Preclinical anticancer properties of potent small molecule inhibitors of protein kinase D

A237 Signal transduction pathways involving protein kinase D (PKD) are frequently deregulated in cancer. This points to an important role for PKD in promoting tumour proliferation and angiogenesis, and as a survival factor. The aims of this study were to firstly further validate PKD as a potential cancer target and second to identify and then determine the anticancer properties of novel small molecule PKD inhibitors. Results showed that SiRNA mediated knockdown of PKD 1 or 2 in a human pancreatic cancer cell line (PANC-1) induced a decrease in proliferation or increased apoptosis, respectively. A high throughput biochemical screen of 65,000 molecules identified 3 structurally distinct pharmacophores. Chemical optimisation of series 1 resulted in potent (sub nM IC 50 ) ATP-competitive pan-PKD inhibitors, exemplified by the prototype compound CRT0059359. The compound showed a good degree of selectivity against other kinases. In cancer cells CRT0059359 abolished phorbol ester stimulated PKD1 serine 916 autophosphorylation when used at low micromolar concentrations. Moreover, exposure of PANC-1 cells to 2-5μM CRT0059359 resulted in an inhibition of proliferation and a marked induction of apoptosis (as measured by increased caspase 3 activity). Mouse pharmacokinetic studies showed that the compound possesses promising drug-like properties (e.g., achievable plasma levels comparable to those required to induce anti-proliferative effects in vitro, a serum half-life of over 2 hours, and some oral bioavailability). Furthermore, a single intraperitoneal dose of 80mg/kg CRT0059359 caused a significant reduction in PKD1 autophosphorylation in tumours of mice bearing PANC-1 subcutaneously implanted xenografts. In addition, chronic dosing (10mg/kg daily, days 1-5 and 8-10) of this prototype molecule caused a slowing of PANC-1 xenograft growth. These data provide good evidence that the inhibition of PKD represents a viable anticancer strategy and suggests that appropriate molecules should be progressed to clinical testing.