Development of a polymeric micellar formulation for valspodar and assessment of its pharmacokinetics in rat

Recent Advances on PEO-PCL Block and Graft Copolymers as Nanocarriers for Drug Delivery Applications

Poly(ethylene oxide)-poly(ε-caprolactone) (PEO-PCL) is a family of block (or graft) copolymers with several biomedical applications. These types of copolymers are well-known for their good biocompatibility and biodegradability properties, being ideal for biomedical applications and for the formation of a variety of nanosystems intended for controlled drug release. The aim of this review is to present the applications and the properties of different nanocarriers derived from PEO-PCL block and graft copolymers. Micelles, polymeric nanoparticles, drug conjugates, nanocapsules, and hybrid polymer-lipid nanoparticles, such as hybrid liposomes, are the main categories of PEO-PCL based nanocarriers loaded with different active ingredients. The advantages and the limitations in preclinical studies are also discussed in depth. PEO-PCL based nanocarriers could be the next generation of delivery systems with fast clinical translation. Finally, current challenges and future perspectives of the PEO-PCL based nanocarriers are highlighted.

Development and Characterization of PEGylated Fatty Acid-Block-Poly(ε-caprolactone) Novel Block Copolymers and Their Self-Assembled Nanostructures for Ocular Delivery of Cyclosporine A

Low aqueous solubility and membrane permeability of some drugs are considered major limitations for their use in clinical practice. Polymeric micelles are one of the potential nano-drug delivery systems that were found to ameliorate the low aqueous solubility of hydrophobic drugs. The main objective of this study was to develop and characterize a novel copolymer based on poly (ethylene glycol) stearate (Myrj™)-block-poly(ε-caprolactone) (Myrj-b-PCL) and evaluate its potential as a nanosystem for ocular delivery of cyclosporine A (CyA). Myrj-b-PCL copolymer with various PCL/Myrj ratios were synthesized via ring-opening bulk polymerization of ε-caprolactone using Myrj (Myrj S40 or Myrj S100), as initiators and stannous octoate as a catalyst. The synthesized copolymers were characterized using 1H NMR, GPC, FTIR, XRD, and DSC. The co-solvent evaporation method was used to prepare CyA-loaded Myrj-b-PCL micelles. The prepared micelles were characterized for their size, polydispersity, and CMC using the dynamic light scattering (DLS) technique. The results from the spectroscopic and thermal analyses confirmed the successful synthesis of the copolymers. Transmission electron microscopy (TEM) images of the prepared micelles showed spherical shapes with diameters in the nano range (<200 nm). Ex vivo corneal permeation study showed sustained release of CyA from the developed Myrj S100-b-PCL micelles. In vivo ocular irritation study (Draize test) showed that CyA-loaded Myrj S100-b-PCL88 was well tolerated in the rabbit eye. Our results point to a great potential of Myrj S100-b-PCL as an ocular drug delivery system.

Design and Development of D‒α‒Tocopheryl Polyethylene Glycol Succinate‒block‒Poly(ε-Caprolactone) (TPGS-b-PCL) Nanocarriers for Solubilization and Controlled Release of Paclitaxel

The objective of this study was to synthesize and characterize a set of biodegradable block copolymers based on TPGS-block-poly(ε-caprolactone) (TPGS-b-PCL) and to assess their self-assembled structures as a nanodelivery system for paclitaxel (PAX). The conjugation of PCL to TPGS was hypothesized to increase the stability and the drug solubilization characteristics of TPGS micelles. TPGS-b-PCL copolymer with various PCL/TPGS ratios were synthesized via ring opening bulk polymerization of ε-caprolactone using TPGS, with different molecular weights of PEG (1–5 kDa), as initiators and stannous octoate as a catalyst. The synthesized copolymers were characterized using ¹H NMR, GPC, FTIR, XRD, and DSC. Assembly of block copolymers was achieved via the cosolvent evaporation method. The self-assembled structures were characterized for their size, polydispersity, and CMC using dynamic light scattering (DLS) technique. The results from the spectroscopic and thermal analyses confirmed the successful synthesis of the copolymers. Only copolymers that consisted of TPGS with PEG molecular weights ≥ 2000 Da were able to self-assemble and form nanocarriers of ≤200 nm in diameter. Moreover, TPGS₂₀₀₀-b-PCL₄₀₀₀, TPGS₃₅₀₀-b-PCL₇₀₀₀, and TPGS₅₀₀₀-b-PCL₁₅₀₀₀ micelles enhanced the aqueous solubility of PAX from 0.3 µg/mL up to 88.4 ug/mL in TPGS₅₀₀₀-b-PCL₁₅₀₀₀. Of the abovementioned micellar formulations, TPGS₅₀₀₀-b-PCL₁₅₀₀₀ showed the slowest in vitro release of PAX. Specifically, the PAX-loaded TPGS₅₀₀₀-b-PCL₁₅₀₀₀ micellar formulation showed less than 10% drug release within the first 12 h, and around 36% cumulative drug release within 72 h compared to 61% and 100% PAX release, respectively, from the commercially available formulation (Ebetaxel^®) at the same time points. Our results point to a great potential for TPGS-b-PCL micelles to efficiently solubilize and control the release of PAX.

