Multivalent polymers for drug delivery and imaging: the challenges of conjugation

Deconstructing Best-in-Class Neoglycoclusters as a Tool for Dissecting Key Multivalent Processes in Glycosidase Inhibition

Multivalency represents an appealing option to modulate selectivity in enzyme inhibition and transform moderate glycosidase inhibitors into highly potent ones. The rational design of multivalent inhibitors is however challenging because global affinity enhancement relies on several interconnected local mechanistic events, whose relative impact is unknown. So far, the largest multivalent effects ever reported for a non-polymeric glycosidase inhibitor have been obtained with cyclopeptoid-based inhibitors of Jack bean α-mannosidase (JBα-man). Here, we report a structure-activity relationship (SAR) study based on the top-down deconstruction of best-in-class multivalent inhibitors. This approach provides a valuable tool to understand the complex interdependent mechanisms underpinning the inhibitory multivalent effect. Combining SAR experiments, binding stoichiometry assessments, thermodynamic modelling and atomistic simulations allowed us to establish the significant contribution of statistical rebinding mechanisms and the importance of several key parameters, including inhitope accessibility, topological restrictions, and electrostatic interactions. Our findings indicate that strong chelate-binding, resulting from the formation of a cross-linked complex between a multivalent inhibitor and two dimeric JBα-man molecules, is not a sufficient condition to reach high levels of affinity enhancements. The deconstruction approach thus offers unique opportunities to better understand multivalent binding and provides important guidelines for the design of potent and selective multiheaded inhibitors.

Nanotherapeutic Heterogeneity: Sources, Effects, and Solutions

Nanomaterials have revolutionized medicine by enabling control over drugs' pharmacokinetics, biodistribution, and biocompatibility. However, most nanotherapeutic batches are highly heterogeneous, meaning they comprise nanoparticles that vary in size, shape, charge, composition, and ligand functionalization. Similarly, individual nanotherapeutics often have heterogeneously distributed components, ligands, and charges. This review discusses nanotherapeutic heterogeneity's sources and effects on experimental readouts and therapeutic efficacy. Among other topics, it demonstrates that heterogeneity exists in nearly all nanotherapeutic types, examines how nanotherapeutic heterogeneity arises, and discusses how heterogeneity impacts nanomaterials' in vitro and in vivo behavior. How nanotherapeutic heterogeneity skews experimental readouts and complicates their optimization and clinical translation is also shown. Lastly, strategies for limiting nanotherapeutic heterogeneity are reviewed and recommendations for developing more reproducible and effective nanotherapeutics provided.

Development of targeted photodynamic therapy drugs by combining a zinc phthalocyanine sensitizer with TSPO or EGFR binding groups: the impact of the number of targeting agents on biological activity

Drug-targeted delivery has become a top priority in the world of medicine in order to develop more efficient therapeutic agents. This is important as a critical underlying problem in cancer therapy stems from the inability to deliver active therapeutic substances directly to tumor cells without causing collateral damage. In this work, zinc(II) phthalocyanine (ZnPc) was selected as a sensitizer and was linked to different targeting agents, which would be recognized by overexpressed proteins in cancer cells. As targeting agents, we first selected the two ligands (DAA1106, PK11195) of the translocator protein (TSPO) and then Erlotinib a binding group of the ATP domain of tyrosine kinase in epidermal growth factor (EGFR). ZnPc was connected via an ethylene glycol chain to either one (n = 1) or four (n = 4) targeting agents. The biological activity of these conjugates ZnPc(ligand)n was investigated on MDA-MB-231 breast human cancer cells and human hepatoma HepG2 cells, first in the dark (cytotoxicity) and then under irradiation (photodynamic therapy). The dark cytotoxicity was extremely low (IC50 ≥ 50 μM) for all of these compounds, which is a required criterion for further photodynamic application. After irradiation at 650 nm, only the conjugates bearing one targeting ligand such as ZnPc-[DAA1106]1, ZnPc-[PK11195]1, and ZnPc-[Erlo]1 showed photodynamic activity, while those linked to 4 targeting agents were inactive. Importantly, fluorescence imaging microscopy showed the colocalization of ZnPc-[DAA1106]1, ZnPc-[PK11195]1 and ZnPc-[erlo]1, at mitochondria, a result that justifies the observed photodynamic activity of these conjugates. This study first shows the impact of the number and the mode of organization of targeting agents on the ability of the sensitizer to cross the cell membrane. When zinc(II) phthalocyanine carries a single targeting agent, a significant photodynamic activity on MDA-MB-231 breast human cancer cells was measured and localization at the mitochondria was demonstrated by fluorescence imaging, thus proving the potential of the sensitizer linked to a targeting agent to improve selectivity. Another important conclusion from this study for the design of future effective PDT drugs using multivalence effects is to control the arrangement of the targeting agents in order to design molecules that will be able to pass the cell membrane barriers.

