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., , and ). 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. , and . It is expected that a designed CRISPR-Cas9 system would able to target extrachromosomal recurrent oncogenes.