A deep eutectic-based,self-emulsifying subcutaneous depot system for apomorphine therapy in Parkinson’s disease

Apomorphine, a dopamine agonist, is a highly effective therapeutic to prevent intermittent off episodes in advanced Parkinson’s disease. However, its short systemic half-life necessitates three injections per day. Such a frequent dosing regimen imposes a significant compliance challenge, especially given the nature of the disease. Here, we report a deep eutectic-based formulation that slows the release of apomorphine after subcutaneous injection and extends its pharmacokinetics to convert the current three-injections-a-day therapy into an every-other-day therapy. The formulation comprises a homogeneous mixture of a deep eutectic solvent choline-geranate, a cosolvent n-methyl-pyrrolidone, a stabilizer polyethylene glycol, and water, which spontaneously emulsifies into a microemulsion upon injection in the subcutaneous space, thereby entrapping apomorphine and significantly slowing its release. Ex vivo studies with gels and rat skin demonstrate this self-emulsification process as the mechanism of action for sustained release. In vivo pharmacokinetics studies in rats and pigs further confirmed the extended release and improvement over the clinical comparator Apokyn. In vivo pharmacokinetics, supported by a pharmacokinetic simulation, demonstrate that the deep eutectic formulation reported here allows the maintenance of the therapeutic drug concentration in plasma in humans with a dosing regimen of approximately three injections per week compared to the current clinical practice of three injections per day.

Parkinson’s disease (PD), the second most common neurodegenerative disease, is characterized by dopamine deficiency arising from the progressive loss of dopaminergic neurons in the pars compacta of the substantia nigra. Multiple motor as well as nonmotor symptoms, such as rigidity, tremor, bradykinesia, and cognitive dysfunction, are associated with PD (1). While a number of disease-modifying therapies to treat PD are currently in clinical trials (2, 3), the approved therapies comprise only those that treat the symptoms. Among them, apomorphine (APO) is a leading drug given to patients to alleviate short intermittent periods of motor complications like dyskinesia, which often develop in advanced PD after long-term prior treatment with oral levodopa (4). APO has poor oral bioavailability and high first pass metabolism, thus leaving subcutaneous injections as the only viable administration mode (Apokyn). However, the short half-life (69.7 ± 25.8 min) of APO in the systemic circulation necessitates frequent injections of Apokyn, namely, three times a day, at the onset of individual off episodes (5). This poses a significant challenge with patient compliance in terms of pain, infection, emetic side effects, inaccurate dosing, lack of manual dexterity, or even inability to self-inject (6–9).Two notable strategies have been evaluated in clinical trials to mitigate the shortcomings of frequent subcutaneous APO injections. Kynmobi, a Food and Drug Administration (FDA)-approved sublingual film containing APO, allows rapid absorption of the drug via buccal administration (10, 11). It consists of two layers, as follows: one labeled as a buffer layer that neutralizes acid generation following drug absorption and another as an active layer that contains APO to allow rapid drug diffusion and absorption. However, it lacks a mechanism for sustained release and thus still requires repeated on-demand administration and induces fluctuations in blood concentrations. The continuous subcutaneous infusion of APO has also been explored as an alternative. The subcutaneous pump continuously injects Apokyn from a prefilled syringe and aims to maintain therapeutic concentrations of APO in systemic circulation and has shown a shortened duration of total daily off episodes in clinical trials. However, this approach is hindered by the complexity of use and local site reactions (12–14). Furthermore, this product recently received Refusal to File from the FDA. Many other preclinical and clinical formulations of APO have attempted to achieve noninvasive administration and prolonged pharmacokinetics (15, 16), for example, prodrug modification for oral delivery (17) or encapsulation in microemulsion for transdermal delivery (18); however, the utility of these approaches is limited by low bioavailability compared to subcutaneous injections. Thus, the development of a safe and simple sustained release formulation of APO remains an unmet clinical need.From a scientific perspective, APO represents one of the most challenging drugs to formulate; it has limited water solubility, is highly susceptible to oxidation, exhibits short plasma half-life (5, 19), and has a tight therapeutic window with a minimum effective concentration (MEC) of 4 ng/mL and a maximum tolerated concentration (MTC) of 10 ng/mL in humans. The use of a large number of sustained release technologies, including microspheres (20, 21), depots (11), liposomes (22), and polymeric as well as solid lipid nanoparticles (23, 24) among others, has been attempted with APO. However, the multiple physicochemical, biological, and clinical constraints have posed a hurdle in delivering APO in a safe and sufficiently sustained manner. Consequently, no long-acting formulation of APO is currently available.Here, we report a strategy for achieving an extended release of APO based simultaneously on the differential miscibility of a deep eutectic solvent, namely, choline and geranic acid (CAGE_1:2) in two solvents, water and n-methyl pyrrolidone (NMP), as well as the differential solubility of APO in each of these three solvents. We designed the formulation to be a homogenous, stable solution of APO in a three-component system (CAGE_1:2/NMP/water). However, upon subcutaneous injection, NMP rapidly diffuses away, and the formulation self-emulsifies into a dispersion of CAGE_1:2 in water while trapping APO in it, thereby achieving sustained release (Fig. 1). This design increased the timescale of APO pharmacokinetics, converting the current clinical standard of three-times-a-day formulation into an every-other-day formulation. While achieving this goal, we satisfied three essential constraints including the following: increased solubility of APO from 10 mg/mL in Apokyn to 30 mg/mL to support long-lasting delivery from a single dose; stability of APO against oxidation; and the use of all components, other than CAGE_1:2, at concentrations already listed in other FDA-approved subcutaneous products, thus facilitating the potential for translation of this strategy. We refer to this formulation as self-emulsifying, APO-releasing therapeutic (SEAPORT). We report the design strategy, ex vivo assessment, in vivo pharmacokinetics in rats, safety in rats, and in vivo pharmacokinetics in pigs.Open in a separate windowFig. 1.Schematic diagram of SEAPORT principle. APO, PEG3350, and SMB are solubilized in a CAGE_1:2/NMP/water (10:42.7:47.3% vol/vol) mixture in SEAPORT, and then upon subcutaneous injection, water-miscible NMP diffuses away quickly and the remaining CAGE_1:2 emulsifies with APO to form a depot, allowing the sustained release of the drug.