Macromolecular therapeutics

Construction of carboxymethyl chitosan-based nanoparticles of hypoxia response for co-loading doxorubicin and tanshinone IIA

As a first-line drug for breast cancer chemotherapy, the effectiveness of doxorubicin (DOX) is challenged by high doses and high toxicity. Studies showed the combination of Tanshinone IIA (TSIIA) and DOX could enhance the efficacy of DOX for cancer and reduce the toxic effects to normal tissues. Unfortunately, free drugs are easily metabolized in the systemic circulation, which are less prone to aggregation at the tumor site to exert anticancer efficacy. In present study, we prepared a carboxymethyl chitosan-based hypoxia-responsive nanoparticles loaded with DOX and TSIIA for the treatment of breast cancer. The results demonstrated that these hypoxia-responsive nanoparticles not only improved the delivery efficiency of the drugs but also enhanced the therapeutic efficacy of DOX. The average size of nanoparticles was about 200-220 nm, the optimal drug loading and encapsulation efficiency of TSIIA in DOX/TSIIA NPs were 9.06 % and 73.59 %, respectively. Hypoxia-responsive behavior were recorded in vitro, while the synergistic efficacy is significantly exhibited in vivo and the tumor inhibitory rate was 85.87 %. Notably, TUNEL assay and immunofluorescence staining verified that the combined nanoparticles exerted a synergistic anti-tumor effect by inhibiting tumor fibrosis, decreasing the expression of HIF-1α and inducing tumor cell apoptosis. Collectively, this carboxymethyl chitosan-based hypoxia-responsive nanoparticles could have promising application prospect for effective breast cancer therapy.

Bone-targeting polyphosphodiesters that promote osteoblastic differentiation

Polymers for pharmaceutical use have been attractive in medical treatments because of the conjugation of multifunctional components and their long circulation time in the blood stream. Bone-targeted drug delivery systems are also no exceptional, and several polymers have been proposed for the treatment of bone diseases, such as cancer metastasis and osteoporosis. Herein, we report that polyphosphodiesters (PPDEs) have a potential to enhance osteoblastic differentiation, and they have a targeting ability to bone tissues in vivo. Two types of PPDEs, poly (ethylene sodium phosphate) (PEP•Na) and poly (propylene sodium phosphate) (PPP•Na), have been synthesized. Regardless of the alkylene structure in the main chain of PPDEs, the gene expression of osteoblast-specific transcription factors and differentiation markers of mouse osteoblastic-like cells (MC3T3-E1 cells) cultured in a differentiation medium was significantly upregulated by the addition of PPDEs. Moreover, it was also clarified that the signaling pathway related to cytoplasmic calcium ions was activated by PPDEs. The mineralization of MC3T3-E1 cells has a similar trend with its gene expression and is synergistically enhanced by PPDEs with β-glycerophosphate. The biodistribution of fluorescence-labeled PPDEs was also determined after intravenous injection in mice. PPDEs accumulated well in the bone through the blood stream, whereas polyphosphotriesters (PPTEs) tended to be excreted from the kidneys. Hydrophilic PEP•Na showed a superior bone affinity as compared with PPP•Na. PPDEs could be candidate polymers for the restoration of bone remodeling and bone-targeting drug delivery platforms.

Spontaneous shrinkage drives macromolecule encapsulation into layer-by-layer assembled biopolymer microgels

HYPOTHESIS

Recently, the anomalous shrinkage of surface-supported hyaluronate/poly-l-lysine (HA/PLL) microgels (µ-gels), which exceeds that reported for any other multilayer-based systems, has been reported [1]. The current study investigates the capability of these unique µ-gels for the encapsulation and retention of macromolecules, and proposes the shrinkage-driven assembly of biopolymer-based µ-gels as a novel tool for one-step surface biofunctionalization.

EXPERIMENTS

A set of dextrans (DEX) and their charged derivatives - carboxymethyl (CM)-DEX and diethylaminoethyl (DEAE)-DEX - has been utilized to evaluate the effects of macromolecular mass and net charge on µ-gel shrinkage and macromolecule entrapment. µ-gels formation on the surface of silicone catheters exemplifies their potential to tailor biointerfaces.

FINDINGS

Shrinkage-driven µ-gel formation strongly depends on the net charge and mass content of encapsulated macromolecules. Inclusion of neutral DEX decreases the degree of shrinkage several times, whilst charged DEXs adopt to the backbone of oppositely charged polyelectrolytes, resulting in shrinkage comparable to that of non-loaded µ-gels. Retention of CM-DEX in µ-gels is significantly higher compared to DEAE-DEX. These insights into the mechanisms of macromolecular entrapment into biopolymer-based µ-gels promotes fundamental understanding of molecular dynamics within the multilayer assemblies. Organization of biodegradable µ-gels at biomaterial surfaces opens avenues for their further exploitation in a diverse array of bioapplications.

Polymer nanomedicines with enzymatically triggered activation: A comparative study of in vitro and in vivo anti-cancer efficacy related to the spacer structure

Polymer nanomedicines with anti-tumor activity should exhibit sufficient stability during systemic circulation to the target tissue; however, they should release the active drug selectively in the tumor. Thus, choice of a tumor-specific stimuli-sensitive spacer between the drug and the carrier is critical. Here, a series of polymer conjugates of anti-cancer drugs doxorubicin and pirarubicin covalently bound to copolymers based on N-(2-hydroxypropyl)methacrylamide via various enzymatically cleavable oligopeptide spacers were prepared and characterized. The highest rate of the drug release from the polymer carriers in presence of the lysosomal protease cathepsin B was determined for the copolymers with Val-Cit-Aba spacer. Copolymers containing pirarubicin were more cytotoxic and showed higher internalization rate than the corresponding doxorubicin counterparts. The conjugates containing GFLG and Val-Cit-Aba spacers exhibited the highest anti-tumor efficacy in vivo against murine sarcoma S-180, the highest rate of the enzymatically catalyzed drug release, and the highest cytotoxicity in vitro.

