PROTAC Enabling Formulation In Vivo: Implications of the Polymeric Carrier Eudragit E PO

Proteolysis targeting chimeras (PROTACs) are heterobifunctional degraders with a unique mode of action that permits access to "undruggable" targets. These molecules pose challenges in terms of solubility and bioavailability due to their physicochemical properties. So far, very little information is available on the potential of enabling formulations of PROTACs in pharmacokinetic studies. In a previous work of our group, amorphous spray-dried formulations (SDDs) of the model PROTAC MS4078 were developed. However, the potential of the amorphous solid dispersions of the PROTAC MS4078 has not yet been examined in vivo. The present study reports on the evaluation of an SDD containing MS4078 and E PO in comparison to a solution vehicle in a pharmacokinetic study in mice. Unexpectedly, very little exposure was found for both formulations. For a deeper investigation of their supersaturation and precipitation performance, the two formulations were tested in a two-stage precipitation assay with media that mimic physiological conditions in mice, which includes various bile salt and phospholipid concentrations. In this assay, the solution vehicle turned out to be a potent solubility enhancer. For the SDD, however, very different and complex dissolution profiles were obtained. The concentration at each time point was dependent on the bile salt and phospholipid concentration. Further in vitro tests revealed that E PO, the bile salt, and phospholipid interacted and induced a phase separation. This affected the solubilization and stabilization of the model PROTAC and may explain the differences regarding its in vitro performance. These findings are important to consider when designing future studies including E PO as polymeric carrier and species with high bile salt and phospholipid concentrations.

Eudragit; amorphous solid dispersions; bile salts; bioavailability; enabling formulation; proteolysis targeting chimeras.