammation, immune activation or T cell populations deregulation. CONCLUSIONS: Herein we conclude that G2-S16 dendrimer has demonstrated sufficient efficacy, biosafety, effectivity and behavior in the closest to the real-life condition model represented by the human healthy donor vaginal tissue explants, to raise G2-S16 dendrimer as a promising candidate to clinical trials to develop an effective microbicide against HIV-1 infection.

Pró-Fármacos dendriméricos potencialmente ativos em Malária e Tuberculose: Síntese e avaliação da atividade biológica / Dendrimeric prodrugs potentially active in malaria and tuberculosis: Synthesis and evaluation of biological activity

HIV/AIDS, tuberculose, malária e as doenças tropicais negligenciadas representam uma grande preocupação em Saúde em muitas regiões do mundo. Os fármacos disponíveis para o tratamento apresentam diversos problemas, tais como toxicidade e resistência ao parasita. Mesmo com esse triste panorama, o investimento em pesquisa nessa área é, ainda, pouco significativo. Assim, dentre os métodos de modificação molecular para melhorar propriedades farmacêuticas, farmacocinéticas e/ou farmacodinâmica de compostos bioativos destaca-se a latenciação. Já os dendrímeros vêm despertando interesse em aplicações biológicas, principalmente como transportadores de fármacos, além de atuarem como transportadores de genes, imagem em diagnóstico e compostos com ação per se. Face ao exposto e tendo em vista o caráter promissor dos dendrímeros como sistemas de drug delivery, o objetivo deste trabalho foi a síntese de pró-fármacos dendriméricos potencialmente ativos em malária e tuberculose. Os dendrímeros de Bis-MPA (gerações 0, 1 e 2) foram sintetizados pelo grupo do Professor Scott Grayson, da Tulane University (EUA). No Brasil, foram feitas as funcionalizações destes compostos, através do acoplamento do ácido succínico (que funciona como espaçante) e as moléculas ativas. Selecionaram-se as seguintes substâncias: (1) primaquina, com ação antimalárica e (2) isoniazida, de ação nos primeiros estágios da tuberculose. Foram sintetizados os pró-fármacos dendriméricos de isoniazida nas gerações 0 e 1 (G0-Iso e G1-Iso), e primaquina nas gerações 0, 1 e 2 (G0-Pq, G1-Pq e G2Pq). Importante mencionar que os resultados de Ressonância Magnética e Nuclear de 1H e de 13C demostraram as obtenções dos respectivos produtos, porém contendo impurezas. Já a análise do resultado proveniente da espectrometria de massas do composto G0-Iso revelou a presença de um subproduto ciclizado da isonizaida succinoilada (CIso-Suc), o qual pode ser um potencial pró-fármaco ou apresentar atividade per se. Como não se conhece este composto, o laboratório coordenado pela Profas Elizabeth Igne Ferreira e Jeanine Giarolla manifestou interesse em pesquisa-lo, principalmente quanto suas propriedades físico- químicas, bem como quanto à atividade biológica. Assim, utilizando metodologia analítica previamente estabelecida para o G0-Iso, os estudos de estabilidade química da CIso-Suc, em diferentes valores de pH, demonstraram a capacidade da forma ciclizada em se converter no protótipo Iso-Suc, majoritariamente em pH 7,4 e 8,5. Como perspectivas, destaca-se a avaliação da estabilidade enzimática deste potencial derivado. Ressalta-se, ainda, a a avaliação da respectiva atividade antimicobacteriana. Em relação aos pró-fármacos, as necessidades de aprimoramentos das sínteses são, também, evidenciadas. Uma vez sintetizados e caracterizados, estes últimos derivados serão avaliados quanto à atividade biológica. Ademais, estudos computacionais, sobretudo simulações de docking molecular, foram desenvolvidos com intuito de se entender o modo de interação de alguns compostos com alvos biológicos pré-determinados

