K-Ras mutant-specific vulnerabilities for novel pancreatic cancer therapies

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 DESCRIPTION (provided by applicant): Despite more than three decades of intense efforts, no clinically effective therapeutic strategies have been developed targeting the KRAS oncogene, which is mutationally activated in >95% of pancreatic ductal adenocarcinoma (PDAC). One reason for this failure has been the perception that "all KRAS mutations are created equal", with most anti-KRAS strategies based on the development of a pan-mutant KRAS inhibitor. There are 134 different missense mutations identified in KRAS in all cancers, with 98% found at one of three hotspots, amino acids G12, G13 or Q61. The recent provocative identification of a small molecule antagonist specific for one mutant, KRAS G12C, has begun to shift the paradigm, supporting the concept that mutation- selective therapeutic approaches may be a more effective strategy. Building on this paradigm, this proposal focuses on two specific KRAS mutations. Aim 1 will determine whether KRAS G12R differentially activates effector signaling compared with the more commonly seen and studied G12D/V/C mutations found in ~70% of all cancers. While KRAS G12R is rare in all cancers (3%), this mutation is the third most common KRAS mutant found in PDAC. As structural analyses found that the G12R mutation, but not G12D/V/C mutations, was altered in a region of the protein critical for effector recognition, it is likely that this mutant has altered downstream effector signaling. Further supporting this possibility is the fact that PDAC patients with G12R mutations had a significantly better overall survival (15.6 months) relative to patients with non-G12R mutations (8.9 months). Consequently, KRAS G12R mutant PDAC may be uniquely susceptible to a distinct effector- targeted therapeutic strategy. Aim 2 focuses on G13 mutations, poorly studied and the least understood mutation hotspot compared with G12 and Q61 mutations. Although G13D is the third most common KRAS mutation in all cancers (13%), it is rarely observed in PDAC (<1%). The G13D mutation causes a biochemically distinct alteration not seen with G12 mutations; thus, G13D mutations may require a distinct therapeutic approach than G12 mutant cancers. Although eight different KRAS missense mutations are found at G13, G13D comprises the vast majority (90%). In contrast, the G13D mutation is rarely seen in the highly related HRAS isoform (4%), with G13R the predominant G13 mutation in HRAS (81%), yet rare in KRAS (1%). Taken together, these striking frequency differences argue that cancer type and RAS isoform-distinct differences in the oncogenic potency of the G13D mutation may exist. Using a human pancreatic cell model, this study will apply kinome-wide protein kinase and phosphorylation profiling together with a mouse model of pancreatic cancer to assess tumorigenic and metastatic growth. In summary, this study will identify KRAS mutation- specific effector signaling that can then be exploited for the design of mutation-selective effector signaling- targeted therapeutic strategies for pancreatic cancer, a disease with no effective therapeutic options and a dismal 5-year survival rate of 6%.