Endosomal pH-Activatable Poly(ethylene oxide)-graft-Doxorubicin Prodrugs: Synthesis, Drug Release, and Biodistribution in Tumor-Bearing Mice

Nanoliposomes as nonviral vectors in cancer gene therapy

Nonviral vectors, such as liposomes, offer potential for targeted gene delivery in cancer therapy. Liposomes, composed of phospholipid vesicles, have demonstrated efficacy as nanocarriers for genetic tools, addressing the limitations of off-targeting and degradation commonly associated with traditional gene therapy approaches. Due to their biocompatibility, stability, and tunable physicochemical properties, they offer potential in overcoming the challenges associated with gene therapy, such as low transfection efficiency and poor stability in biological fluids. Despite these advancements, there remains a gap in understanding the optimal utilization of nanoliposomes for enhanced gene delivery in cancer treatment. This review delves into the present state of nanoliposomes as carriers for genetic tools in cancer therapy, sheds light on their potential to safeguard genetic payloads and facilitate cell internalization alongside the evolution of smart nanocarriers for targeted delivery. The challenges linked to their biocompatibility and the factors that restrict their effectiveness in gene delivery are also discussed along with exploring the potential of nanoliposomes in cancer gene therapy strategies by analyzing recent advancements and offering future directions.

Formulation development of lipid polymer hybrid nanoparticles of doxorubicin and its in-vitro, in-vivo and computational evaluation

The purpose of this study was to assess the parameters of doxorubicin (DOX) loaded lipid polymer hybrid nanoparticles (LPHNs) formulation development, and then the bioavailability of DOX were determined in the rabbit model, in order to evaluate the intrinsic outcome of dosage form improvement after the oral administration. LPHNs were prepared by combine approach, using both magnetic stirring and probe sonication followed by its characterization in terms of size-distribution (Zeta Size), entrapment efficiency (EE), loading capacity, and the kinetics of DOX. LPHNPs were further characterized by using scanning electron microscopy (SEM), powder X-Ray diffractometry (P-XRD), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), in vitro and in vivo studies. The molecular modeling was determined through the density functional theory (DFT) simulations and interactions. DOX loaded and unloaded LPHNs were administered orally to the rabbits for bioavailability and pharmacokinetic parameters determinations. The plasma concentration of DOX was determined through high performance liquid chromatography (HPLC). The average size of DOX-loaded LPHNs was 121.90 ± 3.0 nm. The drug loading of DOX was 0.391% ± 0.01 of aqueous dispersion, where its encapsulation efficiency was 95.5% ± 1.39. After oral administration of the DOX-LPHNs, the area under the plasma drug concentration-time curve (AUC) improved about 2-folds comparatively (p < 0.05). DFT simulations were used to understand the interactions of polymers with different sites of DOX molecule. The larger negative binding energies (-9.33 to -18.53 kcal/mol) of the different complexes evince that the polymers have stronger affinity to bind with the DOX molecule while the negative values shows that the process is spontaneous, and the synthesis of DOX-LPHNs is energetically favorable. It was concluded that DOX-LPHNs provides a promising new formulation that can enhance the oral bioavailability, which have optimized compatibilities and improve the pharmacokinetic of DOX after oral administration.

Harnessing Folate-Functionalized Nasal Delivery of Dox-Erlo-Loaded Biopolymeric Nanoparticles in Cancer Treatment: Development, Optimization, Characterization, and Biodistribution Analysis

The aim of the present study is to develop Doxorubicin-Erlotinib nanoparticles (Dox-Erlo NPs) and folate-armored Dox-Erlo-NP conjugates for targeting glioma cancer. Glioma is one of the most common progressive cancerous growths originating from brain glial cells. However, the blood-brain barrier (BBB) is only semi-permeable and is highly selective as to which compounds are let through; designing compounds that overcome this constraint is therefore a major challenge in the development of pharmaceutical agents. We demonstrate that the NP conjugates studied in this paper may ameliorate the BBB penetration and enrich the drug concentration in the target bypassing the BBB. NPs were prepared using a biopolymer with a double-emulsion solvent evaporation technique and functionalized with folic acid for site-specific targeting. Dox-Erlo NPs and Dox-Erlo-NP conjugates were extensively characterized in vitro for various parameters. Dox-Erlo NPs and Dox-Erlo-NP conjugates incurred a z-average of 95.35 ± 10.25 nm and 110.12 ± 9.2 nm, respectively. The zeta potentials of the Dox-Erlo NPs and Dox-Erlo-NP conjugates were observed at -18.1 mV and -25.1 mV, respectively. A TEM image has shown that the NPs were well-dispersed, uniform, de-aggregated, and consistent. A hemolytic assay confirmed hemocompatibility with the developed formulation and that it can be safely administered. Dox-Erlo-NP conjugates significantly reduced the number of viable cells to 24.66 ± 2.08% and 32.33 ± 2.51% in U87 and C6 cells, respectively, and IC50 values of 3.064 µM and 3.350 µM in U87 and C6 cells were reported after 24 h, respectively. A biodistribution study revealed that a significant concentration of Dox and Erlo were estimated in the brain relative to drug suspension. Dox-Erlo-NP conjugates were also stable for three months. The findings suggest that the developed Dox-Erlo-NP conjugates may be a promising agent for administration in glioma therapy.