HIV/AIDS, tuberculosis, malaria and neglected diseases are a major health concern in many regions of the world. The drugs available present various problems, such as toxicity and parasite resistance. Even with this sad outlook, research investment in this area is still insignificant. Among the molecular modification methods to improve the pharmaceutical, pharmacokinetic and/or pharmacodynamic properties we stands out prodrug design. On the other hand, dendrimers are arousing interest in biological applications, mainly as drug carriers, besides gene delivery, diagnostic imaging, as well as acting as compounds with activity per se. Considering that, added to the promising dendrimer drug delivery features, the aim of this study was to synthesize potentially active dendrimer prodrugs in malaria and tuberculosis. Bis-MPA dendrimers (generations 0, 1 and 2) were synthesized by the group of Professor Scott Grayson of Tulane University (USA). Herein in Brazil, the compounds were functionalized by coupling succinic acid (spacer group), as well as the active molecules. We selected the following substances: (1) primaquine, with antimalarial action and (2) isoniazid, acting in the early stages of tuberculosis. Isoniazid dendrimer prodrugs were synthesized generations 0 and 1 (G0-Iso and G1-Iso), and primaquine in generations 0, 1 and 2 (G0-Pq, G1-Pq and G2-Pq). It is important to mention that the results related to Nuclear and Magnetic Resonance 113C showed chemical structures features, however with impurities. Analysis of the mass spectrometry regarding G0-Iso has revealed the presence of a cyclized by-product of succinylated isonized (CIso-Suc), which may be a potential prodrug or may presentactivity itself. Using the analytical methodology performed for G0-Iso, ICso-Suc demonstrated its ability to convert the Iso-Suc prototype at different pH values, especially at pH 7.4 and 8.5. As perspectives, we highlight the determinations of the chemical stability of ICsoSuc at pH 1.5 and 6.0, as well as the evaluation of the enzymatic stability. We will also investigate the respective antimicobacterial activities. Regarding prodrugs, the needs for synthesis enhancements are also necessary. Once synthesized and characterized, these latter derivatives will be evaluated for biological activity. Moreover, computational studies, especially molecular docking simulations, were developed in order to understand the mode of interaction of some compounds with predetermined biological targets

Emergence of Nanotechnology to Fight HIV Sexual Transmission: The Trip of G2-S16 Polyanionic Carbosilane Dendrimer to Possible Pre-Clinical Trials.

Development of new, safe, and effective microbicides to prevent human immunodeficiency virus HIV sexual transmission is needed. Unfortunately, most microbicides proved ineffective to prevent the risk of HIV-infection in clinical trials. We are working with G2-S16 polyanionic carbosilane dendrimer (PCD) as a new possible vaginal topical microbicide, based on its short reaction times, wide availability, high reproducibility, and quantitative yields of reaction. G2-S16 PCD exerts anti-HIV activity at an early stage of viral replication, by blocking gp120/CD4/CCR5 interaction, and providing a barrier against infection for long periods of time. G2-S16 PCD was stable at different pH values, as well as in the presence of seminal fluids. It maintained the anti-HIV activity against R5/X4 HIV over time, did not generate any type of drug resistance, and retained the anti-HIV effect when exposed to semen-enhanced viral infection. Importantly, G2-S16 PCD did not modify vaginal microbiota neither in vitro or in vivo. Histopathological examination did not show vaginal irritation, inflammation, lesions, or damage in the vaginal mucosa, after administration of G2-S16 PCD at different concentrations and times in female mice and rabbit animal models. Based on these promising data, G2-S16 PCD could become a good, safe, and readily available candidate to use as a topical vaginal microbicide against HIV.

Are Poly(amidoamine) Dendrimers Safe for Ocular Applications? Toxicological Evaluation in Ocular Cells and Tissues.

Purpose: The human eye is a sophisticated and sensitive sensory organ. Because of the existence of the blood-ocular barrier and corneal-scleral barrier, safe and efficient ocular drug delivery system is highly desired; yet, it remains an unsolved issue. Due to the unique structure and drug loading property, Poly(amidoamine) (PAMAM) has received much attention in the ocular drug delivery investigation. Herein, we evaluated the ocular cytotoxicity and biosafety of PAMAM dendrimers. Methods: The ocular cytotoxicity and biosafety of PAMAM dendrimers were evaluated by conducting in vitro and in vivo experiments on ocular systems. The in vitro effect of PAMAM dendrimer of different generations (G4.0, G5.0, and G6.0) and concentrations on ocular cell metabolism, apoptosis, and oxidative damage were quantitatively assessed. In vivo biosafety of PAMAM dendrimers were further investigated on intraocular tissue by ocular irritation and intravitreal injection approaches. Results: It is found that that the cytotoxicity of PAMAM was time and generation dependent. PAMAM at a concentration below 50 µg/mL had minimal impact on the ocular tissue, whereas it caused apparent damage when above 50 µg/mL in the investigated situation. Further, our in vivo results showed that higher concentration of dendrimer (100 µg/mL) was associated with functional impairment demonstrated via optical coherence tomography and electroretinogram, although macroscopic structural changes were absent in fundus and histopathological studies. Overall, a higher concentration of PAMAM, such as above 50 µg/mL, may cause ocular functional damage. Conclusion: The PAMAM at the concentrations lower than 50 µg/mL showed good biocompatibility and biosafety in human ocular cells and tissues.