Synthetic nanoparticles for the delivery of CRISPR/Cas9 gene editing system: classification and biomedical applications

Gene editing has great potential in biomedical research including disease diagnosis and treatment. Clustered regularly interspaced short palindromic repeats (CRISPR) is the most straightforward and cost-effective method. The efficient and precise delivery of CRISPR can impact the specificity and efficacy of gene editing. In recent years, synthetic nanoparticles have been discovered as effective CRISPR/Cas9 delivery vehicles. We categorized synthetic nanoparticles for CRISPR/Cas9 delivery and discribed their advantages and disadvantages. Further, the building blocks of different kinds of nanoparticles and their applications in cells/tissues, cancer and other diseases were described in detail. Finally, the challenges encountered in the clinical application of CRISPR/Cas9 delivery materials were discussed, and potential solutions were provided regarding efficiency and biosafety issues.

Applications of AFM-IR for drug delivery vector characterization: infrared, thermal, and mechanical characterization at the nanoscale

The development of effective drug delivery systems requires in-depth characterization of the micro- or nanostructure of the material vectors with high spatial resolution, resulting in a deep understanding of the design-function relationship and maximum therapeutic efficacy. Atomic force microscopy-infrared spectroscopy (AFM-IR) combines the high spatial resolution of AFM and the capabilities of IR spectroscopy to identify chemical composition and it has emerged as a powerful tool for the detailed characterization of a drug delivery system at the nanoscale. In addition, the instruments also allow thermal and mechanical evaluation at the nanoscale. In this review, we highlight the applications of AFM-IR in various drug delivery systems, including polymer-based carriers, lipid-contained nanocarriers, and metal-based nanocarriers. The existing challenges as well as the future perspectives for the application of AFM-IR for drug delivery vector characterization are also discussed.

Multifunctional PEG Carrier by Chemoenzymatic Synthesis for Drug Delivery Systems: In Memory of Professor Andrzej Dworak

This paper describes the synthesis and characterization of new bivalent folate-targeted PEGylated doxorubicin (FA₂-dPEG-DOX₂) made by modular chemo-enzymatic processes using Candida antarctica lipase B (CALB) as a biocatalyst. Unique features are the use of monodisperse PEG (dPEG) and the synthesis of thiol-functionalized folic acid yielding exclusive γ-conjugation of folic acid (FA) to dPEG. The polymer-based drug conjugate is built up by a series of transesterification and Michael addition reactions all catalyzed be CALB. In comparison with other methods in the literature, the modular approach with enzyme catalysis leads to selectivity, full conversion and high yield, and no transition metal catalyst residues. The intermediate product with four acrylate groups is an excellent platform for Michael-addition-type reactions for a wide variety of biologically active molecules. The chemical structures were confirmed by nuclear magnetic resonance spectroscopy (NMR). Flow cytometry analysis showed that, at 10 µM concentration, both free DOX and FA₂-dPEG-DOX₂ were taken up by 99.9% of triple-negative breast cancer cells in 2 h. Fluorescence was detected for 5 days after injecting compound IV into mice. Preliminary results showed that intra-tumoral injection seemed to delay tumor growth more than intravenous delivery.

Designing Functional Bionanoconstructs for Effective In Vivo Targeting

The progress achieved over the last three decades in the field of bioconjugation has enabled the preparation of sophisticated nanomaterial–biomolecule conjugates, referred to herein as bionanoconstructs, for a multitude of applications including biosensing, diagnostics, and therapeutics. However, the development of bionanoconstructs for the active targeting of cells and cellular compartments, both in vitro and in vivo, is challenged by the lack of understanding of the mechanisms governing nanoscale recognition. In this review, we highlight fundamental obstacles in designing a successful bionanoconstruct, considering findings in the field of bionanointeractions. We argue that the biological recognition of bionanoconstructs is modulated not only by their molecular composition but also by the collective architecture presented upon their surface, and we discuss fundamental aspects of this surface architecture that are central to successful recognition, such as the mode of biomolecule conjugation and nanomaterial passivation. We also emphasize the need for thorough characterization of engineered bionanoconstructs and highlight the significance of population heterogeneity, which too presents a significant challenge in the interpretation of in vitro and in vivo results. Consideration of such issues together will better define the arena in which bioconjugation, in the future, will deliver functional and clinically relevant bionanoconstructs.

Anti-tumor Effect of Folate-Binding Protein: In Vitro and In Vivo Studies

Folate receptor (FR) overexpression in a wide range of solid tumors provides an opportunity to develop novel, targeted cancer therapeutics. In this study, we investigated whether prebinding the chemotherapeutic methotrexate (MTX) to folate-binding protein (FBP), the soluble form of FR, would enable the protein to serve as a targeted therapeutic vector, enhancing uptake into tumor cells and improving therapeutic efficacy. In an in vivo study, using an FR-overexpressing KB xenograft model in SCID mice, modest improvement in inhibiting tumor growth was observed for the MTX/FBP mixtures as compared to saline control and free MTX. Surprisingly, FBP alone inhibited tumor growth compared to saline control, free MTX, and FBP/MTX. In order to better understand this effect, we investigated the cytotoxicity of micromolar concentrations of FBP in vitro using the KB, HeLa, and A549 cancer cell lines. Our results revealed concentration-dependent apoptosis (24 h; 10-50 μM) in all three cell lines accompanied by a time- and concentration-dependent reduction (6, 12, and 24 h; 10-50 μM) in metabolic activity and compromised cell plasma membrane integrity. This study demonstrates an apoptosis pathway for cytotoxicity of FBP, an endogenous serum protein, in cancer cell lines with widely varying levels of FR expression. Furthermore, in vivo tumor growth suppression for xenograft KB tumors in SCID mice was observed. These studies suggest novel strategies for the elimination of cancer cells employing endogenous, serum transport proteins.