Allyl group-containing polyvinylphosphonates as a flexible platform for the selective introduction of functional groups via polymer-analogous transformations

Polyvinylphosphonates are highly promising candidates for (bio)medical applications as they exhibit a tunable lower critical solution temperature, high biocompatibility of homo- and copolymers, and a broad foundation for post-synthetic modifications. In this work we explored polymer-analogous transformations with statistical polyvinylphosphonates comprising diethyl vinylphosphonate (DEVP) and diallyl vinylphosphonate (DAlVP). The C[double bond, length as m-dash]C double bonds were used as a starting point for a cascade of organic transformations. Initially, the reactive moieties were successfully introduced via bromination, epoxidations with OXONE and mCPBA, or thiol-ene click chemistry with methyl thioglycolate (6). The obtained substrates were then employed in a variety of consecutive reactions depending on the introduced functional motif: (1) the brominated substrates were converted with sodium azide to enable the copper-mediated alkyne-azide coupling with phenylacetylene (1). (2) The epoxides were reacted with sodium azide for an alkyne-azide click coupling with 1 as well as small nucleophilic compounds (phenol (2), benzylamine (3), and 4-amino-2,1,3-benzothiadiazol (4)). Afterwards the non-converted allyl groups were reacted with thiochloesterol (5) to form complex polymer conjugates. (3) An acid-labile hydrazone-linked conjugate was formed in a two-step approach. The polymeric substrates were characterized by NMR, FTIR, and UV/Vis spectroscopy as well as elemental analysis and gel permeation chromatography to monitor the structural changes of the polymeric substrates and to prove the success of these modification approaches.

Smart stimuli-responsive biopolymeric nanomedicines for targeted therapy of solid tumors

Solid tumors form a permissive microenvironment with irregular features, including high pressured tumor interstitial fluid with acidic pH, co-adaptation of cancer cells with other cells like the immune system cells, abnormal metabolism and anomalous overexpression of various pieces of molecular machinery. The functional expressions of several oncomarkers in different solid tumors have led to the development of targeted drug-delivery systems (DDSs). As a new class of DDSs, stimuli-responsive nanomedicines (SRNMs) have been developed using advanced nanobiomaterials such as biopolymers that show excellent biocompatibility with low inherent immunogenicity. In this review, we aim to overview different types of SRNMs, present deep insights into the stimuli-responsive biopolymers and discuss the most up-to-date progress in the design and development of SRNMs used as advanced DDSs for targeted therapy of cancer.

Smart Targeting To Improve Cancer Therapeutics

Cancer is the second largest cause of death worldwide with the number of new cancer cases predicted to grow significantly in the next decades. Biotechnology and medicine can and should work hand-in-hand to improve cancer diagnosis and treatment efficacy. However, success has been frequently limited, in particular when treating late-stage solid tumors. There still is the need to develop smart and synergistic therapeutic approaches to achieve the synthesis of strong and effective drugs and delivery systems. Much interest has been paid to the development of smart drug delivery systems (drug-loaded particles) that utilize passive targeting, active targeting, and/or stimulus responsiveness strategies. This review will summarize some main ideas about the effect of each strategy and how the combination of some or all of them has shown to be effective. After a brief introduction of current cancer therapies and their limitations, we describe the biological barriers that nanoparticles need to overcome, followed by presenting different types of drug delivery systems to improve drug accumulation in tumors. Then, we describe cancer cell membrane targets that increase cellular drug uptake through active targeting mechanisms. Stimulus-responsive targeting is also discussed by looking at the intra- and extracellular conditions for specific drug release. We include a significant amount of information summarized in tables and figures on nanoparticle-based therapeutics, PEGylated drugs, different ligands for the design of active-targeted systems, and targeting of different organs. We also discuss some still prevailing fundamental limitations of these approaches, eg, by occlusion of targeting ligands.

