Pharmacodynamics of Akt drugs revealed by a kinase-modulated bioluminescent indicator
Understanding pharmacodynamics (PD)—how drugs exert biochemical effects over time—is essential for effective therapeutic design, yet conventional PD assessments require extensive animal use and tissue sampling. In this study, Wu and colleagues developed an Akt kinase-modulated bioluminescent indicator (Akt KiMBI) that enables rapid, noninvasive, real-time imaging of Akt drug activity in living animals. The indicator is based on the ATP-independent luciferase NanoLuc, which undergoes complementation and light emission upon Akt inhibition.
The authors engineered and optimized the reporter through systematic domain and linker testing to achieve a tenfold signal increase upon Akt inhibition. Validation in cell lines and mouse xenograft models demonstrated that KiMBI specifically reports Akt pathway inhibition, distinguishing it from unrelated kinase activities. Using this system, the researchers accurately recapitulated the known PD profile of the FDA-approved Akt inhibitor capivasertib, confirming KiMBI’s reliability.
They then applied KiMBI to investigate the brain penetrance and duration of several Akt inhibitors. The tool revealed that ipatasertib, but not capivasertib, effectively crossed the blood–brain barrier and inhibited Akt in the mouse brain. Further, two novel ipatasertib analogs—ML-B01 and ML-B02—were synthesized and characterized. ML-B01 retained strong brain activity, while ML-B02 lost efficacy, emphasizing how small chemical changes can dramatically affect drug bioavailability and PD.
Importantly, KiMBI imaging revealed that all tested small-molecule Akt inhibitors—capivasertib, ipatasertib and ML-B01—exhibited PD effects that outlasted their pharmacokinetic (PK) profiles, suggesting intracellular retention or pathway-level effects beyond plasma clearance. Finally, the authors demonstrated that an Akt-targeted proteolysis-targeting chimera (PROTAC), INY-05-040, produced sustained Akt degradation lasting more than three days, indicating that degradation-based therapeutics can achieve much longer PD duration than conventional inhibitors.
Collectively, this study introduces a powerful bioluminescent approach for noninvasive PD measurement, reducing the number of animals and drug quantities required for preclinical testing. The genetically encoded Akt KiMBI platform provides a versatile and quantitative strategy to accelerate drug optimization, especially for kinase inhibitors and degraders targeting cancer and neurological diseases.
Keywords: pharmacodynamics, Akt kinase, NanoLuc luciferase, bioluminescence imaging, kinase inhibitor, ipatasertib, capivasertib, PROTAC, brain drug delivery, noninvasive monitoring.