Molecular level precision and high molecular weight peptide dendrimers for drug-specific delivery

Peptide dendrimers have a broad application in biomedical science due to their biocompatibility, diversity, and multifunctionality, but the precision synthesis of high-molecule weight peptide dendrimers remains challenging. We here report the facile and liquid-phase synthesis of molecular level precision and amino-acid built-in polylysine (PLL) dendrimers with molecular weights as high as ∼60 kDa. Three types of polyhedral oligosilsesquioxane (POSS)-cored PLL dendrimers with phenylalanine, tyrosine, or histidine as building blocks were synthesized. The precise structures of the dendrimers were confirmed by MALDI-TOF MS, GPC, and ¹H NMR spectroscopy. The interior functionalized peptide dendrimers improved the encapsulation capability of SN38 and sustained the release profiles. Enhanced molecular interactions between the peptide dendrimers and drugs were explored by both NMR experiments and computer simulations. The peptide dendrimer/SN38 formulations showed potent antitumor activity against multiple cancer cell lines. We believe that this strategy can be applied to the synthesis of tailor-made functional peptide dendrimers for drug-specific delivery and other diverse biomedical applications.

Polymer-based nano-therapies to combat COVID-19 related respiratory injury: progress, prospects, and challenges

The recent coronavirus disease-2019 (COVID-19) outbreak has increased at an alarming rate, representing a substantial cause of mortality worldwide. Respiratory injuries are major COVID-19 related complications, leading to poor lung circulation, tissue scarring, and airway obstruction. Despite an in-depth investigation of respiratory injury's molecular pathogenesis, effective treatments have yet to be developed. Moreover, early detection of viral infection is required to halt the disease-related long-term complications, including respiratory injuries. The currently employed detection technique (quantitative real-time polymerase chain reaction or qRT-PCR) failed to meet this need at some point because it is costly, time-consuming, and requires higher expertise and technical skills. Polymer-based nanobiosensing techniques can be employed to overcome these limitations. Polymeric nanomaterials have the potential for clinical applications due to their versatile features like low cytotoxicity, biodegradability, bioavailability, biocompatibility, and specific delivery at the targeted site of action. In recent years, innovative polymeric nanomedicine approaches have been developed to deliver therapeutic agents and support tissue growth for the inflamed organs, including the lung. This review highlights the most recent advances of polymer-based nanomedicine approaches in infectious disease diagnosis and treatments. This paper also focuses on the potential of novel nanomedicine techniques that may prove to be therapeutically efficient in fighting against COVID-19 related respiratory injuries.

Multivalent Probes in Molecular Imaging: Reality or Future?

The rapidly developing field of molecular medical imaging focuses on specific visualization of (patho)physiological processes through the application of imaging agents (IAs) in multiple clinical modalities. Although our understanding of the principles underlying efficient IAs design has increased tremendously, many IAs still show poor in vivo imaging performance because of low binding affinity and/or specificity. These limitations can be addressed by taking advantage of multivalency, in which multiple copies of a ligand are employed to strengthen the interaction. We critically address specific challenges associated with the application of multivalent compounds in molecular imaging, and we give directions for a stepwise approach to the design of multivalent imaging probes to improve their target binding and pharmacokinetics (PK) for improved diagnostic potential.

Celecoxib substituted biotinylated poly(amidoamine) G3 dendrimer as potential treatment for temozolomide resistant glioma therapy and anti-nematode agent

Glioblastoma multiforme (GBM) is a one of the most widely diagnosed and difficult to treat type of central nervous system tumors. Resection combined with radiotherapy and temozolomide (TMZ) chemotherapy prolongs patients' survival only for 12 - 15 months after diagnosis. Moreover, many patients develop TMZ resistance, thus important is search for a new therapy regimes including targeted drug delivery. Most types of GBM reveal increased expression of cyclooxygenase-2 (COX-2) and production of prostaglandin E2 (PGE₂), that are considered as valuable therapeutic target. In these studies, the anti-tumor properties of the selective COX-2 inhibitor celecoxib (CXB) and biotinylated third generation of the poly(amidoamine) dendrimer substituted with 31 CXB residues (G3BC31) on TMZ -resistant U-118 MG glioma cell line were examined and compared with the effect of TMZ alone including viability, proliferation, migration and apoptosis, as well as the cellular expression of COX-2, ATP level, and PGE₂ production. Confocal microscopy analysis with the fluorescently labeled G3BC31 analogue has shown that the compound was effectively accumulated in U-118 MG cells in time-dependent manner and its localization was confirmed in lysosomes but not nuclei. G3BC31 reveal much higher cytotoxicity for U-118 MG cells at relatively low concentrations in the range of 2-4 µM with compared to CBX alone, active at 50-100 µM. This was due to induction of apoptosis and inhibition of proliferation and migration. Observed effects were concomitant with reduction of PGE₂ production but independent of COX-2 expression. We suggest that investigated conjugate may be a promising candidate for therapy of TMZ-resistant glioblastoma multiforme, although applicable in local treatment, since our previous study of G3BC31 did not demonstrate selectivity against glioma cells compared to normal human fibroblasts. However, it has to be pointed that in our in vivo studies conducted with model organism, Caenorhabditis elegans indicated high anti-nematode activity of G3BC31 in comparison with CXB alone that confirms of usefulness of that organism for estimation of anti-cancer drug toxicity.

