Conjugation of a smart polymer to doxorubicin through a pH-responsive bond for targeted drug delivery and improving drug loading on graphene oxide

Polymeric nanoparticles have emerged as efficient carriers for anticancer drug delivery because they can improve the solubility of hydrophobic drugs and also can increase the bio-distribution of drugs throughout the bloodstream. In this work, a computational study is performed on a set of new pH-sensitive polymer–drug compounds based on an intelligent polymer called poly(β-malic acid) (PMLA). The molecular dynamics (MD) simulation is used to explore the adsorption and dynamic properties of PMLA–doxorubicin (PMLA–DOX) interaction with the graphene oxide (GOX) surface in acidic and neutral environments. The PMLA is bonded to DOX through an amide bond (PMLA-ami-DOX) and a hydrazone bond (PMLA-hz-DOX) and their adsorption behavior is compared with free DOX. Our results confirm that the polymer–drug prodrug shows unique properties. Analysis of the adsorption behavior reveals that this process is spontaneous and the most stable complex with a binding energy of −1210.262 kJ mol⁻¹ is the GOX/PMLA-hz-DOX complex at normal pH. On the other hand, this system has a great sensitivity to pH so that in an acidic environment, its interaction with GOX became weaker while such behavior is not observed for the PMLA-ami-DOX complex. The results obtained from this study provide accurate information about the interaction of the polymer–drug compounds and nanocarriers at the atomic level, which can be useful in the design of smart drug delivery systems.

Polymeric nanoparticles have emerged as efficient carriers for anticancer drug delivery because they can improve the solubility of hydrophobic drugs and also can increase the bio-distribution of drugs throughout the bloodstream.     

pH-triggered degradation and release of doxorubicin from zeolitic imidazolate framework-8 (ZIF8) decorated with polyacrylic acid

Zeolite imidazolate framework-8 (ZIF8) represents a class of highly porous materials with a very high surface area, large pore volume, thermal stability, and biocompatibility. In this study, ZIF8-based nanostructures demonstrated a high loading capacity for doxorubicin (62 mg Dox per g ZIF8) through the combination of π–π stacking, hydrogen bonding, and electrostatic interactions. Dox-loaded ZIF8 was subsequently decorated with polyacrylic acid (PAA) (ZIF8–Dox@PAA) that showed good dispersity, fluorescent imaging capability, and pH-responsive drug release. The stable localization and association of Dox in ZIF8@PAA were investigated by C¹³ nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy. The NMR chemical shifts suggest the formation of hydrogen bonding interactions and π–π stacking interactions between the imidazole ring of ZIF8 and the benzene ring of Dox that can significantly improve the storage of Dox in the ZIF8 nanostructure. Additionally, the release mechanism of ZIF8–Dox@PAA was discussed based on the detachment of the PAA layer, enhanced solubility of Dox, and destruction of ZIF8 at different pH conditions. In vitro release test of ZIF8–Dox@PAA at pH 7.4 showed the low release rate of 24.7% even after 100 h. However, ZIF8–Dox@PAA at pH 4.0 exhibited four stages of release profiles, significantly enhanced release rate of 84.7% at the final release stage after 30 h. The release kinetics of ZIF8–Dox@PAA was analyzed by the sigmoidal Hill, exponential Weibull, and two-stage BiDoseResp models. The ZIF8–Dox@PAA nanocarrier demonstrated a promising theranostic nanoplatform equipped with fluorescent bioimaging, pH-responsive controlled drug release, and high drug loading capacity.

The ZIF8–Dox@PAA nanocarrier demonstrated pH-triggered drug release through the detachment of the PAA layer along with the destruction of ZIF8 framework in acidic pH environment.     

Self-assemblies of pluronic micelles in partitioning of anticancer drugs and effectiveness of this system towards target protein

Micelles formed by pluronic triblock copolymers are known to be a promising class of drug delivery vehicles. Quantitative mechanistic insights into the ability of pluronic micelles to improve the solubility of poorly water soluble drugs, encapsulation and delivery of hydrophilic drugs are not available. The current study evaluated the energetics of encapsulation of chemotherapeutic drugs gemcitabine, cytarabine, and hydroxyurea in pluronic F127 and F68 micelles. In addition, the interactions of the drugs released from pluronic micellar media with serum albumin, which is a major circulatory transport protein, and subsequent conformational changes have also been analyzed with the help of calorimetry and spectroscopy. All the drugs showed improved partitioning in F127 micelles, the extent of which slightly increased with temperature rise. Interestingly, drug–protein binding is enhanced upon delivery from pluronic micelles without affecting the conformational integrity of the protein. This study highlights the role of drug functionalities, hydrophobicity, and steric factors towards their partitioning in pluronic micelles. Such studies are important in understanding physicochemical aspects of drug encapsulation and release, and lead to establishing structure–property–energetics correlations for developing suitable nano-drug delivery vehicles.

Micelles formed by pluronic triblock copolymers are known to be a promising class of drug delivery vehicles.     

Comparison of the performance of magnetic targeting drug carriers prepared using two synthesis methods

In this paper, two methods were used to prepare the magnetic targeting drug carrier Fe₃O₄–PVA@SH, the step-by-step method and the one-pot method. The loading and release properties of the compound were measured. The results show that the Fe₃O₄–PVA@SH prepared using both methods exhibited excellent drug delivery properties in an environment that simulates human body fluid (pH 7.2) and a lysosomal in vitro simulation (pH 4.7). In applications such as drug delivery, magnetic targeted drug carriers prepared by both methods demonstrated superparamagnetism, high fat solubility, high hydroxyl content, and good water solubility.