Active transport nanochelators for the reduction of liver iron burden in iron overload

Liver dysfunction and failure account for a major portion of premature deaths in patients suffering from various iron associated pathogeneses, particularly primary and secondary iron overload disorders, despite intensive treatment. The liver is a central player in iron homeostasis and a major iron storage organ, and currently, there are no active approaches for the excretion of excess liver iron. Herein, we report a new method for the rapid reduction of iron burden in iron overload diseases by developing a new class of liver targeted nanochelators with favorable pharmacokinetics and biodistribution. The new nanochelators bypass the reticuloendothelial system and specifically target hepatocytes without non-specific accumulation in other organs. The targeted nanochelators bound and neutralized excess iron in the liver and from the vasculature and, eventually leading to rapid hepatobiliary excretion of labile iron. Further, these rapidly excreted nanochelators did not induce toxicity in the liver, were highly cytocompatible in both iron overload and non-loaded conditions, and were promising in mitigating iron triggered free radical oxidative damage. These studies provide key insights into the development of organ targeted nanochelating systems and the rapid reduction of iron burden in vivo. This methodology allows for further development of nanotherapeutics for specific iron overload diseases.

Aggregation of Lactoferrin Caused by Droplet Atomization Process via a Two-Fluid Nozzle: The Detrimental Effect of Air-Water Interfaces

Biological macromolecules, especially therapeutic proteins, are delicate and highly sensitive to denaturation from stresses encountered during the manufacture of dosage forms. Thin-film freeze-drying (TFFD) and spray freeze-drying (SFD) are two processes used to convert liquid forms of protein into dry powders. In the production of inhalable dry powders that contain proteins, these potential stressors fall into three categories based on their occurrence during the primary steps of the process: (1) droplet formation (e.g., the mechanism of droplet formation, including spray atomization), (2) freezing, and (3) frozen water removal (e.g., sublimation). This study compares the droplet formation mechanism used in TFFD and SFD by investigating the effects of spraying on the stability of proteins, using lactoferrin as a model. This study considers various perspectives on the denaturation (e.g., conformation) of lactoferrin after subjecting the protein solution to the atomization process using a pneumatic two-fluid nozzle (employed in SFD) or a low-shear drop application through the nozzle. The surface activity of lactoferrin was examined to explore the interfacial adsorption tendency, diffusion, and denaturation process. Subsequently, this study also investigates the secondary and tertiary structure of lactoferrin and the quantification of monomers, oligomers, and, ultimately, aggregates. The spraying process affected the tertiary structure more negatively than the tightly woven secondary structure, resulting in the peak position corresponding to the tryptophan (Trp) residues red-shifting by 1.5 nm. This conformational change can either (a) be reversed at low concentrations via relaxation or (b) proceed to form irreversible aggregates at higher concentrations. Interestingly, when the sample was allowed to progress into micrometer-sized aggregates, such a dramatic change was not detected using methods such as size-exclusion chromatography, polyacrylamide gel electrophoresis, and dynamic light scattering at 173°. A more complete understanding of the heterogeneous protein sample was achieved only through a combination of 173 and 13° backward and forward scattering, a combination of derived count rate measurements, and microflow imaging (MFI). After studying the impact of droplet formation mechanisms on aggregation tendency of lactoferrin, we further investigated two additional model proteins with different surface activity: bovine IgG (serving as a non surface-active negative reference), and β-galactosidase (another surface-active protein). The results corroborated the lactoferrin findings that spray-atomization-related stress-induced protein aggregation was much more pronounced for proteins that are surface active (lactoferrin and β-galactosidase), but it was minimal for non-surface-active protein (bovine IgG). Finally, compared to the low-shear dripping used in the TFFD process, lactoferrin underwent a relatively fast conformational change upon exposure to the high air-water interface of the two-fluid atomization nozzle used in the SFD process as compared to the low shear dripping used in the TFFD process. The interfacial-induced denaturation that occurred during spraying was governed primarily by the size of the atomized droplets, regardless of the duration of exposure to air. The percentage of denatured protein population and associated activity loss, in the case of β-galactosidase, was determined to range from 2 to 10% depending on the air-flow rate of the spraying process.

GSH-sensitive polymeric prodrug: Synthesis and loading with photosensitizers as nanoscale chemo-photodynamic anti-cancer nanomedicine

Precisely delivering combinational therapeutic agents has become a crucial challenge for anti-tumor treatment. In this study, a novel redox-responsive polymeric prodrug (molecular weight, MW: 93.5 kDa) was produced by reversible addition-fragmentation chain transfer (RAFT) polymerization. The amphiphilic block polymer-doxorubicin (DOX) prodrug was employed to deliver a hydrophobic photosensitizer (PS), chlorin e6 (Ce6), and the as-prepared nanoscale system [NPs(Ce6)] was investigated as a chemo-photodynamic anti-cancer agent. The glutathione (GSH)-cleavable disulfide bond was inserted into the backbone of the polymer for biodegradation inside tumor cells, and DOX conjugated onto the polymer with a disulfide bond was successfully released intracellularly. NPs(Ce6) released DOX and Ce6 with their original molecular structures and degraded into segments with low MWs of 41.2 kDa in the presence of GSH. NPs(Ce6) showed a chemo-photodynamic therapeutic effect to kill 4T1 murine breast cancer cells, which was confirmed from a collapsed cell morphology, a lifted level in the intracellular reactive oxygen species, a reduced viability and induced apoptosis. Moreover, ex vivo fluorescence images indicated that NPs(Ce6) retained in the tumor, and exhibited a remarkable in vivo anticancer efficacy. The combinational therapy showed a significantly increased tumor growth inhibition (TGI, 58.53%). Therefore, the redox-responsive, amphiphilic block polymeric prodrug could have a great potential as a chemo-photodynamic anti-cancer agent.

