Application of CRISPR in Skin Cancer Treatment

Abstract

Cancer is a devastating disease that occurs due to the uncontrolled and abnormal growth of cells. In early stages, conventional methods such as surgery, radiation, and chemotherapy are effective, but they fail to treat advanced stages of cancer. Also, they do not target the genetic mutations that cause cancer. Gene editing with CRISPR/Cas9-based technology now makes it possible to target mutations precisely and irreversibly, providing a chance to utilize the system to target oncogenic mutations. This paper examines the potential use of CRISPR to treat skin cancer by targeting genes such as TP53, BRAF, NRAS, PTCH1, and TERT. Each of these genes plays a different role in how skin cancer grows or spreads. CRISPR could offer a way to make treatment more exact and possibly long-term. However, CRISPR comes with its own set of limitations, like the chance of editing the wrong part of the DNA, and questions about fairness and safety. These points show that while the tool is groundbreaking, scientists still have a lot of research to do before it can be used on real patients in clinics. This paper tries to give a clear look at both the advantages and disadvantages of using CRISPR for cancer treatment.

Keywords: skin cancer, CRISPR, treatment, mutations, genes mutated in skin cancer

1.0 Introduction

Cancer mortality and incidence are increasing rapidly around the globe. Each year, over 19 million new cancer cases are diagnosed globally, and this number is expected to rise to nearly 30 million by 2040 (International Agency for Research on Cancer [IARC], 2020). Cancer occurs when normal cells undergo genetic alterations, in the form of mutations, that disrupt the genes regulating cell growth, division, and death. The mutations occur in tumor suppressor genes, oncogenes, or DNA repair genes, enabling cells to grow and divide uncontrollably and form tumors. Some gene mutations are inherited, but most result from environmental factors such as smoking, radiation, pollution, or viral infections (Centers for Disease Control and Prevention [CDC], 2023).

Among many cancers, skin cancer is one of the most common to be diagnosed worldwide, especially in individuals with fair skin. It is estimated to cause approximately one in every three cancers diagnosed worldwide (Apalla et al., 2017). The primary cause is ultraviolet (UV) radiation that causes DNA damage in skin cells and results in gene mutations in genes such as TP53, which otherwise would inhibit the abnormal growth of the cells (Brash, 2015). Although generally avoidable, skin cancer is a public health issue owing to its high prevalence and increasing global burden.

Skin cancer is typically treated with surgery, radiation, and topical chemotherapy with agents such as 5-fluorouracil or imiquimod. These modalities are effective in the vast majority of early cancers and remain the mainstay of treatment. However, they typically do not target the underlying genetic defect, leading to recurrence or resistance (Alam et al., 2014). In addition, treatments like surgery and radiation have the potential to cause scarring, tissue damage, or fail in aggressive or metastatic tumors (Linos et al., 2010). Such disadvantages highlight the need for more precise and longer-lasting treatments.

Before the discovery of CRISPR, gene editing was based on technologies such as zinc finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs). These technologies provided researchers with the ability to introduce targeted modifications into DNA by inducing double-strand breaks at particular locations (Gaj et al., 2013). Although revolutionary during their time, both ZFNs and TALENs have weaknesses. They were difficult to design, expensive, and prone to imprecision, resulting in off-target mutations (Urnov et al., 2010). Moreover, the delivery of these tools into human cells with high efficiency was still a major problem, particularly in the clinical context. All these disadvantages rendered gene editing less accessible and less reliable.

CRISPR-Cas9 is a cutting-edge gene-editing technology that has simplified and made it more accurate to edit cancer genes such as TP53 and BRAF in skin cancer research (Sánchez-Rivera & Jacks, 2015). Compared to previous technologies, CRISPR is less expensive, quicker, and more precise, and hence better suited to the study of tumor formation. Yet, it also continues to struggle with off-target effects and the problem of delivering the system safely into human cells (Kosicki et al., 2018). Nevertheless, CRISPR has brought new avenues in developing tailored skin cancer therapies.

The emergence of technologies such as CRISPR has made what was previously unimaginable: fixing cancer-causing mutations at their source. This shift from symptom-reducing to rewriting the blueprint of disease is a dynamic new chapter in medicine. This paper discusses the potential use of CRISPR in skin cancer treatment, its advantages, and limitations.

2.0 Mechanism of skin cancer

Skin cancer typically begins when skin cell DNA is affected by ultraviolet (UV) light from sunlight or tanning beds. Such radiation can form errors within the DNA, like thymine dimers, that disrupt normal cellular processes (Brash, 2015). Unless repaired, these errors lead to mutations in critical genes. This process is illustrated in Figure 1, which shows how UV radiation causes DNA damage and leads to skin cancer development. One of the most impacted is TP53, which should otherwise prevent the proliferation of damaged cells. On mutation of TP53, damaged cells are permitted to proliferate and divide without check (Kulesza et al., 2013).