Roadmap for the synthesis of Fe₃O₄–PVA@SH using the step-by-step method and one-pot method.     

Polypeptide – decorated nanoliposomes as novel delivery systems for lutein

Lutein (LUT) is a bioactive food compound found in various vegetables and plays a critical role in the promotion of health and well-being. However, lutein is an unstable molecule which has a very low bioavailability caused by its poor solubility in aqueous media, and is poorly absorbed when administered orally. To enhance the stability, release and bioactivity of lutein, poly-l-lysine (PLL) decorated nanoliposomes (PLL–LUT-NLP) were developed as novel delivery systems for lutein. The mean particle size of PLL–LUT-NLP was found to be in the range 264–367 nm with a low polydispersity index (PDI < 0.4). The zeta potential changed from −38.6 mV in undecorated nanoliposomes to −27.9 mV in PLL-decorated nanoliposomes. Furthermore, the lutein entrapment efficiency (EE%) of PLL–LUT-NLP was found to be highest in nanoliposomes decorated with 0.06% (w/v) PLL. PLL could protect lutein in nanoliposomes from degradation and promote the lutein release from the nanoliposomes in gastrointestinal fluid conditions. Additionally, the PLL-decorated nanoliposomes maintained the antioxidant activity of the lutein, and the antiproliferative activity was more significant than that of undecorated nanoliposomes in inhibiting the proliferation of human tumor cells. These results suggest that PLL-decorated nanoliposomes have potential to be used for efficient delivery of lutein and further improve its bioavailability.

Polypeptide decorated nanoliposomes were prepared as novel delivery systems to enhance the stability, release and bioactivity of lutein.     

Pluronic F127 self-assembled MoS2 nanocomposites as an effective glutathione responsive anticancer drug delivery system

In this study, bio-responsive polymeric MoS₂ nanocomposites were prepared for use as a drug carrier for cancer therapy. Herein, we report the synthesis and demonstrate the self-assembly of pluronic F127 (PF127) on a cystamine–glutathione–MoS₂ (CYS–GSH–MoS₂) system, which can be used for GSH-triggered drug release under biological reducing conditions. The reduction-sensitive disulfide bond containing CYS was incorporated between the amphiphilic copolymer PF127 and GSH–MoS₂ to achieve feasible drug release. Percent drug loading capacity and encapsulation efficiency were 51.3% and 56%, respectively. In addition, when the MoS₂–GSH–CYS–PF127 nanocomposite was incubated in a GSH environment, the morphology of the nanocomposite tended to change, ultimately leading to drug release. The drug-loaded PF127–CYS–GSH–MoS₂ polymeric nanocomposites efficiently released 52% of their drug content after 72 h of incubation in a GSH reduction environment. The HeLa cells treated with DOX loaded MoS₂–GSH–CYS–PF127 showed 38% toxicity at drug concentration of 40 μg, which indicated that the successfully released of drug from carrier and caused the cell death. Further, fluorescence microscopy images of HeLa cells revealed the potential behavior of the MoS₂–GSH–CYS–PF12 nanocomposite during the 2- and 4 h incubation periods; the nanocomposite was only found in the cytoplasm of HeLa cells. Interestingly, after 6 h of incubation, the drug was slowly released from the nanocomposite and could enter the nucleus as confirmed by fluorescence imaging of HeLa cells. Altogether, our synthesized PF127-coated MoS₂ nanocomposite could be effectively adopted in the near future as a GSH-sensitive drug carrier.

In this study, bio-responsive polymeric MoS₂ nanocomposites were prepared for use as a drug carrier for cancer therapy.     

Flowery nickel–cobalt hydroxide via a solid–liquid sulphur ion grafting route and its application in hybrid supercapacitive storage

In our research, a two-step solid–liquid route was employed to fabricate flowery nickel–cobalt hydroxide with sulphur ion grafting (Ni1Co2–S). The utilization of NaOH/agar and Na₂S/agar could efficiently retard the release rates of OH⁻ or S²⁻ ions at the solid–liquid interface due to strong bonding between agar hydrogel and these anions. Ni1Co2–S generally displays ultrathin flowery micro-frame, ultrathin internal nanosheets and expanded pore size. Besides, the introduction of suitable sulphide species into nickel–cobalt hydroxide could improve its conductivity due to the lower band gap of Ni–Co sulphide. The supercapacitive electrode Ni1Co2–S presented capacitance of 1317.8 F g⁻¹ (at 1 A g⁻¹) and suitable rate performance (77.9% at 10 A g⁻¹ and 59.3% at 20 A g⁻¹). Furthermore, a hybrid supercapacitor (HSC) was developed utilizing positive Ni1Co2–S and negative activated carbon electrodes. As expected, the HSC device exhibited excellent specific capacitance (117.1 F g⁻¹ at 1 A g⁻¹), considerable energy densities (46.7 W h kg⁻¹ at 0.845 kW kg⁻¹ and 27.5 W h kg⁻¹ even at 9 kW kg⁻¹) and suitable cycling performance, which further illuminated the high energy storage capacity of Ni1Co2–S.

The Ni1Co2–S material fabricated via a solid–liquid route achieves high-performance supercapacitive storage.     

