Potential of using CRISPR-CAS9 to treat BRCA1 and BRCA2 associated hereditary breast cancer
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Abstract
Breast cancer is one of the major causes of death. About 22.9% of all cancer in women is breast cancer (Pohlreich et al., 2005). Although there are many known risk factors, genetics play a major role in breast cancer. Of which, germ-line mutations in BRCA1(BReast-CAncer susceptibility gene 1) and BRCA2 (BReast-CAncer susceptibility gene 2) genes are responsible for about 90% of all hereditary breast cancer cases, as well as most of hereditary ovarian cancer cases (Calderón-Garcidueñas et al., 2005). The BRCA1 and BRCA2 genes code for Tumor Suppressor Gene proteins which act as cell growth suppressors. BRCA1 and BRCA2 also help repair damaged DNA (Mehrgou & Akouchekian, 2016). Damage to one of these two genes could result in impaired repair of damaged DNA, which can lead to the accumulation of unrepaired DNA mutations and eventually lead to cancer. (Mehrgou & Akouchekian, 2016). The most common mutation forms for BRCA1 and BRCA2 are small insertions, deletions, nonsense mutations, missense mutations that cause premature transcription terminations and altered splicing (Pylkäs et al., 2008). Breast Information Core reports that the majority of cancerous mutations in BRCA1 and BRCA2 genes result in the generation of a truncated protein through nonsense, frameshift, and splicing mutations (Pohlreich et al., 2005). There is significant morbidity and mortality associated with BRCA1 and BRCA2-associated hereditary breast cancer.
Clustered regularly interspersed short palindromic repeats (CRISPR) and CRISPR-associated proteins (Cas), combined as CRISPR/Cas9 has garnered tremendous interest in the scientific community for its myriad applications from diagnostics, imaging, and most importantly in genome editing (Zhan et al., 2019). Two RNAs activate and guide Cas9, a DNA endonuclease, to bind specific DNA sequences. Cas9, then, subsequently cleaves the DNA at that site (Zhan et al., 2019). When a double-strand break is introduced in the target sequence by the Cas9 endonuclease, there are two different mechanisms of repair that are used by the host cell to respond. (1) The host cell may respond with a non-homologous end joining (NHEJ), a repair mechanism that often leads to insertions or deletions. This may be beneficial if the study, in question, aims to render a target gene functionless. (2) The second method is via homology-directed repair which recombines DNA donor templates to reconstruct damaged DNA (Zhan et al., 2019). This feature is helpful as it allows for site-specific editing, if the target gene in question, contains a mutation that leads to reduced expression, no expression, or results in cancer. In this thesis, I wish to explore the use of CRISPR-Cas9 as a possible tool for preventative therapy in BRCA1 and BRCA2-associated hereditary breast cancer.
The specific aims of the following thesis include:
1. A comprehensive review of literature on CRISPR-Cas9 and breast cancer, specifically due to mutations in BRCA1 and BRCA2 genes.
2. Investigation into current evidence for CRISPR-Cas9 use in diseases.
3. Conclusion on the challenges and limitations of CRISPR-Cas9 as a potential tool for preventative therapy for BRCA1 and BRCA2- associated hereditary breast cancer.