A phase 2, double-blind, multicenter, randomized, placebo-controlled, dose­ranging study of the efficacy and safety of Astodrimer Gel for the treatment of bacterial vaginosis.

BACKGROUND: Astodrimer Gel contains a novel dendrimer intended to treat and prevent bacterial vaginosis. We assessed the efficacy and safety of Astodrimer Gel for treatment of bacterial vaginosis. METHODS: 132 women with bacterial vaginosis were randomized 1:1:1:1 to Astodrimer 0.5% (N = 34), 1% (N = 33), or 3% (N = 32) Gel or hydroxyethyl cellulose placebo gel (N = 33) at a dose of 5 g vaginally once daily for 7 days at 6 centers in the United States. The primary endpoint was clinical cure (no bacterial vaginosis vaginal discharge and no more than one of 1) vaginal pH ≥4.5; 2) ≥20% clue cells; or 3) positive whiff test) at study days 21-30. Secondary analyses included clinical cure at study days 9-12, patient-reported symptoms, acceptability and adverse events. RESULTS: The Astodrimer 1% Gel dose was superior to placebo for the primary and selected secondary efficacy measures in the modified intent-to-treat population. Clinical cure rates at day 9-12 were superior to placebo for the Astodrimer 3%, 1% and 0.5% Gel groups (62.5% [15/24; P = .002], 74.1% [20/27; P < .001], and 55.2% [16/29; P = .001], respectively, vs. 22.2% [6/27]). At day 21-30, clinical cure rates were 46.2% (12/26) for the 1% dose vs. 11.5% for placebo (3/26; P = .006). A greater proportion of patients reported absence of vaginal discharge and vaginal odor at day 9-12 and day 21-30 for Astodrimer Gel groups compared with placebo. Adverse events considered potentially treatment-related occurred in only 25% of Astodrimer Gel-treated patients vs. 22% of placebo patients. CONCLUSION: Astodrimer Gel once daily for 7 days was superior to placebo for treatment of bacterial vaginosis and was well-tolerated. The 1% dose consistently showed the strongest efficacy across endpoints. These results support a role for Astodrimer Gel, 1%, as an effective treatment for bacterial vaginosis.

Biodistribution and Biosafety of a Poly(Phosphorhydrazone) Dendrimer, an Anti-Inflammatory Drug-Candidate.

Dendrimers are nanosized, arborescent polymers of which size and structure are perfectly controlled. This is one reason why they are widely used for biomedical purposes. Previously, we showed that a phosphorus-based dendrimer capped with anionic azabisphosphonate groups (so-called ABP dendrimer) has immuno-modulatory and anti-inflammatory properties towards human immune cells in vitro. Thereafter, we have shown that the ABP dendrimer has a promising therapeutic efficacy to treat models of chronic inflammatory disorders. On the way to clinical translation, the biodistribution and the safety of this drug-candidate has to be thoroughly assessed. In this article, we present preliminary non-clinical data regarding biodistribution, hematological safety, genotoxicity, maximal tolerated doses, and early cardiac safety of the ABP dendrimer. One of the genotoxicity assays reveals a potential mutagen effect of the item at a concentration above 200 µM, i.e., up to 100 times the active dose in vitro on human immune cells. However, as the results obtained for all the other assays show that the ABP dendrimer has promising biodistribution and safety profiles, there is no red flag raised to hamper the regulatory pre-clinical development of the ABP dendrimer.

