54 (PB044) - Non-clinical identification and characterization of KRAS G12D inhibitors

Abstract

KRAS G12D is the most prevalent KRAS oncogenic mutant and occurs frequently in pancreatic ductal adenocarcinoma (PDAC), colorectal adenocarcinoma (CRC), and non-small cell lung cancer (NSCLC; 37%, 12% and 4%, respectively). KRAS G12D cycles between inactive (GDP) and active (GTP) states to regulate the RAS/MAPK pathway. Although the rate of intrinsic and GAP (GTPase activating protein) mediated hydrolysis is significantly slower in KRAS G12D than in KRAS wild-type (KRAS WT), we were able to build upon success of targeting the GDP state of KRAS G12C and designed novel KRAS G12D lead compounds with promising in vitro and in vivo activity. Our KRAS G12D inhibitors preferentially bind to KRAS G12D GDP as indicated by differential scanning fluorimetry (DSF), block KRAS G12D SOS1-mediated nucleotide exchange, and inhibit KRAS G12D binding to the RAS binding domain of C-RAF (RAF-RBD) with single digit nanomolar potency. Our leads effectively inhibit ERK1/2 phosphorylation (pERK) in AsPC-1 PDAC cells and inhibit cell proliferation in 3-dimensional Cell-Titer Glo assays in a panel of KRAS G12D mutant PDAC, CRC, and NSCLC cell lines. This in vivo activity translates in vitro where robust pharmacodynamic modulation in the PDAC AsPC-1 CDX model was induced. Tumor growth inhibition studies in this model revealed robust dose-dependent tumor growth inhibition and tumor regression in the absence of overt toxicity. In summary, we have identified potent and selective KRAS G12D inhibitors with robust dose-dependent tumor growth inhibition and regression activity in a PDAC CDX model. Lead optimization is ongoing with the aim of identifying a development candidate. No conflict of interest.