Tuning the Brightness and Photostability of Organic Dots for Multivalent Targeted Cancer Imaging and Surgery

Specific labeling of biomarkers with bright and high photostable fluorophores is vital in fluorescent imaging applications. Here, we report a general strategy to develop single-molecule dendritic nanodots with finely tunable optical properties for in vivo fluorescent imaging. The well-defined nanodots are based on the divergent growth of biodegradable polylysine dendrimers with a fluorophore as the core. By tuning the size and surface chemistry, we obtained fluorescent nanodots with excellent brightness and photostability, favorable pharmacokinetics, and multivalent tumor-targeting capability. The nanodots provided robust, stable, long-lasting, and specific fluorescence enhancement in tumor tissue with an in situ tumor-to-normal ratio (TNR) of ∼3 and lasting over 5 days and an ex vivo TNR up to ∼17, holding considerable promise for cancer imaging and image-guided surgery. This strategy significantly improves the in vivo performance of fluorophores and can be applied to other modality imaging probes.

Influence of Binding Site Affinity Patterns on Binding of Multivalent Polymers

Using inspiration from biology, we can leverage multivalent binding interactions to enhance weak, monovalent binding between molecules. While most previous studies have focused on multivalent binders with uniform binding sites, new synthetic polymers might find it desirable to have multiple binding moieties along the chain. Here, we probe how patterning of heterogeneous binding sites along a polymer chain controls the binding affinity of a polymer using a reactive Brownian dynamics scheme. Unlike monovalent binders that are pattern-agnostic, we find that divalent binding is dependent on both the polymer pattern and binding target concentration. For dilute targets, blocky polymers provide high local concentrations of high-affinity sites, but at high target concentrations, competition for binding sites makes alternating polymers the strongest binders. Subsequently, we show that random copolymers are robust to target concentration fluctuations. These results will assist in the rational design of multivalent polymer therapeutics and materials.

Application and biomolecular study of functionalized folic acid-dendrimer nanoparticles in drug delivery

We determined the loading efficacy of folic acid - PAMAM - G3 and folic acid - PAMAM - G4 nanoparticles with doxorubicin (Dox), tamoxifen (Tam) and tetracycline (Tet) in aqueous solution at pH 7.2. Thermodynamic parameters ΔH⁰ -16 to -4 (kJ mol^-1), ΔS⁰ 31 to -0.3 (J mol^-1K^-1) and ΔG⁰ -14 to -11 (kJ mol^-1) showed drug folic acid-PAMAM bindings are via ionic, H-bonding and van der Waals interactions. As acid - PAMAM size increased the stability and loading efficacy of drug-polymer conjugates were increased. The order of stability for drug-nanoparticles was doxorubicin > tetracycline > tamoxifen. TEM analysis showed major polymer morphological changes, upon drug encapsulation. Folic acid-PAMAM conjugates are effective drug delivery tools in vitro. Communicated by Ramaswamy H. Sarma.

Therapeutic potential of polypeptide-based conjugates: Rational design and analytical tools that can boost clinical translation

The clinical success of polypeptides as polymeric drugs, covered by the umbrella term "polymer therapeutics," combined with related scientific and technological breakthroughs, explain their exponential growth in the development of polypeptide-drug conjugates as therapeutic agents. A deeper understanding of the biology at relevant pathological sites and the critical biological barriers faced, combined with advances regarding controlled polymerization techniques, material bioresponsiveness, analytical methods, and scale up-manufacture processes, have fostered the development of these nature-mimicking entities. Now, engineered polypeptides have the potential to combat current challenges in the advanced drug delivery field. In this review, we will discuss examples of polypeptide-drug conjugates as single or combination therapies in both preclinical and clinical studies as therapeutics and molecular imaging tools. Importantly, we will critically discuss relevant examples to highlight those parameters relevant to their rational design, such as linking chemistry, the analytical strategies employed, and their physicochemical and biological characterization, that will foster their rapid clinical translation.