Systemic delivery of peptides by the oral route: Formulation and medicinal chemistry approaches

In its 33 years, ADDR has published regularly on the po5tential of oral delivery of biologics especially peptides and proteins. In the intervening period, analysis of the preclinical and clinical trial failures of many purported platform technologies has led to reflection on the true status of the field and reigning in of expectations. Oral formulations of semaglutide, octreotide, and salmon calcitonin have completed Phase III trials, with oral semaglutide being approved by the FDA in 2019. The progress made with oral peptide formulations based on traditional permeation enhancers is against a background of low and variable oral bioavailability values of ~1%, leading to a current perception that only potent peptides with a viable cost of synthesis can be realistically considered. Desirable features of candidates should include a large therapeutic index, some stability in the GI tract, a long elimination half-life, and a relatively low clearance rate. Administration in nanoparticle formats have largely disappointed, with few prototypes reaching clinical trials: insufficient particle loading, lack of controlled release, low epithelial particle uptake, and lack of scalable synthesis being the main reasons for discontinuation. Disruptive technologies based on engineered devices promise improvements, but scale-up and toxicology aspects are issues to address. In parallel, medicinal chemists are synthesizing stable hydrophobic macrocyclic candidate peptides of lower molecular weight and with potential for greater oral bioavailability than linear peptides, but perhaps without the same requirement for elaborate drug delivery systems. In summary, while there have been advances in understanding the limitations of peptides for oral delivery, low membrane permeability, metabolism, and high clearance rates continue to hamper progress.

MDR in cancer: Addressing the underlying cellular alterations with the use of nanocarriers

Multidrug resistance (MDR) is associated with a wide range of pathological changes at different cellular and intracellular levels. Nanoparticles (NPs) have been extensively exploited as the carriers of MDR reversing payloads to resistant tumor cells. However, when properly formulated in terms of chemical composition and physicochemical properties, NPs can serve as beyond delivery systems and help overcome MDR even without carrying a load of chemosensitizers or MDR reversing molecular cargos. Whether serving as drug carriers or beyond, a wise design of the nanoparticulate systems to overcome the cellular and intracellular alterations underlying the resistance is imperative. Within the current review, we will initially discuss the cellular changes occurring in resistant cells and how such changes lead to chemotherapy failure and cancer cell survival. We will then focus on different mechanisms through which nanosystems with appropriate chemical composition and physicochemical properties can serve as MDR reversing units at different cellular and intracellular levels according to the changes that underlie the resistance. Finally, we will conclude by discussing logical grounds for a wise and rational design of MDR reversing nanoparticulate systems to improve the cancer therapeutic approaches.

Toxicity evaluation of methoxy poly(ethylene oxide)-block-poly(ε-caprolactone) polymeric micelles following multiple oral and intraperitoneal administration to rats

Methoxy poly(ethylene oxide)-block-poly(ɛ-caprolactone) (PEO-b-PCL) copolymers are amphiphilic and biodegradable copolymers designed to deliver a variety of drugs and diagnostic agents. The aim of this study was to synthesize PEO-b-PCL block copolymers and assess the toxic effects of drug-free PEO-b-PCL micelles after multiple-dose administrations via oral or intraperitoneal (ip) administration in rats. Assembly of block copolymers was achieved by co-solvent evaporation method. To investigate the toxicity profile of PEO-b-PCL micelles, sixty animals were divided into two major groups: The first group received PEO-b-PCL micelles (100 mg/kg) by oral gavage daily for seven days, while the other group received the same dose of micelles by ip injections daily for seven days. Twenty-four hours following the last dose, half of the animals from each group were sacrificed and blood and organs (lung, liver, kidneys, heart and spleen) were collected. Remaining animals were observed for further 14 days and was sacrificed at the end of the third week, and blood and organs were collected. None of the polymeric micelles administered caused any significant effects on relative organ weight, animal body weight, leucocytes count, % lymphocytes, liver and kidney toxicity markers and organs histology. Although the dose of copolymers used in this study is much higher than those used for drug delivery, it did not cause any significant toxic effects in rats. Histological examination of all the organs confirmed the nontoxic nature of the micelles.

