In vitro cytotoxicity, pharmacokinetics, tissue distribution, and metabolism of small-molecule protein kinase D inhibitors, kb-NB142-70 and kb-NB165-09, in mice bearing human cancer xenografts
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Protein kinase D (PKD) mediates diverse biological responses including cell growth and survival. Therefore, PKD inhibitors may have therapeutic potential. We evaluated the in vitro cytotoxicity of two PKD inhibitors, kb-NB142-70 and its methoxy analogue, kb-NB165-09, and examined their in vivo efficacy and pharmacokinetics.
The in vitro cytotoxicities of kb-NB142-70 and kb-NB165-09 were evaluated by MTT assay against PC-3, androgen-independent prostate cancer cells, and CFPAC-1 and PANC-1, pancreatic cancer cells. Efficacy studies were conducted in mice bearing either PC-3 or CPFAC-1 xenografts. Tumor-bearing mice were euthanized between 5 and 1,440 min after iv dosing, and plasma and tissue concentrations were measured by HPLC–UV. Metabolites were characterized by LC–MS/MS.
kb-NB142-70 and kb-NB165-09 inhibited cellular growth in the low–mid μM range. The compounds were inactive when administered to tumor-bearing mice. In mice treated with kb-NB142-70, the plasma Cmax was 36.9 nmol/mL, and the PC-3 tumor Cmax was 11.8 nmol/g. In mice dosed with kb-NB165-09, the plasma Cmax was 61.9 nmol/mL, while the PANC-1 tumor Cmax was 8.0 nmol/g. The plasma half-lives of kb-NB142-70 and kb-NB165-09 were 6 and 14 min, respectively. Both compounds underwent oxidation and glucuronidation.
kb-NB142-70 and kb-NB165-09 were rapidly metabolized, and concentrations in tumor were lower than those required for in vitro cytotoxicity. Replacement of the phenolic hydroxyl group with a methoxy group increased the plasma half-life of kb-NB165-09 2.3-fold over that of kb-NB142-70. Rapid metabolism in mice suggests that next-generation compounds will require further structural modifications to increase potency and/or metabolic stability.
KeywordsProtein kinase D (PKD) inhibitors Pharmacokinetics Prostate cancer Pancreatic cancer kb-NB142-70 kb-NB165-09
This study was supported in part by US Public Health Service National Institutes of Health grant CA78039, CA129127, and CA142580. This project used the UPCI Clinical Pharmacology Analytical Facility (CPAF) and was supported in part by award P01CA078039. We acknowledge Diane Mazzei and other members of DLAR for the excellent care of the animals used in these studies. We also acknowledge the UPCI Writing Group for their helpful comments.
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