Biodegradable Microneedle Patch Delivering Antigenic Peptide-Hyaluronate Conjugate for Cancer Immunotherapy

Antigenic peptide-delivery systems have been extensively investigated to harness the immune system for cancer therapy. Cytotoxic T-cell epitope peptide can induce an antigen-specific CD8⁺ T-cell response, which subsequently inhibits the growth of antigen-bearing tumors. However, there are only a few facile tailored delivery systems of antigenic peptide for effective cancer immunotherapy. Here, we developed a biodegradable microneedle patch delivering a hyaluronate (HA)-antigenic peptide conjugate for prophylactic cancer immunotherapy. Cytotoxic T-cell epitope peptide (SIINFEKL) was conjugated to HA, which was loaded into a biodegradable HA microneedle (MN) patch to efficiently deliver an antigen to the immune system in the skin. HA could act as a transdermal vaccine carrier eliciting strong immune responses by the efficient stimulation of immunocompetent cells. The HA-SIINFEKL conjugates loaded into biodegradable MNs were localized near the MN administration site, exhibiting long-term residence for more than 24 h post-administration. Remarkably, a single transdermal vaccination with the MN patch containing HA-SIINFEKL conjugates resulted in a statistically significant inhibition of tumor growth in B16 melanoma model mice by enhancing antigen-specific cytotoxic T-cell responses.

Nanoparticle heterogeneity: an emerging structural parameter influencing particle fate in biological media?

Drug nanocarriers' surface chemistry is often presumed to be uniform. For instance, the polymer surface coverage and distribution of ligands on nanoparticles are described with averaged values obtained from quantification techniques based on particle populations. However, these averaged values may conceal heterogeneities at different levels, either because of the presence of particle sub-populations or because of surface inhomogeneities, such as patchy surfaces on individual particles. The characterization and quantification of chemical surface heterogeneities are tedious tasks, which are rather limited by the currently available instruments and research protocols. However, heterogeneities may contribute to some non-linear effects observed during the nanoformulation optimization process, cause problems related to nanocarrier production scale-up and correlate with unexpected biological outcomes. On the other hand, heterogeneities, while usually unintended and detrimental to nanocarrier performance, may, in some cases, be sought as adjustable properties that provide NPs with unique functionality. In this review, results and processes related to this issue are compiled, and perspectives and possible analytical developments are discussed.

Orthogonally functionalizable polyacetals: a versatile platform for the design of acid sensitive amphiphilic copolymers

Dually functionalized amphiphilic copolyacetals as rational approach to the development of pH-responsive site-specific drug delivery systems.

Micelle-like nanoparticles as siRNA and miRNA carriers for cancer therapy

Gene therapy has emerged as an alternative in the treatment of cancer, particularly in cases of resistance to chemo and radiotherapy. Different approaches to deliver genetic material to tumor tissues have been proposed, including the use of small non-coding RNAs due to their multiple mechanisms of action. However, such promise has shown limits in in vivo application related to RNA's biological instability and stimulation of immunity, urging the development of systems able to overcome those barriers. In this review, we discuss the use of RNA interference in cancer therapy with special attention to the role of siRNA and miRNA and to the challenges of their delivery in vivo. We introduce a promising class of drug delivery system known as micelle-like nanoparticles and explore their synthesis and advantages for gene therapy as well as the recent findings in in vitro, in vivo and clinical studies.

Distributions: The Importance of the Chemist's Molecular View for Biological Materials

Characterization of materials with biological applications and assessment of physiological effects of therapeutic interventions are critical for translating research to the clinic and preventing adverse reactions. Analytical techniques typically used to characterize targeted nanomaterials and tissues rely on bulk measurement. Therefore, the resulting data represent an average structure of the sample, masking stochastic (randomly generated) distributions that are commonly present. In this Perspective, we examine almost 20 years of work our group has done in different fields to characterize and control distributions. We discuss the analytical techniques and statistical methods we use and illustrate how we leverage them in tandem with other bulk techniques. We also discuss the challenges and time investment associated with taking such a detailed view of distributions as well as the risks of not fully appreciating the extent of heterogeneity present in many systems. Through three case studies showcasing our research on conjugated polymers for drug delivery, collagen in bone, and endogenous protein nanoparticles, we discuss how identification and characterization of distributions, i.e., a molecular view of the system, was critical for understanding the observed biological effects. In all three cases, data would have been misinterpreted and insights missed if we had only relied upon spatially averaged data. Finally, we discuss how new techniques are starting to bridge the gap between bulk and molecular level analysis, bringing more opportunity and capacity to the research community to address the challenges of distributions and their roles in biology, chemistry, and the translation of science and engineering to societal challenges.

Synthesis and peptide functionalization of hyperbranched poly(arylene oxindole) towards versatile biomaterials

An azide derivative of hyperbranched poly(arylene oxindole) is synthesized for postgrafting by CuAAC. RGDS functionalization promotes cell attachment and proliferation.

Enhanced Targeted Gene Transduction: AAV2 Vectors Conjugated to Multiple Aptamers via Reducible Disulfide Linkages

Enhanced targeted gene transduction by AAV2 vectors is achieved by linking the vector to multiple sgc8 aptamers, which are selective for cell membrane protein PTK7. Aptamer molecules are conjugated to multiple sites on a DNA dendrimer (G-sgc8), which is then linked to AAV2 via a dithiobis(succinimidyl propionate) cross-linker containing a disulfide group, which can facilitate the release of AAV2 vectors by reaction with the reduced form of intracellular glutathione. The G-sgc8-AAV2 vectors showed a 21-fold enhancement in binding affinity and an enhanced ability to protect sgc8 aptamers against nuclease degradation to cells expressing PTK7 compared to single aptamer-AAV2 conjugates. The transduction efficiency was tested by loading AAV2 with the gene for green fluorescent protein. Therefore, this modified recombinant vector is an attractive and promising tool for targeted biomedical applications.