PEGylated Oligothioetheramide Prodrugs Activated by Host Serum Proteases

Due to the increasing prominence of antibiotic resistance, novel drug discovery and delivery approaches targeting bacteria are essential. In this work we evaluate a prodrug design to improve the cytotoxic profile of polycationic oligothioetheramides (oligoTEAs), which are promising antimicrobials. Herein we chemically modify the oligoTEA, PDT-4G, with a polyethylene glycol (PEG) and show that 1, 2, and 5 kDa PEGs mitigate cytotoxicity. As PEGylation reduces antibacterial activity, we evaluate two peptide linkers which, unlike oligoTEAs, are susceptible to proteolytic cleavage in serum. To gain insight into the prodrug reactivation, two linkers were tested, the 5-residue peptide sequence LMPTG, and the dipeptide sequence VC-PABC. In the presence of 20 % serum, prodrugs made with the VC-PABC linker successfully inhibited bacterial growth. Overall, we observed reactivation of oligoTEAs facilitated by serum protease cleavage of the peptide linkers. This work opens the door to the future design of antimicrobial prodrugs with tunable release profiles.

Predictive Platforms of Bond Cleavage and Drug Release Kinetics for Macromolecule–Drug Conjugates

Macromolecule–drug conjugates (MDCs) occupy a critical niche in modern pharmaceuticals that deals with the assembly and combination of a macromolecular carrier, a drug cargo, and a linker toward the creation of effective therapeutics. Macromolecular carriers such as synthetic biocompatible polymers and proteins are often exploited for their inherent ability to improve drug circulation, prevent off-target drug cytotoxicity, and widen the therapeutic index of drugs. One of the most significant challenges in MDC design involves tuning their drug release kinetics to achieve high spatiotemporal precision. This level of control requires a thorough qualitative and quantitative understanding of the bond cleavage event. In this review, we highlight specific research findings that emphasize the importance of establishing a precise structure–function relationship for MDCs that can be used to predict their bond cleavage and drug release kinetic parameters.

1-MT grafted carboxymethyl chitosan and its nanoparticles: Preparation, characterization and evaluation

This work aims to synthesize two novel 1-MT (1-Methyl-DL-tryptophan) grafted CMCS (carboxymethyl chitosan) polymer prodrugs CMCS-amido-1-MT and CMCS-ester-1-MT, and to further manufacture their nanoparticles for potential biomedical applications. The polymeric prodrugs are prepared by three-step chemical synthesis. The chemical structure of drugs is confirmed by FTIR and 1H-NMR. The drug loadings of the CMCS-amido-1-MT NPs and CMCS-ester-1-MT NPs are 11.43% and 10.18%, respectively. The surface morphology of the nanoparticles is spherical or nearly spherical, while the surface is smooth and the size distribution is uniform. The average particle size is both about 200 nm, while the polydispersity index is both about 0.15. The nanoparticles have a negative charge on the surface. The particle size and its distribution change little, when the two nanoparticles are tested in the simulated blood pH environment for 7 days. However, only the CMCS-ester-1-MT nanoparticles are pH-sensitive. The cell toxicity of the CMCS-ester-1-MT nanoparticles and the original drug are both in a dose- and time-dependent manner, while the nanoparticles enter cells by endocytosis. In ECA109 cells, the CMCS-ester-1-MT nanoparticles and the original drug both induce the apoptosis. CMCS-ester-1-MT NPs can activate the ATF4/CHOP pathway in endoplasmic reticulum stress, and achieve cancer suppression through mitochondrial-related apoptosis.

HPMA Copolymer-Based Nanomedicines in Controlled Drug Delivery

Recently, numerous polymer materials have been employed as drug carrier systems in medicinal research, and their detailed properties have been thoroughly evaluated. Water-soluble polymer carriers play a significant role between these studied polymer systems as they are advantageously applied as carriers of low-molecular-weight drugs and compounds, e.g., cytostatic agents, anti-inflammatory drugs, antimicrobial molecules, or multidrug resistance inhibitors. Covalent attachment of carried molecules using a biodegradable spacer is strongly preferred, as such design ensures the controlled release of the drug in the place of a desired pharmacological effect in a reasonable time-dependent manner. Importantly, the synthetic polymer biomaterials based on N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers are recognized drug carriers with unique properties that nominate them among the most serious nanomedicines candidates for human clinical trials. This review focuses on advances in the development of HPMA copolymer-based nanomedicines within the passive and active targeting into the place of desired pharmacological effect, tumors, inflammation or bacterial infection sites. Specifically, this review highlights the safety issues of HPMA polymer-based drug carriers concerning the structure of nanomedicines. The main impact consists of the improvement of targeting ability, especially concerning the enhanced and permeability retention (EPR) effect.