One-Pot Synthesis of pH/Redox Responsive Polymeric Prodrug and Fabrication of Shell Cross-Linked Prodrug Micelles for Antitumor Drug Transportation

Shell cross-linked (SCL) polymeric prodrug micelles have the advantages of good blood circulation stability and high drug content. Herein, we report on a new kind of pH/redox responsive dynamic covalent SCL micelle, which was fabricated by self-assembly of a multifunctional polymeric prodrug. At first, a macroinitiator PBYP- ss- iBuBr was prepared via ring-opening polymerization (ROP), wherein PBYP represents poly[2-(but-3-yn-1-yloxy)-2-oxo-1,3,2-dioxaphospholane]. Subsequently, PBYP- hyd-DOX- ss-P(DMAEMA- co-FBEMA) prodrug was synthesized by a one-pot method with a combination of atom transfer radical polymerization (ATRP) and a Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction using a doxorubicin (DOX) derivative containing an azide group to react with the alkynyl group of the side chain in the PBYP block, while DMAEMA and FBEMA are the abbriviations of N, N-(2-dimethylamino)ethyl methacrylate and 2-(4-formylbenzoyloxy)ethyl methacrylate, respectively. The chemical structures of the polymer precursors and the prodrugs have been fully characterized. The SCL prodrug micelles were obtained by self-assembly of the prodrug and adding cross-linker dithiol bis(propanoic dihydrazide) (DTP). Compared with the shell un-cross-linked prodrug micelles, the SCL prodrug micelles can enhance the stability and prevent the drug from leaking in the body during blood circulation. The average size and morphology of the SCL prodrug micelles were measured by dynamic light scattering (DLS) and transmission electron microscopy (TEM), respectively. The SCL micelles can be dissociated under a moderately acidic and/or reductive microenvironment, that is, endosomal/lysosomal pH medium or high GSH level in the tumorous cytosol. The results of DOX release also confirmed that the SCL prodrug micelles possessed pH/reduction responsive properties. Cytotoxicity and cellular uptake analyses further revealed that the SCL prodrug micelles could be rapidly internalized into tumor cells through endocytosis and efficiently release DOX into the HeLa and HepG2 cells, which could efficiently inhibit the cell proliferation. This study provides a fast and precise synthesis method for preparing multifunctional polymer prodrugs, which hold great potential for optimal antitumor therapy.

Synthesis and Self-Assembly of the pH-Responsive Anionic Copolymers for Enhanced Doxorubicin-Loading Capacity

Polyelectrolyte complex micelles self-assembled from an ionic polymer and oppositely charged small molecules are a promising drug delivery system. In this study, the anionic block copolymers composed of poly(ethylene glycol), poly(ε-caprolactone), and carboxyl modified poly(ε-caprolactone), COOH-PCEC, were designed to encapsulate doxorubicin (DOX) via electrostatic and hydrophobic interactions to form spherical micelles with a particle size of 90-140 nm. The higher payload capacity of these micelles than noncharged micelles of PCL-poly(ethylene glycol)-PCL (PCEC) was achieved, and it was strongly dependent on the composition of the micelles. In vitro drug release studies showed that the release of DOX from the micelles was faster at pH 5.5 than at pH 7.4, which was mainly due to the protonation of carboxyl groups and the solubility of DOX. Studies of intracellular uptake demonstrated that the DOX-loaded micelles could be internalized effectively by HeLa cells. In vitro cytotoxicity revealed that the blank COOH-PCEC micelles had a low cytotoxicity against both L929 and HeLa cells. However, the DOX-loaded micelles inhibited the growth of HeLa cells remarkably, demonstrating their potential for use as an efficient carrier for the delivery of DOX.

Cleavable PEGylation: a strategy for overcoming the "PEG dilemma" in efficient drug delivery

To prolong the circulation time of drug, PEGylation has been widely used via the enhanced permeability and retention (EPR) effect, thereby providing new hope for better treatment. However, PEGylation also brings the "PEG dilemma", which is difficult for the cellular absorption of drugs and subsequent endosomal escape. As a result, the activity of drugs is inevitably lost after PEG modification. To achieve successful drug delivery for effective treatment, the crucial issue associated with the use of PEG-lipids, that is, “PEG dilemma” must be addressed. In this paper, we introduced the development and application of nanocarriers with cleavable PEGylation, and discussed various strategies for overcoming the PEG dilemma. Compared to the traditional ones, the vehicle systems with different environmental-sensitive PEG-lipids were discussed, which cleavage can be achieved in response to the intracellular as well as the tumor microenvironment. This smart cleavable PEGylation provides us an efficient strategy to overcome “PEG dilemma”, thereby may be a good candidate for the cancer treatment in future.

