Effect of polymer composition on rheological and degradation properties of temperature-responsive gelling systems composed of acyl-capped PCLA-PEG-PCLA.

In this study, the ability to modulate the rheological and degradation properties of temperature-responsive gelling systems composed of acyl-capped poly(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-lactide) (PCLA-PEG-PCLA) triblock copolymers was investigated. Eight polymers with varying molecular weight of PCLA, caproyl/lactoyl ratio (CL/LA) and capped with either acetyl- or propionyl-groups were synthesized by ring-opening polymerization of L-lactide and ε-caprolactone in toluene using PEG as initiator and tin(II) 2-ethylhexanoate as catalyst, and subsequently reacted in solution with an excess of acyl chloride to yield fully acyl-capped PCLA-PEG-PCLA. The microstructure of the polymers was determined by (1)H NMR, and the thermal properties and crystallinity of the polymers in dry state and in 25 wt % aqueous systems were studied by differential scanning calorimetry and X-ray diffraction. Rheological and degradation/dissolution properties of aqueous systems composed of the polymers in 25 wt % aqueous systems were studied. (1)H NMR analysis revealed that the monomer sequence in the PCLA blocks was not fully random, resulting in relatively long CL sequences, even though transesterification was demonstrated by the enrichment with lactoyl units and the presence of PEG-OH end groups. Except the most hydrophilic polymer composed of acetyl-capped PCLA1400-PEG1500-PCLA1400 having a CL/LA molar ratio of 2.5, the polymers at 25 wt % in buffer were sols below room temperature and transformed into gels between room temperature and 37 °C, which makes them suitable as temperature-responsive gelling systems for drug delivery. Over a period of weeks at 37 °C, the systems containing polymers with long CL sequences (~8 CL) and propionyl end-groups became semicrystalline as shown by X-ray diffraction analysis. Degradation of the gels by dissolution at 37 °C took 100-150 days for the amorphous gels and 250-300 days for the semicrystalline gels. In conclusion, this study shows that changes in the polymer composition allow an easy but significant modulation of rheological and degradation properties.

A novel sustained-release cysteamine bitartrate formulation for the treatment of cystinosis: Pharmacokinetics and safety in healthy male volunteers.

The strict intake regimen of cysteamine bitartrate formulations, associated with side effects, is a concern for the treatment compliance in cystinosis therapy. Therefore, there is a need for a cysteamine formulation with an improved pharmacokinetic profile. This study investigated the pharmacokinetics, safety and tolerability of a new sustained-release cysteamine dosage form, PO-001, in healthy volunteers. This was a randomized, investigator-blinded, three-way cross-over study to compare single doses (600 mg) of PO-001 with Cystagon® (immediate-release) and Procysbi® (delayed-release). Collected blood samples were analyzed for plasma cysteamine concentrations and pharmacokinetic parameters were estimated by noncompartmental analysis. In addition, plasma cysteamine concentrations were analyzed using a population pharmacokinetic approach using NONMEM® . Pharmacokinetics showed clear sustained-release characteristics of PO-001 over time with a lower Cmax and longer Tmax compared to Cystagon® and Procysbi® . All treatment-emergent adverse events were of mild severity, with the exception of two subjects who reported moderate severity gastrointestinal problems including vomiting and diarrhea, which were related to Cystagon® intake. Population PK simulations showed a favourable PK profile based on Cmax and Ctrough concentrations at steady state. In conclusion, a single dose of 600 mg PO-001 was well tolerated with no findings of clinical concern. This new cysteamine bitartrate formulation showed pharmacokinetics of a sustained-release formulation, which may be beneficial for the treatment of cystinosis patients. This study supports advancing this type of sustained-release formulation into a subsequent study to confirm reduced dosing frequency with efficient control of white blood cells (WBCs) cystine levels. Netherlands Trial Registry (NTR) (NL67638.056.18).

First-in-Human Study of the Safety, Tolerability, Pharmacokinetics and - Preliminary Dynamics of Neuroprotectant 2-Iminobiotin in Healthy Subjects.

