233 Background: Pancreatic cancer (PC) is a deadly disease in urgent need of novel molecularly targeted drugs. Gene copy number amplification studies in PC patient cohorts has shown amplification of the p21-activated kinase (PAK) family member PAK4. PAK4 acts as a key effector of the Rho family GTPases downstream of Ras signaling. Moreover, PAK4 protein is over-expressed in PC cell lines but not in normal human pancreatic ductal epithelial (HPDE) cells. Most importantly, RNA interference of PAK4 has been shown to suppress PC cell proliferation. These studies clearly make PAK4 an attractive therapeutic target especially because direct targeting of Kras has been a failure. Methods: We have identified a new class of PAK4 allosteric modulators that show anti-proliferative activity against several PC cell lines (IC50s <250nM) while sparing normal HPDE (IC50s5 fold higher). Results: Cell growth inhibition is concurrent with apoptosis induction and suppression of colony formation in the PC cell lines (and not in HPDE cells). Our small molecule PAK4 allosteric modulator, KPT-7189, suppresses PAK4 protein expression and caused reversal of anti-apoptotic signaling. PAK4 RNA interference enhances KPT-7189 activity, and co-immunoprecipitation experiments showed disruption of PAK4 binding partners. KPT-7189 also inhibited spheroid forming ability of highly resistant PC cells carrying markers of cancer stem cells (CSCs;triple positive for CD33+CD44+EpCAM+) consistent with epithelial-to-mesenchymal (EMT) phenotype. Molecular analyses of KPT-7189 treated CD33+CD44+EpCAM+ spheroids showed suppression of EMT and CSC markers with re-expression of epithelial phenotype markers. Another potent PAK allosteric modulator in the same series, KPT-7651 showing good oral bioavailability (%F = 95%) was well tolerated by mice with a maximum tolerated dose of 60 mg/kg following oral administration. Pre-clinical animal efficacy trial in sub-cutaneous, orthotopic and LSL-KrasG12D/+;LSL-Trp53R172H/+;Pdx-1-Cre transgenic mice model is currently under investigation. Conclusions: This is the first proof of concept study demonstrating the development of a PAK4-targeted drug for the treatment of PC, and thus further pre-clinical and clinical investigations are warranted.
P21-activated kinase 1 (Pak1) signaling influences therapeutic outcome in pancreatic cancer