Enhancement of oral bioavailability of doxorubicin through surface modified biodegradable polymeric nanoparticles

Background

Doxorubicin hydrochloride (DOX·HCl), an anthracycline glycoside antibiotic, exhibits low oral bioavailability due to active efflux from intestinal P-glycoprotein receptors. The oral administration of DOX remains a challenge hence; no oral formulation for DOX is marketed, till date.

Aim of the study

To improve the oral bioavailability of DOX through, preparation of a nanoformulation i.e. PEGylated-doxorubicin(DOX)-loaded-poly-lactic-co-glycolic acid (PLGA)-Nanoparticles (NPs) and to develop and validate an ultra-high performance liquid chromatography electrospray ionization-synapt mass spectrometric bioanalytical method (UHPLC/ESI-QTOF–MS/MS) for plasma (Wistar rats) DOX quantification.

Materials and methods

For chromatography, Waters ACQUITY UPLC™ along with a BEH C-18 column (2.1 mm × 100 mm; 1.7 μm), mobile phase conditions (acetonitrile: 0.1% formic acid::1:1 v/v) and flow rate (0.20 ml/min) was used. For analyte recovery from rat plasma, a liquid–liquid extraction method (LLE), using Acetonitrile: 5 mM ammonium acetate in a ratio of 6:4 v/v at pH 3.5, was used.

Results

Nanoformulation with a particle size (183.10 ± 7.41 nm), zeta potential (− 13.10 ± 1.04 mV), drug content (42.69 ± 1.97 µg/mg) and a spherical shape and smooth surface was developed. An elution time of 1.61 and 1.75 min along with a transition at m/z 544.42/397.27 and 528.46/321.41 were observed for DOX and internal standard (IS) Daunorubicin, respectively. In addition, a linear dynamic range with r² ≥ 0.9985 over a concentration range of 1.00–2500.0 ng/ml was observed for different processes and parameters used in the study. Similarly a marked improvement i.e. 6.8 fold was observed, in PEGylated-DOX-PLGA-NPs as compared to DOX-S, in pharmacokinetics studies.

Conclusion

The promising approach of PEGylated-DOX-PLGA-NPs may provide an alternate to intravenous therapy for better patient care.

Designing Smart Polymer Conjugates for Controlled Release of Payloads

Incorporating labile bonds inside polymer backbone and side chains yields interesting polymer materials that are responsive to change of environmental stimuli. Drugs can be conjugated to various polymers through different conjugation linkages and spacers. One of the key factors influencing the release profile of conjugated drugs is the hydrolytic stability of the conjugated linkage. Generally, the hydrolysis of acid-labile linkages, including acetal, imine, hydrazone, and to some extent β-thiopropionate, are relatively fast and the conjugated drug can be completely released in the range of several hours to a few days. The cleavage of ester linkages are usually slow, which is beneficial for continuous and prolonged release. Another key structural factor is the water solubility of polymer-drug conjugates. Generally, the release rate from highly water-soluble prodrugs is fast. In prodrugs with large hydrophobic segments, the hydrophobic drugs are usually located in the hydrophobic core of micelles and nanoparticles, which limits the access to the water, hence lowering significantly the hydrolysis rate. Finally, self-immolative polymers are also an intriguing new class of materials. New synthetic pathways are needed to overcome the fact that much of the small molecules produced upon degradation are not active molecules useful for biomedical applications.

Photoresponsive Block Copolymer Prodrug Nanoparticles as Delivery Vehicle for Single and Dual Anticancer Drugs