BACKGROUND: 2-iminobiotin (2-IB) is an investigational neuroprotective agent in development for the reduction of brain cell injury after cerebral hypoxia-ischemia. OBJECTIVE: The present first-in-human study evaluated the safety, tolerability, pharmacokinetics (PK) and -dynamics (PD) of 2-IB in healthy male subjects, intravenously infused with or without Captisol® as a solubilizing agent. METHODS: This randomized, double-blind, placebo-controlled, dose-escalation study was executed in 2 groups of 9 healthy male subjects. A single dose of 2-IB 0.6 mg/kg or placebo was infused over periods between 15 min and 4 h, and repeated doses escalating from 0.6 mg/kg to 12 mg/kg, or placebo were infused every 4 h for 6 administrations in total. RESULTS: Single and multiple doses of 2-IB up to 6 doses of 6 mg/kg with and without Captisol® were safe and well-tolerated in healthy male subjects. 2-IB proved to be a high-clearance drug with a volume of distribution slightly exceeding total body water volume, and with linear PK that appeared not to be affected by the presence of Captisol®. CONCLUSION: Sulfobutyletherbeta-cyclodextrin (SBECD) in Captisol® had a low-clearance profile with a small volume of distribution, with time-independent PK. Preliminary PD characterization of repeated iv dosing of 2-IB in an acute peripheral hypoxic ischemia model in healthy subjects did not reveal any notable effects of 2-IB, noting that this model was not selected to guide efficacy in the currently pursued indication of cerebral hypoxia-ischemia.

Novel controlled-release Lemna-derived IFN-alpha2b (Locteron): pharmacokinetics, pharmacodynamics, and tolerability in a phase I clinical trial.

Locteron, a newly developed controlled-release formulation of Lemna-derived free (unpegylated) recombinant interferon-alpha2b (IFN-alpha2b, Biolex Therapeutics, Pittsboro, NC) in poly(ether-ester) microspheres (PolyActive, OctoPlus N.V., Leiden, the Netherlands), was evaluated in 27 volunteers injected with either 20, 80, or 320 microg Locteron (equivalent to 6.25, 25, or 100 x 10(6) IU, respectively), 80 microg pegylated IFN-alpha2b (PEG-IFN-alpha2b), microspheres not containing IFN-alpha2b, or placebo. Serum free or PEG-IFN-alpha2b and two biomarkers of IFN activity, neopterin and 2',5'-oligoadenylate synthetase (2',5'-OAS), were measured. After injection of 320 microg Locteron, serum IFN-alpha2b remained elevated through 14 days. The elimination half-life of Locteron was more than 2-fold that of PEG-IFN-alpha2b. The effects of 80 microg Locteron and 80 microg PEG-IFN-alpha2b on both neopterin and 2',5'-OAS were in a comparable range. Serum persistence of both these biomarkers was similar at 14 days after 320 microg Locteron compared with 7 days after 80 microg PEG-IFN-alpha2b. Mild, moderate, or severe influenza-like symptoms developed in all 6 subjects receiving 80 microg PEG-IFN-alpha2b. No such symptoms occurred after 20 or 80 microg Locteron doses. Among the 4 recipients of 320 microg Locteron, 1 experienced mild and 2 experienced moderate influenza-like symptoms. Locteron merits further clinical investigation as a hepatitis C therapy suitable for dosing once per 2 weeks.

The effect of core composition in biodegradable oligomeric micelles as taxane formulations.

