Brazilian scientists are the first to use DNA editing technique against thyroid tumor

Thyroid cancer is one of the most common endocrine cancers and the most rapidly increasing cancer in incidence. Fortunately, most cases are easily treated, and the chances of remission are high. However, some aggressive forms of thyroid tumor are more challenging to deal with. Anaplastic thyroid cancer (ATC) is the most aggressive thyroid cancer type, and its pathogenesis remains incompletely understood. ATC develops from well-differentiated tumors, and the main genetic alterations detected in ATC are TP53, BRAF, and TERT mutations. Unfortunately, most ATC cases are fatal due to the rapidly progressing tumors that become resistant to radioiodine therapy and develop metastatic disease¹. 

A micro RNA called miR-17-92 is responsible for this problem. High levels of this micro RNA have been detected in ATC, linked to a more aggressive disease¹. Micro RNAs are potent regulators of gene expression; they target post-transcriptional regulation of mRNAs, modulating tumor development and progression. De-regulation of micro RNAs are regarded as one of the hallmarks of cancer. 

One group of scientists in Brazil targeted miR-17-92 in aggressive thyroid tumor cells. César Seigi Fujiwara, a researcher at the Molecular Biology Laboratory of the thyroid of the Institute of Biomedical Sciences (ICB) at USP (Sao Paulo University), coordinated by Professor Edna Kimura, was able to edit the DNA of this microRNA (miR-17-92) using the CRISPR method. The scientists edited anaplastic thyroid carcinoma cells, the most lethal kind¹. 

The researchers said it was challenging because miR-17-92 is a cluster (oncomiR-1) that transcribes seven different micro RNAs (miR-17-5p, miR-17-3p, miR-18a, miR-19a, miR-20a, miR-19b, and miR-92a). They have a pro-oncogenic effect in various types of cancers, including small-cell lung cancer, colon cancer, neuroblastomas, medulloblastoma, and gastric cancer¹. The results of the study showed that inhibition of miR-17-92 made the cells lose their ability to migrate, invade other tissues, and proliferate. Thus, becoming less aggressive¹. 

They also analyzed cell differentiation and their ability to express genes related to iodine metabolism. This was done because radioactive iodine is the primary treatment for this type of cancer. They've noticed that cell's differentiation capacity was increased, but it was not sufficient to regenerate the cell's ability to absorb iodine¹. The authors believe that gene editing can be used in conjunction with other therapies to aid in the treatment of aggressive cancers.

They are currently investigating the gene mutation BRAF, present in more than 40% of thyroid carcinomas. The BRAF oncogene is associated with a loss of expression of the sodium iodide symporter, which induces genomic instability in normal thyroid follicular cells, contributing to the resistance to radioiodine therapy and disease progression, as observed in the aggressive forms of ATC¹. 

The goal of this research is to understand the effect of this mutation over the expression of miR-17-92. In the future, scientists intend to target this mutation

to test the use of these two inhibitors together to see if the inhibition is more significant¹. Although there is a long way to the possible therapeutic use of the discovery, the positive results have brought some hope for those who suffer from aggressive cancers with high levels of expression of miR-17-92.

About CRISPR technology

CRISPR/Cas9 is a type of genome editing technique. It is a natural process used by bacteria to protect from viruses infection. When viruses infect bacteria, they can capture the virus DNA and create DNA segments (CRISPR arrays). On a second infection, bacteria use this DNA to produce RNA segments and attack the virus. They use the Cas9 protein, an enzyme used to cut the virus DNA, disabling them². 

CRISPR technology's applications are endless, and several research groups worldwide are trying to find a cure for human diseases, such as cancer².

See how CRISPR is being used to fight cancer

In 2019, researchers at the University of Pennsylvania launched the first trial testing a CRISPR-based cancer therapy in humans. The technique works similarly to immunotherapy, where the patient's immune cells are modified to recognize the cancerous cells and kill them³. 

In this case, a synthetic gene is added to give T cells a receptor that recognizes a specific protein called NY-ESO-1 in cancer cells. Additionally, three other genes are removed. Two of them interfere with NY-ESO-1 receptor, and the other limits the inactivation of the cancer cell. The modified cells are grown in the laboratory and infused into the patients. The study showed that the technique is safe; however, the treatment showed a mild effect, with tumors growing back after a few weeks. Moreover, it didn't worked for all the patients³. 

Other trials are investing in CART-cell therapy, another type of immunotherapy. CART-cells are human T cells that have been obtained from a patient and genetically engineered to recognize specific proteins on the patient's cancer cells⁴. 

In the beginning, T cells engineering depended on viral vectors to deliver DNA fragments into a cell, which is a costly technique⁵. Nowadays, scientists are using CRISPR/Cas9 to generate deletions and insertions into T cells. Strategies to produce CART-cells involve knock-in of functional genes such as interleukins and suicide genes, or knock-out of endogenous genes, such as TCRs and MHCs, deletion of target genes to avoid self-kiling of CART-cells⁶. 

For example, a phase I trial is testing CRISPR-Cas9-engineered CAR-T therapy targeting CD-19 (a signaling protein in B cells) in patients with relapsed or refractory B-cell malignancies. Early Results from this trial have shown that the therapy induced a dose-dependent anti-tumor activity and an acceptable safety profile⁷. 

Future directions 

Preliminary results from the first clinical trial using CRISPR were promising, showing that the technique is safe in humans. The positive results that are being obtained in the treatment of cancer in humans are certainly encouraging. However, we still have a long way to go until we have approved drugs for commercialization. Besides, ethical and regulatory issues regarding gene-editing techniques still need to be better discussed by authorities and the scientific community.

Anyway, advances in the area do not deny; we will still hear a lot about CRISPR in the future.

References

1. USP J da. Cientistas da USP são pioneiros na edição do DNA de tumor agressivo de tireoide. 2020. 

2. Plus M. What are genome editing and CRISPR-Cas9? 

3. Institute NC. How CRISPR Is Changing Cancer Research and Treatment [Internet]. Available from: https://www.cancer.gov/news-events/cancer-currents-blog/2020/crispr-cancer-research-treatment#:~:text=The first trial in the,see” and kill their cancer.

4. Press M. Excellent research results for CAR-T Cell therapy against Hodgkin lymphoma [Internet]. 2020. Available from: https://medicalxpress.com/news/2020-07-excellent-results-car-t-cell-therapy.html

5. Research N. CRISPR expands CAR T cell possibilities [Internet]. 2020. Available from: https://www.nature.com/articles/d42473-019-00443-7#:~:text=T cells engineered to express chimeric antigen receptors%2C known as,help patients with blood cancer.&text=A year later came another,its use in eukaryotic cells.

6. Li C, Mei H, Hu Y. Applications and explorations of CRISPR/Cas9 in CAR T-cell therapy. Brief Funct Genomics [Internet]. 2020 May 20;19(3):175–82. Available from: https://doi.org/10.1093/bfgp/elz042

7. Trials C. A Safety and Efficacy Study Evaluating CTX110 in Subjects With Relapsed or Refractory B-Cell Malignancies (CARBON) [Internet]. 2020. Available from: https://clinicaltrials.gov/ct2/show/NCT04035434

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