Discovery of Orally Bioavailable and Brain-Penetrable Prodrugs of the Potent nSMase2 Inhibitor DPTIP

Abstract

Extracellular vesicles (EVs) can carry pathological cargo and play an active role in disease progression. Neutral sphingomyelinase-2 (nSMase2) is a critical regulator of EV biogenesis, and its inhibition has shown protective effects in multiple disease states. 2,6-Dimethoxy-4-(5-phenyl-4-thiophen-2yl-1H-imidazol-2-yl)phenol (DPTIP) is one of the most potent (IC 50 = 30 nM) inhibitors of nSMase2 discovered to date. However, DPTIP exhibits poor oral pharmacokinetics (PK), limiting its clinical development. To overcome DPTIP's PK limitations, we synthesized a series of prodrugs by masking its phenolic hydroxyl group. When administered orally, the best prodrug (P18) with a 2′,6′-diethyl-1,4′-bipiperidinyl promoiety exhibited >fourfold higher plasma (AUC 0−t = 1047 pmol•h/mL) and brain exposures (AUC 0−t = 247 pmol•h/g) versus DPTIP and a significant enhancement of DPTIP half-life (2 h vs ∼0.5 h). In a mouse model of acute brain injury, DPTIP released from P18 significantly inhibited IL-1β-induced EV release into plasma and attenuated nSMase2 activity. These studies report the discovery of a DPTIP prodrug with potential for clinical translation.

Dendrimer-Conjugated nSMase2 Inhibitor Reduces Tau Propagation in Mice

“…DPTIP is the most potent nSMase2 inhibitor identified to date [ 29 ]. However, it suffers from poor pharmacokinetic properties (oral bioavailability < 5% and rapid clearance with a t 1/2 < 0.5 h) [ 30 , 31 ]. Unfortunately, significant medicinal chemistry efforts around DPTIP did not result in any inhibitors with improved PK properties [ 31 ].…”

“…Our data support the utility of dendrimer conjugation to improve the pharmacokinetics of small molecule inhibitors. First, we show that a single oral dose of D-DPTIP inhibits EV release in vivo up to 72 h post administration, which is significantly improved compared to DPTIP, which has a t 1/2 of < 0.5 h [ 30 , 31 ]. Secondly, when equimolar doses are directly compared, oral D-DPTIP is significantly more effective than the unconjugated compound at inhibiting EV release ( Figure 4 B,C).…”

“…Quantitation of DPTIP released from D-DPTIP was performed using our published DPTIP bioanalytical LC/MS/MS method [ 30 ], with minor modifications. Briefly, calibration standards of DPTIP were prepared using naïve brain tissue from untreated mice.…”

“…The second HTS confirmed hit was 2,6-Dimethoxy-4-(5-Phenyl-4-Thiophen-2-yl-1H-Imidazol-2-yl)-Phenol (DPTIP), which was found to be potent (30 nM) and selective [ 28 , 29 ]. However, its translational potential is limited by poor oral bioavailability, modest brain penetration, and rapid clearance [ 30 , 31 ]. Our efforts to optimize DPTIP did not produce substantial improvements [ 31 ].…”

“…We have recently also employed drug delivery strategies to address these pharmacokinetic limitations. In the first strategy, we synthesized a series of prodrugs by masking DPTIP’s phenolic hydroxyl group, and demonstrated an improvement in plasma and brain exposures, as well as an increased plasma t 1/2 [ 30 ]. While the prodrugs were improved vs. DPTIP, their oral bioavailability was still limited and their plasma t 1/2 < 3 h, which is not ideal for a chronic therapy.…”