The more mutations occur, the more the systems that regulate cell growth deteriorate. In basal cell carcinoma, a type of skin cancer, mutations in a gene known as PTCH1 spur on the Hedgehog pathway, which instructs cells to continue growing even when they are not supposed to (Epstein, 2008). In melanoma, another severe type of skin cancer, BRAF gene mutations—particularly a substitution known as V600E—turn on the MAPK/ERK pathway, inducing cells to grow too rapidly (Davies et al., 2002). Other mutated genes, such as NRAS, CDKN2A, and TERT, also prevent cancer cells from dying and continue to grow (Hodis et al., 2012).

Figure 1. Pathway of Skin Cancer Development. Exposure of normal skin to UV light can lead to DNA damage in epidermal cells, resulting in mutations in genes like BRAF and TP53. This can lead to the development of precancerous lesions, the formation of basal cell carcinoma, squamous cell carcinoma, or melanoma. Source: Mai et al., 2023 (Cancers, MDPI)

The cancer cells eventually learn to evade the immune system, which, under normal circumstances, kills off abnormal cells. They camouflage themselves by lowering some proteins known as MHC molecules or by creating signals such as PD-L1, which slow down the immune system (Spranger et al., 2015). They also create new blood vessels to supply the tumor. These adaptations make the cancer more resilient and able to spread to other areas of the body. Researchers now target these molecules to make new treatments, including gene editing technologies such as CRISPR.

There are three major types of skin cancer: basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and melanoma. Each begins in a different type of skin cell and follows a slightly different development pathway. BCC, the most common type, starts in the basal cells at the bottom layer of the epidermis and is usually slow-growing. SCC originates in squamous cells and is more likely to spread if left untreated. Melanoma is the most dangerous, although it occurs the least. All three types can be caused by prolonged exposure to UV radiation, which damages DNA and leads to abnormal growth of cells. Understanding the differences between these cancers helps researchers design more targeted treatments, including gene-based therapies like CRISPR.

3.0 Mechanism of CRISPR

CRISPR, short for Clustered Regularly Interspaced Short Palindromic Repeats, is a gene-editing system in which scientists can make specific alterations to DNA. It was originally found within the bacterial defense system, where bacteria use it to identify and slice viruses' DNA that infects them (Jinek et al., 2012). Scientists engineered this innate system into an effective gene-editing system for organisms.

The most widely used research CRISPR system contains two primary components: Cas9, a DNA-cutting enzyme, and a guide RNA (gRNA) that guides Cas9 to the precise position in the genome. The gRNA is engineered to match a particular DNA sequence, and when it binds with its target, Cas9 functions as molecular scissors, cutting the DNA at that position (Cong et al., 2013). After the DNA is cleaved, the cell attempts to mend it, and researchers can make use of this repair mechanism to inactivate a gene or add a corrected copy.

Figure 2. CRISPR-Cas9 gene editing process. The DNA double helix contains a specific target gene. A guide RNA (orange strand) is designed to match this target sequence and directs the Cas9 enzyme (green structure) to the correct location. Once bound, Cas9 cuts both strands of the DNA at the target site. This break allows for gene editing—scientists can either disable the gene, remove a mutation, or insert new genetic material. (Made using Canva)

One of the greatest advantages of CRISPR is its precision and versatility. By adjusting the guide RNA, scientists can modify virtually any gene. CRISPR is less expensive, quicker, and simpler to perform than traditional techniques, making it one of the greatest advances in contemporary genetics. It has already been employed to examine and treat diseases such as sickle cell anemia, inherited blindness, and most cancers (Doudna & Charpentier, 2014). In the study of skin cancer, CRISPR provides a method to directly attack and correct the mutated genes that cause tumor growth (Figure 2).

4.0 CRISPR Targeting Molecules That Cause Skin Cancer

CRISPR technology provides a potential method of treating skin cancer by directly modifying genes that cause abnormal cell growth. Scientists are investigating how to employ CRISPR to attack the particular mutations that cause cancers such as melanoma and basal cell carcinoma (Sánchez-Rivera & Jacks, 2015). Some of the most-researched targets are listed below.

4.1 TP53

TP53 is a cancer suppressor gene that would otherwise repair DNA or induce the death of damaged cells. If mutated, skin cells may proliferate unchecked. Researchers have employed CRISPR to edit out TP53 mutations in cancer cells, restoring its normal function (Liu et al., 2017). This restores the gene's function of inhibiting cell proliferation and causing apoptosis, potentially inhibiting tumor growth.