Solubility and biological activity enhancement of docetaxel via formation of inclusion complexes with three alkylenediamine-modified β-cyclodextrins

Docetaxel (DTX) is an effective and commonly used chemotherapeutic drug for cancer. However, its efficacy is greatly compromised because of its toxicity and poor water solubility. In order to overcome these disadvantages, three inclusion complexes between DTX and alkylenediamine-modified β-cyclodextrins (H1–3) with ethylene, propylene and butylene segments were prepared and characterized. The phase solubility studies demonstrated that the stoichiometry of the inclusion complexes between H1–3 and DTX were 1 : 1. The binding abilities of host H1–3 towards DTX decrease in the following order: H3 > H2 > H1, which had good consistency with the decreasing alkylene lengths of these hosts. The water solubility of DTX is remarkably increased 216, 242 and 253 times after forming inclusion complexes with H1–3, respectively. In vitro release studies of DTX from H1–3/DTX into NaAc–HAc buffer solution (pH 5.0) or PBS (pH 7.4) exhibited a preliminary stage burst effect and followed by a slow drug release. The cytotoxicity studies revealed that the H1–3/DTX inclusion complexes exhibited better cytotoxicity profiles against MCF-7, SW480 and A-549 cells than that of DTX. Furthermore, compared with the treatment of DTX, the H1/DTX inclusion complex significantly increased the cell apoptosis percentage from 17.2% to 30.2% (5 μg mL⁻¹), 19.0% to 31.0% (10 μg mL⁻¹), and 19.3% to 32.2% (15 μg mL⁻¹), respectively. These results will provide useful information for H1–3/DTX inclusion complexes as safe and efficient anticancer drug formulations.

Docetaxel (DTX) is an effective and commonly used chemotherapeutic drug for cancer.     

Self-assembly of the monohydroxy triterpenoid lupeol yielding nano-fibers,sheets and gel: environmental and drug delivery applications

Lupeol is a medicinally important naturally abundant triterpenoid having a 6–6–6–6–5 fused pentacyclic backbone and one polar secondary “–OH” group at the C3 position of the “A” ring. It was extracted from the dried outer bark of Bombax ceiba and its self-assembly properties were investigated in different neat organic as well as aquous-organic binary liquid mixtures. The triterpenoid having only one polar “–OH” group and a rigid lipophilic backbone self-assembled in neat organic non-polar liquids like n-hexane, n-heptane, n-octane and polar liquids like DMSO, DMF, DMSO–H₂O, DMF–H₂O, and EtOH–H₂O yielding supramolecular gels via formation of nano to micrometre long self-assembled fibrillar networks (SAFINs). Morphological investigation of the self-assemblies was carried out by field emission scanning electron microscopy, high resolution transmission electron microscopy, atomic force microscopy, optical microscopy, concentration dependent FTIR and wide angle X-ray diffraction studies. The mechanical properties of the gels were studied by concentration dependent rheological studies in different solvents. The gels were capable of removing toxic micro-pollutants like rhodamine-B and 5,6-carboxyfluorescein as well as the toxic heavy metal Cr(vi) from contaminated water. Moreover release of the chemotherapeutic drug doxorubicin from a drug loaded gel in PBS buffer at pH 7.2 has also been demonstrated by spectrophotometry.

The monohydroxy triterpenoid lupeol forms gels in organic and aqueous organic liquids via self-assembly. The resulting supramolecular gels could be utilized for pollutant capture, drug entrapment and release applications.     

Physiologically stable F127-GO supramolecular hydrogel with sustained drug release characteristic for chemotherapy and photothermal therapy

A synthetic method for preparing a Pluronic F127 (F127)-stabilized graphene (GO) supramolecular hydrogel as a safe nanovehicle for combination treatment has been studied. Doxorubicin (DOX) as a model drug is non-covalently bound on the great surface area of GO due to strong π–π interaction, hydrophobic interaction, and the strongest hydrogen bonding. In vitro drug release experiments revealed that this F127-stabilized GO supramolecular hydrogel has a sustained drug release characteristic. Furthermore, the supramolecular hydrogel showed better in vitro antitumor ability under NIR (near infrared) laser irradiation because of the excellent photothermal effect of GO. Moreover, we evaluated its antitumor ability in vivo and the results show that the hydrogel system can also markedly inhibit the growth of a tumor when administered individually, especially under laser irradiation. All these findings make the supramolecular hydrogel system promising for combination therapy with good bioavailability and minimal side effects.

The F127-GO-DOX supramolecular hydrogel system with sustained drug release characteristic for chemotherapy and photothermal therapy.     

Efficient adsorption of methyl orange and methyl blue dyes by a novel triptycene-based hyper-crosslinked porous polymer

It is still a great challenge to develop new materials for the highly efficient entrapment of organic dyes from aqueous solution. Herein, a novel triptycene-based hyper-crosslinked porous polymer (TPP–PP) was designed and synthesized by a simple Friedel–Crafts reaction. The obtained polymer TPP–PP has a high surface area, abundant pore structure and stable thermal performance. Due to the above characteristics, TPP–PP has good adsorption performance for anionic methyl orange solution (MO) and cationic methyl blue solution (MB). Under the optimal experiment conditions, the TPP–PP showed an excellent adsorption capacity for MO (220.82 mg g⁻¹) and MB (159.80 mg g⁻¹), respectively. The adsorption kinetics fitted the pseudo-second-order model. The adsorption of MO by TPP–PP reaches equilibrium within 180 minutes, and the adsorption of MB reaches equilibrium within 150 minutes. The adsorption behavior was not only spontaneous but also endothermic in reality. At the same time, TPP–PP also has good reusability. After 5 cycles of experiments, the removal rate of MO and MB by TPP–PP can still reach more than 80%. Thus, the Friedel–Crafts reaction crosslinked method might be a promising approach for the synthesis of novel material for the highly efficient extraction of dye wastewater.

A novel triptycene-based hyper-crosslinked porous polymer was developed for the highly efficient entrapment of organic dyes from aqueous solution.     

