Cancer is a highly debilitating condition that continues to effects millions across the globe. Over the years, numerous researches and discoveries have been made by the experts in order to come up with more accurate and more advanced cancer diagnosis, management, and treatment tools and methods that may allow these patients to live a longer life. Some methods that are usually used for the treatment of this condition include chemotherapy, radiotherapy, and a surgical procedure which may be conducted separately or in a combination, depending on the extent of the spread and severity of cancer. Even though these methods may prove to be efficient in getting rid of the majority of cancer and cause remission, they have numerous harmful effects on the individual and negatively affect their quality of life. Genetic engineering is a new field that has gained a lot of popularity over the last few years, where systems like CRISPR may be used in combination with Cas9.
Types of Cancers and Its Development
Cancers are of different types depending on location in the body and the cell of origin. Some cells lead to a more aggressive form of cancer, while others may not be as aggressive. Moreover, the treatment of cancer also depends on whether or not cancer has spread to other sites of the body. Hence if it is of benign type, it may stay limited to its site of origin and may not spread to other parts of the body, which is why it may be simple extracted by a surgical procedure. However, if it is malignant, it spreads all over the body and involves more complex treatment methods. (1)
They are commonly caused by a gene mutation, and studies have now recognized at least 140 genes that may be responsible for their development. Due to the numerous genes and associated mutations, it is difficult to come up with an exact treatment plan which will be effective for all cancers.
How does CRISPR Genome Editing Work?
Gene editing technologies like CRISPR work by breaking the double-strand in a specified part of the genome, which may then be made to undergo repair by certain cellular processes. Previous gene tools included Zinc-finger nucleases and transcription activator effector nucleases; however, ever since the introduction of the CRISPR/Cas system, the field of genome editing was completely revolutionized. Researchers and Experts all opted for the CRISPR/Cas system to conduct their studies and introduce new diagnostic and treatment strategies due to the ease f use of the system, its scalability, and affordability.
This system is commonly classified into three types, which can further be divided into several subgroups. Of all the types of the CRISPR system, the most commonly used is the Type II CRISPR-Cas system, which is made up of three main components, including The Trans activating crRNA, The CRISPR RNA, and an endonuclease.(2)
What is the CRISPR-Cas9 System?
The CRISPR/Cas9 is an adaptive and programmable system that is composed of an RNA molecule that guides its associated Cas9 endonuclease to specific sequences in the genome, which might require alterations. The CRISPR/Cas9 system is composed of two main constituents: A Cas9 endonuclease and a single-stranded RNA. The role of the single-stranded RNA is that it guides the Cas9 to endonuclease to be directed towards the target sequence of the genome and cause cleave of its DNA strands. After the successful breakdown of the double strand of the target DNA, it may be repaired by certain repair mechanisms like the DNA-DSB systems. Hence the CRISPR/Cas9 system allows target genome editing, which may involve insertion and deletion of particular genes, which may, in turn, allow it to be used for the purposes of treatment and diagnosis. (3)
The Mechanism of Action of CRISPR-Cas9 System for Cancer Treatment
Numerous studies have now proved the potential role of CRISPR-Cas9 systems as an effective cancer treatment due to their ability to allow targeting genome editing. This system is mainly based on the insertion of foreign nucleic acid into the targeted sites to allow a prokaryotic adaptive immunity. The locus of the CRISPR/Cas 9 system is linked by the Cas9 operon, which is composed of repeating sequences, which are separated by the non-repeating sequences via spacers and tracrRNA.
When the phage of the CRISPR-Cas9 system targets and infects a specific bacterium, it inserts a foreign DNA inside it, which may also be referred to as the Spacer sequence. After the successful incorporation of the spacer sequence, the CRISPR-Cas9 system allows its co-transcription inside the new host and facilitates the formation of an immature segment known as the pre-crRNA. This immature crRNA is composed of repeat segments and spacers from both the host and the foreign DNA. This immature crRNA is then converted to mature crRNA, but the co-processing of trancr-RNA and pre-crRNA by the help of enzyme RNase III. This may then be cleaved into a 20 nucleotides long sequence. (4)
This ability of the CRISPR/Cas9 system allows it to be potentially used to create oncolytic engineered viruses and immune cells to allow target cancer therapy. Moreover, it can also be used to directly target specific genes which may be responsible for one’s cancer development and prove as an excellent cure to cancer.
The Future of the CRISPR system for Cancer Treatment
The CRISPR system has gained a lot of popularity over the years, and it is expected to develop rapidly and become a part of the diagnostic and treatment procedures in hospitals in the near future. It has also revolutionized scientific research, which could only be conducted at a basic level in the past, but with CRISPR technology, it is possible to apply it at clinical levels and promote more advancements in cancer biology and treatment. This is because this system may not only be able to precisely edit specific genes without affecting any other part of the body, but it may also allow the development of complete genomic libraries for cancer patients to allow them to avail personalized cancer treatment in the near future. (5)
- Khan FA, Pandupuspitasari NS, Chun-Jie H, et al. CRISPR/Cas9 therapeutics: a cure for cancer and other genetic diseases. Oncotarget. 2016;7(32):52541-52552. doi:10.18632/oncotarget.9646
- Jinek M, Chylinski K, Fonfara I, Hauer M, Doudna JA, Charpentier E. A programmable dual-RNA-guided DNA endonuclease in adaptive bacterial immunity. Science. 2012 Aug 17;337(6096):816-21. doi: 10.1126/science.1225829. Epub 2012 Jun 28. PMID: 22745249; PMCID: PMC6286148.
- Tian X, Gu T, Patel S, Bode AM, Lee MH, Dong Z. CRISPR/Cas9 – An evolving biological tool kit for cancer biology and oncology. NPJ Precis Oncol. 2019;3:8. Published 2019 Mar 18. doi:10.1038/s41698-019-0080-7
- Khalaf K, Janowicz K, Dyszkiewicz-Konwińska M, et al. CRISPR/Cas9 in Cancer Immunotherapy: Animal Models and Human Clinical Trials. Genes (Basel). 2020;11(8):921. Published 2020 Aug 11. doi:10.3390/genes11080921
- Akram F, Ikram Ul Haq, Ahmed Z, Khan H, Ali MS. CRISPR-Cas9, A Promising Therapeutic Tool for Cancer Therapy: A Review. Protein Pept Lett. 2020;27(10):931-944. doi: 10.2174/0929866527666200407112432. PMID: 32264803.