Use of Polyamidoamine Dendrimers in Brain Diseases.

Polyamidoamine (PAMAM) dendrimers are one of the smallest and most precise nanomolecules available today, which have promising applications for the treatment of brain diseases. Each aspect of the dendrimer (core, size or generation, size of cavities, and surface functional groups) can be precisely modulated to yield a variety of nanocarriers for delivery of drugs and genes to brain cells in vitro or in vivo. Two of the most important criteria to consider when using PAMAM dendrimers for neuroscience applications is their safety profile and their potential to be prepared in a reproducible manner. Based on these criteria, features of PAMAM dendrimers are described to help the neuroscience researcher to judiciously choose the right type of dendrimer and the appropriate method for loading the drug to form a safe and effective delivery system to the brain.

Structure-activity relationship of novel low-generation dendrimers for gene delivery.

Structure-activity relationship (SAR) studies are very critical to design ideal gene vectors for gene delivery. However, It is difficult to obtain SAR information of low-generation dendrimers due to the lack of easy structural modification ways. Here, we synthesized a novel family of rigid aromatic backbone-based low-generation polyamidoamine (PAMAM) dendrimers. According to the number of primary amines, they were divided into two types: four-amine-containing PAMAM (DL1-DL5) and eight-amine-containing PAMAM (DL6-DL10). Due to the introduction of a rigid aromatic backbone, the low-generation PAMAM could be modified easier by different hydrophobic aliphatic chains. Several assays were used to study the interactions of the PAMAM dendrimers with plasmid DNA, and the results revealed that they not only had good DNA binding ability but also could efficiently condense DNA into spherical-shaped nanoparticles with suitable sizes and zeta potentials. The SAR studies indicated that the gene-transfection efficiency of the synthesized materials depended on not only the structure of their hydrophobic chains but also the number of primary amines. It was found that four-amine-containing PAMAM prepared from oleylamine (DL5) gave the best transfection efficiency, which was 3 times higher than that of lipofectamine 2000 in HEK293 cells. The cellular uptake mechanism mediated by DL5 was further investigated, and the results indicated that DL5/DNA complexes entered the cells mainly via caveolae and clathrin-mediated endocytosis. In addition, these low-generation PAMAMs modified with a single hydrophobic tail showed lower toxicity than lipofectamine 2000 in MC3T3-E1, MG63, HeLa, and HEK293 cells. These results reveal that such a type of low-generation polyamidoamines might be promising non-viral gene vectors, and also give us clues for the design of safe and high-efficiency gene vectors.

Phosphorus dendrimers for nanomedicine.

From biomaterials to imaging, and from drug delivery to drugs by themselves, phosphorus-containing dendrimers offer a large palette of biological properties, depending essentially on their types of terminal functions. The most salient examples of phosphorus dendrimers used for the elaboration of bio-chips and of supports for cell cultures, for imaging biological events, and for carrying and delivering drugs or biomacromolecules are presented in this feature article. Several phosphorus dendrimers can be considered also as drugs per se (by themselves) in particular to fight against cancers, neurodegenerative diseases, and inflammation, both in vitro and in vivo. Toxicity assays are also reported.

Dendrimers Effects on the Immune System: Insights into Toxicity and Therapeutic Utility.

BACKGROUND: Dendrimers are hyperbranched polymeric nanomaterials increasingly used in research, industrial and biomedical applications. Establishing safety profile of these particles includes an understanding of their interactions with blood components and the immune system. METHOD: Herein I review the literature demonstrating how tuning dendrimer physicochemical properties influences their interaction with erythrocytes, platelets, plasma proteins, complement and coagulation systems. Dendrimer immunogenicity, adjuvanticity, allergenicity, anti-inflammatory, immunosuppressive and antibacterial properties are also discussed. CONCLUSION: Dendrimers hemato- and immune- compatibility are determined by particle size, architecture, type and density of surface functional groups. Case studies from the literature are discussed to support this conclusion. The review also highlights questions which require more thorough investigation to fill the gaps in our understanding of immunological properties of dendrimers.

Poly(amido amine) dendrimers in oral delivery.

