Evaluation of the oral delivery of goserelin with Pheroid® technology
The therapeutic amphiphilic peptide, goserelin, being investigated in these studies, is a type of hormone therapy generally used in addition to standard adjuvant therapy. Goserelin serves as treatment for numerous hormone-dependent disorders, for instance benign conditions (e.g. uterine fibroids, menorrhagia, endometriosis etc.) or malignant tumours (breast, ovarian, endometrial and prostate carcinoma). Goserelin is a synthetic analogue of the naturally occurring gonadotropin-releasing hormone (GnRH), which is also commonly known as a GnRH agonist. Goserelin acts directly on the hypothalamic-pituitary axis, consequently leading to receptor down-regulation, which in turn leads to the inhibition of the secretion of the pituitary gonadotropins. This causes a decrease of endogenous testosterone in males and oestrogen in females. Through this, a hypogonadal status is achieved. Goserelin in combination with menotropins or recombinant follicle-stimulating hormone (FSH) is commonly used for women undergoing in vitro fertilisation (IVF), as it aids in inducing folliculogenesis for controlled ovarian hyperstimulation. Currently, goserelin is administered as a slow releasing subcutaneous depot (slow releases goserelin over a period of 28 days); this is typically a more invasive administration regimen and commonly not usually tolerated well by patients, thus changing the administration route from subcutaneous to oral may yield great advantages. Goserelin, being a peptide, will face several challenges after oral administration, such as the acidic and enzymatic degradation in the gastrointestinal tract (GI) tract; however, these can be overcome by different strategies, such as formulation and chemical technologies. Using a particulate drug delivery system (DDS) to protect peptide drugs is an example of a formulation technology. Pheroid® is a novel colloidal DDS, with the capability of protecting a therapeutic drug and consequently increasing the bioavailability. In this study, goserelin was used in combination with Pheroid® technology to determine the pharmacokinetics and pharmacodynamics of goserelin after administration of an oral dose of a novel pro-Pheroid®-goserelin formulation, in comparison to the existing goserelin subcutaneous implant (Zoladex®) in male and female BALB/c mice. The physicochemical characteristics, i.e. particle size, colloidal stability and morphology, of this novel Pheroid® formulation of goserelin were also investigated. The effect of entrapment of goserelin in Pheroid® on its gastrointestinal stability was determined by comparing the stability of goserelin and pro-Pheroid®-goserelin in simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). The characteristics of Pheroid® revealed no change after the addition of goserelin to pro-Pheroid®. The stability study was non-conclusive due to loss of sample during centrifugation of the SIF and SGF of the pro-Pheroid®-goserelin samples. An optimised and revised stability study will be conducted in the near future. The male BALB/c mice were divided into three groups: group 1 received the peptide subcutaneously, group 2 received pro-Pheroid®-goserelin as an oral dose of 2 mg/kg and group 3 received pro-Pheroid®-goserelin as an oral dose of 4 mg/kg. Blood samples were collected at different time points and the plasma was analysed for testosterone and goserelin concentrations using LC-MS/MS. From the goserelin concentration-time profile, the observed peak plasma concentration (Cmax) and time to maximum concentration (Tmax) were reported and statistically compared. An expected significantly higher Cmax and Tmax were observed in the subcutaneous group. The 2 mg/kg pro-Pheroid® goserelin resulted in a significantly higher Cmax compared to the 4 mg/kg dose. An initial (0 - 30 minutes) increase in the testosterone concentration for each group was observed, thus adhering to the flare-up effect. Both the 2 mg/kg and 4 mg/kg pro-Pheroid® groups proved to have an effect on the testosterone concentration. The 4 mg/kg pro-Pheroid®-goserelin was chosen for further investigation in female BALB/c mice. Hence, it can be concluded that goserelin did succeed in reaching the blood and consequently caused a decrease in the testosterone concentration after the oral administration with pro-Pheroid®. The female BALB/c mice were also divided into three groups; group 1 received goserelin subcutaneously, group 2 received 4 mg/kg pro-Pheroid®-goserelin through oral gavage and group 3, the negative control group, received only pro-Pheroid®. Evaluation for the daily vaginal smears was done by vaginal cytology for 21 days, to track the disruption or lack thereof of the 4-stage oetrous cycle. The vaginal cytology revealed disruption in the oestrous cycle in groups 1 and 2. Thus it can be concluded that the oral administration of goserelin in pro-Pheroid resulted in sufficient uptake to cause the hormonal effects. The pro-Pheroid®-goserelin formulation in both the male and female studies resulted in bioavailable goserelin as indicated by the related pharmacodynamic (PD) results. In summary, therefore, Pheroid® technology proved to protect goserelin from the degradation in the GI tract and could thus be a helpful DDS for oral delivery of therapeutic drugs.
- Health Sciences