FK506-binding protein (FKBP) partitions a modified HIV protease inhibitor into blood cells and prolongs its lifetime in vivo

Abstract

HIV protease inhibitors are a key component of anti-retroviral therapy, but their susceptibility to cytochrome P 450 metabolism reduces their systemic availability and necessitates repetitive dosing. Importantly, failure to maintain adequate inhibitor levels is believed to provide an opportunity for resistance to emerge; thus, new strategies to prolong the lifetime of these drugs are needed. Toward this goal, numerous prodrug approaches have been developed, but these methods involve creating inactive precursors that require enzymatic processing. Using an alternative strategy inspired by the natural product FK506, we have synthetically modified an HIV protease inhibitor such that it acquires high affinity for the abundant, cytoplasmic chaperone, FK506-binding protein (FKBP). This modified protease inhibitor maintains activity against HIV-1 protease (IC 50 ‫؍‬ 19 nM) and, additionally, it is partitioned into the cellular component of whole blood via binding to FKBP. Interestingly, redistribution into this protected niche reduces metabolism and improves its half-life in mice by almost 20-fold compared with the unmodified compound. Based on these findings, we propose that addition of FKBP-binding groups might partially overcome the poor pharmacokinetic properties of existing HIV protease inhibitors and, potentially, other drug classes.AIDS ͉ bifunctional molecules ͉ chemical inducers of dimerization ͉ pharmacology ͉ prodrugs

Synthesis of orthogonally reactive FK506 derivatives via olefin cross metathesis

“…Next, we confirmed that the corresponding SLF-modified derivative 8 showed a strong (~9-fold) preference for the cellular fraction (Figure 6)35. Remarkably, the FK506-modified derivative 7 was concentrated by more than ~22-fold in the blood cell compartment.…”

“…We recently reported that appending SLF to an HIV protease inhibitor partitions the resulting molecule into blood cells and prolongs its lifetime 20-fold in vivo 35. Evidence suggests that this improved persistence results from the modified compound being sequestered into the cytoplasm of the blood cells, which is an environment that contains high levels of FKBP but is nearly devoid of the P450 enzymes that metabolize xenobiotics.…”

“…Towards that goal, we coupled the reactive FK506 derivative 2 in a single step to an amprenavir-like core to yield the bifunctional molecule 7 (Figure 5A). Coupling of the core inhibitor to the FK506 derivative occurred through a pendant amine, which is known to be a well tolerated attachment point (Figure 5B)35,36.…”

“…This reaction was stirred at room temperature overnight and the resulting product 7 purified in 75% yield by HPLC as described above. The blood partitioning experiments were performed as described 35. The synthesis of the amprenavir core structure and compound 8 have been reported35.…”

Targeting Prostate Cancer with Bifunctional Modulators of the Androgen Receptor

“…The enhanced potency may be a reflection of increased cellular uptake or retention provided by the FK506 group, particularly because FK506 can serve as a substrate and inhibitor of drug efflux transporters such as multidrug resistance protein 1 (41). Notably, the favorable pharmacokinetic properties provided by FK506 have been recently demonstrated for drug conjugates both in vitro and in vivo (42,43). Similarly, conjugation of GR antagonists to bile acids has been explored as a means to target GR antagonism to the liver (28).…”