Evaluation of Oral PROTAC Guidelines: Efflux Ratio Outweighs Chameleonicity Descriptors

Oral bioavailability of PROTACs, which often fall outside the Rule-of-Five space, is still not perfectly understood. Thus, the design of orally bioavailable PROTACs remains challenging. Chameleonicity, the ability of a compound to adapt its conformation to different environments (solvent or membrane), has been suggested as a key molecular property. Here, using a diverse set of PROTACs from our portfolio, we evaluate whether published guidelines including predicted or experimental chameleonicity descriptors could refine AstraZeneca's internal guidelines for designing orally absorbed PROTACs. We did not find such a trend. Instead, reducing the efflux ratio in Caco-2 cells emerged as a useful addition to our guidelines.