KRAS is mutated in ∼20% of human cancers and is one of the most sought-after targets for pharmacological modulation, despite having historically been considered “undruggable.” The discovery of potent covalent inhibitors of the KRAS G12C mutant in recent years has sparked a new wave of interest in small molecules targeting KRAS. While these inhibitors have shown promise in the clinic, we wanted to explore PROTAC-mediated degradation as a complementary strategy to modulate mutant KRAS. Herein, we report the development of LC-2, the first PROTAC capable of degrading endogenous KRAS G12C . LC-2 covalently binds KRAS G12C with a MRTX849 warhead and recruits the E3 ligase VHL, inducing rapid and sustained KRAS G12C degradation leading to suppression of MAPK signaling in both homozygous and heterozygous KRAS G12C cell lines. LC-2 demonstrates that PROTAC-mediated degradation is a viable option for attenuating oncogenic KRAS levels and downstream signaling in cancer cells.

Targeted protein degradation (TPD) has emerged as an exciting new era in chemical biology and drug discovery. PROteolysis TArgeting Chimera (PROTAC) technology targets cellular proteins for degradation by co-opting the ubiquitin-proteasome system. Over the last 5 years, numerous studies have expanded our understanding of the unique mode of action and advantages of PROTACs, which has in turn spurred interest in both academia and industry to explore PROTACs as a novel therapeutic strategy. In this review, we first highlight the key advantages of PROTACs and then discuss the spatiotemporal regulation of protein degradation. Next, we explore current chemically tractable E3 ligases focusing on expanding the existing repertoire with novel E3 ligases to uncover the full potential of TPD. Collectively, these studies are guiding the development of the PROTAC technology as it emerges as a new modality in precision medicine. ll

Highlights d TRAFTACs are heterobifunctional chimeric oligos d Transcription factors are recruited to the double-stranded DNA of the chimeric TRAFTACs d TRAFTACs are generalizable d Brachyury-TRAFTAC induces no tail phenotype in zebrafish embryos

Histone deacetylase (HDAC) proteins are promising targets for cancer treatment, as shown by the approval of two HDAC inhibitors for the treatment of cutaneous T-cell lymphoma. HDAC1 in particular has been linked to cell growth and cell cycle regulation and is therefore an attractive target for anticancer drugs. The HDAC1 active site contains a hydrophobic 11 Å active-site channel, with a 14 Å internal cavity at the bottom of the active site. Several computational and biochemical studies have proposed an acetate-escape hypothesis where the acetate byproduct of the deacetylation reaction escapes via the 14 Å internal cavity. Selective HDAC inhibitors that bind to the 14 Å cavity have also been created. To understand the influence of amino acids lining the HDAC1 14 Å cavity in acetate escape and inhibitor binding, we used mutagenesis coupled with acetate competition assays. The results indicate that amino acids lining the 14 Å cavity are critical for catalytic activity and acetate competition, confirming the role of the cavity in acetate escape. In addition, these mutagenesis studies will aid in HDAC1-inhibitor design that exploits the 14 Å cavity.