Project Summary The proto-oncogene KRAS is one of the most critical genes in cancer, yet, as a drug target, it has proven to be among the most elusive. A remarkable 30% of lung adenocarcinomas, 45% of colon, and 98% of pancreatic cancers are driven by KRAS mutations. These cancers account for the top 3 causes of cancer-related deaths in the United States. Most cancer associated KRAS mutations result in a constitutively active protein, which drives aberrantly high downstream signaling of pro-proliferative and pro-survival effectors including the MAPK and PI3K pathways. Kinase inhibitors have revolutionized treatment of many cancers driven by other molecular aberrations, yet, unfortunately a lack of such success in KRAS-driven cancers has led to KRAS itself to be widely regarded as “undruggable”. EnFuego Therapeutics, Inc. (EFTX) was founded to address the growing number of “undruggable” targets in cancer using RNA interference (RNAi)-based therapeutics. RNAi is particularly attractive for KRAS targeting because it can be optimized to enable selective silencing of mutant transcripts while sparing wild type transcripts, which is important for maintaining normal function in nonmalignant tissue. Mutation-specific therapeutics against KRAS are under development by several companies such as Amgen and Mirati, and rely on small molecules (specific only to G12C mutations). Unlike prior RNAi strategies in cancer, the EFTX approach employs nucleotide modification and ligand conjugation chemistries to promote in vivo stability and affinity-based targeting in cancer cells. In particular, ligand conjugation represents a significant advantage over legacy delivery technologies such as lipid nanoparticles. We have shown that EnFuego siRNAs targeting mutant KRAS transcripts result in: 1) reduced oncogenic MAPK signaling, 2) reduced cancer cell proliferation, and 3) reduced tumor burden in murine cancer models. Based on these preliminary data, this Fast Track program will further develop EFTX siRNA technologies for targeting mutant KRAS in humans. During Phase I, we will focus on optimization of fully chemically modified (FM) siRNA compounds that potently and specifically silence mutant G12V transcripts, exhibit serum stability and immune stealth, and inhibit downstream cancer cell signaling. Two to three FM siRNAs will be selected as lead compound candidates for progression to Phase II studies. Phase II Specific Aims will focus on optimization of pharmacokinetics, tissue targeting, and efficacy in murine models of metastatic lung cancer. These data will inform the selection of a single candidate for scale up and a 4-week GLP safety assessment study. As such, this Fast Track program will accelerate progression of this novel therapeutic strategy toward filing an Investigational New Drug application for metastatic lung cancer therapy.