(W0930-09-51) Evaluating Formulation Platforms for Poorly Soluble APIs to Mimic PROTACs

Purpose: Proteolysis Target Chimeras (PROTACs) are a promising therapeutic strategy for treating “undruggable diseases”. PROTACs are heterobifunctional molecules with three chemical elements: two binding ligands (target protein and E3 ubiquitin ligase), with a linker connecting them. The general mechanism-of-action of PROTACs involves exploiting the ubiquitination and subsequently degrading the target protein. Despite the progress of PROTACs to phase I, II and III clinical trials, many challenges remain to be addressed, e.g., the development of orally bioavailable PROTACs. PROTACs are likely categorized as Biopharmaceutics Classification System (BCS) class IV compounds with high molecular weight, i.e. low solubility and low permeability. Therefore, selecting model drugs with some similar characteristics may be a way to inform, in a limited capacity/extent, the behavior of these molecules. Here, three BCS class IV drugs: Lopinavir (LPV), Ritonavir (RTV) and Nilotinib (NTB), were chosen to explore the early-stage formulation development focusing on the oral delivery of PROTACs. Accordingly, two distinct types of formulation platforms were selected: Amorphous Solid Dispersion (ASD) and Self-Nanoemulsifying Drug Delivery System (SNEDDS). We aimed to assess the impact of excipient's choice in both strategies with a perspective on improving dissolution, as well as drug loading.

Methods: 20% (w/w) ASDs were prepared using four different polymers (PVP, Kollidon® VA64, Soluplus® and HPMCAS) by two methods: quench-cooling (LPV, RTV) and ball-mill griding (NTB). The samples were characterized by Differential Scanning Calorimetry (DSC) and Powder X-Ray Diffraction (PXRD). Dissolution assays of all ADSs were carried out in a µDISS Profiler™ using fasted state simulating intestinal fluid (FaSSIF) media at pH 6.5 and 37 ºC, under non-sink conditions. Absorbance was measured at 226 nm (LPV), 240 nm (RTV), and 268 nm (NTB). Dissolution rate (D_R) was determined during the first 1h of experiment. Solubility in lipid excipients was determined by adding an excess of the model drugs in 1g of each excipient, in triplicates. The samples were rotated for 72h in a heat cabinet at 37 ºC, centrifuged for phase separation, and the supernatant was weighted and diluted to be analyzed by High Performance Liquid Chromatograph (HPLC). SNEDDS formulations in distinct ratios were then prepared, submitted to solubility tests under the same conditions previously described and the droplets size were analyzed using a Zetasizer. The formulation optimization was conducted by choosing the SNEDDS with a higher drug load and lower size (nm) in the ternary diagram (oil phase, hydrophilic surfactant and lipophilic surfactant), obtained by the software MODDE13.

Results: Dissolution studies shows that the polymer HPMCAS enhanced D_R for all model drugs, faster than the other polymers (Table 1). Also, ASDs based on HPMCAS resulted in the highest concentration at 6h for all three drugs. However, for NTB there was no significant difference between the concentration reached at 6 h for Kollidon® VA64 and HPMCAS. Fig. 1a. shows the that all drugs have the highest solubility in Castor oil (long chain hydroxylated triglyceride), most likely due to its hydroxylated structure. Labrafac^™ MC60 (glycerol mono-caprylocaprate) showed the better solubility for the lipophilic surfactants/co-surfactants, and Labrasol^® ALF (Caprylocaproyl Polyoxyl-8 glycerides) was able to dissolve more drug than others hydrophilic surfactants. Based on the solubility results, the first three hydrophilic surfactants: Labrasol^® ALF, Tween^® 20 (PEG-20 sorbitan monolaurate), and Kolliphor^® EL (macrogolglycerol ricinolate) were evaluated in SNEDDS combined with Castor oil and Labrafac™ MC60 as oil phase and lipophilic surfactant, at different ratios. The results showed sizes out of the range ( > 2000 nm), or large values of polydispersity index (PDI) when lower than 200 nm, suggesting unstable formulations. Therefore, Kolliphor^® RH40 (macrogolglycerol hydroxystearate), was tested as hydrophilic surfactant. Fig. 1b presents the ternary diagram of LPV using Kolliphor^® RH40, Castor oil and Labrafac™ MC60. As observed, the combination of these three lipid excipients reached a good range of size (20 nm – 140 nm), and the highest solubility. The excipients also worked for RTV and NTB, showing similar results. The optimized ratio for each SNEDDS formulation is therefore dependent particularly on their ternary diagram, including PROTACs.

Conclusion: Dissolution of ASDs shows that HPMCAS has higher potential to enhance dissolution rate when compared to other polymers tested. The superior release of all drugs at 6h of dissolution indicates that this polymer is a good choice for class IV drugs with similar characteristics of PROTACs. Solubility studies in lipid excipients demonstrated that LPV, RTV and NTB have similar solubilities in different classes of lipids. However, the optimized SNEDDSs showed the highest drug load and lower size, when combining castor oil, Kolliphor^® RH40 and Labrafac^™ MC60.

References: 1. Gao H, Sun X, Rao Yu, PROTAC Technology: Opportunities and Challenges. ACS Medicinal Chemistry Letters 11, 3 (2020) 237-240.
2. Zeng S. et al, Current advances and development strategies of orally bioavailable PROTACs. European Journal of Medicinal Chemistry 261 (2023) 115793.
3. Yang W. et al, Early evaluation of opportunities in oral delivery of PROTACs to overcome their molecular challenges. Drug Discovery Today. 29, 2 (2024) 103865

Acknowledgements: The authors thank the Department of Pharmacy - University of Copenhagen and AstraZeneca Gothenburg, for institutional and financial support.

Table 1. Dissolution data of the 20% (w/w) amorphous solid dispersions (ASDs) in fasted state simulated intestinal fluid (FaSSIF) at pH= 6,5 (37 ºC, 100 rpm, 6 hours).

Fig 1. a) Normalized solubility (mg/g) of LPV, RTV and NTB in different lipid excipients at 37 ºC. b) Ternary diagrams (solubility (mg/g) and size (nm)) of LPV using castor oil, Labrafac™ MC60, and Kolliphor® RH40.