Development CRISPR-Cas12-based rapid EGFR mutation detection kit.

Abstract

e13669 Background: Recently, several cancer gene panel tests have been developed to determine many driver mutations including lung cancer simultaneously. However, the current next-sequencing based platform is not ideal testing method in the clinical practice due to the high examination cost and the time required for the result to reach the field. By refining recently reported CRISPR-Cas-based nucleic acid detection methods, we developed a novel CRISPR-Cas12 family based rapid-detection kit for targetable EGFR mutations in non-small lung cancer (NSCLC) patients. Methods: To develop a powerful CRISPR-based testing method, we focused on unique Cas12 family proteins which contain a single RuvC nuclease domain that cleave target double-stranded DNA adjacent to protospacer adjacent motif (PAM) sequences as well as non-target single-stranded DNA (ssDNA) collaterally. We purified 6 Cas12 family proteins (Cas12a, Cas12c1, Cas12c2, Cas12g, Cas12i1, and Cas12i2) as well as two types of target-defined guide RNA for EGFR Ex.19 del(E746-A750) and L858R mutations. The target sequences including EGFR Ex.19(E746-A750) and L858R mutations were amplified from EGFR mutated cell lines, FFPE lung cancer tissues or cell free DNA (cfDNA) of NSCLC patients using PCR with PrimeSTAR GXL DNA polymerase (Takara, Shiga, Japan) or isothermal recombinase polymerase amplification (RPA) with TwistAmp Basic (TwistDx, Cambridge, UK). CRISPR-Cas12-based cleavage assay was conducted in a reaction buffer consisting of 10 nM Cas12 proteins, 10 nM purified guide RNA, 0.4nM target DNA, and 50 nM collateral ssDNA (quenched fluorescent DNA reporter) in a 20 μl volume at 37 °C for 1 h. The excited fluorescence, which is an indicator of the presence of target cancer mutation, was measured by Synergy H1 hybrid Multi-Mode Reader (BioTek, Vermont, USA). For simpler instrument-free and portable detection lateral flow readouts were also developed and tested using Milenia HybriDetect1 kit (TwistDx). Results: Cas12a, Cas12i1, Cas12i2-based assays successfully detected the EGFR Ex.19 del(E746-A750) and L858R mutations from PCR and RPA products. Lateral flow readout kit could also detect EGFR Ex.19 del (E746-A750) mutation from cfDNA derived from NSCLC patients. It took about 3 hours from plasma collection to DNA extraction, RPA, and measurement with the kit. Conclusions: CRISPR-Cas based lateral flow readout kit can detect EGFR mutation at an unprecedented pace with low cost. Our developed system will be an innovative testing tool for lung cancer patients with low cost, rapid, multiplexable, and noninvasive procedure.