Exploiting the CRISPR/Cas9 PAM Constraint for Single-Nucleotide Resolution Interventions

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• CRISPR/Cas9 is a powerful RNA-guided genome engineering tool.
• The Protospacer Adjacent Motif (PAM) is a critical DNA binding requirement for Cas9.
• Targeting specific mutations while sparing wild-type alleles remains a challenge.

Purpose of the Study:

• To exploit the Cas9 PAM requirement for precise targeting of heterozygous mutations.
• To investigate the therapeutic potential of PAM-guided CRISPR/Cas9 in colorectal cancer.
• To reverse drug resistance associated with KRAS mutations.

Main Methods:

• Utilized CRISPR/Cas9 genome editing technology.
• Designed guide RNA (gRNA) to target the Cas9 enzyme to a specific PAM sequence.
• Targeted the heterozygous G13A activating mutation in KRAS within colorectal cancer cells.

Main Results:

• Demonstrated successful targeting of single-nucleotide heterozygous mutations.
• Showed no aberrant effects on wild-type alleles.
• Achieved reversal of drug resistance to a MEK small-molecule inhibitor.

Conclusions:

• The PAM requirement of Cas9 can be leveraged for highly specific genome editing.
• This approach enables targeted therapy for KRAS-mutated colorectal cancer.
• Introduces a novel paradigm for therapeutic genome engineering using gRNA-guided Cas9 targeting of PAM sequences.