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Varshit Dusad
Gene therapy has rapidly become one of the most promising new medical developments of our time. It has significant advantages over traditional therapies including the potential for one-time dosage instead of recurring treatment and higher specificity compared to traditional chemotherapy.
Cancer is a genetic disease! It occurs when normal cells malfunction and lose their normal safety checks due to mutations in checkpoint regulators or due to gaining new functions that cause incessant growth. However, “what’s broken can be fixed” is the motto of gene therapy.
The primary use case for gene therapy is replacing a non-functioning gene with its functional counterpart. For example, mutations in p53, a very important tumor suppressor protein, causes it to lose its capability to regulate the cell, potentially leading to many different types of cancer. Through gene therapy, a patient’s defective p53 gene can be replaced with a working copy. Alternatively, gene therapy can be used to fix genes that have gained new mutations that cause the proliferation of cancer.
However, apart from fixing what went wrong in cancer, gene therapy also allows alternative strategies to traditional cancer treatment i.e. to find and destroy cancerous cells. Here, it can work in conjunction with classical chemotherapy and radiation therapy to introduce new genes to cancer cells that make them more susceptible to chemo- and radiation-based treatment. Some innovative strategies also aim to annihilate cancer cells directly by introducing “suicidal genes,” which can induce apoptosis (a common behavior in a healthy body to keep cell growth in check). Other gene therapy programs are focusing on engineering the immune system to better detect and kill cancer cells. Here, T-cells are edited outside of the body to specifically equip them with receptors that sense and attack tumorous cells. This strategy is known as “Chimeric Antigen Receptor T-cell therapy” or CAR-T therapy and has been covered in large detail here at Oncobites.
Where does cancer gene therapy stand compared to rare diseases?
The benefits of gene therapy today can be best exemplified by their role in treating rare genetic disorders. These diseases affect a small population across the globe and involve a mutation-driven malfunction of genes. Many among these, such as metachromatic leukodystrophy, Danon disease, Leukocyte Adhesion Deficiency etc., currently have no cure and are either fatal or require life-time medical treatment. However, gene therapy has had resounding success in clinical trials with the potential of not only alleviating the symptoms of disease but also potentially actual life-long cures.
Most of the rare diseases that are currently being targeted are monogenic, i.e. the disease is caused by the loss of function of a single gene. Both of these characteristics are important considerations for current industrial gene therapy products because targeting a single gene is easier than multiple genes. Treating multiple genes increases “failure modes” i.e. the number of places a mistake can cause the gene therapy to fail. Further, a “loss of function” mutation is easier to handle than “abnormal function”. This is because when a gene loses its function, any intervention that introduces gain of function is helpful, however when aiming to inhibit a malfunctioning gene, even a few cells that escape treatment can cause disease.
This second challenge of not being able to stop a malfunctioning gene is a great challenge in cancer biology because many genes gain new pro-cancerous functions. However, it is important to highlight that the two above-mentioned challenges affect industrial decisions to choose which diseases to treat based on the likelihood of success. On the other hand, academic research is still largely interested in taking these more difficult challenges head-on to develop a new and effective treatment for cancer.
Is the price of gene therapy too high?
The cost of gene therapy is currently extremely high, with treatment prices ranging from several hundreds of thousands of dollars and to over one million. As a novel treatment paradigm (despite great promise during clinical trials), its actual success in the real world is unknown, and thus payers (both public and private insurance) are reluctant to pay the hefty price for gene therapies. However, companies advocate the value of their therapies due to successes seen in clinical trials, suggesting that the high cost of the therapy is well-priced given the high costs of research and development and the value they can add to the quality of life of the patient.
The increasing potential for cancer gene therapy may change the economics of this market. One of the reasons gene therapy for rare diseases is expensive is because there are very few patients for each disease across the world, effectively making the market too small for most pharma companies to focus on. However, cancer is not rare, and a successful gene therapy treatment could benefit a much larger patient population. In such a scenario, cancer gene therapy may actually improve the overall state of the gene therapy by attracting more grants and investments while also standardizing the process, thus decreasing the costs of the treatment over time.
Conclusion
Gene therapy is a novel medicinal paradigm with significant promise for the treatment of cancer. It has the flexibility to provide treatment in two ways i.e. by attacking the cancer cells directly and actually reverting the dangerous mutations that are at the root of cancer development. Out of the two, the former is most popular in cancer treatment, as in the case of CAR-T therapy, and the latter (gene replacement therapy) is still in investigative phases due to complex genetics and high costs of treatment. However, as is the case with most technological advances, once the technology becomes more widely used, it will become less expensive and commoditized. With increased access to gene therapy, the world can expect improved outcomes for many cancer patients worldwide.
Edited by Morgan McSweeney
References
1. Keeler AM, Elmallah MK, Flotte TR. Gene Therapy 2017: Progress and Future Directions. Clin Transl Sci. 2017;10(4):242-248.
2. Amer MH. Gene therapy for cancer: present status and future perspective. Mol Cell Ther. 2014;2:27.
3.https://blog.dana-farber.org/insight/2018/04/gene-therapy-used-treat-cancer/
4. Hampson G, Towse A, Pearson SD, Dreitlein WB, Henshall C. Gene therapy: evidence, value and affordability in the US health care system. J Comp Eff Res. 2018;7(1):15-28.
5. Li Y, Zhang Y, Li X, Yi S, Xu J. Gain-of-Function Mutations: An Emerging Advantage for Cancer Biology. Trends Biochem Sci. 2019;44(8):659-674.
Image Credits
Source: https://commons.wikimedia.org/wiki/File:Gene_therapy.jpg
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