Extrachromosomal Circular DNAs, Amplified Oncogenes, and CRISPR-Cas9 System

Structurally rearranged extrachromosomal circular DNAs (eccDNAs) have been identified in tumor cells, many of which carry regions related to recurrent cancer driver oncogenes (e.g., CCND1, EGFR, and MYC). In a tumor cell, eccDNAs are carrying regions associated with oncogene amplification (>10-fold amplified-copy numbers in human tumors) and poor outcome across multiple cancers. Even though dual-delivery of pairs of CRISPR and CRISPR-associated protein 9 (Cas9) guiding RNAs into normal human cells was reported to induce circularization of genes and chromosomes, in bacteria, the CRISPR-Cas9 system primarily targets extrachromosomal rearranged elements. Likewise, in cancer cells, it is expected that a designed CRISPR-Cas9 system would be able to target extrachromosomal copy number amplifications and produce double strand breaks detrimental to cellular fitness by dictating gene-independent copy number loss-of-fitness effects and antiproliferative responses. A system designed against amplified amplicons may provide a novel approach for cancer therapy and propose a practical implication for CRISPR-Cas9 pairs as a pathway in therapeutic strategies of cancer. SIGNIFICANCE STATEMENT: Structurally rearranged extrachromosomal circular DNAs (eccDNAs) have been identified in tumor cells. Many eccDNAs are carrying regions related to recurrent cancer driver oncogenes (e.g. CCND1, EGFR and MYC). It is expected that a designed CRISPR-Cas9 system would able to target extrachromosomal recurrent oncogenes.