In recent decades, drug delivery systems (DDSs) based on polymer nanoparticles have been explored due to their potential to deliver drugs with poor water solubility. Some of the limitations of nanoparticle-based DDSs can be overcome by developing an appropriate polymer prodrug. In this work, poly(NIPA)-b-poly(HMNPPA)-b-poly(PEGMA-stat-BA) was synthesized using reversible addition fragmentation chain transfer polymerization and Chlorambucil (Cbl), an anticancer drug, was conjugated to the copolymer via 3-(3-(hydroxymethyl)-4-nitrophenoxy)propyl acrylate (HMNPPA) units to prepare the prodrug. A few biotin acrylate (BA) units were also incorporated to bring potential targeting capability to the prodrug in the copolymer. This polymer prodrug formed spherical micellar nanoparticles in physiological conditions, which were characterized by dynamic light scattering and transmission electron microscopy measurements. The very low critical aggregation concentration (cac) (0.011 mg/mL) of the prodrug, as measured from Nile Red fluorescence, makes it stable against dilution. The polymer prodrug was shown to release Cbl on photoirradiation by soft UV (λ ≥ 365 nm) and laser (λ = 405 nm) light. The prodrug micellar nanoparticles were capable of encapsulating a second drug (doxorubicin, DOX) in their hydrophobic core. On photoirradiation with UV and laser light of the DOX-loaded nanoparticles, both Cbl and DOX were released. Light-induced breaking of photolabile ester bond resulted in the release of Cbl and caused disruption of the nanoparticles facilitating release of DOX. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay confirmed the nontoxicity of the polymers and effectiveness of the dual drug-loaded micellar nanoparticles toward cancer cells. Confocal microscopy results showed a better cellular internalization capability of the DOX-loaded nanoparticles in cancer cells, possibly due to the presence of cancer cell targeting biotin molecules in the polymer. This new photoresponsive potentially biocompatible and cancer cell-targeted polymer prodrug may be useful for delivery of single and/or multiple hydrophobic drugs.

Enhancing Photochemical Internalization of DOX through a Porphyrin-based Amphiphilic Block Copolymer

Drug resistance is a primary obstacle that seriously reduces the therapy efficiency of most chemotherapeutic agents. To address this issue, the photochemical internalization (PCI) was employed to help the anticancer drug escape from lysosome and improve their translocation to the nucleus. A pH-sensitive porphyrin-based amphiphilic block copolymer (PEG₁₁₃-b-PCL₅₄-a-porphyrin) was synthesized, which was acted not only as a carrier for the delivery of DOX but also as a photosensitizer for PCI. PEG₁₁₃-b-PCL₅₄-a-porphyrin as a drug carrier exhibited a higher drug loading capacity, entrapment efficiency, and DOX release content. The PCI effect of PEG₁₁₃-b-PCL₅₄-a-porphyrin was studied by confocal laser scanning microscopy, and the results showed that most of DOX could be translocated into the nucleus for DOX-loaded PEG₁₁₃-b-PCL₅₄-a-porphyrin micelles. Moreover, the IC₅₀ of pH-sensitive DOX-loaded PEG₁₁₃-b-PCL₅₄-a-porphyrin micelles was much lower than that of its counterpart without pH-responsiveness, DOX-loaded PEG₁₁₃-b-PCL₅₄-porphyrin micelles. Therefore, this drug delivery system based on pH-sensitive porphyrin-containing block copolymer would act as a potential vehicle for overcoming drug resistance in chemotherapy.

A self-immolative prodrug nanosystem capable of releasing a drug and a NIR reporter for in vivo imaging and therapy

In vivo monitoring of the biodistribution and activation of prodrugs is highly attractive, and the self-immolative dendritic architecture is deemed as a promising approach for constructing theranostic prodrug in which the release/activation of different payloads is needed. Herein, A GSH-triggered and self-immolative dendritic platform comprising an anticancer drug camptothecin (CPT), a cleavable linker and a two-photon NIR fluorophore (dicyanomethylene-4H-pyran, DCM) has been developed for in situ tracking of drug release and antitumour therapy. In vitro experiments demonstrate that, the presence of glutathione (GSH) induces the cleavage of the self-immolative linker, resulting in comitant release of the drug and the dye. Upon cell internalization and under one- or two-photon excitation, prominent intracellular fluorescence can be observed, indicating the release of the payloads in live cells. Upon loaded in phospholipid vesicles, the prodrug has also been successfully utilized for in vivo and in situ tracking of drug release and cancer therapy in a mouse model. Several hours post injection, the prodrug generates strong fluorescence on tumour sites, demonstrating the prodrug's capability of monitoring the on-site drug release. Moreover, the prodrug shows considerable high activity and exerts obvious inhibition towards tumour growth. This work suggests that the prodrug with self-immolative dendritic structure can work well in vivo and this strategy may provide an alternative approach for designing theranostic drug delivery systems.

Platinum covalent shell cross-linked micelles designed to deliver doxorubicin for synergistic combination cancer therapy

The preparation of polymer therapeutics capable of controlled release of multiple chemotherapeutic drugs has remained a tough problem in synergistic combination cancer therapy. Herein, a novel dual-drug co-delivery system carrying doxorubicin (DOX) and platinum(IV) (Pt[IV]) was developed. An amphiphilic diblock copolymer, PCL-b-P(OEGMA-co-AzPMA), was synthesized and used as a nanoscale drug carrier in which DOX and Pt(IV) could be packaged together. The copolymers were shell cross-linked by Pt(IV) prodrug via a click reaction. Studies on the in vitro drug release and cellular uptake of the dual-drug co-delivery system showed that the micelles were effectively taken up by the cells and simultaneously released drugs in the cells. Futhermore, the co-delivery polymer nanoparticles caused much higher cell death in HeLa and A357 tumor cells than either the free drugs or single-drug-loaded micelles at the same dosage, exhibiting a synergistic combination of DOX and Pt(IV). The results obtained with the shell cross-linked micelles based on an anticancer drug used as a cross-linking linkage suggested a promising application of the micelles for multidrug delivery in combination cancer therapy.