Targeted Nanotherapeutics for Respiratory Diseases: Cancer, Fibrosis, and Coronavirus

Systemic delivery of therapeutics for treatment of lung diseases has several limitations including poor organ distribution of delivered payload with relatively low accumulation of active substances in the lungs and severe adverse side effects. In contrast, nanocarrier based therapeutics provide a broad range of opportunities due to their ability to encapsulate substances with different aqueous solubility, transport distinct types of cargo, target therapeutics specifically to the deceased organ, cell, or cellular organelle limiting adverse side effects and increasing the efficacy of therapy. Moreover, many nanotherapeutics can be delivered by inhalation locally to the lungs avoiding systemic circulation. In addition, nanoscale based delivery systems can be multifunctional, simultaneously carrying out several tasks including diagnostics, treatment and suppression of cellular resistance to the treatment. Nanoscale delivery systems improve the clinical efficacy of conventional therapeutics allowing new approaches for the treatment of respiratory diseases which are difficult to treat or possess intrinsic or acquired resistance to treatment. The present review summarizes recent advances in the development of nanocarrier based therapeutics for local and targeted delivery of drugs, nucleic acids and imaging agents for diagnostics and treatment of various diseases such as cancer, cystic fibrosis, and coronavirus.

Say no to drugs: Bioactive macromolecular therapeutics without conventional drugs

The vast majority of nanomedicines (NM) investigated today consists of a macromolecular carrier and a drug payload (conjugated or encapsulated), with a purpose of preferential delivery of the drug to the desired site of action, either through passive accumulation, or by active targeting via ligand-receptor interaction. Several drug delivery systems (DDS) have already been approved for clinical use. However, recent reports are corroborating the notion that NM do not necessarily need to include a drug payload, but can exert biological effects through specific binding/blocking of important target proteins at the site of action. The seminal work of Kopeček et al. on N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers containing biorecognition motifs (peptides or oligonucleotides) for crosslinking cell surface non-internalizing receptors of malignant cells and inducing their apoptosis, without containing any low molecular weight drug, led to the definition of a special group of NM, termed Drug-Free Macromolecular Therapeutics (DFMT). Systems utilizing this approach are typically designed to employ pendant targeting-ligands on the same macromolecule to facilitate multivalent interactions with receptors. The lack of conventional small molecule drugs reduces toxicity and adverse effects at off-target sites. In this review, we describe different types of DFMT that possess biological activity without attached low molecular weight drugs. We classified the relevant research into several groups by their mechanisms of action, and compare the advantages and disadvantages of these different approaches. We show that identification of target sites, specificity of attached targeting ligands, binding affinity and the synthesis of carriers of defined size and ligand spacing are crucial aspects of DFMT development. We further discuss how knowledge in the field of NM accumulated in the past few decades can help in the design of a successful DFMT to speed up the translation into clinical practice.

Functional gadolinium-based nanoscale systems for cancer theranostics

Cancer theranostics is a new strategy for combating cancer that integrates cancer imaging and treatment through theranostic agents to provide an efficient and safe way to improve cancer prognosis. Design and synthesis of these cancer theranostic agents are crucial since these agents are required to be biocompatible, tumor-specific, imaging distinguishable and therapeutically efficacious. In this regard, several types of gadolinium (Gd)-based nanomaterials have been introduced to combine different therapeutic agents with Gd to enhance the efficacy of therapeutic agents. At the same time, the entire treatment procedure could be monitored via imaging tools due to incorporation of Gd ions, Gd chelates and Gd/other imaging probes in the theranostic agents. This review aims to overview recent advances in the Gd-based nanomaterials for cancer theranostics and perspectives for Gd nanomaterial-based cancer theranostics are provided.

Telodendrimer-Based Macromolecular Drug Design using 1,3-Dipolar Cycloaddition for Applications in Biology

An architectural polymer containing hydrophobic isoxazole-based dendron and hydrophilic polyethylene glycol linear tail is prepared by a combination of the robust ZnCl2 catalyzed alkyne-nitrile oxide 1,3-dipolar cycloaddition and esterification chemistry. This water soluble amphiphilic telodendrimer acts as a macromolecular biologically active agent and shows concentration dependent reduction of glioblastoma (U251) cell survival.

Nanotechnology based therapeutics for lung disease

Nanomedicine is a multidisciplinary research field with an integration of traditional sciences such as chemistry, physics, biology and materials science. The application of nanomedicine for lung diseases as a relatively new area of interdisciplinary science has grown rapidly over the last 10 years. Promising research outcomes suggest that nanomedicine will revolutionise the practice of medicine, through the development of new approaches in therapeutic agent delivery, vaccine development and nanotechnology-based medical detections. Nano-based approaches in the diagnosis and treatment of lung diseases will, in the not too distant future, change the way we practise medicine. This review will focus on the current trends and developments in the clinical translation of nanomedicine for lung diseases, such as in the areas of lung cancer, cystic fibrosis, asthma, bacterial infections and COPD.