Poly(amidoamine) (PAMAM) dendrimers have been extensively investigated for oral delivery applications due to their ability to translocate across the gastrointestinal epithelium. In this Review, we highlight recent advances in the evaluation of PAMAM dendrimers as oral drug delivery carriers. Specifically, toxicity, mechanisms of transepithelial transport, models of the intestinal epithelial barrier including isolated human intestinal tissue model, detection of dendrimers, and surface modification are discussed. We also highlight evaluation of various PAMAM dendrimer-drug conjugates for their ability to transport across gastrointestinal epithelium for improved oral bioavailability. In addition, current challenges and future trends for clinical translation of PAMAM dendrimers as carriers for oral delivery are discussed.

A novel doxorubicin loaded folic acid conjugated PAMAM modified with borneol, a nature dual-functional product of reducing PAMAM toxicity and boosting BBB penetration.

Effective targeting drug delivery system for glioma treatment is still greatly challenged by the existence of the blood-brain barrier (BBB) and the intracranial overspreading of anti-tumor drug. Herein, we presented a dual-functional glioma targeting delivery of doxorubicin based on the PAMAM G5 dendrimer, modified with folic acid (FA) to target tumor cell, also borneol (BO), a well known safe material derived from traditional Chinese medicine, to facilitate the BBB permeability and reduce the toxicity of naked PAMAM. The intracranial transportation and glioma targeting ability were evaluated on the BBB model and C6 glioma cells in vitro. Also, pharmacokinetics and biodistribution were studied on C6 glioma-bearing rats in vivo. It indeed reduced the cytotoxicity of PAMAM against both HBMEC and C6 cells by coupling BO on the surface, while efficiently boosted BBB permeability with the improvement of transportation ratio by 2 folds to the BO-unmodified conjugates. Furthermore, conjugated FA increased total uptake amount by C6 cells leading to strong inhibition with the 3-fold lower IC50 value than FA-unmodified DOX conjugate. In comparison with DOX solution, FA-BO-PAMAM/DOX exhibited significantly prolonged half-life time and increased area under the curve and improved DOX accumulation in brain tumor. The tumor growth inhibition, in vivo, was significantly increased up to 57.4%. The median survival time of xenograft rats after administering FA-BO-PAMAM/DOX (28days) was significantly prolonged compared to free DOX (18days, P<0.05) or other controls. In conclusion, this strategy of novel targeting nanocarrier provides a promising method to increase the drug accumulation in the tumor site for therapy of glioma.

High-performance dendritic contrast agents for X-ray computed tomography imaging using potent tetraiodobenzene derivatives.

The use of computed tomography (CT) for vascular imaging is critical in medical emergencies requiring urgent diagnostic decisions, such as cerebral ischemia and many cardiovascular diseases. Small-molecule iodinated contrast media are often injected intravenously as radiopaque agents during CT imaging to achieve high contrast enhancement of vascular systems. The rapid excretion rate of these agents is overcome by injecting a significantly high dose of iodine, which can have serious side effects. Here we report a simple method to prepare blood-pool contrast agents for CT based on dendrimers for the first time using tetraiodobenzene derivatives as potent radiopaque moieties. Excellent in vivo safety has been demonstrated for these small (13-22nm) unimolecular water-soluble dendritic contrast agents, which exhibit high contrast enhancement in the blood-pool and effectively extend their blood half-lives. Our method is applicable to virtually any scaffold with suitable surface groups and may fulfill the current need for safer, next-generation iodinated CT contrast agents.

Anti-Human Immunodeficiency Virus Activity of Thiol-Ene Carbosilane Dendrimers and Their Potential Development as a Topical Microbicide.

The concept of a "microbicide" was born out of the lack of a vaccine against HIV and the difficulty of women in ensuring the use of preventive prophylaxis by their partners, especially in developing countries. Approaches using polyanionic carbosilane dendrimers have shown promise in the development of new microbicides. We have developed and evaluated two anionic carbosilane dendrimers with sulfonate and carboxylate terminal groups, G2-STE16 and G2-CTE16. Both dendrimers showed high biosafety in human epithelial cell lines derived from the vagina and in primary blood human cells (PBMCs). The dendrimers not only have a greater capacity to block the entry of different X4- and R5-HIV-1 isolates into epithelial cells but also prevent the HIV-1 infection of activated PBMCs. The treatment of epithelial cells with different carbosilane dendrimers did not produce changes in the activation or proliferation of PBMCs or in the expression of CD4, CCR5 or CXCR4. Computational modeling showed significantly higher affinities for the complexes G2-STE16/gp120 and G2-CTE16/gp120. Moreover, no irritation or vaginal lesions were detected in female BALB/c mice after vaginal administration of the dendrimers. Summing up, G2-STE16 and G2-CTE16 are easy to synthesize and compatible with functional groups, and the purification steps are easy and short. Our results have clearly demonstrated that these dendrimers have high potency as a topical microbicide against HIV-1 infection.