Folate-decorated PEGylated triblock copolymer as a pH/reduction dual-responsive nanovehicle for targeted intracellular co-delivery of doxorubicin and Bcl-2 siRNA

Co-delivery of chemotherapeutic drug and small interfering RNA (siRNA) within a single nanovehicle has emerged as a promising combination therapy approach to treating cancers because of their synergistic effect. Nanocarrier delivery systems with low cytotoxicity and high efficiency are needed for such a purpose. In this study, a novel folate-conjugated PEGylated cationic triblock copolymer, poly(acrylhydrazine)-block-poly(3-dimethylaminopropyl methacrylamide)-block-poly(acrylhydrazine) (PAH-b-PDMAPMA-b-PAH), was synthesized and evaluated as a stimuli-sensitive vehicle for the targeted co-delivery of doxorubicin (DOX) and Bcl-2 siRNA into breast cancer MCF-7 cells. The synthetic process of the PEGylated triblock copolymer involved sequential reversible addition-fragmentation chain transfer polymerization, PEGylation and removal of tert-butoxy carbamate protecting groups. Folate-conjugated and/or -unconjugated poly(ethylene glycol) segments were grafted onto PAH-b-PDMAPMA-b-PAH via a reduction-sensitive disulfide linkage. The synthetic polymers were characterized by ¹H NMR and gel permeation chromatography. The PEGylated triblock copolymer could chemically conjugate DOX onto PAH blocks via pH-responsive hydrazone bonds and simultaneously complex negatively charged Bcl-2 siRNA with cationic PDMAPMA blocks through electrostatic interactions at N/P ratios≥32:1 to form multifunctional nanomicelleplexes. The nanomicelleplexes exhibited spherical shape, possessed a positively charged surface with a zeta potential of +22.5mV and had a desirable and uniform particle size of 187nm. In vitro release studies revealed that the nanomicelleplexes could release DOX and Bcl-2 siRNA in a reduction and pH dual-sensitive manner and the payload release was significantly enhanced in a reductive acidic environment mimicking the endosomes/lysosomes of cancer cells compared to under physiology conditions. Furthermore, the release of both DOX and siRNA was found to follow Higuchi kinetic model. Confocal laser scanning microscopy, flow cytometry and MTT analyses confirmed that, compared with folate-undecorated nanomicelleplexes, folate-decorated nanomicelleplexes could more effectively co-deliver DOX and Bcl-2 siRNA into MCF-7 cells and showed a stronger cell-killing effect. The pristine PEGylated triblock copolymer exhibited good cytocompatibility. Moreover, co-delivery of DOX and Bcl-2 siRNA achieved a significant synergistic antitumor efficacy. These findings suggested that the folate-decorated PEGylated cationic triblock copolymer might be a promising vehicle for targeted intracellular co-delivery of DOX and siRNA in MCF-7 cells, representing a potential clinical combination therapy for breast cancer treatment.

Dual-sensitive and biodegradable core-crosslinked HPMA copolymer–doxorubicin conjugate-based nanoparticles for cancer therapy

The nanoplatform of biosafe crosslinked copolymer-NPs efficiently delivers anticancer drugs to tumor cellsviablood circulation.

Hydrazone linkages in pH responsive drug delivery systems

Stimuli-responsive polymeric drug delivery systems using various triggers to release the drug at the sites have become a major focus area. Among various stimuli-responsive materials, pH-responsiveness has been studied extensively. The materials used for fabricating pH-responsive drug delivery systems include a specific chemical functionality in their structure that can respond to changes in the pH of the surrounding environment. Various chemical functionalities, for example, acetal, amine, ortho ester, amine and hydrazone, have been used to design materials that are capable of releasing their payload at the acidic pH conditions of the tumor or infection sites. Hydrazone linkages are significant synthons for numerous transformations and have gained importance in pharmaceutical sciences due to their various biological and clinical applications. These linkages have been employed in various drug delivery vehicles, such as linear polymers, star shaped polymers, dendrimers, micelles, liposomes and inorganic nanoparticles, for pH-responsive drug delivery. This review paper focuses on the synthesis and characterization methods of hydrazone bond containing materials and their applications in pH-responsive drug delivery systems. It provides detailed suggestions as guidelines to materials and formulation scientists for designing biocompatible pH-responsive materials with hydrazone linkages and identifying future studies.

