Original Article

Cancer Chemotherapy and Pharmacology

, Volume 67, Issue 5, pp 995-1006

Improved oral bioavailability in rats of SR13668, a novel anti-cancer agent

  • Carol E. GreenAffiliated withBiosciences Division, SRI International Email author 
  • , Robert SwezeyAffiliated withBiosciences Division, SRI International
  • , James BakkeAffiliated withBiosciences Division, SRI International
  • , Walter ShinnAffiliated withBiosciences Division, SRI International
  • , Anna FurimskyAffiliated withBiosciences Division, SRI International
  • , Naveen BejugamAffiliated withBiosciences Division, SRI International
  • , Gita N. ShankarAffiliated withBiosciences Division, SRI International
  • , Ling JongAffiliated withBiosciences Division, SRI International
  • , Izet M. KapetanovicAffiliated withNational Cancer Institute

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Abstract

Purpose

SR13668, a bis-indole with potent activity in vitro and in vivo against various cancers and promising cancer chemopreventive activity, was found to have very low oral bioavailability, <1%, in rats during pilot pharmacokinetic studies. The objective of these studies was to better understand the source of low oral exposure and to develop a formulation that could be used in preclinical development studies.

Methods

An automated screening system for determining solubility in lipid-based vehicles, singly and in combination, was used to identify formulations that might enhance absorption by improving solubility of SR13668, and these results were confirmed in vivo using Sprague–Dawley rats. Pharmacokinetics of SR13668 was then determined in male and female Sprague–Dawley rats administered 1 mg/kg iv, 1, 10, and 30 mg/kg po formulated in PEG400:Labrasol® (1:1 v/v). Blood was collected at time points through 24 h and the concentration of SR13668 determined using HPLC with UV and fluorescence detection.

Results

SR13668 was found to be resistant to plasma esterases in vitro and relatively stable to rat and human liver microsomal metabolism. SR13668 concentrates in tissues as indicated by significantly higher levels in lung compared to blood, blood concentrations ~2.5-fold higher than plasma levels, and apparent volume of distribution (V) of ~5 l/kg. A marked sex difference was observed in exposure to SR13668 with area under the curve (AUC) significantly higher and clearance (CL) lower for female compared to male rats, after both iv and oral administration. The oral bioavailability (F) of SR13668 was 25.4 ± 3.8 and 27.7 ± 3.9% (30 mg/kg), for males and females, respectively. A putative metabolite (M1), molecular weight of 445 in the negative ion mode (i.e., SR13668 + 16), was identified in blood samples from both the iv and po routes, as well as in vitro microsomal samples.

Conclusions

In summary, while SR13668 does undergo metabolism, probably by the liver, the oral bioavailability of SR13668 in rats was dramatically improved by the use of formulation that contained permeation enhancers and promoted better solubilization of the drug.

Keywords

SR13668 Formulation Pharmacokinetics Absorption enhancer Bioavailability Chemoprevention Rat Drug metabolism