Design of Safe Nanotherapeutics for the Excretion of Excess Systemic Toxic Iron

Chronic transfusion of red blood cells (RBCs) to patients with β-thalassemia, sickle cell disease, and other acquired anemic disorders generates significant amounts of bioactive iron deposits in the body. The inactivation and excretion of redox active iron(III) from the blood pool and organs are critical to prevent organ damage, and are the focus of iron chelation therapy (ICT) using low molecular weight Fe(III) specific chelators. However, the current ICT is suboptimal because of the short circulation time of chelators, toxicity, severe side effects, difficult regime of administration, and patient noncompliance. To address this issue, we have designed long circulating and biodegradable nanoconjugates with enhanced circulation time and well-defined biodegradability to improve iron excretion and avoid nonspecific organ accumulation. A series of iron chelating nanoconjugates were generated with deferoxamine (DFO) as the iron(III) specific chelator using polymer scaffolds containing structurally different acidic pH sensitive ketal groups. The type of degradation linkages used in the polymer scaffold significantly influenced the vascular residence time, biodistribution, and mode of excretion of chelators in mice. Remarkably, the conjugate, BGD-60 (140 kDa; R h, 10.6 nm; cyclic ketal), exhibited the long circulation half-life (t 1/2β, 64 h), a 768-fold increase compared to DFO, and showed minimal polymer accumulation in major organs. The nanoconjugates were found to be nontoxic and excreted iron significantly better than DFO in iron overloaded mice. BGD-60 showed greater iron mobilization from plasma (p = 0.0390), spleen (p < 0.0001), and pancreas (p < 0.0001) whereas BDD-200 (340 kDa; R h, 13.7 nm; linear ketal) mobilized iron significantly better from the spleen, liver, and pancreas (p < 0.0001, p < 0.0001, and p < 0.0001, respectively) compared to DFO at equivalent doses. The nanoconjugate's favorable long blood circulation time, biodegradability, and iron excretion profiles highlight their potential for future clinical translation.

Anticancer polymers designed for killing dormant prostate cancer cells

The discovery of anticancer therapeutics effective in eliminating dormant cells is a significant challenge in cancer biology. Here, we describe new synthetic polymer-based anticancer agents that mimic the mode of action of anticancer peptides. These anticancer polymers developed here are designed to capture the cationic, amphiphilic traits of anticancer peptides. The anticancer polymers are designed to target anionic lipids exposed on the cancer cell surfaces and act by disrupting the cancer cell membranes. Because the polymer mechanism is not dependent on cell proliferation, we hypothesized that the polymers were active against dormant cancer cells. The polymers exhibited cytotoxicity to proliferating prostate cancer. Importantly, the polymer killed dormant prostate cancer cells that were resistant to docetaxel. This study demonstrates a new approach to discover novel anticancer therapeutics.

Reinforcement of polymeric nanoassemblies for ultra-high drug loadings, modulation of stiffness and release kinetics, and sustained therapeutic efficacy

The optimization of current polymeric nanoparticle therapies is restricted by low drug loadings and limited tunability of core properties. To overcome these shortcomings, a novel self-association approach is utilized to fabricate a dual-loaded poly(1,2-glycerol carbonate)-graft-succinic acid-paclitaxel (PGC-PTX) conjugate nanoparticle (NP) in which the physical entrapment of free paclitaxel (PTX) affords unprecedented ultra-high drug loadings >100 wt%, modulation of mechanical stiffness, and tunable release kinetics. Despite high incorporation of free PTX (up to 50 wt%), the dual-loaded PGC-PTX nanocarriers (i.e., PGC-PTX + PTX NPs) exhibit controlled and sustained drug release over 15 days, without burst release effects. Importantly, optimization of drug/material efficiency concomitantly affords improved in vitro efficacy. In vivo, PGC-PTX + PTX NPs are safely administered at doses exceeding the median lethal dose of standard PTX, while a single high dose significantly extends survival relative to weekly PTX administrations in a murine model of peritoneal carcinomatosis.

Main-chain polyacetal conjugates with HIF-1 inhibitors: temperature-responsive, pH-degradable drug delivery vehicles

Main-chain polymer-drug conjugates are prepared from polyacetals (PA) and three hydrophobic diol-based HIF-1 inhibitors. The new conjugates are temperature-responsive with lower critical solution temperature (LCST) behavior and are intrinsically pH-degradable. While soluble in plasma at room temperature, they lose solubility above a target temperature that can be adjusted to virtually any temperature of physicological interest, providing mechanisms for site-specific delivery by active thermal targeting or temperature-induced gelation. The reverse phase transition temperature can be precisely tuned by proper choice of four structural variables that characterize the amphiphilic diol and divinyl ether monomers used in the synthesis, or by adjusting the content of drug incorporated within the polymer. These main-chain PA-drug conjugates also allow for site-specific controlled release as they degrade in acidic microenvironments such as tumors. The degradation rates increase with decreasing pH, degradation products are neutral, and pristine drug is released, without any remnants of the conjugation chemistry.

Templated Polymer Replica Nanoparticles to Facilitate Assessment of Material-Dependent Pharmacokinetics and Biodistribution

Surface modification is frequently used to tailor the interactions of nanoparticles with biological systems. In many cases, the chemical nature of the treatments employed to modify the biological interface (for example attachment of hydrophilic polymers or targeting groups) is the focus of attention. However, isolation of the fundamental effects of the materials employed to modify the interface are often confounded by secondary effects imparted by the underlying substrate. Herein, we demonstrate that polymer replica particles templated from degradable mesoporous silica provide a facile means to evaluate the impact of surface modification on the biological interactions of nanomaterials, independent of the substrate. Poly(ethylene glycol) (PEG), poly(N-(2 hydroxypropyl)methacrylamide) (PHPMA), and poly(methacrylic acid) (PMA) were templated onto mesoporous silica and cross-linked and the residual particles were removed. The resulting nanoparticles, comprising interfacial polymer alone, were then investigated using a range of in vitro and in vivo tests. As expected, the PEG particles showed the best stealth properties, and these trends were consistent in both in vitro and in vivo studies. PMA particles showed the highest cell association in cell lines in vitro and were rapidly taken up by monocytes in ex vivo whole blood, properties consistent with the very high in vivo clearance subsequently seen in rats. In contrast, PHPMA particles showed rapid association with both granulocytes and monocytes in ex vivo whole blood, even though in vivo clearance was less rapid than the PMA particles. Rat studies confirmed better systemic exposure for PEG and PHPMA particles when compared to PMA particles. This study provides a new avenue for investigating material-dependent biological behaviors of polymer particles, irrespective of the properties of the underlying core, and provides insights for the selection of polymer particles for future biological applications.

