Biocompatible Reverse Thermal Gel Sustains the Release of Intravitreal Bevacizumab In Vivo

PURPOSE. We assessed the in vivo release profile of bevacizumab from and biocompatibility of poly(ethylene glycol)-poly-(serinol hexamethylene urethane), or ESHU, a thermoresponsive hydrogel administered intravitreally for drug delivery. METHODS. The technical feasibility of injection was assessed quantitatively via mechanical testing. For in vivo studies, New Zealand White rabbit eyes were injected intravitreally with 0.05 mL of either: ESHU dissolved in 25 mg/mL bevacizumab, ESHU dissolved in PBS, or 25 mg/mL bevacizumab. Clinical examination included IOP measurements and examination with indirect ophthalmoscopy for signs of inflammation. Additionally, eyes were examined histologically following euthanasia. To quantify bevacizumab release, aqueous humor samples were obtained via anterior chamber paracentesis and ELISA was used to determine the concentration of drug weekly. In vitro cytotoxicity testing also was performed using bovine corneal endothelial cells. RESULTS. The ESHU was injected easily through a 31-gauge needle, was well tolerated in vivo, and caused minimal cell death in vitro when compared to other common materials, such as silicone oil. The long-term presence of the gel did not affect IOP, and there was no evidence of inflammation histologically or through indirect observation. The ESHU sustained the release of bevacizumab for over 9 weeks and maintained a drug concentration that averaged 4.7 times higher than eyes receiving bolus bevacizumab injections. CONCLUSIONS. To our knowledge, this is the first report demonstrating sustained bevacizumab release in vivo from an intravitreally injected hydrogel formulation, suggesting that this delivery system may be a promising candidate for ocular drug delivery. Keywords: thermally responsive hydrogel, ocular drug delivery, sustained release, biocompatibility, injectable gel C horoidal neovascularization (CNV) is the hallmark of many blinding disorders, most notably wet age-related macular degeneration (AMD) and diabetic retinopathy. It is characterized by pathologic blood vessel growth, which originates in the choroid and progresses through the Bruch's membrane into the subretinal space. 1 These vessels are fragile and permeable, causing hemorrhage, retinal detachment, scarring, and ultimately, loss of central vision. Elevated levels of VEGF is a central cause of CNV. 2-4 Thus, intravitreal injection of anti-VEGF medications, such as bevacizumab (Avastin) or ranibizumab (Lucentis), has emerged as a leading treatment strategy. 10-13 Therefore, a delivery system that extends the presence of intravitreal drugs in the eye is highly desirable for reducing injection frequency and adverse effects, while maximizing therapeutic outcomes. A number of polymeric delivery systems have been considered by researchers for intravitreal drug delivery, including microparticles, which are well tolerated in the eye and are capable of delivering drugs over a longer period of time. 14,15 For example, microparticle-encapsulated or PEGylated bevacizumab is more effective than bevacizumab alone in treating CNV in rats

Biocompatibility of a coacervate-based controlled release system for protein delivery to the injured spinal cord

The efficacy of protein-based therapies for treating injured nervous tissue is limited by the short half-life of free proteins in the body. Affinity-based biomaterial delivery systems provide sustained release of proteins, thereby extending the efficacy of such therapies. Here, we investigated the biocompatibility of a novel coacervate delivery system based on poly(ethylene argininylaspartate diglyceride) (PEAD) and heparin in the damaged spinal cord. We found that the presence of the [PEAD:heparin] coacervate did not affect the macrophage response, glial scarring, or nervous tissue loss, which are hallmarks of spinal cord injury. Moreover, the density of axons, including serotonergic axons, at the injury site and the recovery of motor and sensorimotor function were comparable in rats with and without the coacervate. These results revealed the biocompatibility of our delivery system and supported its potential to deliver therapeutic proteins to the injured nervous system