Conjugation Dependent Interaction of Folic Acid with Folate Binding Protein

Serum proteins play a critical role in the transport, uptake, and efficacy of targeted drug therapies, and here we investigate the interactions between folic acid-polymer conjugates and serum folate binding protein (FBP), the soluble form of the cellular membrane-bound folate receptor. We demonstrate that both choice of polymer and method of ligand conjugation affect the interactions between folic acid-polymer conjugates and serum FBP, resulting in changes in the folic acid-induced protein aggregation process. We have previously demonstrated that individual FBP molecules self-aggregate into nanoparticles at physiological concentrations. When poly(amidoamine) dendrimer-folic acid conjugates bound to FBP, the distribution of nanoparticles was preserved. However, the dendritic conjugates produced larger nanoparticles than those formed in the presence of physiologically normal human levels of folic acid, and the conjugation method affected particle size distribution. In contrast, poly(ethylene glycol)-folic acid conjugates demonstrated substantially reduced binding to FBP, did not cause folic acid-induced aggregation, and fully disrupted FBP self-aggregation. On the basis of these results, we discuss the potential implications for biodistribution, trafficking, and therapeutic efficacy of targeted nanoscale therapeutics, especially considering the widespread clinical use of poly(ethylene glycol) conjugates. We highlight the importance of considering specific serum protein interactions in the rational design of similar nanocarrier systems. Our results suggest that prebinding therapeutic nanocarriers to serum FBP may allow folate-specific metabolic pathways to be exploited for delivery while also affording benefits of utilizing an endogenous protein as a vector.

Photothermal, Targeting, Theranostic Near-Infrared Nanoagent with SN38 against Colorectal Cancer for Chemothermal Therapy

Cancer research regarding near-infrared (NIR) agents for chemothermal therapy (CTT) has shown that agents with specific functions are able to inhibit tumor growth. The aim of current study was to optimize CTT efficacy for treatment of colorectal cancer (CRC) by exploring strategies which can localize high temperature within tumors and maximize chemotherapeutic drug uptake. We designed a new and simple multifunctional NIR nanoagent composed of the NIR cyanine dye, polyethylene glycol, and a cyclic arginine-glycine-aspartic acid peptide and loaded with the anti-CRC chemotherapeutic agent, 7-ethyl-10-hydroxy-camptothecin (SN38). Each component of this nanoagent exhibited its specific functions that help boost CTT efficacy. The results showed that this nanoagent greatly strengthens the theranostic effect of SN38 and CTT against CRC due to its NIR imaging ability, photothermal, enhanced permeability and retention (EPR) effect, reticuloendothelial system avoidance, and angiogenic blood vessel-targeting properties. This NIR nanoagent will help facilitate development of new strategies for treating CRC.

Limiting the valence: advancements and new perspectives on patchy colloids, soft functionalized nanoparticles and biomolecules

Artistic representation of limited valance units consisting of a soft core (in blue) and a small number of flexible bonding patches (in orange).

Facile fabrication of poly(acrylic acid) coated chitosan nanoparticles with improved stability in biological environments

Chitosan is one of the most important and commonly used natural polysaccharides in drug delivery for its biocompatible and biodegradable properties. However, poor blood circulation of the chitosan nanoparticles due to their cationic nature is one of the major bottlenecks of chitosan-based drug delivery systems. To address this problem, a versatile platform based on poly(acrylic acid) (PAA) coated ionically cross-linked chitosan/tripolyphosphate nanoparticles (CTS/TPP-PAA NPs), is reported. The zeta potentials of CTS/TPP and CTS/TPP-PAA NPs are approximately 33mV and -25mV, respectively. CTS/TPP NPs quickly aggregate in PBS (phosphate buffered saline) and DMEM (Dulbecco's modified Eagle's medium). Conversely, CTS/TPP-PAA NPs exhibit excellent colloidal stability in plasma solution for more than 24h. The PAA coating also endows CTS/TPP-PAA NPs with decreased protein adsorption capacity and improved buffering capacity. More importantly, the residual carboxyl and amino groups on CTS/TPP-PAA NPs provide abundant reactive sites for further functional modifications. Therefore, the CTS/TPP-PAA NPs reported here may be useful as an alternative drug delivery system.