Biodegradable Copolymer for Stimuli-Responsive Sustained Release of Doxorubicin

Pendent functionalization of biodegradable polymers provides unique importance in biological applications. In this work, we have synthesized a polymeric nanocarrier for the controlled release of the anticancer drug doxorubicin (DOXI). Inspired by the pH responsiveness of acylhydrazine bonds along with the interesting self-assembly behavior of amphiphilic copolymers, this report delineates the development of a PEG-SS-PCL-DOXI copolymer consisting of DOXI, PEG, and a caprolactone backbone. First, the inclusion of a PEG moiety in the copolymer helps to achieve biocompatibility and aqueous solubility as well as a prolonged circulation time of the nanocarrier. Second, an acid-sensitive acylhydrazine-based linkage is chosen to attach DOXI to trigger sustained drug release, whereas the inclusion of an enzymatically cleavable disulfide linkage in the backbone adds to the advantage of backbone biodegradability at the intracellular level.

In Vitro Evaluation of Doxorubicin Conjugates Based on Sugar Core Nonlinear Polymethacrylates toward Anticancer Drug Delivery

V-shaped and star-shaped hydroxylamine-functionalized polymethacrylates designed as nanosized conjugates (<120 nm) with anticancer agent, namely, doxorubicin (DOX), were evaluated in vitro toward their potential usage as drug delivery systems in breast cancer (MCF-7) treatment. Statistical analysis of MTS assay results showed that the 4-arm conjugate (n(DOX) = 16) was the most effective polymeric system against MCF-7/W (wild type) and MCF-7/R (DOX resistant) cell lines. Apoptosis assay analysis showed that MCF-7/R cells cultured with nonlinear copolymers died due to necrosis and late apoptotis, whereas MCF-7/W cells were in early and late apoptosis. Among all tested conjugates, the most promising results with induction of apoptosis without inducing necrosis in both MCF-7 cell lines were obtained for conjugate based on 4-arm stars with low content of DOX. The cell cycle assay revealed that increase of MMA units in 4-arm copolymers induced MCF-7/R cell arrest in the SubG1 phase. In the same cell line, the corresponding conjugates triggered S and G2/M arrest. Gradual internalization of the chosen conjugate by MCF-7/R cells was monitored via fluorescence microscopy showing its main localization in the cytoplasm.

Reduction/pH dual-responsive nano-prodrug micelles for controlled drug delivery

We provided a facile strategy to fabricate reduction/pH dual-responsive nano-prodrug micelles for controlled drug delivery.

Polymeric prodrugs conjugated with reduction-sensitive dextran–camptothecin and pH-responsive dextran–doxorubicin: an effective combinatorial drug delivery platform for cancer therapy

Two types of stimuli-sensitive polymeric prodrugs for combinatorial cancer therapy have been prepared and found to exhibit favorable anticancer activity in vitro and in vivo.

Prodrug Micelles Based on Norbornene-Functional Poly(lactide)s Backbone for Redox-Responsive Release of Paclitaxel

Norbornene-functional poly(lactide)s backbone-based amphiphilic copolymer, P(LA-g-mOEG)-b-P(LA-SS-COOH), was synthesized as the polymeric scaffold and paclitaxel (PTX) was directly conjugated to the carboxyl groups of the amphiphilic copolymer to obtain redox-responsive P(LA-g-mOEG)-b-P(LA-SS-PTX) prodrugs. The dynamic light scattering and transmission electron microscopy analyses showed that P(LA-g-mOEG)-b-P(LA-SS-PTX) self-assembled into prodrug micelles with a diameter of 60–70 nm and a low polydispersity in aqueous solution. Remarkably, in vitro release studies revealed that 80 % of PTX was released in 72 h under a reductive environment, whereas only 23 % of PTX was released in 72 h under non-reductive conditions. In addition, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays showed that P(LA-g-mOEG)-b-P(LA-SS-PTX) prodrug micelles retained high anti-tumour activity while polymer carriers were non-toxic up to a tested concentration of 1.0 mg mL–1. These redox-responsive prodrug micelles have tremendous potential for anti-tumour drug delivery.

The suppression of metastatic lung cancer by pulmonary administration of polymer nanoparticles for co-delivery of doxorubicin and Survivin siRNA

DOX and siRNA were sprayed into trachea, bronchi and alveoli, and were co-delivered to cancer cells.