Stabilization and sustained release of zeylenone, a soft cytotoxic drug, within polymeric micelles for local antitumor drug delivery

Use of soft drugs has resulted in mixed success with the applicability to chemotherapeutics yet being confirmed. We hypothesize that incorporation of a soft cytotoxic agent into polymeric micelles, which confer to stabilizing and sustained release effect, will improve and prolong the local antitumor efficacy, thus achieving the therapeutic potential of soft cytotoxic agents. We incorporated a model soft cytotoxic agent, zeylenone, into mPEG-PLGA micelles by solvent evaporation method. The drug loaded micelles were characterized in terms of drug encapsulation, dynamic size, zeta potential, drug stability and in vitro and in vivo release. The in vivo antitumor efficacy was evaluated in A549 tumor-bearing mice. Zeylenone-loaded micelles exhibited core-shell morphology with dynamic size of about 36 nm and offered efficient solubilizing and stabilizing effects. In vitro release and in vivo pharmacokinetic results indicated sustained release of zeylenone in micelles. In addition, local delivered zeylenone-loaded micelles showed improved and sustained antitumor effect in vivo, compared with intravenous administration or local delivery of free drug solution. This study demonstrates the feasibility of soft cytotoxic agent to achieve local antitumor efficacy after the drug was stabilized and sustained the release within polymeric micelles.

Characterization of the thermo- and pH-responsive assembly of triblock copolymers based on poly(ethylene glycol) and functionalized poly(ε-caprolactone)

A series of novel triblock copolymers composed of poly(ethylene glycol) (PEG) and poly(ε-caprolactone)-bearing benzyl carboxylate on the α-carbon of ε-caprolatone were synthesized through ring opening polymerization of α-benzyl carboxylate-ε-caprolactone by dihydroxylated PEG. The debenzylation of the synthesized copolymer, i.e., poly(α-benzyl carboxylate-ε-caprolactone)-b-PEG-b-poly(α-benzyl-carboxylate-ε-caprolactone) (PBCL-b-PEG-b-PBCL), in the presence of hydrogen gas using different levels of catalyst, was carried out to achieve copolymers with various degrees of free α-carboxyl to α-benzyl-ε-carboxylate groups on the hydrophobic block. Incomplete reduction of PBCL led to the formation of poly(α-carboxyl-co-benzyl caboxylate-ε-caprolactone) PCBCL in the lateral blocks at 27%, 50% and 75% carboxyl group substitution. The molecular weight and polydispersity of the resultant copolymers were estimated by (1)H NMR and MALDI-TOF. Synthesized triblock copolymers formed stable micelles at low concentrations (critical micellar concentrations (CMC) of 0.34-12.5 μg ml(-1)). Polymers containing carboxyl groups in their structure showed a pH-dependent increase in CMC. As the pH was raised from 4.0 to 9.0, CMC increased from 0.76 to 1.06 μg ml(-1), for 27% debenzylated polymer, and from 1.30 to 2.20 μg ml(-1), for 50% debenzylated polymers. In contrast, the CMC in polymers without carboxyl group was independent of pH (0.55 μg ml(-1)). Different changes in micellar size as a function of temperature was observed depending on the degree of debenzylation on the PCBCL block: polymers with 27% degree of debenzylation illustrated a rise in micelle size from ~38 to 55 nm as the temperature increased above 29°C, while polymers with 50% debenzylation showed a decrease in micelle size, from ~52 to 38 nm, with increase in temperature. A similar trend was observed at pH 4.5, 7.0 and 9.0 for polymers containing carboxyl groups on their hydrophobic block. The temperature for the onset of size change and/or the extent of aggregate size change was found to be dependent on the pH of the medium and the polymer concentration. The results point to a potential for the formation of thermo- and pH-responsive micelles from triblock copolymers of PEG and carboxyl substituted caprolactone. The results also imply a potential for the 27% debenzylated PCBCL-b-PEG-b-PCBCL copolymers to form a biodegradable thermoreversible gel with a transition temperature a few degrees below 37°C.