Design, Synthesis, and Characterization of a Series of Cytochrome P₄₅₀3A-Activated Prodrugs (HepDirect Prodrugs) Useful for Targeting Phosph(on)ate-Based Drugs to the Liver^§

Abstract

A new class of phosphate and phosphonate prodrugs, called HepDirect prodrugs, is described that combines properties of rapid liver cleavage with high plasma and tissue stability to achieve increased drug levels in the liver. The prodrugs are substituted cyclic 1,3-propanyl esters designed to undergo an oxidative cleavage reaction catalyzed by a cytochrome P(450) (CYP) expressed predominantly in the liver. Reported herein is the discovery of a prodrug series containing an aryl substituent at C4 and its use for the delivery of nucleoside-based drugs to the liver. Prodrugs of 5'-monophosphates of vidarabine, lamivudine (3TC), and cytarabine as well as the phosphonic acid adefovir were shown to cleave following exposure to liver homogenates and exhibit good stability in blood and other tissues. Prodrug cleavage required the presence of the aryl group in the cis-configuration, but was relatively independent of the nucleoside and absolute stereochemistry at C4. Mechanistic studies suggested that prodrug cleavage proceeded via an initial CYP3A-catalyzed oxidation to an intermediate ring-opened monoacid, which subsequently was converted to the phosph(on)ate and an aryl vinyl ketone by a beta-elimination reaction. Studies in primary rat hepatocytes and normal rats comparing 3TC and the corresponding HepDirect prodrug demonstrated the ability of these prodrugs to effectively bypass the rate-limiting nucleoside kinase step and produce higher levels of the biologically active nucleoside triphosphate.

Probing cytochrome P450-mediated activation with a truncated azinomycin analogue

“…13,14 Further development of such a bioprecursor approach could provide a strategy to exploit the azinomycins for therapeutic use. While CYP1A1 and 1B1 provide selective cancer drug targets, the hepatic CYP3A4 enzyme could be exploited for liver specific treatment of hepatitis B, hepatitis C and hepatocellular carcinoma 22 or with the reemergence of the oncolytic virus, a 'suicide' GDEPT approach also exists as a therapeutic strategy. 23 …”

Preclinical Pharmacokinetics of a HepDirect Prodrug of a Novel Phosphonate-Containing Thyroid Hormone Receptor Agonist

“…The expected general pharmacokinetic properties of HepDirect liver-targeted prodrugs are 1) high plasma clearance relative to hepatic blood flow, 2) a high volume of distribution relative to body water volume, and 3) good absorption (Ͼ20%) from the gut despite 4) poor absolute oral bioavailability (Ͻ20%) as assessed by systemic circulation exposure (Erion et al, 2004). The compounds of this novel class of prodrugs are intended to be susceptible to hepatic first-pass effects as they are designed to be readily converted to their active metabolites or active metabolite precursors by liver CYP3A.…”

“…The HepDirect approach enables the delivery of certain phosphate and phosphonate drugs to the liver with high specificity (Erion, 2006;Hecker et al, 2007). By masking the phosphate or phosphonate groups, HepDirect prodrugs are predicted to increase the absorption of the active metabolite by increasing its permeability across the gut membrane (Erion et al, 2004). HepDirect prodrugs are then specifically activated by CYP3A, a P450 enzyme that is localized predominantly in the liver, releasing the active metabolite or active metabolite precursor and a by-product that is neutralized by conjugation with glutathione (Erion et al, 2005b), which is present at millimolar concentrations in liver.…”

Design, Synthesis and Anti Flaviviridae Activity of N6-, 5',3'-O- and 5',2'-O-Substituted Adenine Nucleoside Analogs

“…Nuclear magnetic resonance spectra were determined in DMSO-d 6 11, 12, 35, 36) 3Ј,5Ј-O-TIPDS derivatives of adenosine, 2Ј-deoxyadenosine or araA were obtained by treatment of the dry nucleoside (1 mmol), suspended in pyridine (10 ml), with 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane (TIPDSCl 2 ) (1 mmol), following a synthetic procedure previously described. 34) Starting from araA, by a one-step reaction, both 35 and 36 were obtained. The crude products were purified by silica gel column chromatography (eluent: CH 2 Cl 2 /MeOH, 100/0→97/03, v/v).…”