Improving the solubility and bioavailability of anti-hepatitis B drug PEC via PEC–fumaric acid cocrystal

PEC is a new generation of phosphamide ester anti-hepatitis B virus drug. It is a prodrug of tenofovir and can be rapidly metabolized to tenofovir. However, its poor solubility in water (0.219 mg mL⁻¹ at 25 °C) has limited its oral bioavailability. In this study, we aimed to improve the solubility and consequently the oral bioavailability of PEC via a cocrystal. A cocrystal of PEC with fumaric acid (FUA) (PEC–FUA, 1 : 1) was successfully obtained and characterized. The crystal structure of this cocrystal was tested using a single crystal X-ray diffraction method. The intrinsic dissolution rate (IDR) characterization was performed in a pH 6.8 buffer. The solubility of this cocrystal in 0.1 M HCl (pH 1.0) and pH 6.8 phosphate buffers was investigated, and the results showed that the solubility of the cocrystal was 3.8 and 4.0 times that of free PEC, respectively. We also studied the pharmacokinetics of beagle dogs. The mean AUC_{0–24 h} of the cocrystal is about 4.2 times that of free PEC, indicating that the solubility and bioavailability of PEC can indeed be improved by forming the cocrystal. It may become an ideal solid form of an active pharmaceutical ingredient suitable for pharmaceutical preparations, and it can be further studied later.

A cocrystal of PEC with fumaric acid (FUA) (PEC–FUA, 1 : 1) was successfully obtained and characterized. The mean AUC_{0–24 h} of the cocrystal is about 4.2 times that of free PEC.     

A biocompatible poly(amidoamine) (PAMAM) dendrimer octa-substituted with α-cyclodextrin towards the controlled release of doxorubicin hydrochloride from its ferrocenyl prodrug

Facile and efficient methods for the synthesis of the first poly(aminodamine) PAMAM G1.0 dendrimer octa-substituted with α-cyclodextrin and a novel ferrocenyl prodrug of doxorubicin hydrochloride are developed. This vector is non-toxic and can bind the designed ferrocenyl prodrug. It also shows a controlled drug release profile and high cytotoxicity against breast cancer cells (MCF-7), as elucidated by the in vitro biological studies performed with an innovative cell-on-a-chip microfluidic system.

A controlled release of doxorubicin hydrochloride from a novel nanoconjugate comprising PAMAM dendrimer octa-substituted with α-cyclodextrin and ferrocenyl prodrug is presented.

