In Situ Forming Injectable Thermoresponsive Hydrogels for Controlled Delivery of Biomacromolecules

Abstract

Due to their relatively large molecular sizes and delicate nature, biologic drugs such as peptides, proteins, and antibodies often require high and repeated dosing, which can cause undesired side effects and physical discomfort in patients and render many therapies inordinately expensive. To enhance the efficacy of biologic drugs, they could be encapsulated into polymeric hydrogel formulations to preserve their stability and help tune their release in the body to their most favorable profile of action for a given therapy. In this study, a series of injectable, thermoresponsive hydrogel formulations were evaluated as controlled delivery systems for various peptides and proteins, including insulin, Merck proprietary peptides (glucagon-like peptide analogue and modified insulin analogue), bovine serum albumin, and immunoglobulin G. These hydrogels were prepared using concentrated solutions of poly(lactide- co -glycolide)– block -poly(ethylene glycol)– block -poly(lactide- co -glycolide) (PLGA–PEG–PLGA), which can undergo temperature-induced sol–gel transitions and spontaneously solidify into hydrogels near the body temperature, serving as an in situ depot for sustained drug release. The thermoresponsiveness and gelation properties of these triblock copolymers were characterized by dynamic light scattering (DLS) and oscillatory rheology, respectively. The impact of different hydrogel-forming polymers on release kinetics was systematically investigated based on their hydrophobicity (LA/GA ratios), polymer concentrations (20, 25, and 30%), and phase stability. These hydrogels were able to release active peptides and proteins in a controlled manner from 4 to 35 days, depending on the polymer concentration, solubility nature, and molecular sizes of the cargoes. Biophysical studies via size exclusion chromatography (SEC) and circular dichroism (CD) indicated that the encapsulation and release did not adversely affect the protein conformation and stability. Finally, a selected PLGA–PEG–PLGA hydrogel system was further investigated by the encapsulation of a therapeutic glucagon-like peptide analogue and a modified insulin peptide analogue in diabetic mouse and minipig models for studies of glucose-lowering efficacy and pharmacokinetics, where superior sustained peptide release profiles and long-lasting glucose-lowering effects were observed in vivo without any significant tolerability issues compared to peptide solution controls. These results suggest the promise of developing injectable thermoresponsive hydrogel formulations for the tunable release of protein therapeutics to improve patient’s comfort, convenience, and compliance.

Pre‐clinical and clinical applications of thermoreversible hydrogels in biomedical engineering: a review

“…147 Figure 5 shows the mechanism of hydrolysis of ester bonds, catalysed either via acid (top) or base (bottom). The most common units that are often combined with PEG to form degradable TRGs are ε-caprolactone (CL), 29,42,[108][109][110][111][112][113][114][115][116][128][129][130][131] lactic acid (LA) [29][30][31][40][41][42][117][118][119][120][121][122][123][124][125][126][127][128][129] and glycolic acid (GA), 30,31,40,41,[117][118][119][120][121][122][123][124][125][...…”

“…113 ABA and BAB triblock copolymers with the B block based on PLGA were also evaluated for in vivo gel formation and injectability. 30,31,40,41,[117][118][119][121][122][123][124][125][126][127] Both PEG-PLGA-PEG (ABA) and PLGA-b-PEG-b-PLGA (BAB) polymers have been patented by Macromed Inc. (acquired by Protherics UK Ltd) in ca 2000, [200][201][202] and several articles have been published by Professor Sung Wan Kim † (1940-2020, co-founder of Macromed Inc. 203 ) and other groups around the world since then. 31,40,118,[123][124][125]127,204,205 The patents cover both ABA and BAB polymers with total molar mass ranging from 2000 to 4990 g mol −1 , hydrophobic content varying from 51 to 83 w/w%, and a range of hydrophobic esters which are polymerised to form a distinct B block at various percentages.…”

“…30,31,40,41,[117][118][119][121][122][123][124][125][126][127] Both PEG-PLGA-PEG (ABA) and PLGA-b-PEG-b-PLGA (BAB) polymers have been patented by Macromed Inc. (acquired by Protherics UK Ltd) in ca 2000, [200][201][202] and several articles have been published by Professor Sung Wan Kim † (1940-2020, co-founder of Macromed Inc. 203 ) and other groups around the world since then. 31,40,118,[123][124][125]127,204,205 The patents cover both ABA and BAB polymers with total molar mass ranging from 2000 to 4990 g mol −1 , hydrophobic content varying from 51 to 83 w/w%, and a range of hydrophobic esters which are polymerised to form a distinct B block at various percentages. [200][201][202] Amongst these, the best performing ones are BAB polymers with MM ≈ 3100-4500 g mol −1 , hydrophobic PLGA content between 51 and 83 w/w% and lactate content in the PLGA ranging from 65 to 85 mol%.…”

“…30,122 Their concentrated solutions (20-25 wt%) were also tested in vivo as drug delivery systems. 30,31,[121][122][123][124][125][126][127] The TRGs successfully served as matrices for sustained release of (i) interleukin-2, thus inhibiting growth of tumour, 126,127 (ii) huperzine A-phospholipid, thus reducing its toxic side effects, 121 (iii) Avastin®, which increased the half-life of the drug, 30 (iv) 5-fluorouracil, which prevented adhesion in the Achilles tendon, important to avoid pain after surgery, 122 (v) dexamethasone acetate for improved ocular drug delivery, 120 (vi) insulin or glucagon-like peptide for the treatment of diabetes [123][124][125] and (vii) irinotecan, and tumour regression was observed. 31 In three studies, end-capped PCLA-b-PEG-b-PCLA triblock copolymers were investigated, where PCLA stands for poly (ε-caprolactone-co-lactide).…”

Injectable Composite Systems Based on Microparticles in Hydrogels for Bioactive Cargo Controlled Delivery

“…Hydrogels are also biocompatible and biodegradable. They also exhibit flexibility similarly to natural tissues, thanks to their water content, which is given by hydrophilic groups [ 5 ].…”