PROTAC Targeting KRAS

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As a leading CRO in the field of drug development, BOC Sciences is committed to providing comprehensive solutions for new drug target exploration and PROTAC development. We offer customized services for the development of PROTAC targeting KRAS, ranging from the design of the KRAS PROTAC synthesis route to the validation of complex molecules to meet your specific needs.

Target - KRAS

About 30% of human cancers are associated with RAS mutations. The RAS family mainly includes three subtypes: KRAS, HRAS, and NRAS, with KRAS mutations accounting for 85% of total RAS gene mutations (NRAS 12%, HRAS 3%). KRAS has become one of the most frequently mutated genes in human cancers, with upregulation or mutation activation of KRAS protein observed in various cancers such as pancreatic, lung, and colon cancers. KRAS mutation subtypes include G12C, G12D, G12V, G13D, G12R, and G12A mutations, or KRAS wild-type amplification.

The KRAS protein, characterized by low hydrophobicity, can overcome its own hydrophobicity through farnesylation modification and bind to the inner side of the cell membrane. Normally, KRAS exists in cells in an inactive form as KRAS-guanosine diphosphate (GDP). Upon stimulation of the receptor protein tyrosine kinase , downstream guanine nucleotide exchange factors (GEFs) are recruited. Under the action of GEF, KRAS releases GDP and rapidly binds to guanosine triphosphate (GTP) to exist in its active form, KRAS-GTP. KRAS protein itself has GTPase activity, enhanced under the regulation of GTPase-activating proteins (GAP), which hydrolyzes the bound GTP to GDP, converting KRAS-GTP to inactive KRAS-GDP. KRAS functions as a switch by transitioning between this inactive state (bound to GDP) and active state (bound to GTP). Most KRAS mutations inhibit GTP hydrolysis, affecting the conversion of KRAS-GTP to KRAS-GDP, leading to abnormal activation of KRAS and cancer development.

KRAS Inhibitor vs PROTAC

The design and development of inhibitors directly targeting KRAS to inhibit its abnormally activated function have been a key strategy in new drug development. Alternatively, inhibitors indirectly targeting KRAS, regulating its cellular distribution and enhanced activity, can be designed. KRAS is involved in regulating three important signaling pathways: MAPK/ERK pathway, PI3K/Akt/mTOR pathway, and Ral/GDS pathway.

Direct targeting regulators include: 1) guanosine analogs acting directly on the GTPase active site; 2) inhibitors directly acting on the switch pocket; 3) PROTAC-based degraders targeting KRAS mutated protein degradation. However, the development of competitive reversible inhibitors targeting specific sites has long faced challenges, and KRAS was once considered an undruggable target. In comparison to traditional small molecule drugs, one of the major advantages of PROTAC is its ability to target challenging or mutated proteins. PROTAC discards the occupancy-driven mechanism relied upon by traditional small molecule inhibitors and adopts an innovative event-driven pharmacological strategy. It can effectively degrade target proteins within cells using catalytic amounts of drugs.

KRAS PROTAC Development

Proteolysis-targeting chimeras (PROTACs) for protein degradation involve a connector linking the ligand for the interest protein and the ligand for the recruitment of the E3 ubiquitin ligase. The E3 ubiquitin ligase attaches ubiquitin to the target protein, marking it for degradation. Subsequently, the 26S proteasome recognizes and degrades the tagged target protein. PROTAC is a new molecular entity that has been promisingly to be designed to target and degrade KRAS.

Fig. 1 KRAS PROTAC LC-2. (Bond, 2020)

BOC Sciences provides research support for KRAS PROTACs, covering molecular design, screening, efficacy, selectivity, etc.

• KRAS PROTAC Design: Selection of KRAS and linker for connecting ligands, optimization of linker length, flexibility and rigidity, polarity, and non-polarity.
• KRAS PROTAC Synthesis and Screening: Optimization of synthesis routes, establishment of PROTAC molecular libraries.
• KRAS PROTAC Validation: Inhibition activity testing for various cell lines with KRAS mutations.
• Animal Experiments: Observation of tumor regression in xenograft mouse models carrying KRAS mutations after administration of candidate KRAS PROTAC molecules.

Progress of KRAS PROTAC

Research on selective inhibitors and pan-inhibitors for KRAS mutations is abundant. FDA-approved KRAS G12C inhibitors such as sotorasib and adagrasib are used to treat metastatic non-small cell lung cancer. In 2020, the Craig M. Crews group reported the first-in-class endogenous KRAS G12C degrader LC-2, combining a KRAS inhibitor and VHL E3 ligase ligand. LC-2 covalently binds to KRAS G12C with adagrasib head, recruits E3 ligase VHL, inducing rapid and sustained degradation of KRAS G12C, leading to inhibition of the MAPK signaling pathway in KRAS G12C cell lines. With the increasing breadth of KRAS inhibitor research, reports on such PROTACs continue to emerge.

Reference

1. Bond, M. J., et al., Targeted Degradation of Oncogenic KRASG12C by VHL-Recruiting PROTACs, ACS Cent. Sci., 2020, 6, 8, 1367-1375.

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