Docetaxel (DCTX) and paclitaxel (PTX) are very potent anti-cancer drugs, but the currently marketed formulations, Taxotere and Taxol, respectively, are associated with vehicle-related toxicity. An attractive alternative to formulate these hydrophobic cytotoxic agents are polymeric micelles. In this study, the loading of taxanes into oligomeric micelles composed of mPEG750-b-oligo(epsilon-caprolactone)5 (mPEG750-b-OCL5) with a hydroxyl (OH), benzoyl (Bz) or naphthoyl (Np) end group was investigated. Next, the release characteristics and cytotoxicity of the loaded micelles were studied. MPEG750-b-OCL5 -OH micelles loaded with taxanes formed unstable particles with rapid leakage of the drug. In contrast, the presence of an aromatic end group (Bz or Np) resulted in the formation of small (10nm), almost monodisperse micelles with stable encapsulation of 10% (w/w) of PTX or DCTX. This was ascribed to a better compatibility between the micellar core and the drug as compared to the oligomers with the hydroxyl end group. 1H NMR studies showed that the micellar core was liquid, and that PTX was molecularly dissolved in the core. The in vitro stability was studied in PBS at 37 degrees C, which showed that leakage of PTX from 10% and 5% (w/w) loaded mPEG750-b-OCL5-Bz micelles started after 8 and 24h, respectively. The presence of albumin did not affect the stability, suggesting that the micelles are not destabilised and the drug was not extracted from the micellar core by this protein. The in vitro cytotoxic effect of the taxane-loaded micelles on C26 carcinoma cells was comparable to that of the commercial formulations, but the empty micelles were far less toxic than the Cremophor EL vehicle. The results show that mPEG-b-oligo(epsilon-caprolactone) micelles hold good promise for the formulation of taxanes.

A mechanistic study on the chemical and enzymatic degradation of PEG-Oligo(epsilon-caprolactone) micelles.

The chemical and enzymatic degradation of monodisperse oligo(epsilon-caprolactone) (OCL) and its amphiphilic block oligomer with methoxy poly(ethylene glycol) (mPEG) were investigated in order to obtain insight into the degradation of mPEG-b-OCL micelles. Hydrolytic degradation was studied as function of pH and dielectric constant of the medium, and enzymatic degradation was investigated at different enzyme and substrate concentrations. The degradation was monitored by HPLC and MS, and the micelle destabilization with DLS. It was found that the hydrolytic degradation followed pseudo first order kinetics, and that the rate depended on the pH and dielectric constant. Degradation essentially occurred via a random scission process, and induced micelle destabilization after approximately 1.5 degradation half-lives. At physiological pH and temperature, OCLs are very stable, reflected by an estimated degradation half-life of mPEG-b-OCL micelles of several years. However, the presence of lipase resulted in an accelerated degradation with half-lives of a few days to hours. The enzymatic degradation of mPEG-b-OCL followed Michaelis-Menten kinetics. The results indicate that mPEG-b-OCL micelles are very stable in vitro, but their susceptibility to enzymes such as lipase makes these systems suitable for the hydrolysis controlled release of drugs in vivo.

In vivo pharmacokinetics of celecoxib loaded endcapped PCLA-PEG-PCLA thermogels in rats after subcutaneous administration.

Injectable thermogels based on poly(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-lactide) (PCLA-PEG-PCLA) containing an acetyl- or propyl endcap and loaded with celecoxib were developed for local drug release. The aim of this study was to determine the effects of the composition of the celecoxib/PCLA-PEG-PCLA formulation on their in vivo drug release characteristics. Furthermore, we want to obtain insight into the in vitro-in vivo correlation. Different formulations were injected subcutaneously in rats and blood samples were taken for a period of 8 weeks. Celecoxib half-life in blood increased from 5 h for the bolus injection of celecoxib to more than 10 days for the slowest releasing gel formulation. Sustained release of celecoxib was obtained for at least 8 weeks after subcutaneous administration. The release period was prolonged from 3 to 6-8 weeks by increasing the injected volume from 100 to 500 µL, which also led to higher serum concentrations in time. Propyl endcapping of the polymer also led to a prolonged release compared to the acetyl endcapped polymer (49 versus 21 days) and at equal injected dose of the drug in lower serum concentrations. Increasing the celecoxib loading from 10 mg/mL to 50 mg/mL surprisingly led to prolonged release (28 versus 56 days) as well as higher serum concentrations per time point, even when corrected for the higher dose applied. The in vivo release was about twice as fast compared to the in vitro release for all formulations. Imaging of organs of mice, harvested 15 weeks after subcutaneous injection with polymer solution loaded with infrared-780 labelled dye showed no accumulation in any of these harvested organs except for traces in the kidneys, indicating renal clearance. Due to its simplicity and versatility, this drug delivery system has great potential for designing an injectable to locally treat osteoarthritis, and to enable tuning the gel to meet patient-specific needs.