HPMA Copolymer-Drug Conjugates with Controlled Tumor-Specific Drug Release

Over the past few decades, numerous polymer drug carrier systems are designed and synthesized, and their properties are evaluated. Many of these systems are based on water-soluble polymer carriers of low-molecular-weight drugs and compounds, e.g., cytostatic agents, anti-inflammatory drugs, or multidrug resistance inhibitors, all covalently bound to a carrier by a biodegradable spacer that enables controlled release of the active molecule to achieve the desired pharmacological effect. Among others, the synthetic polymer carriers based on N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers are some of the most promising carriers for this purpose. This review focuses on advances in the development of HPMA copolymer carriers and their conjugates with anticancer drugs, with triggered drug activation in tumor tissue and especially in tumor cells. Specifically, this review highlights the improvements in polymer drug carrier design with respect to the structure of a spacer to influence controlled drug release and activation, and its impact on the drug pharmacokinetics, enhanced tumor uptake, cellular trafficking, and in vivo antitumor activity.

A tumor-targeted polymer theranostics platform for positron emission tomography and fluorescence imaging

Here, we describe a novel polymer platform suitable for efficient diagnostics and potential theranostics based on ⁸⁹Zr-labeled N-(2-hydroxypropyl)methacrylamide (HPMA)-based copolymer conjugates. A set of polymers differing in molecular weight with either low dispersity or high dispersity were designed and synthesized and their biodistribution in vivo was successfully and precisely observed over 72 h. Moreover, the feasibility of two imaging techniques, fluorescence imaging (FI) and positron emission tomography (PET), was compared using labeled polymer conjugates. Both methods gave comparable results thus showing the enhanced diagnostic potential of the prepared polymer-dye or polymer-chelator-⁸⁹Zr constructs. The in vivo and ex vivo PET/FI studies indicated that the dispersity and molecular weight of the linear HPMA polymers have a significant influence on the pharmacokinetics of the polymer conjugates. The higher molecular weight and narrower distribution of molecular weights of the polymer carriers improve their pharmacokinetic profile for highly prolonged blood circulation and enhanced tumor uptake. Moreover, the same polymer carrier with the anticancer drug doxorubicin bound by a pH-sensitive hydrazone bond showed higher cytotoxicity and cellular uptake in vitro. Therefore, HPMA copolymers with low dispersity and a molecular weight near the limit of renal filtration can be used as highly efficient polymer carriers of tumor-targeted therapeutics or for theranostics with minimal side effects.

Biophysical and biological studies of some polymer grafted metallo-intercalators

Two water-soluble polymer-copper(II) complexes, [Cu(ip)₂(BPEI)](ClO₄)₂·H₂O (Complex 1) and [Cu(dppz)₂BPEI](ClO₄)₂·H₂O (Complex 2) with different degree of coordination have been synthesized and characterized. The interaction between the prepared complexes and CTDNA has been assessed by various physico-chemical methods The spectroscopic and the cyclic voltammetry studies have revealed that both the complexes interact with CTDNA through intercalation binding mode. Among the two complexes, Complex 2 has higher binding affinity with CTDNA. The antiproliferative activity of the complexes has been examined on human breast cancer cells, MDAMB231, adopting various techniques. The results indicate that both the polymer-copper(II) complexes are effective against the breast cancer cell line and the order of the activity is consistent with the DNA-binding ability.

High-molecular-weight HPMA-based polymer drug carriers for delivery to tumor

In this work, design and synthesis of high-molecular-weight N-(2-hydroxypropyl)methacrylamide-based polymer drug delivery systems tailored for cancer therapy is summarized. Moreover, the influence of their architecture on tumor accumulation and in vivo anti-cancer efficacy is discussed. Mainly, the high-molecular-weight delivery systems, such as branched, grafted, multi-block, star-like or micellar systems, with molecular weights greater than the renal threshold are discussed and reviewed in detail.

Rational Design of Cancer Nanomedicine: Nanoproperty Integration and Synchronization

Current cancer nanomedicines can only mitigate adverse effects but fail to enhance therapeutic efficacies of anticancer drugs. Rational design of next-generation cancer nanomedicines should aim to enhance their therapeutic efficacies. Taking this into account, this review first analyzes the typical cancer-drug-delivery process of an intravenously administered nanomedicine and concludes that the delivery involves a five-step CAPIR cascade and that high efficiency at every step is critical to guarantee high overall therapeutic efficiency. Further analysis shows that the nanoproperties needed in each step for a nanomedicine to maximize its efficiency are different and even opposing in different steps, particularly what the authors call the PEG, surface-charge, size and stability dilemmas. To resolve those dilemmas in order to integrate all needed nanoproperties into one nanomedicine, stability, surface and size nanoproperty transitions (3S transitions for short) are proposed and the reported strategies to realize these transitions are comprehensively summarized. Examples of nanomedicines capable of the 3S transitions are discussed, as are future research directions to design high-performance cancer nanomedicines and their clinical translations.

