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

Abstract

Purpose 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 analog, kb-NB165-09, and examined their in vivo efficacy and pharmacokinetics. Methods 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 1440 min after iv dosing, and plasma and tissue concentrations were measured by HPLC-UV. Metabolites were characterized by LC-MS/MS. Results 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. Conclusions 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.

Protein Kinase D as a Potential Chemotherapeutic Target for Colorectal Cancer

“…As one example, kb-NB142-70, demonstrated significantly improved in vitro activity compared to the structurally related CID755673, but exhibited no antitumor activity in vivo, which is most likely due to rapid metabolism (17). Alternatively, a naphthyridine-based PKD inhibitor showed PKD inhibition and suppression of PKD-dependent downstream pathways in an in vivo rat model (35).…”

“…kb-NB142-70 also significantly inhibited cell proliferation, migration, and invasion. Unfortunately, kb-NB142-70 did not exhibit in vivo antitumor activity due to rapid metabolism (17). CRT0066101 is a small molecule PKD-specific inhibitor developed by investigators in the U.K., and it exhibited in vitro antitumor activity in human pancreatic cancer cells.…”

SD-208, a Novel Protein Kinase D Inhibitor, Blocks Prostate Cancer Cell Proliferation and Tumor Growth In Vivo by Inducing G2/M Cell Cycle Arrest

“…After the discovery of the first potent, selective, and cell-active small molecule inhibitor CID 755673 by our group [ 20 , 21 ] we directed significant efforts at improving its potency and selectivity through chemical modifications. While we developed leads with much improved potency and selectivity, such as kb-NB142-70 [ 20 , 22 ], the in vivo efficacy and applicability of this class of inhibitors remained limited [ 23 ]. A recent study utilizing targeted libraries of small organic kinase inhibitors has also identified a novel ATP-competitive 4-azaindole scaffold, and a set of pyrazolopyrimidine small molecule inhibitors with low nanomolar potency for in vitro inhibition of PKD that potently blocked prostate cancer cells proliferation and growth [ 18 , 24 , 25 ].…”

Protein kinase D signaling in cancer: A friend or foe?

“…In support of our view, using several classes of structurally distinct small molecule inhibitors of PKD discovered by our group, including CID755673 and its analogs SD-208, kb-NB142-70, 1-naphthyl PP1 (1-NA-PP1), Compound 139 [128, 133–136], which are all nanomolar cell-active pan-PKD inhibitors, we demonstrated that targeted inhibition of PKD by these inhibitors led to reduced proliferation, migration and invasion of prostate cancer cells. Altogether, these studies have validated PKD as a potential therapeutic target for prostate cancer.…”