4.2 BRAF (V600E Mutation)

The BRAF V600E mutation is present in approximately 50% of melanomas and results in continuous activation of the MAPK/ERK pathway, which triggers fast cell growth (Davies et al., 2002). CRISPR has been used to silence or edit out this mutated form of the BRAF gene. Experiments conducted in the laboratory have indicated that deletion of the mutation slows down melanoma cell growth (Zhou et al., 2020).

4.3 NRAS and CDKN2A

NRAS mutations also turn on growth pathways in melanoma. CRISPR can knock out mutant NRAS to slow tumor development (Li et al., 2020). Likewise, CDKN2A, a cell cycle-stopping gene, tends to be deleted in skin cancer. Restoring CDKN2A with CRISPR has shown promise in reducing cancer cell survival in early research (Shi et al., 2019).

4.4 PTCH1 (Hedgehog Pathway)

In basal cell carcinoma, PTCH1 mutations hyperactivate the Hedgehog signaling cascade. CRISPR can inactivate the mutant PTCH1 gene or inhibit its downstream effects. This could potentially halt the growth of tumors without damaging healthy skin cells (Atwood et al., 2015).

4.5 TERT Promoter

TERT promoter mutations raise telomerase activity, turning cells "immortal." These mutations are present in most melanomas. CRISPR has been used to disrupt TERT promoter mutations, reducing cancer cell survival. This may be crucial for preventing aggressive skin cancers (Chiba et al., 2017).

Together, these studies illustrate how CRISPR could enable scientists to cut out the very errors that give rise to skin cancer. Though human clinical trials are still in their infancy, laboratory research is happening rapidly, offering hope for precision-based skin cancer therapy sooner rather than later.

5.0 Limitations of CRISPR in Skin Cancer

Although CRISPR holds potential for the cure of skin cancer, numerous challenges must be overcome before it can be widely used in patients. One of the major concerns is off-target effects, where CRISPR edits the wrong part of the DNA. The slightest mistake in the genome can result in new mutations or unanticipated side effects (Kosicki et al., 2018). This is especially hazardous in cancer, where the cells are already genetically unstable. Scientists are attempting to make CRISPR more precise, but perfect precision is difficult to achieve.

Another limitation is CRISPR delivery to skin cancer cells. Delivering the CRISPR components (guide RNA and Cas9) to tumors safely and efficiently is still a key challenge. The majority of existing approaches, such as viral vectors or nanoparticles, are likely to reach only some of the cancer cells, particularly in metastatic or deep cancers (Lino et al., 2018). The body can trigger immune reactions against the CRISPR components themselves. Eventually, if CRISPR is able to safely edit multiple cancer genes at once, it could replace many current therapies. However, this could also lead to dependence on expensive biotech tools and shift cancer care toward highly specialized centers.

Also, most skin cancers are genetically multifaceted. Even if one mutation, such as BRAF or TP53, is targeted, other cancer-inducing mutations can still be present. The skin tumors can evolve rapidly and become resistant to therapy. Thus, CRISPR might have to be used in conjunction with other therapies to be effective (Tang et al., 2021).

Lastly, ethical and regulatory concerns remain contentious. Applying CRISPR to humans is a cause for concern regarding long-term safety, off-target effects, and access to therapy. Though results from the laboratory are encouraging, additional research and clinical trials must be conducted before CRISPR becomes an accepted therapy for skin cancer. Also, CRISPR is going to be expensive, and thus it would only remain available to high-income individuals of developed countries. This would render it challenging for individuals in underdeveloped nations or low-income regions to take advantage, even when the treatments work. This is a very serious ethical concern about fairness and equity. If CRISPR becomes a viable means of cancer treatment, then it must be accessible to all and not merely the rich. Governments and scientists must collaborate to develop regulations and policies to make CRISPR affordable for all.

6.0 Conclusion

Skin cancer is among the most prevalent cancers globally, and it is primarily due to damage inflicted by UV light. Over time, this leads to mutation in critical genes such as TP53 and BRAF, which are in charge of regulating the way cells grow and multiply. When such genes fail to function properly, skin cells may start growing uncontrollably and develop tumors.

Due to advancements in genetics, researchers now know much more about the mutations that cause skin cancer. This has created new treatment options, such as CRISPR, which is a technology that edits DNA. CRISPR has already demonstrated its promise in the laboratory by targeting cancer-related genes and even reversing some of their actions (Doudna & Charpentier, 2014). As an illustration, correcting a dangerous BRAF mutation may help prevent the growth of melanoma cells.

