Application of the CRISPR/Cas9 System to Drug Resistance in Breast Cancer

Abstract

Clinical evidence indicates that drug resistance is a great obstacle in breast cancer therapy. It renders the disease uncontrollable and causes high mortality. Multiple mechanisms contribute to the development of drug resistance, but the underlying cause is usually a shift in the genetic composition of tumor cells. It is increasingly feasible to engineer the genome with the clustered regularly interspaced short palindromic repeats (CRISPR)/associated (Cas)9 technology recently developed, which might be advantageous in overcoming drug resistance. This article discusses how the CRISPR/Cas9 system might revert resistance gene mutations and identify potential resistance targets in drug-resistant breast cancer. In addition, the challenges that impede the clinical applicability of this technology and highlight the CRISPR/Cas9 systems are presented. The CRISPR/Cas9 system is poised to play an important role in preventing drug resistance in breast cancer therapy and will become an essential tool for personalized medicine.

Keywords: CRISPR/Cas9; breast cancer; drug resistance; drug therapy; reverting resistance.

Figure 1

Schematic illustration of genome engineering using the CRISPR/Cas9 system. Top: The Streptococcus pyogenes‐derived CRISPR/Cas9 RNA‐guided DNA endonuclease can recognize a coding exon of a gene of interest (blue) via a sgRNA sequence. sgRNA can anneal to a specific target sequence adjacent to a PAM sequence in the form of NGG or NAG. Cas9‐mediated induction of a DSB (red arrows) in the DNA target sequence leads to indel mutations via NHEJ or precise gene modification via HDR. Bottom: Catalytically inactive dCas9 can target promoters or enhancers of genes of interest (orange). Chimeric sgRNAs containing aptamers can bind to RNA‐binding domains fused to effector domains, such as transcriptional activators/repressors, chromatin modifiers, or fluorescent proteins (purple).

Figure 2

Schematic representation of several possible mechanisms involved in drug resistance in breast cancer therapy. This mainly includes drug resistance analysis of pharmacological agents used in endocrine therapy and targeted signaling molecules, and chemotherapy resistance. The blue rectangle refers to the section of endocrine therapy, black rectangle refers to the section of targeting signaling molecules, and red rectangle refers to the section of chemotherapy‐resistance. The crosstalk is what is in common of the three kinds of drug resistance mechanisms, which has a complicated network and is responsible for drug resistance. CRISPR/Cas9 can mainly apply to drug resistance based on crosstalk, the target mutation/alteration, and drug resistance genes.

Figure 3

High‐throughput experimental approaches used in cancer drug‐ resistance studies. The top schemes represent the CRISPR/Cas9 expression vector, including sgRNA libraries (green). At the bottom, gain‐of‐function screen using ORF libraries to identify candidate drivers of resistance. Breast cancer cell targeting is conducted in multiwell plates using viral transduction. The readout is based on cell population measurement of individual wells after drug treatment.