Poly(amidoamine) (PAMAM) dendrimers are of the highest interest to general medicinal chemistry.^1–3 These dendrimers show beneficial physicochemical or biological properties in comparison with the respective polyamine polymers, e.g., polyethylenimine (PEI). In general, the cytotoxicity of PAMAM dendrimers is lower in comparison to that of PEI, which is an important factor in terms of the development of non-viral drugs or gene delivery vectors. The unique shape of PAMAM dendrimers as well as the presence of highly reactive amino groups imply interesting possibilities towards the construction of novel systems dedicated to modern therapies in humans.In recent years, the chemistry and application of PAMAM dendrimer nanoconjugates with cyclodextrins (CDs) has drawn an unflagging interest.^4–7 CDs are the supramolecules formed of six, seven or eight d-glucose units, which are coupled via α-1,4-glycosidic bonds.^8,9 CDs form cup-shaped molecules. Their cavity is hydrophobic, whilst the exterior is hydrophilic. As a result, CDs show unique properties towards the formation of host–guest complexes with hydrophobic compounds, including drugs.^10–12 From the point of view of applied medicinal chemistry, the presence of CDs in the therapeutic system provides the possibility to release a drug in a controlled way. It is associated with the strategy of stepwise release of a drug from the inner cavity of CD. Furthermore, CDs increase the water solubility and/or biocompatibility of the drug delivery vector. The abovementioned features make CDs promising candidates for the decoration of PAMAM dendrimers. PAMAM dendrimers grafted with CD moieties can be used as versatile delivery agents. The uses of such macromolecular species cover the binding and release of various therapeutic species, including nucleic acids (e.g., siRNA or DNA)^13–16 or drugs (e.g., doxorubicin or sodium methotrexate).^6,17,18 These dendrimeric structures showed encouraging biological properties towards their use in medicinal chemistry, especially in terms of the design of novel anticancer agents. In some cases, additional structural motifs were introduced to these vectors, such as poly(ethylene glycol) (PEG) residues, towards providing specific biological or physicochemical properties.^18,19 The studies dealing with the application of PAMAM-CD architectures towards the construction of biosensors were also reported.^20,21 Furthermore, interesting studies on the solubilisation of highly hydrophobic fullerenes with PAMAM-CD-PEG vectors¹⁹ or cobaltocene-bridged PAMAM-CD dendrimers were also reported. These examples clearly elucidate the capabilities of PAMAM-CD nanoconjugates towards their use in modern applied chemistry, including nanomedicine.The use of ferrocene (Fc) in medicinal chemistry has been studied over the years.^22–31 Some of the reports deal with the synthesis of Fc-templated drugs^23,24 or prodrugs.^25–31 The latter concept is especially interesting from the point of view of applied medicinal chemistry, since prodrug technology may improve the biocompatibility and/or bioaccessibility of a drug.^32–34 However, the reports dealing with the formation of Fc-based prodrugs are still sparse; they cover, e.g., the synthesis of Fc-functionalized nucleobases³¹ or synthesis and biological evaluation of the prodrugs bearing Fc and boronic acid moieties.^25,26 Interestingly, Fc is known for the formation of stable host–guest inclusion complexes with CD.^27,28 Fc is not soluble in water, thus, it is not released from its complex with CD in an aqueous medium. Fc release can be only achieved via a redox process (ferrocenyl cation does not form stable inclusion complexes) and the employment of this concept can be indeed found in the literature.^29,30 Thus, Fc can also be employed as the building block for macromolecular therapeutic systems, including self-assembling drug delivery systems.^35–38 An interesting example is the formation of a pH-responsive supramolecular system for controlled drug release, which is based on the self-assembly of the Fc-PEG conjugate and β-cyclodextrin-functionalized doxorubicin hydrochloride.³⁵ The drug in this system, that is doxorubicin hydrochloride (DOX*HCl), was released by means of an oxidant-dependent process. This system showed promising biological features towards cancer treatments. In fact, DOX*HCl is commonly the first and/or best choice drug for the treatment of various cancers, including breast or lung cancer.^39–41In pursuit of the design of novel anticancer agents, herein, we present efficient and facile methods for the preparation of the first PAMAM G1.0 dendrimer octa-substituted with α-cyclodextrin (octa-αCD-PAMAM) and a novel DOX*HCl prodrug, namely ferrocenyl ester of doxorubicin hydrochloride (Fc–COO–DOX*HCl). Octa-αCD-PAMAM is non-toxic and has the property to bind Fc–COO–DOX*HCl. The in vitro studies revealed encouraging biological features of the designed nanoconjugate, namely controlled drug release behavior and high cytotoxicity against breast cancer cell line (MCF-7). In vitro biological assays were performed with an innovative cell-on-a-chip microfluidic system. We anticipate our findings will further stimulate the progress in medicinal chemistry with the use of macromolecular therapeutic systems exhibiting a controlled drug release profile.The procedure for the synthesis of octa-αCD-PAMAM (3) is presented in Fig. 1. In general, this derivative of PAMAM G1.0 (1) was obtained in good yield (80%) by means of a reductive amination approach with the use of α-cyclodextrin monoaldehyde (αCD-CHO; 2). The reaction occurred between each of the eight terminals, primary amino groups of 1, and formyl moieties of 2. In the first step of the reaction, imine-bonds were formed and then they were reduced to CH₂NH₂ linkages by means of the treatment with sodium triacetoxyborohydride.⁴² The obtained octa-αCD-PAMAM (3) was characterized with NMR and FT-IR spectroscopies, as well as with ESI-MS.⁴³ It is noteworthy that elemental analysis and ESI-MS experiment ultimately confirmed the introduction of eight αCD residues to one molecule of PAMAM G1.0; the calculated and found data were highly consistent. It means that the herein developed methodology enables the full functionalization of PAMAM''s terminal amino groups with biocompatible, αCD residues.Open in a separate windowFig. 1Synthesis of octa-αCD-PAMAM (3).The ferrocenyl ester of DOX*HCl (Fc–COO–DOX*HCl; 5) was obtained by means of the treatment of DOX*HCl with ferrocenecarboxylic acid (Fc-COOH; 4). The synthetic scheme is presented in Fig. 2. This process was based on the carbodiimide-mediated ester bond formation reaction (Steglich esterification) with the inclusion of a carboxyl group of 4 and the terminal CH₂OH moiety of DOX*HCl.⁴² It is worth noting that no reaction occurred between the amino group of DOX*HCl since this moiety remained in the form of hydrochloride during all the reaction and purification steps (no alkaline conditions were applied in our synthesis). Thus, in our methodology native DOX*HCl can be used, without the need for amino group protection⁴⁴ or use of enzymatic process.⁴⁵ Combination of NMR and FT-IR spectroscopies, as well as high-resolution mass spectrometry (HRMS) confirmed the formation of pure Fc–COO–DOX*HCl (5), a novel DOX*HCl prodrug, which bears the ferrocenyl moiety.⁴³Open in a separate windowFig. 2Synthesis of Fc–COO–DOX*HCl (5).With both octa-αCD-PAMAM (3) and Fc–COO–DOX*HCl (5) at hand, we began to merge their chemistries (Fig. 3). Our concept originated from the following facts. Fc is known for its capability to form very stable complexes with αCD.^27,28 αCD can accommodate one Fc residue, since the width of the inner cavity of αCD equals to 5.7 Å, whilst its depth is 7.8 Å. On the other hand, DOX*HCl molecule is too big to be effectively complexed inside the inner cavity of αCD; for this purpose, a larger CD should be used, such as β-cyclodextrin (width of inner cavity 7.8 Å) or γ-cyclodextrin (width of inner cavity 8.8 Å).^46–48 Therefore, in our system, Fc-mediated complexation with Fc–COO–DOX*HCl (5) and αCD units of octa-αCD-PAMAM (3) occurs. We have successfully obtained the desired nanoconjugate {Fc–COO–DOX*HCl}@{octa-αCD-PAMAM} (6) in quantitative yields using a combination of solution and lyophilisation methodology.⁴² FT-IR spectroscopy suggested the anticipated Fc-oriented complexation for this nanoconjugate, since no absorption bands coming from Fc moiety of 5 were observed in the spectrum of nanoconjugate 6, whilst absorption bands coming from DOX*HCl were found.