409 Optimizing the Therapeutic Potential of PD-L1 Blockade as a Single Agent and Through Combination Therapy

constitutive KRAS activity. Our experience developing PH-domain inhibitors for other signaling proteins led us to use molecular docking and an in silico compound library to find CNKSR1 inhibitors. We identified small molecule lead compounds that using surface plasmon resonance spectroscopy we found bound to the PH-domain of CNKSR1. The most active compound was PHT-782 (Kd1.8 mM). PHT-782 showed activity similar to CNKSR1 knockdown and inhibited mut-KRAS signaling and the growth of mut-KRAS isogenic and NSCLC cell lines (IC50 ~30 mM) as effectively as siRNA knockdown of KRAS. In mice PHT-782 exhibited oral bioavailability and plasma t12 > 4 hr, and had moderate antitumor activity against a mut-KRAS xenograft model without observable toxicity at doses up to 200mg/kg. To improve potency and selectivity we have undertaken iterative modeling using PHuDock a proprietary computational modeling platform and have identified additional leads with improved binding potency. The results of our study show that the PH domain of CNKSR1 can be targeted by small molecule inhibitors giving agents that block oncogenic KRAS signaling and cell growth, thus creating a therapeutic potential for patients with mut-KRAS for which there is currently no effective therapy.