Release of the GRF29NH2 analog of human GRF44NH2 from a PLA/GA matrix

Intraocular delivery considerations of ocular biologic products and key preclinical determinations

INTRODUCTION

Ophthalmic diseases of the retina are a significant cause of vision loss globally. Despite much progress, there remains an unmet need for durable, long-acting treatment options. While biologic therapies show great promise, they present many challenges, including complexities in biochemical properties, mechanism of action, manufacturing considerations, preclinical evaluation, and delivery mechanism; these are confounded by the unique anatomy and physiology of the eye itself.

AREAS COVERED

This review describes the current development status of intravitreally administered drugs for the treatment of ophthalmic disease, outlines the range of approaches that can be considered for sustained drug delivery to the eye, and discusses key preclinical considerations for the evaluation of ocular biologics.

EXPERT OPINION

The required frequency of dosing in the eye results in a great burden on both patients and the health care system, with direct intraocular administration remaining the most reliable and predictable route. Sustained and controlled ophthalmic drug delivery systems will go a long way in reducing this burden. Sustained delivery can directly dose target tissues, improving bioavailability and reducing off-target systemic effects. Maintaining stability and activity of compounds can prevent aggregation and enable extended duration of release, while sustaining dosage and preventing residual polymer after drug depletion.

Interactions of GRF(1–29)NH2 with plasma proteins and their effects on the release of the peptide from a PLAGA matrix

The administration of the GRF(1-29)NH2 Growth Hormone Releasing Hormone analog is known as relevant of the concept of drug delivery system using a bioresorbable matrix. However, the release of this peptide from poly(dl-lactic acid-co-glycolic acid) matrices is affected by its insolubility at neutral in salted media and in plasma as well. In order to investigate the origin and the nature of the insolubility in these media in more details, the precipitates collected when the peptide was set in contact with saline, isotonic pH=7.4 phosphate buffer and plasma were analyzed by various techniques, namely weighting, gel chromatography, 1D- and 2D-immunoelectrophoresis, and dialysis to discern the soluble from the insoluble or aggregated fractions. It is shown that precipitation in protein-free salted media is due to a salting out phenomenon complemented by the neutralization of the solubilizing electrostatic charges in the isotonic buffer. In contrast, the precipitation in plasma is due to inter polyelectrolyte-type complexation that involved polyanionic proteins having a rather low isoelectric point like albumin, transferin, haptoglobulin and IgG immunoglobulins. When a rather large quantity of GRF(1-29)NH2 was entrapped in bioresorbable pellets working at a percolating regime after subcutaneous implantation in rats, the peptide was slowly released despite the complexation with plasma proteins. However only a very small part of the peptide was found in blood, this small part being still large enough to cause a detectable increase of the circulating growth hormone concentration. Attempts made to increase the solubility of the peptide in plasma were successful when the peptide was combined with arginine, an amino acid known to promote the poor hormonal activity of injected GRF(1-29)NH2 solutions under clinical conditions.

The use of additives to modulate the release of a sparingly water soluble drug entrapped in PLA50 microparticles

One of the major problems raised by the microencapsulation of drugs which are sparingly soluble in water is the difficulty to achieve a controlled and total release of the drug. It was previously shown that the microencapsulation of a model water insoluble drug, namely 1-[2-(4-fluorobenzoyl)aminoethyl]-4-(7-methoxynaphthyl) piperazine hydrochloride (FAMP) with a hydrophilic additive like low molar mass poly(ethylene glycol)s (PEG) can fulfil these requirements, provided all the drug + additive matter is in contact with the surrounding liquid medium via open pores and percolating channels. In this paper, PEG was replaced by other additives, selected because of their potential ability to increase the solubility of FAMP in pH = 7.4 isosomolar phosphate buffer (PBS). The idea was that increasing the solubility locally in microparticles could allow the drug to be released, despite its poor solubility in aqueous media like body fluids, and be absorbed before recrystallization. The solubility in PBS of FAMP mixed with additive, in the form of solid dispersions, was determined for various additives, namely citric acid, dimyristoyl DL-alpha-phosphatidyl choline (DMPC), poloxamer copolymers of different compositions and poly(dodecyl L-lysine citramidate) (PLCAC12(100)), an aggregate-forming hydrophilic polyelectrolyte containing 100%, hydrophobizing ester groups which can accommodate lipophilic compounds in hydrophobic pockets present in the aggregates. PEG was taken as a reference. It was found that DMPC, some poloxamers and the hydrophobized polyelectrolyte do increase the solubility of FAMP in PBS. Investigation was made of the release of FAMP from ground microparticles, whose loads were composed of FAMP combined with these solubilization-promoting additives. It was found that the release rate of FAMP from such systems can be increased and modulated to achieve an in vitro sustained release over a 20-30 day period and secure exhaustion of the particles at the end of this period.

In vitro delivery of a sparingly water soluble compound from PLA50 microparticles

The administration of a sparingly soluble drug is always problematic, especially when the drug has to be released from the degradable matrix of a polymeric drug delivery system. Attempts were made to achieve the complete release of 1-[2-(fluorobenzoyl) aminoethyl]-4-(7-methoxynaphtyl)piperazine (FAMP), a potential anxiolytic and antidepressor hydrophobic compound, from racemic poly(lactic acid) (PLA50)-based microparticles, 100% release was required at a low rate in order to allow monthly repeated S.C. or I.M. injections of this potent compound. FAMP-polymer combinations were made in the form of microspheres by the solvent evaporation technique. Release profiles were investigated under dynamic conditions by using a constant flow rate of pH 7.4 0.15 M phosphate buffer, used as a model of body fluids. Under these conditions, none of the microsphere compositions led to total release within a month, even when hydrophilic excipients, namely fructose and PEG were added. PLA50-FAMP microparticles with compositions and sizes similar to those of the microspheres, were then made by direct blending in dichloromethane, evaporation of the solvent, grinding and sieving. These formulations also failed in providing total drug release within 30 days, even at a high drug load. FAMP/PLA50/water-soluble additive, ternary grounded particles were finally prepared with fructose, PLA50 oligomers or poly(ethylene glycol) (PEG) as the additive. Only PLA50 grounded particles with percolating FAMP-PEG microdomains allowed 100% release of FAMP over a 30 day period, at a quasi constant rate which depended primarily on solubility and channelling provided the flow was slow enough. Data are discussed in terms of the accessibility of the entrapped drug to the aqueous medium.

Somatotropin delivery to farmed animals

Bovine somatotropin (bST) is marketed worldwide for increased milk production in cows while porcine somatotropin (pST) is approved in one country for increasing growth in swine. Somatotropin physicochemical properties, animal production method limitations and the need for cost effectiveness each contribute to the type of formulation developed. Various somatotropin physicochemical properties made formulation design difficult: heat and enzyme lability, tendency to aggregate, pH dependent solubility and stability, complicated degradation pathways and rapid in vivo clearance. The main problem of improving chemical and physical stability has been partially solved using certain excipients and vehicles. Formulations design to prolong somatotropin release include implants (matrix, osmotic), oleaginous suspensions and microparticles. This article presents the current status of somatotropin delivery in farmed animals, reviews the challenges encountered with formulation development, summarizes formulation approaches and discusses future somatotropin uses.