⁴⁹ Importantly, ESI-MS and elemental analysis confirmed the formation of the desired nanoconjugate 6; the calculated and obtained data were highly consistent.⁴³ Additionally, we further studied the complex formation phenomenon with NMR techniques. At first, the Fc-oriented complexation was tracked with ¹H–¹H ROESY NMR.²⁵ The ¹H–¹H ROESY NMR spectrum of 6 featured the cross-correlations between Fc''s cyclopentadienyl signals (H_Cp) and H-3, H-5 inner protons of α-CD (Fig. 4). It was ascribed to the inclusion of Fc inside α-CD''s inner cavity. It stands for the successful formation of inclusion complexes between guest 5 and α-CD units of 3. Secondly, the results of ¹H DOSY NMR analysis suggested the formation of a single host–guest system. ¹H DOSY NMR technique involves the measurement of the diffusion coefficient of the compounds forming a sample and is a powerful and versatile NMR method for the analyses of the supramolecular systems, including host-guest complexes.^25,50,51 The ¹H DOSY NMR spectrum of nanoconjugate 6 showed one diffusion coefficient value (0.358 10⁻¹⁰ m² s⁻¹).^52b Thus, we hypothesized that a single host-guest system might have been formed. In other words, we claim that neither unbound 5 nor other dendrimeric structures (i.e., bearing less than eight complexed molecules of 5) were found in the sample. To further support this hypothesis, ¹H DOSY NMR spectra in the same solvent were acquired for native host 3 and guest 5.^52a Both of these showed higher diffusion coefficient values than the resultant nanoconjugate 6. As expected, the diffusion coefficient value for 5 (3.699 10⁻¹⁰ m² s⁻¹) was found to be higher than that for 3 (0.746 10⁻¹⁰ m² s⁻¹; this is because 3 is much bigger than 5). This clear difference in the diffusion coefficient values between the molecules forming the system (3, 5) and their resultant inclusion complex 6 support our claim on the host–guest chemistry behaviour for the studied system.⁵² Finally, UV-Vis spectroscopy was applied to provide an insight into the stoichiometry of the host-guest complexes of 3 and 5.²⁵ The UV-Vis spectra of guest 5 featured an increase in the absorbance in the presence of host 3, as well as some slight blue shift behaviour.^52b These features were ascribed to the inclusion phenomenon. This change differed between the samples that enabled the estimation of complex stoichiometry. The complex stoichiometry was estimated on the basis of Job''s plot analysis.²⁵ The estimated stoichiometry was found to be 1 : 8 (host : guest);^52b this conclusion supported the outcomes from the ESI-MS experiment and is highly consistent with other above-presented supramolecular analyses. All these important features mentioned above mean that the herein developed methodology enables full “blocking” of αCD''s cavities with ferrocenyl units of DOX*HCl prodrug 5 by means of the formation of Fc-oriented complexes.Open in a separate windowFig. 3Synthesis of Fc–COO–DOX*HCl (5). For the structures of 3 and 5, see Fig. 1 and ​and22.Open in a separate windowFig. 4The 4.30–3.45 ppm inset of the ¹H–¹H ROESY NMR (DMSO-d₆: D₂O = 1 : 1 v/v, 500 MHz) spectrum of nanoconjugate {Fc–COO–DOX*HCl}@{octa-αCD-PAMAM} (6) presenting the crucial cross-correlations standing for the inclusion phenomenon (these cross-correlations are marked in blue). The graphical representation of the complex is also shown.We envision that DOX*HCl might be released from nanoconjugate 6 under acidic conditions. Our hypothesis was based on two facts. Firstly, DOX*HCl is bound to this nanoconjugate in the form of its ferrocenyl prodrug (ester bond) by means of Fc-oriented complexation. Ester bonds are known for their prospective use in prodrug technologies.^32–34 Secondly, the pH of cancer cells was found to be acidic (pH 4–6).^53–55 It gives the possibility of a controlled drug release at the therapeutic target (cancer cell environment). In order to examine the possibility of DOX*HCl release from nanoconjugate 6 and the profile of this release, in vitro controlled drug release trials at pH 4.7 were performed.⁵⁶ The DOX*HCl release curve is presented in Fig. 5a, blue curve. This curve resembles the characteristic controlled drug release profile. It means that DOX*HCl release from nanoconjugate 6 was stepwise. This controlled release was ascribed to the hydrolysis of ester bonds between Fc and DOX*HCl parts of compound 5 complexed inside αCD units within nanoconjugate 6. The cumulative release of DOX*HCl after 24 hours equalled to ca. 78% and the final cumulative release (after 72 hours) was found to be ca. 87%. The first, relatively fast, DOX*HCl release segment up to ca. 12 h was ascribed to the release of DOX*HCl molecules that were close to the dendrimer–buffer interface.⁵⁷ Subsequently, the cumulative release of DOX*HCl increased gradually with the contact time. The plateau segment was achieved between 48 h and 72 h. This high total cumulative release value at a rationally short time constitutes a good starting point for the design of novel macromolecular therapeutics exhibiting a controlled drug release profile. For comparison, drug release trials were also performed at pH 7.4 (physiological pH; Fig. 5a, red curve). No significant drug release was found in this environment (cumulative DOX release was lower than ca. 1.5%, which means that in practise no compound, neither 5 nor any of its subpart (e.g., DOX), was released from 6). This finding means that (i) for our system simple equilibrium displacement during the dialysis did not take place, which confirms that the release of the drug is driven by acidic pH (hydrolysis of an ester bond), (ii) no unbound 5 was present in nanoconjugate 6.Open in a separate windowFig. 5(a) DOX*HCl release curves from nanoconjugate 6 at pH 4.7 and pH 7.4; (b) MCF-7 cell viability after treatment during long-term spheroid culture.Encouraged by the above-presented results, we estimated the cytotoxicity profile of the designed nanoconjugate 6 against breast cancer (MCF-7) spheroids. These studies were performed using an innovative cell-on-a-chip microfluidic system. Cell-on-a-chip are miniature, microfluidic devices that contain in vitro cell cultures under flow conditions that simulate physiology at the tissue level.⁵⁸ Unlike conventional in vitro cell culture methods, microfluidic-based cell cultures to a greater extent reproduce the in vivo conditions. It is associated with the combination of surfaces mimicking extracellular matrix geometries and microfluidic channels that regulate fluid transport (nutrients important for cells).⁵⁹ In our research, we used the innovative microfluidic device for long-term three-dimensional (3D) spheroid cell culture.⁶⁰ The use of three-dimensional cell contact and the flow conditions in a single device allowed more than standard two-dimensional cell cultures to reproduce the in vivo environment of breast cancer. Moreover, this device allowed us to perform quick and precise microscopic and fluorescence analysis after the drug treatment. The microscopic analysis involved the observation of morphological spheroid changes (in single, always the same spheroid) while fluorescence analysis involved the evaluation of the metabolic activity of spheroids (their viability). The results of biological assays are shown in Fig. 5b.⁶¹ At first, the cytotoxicity profile of octa-αCD-PAMAM (3) was estimated. This dendrimeric vector in each tested concentration was found to be non-toxic, which is beneficial in terms of its use as a drug delivery vector. The same situation was observed with free DOX*HCl. On the other hand, nanoconjugate 6 showed different cytotoxicity profiles; nanoconjugate 6 was found to be highly toxic to breast cancer cells. Cell viability after 72 h equated to ca. 40%. In comparison, this viability for octa-αCD-PAMAM (3) and free DOX*HCl (50 μg mL⁻¹, 72 h) was ca. 95% and ca. 81%, respectively. During our studies, we also observed that higher concentrations of the tested substances were less toxic to breast cancer cells. This can be related to the defense mechanism of cancer tumors; cancer tumors recognize higher concentrations of toxic substances and do not absorb them from the external environment.⁶² In addition, higher cell viability may be associated with the stimulation of cell proliferation after using higher concentrations of octa-αCD-PAMAM. We observed that the free drug carrier at higher concentrations increases the viability of MCF-7 cells (Fig. 5b). Similarly, the MCF-7 viability after treatment with a higher concentration of nanoconjugate 6 was also higher.     

