Novel protein kinase D inhibitors cause potent arrest in prostate cancer cell growth and motility

After initial activity screening, five analogs with equal or greater potencies as CID755673 were chosen for further analysis: kb-NB142-70, kb-NB165-09, kb-NB165-31, kb-NB165-92, and kb-NB184-02. Our data showed that modifications to the aromatic core structure in particular significantly increased potency while retaining high specificity for PKD. When tested in prostate cancer cells, all compounds inhibited PMA-induced autophosphorylation of PKD1, with kb-NB142-70 being most active. Importantly, these analogs caused a dramatic arrest in cell proliferation accompanying elevated cytotoxicity when applied to prostate cancer cells. Cell migration and invasion were also inhibited by these analogs with varying potencies that correlated to their cellular activity.Throughout the battery of experiments, the compounds kb-NB142-70 and kb-NB165-09 emerged as the most potent and specific analogs in vitro and in cells. These compounds are undergoing further testing for their effectiveness as pharmacological tools for dissecting PKD function and as potential anti-cancer agents in the treatment of prostate cancer.The PKD family is a novel family of serine/threonine kinases and diacyglycerol (DAG) receptors. Three isoforms of PKD have been identified so far: PKD1 (formerly PKCμ), PKD2, and PKD3 (PKCν) [1-4]. Originally classified as a member of the protein kinase C (PKC) family, the PKD family is now recognized as a subfamily of the calcium/calmodulin-dependent kinase superfamily, and is only distantly related to PKC in structure [5,6]. All isoforms contain a catalytic domain, a cysteine-rich DAG-binding domain (C1), and a pleckstrin homology (PH) domain that negatively regulates PKD activity [7]. DAG regulates the localization of PKD through binding to its C1 domain [4] and its activity through regulating PKC-dependent phosphorylation of PKD on serines 738 and 742 (Ser738/742) in the activation loop [8,9]. Rapid, early activation of PKD by PKC then leads to autophosphorylation of P