Dendrimers in oral drug delivery application: current explorations, toxicity issues and strategies for improvement.

Dendrimers are emerging as potential novel nano-scaled material in drug delivery applications. An interesting area of application is oral drug delivery. In oral drug delivery, many drugs suffer from low bioavailability due to the presence of various biological barriers. Dendrimers have been shown to modulate tight junctions and the integrity of cellular membranes. This effect gives hope for dendrimer to be applied in oral drug delivery. Based on such properties, dendrimers are further surface-modified so that the system will be more suitable for oral delivery applications. Cationic dendrimers are commonly conjugated with neutral or negatively charged ligands, such as polyethylene glycol (PEG), to reduce potential toxicity in gastrointestinal (G.I.) tract. Dendrimers are also surfacemodified to inhibit the efflux effect of P-glycoprotein, which is one of the major drug efflux pumps in G.I. tract. Another interesting strategy is to directly conjugate or mix dendrimer with drugs either to form a dendrimer-drug conjugation or complex to deliver the drug. In this review, application of dendrimers in oral drug delivery will be discussed. The main focus is on the various surface modification strategies to design a more desirable dendrimer-based delivery system that fits the need in oral drug delivery.

Characterization and evaluation of amphotericin B loaded MDP conjugated poly(propylene imine) dendrimers.

This paper describes a novel strategy for targeted delivery of amphotericin B (AmB) to macrophages with muramyl dipeptide (MDP) conjugated multimeric poly(propyleneimine) (PPI) dendrimers. Synergistic antiparasitic activity due to immunostimulation by multimeric presentation of MDP on dendrimers was anticipated. MDP conjugated 5.0G PPI (MdPPI) dendrimers were synthesized and characterized. Therapeutic activity and toxicity of dendrimeric formulation of AmB (MdPPIA) were compared with marketed formulations of AmB. Highly significant (P<0.01) reduction in toxicity was observed in hemolytic toxicity and cytotoxicity studies in erythrocytes and J774A.1 macrophage cells, respectively. Formulation MdPPIA showed appreciable macrophage targeting potential and higher or equivalent antiparasitic activity against parasite infected macrophage cell lines and in vivo infection in Balb/c mice. These results suggest the developed MDP conjugated dendrimeric formulation of AmB as a promising immunostimulant targeted drug delivery system and a safer alternative to marketed formulations. From the clinical editor: Parasitic infections remain a significant issue in the clinical setting. The authors in this article studied the use of ligand anchored dendrimeric formulation of Amphotericin B to target infected macrophages and showed reduced toxicity, high anti-leishmanial activity. This may add another treatment option to available formulations in the future.

PAMAM dendrimers: destined for success or doomed to fail? Plain and modified PAMAM dendrimers in the context of biomedical applications.

PAMAM (polyamidoamine) dendrimers are commonly considered promising polymers that can be successfully used in various biomedical applications. Nevertheless, direct clinical adaptations of plain unmodified PAMAM dendrimers may be limited at present, mainly because of their toxicity, unpredictable behavior in living organisms, unknown bioavailability, biocompatibility or pharmacokinetic profile, problematic therapeutic dose selection, or high cost of production. On the basis of our studies concerning the possible use of unmodified PAMAM dendrimers as the scavengers of glucose and carbonyl stress in animal models of human pathology, as well as considering available literature on experimental data of other researchers, we have prepared the brief critical review of the biomedical activities of these unmodified compounds and their most alluring derivatives, especially in the context of possible future perspectives of PAMAMs. Thus, on the pages of this review, we made an attempt to briefly summarize obstacles, emerging from experimental, technical, and human limitations, that may, to some extent, restrain our belief in a brighter future of plain amine-terminated PAMAM dendrimers.