Synthesis, self-assembly, and immunological activity of α-galactose-functionalized dendron-lipid amphiphiles

Nanoassemblies presenting multivalent displays of biologically active carbohydrates are of significant interest for a wide array of biomedical applications ranging from drug delivery to immunotherapy. In this study, glycodendron-lipid hybrids were developed as a new and tunable class of dendritic amphiphiles. A modular synthesis was used to prepare dendron-lipid hybrids comprising distearylglycerol and 0 through 4th generation polyester dendrons with peripheral protected amines. Following deprotection of the amines, an isothiocyanate derivative of C-linked α-galactose (α-Gal) was conjugated to the dendron peripheries, affording amphiphiles with 1 to 16 α-Gal moieties. Self-assembly in water through a solvent exchange process resulted in vesicles for the 0 through 2^nd generation systems and micelles for the 3^rd and 4^th generation systems. The critical aggregation concentrations decreased with increasing dendron generation, suggesting that the effects of increasing molar mass dominated over the effects of increasing the hydrophilic weight fraction. The binding of the assemblies to Griffonia simplicifolia Lectin I (GSL 1), a protein with specificity for α-Gal was studied by quantifying the binding of fluorescently labeled assemblies to GSL 1-coated beads. It was found that binding was enhanced for amphiphiles containing higher generation dendrons. Despite their substantial structural differences with the natural ligands for the CD1d receptor, the glycodendron-lipid hybrids were capable of stimulating invariant natural killer T (iNKT) cells, a class of innate-like T cells that recognize lipid and glycolipid antigens presented by CD1d and that are implicated in a wide range of diseases and conditions including but not limited to infectious diseases, diabetes and cancer.

Sticky Patches on Lipid Nanoparticles Enable the Selective Targeting and Killing of Untargetable Cancer Cells

Effective targeting by uniformly functionalized nanoparticles is limited to cancer cells expressing at least two copies of targeted receptors per nanoparticle footprint (approximately ≥2 × 10(5) receptor copies per cell); such a receptor density supports the required multivalent interaction between the neighboring receptors and the ligands from a single nanoparticle. To enable selective targeting below this receptor density, ligands on the surface of lipid vesicles were displayed in clusters that were designed to form at the acidic pH of the tumor interstitium. Vesicles with clustered HER2-targeting peptides within such sticky patches (sticky vesicles) were compared to uniformly functionalized vesicles. On HER2-negative breast cancer cells MDA-MB-231 and MCF7 {expressing (8.3 ± 0.8) × 10(4) and (5.4 ± 0.9) × 10(4) HER2 copies per cell, respectively}, only the sticky vesicles exhibited detectable specific targeting (KD ≈ 49-69 nM); dissociation (0.005-0.009 min(-1)) and endocytosis rates (0.024-0.026 min(-1)) were independent of HER2 expression for these cells. MDA-MB-231 and MCF7 were killed only by sticky vesicles encapsulating doxorubicin (32-40% viability) or α-particle emitter (225)Ac (39-58% viability) and were not affected by uniformly functionalized vesicles (>80% viability). Toxicities on cardiomyocytes and normal breast cells (expressing HER2 at considerably lower but not insignificant levels) were not observed, suggesting the potential of tunable clustered ligand display for the selective killing of cancer cells with low receptor densities.

Increase in Dye:Dendrimer Ratio Decreases Cellular Uptake of Neutral Dendrimers in RAW Cells

Neutral generation 3 poly(amidoamine) dendrimers were labeled with Oregon Green 488 (G3-OG_n) to obtain materials with controlled fluorophore:dendrimer ratios (n = 1-2), a mixture containing mostly 3 dyes per dendrimer, a mixture containing primarily 4 or more dyes per dendrimer (n = 4+), and a stochastic mixture (n = 4_avg). The UV absorbance of the dye conjugates increased linearly as n increased and the fluorescence emission decreased linearly as n increased. Cellular uptake was studied in RAW cells and HEK 293A cells as a function of the fluorophore:dendrimer ratio (n). The cellular uptake of G3-OG _n (n = 3, 4+, 4_avg) into RAW cells was significantly lower than G3-OG _n (n = 1, 2). The uptake of G3-OG _n (n = 3, 4+, 4_avg) into HEK 293A cells was not significantly different from G3-OG₁. Thus, the fluorophore:dendrimer ratio was observed to change the extent of uptake in the macrophage uptake mechanism but not in the HEK 293A cell. This difference in endocytosis indicates the presence of a pathway in the macrophage that is sensitive to hydrophobicity of the particle.

Binding kinetics and multi-bond: Finding correlations by synthesizing interactions between ligand-coated bionanoparticles and receptor surfaces

The number of bonds formed between one single bionanoparticle and many surface receptors is an important subject to be studied but is seldom quantitatively investigated. A new evaluation of the correlation between binding kinetics and number of bonds is presented by varying ligand density and receptor density. An experimental system was developed using measurements with surface plasmon resonance spectroscopy. A corresponding multi-site adsorption model elucidated the correlation. The results show that with the increase of the receptor density, the adsorption rate first decreased when the number of bonds was below a maximum value and then increased when the number of bonds stayed at this maximum value. The investigation on ligand density variation suggests that the coating density on top of the bionanoparticle surface may have a particular value below which more ligand will accelerate the adsorption rate. The ratio of ligand amount bound by the receptors to the total ligand amount associated with a single bionanoparticle will remain constant even if one attaches more ligands to a bionanoparticle. We envision that the bionanoparticle desorption will not depend on density changes from either ligand or receptor when the number of bonds reaches a specific efficient value.