Still, there are limitations. CRISPR does not always target the precise location in the DNA, which could cause other problems. Delivering it safely into human cells is also difficult, and cancer itself is often more complex than just one or two mutations; therefore, CRISPR is not yet a definitive cure. To conclude, CRISPR offers a hopeful new approach to treating skin cancer. While it’s still being tested, it could one day be part of a safer, more effective way to treat or even prevent this disease.

References

Alam, M., et al. (2014). The use of radiation therapy in nonmelanoma skin cancer.

Journal of the American Academy of Dermatology, 70(6), 1032–1039.

Apalla, Z., Lallas, A., Sotiriou, E., Lazaridou, E., & Ioannides, D. (2017).

Epidemiological trends in skin cancer. Dermato-Endocrinology, 9(1), e1234562.

Atwood, S. X., et al. (2015). Smoothened variants explain resistance to the Hedgehog pathway

inhibitor in basal cell carcinoma. Cancer Cell, 27(3), 327–341.

Brash, D. E. (2015). UV signature mutations. Photochemistry and Photobiology, 91(1), 15–26.

https://doi.org/10.1111/php.12377

Centers for Disease Control and Prevention. (2023). What is cancer?

https://www.cdc.gov/cancer/basics/what-is-cancer.htm

Chiba, K., et al. (2017). Cancer-associated TERT promoter mutations abrogate telomerase

silencing. eLife, 6, e29278.

Cong, L., et al. (2013). Multiplex genome engineering using CRISPR/Cas systems. Science,

339(6121), 819–823.

Davies, H., et al. (2002). Mutations of the BRAF gene in human cancer. Nature, 417(6892), 949–

954.

Doudna, J. A., & Charpentier, E. (2014). The new frontier of genome engineering with CRISPR-

Cas9. Science, 346(6213), 1258096.

Epstein, E. H. (2008). Basal cell carcinomas: Attack of the Hedgehog. Nature Reviews Cancer,

8(10), 743–754.

Gaj, T., Gersbach, C. A., & Barbas, C. F. (2013). ZFN, TALEN, and CRISPR/Cas-based methods for

genome engineering. Trends in Biotechnology, 31(7), 397–405.

Hodis, E., et al. (2012). A landscape of driver mutations in melanoma. Cell, 150(2), 251–263.

International Agency for Research on Cancer. (2020). Global Cancer Observatory: Cancer

tomorrow.

Jinek, M., et al. (2012). A programmable dual-RNA–guided DNA endonuclease in adaptive

bacterial immunity. Science, 337(6096), 816–821.

Kosicki, M., Tomberg, K., & Bradley, A. (2018). Repair of double-strand breaks induced by CRISPR–

Cas9 leads to large deletions and complex rearrangements. Nature Biotechnology, 36(8), 765–771.

Lino, C. A., Harper, J. C., Carney, J. P., & Timlin, J. A. (2018). Delivering CRISPR: A review of the

challenges and approaches. Drug Delivery, 25(1), 1234–1257.

Linos, E., et al. (2010). Skin cancer in the elderly: A population-based study of treatment practices

and outcomes. Journal of the American Geriatrics Society, 58(12), 2247–2252.

Liu, X., et al. (2017). Restoration of TP53 activity in human cancer cells using CRISPR/Cas9. Cell

Reports, 20(12), 2820–2830.

Mai, Y., Wu, H., Wang, W., Huang, Z., Zhang, Y., Xu, M., Lu, C., & Yao, W. (2023). A review of

CRISPR/Cas9-based genome editing: New strategies for the treatment of skin cancer.

Cancers, 15(15), 3819.

Sánchez-Rivera, F. J., & Jacks, T. (2015). Applications of the CRISPR–Cas9 system in cancer biology.

Nature Reviews Cancer, 15(7), 387–395.

Shi, L., et al. (2019). CDKN2A restoration inhibits melanoma cell proliferation via cell cycle arrest.

Oncology Reports, 41(3), 1481–1490.

Spranger, S., et al. (2015). Melanoma-intrinsic β-catenin signaling prevents anti-tumor

immunity. Nature, 523(7559), 231–235.

Tang, L., et al. (2021). CRISPR/Cas9 in cancer therapy: A promising but double-edged sword.

Cancer Letters, 505, 1–9.

Urnov, F. D., Rebar, E. J., Holmes, M. C., Zhang, H. S., & Gregory, P. D. (2010). Genome editing with

engineered zinc finger nucleases. Nature Reviews Genetics, 11(9), 636–646.

Zhou, Y., et al. (2020). CRISPR/Cas9-mediated knockout of mutant BRAF inhibits melanoma cells

growth. Cancer Genetics, 245, 29–35.