Covalent nano delivery systems for selective imaging and treatment of brain tumors

Nanomedicine is a rapidly evolving form of therapy that holds a great promise for superior drug delivery efficiency and therapeutic efficacy than conventional cancer treatment. In this review, we attempt to cover the benefits and the limitations of current nanomedicines with special attention to covalent nano conjugates for imaging and drug delivery in the brain. The improvement in brain tumor treatment remains dismal despite decades of efforts in drug development and patient care. One of the major obstacles in brain cancer treatment is the poor drug delivery efficiency owing to the unique blood-brain barrier (BBB) in the CNS. Although various anti-cancer agents are available to treat tumors outside of the CNS, the majority fails to cross the BBB. In this regard, nanomedicines have increasingly drawn attention due to their multi-functionality and versatility. Nano drugs can penetrate BBB and other biological barriers, and selectively accumulate in tumor cells, while concurrently decreasing systemic toxicity.

Drug-Free Macromolecular Therapeutics--A New Paradigm in Polymeric Nanomedicines

This review highlights a unique research area in polymer-based nanomedicine designs. Drug-free macromolecular therapeutics induce apoptosis of malignant cells by the crosslinking of surface non-internalizing receptors. The receptor crosslinking is mediated by the biorecognition of high-fidelity natural binding motifs (such as antiparallel coiled-coil peptides or complementary oligonucleotides) that are grafted to the side chains of polymers or attached to targeting moieties against cell receptors. This approach features the absence of low-molecular-weight cytotoxic compounds. Here, we summarize the rationales, different designs, and advantages of drug-free macromolecular therapeutics. Recent developments of novel therapeutic systems for B-cell lymphomas are discussed, as well as relevant approaches for other diseases. We conclude by pointing out various potential future directions in this exciting new field.

Passive Tumor Targeting of Polymer Therapeutics: In Vivo Imaging of Both the Polymer Carrier and the Enzymatically Cleavable Drug Model

The enzymatic release of a model drug from a polymer carrier inside a tumor using multispectral optical imaging in vivo in nude mice bearing colorectal carcinomas HT-29 and DLD-1 is demonstrated. Much higher release rate in vivo from a linear (30 kDa) (N-2-hydroxypropyl)methacrylamide-based polymer compared with a high molecular weight branched (170 kDa) polymer conjugate is observed, probably due to steric hindrance of the cleavable spacer of the latter polymer to proteolytic enzymes. There is no significant difference in the relative biodistribution of the two polymers, but the branched polymer circulates much longer. Both polymers are labeled with two different fluorophores. Dyomics-676 as a drug model is attached to the polymer via an enzymatically cleavable Gly-Phe-Leu-Gly spacer; Dyomics 782 is bound to the same polymer via a nondegradable amide bond, enabling the tracking of the polymer carrier after i.v. application to mice.

Improved Tumor-Specific Drug Accumulation by Polymer Therapeutics with pH-Sensitive Drug Release Overcomes Chemotherapy Resistance

The success of chemotherapy is limited by poor selectivity of active drugs combined with occurrence of tumor resistance. New star-like structured N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer-based drug delivery systems containing doxorubicin attached via a pH-sensitive hydrazone bond were designed and investigated for their ability to overcome chemotherapy resistance. These conjugates combine two strategies to achieve a high drug concentration selectively at the tumor site: (I) high accumulation by passive tumor targeting based on enhanced permeability and retention effect and (II) pH-sensitive site-specific drug release due to an acidic tumor microenvironment. Mice bearing doxorubicin-resistant xenograft tumors were treated with doxorubicin, PBS, poly HPMA (pHPMA) precursor or pHPMA-doxorubicin conjugate at different equivalent doses of 5 mg/kg bodyweight doxorubicin up to a 7-fold total dose using different treatment schedules. Intratumoral drug accumulation was analyzed by fluorescence imaging utilizing intrinsic fluorescence of doxorubicin. Free doxorubicin induced significant toxicity but hardly any tumor-inhibiting effects. Administering at least a 3-fold dose of pHPMA-doxorubicin conjugate was necessary to induce a transient response, whereas doses of about 5- to 6-fold induced strong regressions. Tumors completely disappeared in some cases. The onset of response was differential delayed depending on the tumor model, which could be ascribed to distinct characteristics of the microenvironment. Further fluorescence imaging-based analyses regarding underlying mechanisms of the delayed response revealed a related switch to a more supporting intratumoral microenvironment for effective drug release. In conclusion, the current study demonstrates that the concept of tumor site-restricted high-dose chemotherapy is able to overcome therapy resistance. Mol Cancer Ther; 15(5); 998-1007. ©2016 AACR.

"Combo" nanomedicine: Co-delivery of multi-modal therapeutics for efficient, targeted, and safe cancer therapy

The dynamic and versatile nature of diseases such as cancer has been a pivotal challenge for developing efficient and safe therapies. Cancer treatments using a single therapeutic agent often result in limited clinical outcomes due to tumor heterogeneity and drug resistance. Combination therapies using multiple therapeutic modalities can synergistically elevate anti-cancer activity while lowering doses of each agent, hence, reducing side effects. Co-administration of multiple therapeutic agents requires a delivery platform that can normalize pharmacokinetics and pharmacodynamics of the agents, prolong circulation, selectively accumulate, specifically bind to the target, and enable controlled release in target site. Nanomaterials, such as polymeric nanoparticles, gold nanoparticles/cages/shells, and carbon nanomaterials, have the desired properties, and they can mediate therapeutic effects different from those generated by small molecule drugs (e.g., gene therapy, photothermal therapy, photodynamic therapy, and radiotherapy). This review aims to provide an overview of developing multi-modal therapies using nanomaterials ("combo" nanomedicine) along with the rationale, up-to-date progress, further considerations, and the crucial roles of interdisciplinary approaches.

