In a recent study, scientists at the Cancer Research Program, Rajiv Gandhi Centre for Biotechnology (RGCB) in Kerala, have devised a new approach that can edit genetic sequences, in cervical cancer cells that can knock out the cancer-causing gene and thus, serve as an alternative therapeutic approach in treating cervical cancer.
Human Papilloma Virus (HPV) is one of causative agents of cervical cancer in women. While most infections caused by HPV clear up on their own, many women, with persistent HPV infections, gradually develop cervical cancer. According to a study, India accounts for one-third of the cervical cancer deaths globally.
Among the two genetic sequences (genotypes) of the virus -- HPV-16 and HPV-18 -- that cause cancer, HPV-16 is the most prevalent gene in India. The recent study, published in Nature’s journal Scientific Reports, the researchers have used a gene editing molecule that can edit the protein producing gene E7, found in HPV, and has a role in causing cervical cancer and making it malignant.
Previous studies have identified two cancer causing proteins, E6 and E7. Hence, many drugs have been designed to target these two proteins. The other alternative is editing/correcting the protein-producing genetic code, much like you would correct a wrongly written sentence! Genome editing, as it is called, has a distinct advantage over all other approaches as a particular area of the DNA can be modified with a single dose of ‘gene-editing’ molecules, which can edit the gene and make it non-functional.
Two such ‘gene-editing’ molecules are Zinc Finger Nucleases (ZFNs) and Transcription Activator-like Effector Nucleases (TALENs). Both are super-tiny, molecular ‘scissors’ that can be designed to chop off specific gene sequences, based on the requirement. TALENs are easier to design and use than ZFNs, and have proven to be effective against infections caused by other viruses like HIV, Hepatitis B and Hepatitis C. Hence, the researchers of this study have used TALEN.
The results of their study showed the total silencing of E7. Even in a HeLa cell line, a type of immortal cell line used in scientific research, the researchers observed 10% editing activity and total elimination of E7 proteins produced by the gene.
But, suppressing the activity of E7 genes is not without consequences. It results in cell death. Biologically, our cells die in two ways. One is a programmed cell death, which is a relatively ‘cleaner’ death, where all the cell contents are promptly recycled. The second, also called ‘necrotic death’, is a messier affair. Here the dead cell bursts out spewing its contents all around it. Usually, genes when edited by TALENs, result in a programmed cell death. However, in this study, the researchers report a cell death by necrosis when TALENs were used to target genes that produce E7 in cervical cancer cells. The advantage of necrotic cell death is that with the cancer cell contents now all spilled outside, the immune system can easily pick this up. Once our immune system knows the presence of these foreign bodies, it triggers pro-inflammatory cytokines -- small proteins helping in cell signaling — leading to tumor-specific immunity. This could, in turn, destroy other malignant cells including those that have been resistant to natural cell death.
So how are these ‘gene editing’ molecules transported to the nucleus of the cells? Molecular biologists use ‘viral vectors’ -- tools used to deliver genetic material into cells. However, because of TALENs’ molecular structure and its tiny size, this method isn’t suitable. Hence, biologists deliver TALENs using ‘messenger RNAs’ or mRNAs, which is less toxic and has fewer regulatory concerns. The researchers of the study report that in the case of HPV, TALENs could be used locally along with surgery. By topical application of TALEN based drugs into the cervix at regular intervals, there could be minimal side effects, high efficacy, and minimum risk of metabolic and enzymatic digestion.
The study, performed on cell lines, suggests that selected TALEN pairs could effectively edit the HPV-E7 gene in cervical cancer cells, and induce their death. However, further studies are required to validate these results in animals. TALEN-based therapy could also prevent recurrence of cancer cells after surgery, claim the researchers. “Such studies offer hope for future therapeutic strategies against HPV infected cells, since these will not be removed by currently available prophylactic vaccines”, signs off Prof. Pillai from Rajiv Gandhi Centre for Biotechnology and the lead researcher of the study.
This article is based on a research paper titled, "TALEN based HPV-E7 editing triggers necrotic cell death in cervical cancer cells” published in Scientific Reports, Nature. Funded by DBT, GoI and CSIR.