Isostructural cocrystals of metaxalone with improved dissolution characteristics

Muscle relaxant and pain reliever metaxalone (MET) is a biopharmaceutical classification systems (BCS) class II drug with poor aqueous solubility and high permeability. The presence of an aromatic skeleton and cyclic carboxamate moiety are the probable reasons for the decreased aqueous solubility, which impacts on its low bioavailability. A high dose (800 mg) of the drug often creates adverse side effects on the central nervous system that needs urgent remedy. Cocrystallization of MET with nicotinamide (NAM), salicylamide (SAM), and 4-hydroxybenzoic acid (HBA) resulted in multicomponent solids that were characterized by PXRD, DSC and single crystal X-ray diffraction. Cocrystals with SAM and NAM form 2D isostructural cocrystals, whereas with HBA the result is a differently packed cocrystal hydrate (or anisole hemisolvate) depending upon the crystallization medium. Similar to the reported MET cocrystals, these cocrystals also confirm the preference for an imide⋯imide homosynthon in the drug. The dominance of the drug–drug homodimer over drug-coformer heterodimers was demonstrated based on binding energy calculations. Further, powder dissolution experiments in pH 6.8 phosphate buffer indicate that the cocrystals improved the apparent solubility compared to the native drug by 3–9 fold. The absence of stronger heterosynthons between MET and the coformers, their lower melting points and the high solubility of the coformers are the probable reasons for the enhanced solubility of the bioactive component. The MET–NAM cocrystal exhibited the highest solubility/dissolution rate among the three binary solid forms, which may offer improved bioavailability and a lower dose with minimal side effects.

Metaxalone forms isostructural cocrystals with nicotinamide and salicylamide that offer a solubility advantage compared to the native drug. A drug–drug homosynthon is retained in all the cocrystal structures.     

Functionalization of MOF-5 with mono-substituents: effects on drug delivery behavior

Metal organic frameworks (MOFs) are widely used in drug carrier research due to their tunability. The properties of MOFs can be adjusted through incorporation of mono-substituents to obtain pharmaceutical carriers with excellent properties. In this study, different functional groups of –NH₂, –CH₃, –Br, –OH and –CH₂ CH are connected to MOF-5 to analyse the effect of mono-substituent incorporation on drug delivery properties. The resulting MOFs have similar structures, except for Br–MOF. The pore size of this series of MOFs ranges from 1.04 nm to 1.10 nm. Using oridonin (ORI) as a model drug, introduction of the functional groups appears to have a significant effect on the drug delivery performance of the MOFs. The IRMOFs can be ranked according to drug-loading capacity: MOF-5 > HO–MOF-5 > H₃C–MOF-5 = Br–MOF-5 > H₂N–MOF-5 > CH₂ CH–MOF-5. The ORI release from ORI @IRMOFs is explored at two different pH values: 7.4 and 5.5, and the ORI@IRMOFs are ranked according to the cumulative release percentage of ORI: ORI@MOF-5 > ORI@Br–MOF-5 > ORI@H₃C–MOF-5 > ORI@H₂N–MOF-5 > CH₂ CH–MOF-5 > ORI@ HO–MOF-5. In particular, the release behaviour of ORI@MOFs is described through a new model. The different drug delivery performance of MOFs may be due to the complex interactions between MOFs and ORI. In addition, the introduction of single substituents does not change the biocompatibility of MOFs. MTT in vitro experiments prove that this series of MOFs has low cytotoxicity. This study shows that the incorporation of single substituents can effectively adjust the drug delivery behaviour of MOFs, which is conducive to realization of personalized drug delivery modes. The introduction of active groups can also facilitate post-synthesis modification to achieve coupling of targeting groups. MOFs incorporated with single substituents perform favorably in terms of use as biomedical drug delivery alternative carriers in effective drug payload and flexible drug release.