Release behavior and intra-articular biocompatibility of celecoxib-loaded acetyl-capped PCLA-PEG-PCLA thermogels.

In this study, we investigated the in vitro and in vivo properties and performance of a celecoxib-loaded hydrogel based on a fully acetyl-capped PCLA-PEG-PCLA triblock copolymer. Blends of different compositions of celocoxib, a drug used for pain management in osteoarthritis, and the acetyl-capped PCLA-PEG-PCLA triblock copolymer were mixed with buffer to yield temperature-responsive gelling systems. These systems containing up to 50 mg celecoxib/g gel, were sols at room temperature and converted into immobile gels at 37 °C. In vitro, release of celecoxib started after a ∼10-day lag phase followed by a sustained release of ∼90 days. The release was proven to be mediated by polymer dissolution from the gels. In vivo (subcutaneous injection in rats) experiments showed an initial celecoxib release of ∼30% during the first 3 days followed by a sustained release of celecoxib for 4-8 weeks. The absence of a lag phase and the faster release seen in vivo were likely due to the enhanced celecoxib solubility in biological fluids and active degradation of the gel by macrophages. Finally, intra-articular biocompatibility of the 50 mg/g celecoxib-loaded gel was demonstrated using µCT-scanning and histology, where no cartilage or bone changes were observed following injection into the knee joints of healthy rats. In conclusion, this study shows that celecoxib-loaded acetyl-capped PCLA-PEG-PCLA hydrogels form a safe drug delivery platform for sustained intra-articular release.

Modulating rheological and degradation properties of temperature-responsive gelling systems composed of blends of PCLA-PEG-PCLA triblock copolymers and their fully hexanoyl-capped derivatives.

In this study, the ability to modulate rheological and degradation properties of temperature-responsive gelling systems composed of aqueous blends of poly(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-lactide) (PCLA-PEG-PCLA) triblock copolymers (i.e. uncapped) and their fully capped derivatives was investigated. Uncapped and capped PCLA-PEG-PCLA triblock copolymers, abbreviated as degree of modification 0 and 2 (DM0 and DM2, respectively), were composed of identical PCLA and PEG blocks but different end groups: namely hydroxyl and hexanoyl end groups. DM0 was synthesized by ring opening polymerization of l-lactide and ε-caprolactone in toluene using PEG as initiator and tin(II) 2-ethylhexanoate as the catalyst. A portion of DM0 was subsequently reacted with an excess of hexanoyl chloride in solution to yield DM2. The cloud point and phase behaviour of DM0 and DM2 in buffer as well as that of their blends were determined by light scattering in a diluted state and by vial tilting and rheological measurements in a concentrated state. Degradation/dissolution properties of temperature-responsive gelling systems were studied in vitro at pH 7.4 and 37°C. The cloud points of DM0/DM2 blends were ratio-dependent and could be tailored from 15 to 40°C for blends containing 15 to 100wt.% DM0. Vial tilting and rheological experiments showed that, with solid contents between 20 and 30wt.%, DM0/DM2 blends (15/85 to 25/75w/w) had a sol-to-gel transition temperature at 10-20°C, whereas blends with less than 15wt.% DM0 formed gels below 4°C and the ones with more than 25wt.% DM0 did not show a sol-to-gel transition up to 50°C. Complete degradation of temperature-responsive gelling systems took ∼100days, independent of the DM0 fraction and the initial solid content. Analysis of residual gels in time by GPC and (1)H-NMR showed no chemical polymer degradation, but indicated gel degradation by dissolution. Preferential dissolution of lactoyl-rich polymers induced enrichment of the residual gels in caproyl-rich polymers. To the best of our knowledge, degradation of temperature-responsive gelling systems by dissolution has not been reported or hypothesized as being the consequence of acylation of polymers. In conclusion, blending of PCLA-PEG-PCLA triblock polymers composed of identical backbones but different end groups provides for a straightforward preparation of temperature-responsive gelling systems with well-characterized rheological properties and potential in drug delivery. Furthermore, acylation of triblock copolymers may allow for the design of bioerodible systems with control over degradation by polymer dissolution.