The plasma pharmacokinetics of novel small molecule inhibitors of perforin.

MR Bull, NA Helsby, WA Denny, JA Spicer. University of Auckland, SMS, FMHS, New Zealand

Inappropriate perforin activity is associated with a number of diseases such as cerebral malaria and type1 diabetes as well as therapy induced allograft rejection and graft versus host disease (GVHD).

A series of small molecule inhibitors of perforin function have recently been developed [1].These aryl-substituted isobenzofuran-1(3H)-one analogues are potent inhibitors of perforin induced cell lysis. Information about the in vivo disposition of these perforin inhibitors was required for the further development of these novel immunosuppressive drugs.

Three of the previously published [1] compounds: 94, 98 and 122, were formulated in DMSO:PEG400:water (15:45:40 v/v) and administered to male CD1 mice (25-35g) at 5mg/kg i.v. Plasma drug concentrations were determined over 6 hours from triplicate samples using an LC/MS/MS method developed for these compounds. Pharmacokinetic parameters were determined using non-compartmental analysis (Phoenix WinNonLin 6.2, Pharsight Corp, USA).

Table 1. Physiochemical parameters, biological activity and pharmacokinetic data for three novel perforin inhibitors (# previously reported in [1]).

The maximum drug concentration achieved after 5mg/kg i.v. dose was higher than the IC50 required for inhibition of perforin activity for all three compounds. However, compound 98 had the highest plasma exposure with an AUC0- ∞ more than 10 fold greater than compound 94. Chemical modification increased the aqueous solubility but this was associated with an increased rate of elimination (k el) and a shorter half-life. The most water soluble compound, 94, had the highest volume of distribution (Vd) and was rapidly cleared relative to the other drugs. Compound 122 had increased solubility and perforin activity and also achieved a suitable AUC relative to the in vitro IC50 (AUC/IC50 = 2.3).

An additional 12 analogues were then administered intravenously to mice. A 25-fold variation in plasma drug exposure (AUC0- ∞) was observed across the extended series (from 197 to 5086 h.ng/ml), and plasma half-life ranged between 1.1 and 4 hours. There was also a 25-fold range in clearance 983-25380 ml/h/kg.

This is the first demonstration that small molecule perforin inhibitors have suitable in vivo characteristics for continued development of these compounds as novel immunosuppressive agents.

Reference:

1. Spicer et al 2012 Bioorganic & Med Chem 20: 1319-1336