Improved tumor targetability of Tat-conjugated PAMAM dendrimers as a novel nanosized anti-tumor drug carrier.

The generation 4-poly-amidoamine-dendrimers (PAMAM G4 dendrimer, P) was conjugated to Tat peptide (Tat, T), a cell-penetrating peptide, in search of an efficient anti-tumor drug delivery vehicle for cancer therapy. In this study, we synthesized BODIPY-labeled Tat-Conjugated PAMAM dendrimers (BPTs) as a novel nanosized anticancer drug carriers and systemically investigated their biodistribution and the tumor accumulation in Sarcoma 180-bearing mice. In addition, the uptake and the cytotoxicity to S180 cells of BPTs thereof were evaluated. The unmodified dendrimer (BP) showed a soon clearance from the blood stream and nonspecific accumulation in tumor. In contrast, the Tat-modified dendrimer, BPT(64) with appropriate particle size showed a better retention in blood and could be accumulated effectively in tumor tissue via the enhanced permeability and retention (EPR) effect. Moreover, BPTs with a high Tat modification rate was accumulated more effectively in tumor tissue. In vitro experiments, these BPTs displayed low cytotoxicity on S180 cells and high uptake to S180 cells. These findings indicate that the nanoparticulate system on the basis of Tat-conjugated PAMAM dendrimers is safer and effective in the concentration range (below 20 µg/ml) to be used as a carrier of anti-tumor drugs for tumor targeting by intravenous administration.

Nontoxic polyphosphate inhibitors reduce thrombosis while sparing hemostasis.

Polyphosphate (polyP) is secreted by activated platelets and has been shown to contribute to thrombosis, suggesting that it could be a novel antithrombotic target. Previously reported polyP inhibitors based on polycationic substances, such as polyethylenimine, polyamidoamine dendrimers, and polymyxin B, although they attenuate thrombosis, all have significant toxicity in vivo, likely due to the presence of multiple primary amines responsible for their polyP binding ability. In this study, we examined a novel class of nontoxic polycationic compounds initially designed as universal heparin reversal agents (UHRAs) to determine their ability to block polyP procoagulant activity and also to determine their utility as antithrombotic treatments. Several UHRA compounds strongly inhibited polyP procoagulant activity in vitro, and 4 were selected for further examination in mouse models of thrombosis and hemostasis. Compounds UHRA-9 and UHRA-10 significantly reduced arterial thrombosis in mice. In mouse tail bleeding tests, administration of UHRA-9 or UHRA-10 was associated with significantly less bleeding compared with therapeutically equivalent doses of heparin. Thus, these compounds offer a new platform for developing novel antithrombotic agents that target procoagulant anionic polymers such as polyP with reduced toxicity and bleeding side effects.

Can metabolic impairments in experimental diabetes be cured with poly(amido)amine (PAMAM) G4 dendrimers? In the search for minimizing of the adverse effects of PAMAM administration.

Poly(amido)amine (PAMAM) G4 dendrimers, given intraperitoneally to diabetic rats, have been reported to scavenge excessive blood glucose and minimize the effects of hyperglycaemia, however, at the cost of reduced survival. This paper is the first to compare the effectiveness of three different routes of PAMAM G4 administration with regard to minimizing the adverse effects of hyperglycaemia in rats. Hence, the aim of the study is to identify the most effective and the least harmful method of dendrimer administration. Control and streptozotocin-diabetic Sprague-Dawley rats were exposed to PAMAM G4 (0.5 µmol/kg b.w.) for 60 days, administered intraperitoneally, intragastrically or subcutaneously. Intraperitoneal and subcutaneous administration of PAMAM G4 was found to be most effective in suppressing the long-term markers of hyperglycaemia, while the intragastric route appeared the least effective. Otherwise, the greatest incidence of adverse effects was associated with intraperitoneal and the lowest with subcutaneous delivery. Harmful effects of intragastrical administration were much lower compared to intraperitoneal route, but at the cost of reduced hypoglycaemizing potential. Otherwise, subcutaneous injection represents the best compromise of moderate PAMAM dendrimer toxicity and effective reduction in the markers of long-term severe hyperglycaemia in chronic experimental diabetes.