(M1030-11-65) Characterization of Long-Acting Injectable Formulation for Pre-Clinical Studies Using Accelerated In Vitro Release (IVR) Technique

Purpose: Long-acting injectable formulations play a vital role in treating various diseases providing sustained drug release over weeks to months. However, the lack of a standardized in-vitro release technique poses significant challenges during the early stages of drug product development, particularly for emerging modalities like PROTACs. Existing USP techniques primarily cater to solid oral dosage forms or transdermal patches, requiring substantial material for testing, which is often unavailable during the discovery and pre-clinical stages. Additionally, alternative techniques (such as USP apparatus 2 and apparatus 4 with modifications) investigated by researchers may not be universally applicable, and the necessary equipment may not be readily available in all labs.

Methods: This study presents a small-scale accelerated method for evaluating drug release kinetics from poly(lactic-co-glycolic acid) (PLGA) formulations using small volume Erlenmeyer flasks equipped with screw caps and an orbital shaker. In this method, 50mg of PLGA gels were added to the pre-warmed IVR media in the flasks, which were then subjected to gentle agitation to simulate interstitial fluid flow around the drug depot. Samples were withdrawn at predetermined intervals, and the media was replenished to maintain sink conditions. Subsequently, samples were filtered using 0.22μm PVDF filters for analysis via high-performance liquid chromatography (HPLC).

Results: In the first experiment, a total of five formulations utilizing API 1 were examined employing the aforementioned method. The alterations in various components aimed to adjust the release rate are detailed in Table 1. Among the first four formulations (API 1-PLGA Gel-01 through API 1-PLGA Gel-04), API content remained constant while modifications were made to polymer content, surfactant type and level, and co-solvents. In contrast, API 1-PLGA Gel-05 was prepared at higher drug loading compared to API 1-PLGA Gel-01. As depicted in Figure 1, the in vitro release (IVR) data validated all theoretical assumptions outlined in Table 1. Specifically, an increase in polymer content or drug loading was associated with a decelerated release rate, while the inclusion of co-solvents mitigated the burst release and higher levels of surfactant 1 accelerated release. In the second experiment, different types of polymers were utilized for the preparation of formulation with API 2 to assess the impact of varying molecular weights/viscosity on release rate. API 2 PLGA-Gel-01 and API 2 PLGA-Gel-02 were both prepared using the same polymer type, with solely the polymer content adjusted to reaffirm the observed trend wherein higher polymer content correlated with slower release rates. Conversely, API 2 PLGA-Gel-03 and API 2 PLGA-Gel-04 were formulated with different polymer types while maintaining consistent polymer levels among them, facilitating the examination of polymer type effects on drug release from PLGA formulations. As illustrated in Figure 2, IVR data confirmed hypotheses outlined in Table 2, the formulation with a lower molecular weight distribution (Mw/Mn) - API 2-PLGA Gel-02 - achieved complete release more rapidly than formulations with higher Mw/Mn. The formulations containing API 3 with low and high molecular weight polymers were administered to mice via subcutaneous injection to evaluate pharmacokinetics. As demonstrated in Table 3, the pharmacokinetic data indicates that the percentage bioavailability (%F) is greater with low molecular weight PLGA compared to the higher molecular weight PLGA, in line with the in-vitro release profile. These results demonstrate that the accelerated sample and separate method is able to discriminate between small changes in formulations and help rank formulations for pre-clinical studies, while also showing correlation with in-vivo results.

Conclusion: The development and evaluation of smaller scale accelerated IVR techniques address the critical need for efficient pre-clinical formulation screening for long-acting injectable formulations, including emerging modalities like PROTACs. By overcoming challenges associated with material availability and accommodating diverse formulation types, this approach enhances the efficiency and effectiveness of early-stage drug product development.


Figure 1 Release of API 1 from different PLGA formulations (same polymer lot)


Figure 2 Release of API 2 from PLGA formulations with different polymers


Table 1 (PLGA Formulation composition for API 1 and release assumptions), Table 2 (PLGA Formulation composition for API 2 and release assumptions) and Table 3 (Pharmacokinetic study of Long-Acting Formulations with different MW polymers)