Substrate-Triggered Exosite Binding: Synergistic Dendrimer/Folic Acid Action for Achieving Specific, Tight-Binding to Folate Binding Protein

Polymer-ligand conjugates are designed to bind proteins for applications as drugs, imaging agents, and transport scaffolds. In this work, we demonstrate a folic acid (FA)-triggered exosite binding of a generation five poly(amidoamine) (G5 PAMAM) dendrimer scaffold to bovine folate binding protein (bFBP). The protein exosite is a secondary binding site on the protein surface, separate from the FA binding pocket, to which the dendrimer binds. Exosite binding is required to achieve the greatly enhanced binding constants and protein structural change observed in this study. The G5Ac-COG-FA1.0 conjugate bound tightly to bFBP, was not displaced by a 28-fold excess of FA, and quenched roughly 80% of the initial fluorescence. Two-step binding kinetics were measured using the intrinsic fluorescence of the FBP tryptophan residues to give a KD in the low nanomolar range for formation of the initial G5Ac-COG-FA1.0/FBP* complex, and a slow conversion to the tight complex formed between the dendrimer and the FBP exosite. The extent of quenching was sensitive to the choice of FA-dendrimer linker chemistry. Direct amide conjugation of FA to G5-PAMAM resulted in roughly 50% fluorescence quenching of the FBP. The G5Ac-COG-FA, which has a longer linker containing a 1,2,3-triazole ring, exhibited an ∼80% fluorescence quenching. The binding of the G5Ac-COG-FA1.0 conjugate was compared to poly(ethylene glycol) (PEG) conjugates of FA (PEGn-FA). PEG2k-FA had a binding strength similar to that of FA, whereas other PEG conjugates with higher molecular weight showed weaker binding. However, no PEG conjugates gave an increased degree of total fluorescence quenching.

Polymeric drugs: Advances in the development of pharmacologically active polymers

Synthetic polymers play a critical role in pharmaceutical discovery and development. Current research and applications of pharmaceutical polymers are mainly focused on their functions as excipients and inert carriers of other pharmacologically active agents. This review article surveys recent advances in alternative pharmaceutical use of polymers as pharmacologically active agents known as polymeric drugs. Emphasis is placed on the benefits of polymeric drugs that are associated with their macromolecular character and their ability to explore biologically relevant multivalency processes. We discuss the main therapeutic uses of polymeric drugs as sequestrants, antimicrobials, antivirals, and anticancer and anti-inflammatory agents.

Targeting breast cancer with sugar-coated carbon nanotubes

AIMS

To evaluate the use of glucosamine functionalized multiwalled carbon nanotubes (glyco-MWCNTs) for breast cancer targeting.

MATERIALS & METHODS

Two types of glucosamine functionalized MWCNTs were developed (covalently linked glucosamine and non-covalently phospholipid-glucosamine coated) and evaluated for their potential to bind and target breast cancer cells in vitro and in vivo.

RESULTS & CONCLUSION

Binding of glyco-MWCNTs in breast cancer cells is mediated by specific interaction with glucose transporters. Glyco-MWCNTs prepared by non-covalent coating with phospholipid-glucosamine displayed an extended blood circulation time, delayed urinary clearance, low tissue retention and increased breast cancer tumor accumulation in vivo. These studies lay the foundation for development of a cancer diagnostic agent based upon glyco-MWCNTs with the potential for superior accuracy over current radiopharmaceuticals.

Fluorophore:dendrimer ratio impacts cellular uptake and intracellular fluorescence lifetime

G5-NH2-TAMRAn (n = 1-4, 5+, and 1.5(avg)) were prepared with n = 1-4 as a precise dye:dendrimer ratio, 5+ as a mixture of dendrimers with 5 or more dye per dendrimer, and 1.5(avg) as a Poisson distribution of dye:dendrimer ratios with a mean of 1.5 dye per dendrimer. The absorption intensity increased sublinearly with n whereas the fluorescence emission and lifetime decreased with an increasing number of dyes per dendrimer. Flow cytometry was employed to quantify uptake into HEK293A cells. Dendrimers with 2-4 dyes were found to have greater uptake than dendrimer with a single dye. Fluorescence lifetime imaging microscopy (FLIM) showed that the different dye:dendrimer ratio alone was sufficient to change the fluorescence lifetime of the material observed inside cells. We also observed that the lifetime of G5-NH2-TAMRA5+ increased when present in the cell as compared to solution. However, cells treated with G5-NH2-TAMRA1.5(avg) did not exhibit the high lifetime components present in G5-NH2-TAMRA1 and G5-NH2-TAMRA5+. In general, the effects of the dye:dendrimer ratio on fluorescence lifetime were of similar magnitude to environmentally induced lifetime shifts.

Multivalent peptides displayed on OEGMA-based copolymers for the modulation of protein–protein interactions

We report a new class of copolymer–peptide conjugates which exploits the comb-shaped pOEGMA as a polymeric backbone, into which multiple copies of peptide chains that can modulate intracellular p53–Mdm2 or p53–Mdm4 protein interactions are incorporated.

The dendrimer paradox – high medical expectations but poor clinical translation

This review was written with the intention to critically evaluate the status of dendrimers as drug carriers and find answers as to why this class of compounds has not translated into the clinic despite 40 years of research.