Metal organic frameworks (MOFs) are widely used in drug carrier research due to their tunability.     

Peptide nanosponges designed for rapid uptake by leukocytes and neural stem cells

The structure of novel binary nanosponges consisting of (cholesterol-(K/D)_nDEVDGC)₃-trimaleimide units possessing a trigonal maleimide linker, to which either lysine (K)₂₀ or aspartic acid (D)₂₀ are tethered, has been elucidated by means of TEM. A high degree of agreement between these findings and structure predictions through explicit solvent and then coarse-grained molecular dynamics (MD) simulations has been found. Based on the nanosponges'' structure and dynamics, caspase-6 mediated release of the model drug 5(6)-carboxyfluorescein has been demonstrated. Furthermore, the binary (DK20) nanosponges have been found to be virtually non-toxic in cultures of neural progenitor cells. It is of a special importance for the future development of cell-based therapies that DK20 nanosponges were taken up efficiently by leucocytes (WBC) in peripheral blood within 3 h of exposure. The percentage of live cells among the WBC was not significantly decreased by the DK20 nanosponges. In contrast to stem cell or leucocyte cell cultures, which have to be matched to the patient, autologous cells are optimal for cell-mediated therapy. Therefore, the nanosponges hold great promise for effective cell-based tumor targeting.

Nanosponges for drug delivery.     

Hierarchical Ni–Co–Mn hydroxide hollow architectures as high-performance electrodes for electrochemical energy storage

In this study, hierarchical Ni–Co–Mn hydroxide hollow architectures were successfully achieved via an etching process. We first performed the synthesis of NiCoMn-glycerate solid spheres via a solvothermal route, and then NiCoMn-glycerate as the template was etched to convert into hierarchical Ni–Co–Mn hydroxide hollow architectures in the mixed solvents of water and 1-methyl-2-pyrrolidone. Hollow architectures and high surface area enabled Ni–Co–Mn hydroxide to manifest a specific capacitance of 1626 F g⁻¹ at 3.0 A g⁻¹, and it remained as large as 1380 F g⁻¹ even at 3.0 A g⁻¹. The Ni–Co–Mn hydroxide electrodes also displayed notable cycle performance with a decline of 1.6% over 5000 cycles at 12 A g⁻¹. Moreover, an asymmetric supercapacitor assembled with this electrode exhibited an energy density of 44.4 W h kg⁻¹ at 1650 W kg⁻¹ and 28.5 W h kg⁻¹ at 12 374 W kg⁻¹. These attractive results demonstrate that hierarchical Ni–Co–Mn hydroxide hollow architectures have broad application prospects in supercapacitors.

An effective etching method is developed for the synthesis of hierarchical Ni–Co–Mn hydroxide hollow architectures, which exhibit high performance in electrochemical energy storage.     

Biodegradable reduction and pH dual-sensitive polymer micelles based on poly(2-ethyl-2-oxazoline) for efficient delivery of curcumin

A series of disulfide-linked amphiphilic polymers polyoxaline-SS-poly(lactide) (PEtOx-SS-PLA) were prepared and self-assembled into nano-micelles in water. The anticancer drug curcumin (Cur) was selected as a model drug, the entrapment of Cur in PEtOx-SS-PLA micelles was investigated and the intracellular transport and release of Cur-loaded micelles was studied in C6 cells. The preparation of Cur-loaded polymer micelles showed that micelle size decreased after drug loading, favoring cell phagocytosis. MTT experiments showed that PEtOx-SS-PLA 52 micelles have a small IC₅₀ (2.05 μg mL⁻¹). The release behavior of PEtOx-SS-PLA 52 drug-loaded micelles in C6 cells showed that polymer micelle enhanced the intracellular release of Cur, and increased the inhibition effect of cancer cells. In a word, these reduction and pH-dual sensitive, biodegradable, hydrophilic shell-discarding PEtOx-SS-PLA micelles have great potential for future tumour administration.

A series of disulfide-linked amphiphilic polymers polyoxaline-SS-poly(lactide) (PEtOx-SS-PLA) were prepared and self-assembled into nano-micelles in water.     

Construction of a graphene/polypyrrole composite electrode as an electrochemically controlled release system

A new class of stimuli responsive drug delivery systems is emerging to establish new paradigms for enhancing therapeutic efficacy. To date, most electro-responsive systems rely on noble metal electrodes that likely cause the limitations for implantation applications. Herein, a graphene/polypyrrole composite electrode (GN–PPy–FL) was fabricated based on two-dimensional (2D) graphene (GN) film and conductive and biocompatible polypyrrole (PPy) nanoparticles loaded with a negative drug model of fluorescein sodium (FL) via chemical oxidation polymerization. The conductive composite electrode was utilized as a drug carrier to realize the electrically controlled release of the FL. The release rate from conductive nanoparticles can be controlled by the applied voltages. The study provides a multi-stimuli responsive drug release system, demonstrating the potential applications of the controlled release of various drugs, peptides or proteins.

A biocompatible conductive composite electrode GN–PPy–FL can realize controlled release of a drug model triggered by low voltages.