A novel PEG–haloperidol conjugate with a non-degradable linker shows the feasibility of using polymer–drug conjugates in a non-prodrug fashion

A PEG–haloperidol conjugate was synthesised, which retains binding to the dopamine D₂receptor, showing the possibility of using polymer-drug conjugates as drugsper se' rather than as prodrugs.

Micelle-forming HPMA copolymer conjugates of ritonavir bound via a pH-sensitive spacer with improved cellular uptake designed for enhanced tumor accumulation

We describe design, synthesis, physico-chemical characterization and preliminary biological evaluation of micelle-forming polymer drug conjugates with controlled drug release intended for tumor treatment.

FRET-trackable biodegradable HPMA copolymer-epirubicin conjugates for ovarian carcinoma therapy

To develop a biodegradable polymeric drug delivery system for the treatment of ovarian cancer with the capacity for non-invasive fate monitoring, we designed and synthesized N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-epirubicin (EPI) conjugates. The polymer backbone was labeled with acceptor fluorophore Cy5, while donor fluorophores (Cy3 or EPI) were attached to HPMA copolymer side chains via an enzyme-cleavable GFLG linker. This design allows elucidating separately the fate of the drug and of the polymer backbone using fluorescence resonance energy transfer (FRET). The degradable diblock conjugate (2P-EPI) was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization using a bifunctional chain transfer agent (Peptide2CTA). The pharmacokinetics (PK) and therapeutic effect of 2P-EPI (Mw ~100 kDa) were determined in mice bearing human ovarian carcinoma A2780 xenografts. Compared to 1st generation conjugate (P-EPI, Mw <50 kDa), 2P-EPI demonstrated remarkably improved PK such as fourfold terminal half-life (33.22 ± 3.18 h for 2P-EPI vs. 7.55 ± 3.18 h for P-EPI), which is primarily attributed to the increased molecular weight of the polymer carrier. Notably, complete tumor remission and long-term inhibition of tumorigenesis (100 days) were achieved in mice (n=5) treated with 2P-EPI. Moreover, in vitro cell uptake and intracellular drug release were determined via FRET intensity changes. The results establish a solid foundation for future in vivo tracking of drug delivery and chain scission of polymeric conjugates by FRET imaging.

Dendritic hexadecapeptide as a cathepsin B degradable carrier for delivery of HSP90 inhibitor

Biodegradable vehicles that degrade specifically at tumor sites are highly desirable since they can cause selective exposure of highly toxic drugs at tumor sites whereas keep the conjugates stable during blood circulation. Here, we evaluate the utility of a dendritic hexadecapeptide comprised of four arms, each having a tetrapeptide sequence recognized by an enzyme cathepsin B as a carrier system for heat shock protein 90 (HSP90) inhibitor geldanamycin (GDM). We report the synthesis of a carrier having GDM conjugated to the terminal end of each arm (>55% wt/wt drug). We further report the stability of the GDM containing peptidic dendrimer in various buffers and in the presence of serum along with its ability to release free drug in the presence of cathepsin B, the enzyme overexpressed in a variety of tumors. Using androgen-independent prostate cancer cell line (DU-145) we further demonstrate that the geldanamycin containing peptidic dendrimer has antiproliferative property similar to the free drug derivative.

Anti-Resorptive Functions of Poly(ethylene sodium phosphate) on Human Osteoclasts

Osteoporosis involves hyperactive osteoclasts. A large number of current drugs result in side effects affecting their efficacy in the clinic. Polyphosphoesters are unique polymeric biomaterials because of their biocompatibility, biodegradability, and bone affinity. We studied the viability and ability of human osteoclasts to resorb bone when dosed with poly(ethylene sodium phosphate) (PEP·Na). This did not trigger any change in osteoblast cell viability, however the polymer diminished human osteoclasts and their ability to resorb bone at concentrations as low as 10(-4) m · mL(-1). This is the first report to validate the possibility of using polyphosphoesters for selective inhibition of human osteoclast functions, indicating its potential to be used as an effective polymer prodrug for treatment of osteoporosis.

N-(2-Hydroxypropyl)methacrylamide Copolymer-Drug Conjugates for Combination Chemotherapy of Acute Myeloid Leukemia

There is a need for new treatment strategies of acute myeloid leukemia (AML). In this study, four different drugs, including cytarabine, daunorubicin, GDC-0980, and JS-K, were investigated in vitro for the two-drug combinations treatment of AML. The results revealed that cytarabine and GDC-0980 had the strongest synergism. In addition, cell cycle analysis was conducted to investigate the effect of the different combinations on cell division. For future in vivo application, N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-cytarabine and GDC-0980 conjugates were synthesized, respectively. In vitro studies demonstrated that both conjugates had potent cytotoxicity and their combination also showed strong synergy, suggesting a potential chemotherapeutic strategy for future AML treatment.

Drug Carriers: Not an Innocent Delivery Man

Biomaterials used as drug carriers are often considered inactive and assumed to have no other roles than modifying pharmacokinetics and biodistribution of a drug. On the other hand, there are several examples in which the carrier materials show bioactivities in the body, which may have been underestimated or inadvertently ignored. This review highlights several examples where biomaterials used as drug carriers bring biological effects, known or newly discovered, and discusses their implications in development of new drug delivery systems.