Preparation and evaluation of PCL–PEG–PCL polymeric nanoparticles for doxorubicin delivery against breast cancer

DOX-loaded polymeric NPs based on PCL–PEG–PCL triblock copolymers were successfully prepared and showed highly efficient targeting and accumulation in tumor via EPR effect. The prepared NPs would be a promising nanosized DDS for cancer therapy.

Synthesis of photoresponsive polymeric propesticide micelles based on PEG for the controlled release of a herbicide

A novel amphiphilic polymer–pesticide conjugate was synthesized which can selfassemble into photoresponsive micelles in aqueous solutions for a controlled release of the herbicide.

Polymerization of Ethylene Oxide, Propylene Oxide, and Other Alkylene Oxides: Synthesis, Novel Polymer Architectures, and Bioconjugation

The review summarizes current trends and developments in the polymerization of alkylene oxides in the last two decades since 1995, with a particular focus on the most important epoxide monomers ethylene oxide (EO), propylene oxide (PO), and butylene oxide (BO). Classical synthetic pathways, i.e., anionic polymerization, coordination polymerization, and cationic polymerization of epoxides (oxiranes), are briefly reviewed. The main focus of the review lies on more recent and in some cases metal-free methods for epoxide polymerization, i.e., the activated monomer strategy, the use of organocatalysts, such as N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs) as well as phosphazene bases. In addition, the commercially relevant double-metal cyanide (DMC) catalyst systems are discussed. Besides the synthetic progress, new types of multifunctional linear PEG (mf-PEG) and PPO structures accessible by copolymerization of EO or PO with functional epoxide comonomers are presented as well as complex branched, hyperbranched, and dendrimer like polyethers. Amphiphilic block copolymers based on PEO and PPO (Poloxamers and Pluronics) and advances in the area of PEGylation as the most important bioconjugation strategy are also summarized. With the ever growing toolbox for epoxide polymerization, a "polyether universe" may be envisaged that in its structural diversity parallels the immense variety of structural options available for polymers based on vinyl monomers with a purely carbon-based backbone.

Bioinspired Nano-Prodrug with Enhanced Tumor Targeting and Increased Therapeutic Efficiency

Nanotechnology-based drug delivery has a great potential to revolutionize cancer treatment by enhancing anticancer drug efficacy and reducing drug toxicity. Here, a bioinspired nano-prodrug (BiNp) assembled by an antineoplastic peptidic derivative (FA-KLA-Hy-DOX), a folate acid (FA)-incorporated proapoptotic peptide (KLAKLAK)(2) (KLA) to doxorubicin (DOX) via an acid-labile hydrozone bond (Hy) is constructed. The hydrophobic antineoplastic agent DOX is efficiently shielded in the core of nano-prodrug. With FA targeting moieties on the surface, the obtained BiNp shows significant tumor-targeting ability and enhances the specific uptake of cancer cells. Upon the trigger by the intracellular acidic microenvironment of endosomes, the antineoplastic agent DOX is released on-demand and promotes the apoptosis of cancer cells. Simultaneously, the liberated FA-KLA can induce the dysfunction of mitochondria and evoke mitochondria-dependent apoptosis. In vitro and in vivo results show that the nano-prodrug BiNp with integrated programmed functions exhibits remarkable inhibition of tumor and achieves a maximized therapeutic efficiency with a minimized side effect.

Thermo/pH Dual Responsive Mixed-Shell Polymeric Micelles Based on the Complementary Multiple Hydrogen Bonds for Drug Delivery

Thermo/pH dual responsive mixed-shell polymeric micelles based on multiple hydrogen bonding were prepared by self-assembly of diaminotriazine-terminated poly(ɛ-caprolactone) (DAT-PCL), uracil-terminated methoxy poly(ethylene glycol) (MPEG-U), and uracil-terminated poly(N-vinylcaprolactam) (PNVCL-U) at room temperature. PCL acted as the core and MPEG/PNVCL as the mixed shell. Increasing the temperature, PNVCL collapsed and enclosed the PCL core, while MPEG penetrated through the PNVCL shell, thereby leading to the formation of MPEG channels on the micelles surface. The low cytotoxicity of the mixed micelles was confirmed by an MTT assay against BGC-823 cells. Studies on the in vitro drug release showed that a much faster release rate was observed at pH 5.0 compared to physiological pH, owing to the dissociation of hydrogen bonds. Therefore, the mixed-shell polymeric micelles would be very promising candidates in drug delivery systems.